# Moonglow The forgotten magic of our heavenly satelllite



## Fishers of Men

*THIS IS REAL LONG, IT TURNED INTO A CONTINUING EDUCATION ABOUT SEAMANSHIP AND WILL TRANSFORM AT THE END TO APPLYING FISHING TACTICS.*
*A COMPILATION BY CAPTAIN AARON VAN BURNETT*

Hope these links work, probably have to enlarge a lil to read. I am going to try to get a post as often as possible that is going to continue from this topic ie: navigation, seamanship, gps, loran, radar navigation, lines of position, lat/long, minutes/degrees, elements of piloting, time, weather, fog situations, current sailing, buoyage system, mariners maps, earths magnetism, compass, deviations/corrections, moons gravity effects, dead reckoning, and I probably forgot to list something but it will come. probably those that don't follow from the beginning will be lost. Questions will be fine, but if you wait a lil bit they most likely will be answered. I figure that this coverage you can only get from expensive schooling and/or a life time of learning will help a bunch of people and refresh some of ours memories. Every new post will move forward and cover more depth. I am going to start with the moon. I wont get into tides much unless someone wants it.

Moonglow The forgotten magic of our heavenly satelllite

phases of the moon and much more. Key words: new moon, night sky, lunar cycle, lunar phases, crescent, synodic month, orbit, rotation, axis, waxing, waning, gibbous. The forgotten magic of our heavenly satellite.

http://i202.photobucket.com/albums/aa305/FishersofMen/1moon.jpg
http://i202.photobucket.com/albums/aa305/FishersofMen/2moon.jpg
http://i202.photobucket.com/albums/aa305/FishersofMen/3moon.jpg
http://i202.photobucket.com/albums/aa305/FishersofMen/4moon.jpg

ZERO HOUR
Over the years run many stories of men who have taken to the boats and found their way over a trackless ocean to land. In these years of many missions, few of those who go down to the sea in ships are without personal knowledge of sane brave man who likewise
guided men to safety. From such men of the seven seas a few suggestions have been gathered that may be useful to others who face the zero hour. The result is far from complete, but it is from the sea, and of the sea, and not from the books, but from a almighty God, the celestial heavens and experience.
The suns apparent motion is caused by the two motions of the earth. The resulting position of the sun over the earth is the greatest factor
affecting the character and mode of existance of the human race. It determines the heat of the tropics, the cold and long artic nights, the calendar, the seasons, and day and night throughout the world. Also it is the most important element of nautical astronomy because its average position measures mean time and because it is most often observed by navigators.
The moons apparent motion westward principally caused by the earths rotation is somewhat slower than that of the other navigational bodies, is characterized by it&#8217;s extremely rapid change of position among the stars. On an average the moon will rise about 51 mm. later each day, in NY&#8217; s latitude, this retardation varies from 13 m to 8O mm. The fact for a navigator to remember is that the rate of increase of the moons GHA ( greenwitch hour angle) may be changing rapidly. The moon is easy to observe, and it&#8217;s observation often gives a much needed line of position obtainable from no other body.
The solar day is the period of the earth&#8217;s rotation relative to the sun. The solar year is based on the period of the earths revolution about the sun, which requires approx. 365-1/4 days. The other units of time, month, week, hour, min, and second have origins deep in mans history. The ancient Egyptians used the rising of certain stars or star groups to divide their calendar into ten day periods. Such stars or star groups, rose successfully at intervals of roughly 40 mm, and so approximately 12 of them could be seen on any night. From this the night was divided into 12 hours and the entire day became 24 hours. The division of hours into 60 mm of 60 seconds each was a development of the ancient babylonian culture. The sun changes longitude at an almost uniform rate of 1511 an hour or 900&#8217;.
"He appointed the moon for seasons" Psalms 104:19
"The moon and stars to rule by night" Psalms 136:9


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## Fishers of Men

Some of you might think that whats this all got to do with me and fishing?
Well believe me it will all show a picture when we get thru this, just like pieces of a jig saw puzzle. I don't want some of you to think it's too confusing and give up, hang in there it will get easier. Might take me all winter, who knows but it's what we all have in common and like. I dont have time in the summer, so I figured with all the GPS questions and such on here that this would help with a lot of issues and making decisions ourselves about where to go, when to go and so on some of us have. All material shown you can follow along if you go to the library and get the "Primer of Navigation" and Duttons Navigation and Piloting " by Elbert S Maloney. I am only going to hit on certain things to an extent because it should be enough understanding to move on your own from there. This information being brought forward is my understanding and 50 yrs of experience on the water are going to be straight from these books and of my opinion only. Debatable issues from these facts can be taken to another thread. And with all the talent I see on this site, I welcome any comments or oversites feel free to chime in.

Today we are going to clarify "time" issues. I know there are confused people over how distance/time/degrees work. You will see how minutes for example shown on gps and lorans, charts, works with distance. I will constantly throughout all of this, remind you to ask yourself "where am I?" That will be very clear before long as to why. 

*TIME*
THE subject of time, always difficult for students of navigation, has been greatly simplified since 1933. Today, with the same kind of time used in civil life, the position of the sun, the moon, or any of the navigational stars or planets may be taken from the Almanacs without the use of apparent or side real time. This simplification does not eliminate the necessity for determining the exact instant of an observation; chronometers and timekeeping are discussed in the next chapter.
2101. The natural measure of time is the sun&#8217;s apparent motion over the earth which causes the periods of darkness and light, as well as the seasons. It does not provide a practical measure, however, because the apparent motion of the true sun is not uniform ( and units of time measured thereby are of varying duration. The variation is slight but clocks cannot be regulated by apparent time)
To retain the advantage of a time based on the sun, an imaginary sun, called the mean sun, is used. The mean sun. is an imaginary body which would appear to move westward around the earth at a uniform rate equal to the average rate of the true sun. If both suns were seen in the sky, following the same track, their positions would coincide at only four instants during the year but would never appear far apart.
2102. Mean time, sometimes called civil mean time or civil time, is time as measured by the motion of the mean sun. Under various names, it is the time we live by and is the only kind of time essential to present- day navigation.
A civil day is the interval of time required for the mean sun to make one revolution about the earth. It is divided into 24 hours of 60 minutes of 60 seconds always of the same duration. The day begins at midnight (Oh) at the instant the mean sun crosses the lower meridian of the observer. As the sun moves westward around the earth, the time increases, The instant of the upper transit of the mean sun across the meridian marks noon (12h) mean time for that meridian. The sun then continues westward until it again crosses the lower meridian, and a civil day of 24 hours, always of the same duration, is ended never to return.

For most purposes of civil life the day is divided into two periods of 12 hours each. Time before noon is marked A which means at or before the sun has crossed the meridian. After noon, time to midnight is marked P.M. indicating time post or after the sun crosses the meridian. In the Almanacs the hours are numbered from 0 to 24 without special designations.
Although the duration of a civil day is the same for all places, the time of day is common only to points on the meridian of longitude from which the momentary east-west position of the mean sun is measured. The sun&#8217;s transit westward over that meridian marks the instant of noon, 12h, mean time, but the sun already will have crossed meridians to the eastward where time is therefore after noon or later; for points westward the time is before noon or earlier.
Listeners to international broadcasts know that standard time at London (75&#176; to the eastward) is five hours later than New York standard time, just as the football fan knows that time on our Pacific Coast (450 to the westward) is three hours earlier than at New York. Minor differences in exact civil time are less well understood. If one walks across Manhattan Island on 42nd Street, New York City, the exact local time will have changed about 9 seconds. To the eastward of New York at Boston, local time is about 12.5 minutes faster; westward, at Philadelphia, the local time is about 5 minutes slower than at New York.
Local Mean Time (L.M.T.). An infinite number of different mean times is possible, each being L.M.T. for the meridian on which the time is based. Comparatively few are in standard use and these are given special designations, the most important to navigators being Greenwich mean time (G.M.T.).
The term L.M.T. as used in navigation generally means local mean time for the meridian of longitude of the ship, although it may mean local time at any place.
*Greenwich mean time* is the local mean time for all points on the meridian of Greenwich, England. The reason for its importance is that some place had to be chosen as a base for the tabulations in the almanacs. Since Greenwich historically is on the prime meridian for the measurement of longitude, the Greenwich meridian became also the meridian of reference for the predicted time of occurrence of astronomical events.
Greenwich mean time, sometimes called Coordinated Universal Time (UTC), is the standard for civil time keeping and for navigation. It is not strictly uniform, but when corrected by a few milliseconds for variations in the earth&#8217;s motion, it gives UT1 for use by geophysicists and others requiring a more uniform measure of time.
Greenwich mean time is the same throughout the world. Hence, activities of world-wide scope keep their clocks and watches set to Greenwich mean time.
244 Primer of Navigation
Military communications and other operations are regulated by this time.
The lower, circular drawing of Fig. 2103 is the sphere of the earth as viewed from above its south pole. Around it is shown the apparent progress of the mean sun around the earth and how its position measures
G.M.T. The upper, rectangular diagram illustrates the same facts by plotting succeeding geographic positions of the mean sun on a map of the world. For convenience the sun is shown as moving westward along the equator (00 Dec l.), a permissible assumption because the westward motion of the mean sun, which is the measure of civil time, is not affected by the sun&#8217;s varying declination.
As always in the measurement of mean time, the day begins at mid night (Oh), the instant the center of the mean sun, marked (0) in the drawing, crosses the lower meridian, 180 degrees E or W, at the time of its lower transit. As the mean sun moves westward at the rate of 15&#176; per hour the time grows later and at (3), having moved westward 45&#176; to the meridian 135&#176; E of Greenwich, G.M.T. is 3h OOm A.M. or simply 0300 when stated in accordance with Navy practice. When the mean sun crosses the meridian of Greenwich at the time of upper transit, or simply transit, G.M.T. is 12M or 1200. For reasons stated later, this instant is almost never the exact time of transit of the true sun. After noon the mean sun continues to travel westward, always at a constant rate of 150 of longitude per hour. When it is 45&#176; west of Greenwich it is 3 P.M. or 1500 G.M.T. and thus onward until its succeeding lower transit marks the end of the day (24b) and a new day begins.
In a similar manner, local mean time for any meridian is measured by the relative position of the mean sun to that meridian.
*Time and longitude.*
Either quantity may be expressed in units of arc or in units of time. Understanding this relation between time and longitude is facilitated by the following considerations:
Longitude is measured in degrees (&#176 and minutes (&#8216 of angular measure. Arcs representing time, however, are often expressed in units of time as a measure of arc. As 24 hours of time are required for the mean sun to traverse a circle of 360&#176; at a uniform rate of 150 per hour, the circle may be divided into 24 hours with each arc further divided into minutes and seconds of time. When an arc is so divided time units may be used as a measure of arc. Useful equivalents of identical arcs measured in degrees and minutes of arc or by units of time may be expressed in these ways:
3600 = 24 hours
15&#176;	1 hour
1&#176;	4 minutes
15&#8217; = 1 minute
1&#8217; = 4 seconds
(I am telling you that it is a different time on opposite sides of the street in NY city at any given time!)
Here is a diagram:
http://i202.photobucket.com/albums/aa305/FishersofMen/timediagram.png


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## Fishers of Men

I will go to the compass now, later on we will incorporate every thing we have discussed into a quiz when I get the time to compile it. We have all winter and these are my favorite topics. The quiz will incorporate all kinds of real life instances on the water ie: conditions, safety, fire, getting home in adverse conditions and so on. Stuff that experience gives, that you can&#8217;t get in any class. I am still learning and appreciate any input. *I cant change the title, maybe a mod can. I think it should say &#8220;seamanship&#8221;. Probably gain more interest. * Please point out any errors or typos, I get burned out eyeballs lookin at this thing. I hope the links are readable, might have to use the magnifing glass or enlarge.

*THE MAGNETIC COMPASS*
The magnetic compass is one of the oldest of the navigator&#8217;s instruments. Its origin is unknown, but apparently the Vikings were familiar with it in the eleventh century. Although records are scanty and inexact, it is probable that the magnetic compass was independently developed by the Chinese at about the same time. The earliest compasses probably consisted of an elongated piece of lodestone, iron ore having magnetic properties, placed on a wood chip and floated in a bowl of water. Rather quickly, this developed into an iron needle thrust through a straw and floated on the surface of a container of water; the lodestone had to be applied to the needle each time the &#8220;compass&#8221; was to be used.
Initially, a compass was used only to indicate north, but soon the concept of marking other directions around the rim of the bowl was introduced. The directions were given the names of the various winds, now known as North, East, South, and West; these are the cardinal directions. Next are the intercardinal directions: NE, SE, SW, and NW. _(comment, the cardinal directions are not used here, they are over seas in countrys not using our system. You will see it mentioned again when we do the bouy system.)_ Still finer subdivisions are the combination directions: NNE, ENE, ESE, etc.; and the by-points: NxE, NNExN, NNExE, etc. This system results in a complete circle divided into 2 points (1 point = 11-1/4&#176 and there are half-points and quarter points. The point system was widely used until relatively modern times, but is now obsolete except for some minor use on sailing craft.
Because of the difficulty at sea in using a needle floating freely in an open bowl of water, the next development was that of using a pivot at the center of a dry bowl. Not for some centuries was the liquid put back in, this time in an enclosed chamber, as now is the case in modern magnetic compasses.
The magnetic compass still retains its importance, despite the invention of the gyrocompass. While the latter is an extremely accurate instrument, it is highly complex, dependent on an electrical power supply, and subject to mechanical damage. The magnetic compass, on the other hand, is entirely self-contained, simple, comparatively rugged, and not easily damaged.
Standard and Most vessels of any size carry at least two magnetic compasses; these steering are the standard compass and the steering compass. The standard compass, whenever possible, is located on the ship&#8217;s centerline&#8230;
For clarification purposes:
http://i202.photobucket.com/albums/aa305/FishersofMen/compass2.png
I can&#8217;t seem to make anything with pics or diagrams post here, so I have to do the link thing.
http://i202.photobucket.com/albums/aa305/FishersofMen/compass3.png
http://i202.photobucket.com/albums/aa305/FishersofMen/comp4.png
*(pay real attention to this magnetic field link)*
continued from the link:
76.1&#176; N, longitude 100.0&#176; W and the south magnetic pole is near 65.8&#176; S, 139.4&#176; E; these locations are somewhat indefinite and change irregularly over a period of years. Some studies have shown that the poles appear to move in daily, cycles over an elliptical path having a major axis of about 50 miles; such movement is, of course, too slight to affect practical navigation in nonpolar latitudes.
*Magnetic meridian*
At the surface of the earth, the lines of force become magnetic meridians. These are irregular lines which cannot be printed on charts covering large areas; their irregularity is primarily caused by the non uniform distribution of magnetic material in the earth.
The magnetic lines of force can be divided into components. For the navigator, the horizontal and vertical components are important, and are discussed as variation and dip in subsequent articles.
Variation 
Magnetic meridians indicate the direction of the earth&#8217;s magnetic field; but only in a very few places do the magnetic and true meridians coincide. The difference at any location between the directions of the magnetic and true meridians is the variation, sometimes called magnetic declination. It is called easterly (E) if the compass needle, aligned with the magnetic meridian, points eastward or to the right of true north, and westerly (W), if it points to the left. Variation results from the horizontal component of the earth&#8217;s magnetic field.
Variation is important to the navigator because the magnetic com pass, responding to the earth&#8217;s magnetic field, is in error in measuring true geographic direction by the amount of the variation (Var. or V). The magnetic variation and its annual change are shown on charts, so that directions indicated by the magnetic compass can be corrected to true directions. Since variation is caused by the earth&#8217;s magnetic field, its value changes with the geographic location of the ship, but is the same for all headings of the ship.
*Secular change* 
The earth&#8217;s magnetic field is not constant in either intensity or direction. The changes are diurnal (daily),yearly, and secular (occurring over a longer period of time). The changes in intensity are too small to have any effect in navigation. The same is true of diurnal changes in direction, except in polar regions, where diurnal changes of 7&#176; have been observed.
The secular change in direction, however, is a real factor in navigation. Although it has been under observation for more than 300 years, the length of its period has not been fully established. The change generally consists of a reasonably steady increase or decrease in the variation, which is the inclination of the magnetic meridian to the true meridian at a given place. This change may continue for many years, sometimes reaching large values, remain nearly stationary for a few years, and then reverse its trend.
http://i202.photobucket.com/albums/aa305/FishersofMen/comp6.png
http://i202.photobucket.com/albums/aa305/FishersofMen/comp7.png
http://i202.photobucket.com/albums/aa305/FishersofMen/comp7-1.png
http://i202.photobucket.com/albums/aa305/FishersofMen/comp8.png
continued from the link:
dination (dip) and for intensity of field, horizontal, vertical, and total; they are revised when required by changes in the earth&#8217;s magnetic field. Of greatest interest to a navigator is DMAHC Chart 42, Magnetic Variation Chart of the World for the Year 1975, a simplified which is shown in Figure 406.
While these charts are useful for planning purposes, the large-scale chart of the area involved should always be consulted in setting a course by magnetic compass or converting a magnetic compass bearing to a true bearing for plotting, since there are many small irregularities in variation that cannot be shown on the small-scale world charts. In addition, there are very small areas of local magnetic disturbance that may or may not be indicated on the chart. At one place off the coast of Australia, near Cossack, the variation changes from 56&#176; E to 26&#176; W in a distance of about 180 yards, less than the length of a ship; areas of local disturbance of lesser magnitude extend over nearly three miles of navigable water. There are many others of less extreme nature, but still of a magnitude and extent that must be taken into account by a navigator.
*Modern compass*
The basic mechanism of modern magnetic compasses is exactly construction the same as that of the very earliest ones used, a small bar magnet freely suspended in the magnetic field of the earth. Refinements have been added for greater accuracy, steadiness of indication, and ease of reading, but the basic mechanism remains unchanged.
*Compass components*
The modern marine magnetic compass is contained in a glass-topped bowl made of nonmagnetic material. The letters in the following description refer to the corresponding components in this illustration. At the forward side of the bowl is the lubber&#8217;s line, which indicates the direction of the ship&#8217;s head). At the center of the bottom of the bowl is a vertical pin, the pivot, upon which the compass card (B) rests. To the bottom of this card are attached two or more magnets (A) aligned with the north-south axis of the compass card. The card is marked around its outer edge with graduations at suitable intervals, 1&#176;, 2&#176;, or 5&#176;, from 000&#176; at the point where the card indicates compass north clockwise through 360&#176;; cardinal and intercardinal directions may also be shown on the card in some designs.
In order to reduce friction on the pivot and to dampen vibration, the compass bowl is filled with a clear fluid (D) which is not subject to freezing at normal temperatures. The card has afloat or air chamber (E), designed so that it will support all but a minute percentage of the weight of the card with the attached magnets. Lastly, the bowl is fitted with an expansion bellows (F) which permits the bowl to remain filled as the liquid expands and contracts with temperature changes.
*Operation of the magnetic compass:
Deviation*
When a compass is mounted on a vessel, its magnets align them selves with the magnetic field in which they exist. Assuming for the moment that there are no local influences (objects of magnetic material or electrical currents), this alignment will be parallel to the horizontal component of the earth&#8217;s magnetic field. The compass card will maintain this alignment regardless of the vessel&#8217;s heading.
As the compass card is attached to the magnets, the 0000 mark on the card always points in the direction of compass north, and the ship&#8217;s compass heading is indicated by the lubber&#8217;s line. If there are no local disturbing influences, no deviation (see Article below), then this is also the magnetic heading. When a compass is installed, great care must be taken to align the lubber&#8217;s line exactly parallel to the center line of the ship. The compass bowl and lubber&#8217;s line are constrained to turn with the ship, thus the direction of the lubber&#8217;s line from the center of the compass always represents the direction of the ship&#8217;s head. Since the 0000 mark on the card is always toward the magnetic north, the direction indicated on the compass card opposite the lubber&#8217;s line is the ship&#8217;s heading. As the ship turns, the lubber&#8217;s line turns with it, while the compass card remains aligned with compass north, so that the heading at any moment is indicated at the lubber&#8217;s line. Remember that it is the lubber&#8217;s line, and not the compass card, that turns.
As stated above, a compass needle free to turn horizontally tends to align itself with the earth&#8217;s magnetic lines of force. Unfortunately, it is not free to do so in a steel ship; such ships have marked magnetic properties of their own, and these tend to deflect the compass from the magnetic meridian. The divergence thus caused between the north-south axis of the compass card and the magnetic meridian is called deviation (Dev. or D). Even in a vessel made of wood or fiber glass there is enough magnetic material on board, engines, fuel and water tanks, rigging, etc. to cause deviation.
The possibility of deviation from electrical circuits must not be overlooked. Direct currents flowing in straight wires establish magnetic fields. Care must be taken that all wiring in the vicinity of a compass is properly installed to eliminate or reduce any effect on the compass; checks must be made for deviation with the circuits turned on and off.
Although deviation differs from variation in that the latter is caused by the earths magnetism, the two are designated in the same manner.
Thus, if no deviation is present, the compass card lies with its axis in the magnetic meridian and its north point indicates the direction of magnetic north. If deviation is present and the north point of the compass points eastward of magnetic north, the deviation is named easterly and marked E. If it points westward of magnetic north, the deviation is named westerly and marked W.
The navigator can easily find the correct variation by referring to the chart of his locality. Deviation, however, is not so simple to ascertain. It varies not only on different ships, but on any particular ship it varies with changes in the ship&#8217;s heading. Also, it often changes with large changes in the ship&#8217;s latitude.
*Compass error*
The algebraic sum of variation and deviation is compass error. The navigator must understand thoroughly how to apply variation, deviation, and compass error, as he is frequently required to use them in converting one kind of direction to another.
From the foregoing it should be apparent that there are three ways in which a direction can be expressed:
As true, when referred to the true (geographic) meridian as the reference of measurement.
As magnetic, when referred to the magnetic meridian as the reference of measurement.
As compass, when referred to the axis of the compass card as the reference of measurement.
Any given direction may be expressed in all three of these ways, if it is understood that:
*True differs from magnetic by variation.
Magnetic differs from compass by deviation.
Compass differs from true by compass error.*
Figure 412a
http://i202.photobucket.com/albums/aa305/FishersofMen/412a.png
This seems complicated from the Duttons book. I will simplify it afterwords.
Outlines a ship in which is shown the card of the standard compass. OC is the direction of the compass needle. OM is the magnetic meridian, and OT the true meridian. The two outer circles, concentric with the standard compass card, represent magnetic and true compass roses, thus indicating magnetic and true directions. The observer is at 0. The magnetic meridian is 12&#176; eastward (right) of the true meridian; therefore, the variation of the locality is 12&#176; E. It is added to the magnetic direction of M (0&#176; on magnetic rose) to obtain the true direction of M (12&#176; on true rose). The compass needle is 8&#176; eastward (right) of the magnetic meridian; therefore, the deviation is 8&#176; E on the ship&#8217;s heading shown. It is added to the compass direction of C (0 degrees on compass card) to obtain the magnetic direction of C
(8&#176; on magnetic rose). The compass error is the algebraic sum of the
variation and deviation or CE= 20&#176; E. It is added to the compass
direction of C (0&#176; on compass card) to obtain the true direction of C
(20&#176; on true rose). The bearing of object A from the ship is shown as
20&#176; psc, (per ships compass) 30&#176; magnetic, and 40&#176; true. In practice, bearings are expressed
in three-numeral groups e.g., 0200, 0300 and 040&#176;. The ship&#8217;s heading is 300&#176; psc (note lubber&#8217;s line LL), 3080 magnetic, and 3200 true.
As already noted, easterly deviation is added (+) to compass in converting to magnetic, easterly variation is added (+) to magnetic in converting to true, and easterly compass error is added (+) to compass in converting to true. Conversely, they are subtracted (&#8212 when converting in the reverse order.
Figures 412b and c will show westerly variation and deviation and demonstrate that the above rules of application should be reversed for westerly errors.
http://i202.photobucket.com/albums/aa305/FishersofMen/412b.png
Westerly variation, but easterly deviation.
*Correcting and uncorrecting*
Compass direction to a magnetic or true direction or of converting a magnetic direction to a true direction is one of &#8220;correcting,&#8221; or removing errors. If easterly errors are added, it is obvious that westerly errors are subtracted, and no separate rule is needed.
The opposite of correcting is called uncorrecting. The process of Un- correcting is one of converting a true direction to a magnetic or com pass direction or a magnetic direction to a compass direction by applying errors. If easterly errors are added and westerly errors subtracted when correcting, then the reverse is true when uncorrecting. Hence, the one rule, correcting add east, is sufficient to cover all four possible situations:
Correcting, add east, subtract west.
Uncorrecting, add west, subtract east.
*Rules for applying compass errors:*
Figure 412c. Westerly variation, but easterly deviation.
http://i202.photobucket.com/albums/aa305/FishersofMen/412c.png
_*T REEL just asked a good question: "Why is the ship center not in the middle of the compass rose center ?" Very good question. It should be in the center since it is supposed to be under a perfect condition, not that the compass should be as close to center as possible deal. I never noticed that. These drawings are right out of the book, I didn't make them. Thank you for noticing the detail. I will make a note on the page.*_


It is convenient to have a thumb rule to serve as an aid to the memory applying the above principles. The following will serve: When correcting, easterly errors are added, or simply, correcting add east. When applying this rule, it is necessary to consider a compass direction as the &#8220;least correct&#8221; expression of direction as it contains two errors, variation and deviation. Magnetic direction is thus &#8220;more correct&#8221; than compass as it contains only one error, variation. This is so even when the axis of the compass card is closer to the true meridian than is the magnetic meridian. Magnetic direction is, however, &#8220;less correct&#8221; than true direction, which contains no errors. 
*Correcting and uncorrecting*
Hence the process of converting a compass direction to a magnetic or true direction or of converting a magnetic direction to a true direction is one of &#8220;correcting,&#8221; or removing errors. If easterly errors are added, it is obvious that westerly errors are subtracted, and no separate rule is needed.
The opposite of correcting is called uncorrecting. The process of Un- correcting is one of converting a true direction to a magnetic or com pass direction or a magnetic direction to a compass direction by applying errors. If easterly errors are added and westerly errors subtracted when correcting, then the reverse is true when uncorrecting. Hence, the one rule, correcting add east, is sufficient to cover all four possible situations:
Correcting, add east, subtract west.
Uncorrecting, add west, subtract east.
C-A-E Now to simplify
Note that to get the other three forms from the basic statement &#8220;correcting add east (which can be memorized as &#8220;C-A-E&#8221, you must change two, but only two, of the three words. If &#8220;correcting&#8221; is changed to &#8220;uncorrecting,&#8221; then either add must be changed to subtract, or east to west. If correcting is not changed to uncorrecting but &#8220;east&#8221; is changed to &#8220;west,&#8221; then &#8220;add&#8221; must be changed to &#8220;subtract.&#8221; The basic phrase, C-A-E, and the rules to change only two words will suffice to meet all problems of correcting and uncorrecting.
C-D-M-V-T An alternative method for remembering the rules of correcting and uncorrecting involves using the first letters of the following words:
Compass, Deviation, Magnetic, Variation, and True and letting these be the initial letters of words that form an easy-to-remember sentence. A convenient one to use is Can Dead Men Vote Twice? Using this sentence to remember the order, write down just the initial letters and arrange them vertically: _(To do it in reverse order you can go TVMDC remembered by: true virgins make dull companions. by which you add W going down and add E going up with the formula. From the + in the middle draw a arrow up and one down.)_
w C ___ 
D __ 
+ M ___ 
V __ 
E T __ 

To the left of the column, draw a double-ended arrow, placing a W at the top, and E at the bottom and a plus sign in the center as illustrated. The addition of &#8220;At Elections&#8221; to the sentence above will assist in remembering that in the direction C-D-M-V-T the procedure is to Add East. The arrow heads have nothing to do with actual direction but apply only to the direction of proceeding through the initial letters of the memory phrase, whether correcting from compass to true or uncorrecting from true to compass.
Now, by placing the given information in the corresponding
blanks, the unknown values can easily be computed following the rule of the form.
Examples of Example 1: A ship is heading 127&#176; per standard compass. For this heading the deviation is 16&#176; E and the variation is 4&#176; W in the area.
Required: (1) The magnetic heading. (2) The true heading.
Solution: The problem is one of correcting. Since the deviation is easterly, it must be added. Hence, the magnetic heading is 127&#176; + 16&#176; = 143&#176;. To find the true direction we are again correcting, and since the variation is westerly, it is subtracted. Hence, the true heading is 143&#176; &#8212; 4&#176; = 139&#176;. In this case the compass error is 16&#176; E &#8212; 4&#176; W = 12&#176; E. Applying this directly to the compass heading, we find the true heading is 127&#176; + 12&#176; = 139&#176;, as previously determined.
Answers: (1) MH 143&#176;, (2) TH 139&#176;.
Example 2: A ship&#8217;s course is 347&#176; psc. The deviation is 4&#176; W and the
variation is 12&#176; E.
Required: (1) The magnetic course. (2) The true course.
Solution: Again the problem is one of correcting. The deviation is subtracted and the magnetic course is 347&#176; &#8212; 4&#176; = 343&#176;. The variation is added and the true course is 343&#176; + 12&#176; = 355&#176;.
Answers: (1) MC 343&#176;, (2) TC 355&#176;.
Example 3: A ship&#8217;s course is 009&#176; psc. The deviation is 2&#176; W and the variation is 19&#176; W.
Required: (1) The magnetic course. (2) The true course.
Solution: The problem is one of correcting and since both errors are
west they are subtracted. The magnetic course is 009&#176; &#8212; 2&#176; = 007&#176;.
The true course is 007&#176; &#8212; 19&#176; = 348&#176;. Since 000&#176; is also 360&#176;, this is the
same as 367&#176; &#8212; 19&#176; = 348&#176;.
Answers: (1) MC 007&#176;, (2) TC 348&#176;.
Example 4: From a chart the true course between two places is found to be 22 1&#176;. The variation is 9&#176; E and the deviation is 2&#176;W.
Required: (1) The magnetic course. (2) The compass course.
Solution: It is necessary to uncorrect; the easterly variation is sub tracted and the westerly deviation is added. The magnetic course is 221&#176; &#8212; 9&#176; 212&#176;. The compass course is 212&#176; + 2&#176; = 2 14&#176;.
Answers: (1) MC 2 12&#176;, (2) CC 2 14&#176;.
Naming variation, Another problem that can arise is that of assigning a &#8220;name&#8221; east or deviation, or west&#8212;to variation, deviation, or compass error when the numerical compass error value has been found by subtraction between two directions. Here, the simple phrase rhymes as follows:
Compass least, error east.
Compass best, error west.
&#8220;Least&#8221; means lesser numerically, and &#8220;best&#8221; means greater numerically. For variation from true directions, &#8220;magnetic&#8221; can be substituted for &#8220;compass&#8221; in the rhyme.
Example 5: A navigator sets up a compass at a spot on shore near the ship&#8217;s anchorage. This compass, not being affected by the iron and steel of the ship, is free from deviation and indicates magnetic direction. From the chart the navigator determines the true bearing of a distant mountain peak to be 320&#176;. By compass it bears 337&#176;. The ship bears 076&#176; by compass from the observation spot ashore.
Required: (1) The variation. (2) The true bearing of the ship.
Solution: The numerical difference between the true and magnetic bearings is 17&#176;; since the magnetic bearing is greater&#8212;&#8221;best&#8221; by the rhyme&#8212;the variation is westerly, 17&#176; W. To find the true bearing of the ship is &#8220;correcting,&#8221; and we use the previous rule&#8212;correcting, subtract west; thus, the true bearing of the ship is 076&#176; &#8212; 17&#176; = 0590.
Answers: (1) V 17&#176; W, (2) TB 0590.
Example 6: Two beacons are so placed ashore that when seen in line from seaward they mark the direction of a channel, 161&#176; T. Seen in line from a ship heading up the channel, they bear 157.5&#176; by compass. The chart shows the variation for the locality to be 2.5&#176; E.
Required: (1) The compass error. (2) The deviation.
Solution: The numerical difference is 161&#176; &#8212; 157.50 = 3.5&#176;. Since &#8220;compass is least&#8221; the &#8220;error is east.&#8221; The compass error is the alge braic um of the variation and deviation. Hence, the deviation is the algebraic difference or 3&#8226;50 &#8212; 2.5&#176; = 1.0&#176; E.
The table below summarizes the six examples; answers that were
determined in each problem are underscored. A line for compass error (CE) has been added.
http://i202.photobucket.com/albums/aa305/FishersofMen/13apic.png
Deviation table 
Deviation changes with a change in the ship&#8217;s heading. The deviation is determined by comparing a direction shown on the compass with the known magnetic direction. Several methods of accomplishing this will be explained later. The deviation on various headings is tabulated on a form called a deviation table, or magnetic compass table, and posted near the compass. A copy of the table should also be kept posted in the chart house.
It provides blanks for filling in certain information regarding the compass and the correctors used to reduce the deviation. Two different columns of deviation are shown, one marked &#8220;DC OFF&#8221; and the other &#8220;DG ON.&#8221; &#8220;DG&#8221; refers to the ship&#8217;s degaussing coils. Since the deviation may be somewhat different when the degaussing coils are energized, it is necessary to determine the deviation under both conditions. A deviation table for a vessel without degaussing coils would be simpler by half.
The deviations shown in this illustration are somewhat larger than would be acceptable under normal conditions of a properly adjusted compass. Such larger values are given here to provide practice in calculation and interpolation, the procedure for determining an intermediate value between two tabular listings.

*Comment: *Every vessel has a different deviation, no two are the same. So a table must be made up for every vessel. Also, any thing you put close to the compass will change the deviation, weather it be a watch, powercord, cigarette wrapper, cell phone etc&#8230;&#8221;wonder why were off course? Shoulda seen the bouy by now, got enough gas?&#8221;
*COMPASSES*
*A) Theory*
Earth is huge magnetic field.
Magnetized pointer lines up with force fields.
North pole is off-center in northern Canada and changing.
All compasses point to that area (boat rotates around it.)
*B) Installing*
Make sure new compass in correct N-S and S-W.
Line up N-S/E-W with 2 books.
Put compass on one book, line up N-S reverse one with compass if not 180 degrees
adjust to 1/2 with no magnetic tool (if 4 degrees error, adjust by 2 degrees) do again until correct repeat for EW
Install on center line of vessel
string a line from bow to center of stern
measure equal distance from line to install
*C) Make deviation card*
Run several courses and record compass reading (better to line up 2 fixed points in front of you) work compass corrections for deviation card
Test for electrical interference by observing for changes when you turn on wipers, radio. If changes remove and twist wires.
Compasses are not really accurate due to off-center poles and electrical interference on your vessel but the &#8220;repeatability&#8221; us extremely accurate.
Always check your compass on leaving the dock and starting your day.
What does it read at the dock or on the first leg of your daily routine?
Does it agree with your GPS?
Remember it&#8217;s the most important piece of navigation equipment:
Stations don&#8217;t go off air, doesn&#8217;t break down and doesn&#8217;t need electricity to run.
*And finally, ONLY HEADINGS HAVE DEVIATION.* and *charts are in TRUE* you *MUST* convert when plotting a course.


----------



## Fishers of Men

Here are links to the Coast Guard Navigational Rules. The definitions are going to be needed to follow along and naturally the rules of the road along with some other needed info.

http://www.navcen.uscg.gov/mwv/navrules/rotr_online.htm

http://boatsafe.com/nauticalknowhow/boating/colregs.html

A partial list of
*NAUTICAL TERMS:*
ABAFT	Any direction between the beam and astern.
ABEAM	Relative bearing of 270 deg or 090 deg.
ADRIFT Loose; not secured to a stationary object.
AGROUND When any part of the ship is resting on the bottom.
ALOFT Above the decks; on the mast or rigging.
ANEMOMETER Instrument for measuring WIND velocity
ANEROID BAROMETER DRY method to measure AIR PRESSURE.
BEAM Measurement of GREATEST WIDTH of a vessel.
BELAY Act of securing line to cleat; also means to disregard.
BOLLARD Large round upright to TIE UP (ON DOCK.)
CLEAT Device to tie up to like a pair of horns.
COCKLE Kink in a rope or line.
DEAD RECKONING Method of navigating from known position with out taking SET and DRIFT into account.
DEVIATION Compass error caused by the VESSEL (correct with Deviation card.)
DRAFT The vertical distance from waterline to the keel.
DRIFT The SPEED that the current is taking you.
DROGUE Sea anchor; any device to hold you into the wind.
EBB The time the tide is flowing OUTWARD.
FLOOD The time that the water is flowing INWARD.
FREEBOARD	The distance from the deck to the waterline.
HEAVE TO The act of stopping or slowing the vessel.
HEAD REACH	The distance from when the prop stops and vessel stops.
LATITUDE The distance NORTH (and SOUTH) of the equator measured in degrees and minutes (a degree is 60 miles; a minute a mile.)
LINE Rope that has been assigned a specific job.
LONGITUDE	Measurement EAST and WEST of PRIME MERIDIAN. (GMT)
MEAN HIGH WATER	Average high tide; used to measure things above.
MEAN LOW WATER	Average low water; used to measure DEPTH.
MEAN SEA LEVEL	Average of low and high water.
NEAP TIDE That tide that has the least RANGE.
PAY OUT Expresses the idea &#8220;to feed out.&#8221;
PELORUS A hand held compass to take bearings. (A HAND HELD HAS NO DEVIATION)
RANGE Distance; two aids to navigation used to line up a narrow approach; the difference between the HIGH and LOW tide.
RIGHT HAND Rope that is twisted to the right; a prop that twists to the RIGHT to move vessel FORWARD
RUNNING LIGHTS Sidelights and stern lights COMBINED.
SEA ANCHOR Any device used to keep vessel into the sea.
SET The direction that natural forces take you.
SIDE LIGHTS Colored lights on the front (RED to PORT.)
SPRING LINE	A mooring line that goes at an angle.
SPRING TIDE	A tide that is higher or lower than normal.
STEERAGE WAY That speed that a vessel may be steered.
TIDE	The RISE and FALL of the water VERTICALLY.
VARIATION	Compass error caused by the off-center poles.
VEER	Allow a line to run out freely.
YAW	A vessel moving sideways violently.
A partial list of
*MISCELLANEOUS:*
1) Lee side = that side sheltered from the wind.
2) Fathom =6 feet.
3) Heave to = stop the vessel
4) Approach a dock or mooring against the wind and tide.
5) Shallow water = a) sluggish rudder.
b) trim is changed. (fore and aft balancing.) c) vessel will squat more.
6) To stop cavitation (prop turning too fast), decrease speed.
7) A V-shaped ripple pointing upstream can be caused by a snag.
8) Pivot point of a vessel:
a) 1/3 distance aft of the bow when going ahead.
b) 1/3 the distance ahead of the stem when backing.
9) Muddy water shows deeper on a depth sounder - two readings are caused by a muddy bottom.
10) Patent log measures the distance traveled through the water.
11) Protect a compass by covering it.
12) Gunwale - the top edge of a hull.
13) Caulk - a temporary patch on a hull leak.
14) Man overboard - approach from leeward. Besides proper maneuvering throw a floating object, turn toward the side he fell off and post a lookout. Make a Williamson Turn (60 degrees from course, hard over then 180&#176; from original course.)
15) The water is deepest at the outside of the curve of a river bend.
16) Bow cushion - effects of navigation in a narrow, steep-sided channel. Bow will be pushed away and stern sucked in.
17) Stern suction - same. (These will cause the bow to be pushed away from the channel side.)
18) Steering, signaling and communications shall be checked before getting underway.
19) Pyrotechnic devices (flares) are good for 3 years.
20) EPIRB (Emergency Position Indicating Beacon) is operating properly when light comes on and ocillating tone heard.
21) Life rafts are equipped with orange smoke signals.

VESSEL HANDLING 
Single screw - turns clockwise in forward if right-hand; wheel backs to port. Left-hand wheel backs to starboard
Twin screw - to clear the inboard wheel using the outboard engine, use after bow spring line with outboard engine ahead.
In forward gear, the bow will always swing toward the drag (engine that is stopped.)
Note: a) if a question about twin screw vessels use a paper or book to simulate the action of the vessel. b) also a twin screw has less or little paddle wheel effect.
A partial list of
*CPR AND ARTIFICIAL RESPIRATION*
1) NORMAL BREATHING RATE IS	12 PER MiNUTE FOR ADULTS
20 PER MINUTE FOR CHILDREN
2) CPR MUST BE CONTINUED. AS LONG AS POSSIBLE.
3) MUST BE STARTED ASAP AS BRAIN DIES IN 4-6 MINUTES.
4)10 APPLY CPR, PINCH NOSE CLOSED AND BREATH INTO MOUTH.
5) IF SUBJECT VOMITS:
TURN HEAD ASIDE
SWEEP OUT VOMIT
CONTINUE
6) PULSE RATE (HEART) IS 60 - 100 BEATS PER MINUTE BEST DETECTED IN CAROTID ARTERY IN NECK
HELICOPTER TRANSFER
A: REQUESTING HELICOPTER
GIVE: ACCURATE POSITION, WEATHER CONDITIONS, TIME, SPEED AND COURSE, WIND DIRECTIONS, TYPE OF VESSEL, MEDICAL CONDITIONS, ANY CHANGE IN PATIENTS CONDITION, ESTABLISH WHAT CHANNEL
B: WHILE UNDERWAY
MAINTAIN CONTINUOUS RADIO CONTACT, (SET UP SCHEDULE TO CONTACT), SELECT AND CLEAR SUITABLE AREA, LIGHT PICKUP AREA, AIM SEARCHLIGHT UPWARD (EASY LOCATION), NOTIFY PILOT OF PICK-UP AREA
C: UPON ARRIVAL
MOVE PATIENT TO PICK UP AREA, SLOW TO BARE STEERAGEWAY, AIM INTO WIND, PUT LIFE JACKET ON PATIENT
D: PICKUP
SIGNAL PILOT TO START, ALLOW BASKET TO TOUCH DECK, (STATIC ELECTRICITY), DO NOT TIE ANYTHING FROM HELICOPTER TO BOAT, IF YOU MUST MOVE THE LITTER, UNHOOK IT, LOAD PATIENT, THEN MOVE IT BACK, ATTACH HOOK TO LITTER, KEEP LITTER FROM SWAYING WITH LINE.

*OVERVIEW*
1. INFORMATION ON CHARTS, IN BOOKS
&#8226; READ INFORMATION IN LEGENDS OR BOOKS.
2. SPEED MADE GOOD (SMG)
&#8226; USUALLY 2 TIMES GIVEN AND 2 POINTS.
&#8226; APPLY 6O DST USING MEASUREMENTS BETWEEN PLACES AND TIME.
3. COURSE MADE GOOD (CMG)
&#8226; GIVEN: &#8226; 2 PLACES.
MARK BOTH, WALK RULERS TO COMPASS ROSE.
4. COMPASS COURSE:
&#8226; SAME AS ABOVE JUST USE COMPASS CORRECTIONS FOR ANSWER.
5. YOUR POSITION BY 3 BEARINGS PSC TO 3 PLACES
A. CONVERT ALL PSC TO TRUE (CAN ONLY DRAW TRUE.)
DEFAULT IS SIGHTING OVER COMPASS,
USE VESSELS HEADING FOR DEVIATION
&#8220;HAND HELD&#8221; COMPASS THERE&#8217;S NO DEVIATION.
B. DRAW THE BEARINGS.
C. WHERE THEY CROSS IS YOUR POSTION (USUALLY THAT SECTION), FIX IS IN MIDDLE OF TRIANGLE.
6. LEEWAY (ESTIMATE OF WIND ON YOUR VESSEL)
A. DRAW THE APPROXIMATE COURSE ON PAPER.
B. DRAW THE DIRECTION OF THE WIND (FROM WHENCE IT COMES.)
C. ADD OR SUBTRACT DEGREES FOR ANSWER.
7. TIDE/CURRENT PROBLEM
&#8226; A. LOOK UP THE CORRECTION IN THE BACK OF THE BOOK.
&#8226; B. WRITE DOWN THE CORRECTiON TIME OR RATIO.)
&#8226; C. NOTE THE REFERENCE STATION AT TOP, WRITE IT DOWN.
&#8226; D. LOOK FOR THE TIDE/CURRENT TIME/RATIO.
&#8226; E. SUBTRACT/ADD TIME OR MULTIPLY BY RATIO FOR CORRECT TIME OR HEIGHT.
8. SET/DRIFT
A. DRAW THE STARTING POINT, DIRECTION AND USED 60 X D divided by S/T FOR DISTANCE, LABEL IT AS DR (SEMICIRCLE, DOT, TIME.)
B. DRAW THE ACTUAL FIX WHERE YOU WERE.
C. DRAW A LINE FROM THE DR TO THE FIX (SET LINE) LABEL WITH a.
D. WALK IT TO COMPASS ROSE AS SET LINE.
E. MEASURE THE DISTANCE FROM DR TO FIX.
F. APPLY 60 X D/ST FOR DRIFT.
9. ESTIMATED POSITION
A. DRAW THE STARTING POINT, DIRECTION AND USED 60 DST FOR DISTANCE, LABEL IT AS DR (SEMICIRCLE. DOT, TIME.)
B. DRAW THE SET (GIVEN) THRU THE DR (LABEL IT WITH A)
C. USE 60 DST TO ASCERTAIN DISTANCE ALONG LINE FOR EP.
10. COURSE TO STEER (COMPENSATING FOR CURRENT)
A. DRAW THE STARTING POINT, DIRECTION AND USE 60 DST FOR DISTANCE, LABEL IT.
B. DRAW THE SET/DRIFT FROM THE INDICATED POINT
C. MEASURE THE LINE &#8220;BACKWARDS&#8221; (TURN INTO CURRENT.)
D. MAKE THAT POINT YOUR POINT TO AIM.
E. DRAW LINE AND WALK TO COMPASS ROSE FOR PTA.
11. TIME TO ARRIVE
A. FIGURE THE DISTANCE.
B.USE 60 DST TO FIGURE TIME.
C. ADD TIME TO TRAVEL FROM START FOR ANSWER
D. SAME AS ABOVE EXCEPT TO SUBTRACT FROM TARGET TIME.
13. WHAT IS DISTANCE FROM? TO?
FIND 2 NAMED PLACES, DRAW LINE, WALK TO LATITUDE SCALE OR, LOOK IN THE BACK OF REED&#8217;S COMPANION FOR ANSWER.
TIME/SPEED AND DISTANCE
60D D=SXT  S=60D T=60D
SXT 60 T S

I) DISTANCE 55 MILES X 45 MINUTES SPEED?________ TO FIND DISTANCE MULTIPLY SPEED TIMES TIME DIVIDE BY 60
D=55X45 =41.25 DISTANCE + 60
2) SPEED DISTANCE 72 MILES IN 112 MINUTES SPEED? SPEED 60X72/112=38.6 KNOTS
14. TIME 45 MILES AT 12 KNOTS
60X45112=225 MINUTES (3 HOUR 45 MINUTES)

*RED FLAG WORDS*
The purpose of this sheet is to alert you when certain problem words show up. 
Most of the errors are misreading not the material.
SAILBOAT Means the vessel is sailing under sail alone (can&#8217;t be anchored)
NUC Exceptional Circumstance broken down, accident / R/R The _(red over red lights)_ captain is dead
RAM Working, paid for doing, designed for / Same fog signal anchored or underway
UNDERWAY Two types making way (wake) / or not making way (wake)
SAFE SPEED ALWAYS BEST ANSWER
ACTION AMPLE and in time
NARROW CHANNEL +20/-20 & sail/fishing/crossing Western River power only downbound/upbound/crossing
TSS -2O/sail/fishing/crossing (grouped together)
OVERTAKING ALL WAYS give-way don&#8217;t mix with OVERTAKEN
SAILBOAT R.O.W. STAND-ON downwind or starboard tack / No maneuvering signals
POWER CROSSING	To right has R.O.W. and give-way don&#8217;t cross ahead
OPEN WATER R.O.W. New reels catch fish so purchase some / Note: assume open water unless stated
FOG No R.O.W. I bear ahead - bare steerageway/ Radar change course alone
GIVE-WAY EARLY and SUBSTANTIAL
STAND-ON Hold course and speed but may take action in doubt must take action in extremis
TOW LIGHT The yellow over white stem light/Not 2 cr3 masthead
MASTHEAD LIGHT 2 FOR PUSH, HIP & -200 ASTERN: 3 for +200 Power only no MH NUC/fish/sail/towed/pilot/ -50 trawl
SAIL LIGHTS Tricolor -20 R/G on any never together
FISHING R/W _(red over white light) _is fishing at night note: same fog signal anchored or underway
TRAWLING NOT TROLLING G/W _(green over white)_ trawling at night! note: aft MH _(masthead)_ if +50
DREDGE NO ANCHOR LIGHTS/Already has seven
CBD Constrained by draft (crushed beer can day symbol) never on Inland
SIGNALS INT&#8217;L: I AM? (except narrow channel) / INT&#8217;L: I INTEND? (exchange signals) ONLY SHORTS ON LIGHT 1/2/3/5 (IN SIGHT ONLY)
FOG SIGS Only used when can&#8217;t SEE/No R.O.W. in fog
AGROUND 3 strokes before and after anchor signal (rapid ring of bell at least every minute)
OVERTAKING NC	INT only/ prolong, prolong +1 or 2 shorts - I intend?
SPECIAL FLASHING	INLAND only on front of barge (yellow 180-225&#176
TOW ASTERN SAME FOR ALL/ Si, 2/3 MH, yellow stern
INLAND TOW HIP/PUSH y/y /No white on Western Rivers
RUNNING LIGHTS	None no wake NUC/RAM/fish/trawl (NURFT) all others on when underway
NO MASTHEAD NUC, fish, trawler-50, sail, pilot note: RAM, CBD, minesweeper shows masthead lights
SAME FOG SIGNAL	Whether anchored or underway - RAM and fishing only
SUBMARINE LIGHT	Yellow 6 flashes (I sec) then off for 6 seconds
SIDE LIGHTS OUT When not making wake: NUC, RAM, FISHING, TRAWLING NURFT - ALFS DUMB BROTHER
NAVIGATION AIDS	White in middle/green on port/red on starboard/ group 2+ 1/yellow for special
PLOT TERMS	C course to steer	PTA point to aim
CMG course made good	SOA speed of advance
SMG speed made good	CPA closest point
PSC per steering (or ship&#8217;s or standard) compass only use when word compass&#8221; is used
T True heading (always use if in doubt)
Your &#8220;memory aid&#8221; and this list will put you very close to your target of 90&#37; on
RULES OF THE ROAD. (Look up the definitions in the rules link)

*PLOTTING HINTS*
Plotting Hints...Navigation by Chart and Problem Data
Locations/Fixes...may be one of or combination of
&#8226; LAT/LONG, LORAN-C or Range(s) and/or Bearing(s) to known object(s).
&#8226; If by three bearings...may get &#8220;cocked hat&#8221;; assume position in center.
&#8226; Bearings &#8220;to Stbd or Port beam 900 relative or 2700, respectively.
Unless the problem dictates you do otherwise
&#8226; Headings, bearings	Use TRUE degrees
&#8226; Distances	Are in NAUTICAL miles
&#8226; Speeds	Are KNOTS (nautical miles per hour)
&#8226; Time	HOURS (take care in additions/subtractions)
Relationships between Speed. Distance and Elapsed Time
Memory Relationship	Distance=Speed X Time	D= S X T
Speed= Distance/Time	S = D/T
Time= Distance/Speed	T = D/S
Develop Plotting Disciplines
&#8226; Use an fine line, sharp pencil for plotting on chart;
&#8226; Indicate Fix by circle, DR and EP by half circle with &#8220;24 hour times&#8221;;
&#8226; Indicate directions of bearings, headings, sets by line with arrow head for direction;
&#8226; Use appropriate abbreviations (see below);
&#8226; Exercise care in &#8216;walking&#8217; headings or bearings from the compass rose and measuring distances with dividers. Slight miscue&#8217;s can mean trouble!
Measuring Distances
&#8226; Always on the VERTICAL scale of the chart, i.e., between parallels of latitude.
Typical Abbreviations for use on the chart plot
&#8226; FIX &#8220;known&#8221; location	&#8226; PTA Point to Aim	&#8226; DR Dead Reckoned Pos.
&#8226; C Course or Heading &#8226; CTS Course To Steer &#8226; EP Estimated Pos.
&#8226; S Speed thru water &#8216;ETA Est. Time of Arrival &#8226; PSC Per Ships (or std.) Compass
&#8226; CMG Course Made Good &#8226; SMG Speed Made Good
Compass Corrections
&#8226; Deviations can change with vessel&#8217;s heading... take note if the problem alters deviation with different headings (normally with &#8216;multiple leg&#8217; problems only);
&#8226; if necessary, make corrections with: TVMDC &#247; W (fall down) after completing problem.
Speeds / Direction
&#8226; RPM or Prop Speeds are speeds of vessel thru water not SMG;
&#8226; Set/Drift... Direction/Speed vessel is carried due to water currents. (* make sure you understand the nature of the vessel speed given.)
Ship&#8217;s Movement... Resultant of several effects
&#8226; Vessel&#8217;s propulsion system (oars, sails, engines, etc.,); PLUS
&#8226; Water currents. i.e., a set (direction) at a drift (current speed) ; PLUS
&#8226; Wind effects known as leeway; (normally NOT taken into account) but if problem requires, it will typically be given as &#8220;westerly (or easterly) leeway degrees&#8221;; simply add (or subtract) to compass corrections as with westerly (or easterly) deviations.


----------



## Fishers of Men

I was asked by REEL and his OGF mail was returned to me undeliverable. So here goes: &#8220;Why does the center of all this have an offset ?&#8221;

We have not got to the center yet.  Hope this answers a hard to answer question. There are too many topics that all coincide to list right now. I am spending a lot of time pulling out my research and thoughts on these matters.
This is mainly a large focus on safety and education for new boaters on the Great Lakes. And a call out to experienced seaman/fishermen to refresh their memories, chime in, and to share information. How conditions are effected by the sun, moon, earths movements, predicting weather patterns on your own, applying conditions to fishing, survival, boat handling, why things work certain ways and so on. I can only pump a bunch of factual info out there and what anyone does with it is up to them. It will get intense and those with little knowledge will probably have a hard time keeping up. I would appreciate it if everyone would write their questions down and periodically I will ask for questions and or/input. I appreciate any oversights I may have or forgotten to mention. I am getting ready to put up a section on charts, applying info that was already posted to show how all these things come together. All the way through I will incorporate pre read posts to new material so the applications are applied and the results seen for themselves. I might not have started in the right order, but I guess you could call it a informal free online maritime course for educational purposes. I am going to cover a lot of material. I figure anyone could print out things that could be used as helpful future referral. A lot of members posted that they had no time for classes and such and would really like to learn. I am thankful for all those that I have boated/fished with and learned from all my life and I have plenty of time to share what I can, and learn more on these never ending processes, with anyone on these topics that I enjoy.
Thanks for the question.


----------



## Fishers of Men

Well, so far we can get an idea here from where the almanac/gps and others get there sun/moon best fishing days/times from. Not covered is tidal info that has to do with all this. Unless someone asks, I'll throw it in. I crammed a lot of info in to start, now I will go a little slower and if questions arise on what is already posted, bring &#8216;em on.

There were posts by Donkey, Ezbite and a few others that stated common sense and knowing your surroundings when you leave the dock and while your on the water to stay aware of all landmarks, bouys, towers, buildings and such at all times. These things are very important navigational aids. Everything we are going to cover is a navigational aid. When on the water you must use ALL the navigational aids available to you, sometimes you wont &#8220;see&#8221; many. We will try to help you notice more aids that can be overlooked. These things will get you home safely whether it be that adverse conditions set in, restricted visibility, strange areas, etc&#8230;day or night. And yes, when we get done here, applying what we have learned could even get a person lost at sea more chance for survival and even back somewhere. A lot of this info will be forgotten and or never used, but might spring back some memory come the day it is needed, even if it&#8217;s only a small segment that would help matters in emergency. Knowledge and experience on the water makes the difference of what different people do out there. For instance, some say that us night guys in the cold and dangerous circumstances are crazy. Not so, with the proper knowledge, experience and wisdom it is a normal everyday thing for us. When situations occur, all this comes into play and you deal with it at the time. Speaking of time, timely means RIGHT NOW, immediately, no hesitation or having to think about it. Many times you don&#8217;t get a second chance. If you have a good educated crew on board, things go automatically and nice and smooth. Not to panic, just deal with it, time is of the essence. Knowledge, experience and respect for the elements. Moving on&#8230;

There is a lot of info on the magnetic forces in a previous post, that need to be recognized for whatever lat/long you are in at the time. If you look on a chart, there are areas that have different compass rows. They are spaced apart in particular areas do to magnetic variations in the earth. In the center of the compass rows is and area that says for example: variation 10 degrees 30&#8217; W and a date. Then under that, it will show an annual increase, of say 6&#8217;. (This &#8216; is all I can show for minutes.) This is do to the magnetic changes in that area effecting your compass. Charts should be of the latest update always, as you will not be where you think you are. The bottom left corner on a chart shows the publication date. Now, if all you have to work with because other means went down (gps etc&#8230 is an old chart, you can take the above example of 6&#8217; and times that difference from the year noted by the variation shown, to the current year to be close. But it is no real cigar. It might help you to miss an obstruction and or get you close to home though. For instance variation 10 degrees 30&#8217;W 1990 and this is 2007, you would subtract 1990 from 2007 = 17 yrs. Now take the 6&#8217; for 17 yrs, 6 X 17= 102 minutes. As you can see, you would have been WAY off course going by the old chart. Always use the compass rows closest to you for reasons explained above. ALL measurements of distance MUST come from the latitude side of a chart, for lines of latitude are smaller circles parallel to the equator around the earth. On most charts parallels of latitude (Lat or L) appear as horizontal straight lines. (I will get into distances in the next post.)
The Earth is oblong, so lines of longitude are &#8220;squeezed&#8221; together at the north and south poles. As shown before, (and I know you printed the links) a mile is 1 minute of latitude, that&#8217;s where the saying comes from &#8220;a mile a minute&#8221;. I think now we should change course for clarification purposes:

*MARINERS&#8217; MAPS*
(charts are NOT maps)
Maps drawn on the surface of a globe correctly represent the curved surface of the earth; maps or charts on a flat surface, especially those of large areas, are necessarily distorted. The smallest globe, although impracticable for the daily work of the navigator, is an invaluable aid to understanding charts and various other matters with which navigators are concerned. Fig. 1100.
*http://i202.photobucket.com/albums/aa305/FishersofMen/1100.png*
*Definitions on a globe. *The drawing of the sphere of the earth illustrates certain definitions important to all mariners.
The earth is assumed to be a sphere with its axis passing through its north pole and its south pole.
*Great circles.* If a plane passes through the center of the earth, as when cutting an orange in half, its intersection with the earth surface is a great circle. The plane must pass through the center or only smaller circles result. Arcs of great circles, often appearing as straight lines, are important elements of chart construction.
Angles, as measured from the center of the earth, are the principal basis for measurements on its surface. An angle is formed by the intersection of two lines and is measured by the divergence of the lines without regard to their length, as in Fig. 1101. 
*http://i202.photobucket.com/albums/aa305/FishersofMen/1101.png*
The units of angular measurement result from dividing any circle, whose center is at the intersection of two lines, into 360 degrees ; each degree is further divided into 60&#8217;, and each minute into 60&#8221;. In practical navigation, it is sufficiently accurate to express seconds (&#8220 of arc by the nearest tenth of a minute (&#8216.
The equator is a great circle around the earth midway between the poles. Its distance from each pole is everywhere 90&#176;, or one-fourth of a circle, but the equator, because it is a complete circle, is divided into 360&#176;.
Meridians are best described as halves of great circles extending from pole to pole always at right angles to the equator. A line drawn through the ship, north and south to the poles, is the meridian of the ship. A similar line through Greenwich is called the prime meridian and is the zero line from which longitude is measured. Meridians on Mercator charts appear as vertical, parallel straight lines.
Parallels of latitude are smaller circles around the earth, parallel to the equator. On most charts, parallels of latitude appear as horizontal straight lines.
*Latitude *(Lat. or L.) defines position on the earth north or south from the equator. The latitude of a place on the surface of the earth is the arc of the meridian between the equator and that place. Latitude is 0 degrees on the equator and never exceeds 90&#176;, which is the latitude of either pole; it is marked N (+) or S (&#8212. Observe how the latitude of Scotland Light ship, off New York, is measured in Fig. 1100.
*http://i202.photobucket.com/albums/aa305/FishersofMen/1100.png*
*Longitude* (Long.) defines position on the earth east or west from the meridian of Greenwich, which is called the prime meridian. Longitude of a place on the earth&#8217;s surface is the arc of the equator between the prime meridian and that of the place. It is measured East (E) or West (W) from the meridian of Greenwich (0&#176; Long.), and therefore does not exceed 180&#176; or halfway around the earth, where east meets west.
_(comment: coincide this with the diagrams on &#8220;time&#8221; from earlier.)_
Position of any point at sea or on the land may be defined by its latitude and longitude. For example, the position of Scotland Lightship is in Lat. 40&#176; 27&#8217; N and Long. 73&#176; 55&#8217; W.
The true direction of a line on the surface of the earth at any point along the line is the angle the line makes with the meridian through that point. It is generally measured from 0&#176; at true north around clockwise to 360 degrees.
A nautical mile (6076 ft.) is the unit of distance used at sea. By international agreement, it is equal to exactly 1852 meters and is approximately equivalent to 1&#8217; of latitude or to 1&#8217; of arc of any great circle of the earth. A nautical mile is approximately one-seventh longer than the statute mile (5280 ft.).
Mercator&#8217;s projection: To represent approximately the spherical surface of the earth on a flat surface, maps are constructed in many different ways according to the purpose for which a particular type of map is devised. Mercator&#8217;s projection, previously outlined is the system by which most maps used by mariners are constructed. Charts of this type have been in use since the publication about 1569 by Gerar dus Mercator, a Flemish geographer, of his then excellent map of the world. The navigator may not be called on to construct a Mercator chart but a knowledge of how such charts are developed is an aid to understanding many things related to voyages at sea. The drawings in Fig. 1102 represent three stages in the development of a Mercator chart.
*http://i202.photobucket.com/albums/aa305/FishersofMen/1102.png*
Imagine the true map of the earth&#8217;s surface on a globe to be unfolded as if an orange were peeled. The segments shown in *(A) *everywhere represent 30&#176; of longitude but are bounded by converging meridians as on the earth. The distance between these meridians at 60&#176; N or 60&#176; S is only 900 miles, whereas at the equator they were 1800 miles apart. The true length of 1&#8217; of longitude continually decreases from 1 mile on the equator to 1/2 mile in 60&#176; N or S and thence to 0 at the poles regardless of how it may appear on any chart. Minutes of longitude are never a measure of nautical miles except on the equator.
The horizontal lines drawn across the segments above and below the equator represent the parallels of 30&#176;, 60&#176;, and 80&#176; N or S latitude. These are parallel lines; they do not converge as do the meridians of longitude, and the actual distance between any two such parallels of latitude is everywhere the same. The length of 1&#8217; of latitude, which is measured on a great circle of the earth, is 1 mile according to one definition of a nautical mile. Minutes of latitude are always a measure of nautical miles in their latitude. For example, the distance between a parallel of 30&#176; and that of 60&#176; is 30&#176; or
30 X 60&#8217; = 1800&#8217; = 1800 nautical miles.
In *(B)* the segments from the globe appear as expanded with their edges joined in vertical, parallel straight lines which represent the meridians on the Mercator chart shown as a cylinder wrapped around the earth. These apparently parallel meridians appear equally distant from one another, whereas on the earth the true distance between them constantly decreases as they converge from the equator to the poles. Except on the equator all of the east and west dimensions on the chart have been expanded, this expansion being greater, the greater the latitude.
To avoid local distortion, the expansion of the longitude scale at any given distance from the equator is applied to the latitude scale in that area. The scale at the sides of the chart which represents a minute or a degree of latitude continually increases from the equator to north or south and becomes impossibly great when approaching the poles. This is why drawings (B) and *(C)* reach only to 800 N; charts of the polar regions cannot be constructed on Mercator&#8217;s projection.
The drawing* (C) *shows half of the cylinder unrolled as a flat chart of the Western Hemisphere, from 60&#176; S to 80&#176; N. Within these limits it represents a Mercator projection of the map shown on the globe (B).
In practice charts of such large areas are seldom used. The drawing, however, illustrates an important characteristic of a Mercator chart. The scale of the chart increases as the latitude scale at the right of the drawing increases. If an area of the earth&#8217;s surface be represented by a 1-inch square figure on the chart at the equator, an equal area at 60&#176; N or S on the same chart will appear as a 2-inch square. On the drawing Greenland looks as large as South America. Actually, the area of our southern neighbor approximates ten times that of Greenland.
Rhumb lines or Mercator tracks. Any straight line on a Mercator chart is a rhumb line as, for example, the line from A to B on the chart in Fig. 1103. 
*http://i202.photobucket.com/albums/aa305/FishersofMen/1103.png*
Note the most important and useful property of a Mercator chart. A rhumb line between two points crosses each meridian at the same angle, which is the true course to steer continuously from one place to the other. All courses plotted on coastwise charts are rhumb lines, and the course to steer remains unchanged all the way along the rhumb line or Mercator track from A to B.
Theoretically, a rhumb line is seldom the shortest track between two points because, with rare exceptions, it is actually a curved line on the earth&#8217;s surface, be its curvature ever so small. Because a rhumb line may not be the shortest track, mariners sometimes follow a series of rhumb lines which approximate a great circle, along which lies the shortest course from one port to another. _(comment: we may discuss more on this later)._
Great circle tracks. The coastwise man, dreaming of voyages to foreign climes, may easily understand the principles of great circle sailing.
Stretch a string or an elastic band between any two points on a globe; it will represent the great circle track which is the shortest distance between the points. On certain long voyages the distance saved by great circle sailing is of importance. This fact and one other characteristic of a great circle course may be illustrated, with a globe, by considering the somewhat extreme case of a voyage from Sydney, Australia, to Valparaiso, Chile. (See Fig. 1105.)
*http://i202.photobucket.com/albums/aa305/FishersofMen/1105.png*
Hold a piece of string which does not stretch, in a straight line on the globe from Sydney to Valparaiso. This string will pass south of New Zealand and slightly below the parallel of 60&#176; S. Cut the string so that its length measures the distance between the two ports. Place one end of this measuring string at Sydney, and apply it to the globe so as to &#8220;run down the latitude&#8221; toward Valparaiso on a rhumb line or Mercator track, about 3&#176;.5 below and parallel to the line on the globe which represents 30&#176; S latitude. The string will not reach Valparaiso by almost 800 miles, which represent the saving in distance by approximating the great circle track on which the length of the string was measured.
Again stretch a string, or better an elastic band, along the great circle from the one port to the other. Note that the initial course from Sydney will be toward the SE quarter but will continually change as the track crosses each meridian until, on approaching Valparaiso, the course will be toward the NE quarter. This is a radical illustration of the general fact that whenever great circle sailing is of practical advantage a ship must change its course from time to time in a manner to approximate the great circle track.
There are no practical advantages in great circle sailing under certain circumstances, which are:
For relatively short distances in any direction, as when sailing coast- wise; since the rhumb line is almost coincident with the great circle track, the possible saving in distance is nil and great circles may be forgotten.
Along meridians which are themselves great circles extending north and south from pole to pole; when the course approximates N or S, there is no saving in distance between two places near the same meridian.
Within the tropics the true map as shown on a globe is almost a Mercator chart; the equator is both a great circle and a rhumb line as are the meridians; the parallels of latitude near the equator are almost rhumb lines. In these regions rhumb line sailing is very nearly as short as great circle sailing.
Summarized in a reverse manner: Great circle sailing is most advantageous when sailing a long voyage east or west in relatively high latitudes.
Atlantic coast yachtsmen are familiar with two such examples: (1) The track of 628 miles of 1460 true from Newport to St. David&#8217;s Head, Bermuda, is only a hair shorter if measured on a great circle. (2) On the other hand, a great circle course across the North Atlantic to Europe is materially shorter than any rhumb line course. The victory of Olin Stephens&#8217; yawl Dorade in the transatlantic race of 1931 was partly due to the fortunate outcome of her owner&#8217;s decision to approximate a great circle course.
Great circle charts furnish a simple graphic method for determining a great circle track. They are so constructed that a straight line between any two points on the chart represents the great circle track. Such a line between two ports of departure and destination at once indicates whether it passes clear of danger or through latitudes which should be avoided at the time of a proposed voyage. Having considered the contingencies, one or more straight lines may be drawn to represent the desired track or tracks.
To attain these useful characteristics, a great circle chart is constructed on the so-called gnomonic projection. Neither meridians nor parallels of latitude appear as parallel lines, and neither courses nor distances can be taken directly from such a chart. However, the charts are arranged so that it is a simple matter to take off the latitude and longitude of several intermediate points on a great circle. These points are then plotted on a Mercator chart; and joined by straight lines which are a series of rhumb lines approximating the selected track. Course and distance represented by each rhumb line are determined as on any Mercator chart. The total distance via these rhumb lines will be only slightly greater than the distance along the great circle.
The nature and use of great circle charts and their relation to Mercator charts are illustrated in Fig. 1105 *http://i202.photobucket.com/albums/aa305/FishersofMen/1105.png *
which diagrams various courses from Sydney to Valparaiso. It is assumed that the shipmaster, out of Sydney, desires to approximate a great circle track because it is shorter and because it takes the ship into the prevailing westerlies of the southern seas. On the great circle chart a straight line from Sydney to Valparaiso represents the great circle track and shows that it clears the southern end of New Zealand but passes below 60 degrees S. To avoid the dangers of such a low latitude, it is decided not to go below 55 degrees S, an assumption which serves the purpose of the illustration. A more probable course would be through Cook Strait between the New Zealand islands.
In the case illustrated, seven rhumb lines are assumed which approximate the great circle track except that the track does not go below 55 degrees S. Each position where course is changed is marked in exactly the same latitude and longitude on either chart. The proposed track is correctly plotted on both charts, as are the great circle and Mercator tracks, although each track has an entirely different appearance when transferred from one chart to the other. The Mercator chart shows the great circle track as a much longer line than the rhumb because on such a chart one inch at 60&#176; S measures only three-fifths as many miles as at 30&#176; S.
Great circle charts have robbed great circle sailing of its mathematical mysteries. The initial great circle course and the great circle distance between any two points may be computed, but for the practical business of great circle sailing the modern mariner uses great circle charts. The student who wishes to pursue this subject should procure one or more such charts and the corresponding Mercator charts.
*Various charts.* Ocean charts and coastwise charts in general use are on Mercator&#8217;s projection, and are scaled by nautical miles. Charts of the Great Lakes and other inland waters use a statute mile scale. (comment: depends where you get the chart from) Ocean charts are on small scales; they show lines of equal variation, steamer tracks, ocean currents, and other general information; only the true compass rose is printed on these charts. Coastwise charts show details on various larger scales and have a magnetic compass rose inside the true rose. There are a variety of special charts, mostly on Mercator&#8217;s projection, whose titles as listed in the chart catalogs indicate their various purposes. Pilot charts for the different oceans contain an amazing variety of information, including the average weather conditions and other useful data. Nowhere can an oceangoing sailorman learn more than from a pilot chart.
*Small-craft charts. *Of major interest to yachtsmen are the NOS small-craft charts now available. These charts are designated by the letters &#8220;SC&#8221; following the chart numbers.
The small-craft charts are issued already folded and are designed for ease of reference and plotting in cramped quarters. They stress the details appreciated by operators of small craft, such as large-scale in sets of small-boat harbors, tide and tidal current tables, weather data, whistle signals, facilities at marinas, suitable anchorages, and often-used courses and distances.
Small-craft charts are available for many areas such as Long Island Sound and the Chesapeake Bay and rivers such as the Potomac and Rappahannock Rivers, commonly used by small boats. These charts are especially useful for craft cruising the important Intracoastal Waterway. 
Plotting sheets are blank charts for use instead of regular nautical charts. They are used when the scales of available ocean charts are too small for practical plotting or when it is desired to plot celestial lines of position without marking up the regular chart. Plotting sheets printed and issued by DMAHC show meridians and parallels drawn on the Mercator projection and include one or more compass roses. 
Homemade plotting sheets for limited areas are easily constructed with sufficient accuracy for plotting part of a day&#8217;s work at sea or for plotting problems. Uniformly ruled paper facilitates their construction, although one, may rule the paper for himself.
The method of constructing a small area plotting sheet is shown in Fig. 1108 
*http://i202.photobucket.com/albums/aa305/FishersofMen/1108.png*
which represents the middle portion of the proposed layouts. Assume that the center of the work you expect to plot is in about 40&#176; N and 70&#176; W. Label a vertical line down the center of the sheet as 70&#176; W. Draw a horizontal line across the middle and label it 400 N. In the drawing, each space between the vertical lines represents 1&#8217; of longitude; therefore label each 10&#8217; of longitude as shown.
To locate a 10&#8217; parallel of latitude according to Mercator&#8217;s projection, draw a line from the center at an angle to the horizontal equal to the middle latitude, in this case 40&#176;. The length of this diagonal intercepted between two meridians 10&#8217; apart is then the length of 10&#8217; of latitude. With this distance, space, rule and label as many 10&#8217; parallels as the problem requires or the paper permits. The graduations of the diagonal line marked by the 1&#8217; meridians give the scale of miles to be used all over the plotting sheet.
There are numerous variations of the above procedure. In any case, the point to remember is to draw the diagonal at an angle with the horizontal equal to the middle latitude of the area to be represented and thus find the latitude scale. The method is not a mere school room fancy, and is often used to plot situations in the navigator&#8217;s work book. 
To construct a Mercator chart. The above methods are theoretically correct at the equator and sufficiently accurate for all small plotting sheets. If the navigator ever should need to construct a Mercator chart of large areas beyond the Tropics, the method of meridional parts given in Bowditch should be used.
All charts published are identified by number sometimes prefixed by letters; as &#8220;SC&#8221; for the small-craft charts. FIG. 1108. HOMEMADE PLOTTING SHEET.
Notices to Mariners. Notice to Mariners, a weekly pamphlet prepared by DMAHC and the U. S. Coast Guard, contains notices of changes in lights, buoys, and other aids to navigation including radio which have occurred throughout the world. Notice to mariners is divided into three sections. Section I has corrections to charts, coast pilots, sailing directions, catalogs and paste on chartlet corrections. Also listed are new charts and publications, depth tabulations and hydrographic notes. Section II has corrections to light lists, radio navigational aids and other publications. Section III contains radio broadcast warnings and lists those warnings which are still effective from previous notices.
The DMAHC also publishes at intervals of about six months a summary of corrections in two volumes which assists the navigator in maintaining up-to-date charts, sailing directions and coast pilots. Volume 1 covers the Atlantic, Arctic and Mediterranean seas. Volume 2 covers the Pacific, Indian and Antarctic seas.
A listing of changes in local aids issued by the Commandant of each Coast Guard District on request is usually sufficient for many mariners who only operate locally. 
Careless mariners may not record all of these changes on an extensive set of charts, but the arrangement of the Notices is simple and permits noting at a glance important changes in any particular area. All charts are stamped near the lower left-hand corner with the date to which they have been corrected before issue from Washington. Dealers do not correct charts and the purchaser should insist that the date of correction be reasonably recent.
Care on small vessels. A good chart desk with drawers is desirable and, when possible, should be within speaking distance of the helmsman. Rolled charts are a nuisance but ideal conditions for filing charts flat without folding may be impracticable. A drawer 37 X 25 >< 3 inches, inside, will take the largest charts folded once, and will accommodate about 75 charts, assuming an average proportion of smaller charts that need not be folded. Fold the charts map side out. Mark the chart number on both sides at the right-hand corner next the folded edge, which should be toward the front of the drawer. File in numerical order; keep the chart catalogs handy and from their index maps select the required chart by number. A drawer of half the above size evidently will hold any chart folded twice, and if drawers are not available vertical files folded against a bulkhead or flat racks under the deck beams will avoid rolling. A plastic case about 25 X 21 inches with transparent sides is useful for protecting the chart on deck and keeping it from blowing away.
Charts are the most important tools of the navigator other than the compass itself. Present-day charts are the result of decades of work by the principal governments of the world, among which the United States and Great Britain have been the leaders. The meaning and use of the infinite detail appearing on modern charts will be discussed later. It is not sufficient partially to understand a chart. The navigator must train himself to interpret the meaning of every mark on a chart and to convert every detail he observes along the coast or at sea into the symbols and the terms used on charts.
We that are going on Lake Erie fishing normally do not do all of these things. Having local knowledge of a familiar area is one thing. But I guarantee you that the experienced Captains are always on top of there surroundings mentally and know where they are at every given moment. They also have had the training that is being brought to you here; these captains have the knowledge and experience necessary to make judgment calls on the spot.
It is a good idea to keep a chart on board if you need it or not. If electronics go down, _advection_ fog sneaks up on you for example and no visible landmarks regardless if you are trying to get home or call for help if you are broke down, you have to know or figure out where you are. 
We will discuss more on chart reading and time/speed/distance next post.


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## Fishers of Men

I guess it's a good time for questions and or input. Thanks


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## fugarwi7

Whew Fishers!!.....I think I'll just turn on my GPS, plug in a "Goto" waypoint, and fiddle with my tackle along the way, periodically glancing at my compass just in case the GPS goes on the fritz!!  

Just kidding with ya...this will be good reading as the winter progresses. And by next spring, I can sell all of my electronics and buy more tackle!


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## Fishers of Men

fugarwi7 said:


> Whew Fishers!!.....I think I'll just turn on my GPS, plug in a "Goto" waypoint, and fiddle with my tackle along the way, periodically glancing at my compass just in case the GPS goes on the fritz!!
> 
> Just kidding with ya...this will be good reading as the winter progresses. And by next spring, I can sell all of my electronics and buy more tackle!


 Hope your compass doesn't die. lol. Keep up with it...it's gonna get better when we start putting this stuff into fishing! Everyone is probably wondering whats it got to do with the fish? Well, we will have to wait and sea. pun intended


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## FISHONAJ

Good read Van ~ you obviously know your stuff. I'll keep checking back as i want to learn more about how all this is gonna get me on more :B 

AJ


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## Fishers of Men

I would like to discuss charts first to make sure everyone has an understanding of them. This way we can start a voyage together on here. Even the best chart is of little value if the mariner is not thoroughly familiar with the various conventions and symbols used in it's compilation. Charting is a dynamic rather than a static activity. Over time charts need to be revised. _( you saw the magnetic forces about the Earth and the Earth is always changing)_
There are many types of charts, you can go to the NOAA website to see these. The purpose of a nautical chart is to provide information necessary to promote safe and efficient marine navigation. The time-honored application of a chart is to provide data that can be used the navigator to fix the vessels position, for example, by taking visual bearings on charted natural and artificial features or ATONs. The fix might be used directly or as a check on the vessels position determined by other means, such as an electronic fix read from a loran or gps reciever. As important as nautical charts are for position fixing, the real utility of a chart lies elsewhere-in orienting the mariner. A position fix merely answers the question "where am I?" But often a more relevent question is "what does it mean to be here?" From a decision theoretic perspective, "here" should not be described by the conventional coordinates of latitude and longitude, but rather in terms of the relevant features of the surroundings and their implications for underway decision making. Charts help answer numerous key questions. Is "here" in the vicinity of rocks, shoals, ledges, reefs, tide rips, sunken wrecks or other potential hazards to navigation which should be avoided? Is "here" on the vicinity of a danger area, prohibited area, TSS or other regulated area? Is "here" near a planned turn point, waypoint or destination? Is here a place where I can anchor safely, and if so, which anchor should I use to maximize my holding power? Is "here" along my intended route, or should I make course adjustments to get back on track? And if "here" is on the desired track, am I on/ahead/behind schedule? If as a result of some unforeseen contingency ( e.g., medical emergency, mechanical problem, fuel shortage), I need to select an alternate destination, how could I reach this alternate efficiently? In short nautical charts furnish information critical to enroute decision making. I see some members calling charts "maps". In a prior post, I mentioned charts are NOT maps. Here's why: Although certainly related, the key difference between a nautical chart and a map is that the chart provides information relevant to marine navigation, whereas the map is oriented to the terrestrial user. The nautical chart differs considerably from the topographic map in it's treatment of the coastline. The topographic map emphasizes the land forms and the representation of relief, with shoreline as an approximate delineation of the water line at mean sea level. In contrast, the nautical chart has such an unique requirement for detailed and accurate representation of the coastline and water forms that it must be considered in a separate category than topographic maps in any discussion of coastal geography. These so important "Aids" show depth contours, soundings, lights, bouys, tss, channels, radio beacons, loran towers, ranges, wrecks, shoals, obstructions, piers, piles, ramps, cable and pipeline areas, bridges, harbors, type of bottom, buildings, tanks, landmarks, distances, anchorage areas, tides, currents, and other related features I probably forgot!

I am going to hit all this info in shorter segments so it can all sink in, plus I need time to think about it  I wouldn't mind seeing a lil more response to see if I am wasting my time or not. Only had 1/2 doz mails. You can post here. I will try to put up chart inserts but it would help if you have one to look at as we go along. I will give you all the definitions and such that is on them, explain how to read them, yes those different colored areas do mean something. Hopefully I can get something up that will print out.


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## Doctor

This is very interesting, you have my attention please keep on.........Thanks.............Doc


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## Fishers of Men

This should print out, copy and paste to word I guess!

INDEX OF CHART ABBREVIATIONS
(Section V of Chart No. 1)
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
A
AERO, Aero .. Aero light ..................................... P 60
AERO RBn ... Aeronautical radiobeacon............ S 16
Aero RC........ Aeronautical radiobeacon............ S 16
Al ..................Alternating.............................. P 10.11
ALP .............. Articulated Loading Platform ....... L 12
Alt .................Alternating.............................. P 10.11
Am................Amber ...................................... P 11.8
anc ............... Ancient ........................................O 84
ANCH, Anch .Anchorage ........................ N 20, O 21
approx .......... Approximate ................................O 90
Apprs ............ Approaches .................................O 22
B
B ................... Bay, bayou ....................................O 4
Bdy Mon ....... Boundary monument ................... B 24
bk ................. Broken .........................................J 33
Bkw .............. Breakwater ................................. F 4.1
Bl .................. Blue.......................................... P 11.4
BM ................Bench mark ................................. B 23
Bn ................. Beacon ..........................................O 4
Bn Tr ............. Beacon tower ................................O 3
Br .................. Breakers ..................................... K 17
brg ................Bearing ....................................... B 62
brk ................Broken .........................................J 33
Bu ................. Blue.......................................... P 11.4
C
c ................... Course .........................................J 32
C................... Can, cylindrical............................Q 21
C................... Cove .............................................O 9
CALM ...........Centenary Anchor Leg Mooring... L 16
Cas ............... Castle ....................................... E 34.2
Cb................. Cobbles ..........................................J 8
Cbl ................Cable .......................................... B 46
Cd................. Candela ...................................... B 54
CD ................Chart datum .................................. H 1
Cem.............. Cemetery .................................... E 19
CG................Coast Guard station .................... T 10
Chan .............Channel ......................................O 14
Ch. ................Church ...................................... E10.1
Chy ............... Chimney ...................................... E 22
Cl ..................Clay................................................J 3
CL ................. Clearance ......................... D 20, D 21
cm ................Centimeter(s) .............................. B 43
Co.................Coral ............................................ J 10
Co rf .............Coral reef ....................................O 26
Cr .................Creek ............................................O 7
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
Appendix B&#8211;Abbreviations B&#8211;1
B.2 NOAA Chart User's Manual
PART I. INDEX OF ABBREVIATIONS (Section V of Chart No. 1)
_____________________________________________________________________________________________________
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
crs ................Course .........................................J 32
Cup, Cup. ..... Cupola ..................................... E 10.4
Cus Ho ......... Customs House .......................... F 61
Cy ................. Clay................................................J 3
D
D................... Destroyed ...................................O 94
Destr ............. Destroyed ...................................O 94
dev ............... Deviation ..................................... B 67
DIA, Dia ........ Diaphone..................................... R 11
Dir ................. Direction ............................. P 30, P 31
dist ................Distant.........................................O 85
dm ................Decimeter(s) ............................... B 42
Dn. ................Dolphin........................................ F 20
Dol. ...............Dolphin........................................ F 20
DW ............... Deep Water route ........ M 27.1, N 12.4
DZ ................Danger Zone ...............................Q 50
E
E ................... East, eastern ............................... B 10
ED ................Existence doubtful .......................... I 1
E E Z .............. Exclusive Economic Zone ........... N 47
E Int .............. Equal interval, isophase ........... P 10.3
Entr ............... Entrance .....................................O 16
Est ................Estuary........................................O 17
exper ............ Experimental ...............................O 93
Explos .......... Explosive .................................... R 10
Exting, exting Extinguished ............................... P 55
F
f .................... Fine ..............................................J 30
F ................... Fixed ........................................ P 10.1
Fd ................. Fjord ..............................................O 5
F Fl ............... Fixed and flashing .................. P 10.10
FISH ............. Fishing ........................................ N 21
F l .................. Flashing ................................... P 10.4
Fla ................Flare stack ................................... L 11
fm ................. Fathom ........................................ B 48
fms ............... Fathoms ...................................... B 48
fne ................Fine ..............................................J 30
Fog Det Lt..... Fog detector light ........................ P 62
Fog Sig ......... Fog signal ..................................... R 1
F P ................. Flagpole ...................................... E 27
FS, FS. ......... Flagstaff ...................................... E 27
ft ................... Foot, feet ..................................... B 47
G
G .................. Gravel ............................................ J 6
G .................. Green ....................................... P 11.3
G .................. Gulf ...............................................O 3
Gp Fl ............ Group flashing .......................... P 10.4
GP Occ......... Group occulting ........................ P 10.2
H
h ................... Hard .............................................J 39
h ................... Hour ............................................ B 49
H................... Pilot transferred by helicopter..... T 1.4
HAT .............. Highest astronomical tide .............. H 3
Hbr Mr .......... Harbormaster .............................. F 60
Historic Wk ... Historic wreck ............................. N 26
Hk ................. Hulk............................................. F 34
Hor ............... Horizontally disposed .................. P 15
Hor Cl ...........Horizontal clearance ................... D 21
Hosp ............. Hospital .................................... F 62.2
hr .................. Hour ............................................ B 49
hrd ................Hard .............................................J 39
I
IALA ............. International Association of
.....................Lighthouse Authorities ...............Q 130
in .................. Inlet ..............................................O10
Intens ........... Intensified.................................... P 45
Int Qk Fl ........ Interrupted quick flashing ......... P 10.6
IQ ................. Interrupted quick flashing ......... P 10.6
Appendix B.Abbreviations. B.3
PART I. INDEX OF ABBREVIATIONS (Section V of Chart No. 1)
____________________________________________________________________________________________________
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
I Qk Fl ...........Interrupted quick flashing ......... P 10.6
Iso ................Isophase .................................. P 10.3
IUQ............... Interrupted ultra quick .............. P 10.8
K
km ................Kilometer(s)................................. B 40
kn ................. Knot(s) ........................................ B 52
L
L ................... Loch, lough, lake ...........................O 6
Lag ............... Lagoon ..........................................O 8
LANBY.......... Large AutomaticNavigationalBuoy ... P 8
Lat, lat ...........Latitude ......................................... B 1
LASH ............ Lighter aboard ship ...................G 184
LAT ............... Lowest astronomical tide ............... H 2
Ldg ............... Landing ....................................... F 17
Ldg ............... Leading ....................................... P 21
Le ................. Ledge ..........................................O 28
L Fl ............... Long flashing............................ P 10.5
Lndg ............. Landing ....................................... F 17
LNG.............. Liquified natural gas ..................G 185
Long, long ..... Longitude ...................................... B 2
LOP .............. Line of position .......... S 21, S 31, S 41
LPG .............. Liquified petroleum gas .............G 186
L S S .............. Life saving station ....................... T 12
Lt .................. Light .............................................. P 1
Lt Ho ............. Lighthouse .................................... P 1
Lt V ............... Light vessel ...................................O 6
M
m.................. Meter(s) ...................................... B 41
m.................. Minute(s) of time ......................... B 50
m.................. Medium (in relation to sand) ......... J 31
M.................. Mud, muddy ...................................J 2
M.................. Nautical mile(s) ........................... B 45
mag .............. Magnetic ..................................... B 61
MHHW.......... Mean higher high water ............... H 13
MHLW...........Mean higher low water ................ H 14
MHW ............ Mean high water ........................... H 5
MHWN.......... Mean high water neaps ............... H 11
MHWS .......... Mean high water springs ............... H 9
Mi ................. Nautical mile(s) ........................... B 45
mn ................Minute of time ............................. B 50
Mk ................Mark ..........................................Q 101
MLHW .......... Mean lower high water ................ H 15
MLLW ...........Mean lower low water ................. H 12
MLW .............Mean low water ............................. H 4
MLWN...........Mean low water neaps ................ H 10
MLWS ...........Mean low water springs ................ H 8
mm ............... Millimeter(s) ................................ B 44
Mo ................Morse ....................................... P 10.9
MON, Mon,
Mon. .......... Monument .......................... B 24, E 24
MSL .............. Mean sea level .............................. H 6
Mt ................. Mountain .....................................O 32
Mth ............... Mouth ..........................................O 19
N
N................... North, northern .............................. B 9
N...................Nun .............................................Q 20
NE ................Northeast .................................... B 13
NM................Nautical mile(s) ........................... B 45
N Mi .............. Nautical mile(s) ........................... B 45
No.................Number .................................... N 12.2
NP ................Neap tide..................................... H 17
NW ............... Northwest .................................... B 15
NWS SIG
S TA ...........Weather signal station ................. T 29
O
Obsc .............Obscured .................................... P 43
Obscd ...........Obscured .................................... P 43
Obs spot ....... Observation spot ......................... B 21
Obstn............ Obstruction ............... K 40, K 41, K 42
B.4 NOAA Chart User's Manual
PART I. INDEX OF ABBREVIATIONS (Section V of Chart No. 1)
_____________________________________________________________________________________________________
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
Obstr ............ Obstruction ................................. K 41
Oc................. Occulting .................................. P 10.2
Occ............... Occulting .................................. P 10.2
Occas ...........Occasional .................................. P 50
ODAS ...........Ocean Data Acquisition System ..Q 58
Or ................. Orange ..................................... P 11.7
P
P ................... Pebbles ..........................................J 7
P ................... Pillar ............................................Q 23
PA................. Position approximate ..................... B 7
Pass ............. Passage, pass ............................O 13
PD ................Position doubtful............................ B 8
PTL STA ....... Pilot station ................................... T 3
Pk ................. Peak ............................................O 35
Post Off ........ Post office ................................... F 63
Priv, priv ........ Private............................... P 65, Q 70
Prod. well ......Production well ............................ L 20
PROHIB........ Prohibited ................ N 2.2, N 20, N 21
Pyl ................Pylon ........................................... D 26
Q
Q .................. Quick........................................ P 10.6
Qk Fl............. Quick flashing .......................... P 10.6
R
R ................... Coast radio station
.....................providing QTG services .............. S 15
R ...................Red .......................................... P 11.2
R ................... Rocky .............................................J 9
Ra................. Radar reference line................... M 32
Ra (conspic) . Radar conspicuous object ............. S 5
Ra Antenna ... Dish aerial ................................... E 31
Racon ...........Radar transponder beacon ........... S 3
Radar Sc. ..... Radar scanner ......................... E 30.3
Radar Tr. ....... Radar tower ............................. E 30.2
Radome, Ra
Dome ........ Radar dome ............................. E 30.4
Ra Ref .......... Radar reflector .............................. S 4
RBn .............. Circular radiobeacon ................... S 10
RC ................Circular radiobeacon ................... S 10
Rd................. Roads, roadstead ........................O 22
RD ................Directional radiobeacon .............. S 11
RDF .............. Radio direction finding station ..... S 14
Ref. ............... Refuge ......................................Q 124
Rep............... Reported ........................................ I 3
Rf .................. Reef ............................................O 26
RG................Radio direction finding station ..... S 14
Rk ................. Rocky .............................................J 9
Rky ............... Rocky .............................................J 9
R Mast .......... Radio mast .................................. E 28
Ro Ro ........... Roll on Roll off ............................. F 50
R Sta ............ Coast radio station
.....................providing QTG services .............. S 15
R Tower ........ Radio tower ................................. E 29
Ru................. Ruins................................. D 8, F 33.1
RW ............... Rotating radiobeacon .................. S 12
S
S ................... Sand ..............................................J 1
S ................... South, southern ........................... B 11
S ................... Spar, spindle ...............................Q 24
s ................... Second of time ............................ B 51
SALM ...........Single Anchor leg Mooring .......... L 12
SBM ............. Single Buoy Mooring ................... L 16
Sc ................. Scanner ................................... E 30.3
Sd ................. Sound .........................................O 12
SD ................Sounding doubtful .......................... I 2
S E ................Southeast .................................... B 14
sec................Second of time ............................ B 51
sf .................. Stiff ............................................... J 36
sft ................. Soft ..............................................J 35
S H ................Shells ...........................................J 12
Shl ................Shoal...........................................O 25
S i .................. Silt ..................................................J 4
so ................. Soft ..............................................J 35
Appendix B.Abbreviations. B.5
PART I. INDEX OF ABBREVIATIONS (Section V of Chart No. 1)
____________________________________________________________________________________________________
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
Abbreviation ........ Meaning ...........................Symbol
(if applicable)
___________________________________________________
Sp ................. Spring tide ................................... H 16
S P ................Spherical .....................................Q 22
Sp. ................Spire ........................................ E 10.3
Spipe ............ Standpipe .................................... E 21
SPM ............. Single point mooring ................... L 12
S S ................Signal station .............................. T 20
st .................. Stones............................................ J 5
stf ................. Stiff ............................................... J 36
stk................. Sticky ...........................................J 34
Str ................. Strait ...........................................O 11
Subm ............ Submerged .................................O 93
Subm piles .... Submerged piles ...................... K 43.1
Subm ruins ... Submerged ruins ...................... F 33.2
sy.................. Sticky ...........................................J 34
SW ............... Southwest ................................... B 16
T
T ................... True ............................................ B 63
t .................... Metric ton(s) ................................ B 53
Tel ................. Telephone, telegraph ................... D 27
Temp, temp ... Temporary ................................... P 54
T k ................. Tank ............................................ E 32
Tr, Tr., TR......Tower .............................. E 10.2, E 20
T T ................. Tree tops .....................................C 14
TV Mast ........ Television mast ........................... E 28
TV Tower ......Television tower .......................... E 29
U
Uncov ...........Uncovers ..................................... K 11
UQ................Ultra quick ................................ P 10.8
V
v ...................Volcanic ....................................... J 37
var ................Variation ...................................... B 60
Vert ...............Vertically disposed ...................... P 15
Vert Cl ...........Vertical clearance ........................ D 20
Vi ..................Violet ........................................ P 11.5
Vil .................Village ........................................... D 4
VLCC............Very large crude carrier .............G 187
vol .................Volcanic ....................................... J 37
VQ ................Very quick ................................ P 10.7
V Qk Fl .........Very quick flash ........................ P 10.7
W
W..................West, western ............................. B 12
W..................White........................................ P 11.1
Wd ................Weed ........................................ J 13.1
WGS .............World Geodetic System .............. S 50
Whf ...............Wharf .......................................... F 13
WHIS, Whis .. Whistle ........................................ R 15
Wk ................Wreck ............ K 20&#8211;23, K 26&#8211;27, K 30
Y
Y ................... Yellow....................................... P 11.6


----------



## Fishers of Men

With the understanding of how to read a chart besides the navigational part, you can pick areas that you will want to concentrate on your fishing trip tomorrow. Take some guess work out of the boat ride, we all get enough of that and want more fishing time, right? Where are we gonna go today? By doing some homework the night before you can cut out some "guess work". For instance, lets use walleye for now, you know what time of year it is, you know what water temperatures the fish prefers at this time, you know what the natural feed is right now and so on. Now where am I going to start out tomorrow so I'm not looking all over the place? Just read the posts??? Ahh...
Lets first check the weather for tomorrow on every site we have available, look at different lake views _(the crib cam can be deceiving because it looks toward shore)_ okay lets see what surface temps we have out there just for the heck of it http://www.coastwatch.msu.edu/twoeries.html and along the contour lines shown I see it changes a lot. Well I know all the elements are causing different currents, so putting an educated guess together since the wind will be southwest (wind blows from, current flows to) I believe I will go to lat something and long something and start trolling on the NE side of the contour line shown on the chart, E to W zig zagging and then if no results turn and work the S side of the line back east and see what happens. Here you have a educated plan and if the fish are there you just need to get your baits to the right depth, speed etc... Not going into tactics/methods, too much controversy. Just giving an example of how a chart comes into play. Also if the plan is left at home then your spouse, lover, girlfriend, nosey neighbor or whoever has/knows your float plan for emergency. We didn't find the fish that we thought would be here (18 miles out in our 17' mod "v"), so we look at the info available and move. Found another contour that swings around like a half circle, temps varying and fish, good. After trolling a while we decide to go to the closest harbor and eat. Look at the chart, decide where and how to get there, how far etc, look at the gps, coincide #'s to chart, and go eat. Get carried away at the restaurant/bar, the table dancers are great, lost track of time. Spouse, lover, girlfriend or nosey neighbor figured you should have been back hours ago and calls CG with your proposed float plan. But we deviated from the float plan so these guys are flyin a helicopter 20 mi from us as we leave the restaurant and see flood lights in the distance. Half way back we run out of gas and the lake is picking up big time, some how the forecasts were off about 6 hrs. Throw a sea anchor out to hold the bow in the wind and look at the chart to see if we are going to drift into any obstructions/ wrecks and such. Get on our radio to the CG on channel 16 and tell them briefly the situation. Change to channel 9 and give the particulars, What kind of boat, how many on board, life jackets are on, lat/long etc...wait...we are "making way" CG says put the anchor out so you stay there. Okay, but it's coming over the bow sometimes and our bilge pumps not working. Whadda ya mean? You don't have a second one on that vessel? ...Glad this guy at least had a radio. So much with starting out with an educated plan!


----------



## Fishers of Men

I realize that some of these things mentioned are impractical for the small boats but use what you can of it.
*EMERGENCY NAVIGATION*
*Planning For Emergency Navigation*
With a complete set of emergency equipment, emergency navigation differs little from traditional shipboard navigation routine. Increasing reliance on complex electronic systems has changed the perspective of emergency
navigation. Today it is more likely that a navigator will suffer failure of electronic devices and be left with little more than a sextant with which to navigate than that he will be forced to navigate a lifeboat. In the event of failure or destruction of electronic systems, navigational equipment and methods may need to be improvised. The officer who regularly navigates by blindly &#8220;filling in the blanks&#8221; or reading the coordinates from &#8220;black boxes&#8221; will not be prepared to use basic principles to improvise solutions in an emergency.
[I*]BASIC TECHNIQUES OF EMERGENCY NAVIGATION*[/I]
The navigator should assemble a kit containing equipment for emergency navigation. Even with no expectation of danger, it is good practice to have such a kit permanently located in the vessel.
1.* A notebook* or journal suitable for use as a deck log
and for performing computations.
2. *Charts and plotting sheets*. A pilot chart is excellent for emergency use. It can be used for plotting and as a source of information on compass
variation, shipping lanes, currents, winds, and weather. Charts for both summer and winter seasons should be included. Plotting sheets are
useful but not essential if charts are available. Universal plotting sheets may be preferred, particularly if the latitude coverage is large. Include maneuvering boards and graph paper.
3.* Plotting equipment.* Pencils, erasers, a straightedge, protractor or plotter, dividers and compasses, and a knife or pencil sharpener should be included. A ruler is also useful.
4. *Timepiece*. A good watch is needed if longitude is to be determined astronomically. It should be waterproof or kept in a waterproof container which permits reading and winding of the watch if necessary without exposing it to the elements. The optimum timepiece is a quartz crystal chronometer,
but any high-quality digital wristwatch will suffice if it is synchronized with the vessels chronometer. A portable radio capable of receiving time signals, togetherwith a good wristwatch, will also suffice.
5*. Sextant.* A marine sextant should be included. If this is impractical, an inexpensive plastic sextant will suffice. Several types are available commercially. The emergency sextant should be used periodically in actual daily navigation so its limitations and capabilities are fully understood. Plastic sextants have been used safely on extensive ocean voyages. Do not hesitate to use them in an emergency.
6.* Almanac*. A current Nautical Almanac contains ephemeral data and concise sight reduction tables. Another year&#8217;s almanac can be used for stars and the sun without serious error by emergency standards. Some form of long-term almanac might be copied or pasted in the notebook.
7.* Tables.* Some form of table will be needed for reducing
celestial observations. The Nautical Almanac produced by the U. S. Naval Observatory contains detailed procedures for calculator sight reduction
and a compact sight reduction table.
8. *Compass.* Each lifeboat must carry a magnetic compass. For shipboard use, make a deviation table for each compass with magnetic material in its normal place. The accuracy of each table should be checked periodically.
9. *Flashlight.* A flashlight is required in each lifeboat or on each lifejacket. Check the batteries periodically and include extra batteries and bulbs in the kit.
10. *Portable radio.* A transmitting-receiving set approved by the Federal Communications Commission for emergency use can establish communications with rescue authorities. A small portable radio may be used as a radio direction finder or for receiving time signals.
11. *An Emergency Position Indicating Radiobeacon*
(EPIRB) is essential. When activated, this device emits a signal which will be picked up by the COSPAS/SARSAT satellite system and automatically relayed to a ground station. It is then routed directly to rescue authorities. The location of the distress can be determined very accurately. Depending on the type of EPIRB, the signal may even identify the individual vessel in distress, thus allowing rescuers to determine how many people are in danger, the type of emergency gear they may have, and other facts to aid in the rescue. Because of this system, the navigator must question the wisdom of navigating away from the scene of the distress. It may well be easier for rescue forces to find him if he remains in one place. 
*Most Probable Position*
In the event of failure of primary electronic navigation systems, the navigator may need to establish the most probable position (MPP) of the vessel. Usually there is usually little doubt as to the position. The most recent fix updated with a DR position will be adequate. But when conflicting information or information of questionable reliability is received, the navigator must determine an MPP. When complete positional information is lacking, or when the available information is questionable, the most probable position might be determined from the intersection of a single line of position and a DR, from a line of soundings, from lines of position which are somewhat inconsistent, or from a dead reckoning position with a correction for current or wind. Continue a dead reckoning plot from one fix to another because the DR plot often provides the best estimate of the MPP. A series of estimated positions may not be consistent because of the continual revision of the estimate as additional information is received. However, it is good practice to plot all MPP&#8217;s, and sometimes to maintain a separate EP plot based upon the best estimate of track and speed made good over the ground. This could indicate whether the present course is a safe one. 
Thats enough on this for now. When all this "crammed" info is pretty well understood we can get into conversations pertaining to any and all aspects. I don't expect anyone to remember all this, but some bits and pieces may come in handy someday. I cant remember a lot of it because it isn't used. Thats why I like to do this, to kinda stay on top of everything the best I can.
Some of the topics mentioned have not been explained yet I know, but thats okay because once we touch on them, later on you'll say " I heard that somewhere before. ``


----------



## Fishers of Men

Trivia:
Anyone know where the old saying " It's cold enough to freeze the balls off a brass monkey" came from?


----------



## ezbite

Fishers of Men said:


> Trivia:
> Anyone know where the old saying " It's cold enough to freeze the balls off a brass monkey" came from?


somewhere cold? hahaha.. 

just kidding. i had to take a break, im seeing double. im ready to keep going.


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## dinkbuster1

dood! being a person like myself that "beleives"..... you really have my attention! give me a couple days to "absorb' all of this (while i am sober lol) and i will get back with you..............


----------



## Fishers of Men

here is a chart of Lorain Harbor, thanks to Marshall McCree. 
here's a link if it works better:
http://i202.photobucket.com/albums/aa305/FishersofMen/lorainharbor.png









First I will mention the colors. 
The tan area is dry land.
The green area is an area that may or may not be under water, such as when tides flow in and out, or as we have seen lately from the low water in Lake Erie. It is an area that can flood or not. Our low water lately is from the weather we have had lately, wind pushing the water east. No they didn't open the gates all up at Niagra falls.  A lot of people were concerned about the low water, if you look on the chart, it shows that dry ground is expected in certain areas. It will return to normal. This kind of phenomena creates currents. Water temps change erratically, warm surface water from the west gets blown east, the colder water that lies heavier will go west to replace the water and such. The bait gets moved, and naturally the predators move. These currents follow the contour lines strongly. These contour lines shown on the chart are basically E to W created by the glacier movement cutting "grooves" in the bottom of the lake.The fish could be here today/gone tomorrow. Walleye have been tracked to move 60 miles in a 24 hour period. Also the wind creates another current area. Enough on currents until we get to that _I got off course and the correction is being made._ Our focus right now is the chart.
The Blue area shows shallow water depths.
The light blue shows even shallower depths.
White areas are deep safe water.
If you notice, the depths change inside to outside the contour lines respectively. 
An area that is a circle indicates a shoal, shallower water and guess what? There is a current if some sort around that area no matter how minute.
These areas can hold bait/fish.
Notice the spoil area outside the East wall? Don't think I want to go there with out local knowledge. It is always a good move to ask a local for knowledge in a strange area.
So for a little starter, you can see where charts are also an aid to fishing, besides navigation.
I am going to try to find another chart to finish this episode because when I enlarge this one it gets blurry and i can't read it. No... I am sober!
*"When your draft exceeds the waters depth you are most assuredly aground"*


----------



## misfit

> Trivia:
> Anyone know where the old saying " It's cold enough to freeze the balls off a brass monkey" came from?


though it's supposedly not really a "proven fact",it refers to old days when cannonballs would fall off the plate where they were stacked, on the ships(monkey) due to cold temps..


----------



## Fishers of Men

misfit said:


> though it's supposedly not really a "proven fact",it refers to old days when cannonballs would fall off the plate where they were stacked, on the ships(monkey) due to cold temps..


Misfit got it, well it goes like this: The base was called the monkey and made of solid brass that had contour/divits on it to hold the cannon balls. Then they stacked the cannon balls up in a pyramid, and it got cold, the brass contracted, then the collapse of the cannon balls came rolling down.


----------



## misfit

not sure when/where i read that,but it was years ago.aftr re-reading my post,i think my wording left a bit to be desired,LOL.the facts are true about storing the cannonballs on a rack called a monkey.and it's also true about them rolling off due to the effects of cold weather.the origins of the quoted phrase is something that most can't seem to verify.probably was coined somewhere along the line by ancestors of guys like dixie chicken,ezbite and the like


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## Columbusslim31

"Son of a gun" is also an old ship reference. Back when sailors would set sail, they would have in their company a few "working women" to keep the men happy. When one of these ladies would pop up pregnant, it was impossible to determine which sailor was responsible. Thus, the child might as well have been a "son of a gun" for all the good it would do to determine the father. I may have paraphrased a little, but that's what I remember of the legend.

Hope I get extra credit!


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## ezbite

misfit said:


> probably was coined somewhere along the line by ancestors of guys like dixie chicken


misfit, i couldn't argee with you more. lol


----------



## misfit

> probably was coined somewhere along the line by ancestors of guys like ezbite


ez,i'm sure dc would also agree


----------



## Fishers of Men

Here's another shot at Greenwich meantime:
http://i202.photobucket.com/albums/aa305/FishersofMen/Greenwichmeantime.png










I wouldn't think the private schools and such would get pi$$ed over this thread because you have to go thru them and pass to get a captains license. 'Course maybe because some only go for the knowledge and maybe they will feel their losing money. But I will recommend them anyway, it's just that you get taught only so much to pass a test and basically it boils down to a license to learn. They do not cover the depth of what I am going to do here unless you take a full fledged Coast Guard coarse It would actually be easier for them if the students came in with an understanding of these things. But all this info has to be purchased and etc. anywhere. This is the ONLY site with a free in depth discussion. If I make any typos or screw up somewhere please bring it to my attention. 
Okay, I know I might be skipping around a little, but I forget and or think of something later. Memory is not what it used to be 
My intentions now are to get you to read and decipher the charts.
Lets go to The Chesapeake Bay Striper fishin.
I can only put some inserts off my full scale chart up (whatever will fit on the scanner) and will post a link also in case you cant enlarge it to read. If you need the file to open in another program so you can zoom let me know which one and I'll send it to ya. Well see how this works.
http://i202.photobucket.com/albums/aa305/FishersofMen/chesapeak1.png










Forgot to mention an important thing, always give latitude first and longitude 2nd. Now if you look at 36 degrees and 76 you will see an important notice. We'll keep those notices in mind while we are running about this place, also the caution at 36 degrees 35 min N and 76 W (each little mark between the degrees; on the inside row is 1 minute, or 1 mile, the left hand side has bolded areas consisting of 10 min or miles.) and this may be a good place to fish also. Moving east (seaward) on the chart we notice certain landmarks like the 3 radio towers with the circle around them, a tank (circle with a dot), hospitals, a TV tower 451 feet tall (circle with a dot), and more aids listed.
http://i202.photobucket.com/albums/aa305/FishersofMen/chesapeak2.png










Looking at this segment we see more important information to remember as land marks for returning and a tidal chart that will not be correct, tide correction tables are a different story/topic. But it will give us an idea when to go to a destination or not. At the bottom is a nautical mileage scale and for the purposes of this thread we are NOT going to use it. Why? I want accurate measurements from the longitude scale ONLY. You'll see why for yourself later. (if you have a pair of dividers, find them. If not a drawing compass with a pencil and sharp point will work, when we go to measure distances later on. Also going to need a parallel rule or two straight edges.) 
Dry features on land are roman characters; sub or floating will be in italic.
We also see some fixed bridges with the span and heights leading to the shallow bay area and a #G1 bouy fl g 2.6s (flashing green every 6 seconds)
and a fl red every 6 s to watch for on the way home But we shouldn't be anywhere near them. 

http://i202.photobucket.com/albums/aa305/FishersofMen/chesapeak3.jpg










Here we see the Chesapeake bridge we must go under, the main channel, a precautionary area while heading out to sea, and a TSS  (where's your symbols I gave you if you don't know) It's traffic separation scheme the place where the arrows go both ways on the chart. This is where the BIG ships, submarines and such will go in and out. Okay, we'll watch for them for sure. And notice that there is an obstruction area just to the south of it, with out further info we think it is probably sunken ships, maybe it will hold some fish. We will do the light symbols later but on our starboard side we see the Cape Henry light, look at the chart and see that it is 164' tall and flashes every 20 sec. (circle with a dot) and labeled. The goofy looking squiggly line that comes from Cape Henry light in a NE direction is the Colregs demarcation line. This is your separation from the rules that you learned in the Colreg link.
See if you didn't do some homework, I told ya you will get lost, just reading posts isn't gonna make it unless you already have _"been" _there.
This is enough work and I am not going to take the time to explain every thing over and over. But don't be afraid to ask questions, NO question is a dumb one.
http://i202.photobucket.com/albums/aa305/FishersofMen/chesapeak4.jpg

On the coast, North of Cape Henry we have Cape Charles lighthouse we can watch for on our return, it's 200' high and a Fl R 4 sec. Can you find it? Notice all the shallow flood zone in blue? Don't run aground!
I'm too tired to go fishin, just thought we would get familiar with the area. Sorry.  
"Thy way is in the sea, and thy path in the great waters, and thy footsteps are not known." Psalms 77:19


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## Fishers of Men

Columbusslim31 said:


> "Son of a gun" is also an old ship reference. Back when sailors would set sail, they would have in their company a few "working women" to keep the men happy. When one of these ladies would pop up pregnant, it was impossible to determine which sailor was responsible. Thus, the child might as well have been a "son of a gun" for all the good it would do to determine the father. I may have paraphrased a little, but that's what I remember of the legend.
> 
> Hope I get extra credit!


2 credits, do we need to start a score sheet?


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## Fishers of Men

If you spend any time at all on the water, sooner or later your going to get caught up in some crap you didn't plan on. Some good things to know:

Here is a basic idea of the line of sight when on the water. This is in a general form, (I'm no artist!) close, but there is math involved for complete accuracy that we don't need right now. General purpose of this is to have a good idea, without depending in electronics, how far you are away from something and how far your radar, vhf etc will work. We will use this info later.










Here's a chart of lightning to ground in seconds (round to the nearest second) that you can estimate how far away the lightning is: 









So if your out in a small boat like most out there fishing, no radar, you see lightning off at a distance roughly at a certain amount of angle degree, time it in seconds, figure out how close/far it is from you. Look at the landmarks that you took notice on when you left shore and see if you can see them or not. Get a rough Idea if you can beat that _front_ in. Depends how fast its moving though and the lakes gonna kick up and you have to slow down...WHERE's my raincoat?

Sounds travel 4800' second IN the water over 25 times as on land. I will make a table up of sound over water tomorrow.

Recap: Parallels of latitude are equal. Used for measuring distance.
1st named and first accurate. 1 degree = 60 NM. Degrees are divided by 60 min which results to a mile a minute.
In the old days the only true measurement was the North Star which was guaged by a sextant, simple level and a protractor.
The higher in the sky the N star is, the FURTHER North you are. So, if the North star is 38 degrees, you are 38 degrees north latitude, thats why it's in and called degrees. That was simple huh? Lost at sea? Not today. We know where we are N and S but what about the longitude? I'll give ya that one tomorrow.  
The circle of the Earth is explained in Isaiah: 40:22 for anyone wanting these type of references.

If anyone has a certain topic you want to hit on, shout it out or I'm just gonna keep wingin it at ya.


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## Fishers of Men

I got caught up doin deer at 1500 and wanted to go to the lake but couldn't get a hold of anyone wanting to go. 
So, here's the *distance sounds travel per second over water table.
4800' sec*
*Interval in sec. = NM*
1 = 0.2
2 = 0.4
3 = 0.5
4 = 0.7
5 = 0.9
6 = 1.1
7 = 1.3
8 = 1.4
9 = 1.6
10 = 1.8
20 = 3.6
30 = 5.4
40 = 7.2
50 = 9.0
60 = 10.8
NM=6080.2 feet at 1' of the equator (yes the distance changes as you get away from the equator) If you don't know why, go back and look at the great circle.
Geographical Mile=6087' at 1' of the equator.
Now the basis elsewhere is:
NM=6076.1'
Statute mile=5280'
Sound travels over land at 1100' per sec.
With that tremendous speed in the water, wonder how boat noise effects the fish? Some spook, some species are attracted. Learn and understand your prey. If you think like a deer you can go kill it. Well some people cant.  Thats just one reason for using planers and such.
*Now to the longitude*
Since these lines converge at the ends and are spread apart at the center, they are not equal and *cannot* be used to measure distance.
This is harder to measure and needs an accurate clock to know exactly when the sun passes directly overhead. This central position is Greenwich England, GMT=0 degrees. (360 degrees)
The lines are measured by how many degrees west or east of Greenwich.
The international date line is 180 degrees. Date changes at midnight when the sun passes over Greenwich, therefore our minutes come into play as a unit of measure. Longitude is measured in degrees and minutes. Either time or longitude may be expressed in units of arc or in units of time. 360 degrees is 24 hrs., 15 degrees is one hour., 1 degree is 4 min.,
As 24 hrs of time are required for the mean sun to traverse a circle of 360 degrees at a uniform rate of 15 degrees an hour, the circle may be divided into 24 hours with each arc further divided minutes and seconds of time.
1 min= 4 seconds., 15'= 1 min.
I know I repeated some things but I hope that clarifies this.
Since we are on time and distances, lets go to *radio beacons.*
When fog prevails these beacons send out identical radio and sound signals at the same instant off time. The radio signal is heard at practically the same time it was sent. The interval of time *Before* the sound signal is heard is a measure of distance. Any radio receiver capable of receiving the radio beacon signals, may determine the time in seconds which elapses between the distance groups of radio dashes and the corresponding part of the sound blasts. Divide the seconds by 5 or more exactly by 0.18 gives the distance in NM or the conversion made by the above table. I'll let this sink in and then we'll do some speed/time/distance problems.
*Longitude:*
"He stretcheth out the north over the empty space, and hangeth the earth on nothing" Job 26:7


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## Fishers of Men

This is really very easy.



















Do you see how the last question (3) was converted?

You draw a line on the chart to your destination with a sharp pointed pencil, measure the distance of the line with dividers, take the dividers to the latitude scale and see what the distance to your desired destination is. Write it down. That and your desired speed you are going to run at will give you your eta.

"Fear not each sudden sound and shock;
'tis of the wave and not the rock;
'Tis but the flapping of the sail,
And not a rent made by the gale.
In spite of rock and tempest roar,
In spite of false lights from the shore,
sail on, no fear to breast the sea,
Our hearts, our hopes are all with thee"

Henry Wadsworth Longfellow


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## Fishers of Men

Here are some of the rules and diagrams for properly lighted vessels and the day shapes that are flown during the day on larger vessels. Many probably have not noticed "this" means of communication on the water and went right by them a "million" times. Now you can know what to look for and what they mean.
*Here are the day shapes:*










Have you read the rules?
Many see these confusing or hard to remember. Just remember, these aids are our communication on the water, along with sounds and flags, it's not just a radio thing.
*Lights and Shapes *
Rules 26 though 31
In the analysis of day shapes, and looking at the crushed beer can symbol, Rule 26 gives an option for INLAND fisherman with boats of less than 20 meters to substitute the two (2) apexes with a basket in the rigging. It is not included in the exhibit of shapes, because it says basket. No one has ever defined as to whether it is large or small basket or a picnic basket, laundry basket or Easter basket ; just basket.

Going into what Donkey posted: "So ya wanna fish at nite?"

*Rule 26: *Red over white  (Fishing tonight) - Whether underway or anchored Green over white  Trawling tonight
We have defined a fishing vessel, but how about trawling? A fishing vessel which is engaged in trawling means dragging dredge nets or other, apparatus (trawls ) through the water to gather fish. These trawlers will show the green over white lights as compared to the red over white light of a fishing vessel, but BOTH will show the same day shape of: yes, the crushed beer can.
When engaged in extending the apparatus, equipment or nets outward from the vessel and there is outlying gear extending MORE than 150 meters horizontally from the vessel, it will show a cone apex upward in the direction of the gear. In this case the apex (point) is up, where the apex (point) being down is a sailing vessel under power. In addition there is a white light in the same direction.
When making way through the water, the vessel must also show the necessary lights of sidelights and a sternlight. _(If you read the definitions, you will know the required degrees for each light)_
Lets not forget that if the vessel is 50 meters or more, we need that masthead light abaft of and higher than the all-round occupational lights.
Before leaving Rule 26, keep in mind that this rule describes lights for fishing. _*(Remember if you are trolling, drifting etc... you are NOT fishing)*_ There are some additional lights that must be mentioned for fishing vessels, and are signals for trawlers. Remember that a trawler, though a fishing vessel has trawls (nets), attached equipment for hauling fish in ,and for the most part are large vessels, usually commercial fishing boats. When engaged in trawling, Annex II of the Rules, has additional signal lights for vessels fishing in close proximity. Obviously, when close together, these lights are necessary to be seen all around the horizon and seen at a distance of at least one (1) mile. They identify the trawling vessels activities with additional lights as follows:
1. When shooting their nets; two (2) WHITE lights in a vertical line.
2. When hauling their nets; One (1) WHITE light over one (1) RED light in a vertical line.
3. When the net has come up fast upon an obstruction; two (2) RED lights in a vertical line.
It should be noted that, if two (2) vessels are engaged in trawling and in what is known as pair trawling, a search light is required and directed forward in the direction of the second vessel in the pair.
You may then see : green over white (trawling) and at a lower level , the two (2) sets of lights described in 1,2 or 3 above and a search light. LOTS OF LIGHTS.
With all of these lights, with trawlers and multiple trawlers, the only day shape, that well see from dawn to dusk, provided the trawlers are under 150 meters out ( highly unlikely in a close proximity area), is that of fishing. The two (2) triangles with the apex together, which by this time we have become familiar with and known, as the crushed beer can. *(IF you see these guys out they, and they are not complying with the rules, get on the radio and report them. They are a dangerous activity to others out there boating.)*

http://i202.photobucket.com/albums/aa305/FishersofMen/lightsandshapespic.png










Rule 27
a) Vessel not under command: Two (2) all-round RED lights in a vertical line. Day Shape 2 black globes.
b) Vessel restricted in her ability to maneuver : Three all-round lights in a vertical line RED, WHITE, RED. Day Shape  Ball, Diamond, Ball.
c) Vessel engaged in towing which severely restricts the towing vessel from deviating from her course shall exhibit the RED, WHITE, RED and the Ball, Diamond, Ball. It must be understood that all towing vessels are not RAM vessels exhibiting the red, white, red and ball, diamond, ball, but only those whose tow restricts them and they cannot deviate from their intended course. Since they are towing astern, the required yellow over white (my tow is tight) lights are also required.
d) The DREDGE.  A vessel which is dredging is one who is dredging the bottom of a river or channel. Another good example is one who is replenishing a blown away beach on the coast by digging ( dredging) and loading sand out off the coast line and bringing it back, then with dredge pipe lines ( spoil lines ) shooting it back on shore to rebuild the sandy shoreline. The vessel, which is always rather large, while engaged in dredging or under water operations will obviously be a RAM and show the RED,WHITE, RED. But now additional lights will also be shown on each side of the dredge : Two (2) RED lights in a vertical line ( 2 black globes for day shapes), on the restricted traffic side to indicate, DO NOT PASS. The side which permits traffic will have two (2) GREEN lights in a vertical line, (2 black diamonds for day shapes) to indicate the side on which the vessels may pass. The lights and day shapes are the same for dredges in both international and inland waters.
e) DIVING  The RAM lights of Red, White, Red are also used for a vessel engaged in diving operations, for obvious reasons, because it is restricted in its ability to maneuver.

http://i202.photobucket.com/albums/aa305/FishersofMen/lightsandShapespic2.png










Where the confusion comes in is with the popular red flag with the white diagonal line. This flag is used to indicate the position of where the diver is down. This diving flag does not exist in the rules of the road and it must be realized that ONLY rigid code alpha is listed in rule 27.
f) Mine clearance even though rarely seen in the waters of North America, is part of rule 27. The mine clearance vessel will exhibit three (3) all-round green lights, (3 balls for day shapes ). One shall be exhibited near the foremast head and one at each end of the foreyard. The rule says that another vessel shall not approach within 1000 meters ( 3280 feet). Dont even come any where near the vessel or the area in which it is doing its clearance or you may find what they are looking for, before they do.
After all this, Rule 27 concludes a that vessel of less than 12 meters (39.4 feet) is not required to exhibit these lights and shapes. One exception is the vessel engaged in diving operations. They will show the Red, White, Red lights and rigid code alpha, regardless of size. It may have been easier to understand, had they begun this rule, with the explanation of: Except for diving operations, all vessels over 12 meters shall exhibit  Perhaps some day, when one of us who has a greater clarity for explanation becomes Secretary of the Department we can change that.

Rule 28 *(NOT in the great lakes, they are just another vessel under power. But common sense tells ya to give them a lot of leeway, they cant stop/turn on a dime. Ships characteristics will be next post) *
Vessels Constrained by their Draft
International only
The lights for a vessel constrained by her draft are three (3) all-round RED lights in a vertical line. The day shape is a cylinder. Of course, remember that if the vessel is underway, the lights of a power driven vessel apply. Again, constrained by draft does not exist in Inland Rules.

Rule 29
Pilot Vessel
A Pilot Vessel is one who carries a pilot aboard. He becomes the Master of a vessel when a boat, usually of considerable size, comes into a harbor from out at sea. The pilot, who is extremely familiar with the harbor area, leaves his own pilot vessel, comes aboard the incoming vessel and pilots her from a reasonable distance away from the harbor all the way to the ships berth. It is his harbor and the boat becomes his vessel. Another means is that the master of the vessel or helmsman will follow the pilot and pilot vessel through channels, etc. until completely docked.
When engaged in such pilot duties or while at anchor, waiting to assume control ( bringing the vessel home ), the pilot vessel will show two (2) all-round lights in a vertical line; the upper being WHITE and the lower RED, thus the saying: white over red  pilot ahead. While waiting at anchor, the pilot vessel will also show the all-round white anchor light and/or a day shape of one (1) black globe which we will now discuss in rule 30 for all vessels which are at anchor or aground. Lets also keep in mind that a pilot vessel when not engaged on pilotage duties shall exhibit the lights and shapes for a similar vessel of her size.

Rule 30 concludes that a vessel at anchor, of 7 meters (23 feet) or less and not in a narrow channel or anchorage area or not in an area open to vessel navigation, does NOT have to have these anchor lights. In addition, a vessel of 12 meters ( 39.4 feet [ it 40 feet] ) or less and AGROUND need not show the lights and/or shapes of a vessel aground. Yet earlier in the rule, it specifically states that vessels aground would show these aground lights if practicable. It boils down to the fact that if you are really aground ( dug in) and/or in any situation of anchoring, you are, or think you are venerable and have a risk of collision then please show ALL of these lights. Its what the rules are all about
PREVENT COLLISION.
NOTE: Inland Only A vessel of less than 20 meters (65.6 feet) when at anchor in a special anchorage area designated by the Secretary, shall not be required to show the anchor lights and shapes required by rule 30.
Rule 31
Seaplanes
It is understandable that seaplanes, which are airplanes, not boats, will not have all necessary lights that would be on a vessel. So rule 31 says that where it is impracticable, which holds true, for the most part, she shall exhibit lights and shapes as closely similar in characteristics and position as possible.

Anchored Vessels and Vessels Aground
Anchoring is an art, requiring nautical skills, and will be discussed in detail later in this book, but the lights and shapes for the professional must be taken serious to exhibit to our maritime neighbors the who, what and where of what is happening. A vessel at anchor shall exhibit one (1) or two (2) all-round white lights where they can best be seen, fore and aft. If less than 50 meters (164 feet) one (1) anchor light in the fore part. If 50meters or over two (2) all-round white lights, the second white anchor light is at a lower level and near the stem of the vessel.
Now we get into the may and shall. _(the word *SHALL *constitutes a fact, "may" could also be may not)_ The rule states that a vessel at anchor may and a vessel of 100 meters or more shall also use available working lights to illuminate her decks. Vessels that are at anchor, particularly large cargo-type vessels, who are anchored and waiting for clearance to arrive at docks in ports to unload, will use these available working deck lights and while waiting will look like a lighted sky scrapper lying in the water, unmistakably illuminated with many lights. This is true of both inland and international ports and can be seen in harbors not only like New York and Boston, but in smaller ports and on the Great Lakes in areas around Cleveland and Detroit. The day shapes corresponding to the anchor lights are one(l) or two (2) black globes.
A vessel aground shall also use these same prescribed anchor lights, however, in addition and where they can best be seen, two (2) all-round red lights in a vertical line. The day shape is three (3) black globes. The rule also uses the words if practicable. I can only say that if you are aground, which is never practicable, and you already have anchor lights or day shapes displayed, how practicable is it to illuminate two(2) additional red lights or hoist three (3) additional black globes. However, this is what the rule states, so if practicable, light them up and hoist them up, that is, if you have the time and its practical. So, if you think youre in trouble and could get hit  light em up.

More on lights later.

COLUMBUS:
Joaquin Miller
These very winds forget their way,
For God from these dread seas Is gone
Now speak brave Admrl; speak and say -
He said: Sail on/sail on! and on


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## snake69

Didn't know if you had this term or not. Fetch:The distance wind can blow unobsrtucted across water! Didn't know if it meant anything to you, but with all the terms you were putting out, I thought I'd add that one.


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## Fishers of Men

snake69 said:


> Didn't know if you had this term or not. Fetch:The distance wind can blow unobstructed across water! Didn't know if it meant anything to you, but with all the terms you were putting out, I thought I'd add that one.


Thanks Snake69,

Here&#8217;s a fetch: &#8220;And there went forth a wind from the Lord, and brought quails from the sea&#8230;&#8221; NU 11:31

Fetch: (geography)

We will hit on this and then it will make more sense when go into the weather.
Everyone talks about the weather but no one does anything about it.

A long fetch creates a high energy wave.
Fetch, often called the fetch length, is a term for the length of water over which a given wind has blown. It is used in geography and meteorology and is usually associated with coastal erosion. It plays a large part in longshore drift as well.

The fetch length along with the wind speed (or strength) determines the size of waves produced. The longer the fetch length and the faster the wind speed, the larger and stronger the wave will be. For example, the winds which travel from the East Coast of the United States and hit the west coast of Ireland would have an extremely large fetch and would produce very large waves if the wind speed was also high.The fetch length determines the power and energy of the wave. If a fetch is very large, then the wave will be very large. If the fetch is very small, the wave will be small. The fetch is related to the orbit of the wave.










Ocean surface waves are surface waves that occur in the upper layer of the ocean. They usually result from wind or geologic effects (like an underwater earthquake) and may travel thousands of miles before striking land. They range in size from small ripples to huge tsunamis. There is little actual forward motion of individual water particles in a wave, despite the large amount of energy and momentum it may carry forward.
The great majority of large breakers one sees on an ocean beach result from distant winds. Three factors influence the formation of "wind waves"
&#8226;	Wind speed 
&#8226;	Distance of open water that the wind has blown over; called fetch 
&#8226;	Length of time the wind has blown over a given area. 
All of these factors work together to determine the size and shape of ocean waves. The greater each of the variables, the larger the waves. Waves are measured by:
&#8226;	Height (from trough to crest) 
&#8226;	Wavelength (from crest to crest) 
&#8226;	Period (time interval between arrival of consecutive crests at a stationary point)

Waves in a given area typically have a range of sizes. For weather reporting and for scientific analysis of wind wave statistics, their size over a period of time is usually expressed as "significant wave height." This figure represents the average height of the highest one-third of the waves in a given time period (usually twelve hours) or in a specific wave or storm system. Given the variability of wave size, the largest individual waves are likely to be twice the reported significant wave height for a particular day or storm.
HHHHHiiii people! 

How many times have you been out there and all of a sudden you go: &#8220;Wow, where did that big hole come from?&#8221; If you take notice on a return trip, at the crests and troughs, they will usually come in sets. Say for example 3 to 5 even ones and then a big one or two then 3- 5 again then a big one. Point is, when they are on a following basis/chop/wave action they come in sets. Let the worst go by, grab a good one and ride it in. Less danger, not as much "fight the wheel", smoother ride...
I re-framed from using the term following sea here because seas are squared from crest to crest or trough to trough, hence, a 12 foot sea is 12X12=144 feet apart. And it can be like a sheet of glass flat. We are dealing with a chop on lake Erie. Whole different topic.

This is why you can&#8217;t rely on your weather forecasters and must make wise decisions on your own for boating. When we get all these puzzle pieces put together over this winter, I am sure it will make us all better/wiser on the water. And guess what, most people are afraid of what they don&#8217;t know, so with all this info brought forward we can go out on the lake with due respect for it, understanding what we are up against and with plenty of confidence.

Hence: "But let him ask in faith, nothing wavering. For he that wavereth is like a wave of the sea driven with the wind and tossed." James 1:6

Wind is the flow of air. More generally, it is the flow of the gases which compose an atmosphere; since wind is not only an Earth based phenomenon.

"Let winds be shrill, let waves roll high,
I fear not wave nor wind:
For I have from my father gone
A mother whom I love,
And have no friends, save these alone
But thee- and One above."
George Gordon Lord Byron

Winds are commonly classified by their spatial scale, their speed, the types of forces that cause them, the geographic regions in which they occur, or their effect.

There are global winds, such as the wind belts which exist between the atmospheric circulation cells. There are upper-level winds which typically include narrow belts of concentrated flow called jet streams. There are synoptic-scale winds that result from pressure differences in surface air masses in the middle latitudes, and there are winds that come about as a consequence of geographic features, such as the sea breezes on coastlines or canyon breezes near mountains. Mesoscale winds are those which act on a local scale, such as gust fronts. At the smallest scale are the microscale winds, which blow on a scale of only tens to hundreds of meters and are essentially unpredictable, such as dust devils and microbursts.
Forces which drive wind or affect it are the pressure gradient force, the Coriolis force, buoyancy forces, and friction forces. When a difference in pressure exists between two adjacent air masses, the air tends to flow from the region of high pressure to the region of low pressure. On a rotating planet, flows will be acted upon by the Coriolis force, in regions sufficiently far from the equator and sufficiently high above the surface.

The three major driving factors of large scale global winds are the differential heating between the equator and the poles (difference in absorption of solar energy between these climate zones), and the rotation of the planet.
Winds can shape landforms, via a variety of eolian processes.

Therefore the western, central and eastern basins are like 3 totally different lakes. The prevailing westerlies "build" do to it's fetch across lake Erie. Now there are other factors, but we will discuss them when we get into weather fronts.

"The wind goeth toward the south and turneth about to the north; it whirleth about continually, and the wind returneth again according to his circuits."
Ecc 1:6

The quote identifies a high pressure system in the northern hemisphere, the southern hemisphere is counter clockwise.

"How thy garments are warm when he quieteth the earth by the south wind"
Job 37:17

Pattern sound familiar?

"Fair weather cometh out of the North;" Job 37:22
"The north wind driveth away rain:" Prov 26:23

Now we all know and have heard the horror stories on the great lakes in November/ December...East wind?
"Thou breakest the ships...with an east wind." Psalms 48:7
What's the saying? East is least/west is best?

I guess since there is so many quotes in here, I'll end this page with another!

"Holding faith and a good conscience; which some have put away concerning faith have made shipwreck." Tim 1:19


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## Fishers of Men

I want to finish up on this part of *Lights and Shapes* for now.

Rule 20 through 31 is again one of the most important and off course misunderstood areas within the rules. The following pages specify and illustrate the lights and shapes that these rules stipulate with colors, configurations, positions and precise angles. They *apply in any weather* and in restricted visibility and shall be complied with from sunset to sunrise.
At this point Id like to stop and explain a very human misinterpretation of the English language. It states from sunset to sunrise. How often the reader, interpreter and analyst will see this and read SUNRISE to SUNSET, not realizing sunset means dark and sunrise means light. Dont reverse it and read anything else except what it says in English. Further, it does read sunrise to sunset in restricted visibility.
*To avoid any confusion:* lights will be used from dark to light and in restricted visibility from light to dark, when necessary and exhibited when good common sense dictates that you want the other mariners to see that you are out there. After all isnt that the purpose of these lights.
The shapes shown on the following pages are part of the Rules and most mariners will say that they are seldom seen during the day, yet they are not only part of the Rules they give a message, a signal and clarification of what that vessel is doing and why. Remember the purposes of lights vessels show at night are replaced by shapes during the day. Know them and use them.
Rule 21
Definitions-Lights
Since there is only one way to define the lights in the Rules, the following
definitions, only, are taken from Rule 21 of the U.S. Department of
Transportation, United States Coast Guard, Navigation Rules, International -
Inland. These definitions are acknowledged as being from that source. 
(a) *Masthead light* means a white light placed over the fore and aft centerline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed as to show the light from right ahead to 225 degrees abaft the beam on either side of the vessel.

Except that on a vessel of less than 12 meters in length the masthead light shall be placed as nearly as practicable to the fore and aft centerline of the vessel.
(b) *Sidelights* means a green light on the starboard side and a red light on the port side each showing an unbroken light over an arc of the horizon of 112.5 degrees and so fixed as to show the light from right ahead to 22.5 degrees the abaft the beam on its respective side. On a vessel of less than 20 meters in length the sidelights may be carried on the fore and aft centerline of the vessel. [ inland]: Except that on a vessel of less than 12 meters in length the sidelights when combined in one lantern shall be placed as nearly as practicable to the fore and aft centerline of the vessel.
(c) *Sternlight* means a white light placed as nearly as practicable at the stem showing an unbroken light over an arc of the horizon of 135 degrees an so fixed as to show the light 67.5 degrees from right aft on each side of the vessel. 
(d) *Towing light* means a yellow light having the same characteristics as the sternlight defined in paragraph ( c) of this Rule.
(e) *All-round light* means a light showing an unbroken light over an arc of the horizon of 360 degrees.
(f) *Flashing light* means a light flashing at regular intervals at a frequency of 120 flashes or more per minute. (either yellow or white)
(g) [ Inland only]: *Special flashing light *means a yellow light flashing at regular intervals at a frequency of 50 to 70 flashes per minute, placed as far forward and as nearly as practicable on the fore and aft centerline of the tow and showing an unbroken light over an arc of the horizon of not less than 180 degrees nor more than 225 degrees and so fixed as to show the light from right ahead to abeam and so fixed as to show the light right ahead to abeam and no more than 22.5 degrees abaft the beam on either side of the vessel. (only on the front of barges)
Visibility of Lights Rule 22
Specifies the minimum ranges of visibility of lights and as listed in the U.S. Coast Guard Navigation Rules are as follows: 
In a vessel of *50 meters or more* in length:
a masthead light, 6 miles;
a sidelight, 3 miles;
a stemlight, 3 miles;
a towing light, 3 miles;
a white, red, green or yellow all-round light, 3 miles; and # a special flashing light, 2 miles.
In a vessel of *12 meters or more* in length but less than 50 meters in length: a masthead light, 5 miles; except that where the length of the vessel is less than 20 meters, 3 miles;
a sidelight, 2 miles;
a sternlight, 2 miles;
a towing light, 2 miles;
a white, red, green or yellow all-round light, 2 miles; and
# a special flashing light, 2 miles.
In a vessel of *less than 12 meters* in length:
a masthead light, 2 miles;
a sidelight, I mile;
a sternlight, 2 miles;
a towing light, 2 miles;
a white, red, green or yellow all-round light, 2 miles; and
# a special flashing light, 2 miles.
In an inconspicuous, partly submerged vessel or object being towed:
a white all-round light, 3 miles.
(#)Inland only








Rule 23 
*Masthead lights* can be one of the most confusing parts, not only within the Lights and Shapes section., but in all of the Rules of the Road. First lets make sure we know the basics : One (1) or two (2) masthead lights depending on length for a power driven-vessel underway and remember power-driven vessel underway. Many a good student mariner has gone astray by not recognizing the terms, power-driven and underway. If it is not defined as just that, then there is a different interpretation.
Now, this Rule 23 states one (1) masthead light for a power-driven vessel of less than 50 meters, (meters not feet). Two (2) masthead lights for a power-driven vessel 50 meters or greater So, if a vessel is 50 meters even, it must have two (2) masthead lights. If it were 49 meters, then only one (1).
Power-driven vessel underway  less than 50 meters in length.
International and US Inland waters.
Power-driven vessel underway.
International and US Inland waters.









*On the Great Lakes (only) however, that second masthead light, thats the one on the stern may (thats right may) be an all-round white light (360 degrees) in lieu of the second masthead light and stem light.*








Normally, the second masthead light, just as the first or forward one has an arc of visibility of 225 degrees, Rule 21(a). A suggested way to remember this is: masthead light = 225 stern light = 135 Rule 2 1(c)
225+135=360
The two together cover the complete circle of 360 degrees.

*Air-Cushion Vessels*
The obvious question that comes to mind is the definition of an air- cushion vessel. We know that a vessel as we are aware of, is a vessel that floats in water. The force of gravity forces the hull into the water and not only floats, but rolls and seeks its own buoyancy level. The forward motion of such a vessel is caused by power and propellers moving it through the water. We refer to this weighted force into the water as displacement.
The air-cushion vessel is one which by design and forced air raises it above the water and with forward thrust moves the vessel above the water level as it travels. This we refer to as nondisplacement.
When an air-cushioned vessel operates in this nondisplacement mode it is required under Rule 23 to exhibit an all-round flashing YELLOW light at the stern of the vessel. Of course it must also abide by the rules by conforming to all of the other required lights, such as masthead lights. sidelights, etc. When the air-cushioned vessel operates in the displacement mode it returns to the status of a vessel moving through the water and conforms to the rules and requirements of any other displacement type craft.
The air-cushion crafts operating in the nondisplacement mode are popular on the Great Lakes, some of which can be seen in the island areas on Lake Erie and operate as passenger carrying crafts which travel at a high speed and have a smooth and comfortable ride. The coastal areas with inlets are also gaining popularity with these vessels for tours because of their uniqueness and appeal.
*Vessel Masthead Lights Exceptions*
Before discussing these all-important masthead lights for towing purposes [it would be wise to understand that power-driven VESSELS of less than 12 meters (39.4 ft.), may, (may again), exhibit an all- round white light of 360 degrees arc in lieu of that white masthead light of 225 degree arc.
So, when we interpret one (1) masthead light for power-driven vessels of less than 50 meters, keep in mind that it is required for power-driven vessels between 12 and 50 meters. However, that 360 degree all-round white light will suffice and can be used for the under 12 meter vessels. DONT FORGET the side lights.
In addition, on these () 12 meter power driven vessels, you MAY, if you wish, use a regular 225 degree masthead light. Should you choose, you MAY use a 360 degree light. Now, either one may be displaced from the fore and aft centerline provided that the sidelights are combined as one lantern, that is the red and green are together (side by side) at the bow and not separate at each side of the vessel.
The 7/7 rule within Rule 23 merely states that if you are operating a vessel of less than 7 meters and that vessel has a maximum speed that does not exceed 7 knots, only an all-round white light is required. Of course should you choose, you MAY exhibit side lights.
( A WISE IDEA!)
Less than 7 meters - less than 7 knots. The 7/7 rule.
Power-driven vessel of less than 7 meters in length whose maximum speed does not exceed 7 knots.

Rule25
Sailing Vessels Underway and Vessels Under Oars
In the discussion of Lights and Shapes, Rule 25 points out certain options for Sailboats and the Sailing Captain. Twenty (20) meters is just over 65 feet [ ft.] and the usual sidelights and stem light which can be carried by a sailing craft, now MAY be combined as one (1) all-round lantern at the top of the mast : red and green with the white sector pointing to stern and all three (3) covering 360 degrees.
Also, another option, should the sailors wish to do so, is that instead of this 360 degree tricolor light, they MAY exhibit two (2) 360 degree lights; the top being red and the lower being green. This is where one of the old mariners sayings comes in: red over green - sailing machine. It must be emphasized though that the usual sidelights and stern lights must also be shown with the red over green and applies to any size sailboat. Under twenty (20) meters however, either the combined lantern or the red over green MAY be shown, not both. Well, where would you put them all anyway?
In a sailing boat of less than seven (7) meters (23.0 ft.) and the sailor finds that it is not practical to have the running lights and stern lights, etc. then he must have an electric torch handy, which again translated means a flashlight, having it ready to use and to alert others so as to prevent collision.
This white electric torch or lantern also applies to vessels under oars, thats rowboats and certainly not the big, old Viking type. Should they not have the prescribed side and stern lights, then they must show in ample time the torch or lantern, to prevent collision.
It becomes obvious that these flashlights in place of the usual prescribed lights for both the (-) 7 meter sailboat and the rowboat are stated in Rule 25 for that all-important statement and reasoning: ... in time to prevent collision.... Isnt that really what the Rules are all about?
The conclusion of Rule 25 discusses a black shape of an apex-down cone to show that it is a sailing vessel under both power and sail. A sailing vessel [ is defined as a vessel moving through the water under wind and sail, [ 3  Definitions ] and of course governed by the Rules for sailing vessels. Once that auxiliary engine or motor kicks in, the sailboat becomes a powerboat and subject to the Rules of a power driven vessel, and then showing that conical shape.
This then becomes an appropriate place to show and examine all the day shapes and lights not only for sail; but fishing, trawling, RAM, etc. and all the previously studied vessel interpretations. We can now affix the applicable day shape and/or light to the activity of that boat which plays such an important part of identification. *Rule 26 through 31 explains the distinctive lights and shapes which the ordinary mariner may or may not have seen or perhaps looked at in wonder as to what the professional or experienced Captain is showing.* Show your experience...at the dock,( you can tell what kind of skipper operates the vessel by the professionalism he/she shows by knots, anchors, organization etc...on the vessel just by walking by) and on the water. By now, we should all know which way a vessel is heading by only what lights we see, and what kind of vessel.
The day shapes as shown on the succeeding pages and according to Annex I of the Rules have a required diameter of not less than 0.6 meters and the vertical distance shall be 1.5 meters apart. However, youll find them smaller, of course. In 20 meter (less than 65.6 feet) craft, Annex I allows for undefined sizes and spacing commensurate with the size of the vessel. Take a look next time out and youll see all sizes, but the professionals still follow the prescribed dimensions.
Lets take a look at all of the day shapes first: A previous post showed a page of shapes, shows them with the identification. Study them. After memorizing the page with the categorizing, see how many you can remember without the names attached. Some are more prevalent than others, for example : fishing. I have no trouble remembering this shape of the two (2) apexes with the points together. At one time, this author was a soldier in a place called Korea. One of the more famous fighting units there was the 3 Infantry Division. The patch that they wore on their shoulder was with the two apexes with the points together. They were known as the Crushed Beer Can Division. The same as the one for fishing. By the way, they also lived up to their name.
We will do barges and towing another time along with some more sailboat issues. Towing is a big thing for the western rivers, The Mississippi and all its tributaries. Ya, I know we got it here too!


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## Fishers of Men

*Characteristics of a ship*

The phrase &#8220;tactical characteristics of a ship&#8221; refers to the manner in which a given naval vessel responds to engine and rudder orders; the more generalized term &#8220;handling characteristics&#8221; is used for merchant ships. So far it has been assumed that at the instant of an ordered course change the vessel came immediately to the new course, and that when a new speed was ordered, the ship attained that speed instantly. Such, of course, is not the case. To increase or decrease speed by 10 knots *may require from one to twenty minutes, or more,* depending on the initial speed, the power available, and the flexibility of the engineering plant. A course change of 90&#176; may require as much as a half mile, or more, of sea room to complete, depending on the type of ship, the rudder angle used, the wind and sea, and other factors. Each ship reacts in a different way to a given rudder or speed order, and reacts differently under different conditions of wind and sea.
When his ship is steaming singly at sea, the navigator may ignore the time and travel required to effect course and speed changes, for the scale of his plot is too small to be affected by the resulting errors.

*Speed and course changes in restricted waters:*
In restricted waters the situation is entirely different. Here, the navigator frequently needs to know his position *within 10 yards *, and the effect of the ship&#8217;s travel in the time required to complete a change of course or speed is so comparatively large that it must be taken into account. The navigator must know his ship&#8217;s handling characteristics; that is, how she will respond to a given order under existing conditions.
This chapter is concerned with the quantitive effects of course and speed changes on the travel of the ship, and the techniques and methods that a navigator uses to allow for these effects when piloting a ship in restricted waters. The term &#8220;precise piloting&#8221; is sometimes applied to the navigation of a vessel taking into consideration these small, but very important, factors. Bringing a ship to anchor in an assigned berth, which requires the use of these same techniques, will also be discussed in some detail later.

*Rule 9 Narrow Channels*
Narrow is a relative term and again if you think your in a narrow channel, you are in a narrow channel. *Nothing in life is totally predictable* and this is accentuated in this situation. In the context of this rule, you are governed by _port and starboard buoys_, markers, and are obviously limited by the direction of travel.
Certain rules within the RULE must be observed.
1. NEVER anchor in a narrow channel.
2. Keep well to starboard.
3. On the Great Lakes, Western Rivers or waters specified by the Secretary, and proceeding *downbound* with a following current shall have the right of way and shall propose the conditions of passage plus initiate any necessary signals.
4. Power does not give way to sail.
5. Good lookouts are an absolute necessity when the channel turns.
6. Be aware of fast flowing currents, remembering that the fastest current is on the outside of the bend.
7. Large vessels cannot deviate from their track, so keep out of the way of big ships.
8. Any vessel nearing a bend shall navigate with alertness and be ready for any eventuality.
9. When nearing a bend, sound _one prolonged blast_, and then wait for the same signal; if no signal is heard, wait, and try again to make sure no vessel is there, and proceed.
10. Repetition is justified when it serves a purpose, so, never anchor in a narrow channel.
*Rule 10
Traffic Separation Schemes (TSS)*
(Remember this from the chart?)
What is a traffic separation scheme? Just as driving on the right side of the road in the USA, larger vessels such as cargo ships, freighters, etc. use the diagrammed routes on the charts for incoming and outgoing traffic for purposes of orderly patterns which will result in a systematized flow of vessel traffic. Of course, all vessels may join in and usually do , because it&#8217;s the best and shortest way to go. This rule, (TSS) *applies to both inbound and outbound traffic*, but does not relieve any ship of it&#8217;s obligation under any of the other rules.
Few small pleasure crafts and sailboats are capable of maintaining the speed of a TSS and to them we say stay out. This is especially true in bad weather, fog and a heavy state of the sea. It should also be noted that sailing vessels do not have a right of way over the larger vessels. Here again it is so very important to have the competent lookouts in position.
Essentially, this rule requires that vessels using these lanes keep to these lanes and travel with the traffic flow without getting close to division lines and separation areas.
One of the most important aspects of this rule is that vessels joining the scheme at other than the ends, do so at as small an angle as possible. On the other hand vessels which must cross the traffic lanes are required to cross at as much of a right angle as can be maneuvered. Now in the entering, we want a small angle to blend in to the flow; and when crossing we want a large angle to show everyone watching what our intentions are in going with or going through. (see diagram)
Again the old rule, as in a narrow channel, avoid anchoring in a traffic separation scheme and if not using it avoid it with as large a margin as possible.
I don&#8217;t know why any one would want to fish in a TSS, but if it&#8217;s a necessity, do not impede the passage of any vessel. Also, any vessel restricted in it&#8217;s ability to maneuver is exempt from complying with rule 10. _(A RAM is excepted from the rule)._








*Rule 13 Overtaking*
The first part of Rule 13 is very specific and means that regardless of what the overtaking vessel may be; sail, fishing or just trying to get around the vessel ahead, it has the responsibility to keep clear. It also means that the overtaken vessel is not home free and also has responsibilities.
A vessel shall be overtaking when coming up on another vessel from a direction of MORE than 22.5 degrees abaft the overtaken vessel&#8217;s beam.(see illustration). The reference here is that if it were night, the overtaking vessel would see only the white sternlight and neither of the red or green sidelights of the vessel being overtaken.








In the overtaking situation, a number of good common sense rules come into play. We have to remember that the overtaken vessel is not always aware that she is being overtaken so let her know. The sound signals (Rule 34 coming up next post) can be used and if necessary fire a white flare. Lookouts (Rule 5) can again become increasingly important and even essential. Let that guy know that you are overtaking him. Once the overtaken vessel realizes she is being overtaken she has *the responsibility to hold course* and speed until the vessel is passed. At this point, the overtaking vessel* CANNOT cross close ahead.* This could be likened to a vehicle passing another vehicle and cutting it of such as to make the passed vehicle slam on the brakes which a boat doesn&#8217;t have.
If there is any doubt as to risk, the overtaking vessel should turn to port and *it should be a natural maneuver* for the overtaken vessel to turn to starboard.
Finally, the Rule leaves *no room for hesitancy*. If you think you are overtaking, you are overtaking, so assume that you are and abide by the Rule.
Rule 18
*Responsibility Between Vessels*
(The order of rights of way in open water)	
Who has the right of way? We can list them and there is a jingle to remember the responsibility between vessels. We can talk about what vessel shall keep out of the way of another, however, there are always exceptions. In Rule 18 the exceptions concern Rule 9 which concerns narrow channels; Rule 10 where Traffic Separation Schemes (TSS) have priority and the responsibility of overtaking in Rule 13 that *may take claim in the rights of way* in this all important, necessary control in open waters.
Unless Rules 9, 10, and 13 otherwise demand, the responsibilities between vessels require the following order also known as the *pecking order:
Inland Rules*
1. Overtaken&#8230; over
2. Not under command&#8230; over
3. Restricted maneuverability&#8230; over 
4. Fishing&#8230; over
5. Sailing vessels&#8230; over
6. Power driven vessels&#8230; over
7. Seaplanes
Over the years I&#8217;ve used this little phrase or jingle using the first letter of each first word to identify to this priority. Over Night Rooms For Sale Plus Sally.
We add &#8220;constrained by draft&#8221; to the pecking order for international rules only. To define constrained by draft is only to take into consideration the draft of the vessel as related to water depth, position and special conditions as regards to navigation. When we talk about water depth and the vessel&#8217;s draft, it would appear that this circumstance should be confined to the inland rules, but, it is just the opposite. _(Doesn&#8217;t make any sense) _There are depths in the oceans deeper than Mount Everest is high, yet there is constrained by draft in international waters and not in inland. _(Maybe if someone that knows what&#8217;s going on gets in charge they will change some of these senseless goof ball rules made by the homeland security clowns)._
It must be remembered that ocean going vessels are required to come into harbors, inlets and docking positions where large draft vessels must consider the navigation surroundings to heed the vulnerability and safety of the vessel. Therefore, the pecking order adds &#8220;constrained by draft&#8221; to the order over fishing, sail, power boats and seaplanes, but, *not over the top of the order of vessels being overtaken, not under command and those restricted in their maneuverability.* So, that big guy cannot be any different than you are when it comes to those 3 rules.
Rule 18 must be regarded as one of the most significant in this array of all rules each important in it&#8217;s own right, but, the right of way of one vessel over others sets forth the priority guide system of precedence that gives organization to prevent confusion, collision and turmoil.
*Subpart III - Conduct of Vessels in Restricted Visibility
Rule 19*
The Rule states in or near restricted visibility and when we&#8217;re near these conditions of fog, mist, snow, rain or similar conditions (Rule 3k), we could be cruising clear for an instance and see nothing in the next. Where seconds before you may have enjoyed sunshine, immediately you may not be able to see your bow and appropriately, vessels can and will change directions in fog, rain, etc. unpredictably. So, every vessel must proceed at a safe speed as discussed in Rule 6, but, now adapted to any kind of restricted visibility, which may mean STOP. If you can find safe, shallow water, drop anchor and wait until it clears. After all, the same fog bank may contain a returning fishing cruiser, a large tanker, a sailboat and you.
This Rule goes on to say that a vessel *using radar alone and detecting a possible collision or close quarters situation, shall avoid a course alteration to port and/or an alteration toward a vessel abeam or abaft the beam.* This again is good seamanship and common sense. _(There was 2 ships that collided in the fog because they did not follow this rule and had a collision when they were originally miles apart. Cant remember their names now, when I do, I'll fill it in.) _ To review the Captain&#8217;s conduct and the actions of his or her vessel, ten good rules to follow in restricted visibility are:
1. All vessels must be prepared to act NOW.
2. Think ahead. There is very little time to make decisions.
3. Be ready at all times for immediate maneuvers.
4. Lookouts are not only necessary, they are imperative. The more eyes and ears, the better.
5. It is difficult in rain, fog, storms, etc. to hear where sounds are coming from, so you may have to stop to listen.
6. Awareness that there could be clear conditions now and blindness seconds later.
7. SLOW, slow and most important, slow to bare steerage way. If necessary, take all way off until danger of collision is over.
8. Listen and have others listen to your radio and for fog signals.
9. Consider anchoring in shallow water until clear or at lest &#8220;seeing&#8221;.
10. Watch radar continuously and stay clear and away.
*What is circled on this chart? Lat/long and description?*








(answer) http://i202.photobucket.com/albums/aa305/FishersofMen/latlongexampleanswer.png

"Neither it is beyond the sea, that tho shouldest say, Who shall go over the sea for us, and bring it unto us, that we may hear it, and do it?" Deut 30:13


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## Fishers of Men

Time for some on the water communications...
*Sound and Light Signals*

Rules 32 through 37 are primarily concerned with sound signals, however, light signals can also be used as a supplement to the sound signals, *but not as a substitute.* The sound signals are an extremely important part of the rules in that they are in effect a means of communication to provide the surrounding mariners with the maneuvering and intention of maneuvering of vessels with, of course, the most important reason being; you guessed it to prevent collision. We all know that many, many sound signals occur out on the waters. Normally, when those blasts happen, *the non professional will undoubtedly come out of the wheel house or cabin and wave generously. * You have seen these kind...or maybe your one of them, lol.
It should be pointed out now and through out our study of these signals, that once radio communications are established between two (2) vessels, sound signals are not necessary.
*Rule 32
Definitions*
Whistle  This word means any sound signal capable of producing prescribed blasts to an audible range that can be heard by surrounding vessels and/or those in the vicinity. Technical details of sound signal appliances, specific ranges of 70525 Hz for different size vessels are listed in Annex III of these rules.
*Bells and gongs* are hollow metal instruments, made of corrosive resistant materials and designed to give a clear metallic tone. It must be noted that each has its own distinctive sound and shall produce a sound pressure level where the sound is recognized as a higher pitch for the bell and much deeper tone for the gong.
As indicated in the following diagrams and examples of sound signals which depicts short and prolonged blasts for different vessels and situations, the definition of a short blast is a blast of approximately one (1) second duration, where a prolonged blast means a blast of from four (4) to six (6) seconds duration. *It must be emphasized at this point before continuing our study of sound signals, that there is NO such thing as a long blast.*
Ru1e33
*Equipment for Sound Signals*
*A vessel of less than 20 meters* (65.6 feet) in length *is not required* to carry a whistle and/or a bell, *but SHALL *have some means of making sounds, which only makes sense. Even a whistle that can be blown or anything that can deliver noise sounds of clamor, blasts or blare, to let others know that you are there in that area, particularly in restricted visibility.
Vessels of 20 meters or more *SHALL* carry a whistle and a bell.
A vessel of 100 meters (328 feet) or more* SHALL*, in addition to the whistle and bell, carry a gong.
The terms foghorn or siren are not used in these rules, however, the bell and/or gong may be replaced by other equipment having the same sound characteristics. An interesting point to note is that on vessels of this size, the whistle is in the direction of the forward axis and shall be placed as high as practical. The bell is also forward and the gong is the aft portion of the vessel. The sounds are, when possible, power driven and electronically controlled. There is not some deckhand running back and forth ringing bells and gongs like some nutcase.
The professional, (the Captain) follows rule 33 and will have the necessary equipment on board or something very close to that required equipment. The rule as stated above . . .some means of making sound... is well intended for safety purposes to the ordinary mariner, However the knowledgeable seaman is certainly aware that *this does not mean* some make-shift *beat on a wash pan with a corncob* hillbilly device that will embarrass the Skipper if or when boarded by the Coast Guard or some legitimate maritime authority. I believe its called - Pride in your work.
*Applying Sound and Light Signals*
For Maneuvering and Warning The BIG 34 and 35
Before moving on to applying the all important sound and light signals on the often to crowded waters, lets briefly look at what happens on the road.
When driving a vehicle and attempting to attract attention the driver will sound or lay on the horn, flip somebody off, flash headlights and wave to try to communicate: Get out of the way, move over, hello there, Im here- parked in front of your house, and will do so with no prescribed time frame per sound or predetermined number of blasts. On the water, sound and light signals, to the professional mariner, *take on a whole different sense of logic* in a completely different environment and here *THEY MEAN SOMETHING.* *They signal maneuvers, intentions, warnings and are designed not only to prevent collision and near collision but to avoid confusion and eliminate doubts.*
Rule 34 and 35 are considered by most if not all experienced mariners as the essential keys and a vital communication that follow a number of blasts and a time per blast sequence. This is certainly not to take away from the other rules but these are the delivery of sounds and lights that let all on board vessels in the vicinity know whats going on.
Rule 34	Vessels in sight of one another
Rule 35	Vessels in restricted visibility








Rule 34
*Maneuvering and Warning Signals
Vessels in Sight of One Another*
*INLAND:*
Power driven vessels within one and one half miles, and in sight of each other and underway shall sound these signals on her whistle:
One (1) short blast : I intend to leave you on my port side.
Two(2) short blasts: I intend to leave you on my starboard side.
Three (3) short blasts: I am operating astern propulsion.
A power driven vessel insight of one another and intending to overtake another vessel shall sound the following:
One (1) short blast: I intend to overtake you on your starboard side.
Two (2) Short blasts : I intend to overtake you on your port side.
Upon hearing these blasts, the other vessel, if agreed, will sound the same signal. Should the other vessel doubt or otherwise have cause, she shall sound the five (5) or more short blasts as the danger signal.
When a power-driven vessel is leaving a dock or berth, she shall sound one (1) prolonged blast. Please note that rule 34 states that operating astern propulsion requires three (3) short blasts. However, a vessel leaving a dock backwards shall sound one (1) prolonged blast. It doesnt matter if she is going backwards, forward or sideways, the priority signal is still one (1) prolonged blast. Should the vessel backing from the dock for some means find it necessary to continue in reverse, the subsequent signal can then be an additional three (3) short blasts. This makes others aware coming or going that you are coming out. Very helpful if some fool is not paying attention.
*Radiotelephone Agreement*
A vessel reaching agreement with another vessel by radiotelephone in a head on, crossing or overtaking situation is not required to sound the whistle or light signals, but she may do so. If radio agreement is not reached, then whistle signals shall be exchanged and shall prevail.
*International:*
Vessels in sight of one another and underway, other than a narrow channel, shall sound these signals on her whistle:
One (1) short blast: I am altering my course to starboard.
Two (2) short blasts: I am altering my course to port.
Three (3) short blasts : I am operating astern propulsion.
When in sight of one another, IN A NARROW CHANNEL OR FAIRWAY, a vessel intending to overtake another vessel shall sound the following: Note the word intend in international waters.
Two (2) prolonged blasts followed by one (1) short blast meaning:
I intend to overtake you on your starboard side.
Two (2) prolonged blasts followed by two (2) short blasts meaning:
I intend to overtake you on your port side.
Agreement by approaching vessels for these overtaking maneuvers shall be:
One (1) prolonged, one (1) short, one (1) prolonged, one (1) short blast.
If for any reason(s) the approaching vessels fail to understand the intended actions of one another, she shall immediately sound the appropriate five (5) or more short blasts danger signals.
*The sound blasts may be supplemented by light flashes.* The word supplement meaning that it is in addition to and not a substitute for the blast(s). The light signals shall be all-round (360 degree) white or yellow lights, of one second duration, and must be synchronized with the whistle. The minimum range of visibility differs in that it is 2 miles for inland waters, (intention) and 5 miles for international waters while the maneuver is being carried out, *(I AM)*.
On both sides of the inland/international demarcation line, when a vessel is nearing a bend or in an area of a narrow channel or fairway where other vessels may be obscured by the bend or an intervening obstruction she *shall *sound one (1) prolonged blast. If there is no answer, [Here it would be wise to repeat the signal(s)], she may proceed with caution. However, if there is another vessel obscured, she is also required to sound the same one (1) prolonged blast.
*Highlights of Rule 34 In Sight of One Another*
*Inland vs. International Signals for Maneuver
Inland/	International:*
ONE SHORT BLAST
*I intend* to leave you on my port side./* I am* altering my course to starboard
TWO SHORT BLASTS
*I intend* to leave you on my starboard side./ *I am* altering my course to port
Please note that in both inland and international rules, the sound signals and the maneuvers are the same *The language is different.* *Inland rules are signals of intention I intend, I desire, I wish to. International rules state I am.*
Short flashes may be used as a supplement and synchronized with the whistle signals but never as a substitute, In academics or study of the sound/light signals any query of light flashes should be interpreted as though sound signals have already been made.
In inland waters where radiotelephone communication agreement has been reached 
(bridge to bridge) with another vessel, in a head-on, crossing or an overtaking situation sound/light signals are not required. But, may be used.
If whistles are fitted on a vessel of more than 100 meters (328 feet) apart, one whistle only shall be used for maneuvering signals.
*The DANGER SIGNAL. . . Stay Away... Dont hesitate to use it.* Then some clown comes out and starts waving "hi" to you again!

















http://i202.photobucket.com/albums/aa305/FishersofMen/12short.png









*Rule 35
Sound Signals in Restricted Visibility*
The Rules define restricted visibility as any condition that restricts visibility (observed conditions), that includes not only fog but mist, falling or heavy blowing snow, torrential rains, sand storms, anything that is blinding from the elements, but does not include darkness such as resulting from nightfall.
In or near these areas of restricted visibility whether by day or by night, the following signals shall apply:
TWO (2) minutes (*not more* than 2 minutes)
One (1) prolonged blast for power driven vessels making way moving through the water.
Two (2) prolonged blasts in succession for power driven vessels stopped and making no way.
One (1) prolonged blast followed by two(2) short blasts:
A vessel not under command
A vessel restricted in her ability to maneuver
Underway or at anchor
A sailing vessel
A vessel engaged in fishing
Underway or at anchor
A vessel engaged in towing or pushing another vessel
One (1) prolonged blast followed by three (3) short blasts:
A vessel or vessels being towed, *IF MANNED*.
If more then one vessel is in the tow, the blast is sounded by the last vessel towed. This signal is normally sounded immediately after the one prolonged two short sounded by the towing vessel.
When a vessel is pushing ahead and the two vessels are rigidly connected to comprise a composite unit, the two are regarded as one vessel and shall give the appropriate signals of one or two prolonged blasts every two minutes.
ONE (1) minute (*not more* than 1 minute)
At anchor:
Rapid ringing of the bell for five (5) seconds
In addition, the vessel MAY sound one (1) short, one (1) prolonged and one (1) short blast. This additional sound signal after the bell is optional depending on visibility conditions and it is determined by the Captain, if he feels it necessary, to warn approaching vessels of his vessels position at anchor and that there is the possibility of collision.
Vessels of one hundred meters (328 feet) or more will have the rapid ringing of the bell in the forepart of the vessel for 5 seconds and a rapid ringing of the gong for about 5 seconds in the after part of the vessel.
Aground:
Rapid ringing of the bell for 5 seconds. If 100 meters and over, a rapid ringing of the gong for 5 seconds. There must also be three (3) separate and distinct strokes on the bell before and after the rapid ringing of the bell. These three (3) additional and separate strokes on the bell before and after the rapid ringing distinguish and identify the vessel as being aground as opposed to being at anchor. The vessel aground has the option of also sounding the one short, one prolonged and one short blasts if it is determined that the possibility of collision exists.
*Pilot Vessel* This is a local Captain familiar with the port that you are accessing that is unfamiliar to you and will pilot your boat in for to port you. Used by freighters, container ships and such.

A pilot vessel, when engaged on pilotage duty and making way or stopped or at anchor *SHALL* give the prescribed and appropriate sound signals required of such vessel underway or not underway or anchored. In addition the pilot vessel MAY sound the identity signals of a pilot vessel of four (4) short blasts.
*RESTRICTED VISIBILITY SOUND SIGNALS
UNDERWAY*
Sounded on whistle at least every TWO (2) minutes
1. Power vessel underway making way  1 prolonged
2. Power vessel underway NOT making way  2 prolonged
3. Not under command - 1 prolonged 2 short
4. Towing - 1 prolonged 2 short
5. Restricted Ability to Maneuver- 1 prolonged 2 short
(includes at anchor)
6. Fishing (includes at anchor) - 1 prolonged 2 short
7. Constrained by Draft - 1 prolonged 2 short
8. Sail - 1 prolonged 2 short
9. Towed Vessel (Mandatory if Manned) - 1 prolonged 3 short
Numbers 3 through 8 are all handicap signals.


----------



## Fishers of Men

*Now we need some of our "street signs"* 
We have _some_ of our means of communication covered...Kinda like learning to talk. We have figured out _some _of where we are going and how we are getting back; (kinda like learning to see (at sea). Didn't know there were (roads) paths and channels out there? Well, lets see...  

"The fowl of the air, and the fish of the sea, and whosoever passes through the paths of the seas..." Psalms 8:8 

*122	DUTTON&#8217;S NAVIGATION AND PILOTING*

*Reflectors *
Unlighted buoys and day beacons are marked with reflective tape. This 
greatly facilitates locating the buoys at night with a searchlight. Reflective areas may be red, green, white, or yellow, and have the same significance as lights of these colors.
*Caution *
Despite their usefulness, buoys must be used with caution. The buoy symbol on a chart is used to indicate the approximate position of the buoy and the anchor which secures it to the seabed. This position is termed &#8220;approximate&#8221; because of the practical limitations in positioning and maintaining buoys in precise geographic locations. These limitations include, but are not limited to, inherent imprecisions in position-fixing methods, prevailing wind and sea conditions, the slope and the make-up of the seabed, and the fact that buoy positions are not under continuous surveillance but are normally checked only during periodic maintenance visits which may occur a year or more apart. It must also be remembered that buoys are moored to an anchor with varying lengths of chain (a scope of three times the depth of the water is typical, but it may be more) and a buoy can be expected to swing in a circle under the varying influences of current, wind, and waves. Buoys are subject to being carried away, shifted, capsized, or sunk; lighted buoys may become extinguished and sound signals may malfunction. (So if it is leaning or blowing one way or the other, there is a length of chain off to the windward side to get hung in)
Buoys marking wrecks will normally not be directly over the hazard due to possible danger to the vessel placing the buoy in position. Such buoys are usually put on the seaward or channelward side of the wreck; if two buoys are used, the wreck may lie between them. Wrecks may shift position due either to normal currents or storm conditions; care must always be exercised in the vicinity of wreck buoys.
As useful as buoys are, a prudent navigator will not completely rely on the position or operation of floating aids to navigation, especially those in exposed waters; he will, whenever possible, give preference to bearings on fixed aids to navigation or natural landmarks.
*U.S. buoyage system *










The waters of the United States are marked for safe navigation by the lateral system of buoyage. 
*What they look like on a chart:*










This system employs a simple arrangement of colors, shapes, numbers, and light characteristics to indicate the side of the vessel on which a buoy should be passed when proceeding in a given direction. The characteristics are determined by the position of the buoy with respect to the navigable channels as the channels are entered from seaward. As all channels do not lead from seaward, arbitrary assumptions must at times be made in order that the system may be consistently applied.
The characteristics of buoys and other aids to navigation along the coasts, in *the Intracoastal Waterways, and on the Great Lakes* are as if a vessel were &#8220;returning from seaward&#8221; when she is proceeding in a *westerly and southerly direction *along the Maine coast, and in a *southerly direction* along the remainder of the Atlantic coast, in a *northerly and westerly* direction along the Gulf coast, in a *northerly direction on the Pacific coast,* and in a *northerly and westerly direction on the Great Lakes* *(except southerly in Lake Michigan)*. Canada maintains a buoyage system which is in general accord with that of the United States lateral system.
Identification of bouys in the U.S. lateral system, the following rules for daytime buoy identification are applied.
All buoys in the lateral system are painted distinctive colors to indicate their purpose or the side on which they should be passed. The meaning of these buoys, when returning from seaward, is indicated by their colors as follows:
*Buoy colors*










Black buoys mark the port (left) side of channels, or the location of wrecks or obstructions which must be passed by keeping the buoy on the port (left) hand.
Red buoys mark the starboard (right) sides of channels, or the location of wrecks or obstructions which must be passed by keeping the buoy on the starboard (right) hand.
Red and black horizontally banded buoys mark junctions in the channel, or wrecks or obstructions which may be passed on either side. If the topmost band is black, the preferred channel will be followed by keeping the buoy on the port (left) hand, as if the whole buoy were black. If the topmost band is red, the preferred channel will be followed by keeping the buoy to starboard.
However, in some instances it may not be feasible for larger vessels to pass on either side of such a buoy, and the chart should always be consulted.
Black and white vertically striped buoys mark the fairway or mid channel. Such buoys are also used in Vessel Traffic Separation Schemes at the entrances to busy ports or in narrow passages congested with heavy traffic.

*Special purpose bouys*
These buoys are not part of the lateral system. Their meaning is indicated by their colors as follows:
White buoys mark anchorage areas.
Yellow buoys mark quarantine anchorage areas.
White buoys with green tops are used in connection with dredging and survey operations.
White and black horizontally banded buoys mark fishnet areas.
White and international orange buoys alternately banded, either
horizontally or vertically, are for special purposes to which neither the lateral-system colors nor the other special-purpose colors apply.
Yellow and black vertically striped buoys are used for seadrome markings and have no marine significance.
*Buoy numbers*
Most buoys are given numbers, letters, or combinations of numbers and letters which are painted conspicuously upon them. These markings facilitate identification and location of the buoys on the charts.
All solid-colored red or black buoys are given numbers, or combinations of numbers and letters. Other colored buoys may be given letters. Numbers increase sequentially from seaward; numbers are sometimes omitted when there are more buoys of one type than another.
Odd numbers are used on solid black buoys. Even numbers are followed by letters are used on solid-colored red or black buoys when a letter is required so as not to disturb the sequence of numbers, such as when an additional buoy is placed after the numbering system has been established. Letters may also be used on certain important buoys, particularly those marking isolated offshore dangers. An example of the latter case would be a buoy marked &#8220;6 WQS.&#8221; In this instance the number has the usual significance, while the letters &#8220;WQS&#8221; indicate the place as Winter Quarter Shoal. Letters without numbers are applied in some cases to black and white vertically striped buoys, red and black horizontally banded buoys, solid yellow or white buoys, and other buoys not solid-colored red or black.
The numbers and letters (as well as portions of the buoy) are of reflective material for better visibility at night.
In order to provide easier identification under certain light conditions where the color may not be readily discerned, certain unlighted buoys are differentiated by their shape.
Nun buoys are used for red buoys or for red and black horizon tally banded buoys where the topmost band is red.
Can buoys are used for black buoys or red and black horizontally banded buoys where the topmost band is black.
In the case of other unlighted buoys and nonlateral system special- purpose buoys, shape has no significance; for example, an unlighted black and white vertically striped buoy may be either a can or nun buoy.
Full reliance should not be placed on the shape of an unlighted buoy alone. Charts and light lists should be consulted to ascertain the significance of unlighted buoys as determined by their colors.
Lighted buoys and sound buoys are not differentiated by shape to indicate the side on which they should be passed. Since no special significance is attached to the shapes of these buoys, their purpose is indicated by the coloring, numbering, or light characteristics.
*Buoy sound signals*
If both bell and gong buoys are used to mark a channel, the gongs are signals usually to port and the bells to starboard.
*Daybeacons*
Where daybeacons are substituted for buoys in the U.S. lateral system, the color of the daymark will be the same and the shape will be roughly similar&#8212;red daymarks will be triangular, approximating the shape of the top of a nun buoy; square daymarks, corresponding to can buoys, will be green (preferred), or black, or white. They will be numbered (and/or lettered) with retro-reflective material in the same manner as a buoy and have a border of that material. Some channels may be marked with a combination of buoys and daybeacons.
*Buoy lights*










Buoys of the U.S. lateral system may be lighted as well as Unlighted; the colors used and the light-phase characteristics aid in their proper identification at night.
*Color of lights.* 
The three standard light colors used for lighted aids to navigation are white, red, and green. Red lights on buoys are used only on red buoys, or red and black horizontally banded buoys with the topmost band red. Green lights on buoys are used only on black buoys, or red and black horizontally banded buoys with the topmost band black. White lights are used on any color buoy when required to distinguish it from other buoys in the vicinity or because of the greater intensity of a white light. Since white lights may be shown on buoys of any color, the color of the light has no lateral significance; and the purpose of the buoy must be found in its body color, number, or light- phase characteristic.
*Light-phase*

Lights shown from buoys and other aids to navigation have distinct characteristics to assist in their identification. These are illustrated, and their abbreviations are given. Lights are described as flashing when the time on is less than the time off. Lights are termed occulting when they are on more than they are off (&#8220;eclipsed&#8221. If the times on and off are equal, the light is designated as equal interval or isophase. The period of a light is the time for it to complete one full cycle of on-and-off changes. By varying the lengths of the periods and the elements of a cycle, a considerable variety of light-phase characteristics can be obtained. Advantage is taken of this to provide the necessary distinction between aids in the same area or to aid in the recognition of a primary seacoast light by the navigator of a vessel making her landfall.
*Light Characteristics in the lateral system*
Lighted buoys and minor lights in the lateral system are assigned phase characteristics as follows:
Flashing Lights (flashing at regular intervals and at a rate of not more than 30 flashes per minute) are placed only on black buoys, red buoys special purpose buoys, and on minor lights equivalent to black and red buoys.
Quick flashing lights (not less than 60 flashes per minute) are placed only on black bouys and red buoys, and on equivalent minor lights, at points where it is desired to indicate that special caution is necessary; for example, at sharp turns, where a channel narrows, or to mark wrecks or other obstructions which must be passed on one side only.
Interrupted Quick-Flashing Lights (groups of six quick flashes repeated at intervals of ten seconds) are placed only on buoys painted with red and black horizontal bands, or on a minor light whose square or triangular daymark is colored red and black divided horizontally, at points where it is desired to indicate junctions in channels, or to mark wrecks or other hazards that may be passed on either side.
Morse (A) Lights (groups consisting of a short flash and a long flash repeated at intervals of eight seconds) are placed on buoys with black and white vertical stripes, and on minor lights whose daymarks are octagonal, colored black and white vertically, placed at points where it is desired to indicate fairways or midchannels, and they should be passed close to on either side. These lights are always white.
*Miscellaneous Light information*
The lights on U.S. buoys are operated by means of electricity supplied from batteries stored in the body of and wired to a flashing mechanism in the base of the lantern. At minor lights, the batteries are in a weatherproof box on a platform near the top of the structure.
In order that lighted buoys and minor lights may function for a reasonably long period of time without requiring a replacement of the batteries, the length of the light flashes is quite short in comparison with the intervening periods of darkness. To further conserve electricity, lights are now equipped with a &#8220;daylight control&#8221; (photoelectric cell) to turn the light off during the day. Battery power supplies at isolated locations are frequently good for a year or more of operation. An automatic bulb-changing mechanism is included to increase the dependability of the light; if a bulb burns out, an internal device operates to put into use one of several spare bulbs.
Navigation lights on bridges
In U.S. waters, the Coast Guard prescribes certain combinations of lights for bridges and other fixed structures across waterways. In general, red lights are used to mark piers and supports, and green lights mark the centerline of the navigable channel through a fixed bridge; if there is more than one channel through the bridge, the preferred route is marked by three white lights placed also used on some drawbridges to indicate that the draw is open and the vessel may proceed.
Full details on the lighting of bridges will be found in the introductory pages of each volume of the Light List. Some bridges may also be equipped with sound signals.
*Cardinal system of buoyage*










In some waters, particularly those of foreign nations, the cardinal system of buoyage is used. The location of each mark indicates its direction from the danger that is marking. There are four quad rants (North, East, South, and West), bounded by the true bearings NW-NE, NE-SE, SE-SW, and SW-NW, respectively, from the point of interest. A distinctive shape, color, and light characteristic (and &#8220;top mark&#8221; if one is used) is assigned to each quadrant.
A cardinal mark is named after the quadrant in which it is placed, and it should be passed on the named side of the mark. A cardinal mark may be used to indicate that the deepest water is on the named side of the mark, or it may be used to indicate the safe side on which to pass a danger. Such a mark may also be used to draw attention to a feature in a channel such as a bend, a junction, or the end of a shoal.
Closely related to the cardinal system are two other types of aids to navigation. An isolated danger mark is one erected on or moored over an isolated hazard that has navigable water all around it and thus may be passed on any side. Somewhat similarly, a safe-water mark also has navigable water all around it, but it does not mark a danger at or beneath it; these include buoys marking midchannel or the centerline of a fair way. A safe-water mark may also be used as an alternative to a cardinal or lateral mark to indicate a landfall.
*Harbor buoys *are normally shown only on harbor charts. An approach chart displays sea buoys, approach buoys, and the beginning of channel buoys or lights. Smaller scale charts show sea buoys only. The position of a buoy is indicated on the chart by a diamond symbol with a dot or small circle marking the approximate position of the anchor. The diamond may be black or nautical purple (magenta)
*In order to obtain full benefit from lights, the navigator must not only understand their use and be able to interpret all data concerning them given in the Lights Lists and on charts, but he must also be able to identify each light correctly.*
One of the most frequent causes of groundings is the failure to identify lights correctly.[/COLOR][/B] When making a landfall, the navigator should consult the charts and the Light Lists to learn the exact characteristics of the light or lights that he expects to see first. When a light is observed, its color is noted and, by means of a watch or clock with a second hand, a note is n of the time required for the light to perform its full cycle of changes. If color, cycle, and number of flashes per cycle agree with the information in the Light List, correct identification has been made. The Light List should be examined to ascertain if any other light in the general locality might be seen and mistaken for the desired light. If there is doubt, a careful timing of the length of all flashes and dark intervals, and comparison with the Light List, is usually conclusive.
In approaching a light with a complex characteristic of different intensities, due allowance must be made for the lesser range of the portion with inferior brightness. For example, affixed and flashing light will have flashes brighter than the fixed light. When observed initially from a distance, it is likely that only the flashes will be seen and the full characteristic will not develop until the observer has come within the range of the fixed light. Another example might be a light with a characteristic of alternating flashing, white and red. The red flashes will be less bright and such a light, when first seen from a distance, will most likely be seen as a simple flashing white characteristic; the intervening red flashes will be seen only after the observer comes closer. At short distances and in clear weather, some flashing lights may show a continuous faint light; this results from the fact that the light does indeed burn continuously with the &#8220;flashes&#8221; being created by a revolving lens.
It is important to note that in Light Lists all bearings are stated in degrees true, reading clockwise from 0000 at north; bearings relating to visibility of lights are given as observed from a vessel; distances are in nautical miles unless otherwise stated; heights are referred to mean high water; depths are referred to the plane of reference on charts.
The great majority of lights have no resident crew tending them; such lights are called &#8220;unwatched.&#8221; Unwatched lights have a high degree of reliability; however, they may become irregular or extinguished. Latitudes and longitudes in the Light Lists are approximate, and are in tended only to facilitate reference to a chart.
*Light sectors *
Sectors of colored glass are placed in the lanterns of certain lighted aids to navigation to mark shoals or to warn mariners off the nearby land. Lights so equipped show one color from most directions and a different color or colors over definite arcs of the horizon indicated in the Light Lists and upon the charts. A sector changes the color of a light, when viewed from certain directions, but not the characteristic. For example, a flashing white light having a red Sector, when viewed from within the sector, will appear flashing red. *(But remember, the red may not be visible at all distances from which the white flashes can be seen.)*
Sectors may be but a few degrees in width, marking an isolated rock or shoal, or of such width as to extend from the direction of the deep water toward shore. Bearings referring to sectors are expressed in degrees as observed from a vessel toward the light.
For example, the List of Lights describes a certain light as displaying a red sector from 045&#176; clockwise to 120&#176;. Both are true bearings as ob served from seaward. Figure 518 is a sketch of this light indicating the limits through which the light would appear red as observed from aboard ship.










In the majority of cases, water areas covered by red sectors should be avoided, the exact extent of the danger being determined from an examination of the charts. In some cases, instead of indicating danger a narrow sector may mark the best water across a shoal.
In some atmospheric conditions white lights may have a reddish hue; the mariner therefore should not trust solely to color where there are sectors, but should verify the position by taking a bearing of the light. On either side of the line of demarcation between white and a colored sector there is always a small sector (about 2&#176 of uncertain color as the edges of a sector cannot be cut off sharply. Note here also that the bearings given on the lines of demarcation on the chart are true bearings of the light as seen from the ship.
At primary and secondary lights, and on lightships, fog signals are operated mechanically. There are several types of such fog signals.
Diaphones produce sound by means of a slotted reciprocating piston actuated by compressed air. Blasts may consist of two tones of different pitch, in which case the first part of the blast is high and the last part is low. These alternate-pitch signals are called &#8220;two tone.&#8221;
Diaphragm horns produce sound by means of a disc diaphragm vibrated by compressed air, steam, or electricity. Duplex or triplex horn units of differing pitch produce a chime signal.
Reed horns produce sound by means of a steel reed vibrated by compressed air.
Sirens produce sound by means of either a disc or a cup-shaped rotor actuated by compressed air,- steam, or electricity.
Whistles produce sound by compressed air or steam directed through a circumferential slot into a cylindrical bell chamber.
Bells are sounded by means of a hammer actuated by hand, by a descending weight, compressed gas, or electricity.
Identification As signals on buoys which are operated by the motion of the sea do not produce sounds on a regular time schedule, identification may be difficult or impossible. While it is easy to differentiate a bell buoy from a gong buoy or a whistle buoy, it is not possible to identify one specific buoy from another of the same type solely by the sound it makes.
Mechanically operated fog signals, however, are placed on a regular cycle of operation, and different types of signals and characteristics can be assigned various locations in the same general area for identification purposes. Fog signals at primary seacoast and secondary lights are usually horns with characteristics varying from one to three blasts in cycles of 10 to 60 seconds length; each blast is normally two or three seconds in duration with pauses of similar duration between blasts if there are more than one. Lightships are usually fitted with a two-tone diaphone; these, too, are assigned an identifying characteristic in terms of number of blasts and length of a cycle. Occasionally, a diaphone is installed on shore, or a siren or bell is used for some local purpose.
Operation Fog signals of the U.S. Coast Guard at locations where a continuous watch is maintained are placed in operation when the visibility decreases to 5 miles, or when the fog signal of a passing ship is heard. Fog signals at stations where no continuous watch is maintained may not always be sounded promptly when fog conditions develop or may operate erratically due to mechanical difficulties. At some stations, fog signals are operated continuously for a portion of each year; the operating period is stated in the Light Lists.
*Caution *
The navigator must always bear in mind that sound signals in fog can be very deceptive. At times, they may be completely inaudible even when near at hand. Again, they may be somewhat refracted; that is, they may appear to be coming from a direction other than the actual bearing of the signal source. Constant soundings should be obtained when operating in fog in coastal areas.

*The Intracoastal Waterway*










(ICW) is a largely sheltered water on ICW way, suitable for year-round use, extending some 2,400 miles along the Atlantic and Gulf coasts of the United States. In general it follows natural waterways. ( and is full of tourists and many other non educated a$$ holes)  
Aids to navigation along the ICW carry special identification marks. The usual daymark and buoy painting schemes are used, but an additional yellow stripe is added under the number. (The former distinctive marks of yellow borders on daymarks and yellow bands on buoys are being phased out.) 
*Colors *
The colors used for ICW aids are governed by the following rules:
The left side of the channel, entering from the north and east, and traversing towards the south and west, is marked with black aids, bearing odd numbers.
The right side of the channel, entering from the north and east, is marked with red aids, bearing even numbers.
All green or black daymarks on daybeacons are square, while the red markers are triangular in shape.
In certain areas, the ICW coincides with other waterways, which are buoyed in accordance with the standard practice; that is, black buoys on the left hand when proceeding from seaward, and red buoys on the right. In such joint waterways the standard system of coloring prevails for buoys, and the ICW numbers and yellow markings are omitted, but yellow triangles or squares are added on the regular aids to designate the ICW. An inspection of the sketch on that page shows that the color of aids may be reversed under such conditions. A vessel proceeding south down the ICW has red aids on her right hand until the nun &#8220;6&#8221; is reached where the channel becomes a joint waterway; at this point the red aids will be on her left hand. However, along this reach of the channel the yellow shapes painted on the buoys can be of assistance, as the squares will be on the red buoys as a reminder that in this joint waterway a red buoy may be on the left-hand for vessels proceeding south.

*My version of the ICW*
I am not going to edit it for repetition:
&#8216;The Intracoastal Waterway

The Intracoastal Waterway ( ICW) is a large noted waterway system slightly inland on the Atlantic coast and flowing north to south. It extends from the north Atlantic states, down the east coast to the tip of Florida and westward along the gulf coast states to Texas covering approximately 2400 to 2500 miles. The ICW is an excellent fishing choice because of all the estuaries. :B 
The ICW follows primarily natural waterways and is used extensively by mariners to travel up and down the coast and who do not wish to travel in open seas. The waters are considered Inland Waters except where it is impractical to remain within the demarcation line and the Captain must go into international waters. It is very popular, with numerous facilities, dockage, fuel supplies and scenic attractions. Well traveled, the ICW has a unique and often misunderstood system of aids to navigation. Traveling north to south from the northern states and up the west coast of Florida and east to west along the gulf states is considered as returning from sea. Therefore, traveling in this direction, red buoys and fixed aids are on the right and green buoys on the left hand side when proceeding down the ICW.
One distinctive feature of the intracoastal is the color yellow. Even though the usual color scheme and numbering organization is used: red and even numbers on the right and green and odd numbers on the left, an additional yellow band is added under the numbers indicating that you are in the ICW. The Yellow borders are no longer in use. This would be all well and good, to follow this &#8220;inside route&#8221; just as one would be on a river except for one big difference. There are other routes coming in from sea which cross over the ICW. These many courses coincide with the ICW in that they also follow the required system of Red Right Returning RRR just as the Captain proceeding up or down the ICW.
It is easy to see where confusion would enter the traffic pattern, in that the Captain traveling north and south on the ICW following RRR would claim priority, while those entering and leaving the mainland and crossing the ICW would also claim that right of way. It is here where the knowledgeable Captain(s) must be alert to follow Dual Markings that are attributed to, and characteristic of, only the ICW. Historical facts of many incidences of running aground, collisions and confrontations are evident of traveling the ICW because of confusion and lack of knowledge of navigating this unique waterway.
So that mariners may safely follow the intracoastal waterway where it coincides with another route, special dual markings are employed. They are applicable to buoys and/or other aids that mark channels in the twofold travel areas of vessels going north and south and vessels traveling into or away from seaward. These special markings consist of either a yellow square or a yellow triangle painted on a very visible part of the aid. The yellow square, which may appear on either a red nun buoy or a green can buoy, should be kept on the left hand side when following the ICW south from New York to Texas, when in the dual purpose area.
The yellow triangle, on either a can or nun buoy should be kept on the right hand side when traveling in the same direction.
Where the yellow squares and triangles are visible on the aids, the typical yellow band representing the ICW is omitted. The mariner then knows that once the yellow bands reappear, he has left the dual marking area and continues to navigate by the standard RRR system again.
In those areas where dual markings are in use, the Captain following the ICW will completely disregard the color and shape of the aids and navigate his vessel strictly by the shape of the yellow squares and triangles.
In summary of this dual marking system, the Captain traveling the intracoastal waterway knows that the east coast and gulf coast has numerous &#8220;capes&#8221; and inlets so very popular for travel in and out of the continental U.S. He further knows that these vessels will use the red right returning arrangement in our system of aids to navigation. The mariner approaching such a body of water realizes the need to be alert and look, not only for the removal of the yellow bands on the buoys, but adapt to a more involved travel scheme of the ICW buoyage system. The Captain now knows that he MUST determine the side of his vessel on which these aids should be passed strictly by the shape of the yellow squares and triangles, always keeping in mind where he is at and the basic direction of his ICW travel.
I have not only experienced, but have been made aware many times, by veteran associates traveling the ICW, of the unsuspected shoals, rocks, shallows and other hazards of this popular, yet sometimes treacherous waterway. Caution and KNOW HOW are the watchwords so absolutely necessary for traveling in these waters. They can be scenic and very enjoyable, provided the skipper at the helm can identify with the signs, aids, schemes, traffic patterns, and the rules of the ICW. So, if you go on vacation to Fla or elsewhere you have to cross the ICW to go out to sea or if you fish it (example the Indian river in fla.) Don&#8217;t be one of those knuckleheads in the news. 

*Western Rivers buoyage system*
Aids to navigation on the &#8220;Western Rivers&#8221; of the U.S.&#8212;the Mississippi River and its tributaries&#8212;are generally similar to those on other U.S. waters, but there are a few differences that should be noted. Buoys are not numbered; their color system conforms to the U.S. lateral system or red-right-returning from sea, with white tops added for improved visibility. (The descriptions &#8220;right side&#8221; and &#8220;left side&#8221; are sometimes used but in terms of a person on a vessel proceeding downstream toward the sea.) Lights and daybeacons are numbered, but not in the even-odd style of the lateral system; numbers relate to the distance upstream in statute miles from some arbitrary point of origin. Lights and lighted buoys on the starboard side proceeding downriver show a single green or white flash; those on the port side show a double red or white flash. Special &#8220;crossing&#8221; daymarks are used at bends where the deeper water channel crosses from one side of the river to the other. 
*Uniform State Waterway Marking System*
To provide for consistent marking of U.S. internal waters not subject to federal jurisdiction, there has been established the Uniform State Waterway Marking System (USWMS). This consists of regulatory signs and buoys, plus buoys in either the lateral system or a &#8220;cardinal&#8221; system.
Systems of other nations
The buoyage system of other nations may or may not be similar nations to that of the United States. If a lateral system is used, the buoys to be left to starboard may be black, rather than red. In other cases, the color of the buoy may not be significant, information being conveyed only by the buoy&#8217;s overall shape or its &#8220;topmark&#8221; (an added shape of one or two spheres, cones, etc., at the top of a buoy&#8212;not used on U.S. buoys). Some nations make regular use of buoys in a cardinal system.
Northwestern Europe buoyage system
The nations of Northwest Europe&#8212;England and France, north to Sweden and Norway, west to Ireland, and east to Poland&#8212;are establishing a uniform system of buoyage using both the lateral and cardinal systems, plus marks for isolated dangers, safe waters, and special indications. Not all types will be used in each area, but where used, the colors, shapes, topmarks, and light characteristics will be consistent with the established rules which are known as &#8220;System A&#8212;The Combined Cardinal and Lateral System (Red to Port).&#8221;
Navigator&#8217;s A navigator must be familiar with the system of buoyage that he will responsibility encounter before he enters the pilot waters of a foreign country. Advance study of the appropriate List of Lights or the appropriate volume of Sailing Directions is absolutely essential.

This post took me 6 hours to do! 

"And the channels of the sea appeared, the foundation of the world were discovered, at the rebuking of the Lord, at the blast of the breath of his nostrils.
He sent from above, he took me; he drew me out of many waters;" II Sam 22:16-17


----------



## Fishers of Men

Bring questions on anytime, it's gonna start gaining weight.


----------



## Fishers of Men

Okay, since no one wanted to discuss anything we are going to do the radio thing. Every time I get out on the lake, I hear the novices talkin their cb crap on a vhf. Well there is plenty of reason not to do it and/or show ignorance instead of professionalism. And here it is:

*Communications
Radio Telephone*
*Communications, communications and most important communications.* Not only important to the mariner but a tool that is life saving. No prudent Captain could even think of taking vessel and passengers out on open water without dependable communications equipment and of course the knowledge of operating it with the proper procedure. What price, what value, what worth could be placed on a functional radio telephone in case of an emergency, when safety or life is at risk. Most professionals will carry two radios, in case the primary radio fails. *All important is the ability to use them and relate to authorities,* fellow mariners and the Coast Guard your situation , should it be emergency, convenience or information on any number of pertinent situations to all involved.
This section will deal with the radio and the proper language, terminology and procedure to communicate all types of information in all types of circumstances in a calm, orderly fashion. This requires not only a knowledge of radio terms and procedures but a reserve and control that enables one to talk and transmit necessary and important information.
This author was associated with a factory environment with a speaker system used to make announcements, etc. over the entire plant area. I was made aware that there are some, if not many people, who cannot pick up a microphone and have their voice speak out over a wide range of listeners. This may be a phobia, but certainly also a determent in emergencies on the water. This must be overcome when an emergency exists on a vessel and the communicator must communicate, A life and or vessel may and on occasion does depend on it.
There are certain authorized marine *transmissions that are reserved for:*
1. Safety
2. Operations
3. Business
4. Ship to Shore or ship to ship
*Certain rules must prevail,* otherwise confusion will reign with misunderstandings and miscommunications that will result in misinterpretation, anger, loss of valuable time and possible fines. In marine radio operation these rules include, but are not limited to:
&#8226; Maintain a watch on channel 16 when the radio is on. This is also the emergency channel which everyone monitors. It follows then, that out on the water, not only do we have the Coast guard listening, but, we have people from all walks of life listening to channel 16. If there were an emergency, ( accident, heart attack, man overboard, accidental poisoning, collision, etc. ), we have such people as medical doctors, nurses, paramedics, and experts in all of life&#8217;s areas that can and &#8216;will come to the rescue and assistance. And just maybe, they are on a boat that s within view of the vessel in need.
&#8226; Use the proper channels for your transmissions. You do not carry on a conversation on channel 16, but establish contact and then switch to an agreed channel as listed below as &#8220;channel usage&#8221;.

&#8226; Limit preliminary calls to 30 seconds or less.
&#8226; Limit ship to ship calls to 3 minutes.
&#8226; Do not use profane, obscene or otherwise deragatory or offensive language.
&#8226; Do not make fraudulent or falsified calls of any nature. It has only been a few years that an individual was sending out illicit MAYDAYS as a joke. It caused the Coast Guard and the listening mariners a great deal of anxieties, a lot of wasted time for the CG and a tremendous amount of money to the government and the taxpayers. Some very sophisticated equipment was brought in and the culprit was caught, on his boat, on the trailer and in his driveway. Needless to say, here is some perpetrator who will not even attempt that again, at least not from his present jail cell residence.
*Avoid unnecessary radio checks: *(How do you read me ) over and over again.
06 Inter-ship safety
09 Inter-ship and ship to coarse
12 USCG port operations
13 bridge to bridge (locks) (*1 watt, Yep turn &#8216;er down!*) 156.65 mhz
16 distress and safety calling 156.8 mhz
22A CG working channel 157.10 mhz
24-28 public telephone (ship to shore)
84-88 public telephone (ship to shore)
65A port operations
68 inter-ship to coast
69 inter-ship to coast
71-72 inter-ship to coast
78 inter-ship to coast
79-80 inter-ship to coast (Great Lakes Only)
*There are three types of calls listed below:
Mayday- Mayday- Mayday*
Pronounced may day and spoken distinctly and loudly.
Extreme emergency which life and/or vessel are in peril. At this point I would like to emphasize that there may be borderline conditions in which the Captain could have doubt as to whether there is a real threat to life. Keep in mind that with a real mayday, the Coast Guard will go to all extremes with all available means. A life and /or vessel is at stake. To this I say, as skipper of my vessel, and there is doubt as to whether one of my passengers may or may not die. I will use mayday. Perhaps it would turn out that my friend(s) could have had a greasy meal and have acute indigestion and causing chest pains. But, I&#8217;m not a physician or paramedic and I certainly do not want to go through the rest of my life thinking I may have caused a death because I didn&#8217;t want to be chewed out by the Coast Guard for misusing mayday. YES, if there is doubt, USE MAYDAY.
If you are out there on a nice day and run out of gas, *DO NOT USE MAYDAY* you probably will go to jail.
*Pan Pan- Pan Pan- Pan Pan* 
pronounced pawn pawn
This differs from a &#8220;mayday&#8221; in that it dues not involve immediate threat to life or vessel, however still involves the safety, safekeeping and wellbeing of ship and/or people. 
*Security- Security- Security *
(Like of you want to report a deadhead floating, old refrigerator, rock sticking out of the water, sailboat on it's side, any kind of navigational hazard.)
pronounced; sa cure a tay
This involves weather reports, climate conditions and hazards to navigation such as buoys out of place, loose and floating objects on or below the surface and abandon barges, rough seas and bad visibility conditions.
*It now becomes very significant in radio communication that the proper procedure is used, particularly as far as identification and location is concerned.* The Coast Guard flies over 65000 rescue missions a year and they must have ALL information possible:
&#8226; Give the name and call letters of the vessel and the type of call:
mayday, security or pan pan. NOTE: If mayday, stay on channel 16, if other switch to a working channel.
&#8226; *Give the message in DETAIL.* What it is......Describe the vessel (size, color, identifying characteristics, features, flags, appearances, details, details). Where it is ..... distance and direction from shore, coordinates, surroundings and all location features to have a vessel or aircraft relate and identify to one particular vessel, without confusion to any other ship.
(WHO, WHERE, WHY, WHAT AND WHAT WENT WRONG)
Remember to keep it clear, precise, loud and above all: free from panic.
&#8226; Signing off or continuing a conversation on a working channel, remains a vital part of radio communication procedure. Once contact is established, the channel is left open for continuous relays of interrelated information by those communicating. This is done by using the word &#8220;over&#8221;. This tells all parties that the transmitted conversation continues and more information is still being communicated. This can go on for a while, talking and transmitting etc., using the word over each time additional information is given. This temporarily committed channel is then dedicated for these transmissions until the exchanged conversation are complete and each exchange is followed by the word...... over. Once all information is interrelated and the conversation is complete, we finalize the transmission(s) with the word: &#8220;out&#8221;. The Coast Guard or another vessel(s) will respond with &#8220;out&#8221;. AGAIN, the word over is used for a continuing relay of information and out when the transmissions are complete.
&#8226; *C.B. jargon such as; roger, roger dodger, over and out, back at ya, got your ears on?, you there good buddy?, etc. is not used and frowned upon by the Coast Guard and professionals.*
Working Channels for Coastal Cities such as Ocean City, MD
06 Inter-ship safety
09 commercial
12 port operations
13 ships bridge to ship to bridge or drawbridge (1 watt, Yep turn &#8216;er down!)
16 distress and calling
18 commercial fishermen
21&22A CG working channel
25 public telephone (ship to shore)
26 public telephone (ship to shore)
65A port operations
68 local recreational fishermen
77 clammers
Time and again I have seen radio failures. It is therefore strongly suggested that on extended travel on the Great Lakes and off shore cruises, two (2) radios are on board. Radios are not that expensive, particularly when compared to the price of a vessel or evaluated with a human life.


----------



## Fishers of Men

Okay, since I have no questions or discussion on any topic covered so far, I am going to figure that everyone here understands everything so far and move on. I figure there are a lot of people out there that don't care and or say, "whats that got to do with me?" well, when we get done they will be the ones to wave at you next spring when you pass on the river or channel and give them 5 short blasts. We will know who they are by how they rig their vessel, how they dock the boat, how they handle it on the water, how they use the vhf, how they don't follow the rules of the road, how they run out of gas, how they are lost in restricted vis, how they complain about not catching fish, why they cant slow enough to troll, why they are afraid of the lake, why they cant hold anchor when trying to get over the perch...I gotta stop, I get irritated thinking about instances and experiences and the goofballs we all run into out there. I apologize for the rant!

Okay, here's a briefing just to get a start on DR, Headings, Bearings, fix and using topics we have covered.

*The Dead Reckoning DR Course
You have got to DR*
The Dead Reckoning DR plot is an essential skill, fundamental to the navigator and used to predict present and future positions and estimated times of arrival at any point until positions are confirmed by a fix. The DR was used by Columbus, Magellan and Cook and is defined as : *An approximate position from a known position without wind and current.* It is obvious that when mariners move from place to place, once they leave a fix, the wind and current, (the two terms combined are called &#8220;current&#8221, moves the vessel from the DR course, but it&#8217;s the best thing we have to indicate where we are until we use electronics or a plotted fix. *You have got to DR; YOU HAVE GOT TO DR.* Everyone from maritime academies through auxiliary and professional schools teach their students not only the significance of the DR, but the standard terminology, symbols and procedures that define a common language to all good navigators to know at least an approximate if not completely reliable position.
*When does the navigator exchange the DR position for a fix?* If there is any doubt about your vessel&#8217;s position in relation to strong currents or possible dangers which may place the vessel in an uncertain risk or there is a suspicion of peril, *then do as the professional Captains do* and establish a fix. *Use common sense and in the mean time- You have got to DR.*
The symbol of a DR position is a dot within a half circle. A known position or fix and a running fix is a dot within a full circle. In order for all crew members to interpret the vessels plot, a standard procedure is followed in labeling.
*1. The course line is drawn in the direction of travel and called point of aim.
2. Always read the compass rose in the direction in which the vessel is traveling. It is common, to read the opposite side of the rose because of the straight line going through both sides of the rose and errors of 180 degrees are easily read.
3. The course C, taken from the compass rose is written above the course line in 3 digits. it is important to remember that only the True course is marked and used even though the magnetic course is given on the inner circle.
4. Speed of the ship is marked below the line. Distance between 2 points may also be listed below the line, provided there is room.
5. The times of the DRs are labeled at an angle to the dotted half circle using four digits (1355).
6. Label a fix with two or more lines of position [ with the time the fix was actually taken and written horizontally with four digits such as 0920, again using the 24 hour clock
7. Mark an estimated position with a small square and the time.
8. A new DR course is started after each fix and is maintained until the next fix.
9. Plot a new DR position every hour on the hour and with every change in course and speed.
10. Neatness and accuracy are the hallmarks of a good navigator.*

DR (dead reckoning) has some saying it got it's name because if you don't do it, you'll be dead. Others say if you soley rely on DR, you'll be dead.
All the old sailors had was DR and a lot of them died. When we get thru the details and importance of it, you decide!

The practical Captain will always plot the DR course line and make every effort to steer the boat along that course and keep track of if the vessel&#8217;s travel progress. It is assumed that the boat moves in a straight line and will continue on that line in a predictable way. This would be true in a perfect world, but in the real world the vessel rarely moves along the DR track. The good pilot recognizes the current effects and must from time to time determine the exact position of the ship by taking bearings.
*A Bearing is the direction from a known object (a fixed object that can't move)to the observer&#8217;s position.* *This is a Line of Position* (L 0 P ) and the navigator knows that his vessel is somewhere on that line; but where? So another bearing is necessary from another known object or from the same object at a different time as the vessel continues to move. Where the two or more LOPs cross is the position of the vessel and known as a *fix*. After determining the fix position on the chart, a DR course line is started from the fix and will continue on the new DR until it is determined that another fix is required. There are different types of bearings and it is essential that the navigator understands these differences and how to use them as L 0 Ps. They are measured clockwise from some reference point or direction in degrees.
*True bearings are the only bearings*, just as true courses, that are drawn on the chart. The bearing of an object with respect to true north as the reference direction is a true bearing. For example, an object due east of the observer would have a true bearing (TB) of 90 degrees just as an object northwest would be 315 degrees.
One of the most common types of LOPs is based on a compass bearing. One can take compass bearings with a boat&#8217;s steering compass which will give reasonable accuracy, if compensated for compass error. Very accurate compass bearings can he taken within a few degrees by steering toward a fixed object such as a light house, range or tower and continually reading the compass.

One of the best methods of taking compass bearings is to use a Hand Bearing Compass. The navigator will hold the instrument &#8220;aiming&#8221; it and sighting through a single vane toward the observer&#8217;s eye and the double vane sighted and lined-up on the object. Read the compass dial (360 degrees clockwise when the object is correctly sighted. Be certain not to stand to close to magnetic interfering metals. In the event that the steering compass is in anyway disabled the hand bearing compass can also be used temporarily as a steering compass. They are inexpensive, easily stored and used and it will get you home.

Once the true bearings are calculated from the compass bearings, the LOPs from the true bearings can be plotted on the chart. There is only one position on the two bearings where the vessel can be located. The new DR is then continued from the fix.










*A Relative Bearing is one relative to the heading of the vessel itself and measured from 000 degrees at the heading clockwise through 369 degrees.* The RB is then the angle between the ship&#8217;s compass lubber line and the object whose bearing is being measured. Stated another way a true bearing is the object&#8217;s angle front true north while a relative bearing Is the object&#8217;s angle from the ship&#8217;s direction of travel. Relative bearings, regardless of direction of travel, can be dead ahead 000 degrees, astern 180 degrees or broad on the beams measuring 90 degrees on the 3darboard or 270 degrees on the port aide. To convert a relative bearing to a bearing from north, so it may be plotted, it is expressed as 0 degrees to 360 degrees and added to the heading.
TH + RB = TH
If the total exceeds 360 degrees, subtract this amount (360). To convert a bearing from North to a relative bearing, subtract the heading.










Since only true bearings can be plotted, compass bearings must be converted to true bearings. As previously discussed in an earlier post, T V M D C is again used. As we added and subtracted variation and deviation for course plotting, we calculate bearings with the same &#8220;formula&#8221; (+ W / -E going down) *with one very different significant feature applied to bearing calculations only. BEARINGS DO NOT HAVE DEVIATIONS.*
This does not mean that the bearings for deviations are 0 degrees, but that the deviation for any bearing comes from the magnetic influences of the vessel from which the bearing is taken. The bearing is that L 0 P between the observed object and the vessel and has no magnetic influence. It comes from the metal on the vessel and applied to the bearings from the ship&#8217;s heading. This principle of using the deviation from the vessel&#8217;s course and applied to the bearing is best illustrated in these examples. Remember, every vessels compass has a different deviation and a table must be made for each individual vessel. This table is an example:
DEVIATION TABLE This doesn't want to save in order.

Magnetic___________Magnetic
Heading__Deviation___Heading_________Deviation
000______1E__________180___________2W
030______2E__________210___________4W
060______3E__________240___________3W
090______2E__________270___________2W
120______1E__________300___________0
150______1W_________330___________2E
Compass Bearings taken = 336, 176, 247, 097 (+E -W) GOING UP 
True Bearings used to plot for a fix = 330, 170, 250,100
Ship&#8217;s
True Bearing # 1 Bearing #2
Course	
T	045 330	__________170	T
V	9W 9W __________ 9W V
M	054 339____________119	M
D	3E 3E ____________ 3E D
C	051 336	___________176 C

II	146 250___________100 T
V	4E 4E____________4E V
M	142 246___________096	M
D	1 W 1 W___________1 W D
C	143 247___________097	C
Deviation of &#8220;3 E&#8221; (I) and &#8220;1 W&#8221; (II) were taken from the Deviation Table of the Ship&#8217;s Magnetic Heading and applied as deviation for Bearings #1 and Bearings #2.


----------



## Fishers of Men

A few things will repeat themselves from previous posts, but thats okay, I want to give a better view for clarification purposes on DR and make sure everyone understands it before moving on.
*Introduction 801 Dead Reckoning from Duttons Navigation and Piloting*
(DR) is one of the four main divisions of navigation. When the earliest mariners became sufficiently daring and skilled to venture beyond their known waters in which they could pilot their vessel, they developed dead reckoning as a means of keeping track of their position. The term is derived from deduced or ded. reckoning, the process by which a ships position was deduced or computed trigonometrically, in relation to a known point of departure. Although highly accurate modern charts permit solution by graphic methods, rather than by laborious mathematics, the term, in its present form, continues in use. While treated as a separate division of navigation in this text, dead reckoning is basic to all phases of navigation.
*DR defined 802*
*Dead reckoning is the process of determining a ships approximate position by applying to its last well-determined position a vector or a series of consecutive vectors representing the run that has since been made, using only the true courses steered, and the distance run as determined by log, engine revolutions, or calculations from speed measurements, without considering current.* By projecting these course and speed vectors ahead of the present position, the ships predicted DR position for any desired time can be determined.
Dead reckoning is normally *a process carried out as a vessel advances along its passage.* It can, however, be done in advance as the planned or projected plot of the movements of the vessel at a later time.
The key elements of dead reckoning may be summarized as follows:
*Only the true courses steered *are used to determine a DR position.
*The distance* used in determining a DR position is obtained by multiplying the ordered engine speed by the time involved in the run.
A DR plot *is always started from an established position*, that is, a fix or running fix. (See Article 804.)
*The effects of current are not considered in determining a DR position.*
*The importance of DR 803 *
*The importance of maintaining an accurate dead reckoning plot cannot be overemphasized.* A means of fixing the ships position is not always available, due to weather, *equipment failure,* etc. Under such conditions, a navigator *must rely on his dead reckoning for an indication of his position. *It is obvious that a DR position *must be used with extreme caution i*n the vicinity of shoal water or other dangers to navigation.
If a ship made good the exact course and speed ordered, and there was no wind or current, dead reckoning would at all times provide an accurate indication of position. However, since such conditions rarely exist, a DR position *is only an approximation of the true position*, and the need for maintaining a constant and accurate dead reckoning plot should be obvious. *A navigator must know his position*, or approximate position, to determine when to make turns, to predict the time of sighting lights or other aids to navigation, and to identify landmarks.
Dead reckoning is customarily done graphically on a chart or plotting sheet appropriate to the area in which the ship is steaming. Graphic solutions enable the navigator to visualize his ships position in relation to landmarks or to dangers to navigation.
*DR terms defined 804 *
A number of terms used in dead reckoning must be defined. Unfortunately, not all books on navigation use exactly the same terms and definitions. The terms used in this book are defined below.
*Heading (Hdg. or SH).* The horizontal direction in which a ship points or heads at any instant, expressed in angular units, clockwise from 0000 through 3600, from a reference direction (Figure 804). 








The heading of a ship is also called ships head. Heading is a constantly changing value as a ship oscillates or yaws across the course due to the effects of the sea and of steering error.
*Course (C).* As applied to marine navigation, the direction in which a vessel is to be steered, or is being steered; the direction of travel through the water. The course is measured from 000° clockwise from the reference direction to 3600. Course may be designated as true, magnetic, compass, or grid as determined by the reference direction.
*Course Line. *In marine navigation, the graphic representation of a ships course, normally used in the construction of a dead reckoning plot.
*Speed (S).* The ordered rate of travel of a ship through the water; normally expressed in knots. (In some areas, where distances are stated in statute miles, such as on the Great Lakes, speed units will be miles per hour.) It is used in conjunction with time to establish a distance run on each of the consecutive segments of a DR plot.
*Fix.* A position established at a specific time to a high degree of accuracy may be determined by any of a number of methods discussed in Chapter 11. A running fix is a position of lesser accuracy based in part on present information and in part on information transferred from a prior time. (We will do running fixes later)
*DR Position. *A position determined by plotting a vector or series of consecutive vectors using only the true course, and distance deter mined by speed through the water, without considering current.
*Estimated Position (EP).* The more probable position of a ship, determined from incomplete data or data of questionable accuracy. In practical usage it is often the DR position modified by the best additional information available.
*Dead Reckoning Plot.* 
Commonly called DR plot. In marine navigation it is the graphical representation on the nautical chart of the line or series of lines which are the vectors of the ordered true courses, and distance run on these courses at the ordered speeds, while proceeding from a fixed point. The DR plot originates at a fix or running fix; it is suitably labeled as to courses, speeds, and times of various dead reckoning positions, usually at hourly intervals or at times of change of course or speed. A DR plot properly represents courses and speeds that have been used; a similar plot may be made in advance for courses and speeds that are expected to be used.
Estimated Time of Departure (ETD). The estimate of the time of departure from a specified location in accordance with a scheduled move to a new location.
196 DUTTONS NAVIGATION AND PILOTING
*Estimated Time of Arrival (ETA).* The best estimate of the time of arrival at a specified location in accordance with a scheduled movement.
Course, speed, time, distance, and position will be stated to an order of precision suitable to the vessel concerned and prevailing conditions; see Appendix C.
A planned or intended path with respect to the earth rather than the water is labeled Track and Speed of Advance; see Chapter 12. (later)
*Labeling a DR plot 805 *
*It is of the utmost importance that all points and lines plotted on a chart be properly labeled.* The use of standardized methods will ensure that the plot will mean the same thing to others as it did to the navigator who made it; this is essential to the safety of the ship.
*The principal rules for labeling DR plots are:*
Immediately after drawing any line or plotting any point, it
should be labeled.
The label for any point on a line should not be close alongside the line; labels for fixes and running fixes should be written horizontally, labels for DR positions at an angle to the horizontal.
The labels indicating direction and speed along a course line should be written along that line.
The label for direction should be the letter C followed by three digits indicating the true course in degrees; this is placed above the course line. (Should course be stated with reference to another base direction, an appropriate letter is added following the digits, such as M for magnetic.)
The label indicating the rate of movement along the course line is the letter S followed by digits indicating the speed, normally in knots. This is placed below the course line, usually directly underneath the direction label.
If a DR plot is drawn as a planning action in advance of actual vessel movement, distances are known; speeds may or may not be known prior to departure. If it is desired to label a DR plot with distance, this is done with the letter D followed by the distance in nautical miles (statute miles in some areas), usually to the nearest tenth of a mile; this is placed below the course line. (Some navigators will label a destination, usually in pilot waters, with its ETA and then intermediate points, marked by a heavy dot, with the ETA there plus the distance measured back from the final destination along the intended track.)
All labels should be printed clearly and neatly.
*The symbol for a fix* is a small circle surrounding a small dot; the time is written horizontally close nearby. (If the position is at the intersection of two lines, the dot may be omitted) The symbol for a running fix is the same as for a fix but the letters R FIX are added following the time.
*197	DEAD RECKONING*
*The symbol for a DR position is a small semicircle around a small dot;* this will be a half-circle on a straight segment of a course line; it will be more or less than a half circle when plotted at a change in direction. The time is written nearby at an angle to the horizontal.
*The dot in a fix, running fix, or DR position symbol is used to emphasize the point of the position;* it should be small and neat. Course lines, properly labeled, are shown in Figure 805.

*Times of DR *
In addition to the rules for the symbols and labels, there are also *six position standard rules which will guide a navigator as to when DR positions and course lines are required to be plotted:*
A DR position shall be plotted every hour on the hour.
A DR position shall be plotted at the time of every course change.
A DR position shall be plotted at the time of every speed change.
A DR position shall be plotted at the time of obtaining a fix or a running fix.
A DR position shall be plotted at the time of obtaining a single line of position.

A new course line shall be plotted from each fix or running fix as soon as the fix or running fix has been determined and plotted on the chart.

These rules of dead reckoning are considered adequate to meet the needs and requirements of navigation in the open waters of the sea. 
(Or the Great Lakes) 
There are occasions, however, when a more frequent plot of the ships dead reckoning position is essential to safe navigation, as when in the confined waters of channels, bays, straits and harbors. Knowledge of when to plot frequent fixes and even more frequent dead reckoning positions when in such waters will come with experience and judgment. This subject will be discussed more fully in Chapter 15.








198	DUTTONS NAVIGATION AND PILOTING
*Example of a DR plot 806* 
The following example outlines a typical dead reckoning problem: see Figure 806.









*A partial extract from a ships deck log reads as follows:*
1045. With Tide Rip Light bearing 315°, distant 6 miles, took departure for operating area V-22 on course 090°, speed 15 knots. 1120-Changed speed to 10 knots to blow tubes. 1130-Changed course to 145° and in creased speed to 20 knots. 1145-Changed course to 075°. 1210-Made radar contact on Buoy 1A bearing 010°, distant 8 miles, 1215-Changed course to 090° and changed speed to 18 knots to arrive at the rendezvous point at 1230 .
It is well to review at this point the applicability of the rules for dead reckoning as they pertain to this example. 
Commencing at the initial known position, the 1045 fix, the navigator plotted the course line in a direction of 0900 corresponding to the ordered course. The rate of travel, speed 15 knots, for an elasped time of 15 minutes and then 20 minutes enabled the navigator to make a scaled plot of the 1100 DR and 1120 DR positions respectively on his chart. Labeling the fix, the 1100 DR, the 1120 DR, and the course line itself completes the graphic description of the ships travel to 1120. At 1120, only the speed was changed. At 1130, both the course and speed were changed, while at 1145, only the course was changed. Each of these occurrences requires a separate DR position on the plot, while segments of the course lines are labeled to indicate what specific change of the course and speed occurred at that time. The 1200 DR was plotted on the whole hour as prescribed. At 1210, since the navigator fixed his position by radar, he must then plot both the 1210 DR on the former course line and the 1210 radar fix from which he commences a new course line. The navigator plots the ship from the fix on a course of 075° at a speed of 20 knots to 1215, at which time the course is changed to 090° and the speed is reduced to 18 knots in order to arrive at the operating area at 1230 as scheduled. The DR plot reflects the course and speed change and includes the 1230 DR as shown.








*199 DEAD RECKONING*
*Planned track 807 *
In actual practice, a preplanned track line is often plotted on a tentative basis before a ship ever gets underway. Called *navigational planning,* it introduces a fundamental principle of safe navigation. Every passage, every departure from and entry into port must be planned in advance, based on all information available to the navigator. The material studied in the course of this planning includes the charts of the areas to be traversed, the *navigational aids expected to be sighted,* the availability of electronic coverage, estimates of currents and weather to be encountered, the contour of the bottom, and other factors that will be discussed later in this book. The *preplanning phase* also includes the construction of danger bearings, ranges, etc. The following description of a short voyage will serve to illustrate many of the principles and concepts enumerated so far in this chapter.
Referring to Figure 807a assume that a ship is located at point A, and receives orders to depart at 0800 for point B, 90 miles distant, arriving at 1300.
Immediately upon receipt of this information, the navigator located points A and B on the appropriate small-scale chart of the area. By measuring the direction of B from A, the course of 070° is determined and noted on the DR plot as C 070. Dividing the rhumbline distance between A and B by five hours, SOA is computed to be 18 knots and labeled accordingly. Next, starting at the known position, or fix, at 0800, the navigator stepped off and marked the successive hourly positions which the ship is expected to occupy. The plot is now a complete and graphic picture. The plan is complete and, barring any unforeseen circumstances, represents the track that the ship will follow from the point of departure to her destination. Note that in this case the vessel was able to order the planned course and speed and arrive at the destination as planned; this very seldom happens in actual practice. The technique of handling deviations from the plan is the subject of the next article.
















200 DUTTONS NAVIGATION AND PILOTING
*Departures from plan 808 *
The ship gets underway as scheduled and sets course 070° true and speed 18 knots to arrive at B at 1300. If the calculations are correct and there is no current or change of course to avoid shipping, the ship should arrive at B as planned. The navigators work now consists of trying to establish his actual position from time to time, in order to be sure that the ship is following the intended track, or, if it is not following it, to recommend changes in course or speed, or both, which will bring the ship safely back to the intended track or to any selected point on it.
The navigator had poor weather and was unable to establish his position until about noon at which time he obtained a 1200 fix When the fix was plotted, he found that the ship was actually about 10 miles south and a bit east of his 1200 DR position see Figure 808 He further noted that if his ship maintained the same course on from the 1200 fix as it had from point A, she would be in danger of grounding on the indicated shoal.
Since the ship will not reach its destination on a course of 070° and a speed of 18 knots, the navigator must determine a new course and speed to arrive at point B by 1300, based upon the relationship between point B and the latest fix at 1200.
Since time was required to record the fix, evaluate it and decide upon a new course and speed, this change cannot be effected from the 1200 fix but rather from a DR position some time later Making a rough estimate of how long it will take him to determine a new course and speed, and get approval, the navigator plots a 1215 DR position based on the old, and still maintained, course and speed. 
From here he calculates a new course and a new speed (or new ETA if the ship is not capable of the greater speed needed to reach point B by 1300). It is very important to rememberthe course line will continue in the direction and at the speed originally ordered during the time required to obtain and plot the fix and decide upon a new course of action. Upon the advice of the navigator in this instance, the captain ordered a course of 028° and a speed of 24 knots at 1215 to direct the ship to arrive at point B at 1300.
Although *it is apparent that a current existed, it is not considered in this example. *The technique and procedures of computing and allowing for current are explained later in Chapter 12; they would have been used by the navigator in the computation of the new course and speed through the water.










The navigator believed that the ship was following the intended track until he obtained and plotted his 1200 fix. This illustrates the fundamental weakness of relying solely on dead reckoning, for dead reckoning is dependent on the assumption that the ship makes good over the ground the same direction that it is traveling through the water, and that the ship makes good over the ground the same speed that it is traveling through the water. Therefore, the *dead reckoning position should not be relied upon* if it is possible to obtain information to determine the position by other means. The many volumes of records on maritime disasters are filled with reports of instances of vessels having been put aground and lost because of a navigators adherence to a course which was laid in safe waters, while the actual movement was an unknown path leading to danger.
*Plotting Techniques 809 *
As stated above, neatness and accuracy in plotting are essential techniques for safe navigation. Skill will come with experience and practice, but a few hints and suggestions may be of assistance toward both accuracy and speed in plotting:
202	DUTTONS NAVIGATION AND PILOTING

A drafting machine should be used whenever available to determine the direction of a line, as it is both more rapid and accurate than other methods. When a drafting machine is not available, a course plotter (or protractor or parallel rulers) is used. Various types are shown in Chapter 7.
Tape the chart to the table or desk used. This will maintain proper orientation of the chart. Tape is preferable to thumbtacks for this purpose.
If the chart is too large to fit on the desk used, determine the extent of the chart that must be used, then fold under the portions of the chart that will not be required to be exposed. Be sure to leave one latitude scale and one longitude scale available for measurement.
*Use a sharp No. 2 pencil. A harder pencil will not erase well, and a softer pencil will smear.*
Draw lines heavy enough to be seen readily, but light enough so that they do not indent the chart paper.
*Avoid drawing unnecessary lines, and erase any lines used only for the purpose of measurement.* Do not extend lines excessively beyond the point at which their direction is to be changed.
Hold the pencil against the straight edge in a vertical position throughout the entire length of a line when drawing it.
Measure all directions and distances carefully. *Accuracy is the mark of good navigation. *
(If you are off just a little bit, later on down the coarse you will be way out of dodge, just like a 4' level being a little off in 4' but 50' down the line is a mess!)
*On Mercator charts, measure distance on the latitude scale* using the portion of the scale which is opposite the line that is being measured. Be neat and exact in plotting work. Use standard symbols and labels and print neatly.
Learn to use dividers with one hand and with either hand if possible.
Lay down a new DR track from each new fix or running fix. Plot a DR position at every change of course, at every change of speed, at the time of obtaining a fix, a running fix, or a single line of position, and on the whole hour.
*Time, speed, and distance calculations 810 *
The navigator may find it convenient to use a nautical slide rule and distance (Figure 724) for the solution of time, speed, and distance problems. Small hand-held electronic calculators (Appendix F) are also useful for the easy, quick, and very accurate solution of these problems. Alternatively, he may use precomputed tables, such as those in Bow- ditch, for such solutions. He must, however, always be able to solve these problems quickly and accurately without the use of any equipment beyond pencil and paper.
Regardless of the tools used, however, it must always be remembered in adding or subtracting values of time (in hours), there are 60 minutes in an hour, and 60 seconds in each minute; dont forget and work in decimal terms of 100 units. (you have to convert, a calculator understands 100 min in an hour not 60, so figure it all in minutes and divide by 60) to convert back to hours.
203 DEAD RECKONING
*Time, distance, and speed calculations*finding the third quantity if the other two are knowncan also be worked graphically using the logarithmic scale printed on larger-scale NOS and DMAHC charts, on some plotting sheets, and as the top line of the nomogram printed near the bottom of Maneuvering Board sheets, DMAHC Pub. No. 5090 and 5091; see Figure 810. The scale, together with a pair of dividers, is used as a slide rule. Let the right leg of a pair of dividers represent time in minutes and the left leg, distance. *Consider speed as distance in 60 minutes.*
The Maneuvering Board sheets also have a three-scale nomogram which can be used as described in Article 1404.
Thus, to obtain time, place the left leg of the dividers on the speed and the right leg on 60. Without changing the spread of the dividers, place the left leg on the required distance and read off the time at the right leg. If distance in a given time is desired, place the right leg on the given time and read off the distance at the left leg. If speed is required, set the left leg of the dividers at distance and the right leg at time and then, without changing the spread, place the right leg on 60 and read the speed at the left leg.
If the problem runs off the scale, solution can be made by using a fraction of the speed, or distance (only one), and multiplying the answer by the inverse of the same fraction.
*If in doubt as to the accuracy of a solution, check it mentally or by simple arithmetic using the formula D = S x T, where D is distance in miles, S is speed in knots, and T, is time in hours.* (you saw this somewhere before, right?)
*A useful rule to use in plotting in confined waters *where frequent fixes and DR positions are required is the so-called *three-minute rule,* applied as follows: the travel of a ship in yards in three minutes is equal to the speed of the ship in knots multiplied by 100. (This uses the assumption that one nautical mile is equal to 2000 yards; not exact, but close enough for practical use.) Where a six-minute DR would be more appropriate than a three-minute plot, the travel of a ship in miles in six minutes is equal to the speed of the vessel divided by 10, a shift of the decimal point one place to the left.
*Example 1:* A navigator desires to plot a three-minute DR from his last fix in Brewerton Channel. The ship is making a speed of 12 knots. To compute the travel of the ship in yards in three minutes, he multiplies the speed in knots, 12, by the factor 100 and determines the DR advance to be 1200 yards.
Answer: Distance 1200 yards.









*Example 2:* A navigator desires to plot a six-minute DR from his last fix in Chesapeake Bay. The ship is making a speed of 15 knots. To compute the travel of the ship in miles, he divides the speed in knots, 15, by the factor 10 and determines the DR advance to be 1.5 miles.
Answer: Distance 1.5 miles.
*Summary 811 *
This chapter has presented the basic information needed to understand the elements of the dead reckoning process. The mechanics of dead reckoning, the standard method of labeling, and when to plot DR positions have been discussed. Graphically portraying the travel of a vessel will come with practice.
*The need for maintaining an accurate and readily understandable dead reckoning plot cannot be overemphasized.* It is axiomatic that the navigator who demonstrates neatness and accuracy in plotting can be expected to demonstrate the same qualities in the other phases of navigation. *It is the lack of these qualities which is frequently found to be a basic cause of groundings.*


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## Fishers of Men

Lets see how much participation I have here, I am curious!
Answer these 5 questions and send them to me e-mail.


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## Fishers of Men

Here is a good example of why you need to decipher bouys. Daytime or night.
This is my stomping grounds in Stuart Fla. If you study this chart (best one I could come up with for now) you will see that as you come in the inlet there are many bouys/lights, obstructions and such. This is the most dangerous inlet in Fla. It is a narrow channel that is like a big funnel, the heave of the sea coming in, and an out going tide creates some enormous ground swells that may shoot up 15' or more like a pyramid and then just as fast, disappear from underneath you. 









The channel is a "dog leg" which you cant see here but after you get in, you must hold the N side, proceed to the R "10" then come immediately south towards the fl G 4 sec, around a sand bar and submerged pilings marking it; to and then head west keeping the R "12" and R "14" well to your right ( you see the depth?) basically right towards the R "16" on your right and R"17" to the port when returning home. Remember the types of bouys? After that it crosses the ICW where there is a bunch of bouys and sandbar shoals. As you approach Rocky point the are plenty of dangers to be aware of. The channel narrows down, sand bars, rocky areas. Now you can go N or S in the ICW or go up the St Lucie River to my place. As we pass nun "4" and the tricky G "5" we proceed to Another tricky spot at nun 6 "A". Here you have a choice to go to the bait shop/beer in Manitee pocket towards port Salerno between R "2" and G "1" and hope you are familiar with the area or you will run aground. Or we can keep going to my house Proceeding to R "10" to 12, 12a, and notice your depths right beside the channel! Then directly to 13a, to the Fl green 4 sec "15" and see the line of travel towards Fl green 4 sec "17"? Doesn't sound right? well you still keep those 2 greens to the port but it's wise in this circumstance to cheat your half of the channel especially depending on the wind and current at the time. The chart is about a mile short for me to take you to my place. Now if you study the areas, you will see all kinds of navigational aids, but how many likely GOOD fishing spots do you see? We have been talking about how things look different at night, you ought to see this place coming in at nite! I wouldn't advise going fast. I was raised there and come in at full plane all they way, as other locals do. Tourist see this and try to do the same or cut "corners" over bars and such and guess what?! Notice all the green areas that are sometimes submerged?


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## Fishers of Men

Okay,, I found a little more chart up the st lucie river. 
I think that last example was a good one showing the importance of charts, so I'll take ya to my place now.










We left off at the Fl G 4sec "18" not shown on this chart but its right across from hell gate. Notice the depth as you round the bend (3' in port and 9' starboard) and the "SO" meaning sand and oysters beds In Hooker Cove as you head towards what we call "19" pole (thats a good fishin spot) Fl G 4 second 16' tall 4 mile visability "19". from there we head to the center lights on the bridge (not shown) Aome one without local knowledge would play it save and go G "1" to G "21" then bear towards Fl R 4sec "22".
I cut the corner from G '1" to G "3" and then haul a$$ towards Rio where you see the sign and pilings, I shoot beside the sign to where you see "pipe" at full plane across the sand bar with only props touching the water, get off it all at once while raising motors timely and coast into the dock (remember there is a serious tidal flow here) with no room for mistake. Yes there has been a few, like someone not getting a hold of the dock, misjudging the current, misjudging the tide, some fool trying to step off the boat onto the dock before it is moored an falling in. Sometimes beer came into play. All the neat fun things. If you follow the river futher it will take you to the South fork where they made James Bond flicks...the North fork goes to lake Okeechobee.
Of anyone is interested in more of this area or like a run to the Bahamas or such, let me know, these ARE my waters. Otherwise I will try to concentrate on Erie. But these things we are covering apply everywhere. If I had a PC planner, I could take Erie stuff off of my chartplotter and it would make it easier. I just gotta wing it I guess. I'll look at Denieds disc and see what charts are there. 
I see a lot of people use this... do you know where it comes from?

Red sky at night/sailors delight, well guess what?

"He answered and said unto them, When it is evening ye say, _it will_ be fair weather for the the sky is red." Matt 16:2

What about: Red sky in the morning, sailors take warning?
"And in the morning. _It will be_ foul weather to day: for the sky is red and lowering. O ye hypocrites, ye can discern the face of the sky; but can ye not discern the signs of the times?" Matt 16:3


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## Fishers of Men

Hey, Ready for some Fire Fighting for a vessel?
Any firefighters out there wanna pitch in, go ahead.










Fire can be one of the most devastating and dramatic events that can occur on a vessel. Ignorance can convert a boat into a floating bomb. This can also happen so easily around a dock.. All fire fighting is based on the Fire Triangle, which is composed of: Heat, Oxygen and Fuel:
Oxygen 
&#916;
Heat	Fuel
Together these 3 agents form the combustion process. This is a chemical procedure in which all 3 agents must be present to have a fire. Remove any one of these and you have eliminated the fire. This is where fire fighting comes in, to remove any one or more of these aids causing the fire.
1. Remove Oxygen &#8212; Carbon Dioxide
2. Remove Heat &#8212; Water
3. Remove Fuel &#8212; Turn off Fuel Source
Classes of Fire;
Class A: Leaves an ash. Includes Wood, paper rags, twigs, dry foliage. Water is the best extinguisher, it removes heat and prevents re ignition.
Class B: Boiling liquids &#8212; Flammable liquids such as grease, oil, hydraulic fluids and of course gasoline.
Class C: f or electrical fires.
Do NOT use water based extinguishing methods. The first thing to do is to turn off the power.
Class D: Flammable metal is highly irregular, but certain metals such as magnesium will burn. Fighting such a fire will involve smothering it with sand, salts and graphite powder.
Heat travels in 3 ways;
1. Conduction - Point to point travel
2. Convection - Air travel
3. Radiation
Note; Recognize what class of fire you&#8217;re dealing with before using extinguishers.
Conditions, circumstances, settings environment, hazards and safety must be understood to properly fight a fire without continued jeopardy to people, vessels and property:
Flammable - means BURN. Non flammable is the opposite and won&#8217;t burn. Ignition temperature &#8212; The lowest temperature to cause combustion of any substance, independent of any other source of outside detonation or explosion. Spontaneous Combustion - Products of combustion are gaseous in nature and the chemical action within these substances can cause an ignition. Piled &#8212;up oil soaked rags is the classical example of spontaneous combustion.
Flash Point &#8212; The temperature at which a liquid gives off flammable vapors. Good housekeeping is essential both on a vessel and around a vessel to prevent circumstances conducive to flammable conditions.
Vessel Fire Fighting Rules;
1. In case of fire, sound the fire alarm first to make all aware of the fire.
2. Turn off all supply sources such as electrical current, pumps and valves.
3. Always leave an exit not only for yourself but passengers as well.
4. Have specific rules for the entire crew for fueling and galley procedures.
5. Before the fire starts, have all aboard aware of location of fire extinguishers and fire fighting equipment.
6. Conduct drills.
7. Do not assume that a fire is completely out. Post a guard against re-ignition.
8. If fire on board, maneuver the vessel, depending on the wind to keep fire from spreading.
a. Fire on bow &#8212; Turn stern into the wind.
b. Fire on stern &#8212; Turn bow into the wind.
9. If approaching a vessel on fire, approach from up-wind position
10. Seek as much assistance as possible from all outside sources. Lives are at stake.
Fire Extinguishers:
Fire extinguishers remove one or more of the agents of a fire.
Soda Acid Water cools and absorbs the heat.:
It is least likely to allow a fire to reignite and is not recommended for oil
fires.
Portable units are turned upside down for activation.
It must be recharged annually and after every use.
It must be aimed at the base of the fire.
Available at all times.
Carbon Dioxide &#8212; Removes the oxygen.
It is preferred because it causes minimum cargo damage.
Effective only when used promptly.
It is most likely to allow a fire to re-ignite.
In order to activate the unit, pull the pin and squeeze the grip.
After discharge or partial discharge, mark empty. Recharge as soon as
practical.
Must be recharged annually.
Must be recharged if 10 &#37; of the charge is lost.
Must be weighed and compared to the weight on the stamp on the
extinguisher.
Do not hold the horn by bare hands since it may cause frostbite.
Does not put out a fire by cooling.
Tare weight is the weight of the empty bottle.
Only complete containment will result in success.
Do not breathe carbon dioxide since it can cause respiratory failure.
Dry Chemical &#8212; Attacks the fuel and oxygen.
It is preferred because the heat shield it provides protects against reflash.
Has a greater range during application.
It has multipurpose extinguishing application.
Not effective on deep seated fires.
It is highly corrosive.
Has been known to flashback when used on a surface of a fire
Recharged annually and after every use.
Activated by pulling a pin and squeezing the grip.
The cartridge is weighed and replaced when necessary.
Aimed downwind at the base of the fire.
Foam &#8212; Sets up a vapor barrier over flammable liquids.
Portable extinguishers are turned upside down to activate.
It is most effective on non-flowing liquids.
It was designed for use on class A and B fires.
Foam units are discharged and refilled at each inspection.
Foam is banked off of a vertical surface.
It absorbs heat from materials that could cause reignition.
Halon &#8212; Extinguishes a fire by disturbing the chain reaction.
Similar to carbon dioxide, however it is toxic.
It must be serviced annually and weighed.
Cannot be used on combustible metals and hydrides.
Activated by pulling the pin and squeezing the grip.
Direct at the source of electrical fires.


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## Fishers of Men

Well, lets see if you remember what you just read last post.
Write your answers down and then go back to the last post for the answers.

FIRE FIGHTING quiz
1) Burning rags are what type. of fire?
A) A
B) B
C) C
D) D

2) Dry chemical extinguisher is good for what type of fire?
A) A
B) B
C) D
D) All

3) For a fire to burn you must have:
A) Fuel
B) Oxygen
C) Heat
D) All the above

4) The horn on a carbon dioxide is dangerous because:
A) It gets very hot
B) It gets very cold
C) It sticks to your hand
D) Its hard to hold

5) How do you apply foam to a B type fire?
A) Apply it directly to the fire
B) Direct it to the adjacent wall
C) Wait for it to cool down
D) Apply it around the edge of the fire

6) How lo you use mist to put out a fire?
A) Drown the fire
B) Clean up after the fire goes out
C) Cool the air around the fire
D) Displace the oxygen

7) Which extinguisher must be professionally recharged?
A) Carbon Dioxide	C) Foam
B) Dry chemical	D) Soda acid

8) The danger of a carbon dioxide extinguisher is:
A) Danger to machinery
B) Displacing the oxygen
C) Being electrocuted
D) Cooling the fire to fast

9) How do you tell when a carbon dioxide extinguisher needs refilling?
A) Look at the gauge on it
B) Check-the date
C) Weigh it
D) Shake it

10) A soda acid extinguisher puts out0 fire by:
A) Smothering it	C) Cooling it down
B) Cutting off the oxygen D) Cutting off the fuel

11) The best way to put out a fire so it doesnt start again is:
A) Cut off the oxygen	C) Let it burn out
B) Cool it down D) Smother it

12) The first thing to do for a C type fire:
A)	Cut off the oxygen	C) Cut off the power
B)	Soak it with water	D) Remove the fuel

13) The danger in a foam extinguisher is:
A) Cutting off the oxygen	C) Conducting electricity
B) Harming machinery	D) Harmful to cargo
14) The best all round fire extinguisher for a vessel is:
A) Foam C) Halon
B) Carbon dioxide	D) Dry Chemical


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## Fishers of Men

How are ya doin with the navigation?
Try this:
AIDS TO NAVIGATION Quiz:
1) The abbreviation on a chart for a fixed light is?
A) FL 
B) Fl 
C) F
D) FX

2) The height of a light on a chart is usually given from:
A) Height of your eye
B) Mean high water 
C) Fifteen feet
D) Mean low water

3) Junctions and obstructions (preferred channel markers) are marked by:
A) Black and red horizontal bands
B) Black can buoys with a bell or a whistle
C) Green and red horizontal bands
D) Black and white vertically striped buoys

4) In the U.S. aids to navigation system, red and green horizontally banded buoys mark:
A) Channels for shallow draft vessels
B) General anchorage area
&#163 Fishing grounds
D) Junctions or bifurcations

5) Navigational marks used for warning or regulatory purpose are:
A) Solid yellow
B) Orange and white horizontally striped
C) Red and white only
D) Green and red horizontally striped

6) Mid-channel buoys (safe water) are marked with:
A) Spherical Buoy	
B) A white light
C) An octagon day shape
D) All of the above

7) Buoys which mark dredged areas are painted:
A) black	
B) Green	
C) Yellow
D) Red

8) Day beacons marking a channel would be:
A) Numbered in the same sequence as the respective buoys
B) The same shape as the respective buoys
C) Day beacons do not mark channels
D) Day beacons are only used to mark a bend

9) Which of the following is the characteristic of an isophase light?
A) Off and flashes on	
B) On and flashes on	
C) Flashes every second
D) Is on 6 seconds and off for 6 seconds

10) A triangle on a buoy means:
A) Danger area
B) You are on the intracoastal waterway
C) It&#8217;s near an anchorage
D) Tow boats are operating in the area

11) A flashing light is:
A) Off and flashes on
B) Lighted and blinks off
C) Flashes twice and then once
D) Marks a junction or obstruction

12) A quick flashing light may mark:
A) Bend in the channel
B) Widening or narrowing of the channel
C) A place to attract attention
D) All of the above

13) What is true of buoys marking a channel returning from the sea?
A) Red nun with red light may mark the starboard side
B) Green can with green light may mark the port
C) Red and green banded may mark an obstruction
D) All of the above

14) A Flashing Blue light on the water is a K-mart special going, on crank baits True or False.

Maybe I'll give ya these answers, but you should look 'em up.


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## Fishers of Men

We are well over due for this rule, so here goes:
Rule 36
Signals to Attract Attention
The language of rule 36 may be difficult to interpret since it states that IF necessary to attract attention of another vessel(s) you MAY make light or sound signals that cannot be mistaken for any other signals authorized elsewhere in these Rules. What kind of other signals ? This is unclear: build a fire and send smoke signals, scream, sing and dance? Not so, but the attention here again is good old common sense and covers the fact that the mariner is trying to communicate ( other than radio ) with another vessel(s) by some means, not to be confused with identity lights of vessels maneuvering signals or any of those discussed within this book or the Rules which are so specific as to their meaning and intention.
Directing the beam of a searchlight is an excellent example of attracting attention, particularly when danger or distress are involved. The rule mentions that the searchlight be used so as not to embarrass other vessels. Lets keep in mind that, not only with the searchlight but any other device or means to attract attention the Captain does not only refrain from embarrassing other vessels but also himself and his own vessel.
Rule 36 concludes that the use of high intensity intermittent or revolving lights such as strobe lights SHALL be avoided. This becomes obvious because they can and usually are very annoying.
Rule 37
Distress Signals
Rule 37 and Annex IV lists in detail the distress signals designated by the Coast Guard. Im sure that some of these could cause controversial discussions, such as flames on the deck and firing a gun (see next pic page for 72 COLREGS). There is one additional signal used in Inland waters only, which is a high intensity white light flashing at regular intervals from 50 to 70 times per minute. The major point here is: when necessary, give an obvious signal to let others know you are in distress, and to come help.
DISTRESS SIGNALS	COME HELP
DANGER SIGNAL	5 short blasts	STAY AWAY
The part that confuses me is flames on a vessel. I guess I wouldnt want to do it in a 5 gal bucket or plastic garbage can, so I have a 55 gal steel drum that I always carry loaded with split green cherry wood and a gal of used motor oil to start it and it is bolted down on the bow. I figure it kills 2 birds with 1 stone, cause everyone can see me coming! Or they might think its an old steamboat.


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## Fishers of Men

*We need to understand the bottom of the lake* to be successful with our fishing. 
Know where there is structure.

*In General:*
*Bathymetry* is the underwater equivalent to topography. The name comes from Greek &#946;&#945;&#952;&#965;&#962;, deep, and &#956;&#949;&#964;&#961;&#959;&#957;, measure. In other words, bathymetry is the study of underwater depth, of the third dimension of lake or ocean floors. A bathymetric map or chart usually shows floor relief or terrain as contour lines, and may additionally provide surface navigational information.
Originally, bathymetry referred to the measurement of ocean depth. Early techniques used pre-measured heavy rope or cable lowered over a ship's side. The greatest limitation of this technique is that it measures the depth only a single point at a time, and so is inefficient. It is also subject to movements of the ship and currents moving the line out of true and therefore is inaccurate.
The data used to make bathymetric maps today typically comes from an echo sounder (sonar) mounted beneath or over the side of a boat, "pinging" a beam of sound downward at the sea floor or from remote sensing LIDAR or LADAR systems. The amount of time it takes for the sound or light to travel through the water, bounce off the sea floor, and return to the sounder tells the equipment how far down the sea floor is. LIDAR/LADAR surveys are usually conducted by airborne systems.

Years ago, the occasional pings of a single-beam sounder might be averaged to make a map. Today, a multibeam echosounder may be used, featuring dozens of very narrow adjacent beams arranged in a fan-like swath of perhaps 90 to 180 degrees across. The tightly packed array of narrow individual beams provides very high angular resolution and accuracy. In general, the wide swath, which is depth dependent, allows a boat to map more sea floor in less time by making fewer passes. The beams update many times per second (typically 1-40 Hz depending on water depth), allowing faster boat speed while maintaining 100&#37; coverage of the sea floor. Attitude sensors correct for the boat's roll, pitch and yaw on the ocean surface, and a gyrocompass provides accurate heading information to correct for vessel yaw. The Global Positioning System specifies where the boat is. Sound velocity profiles (speed of sound in water) of the water column correct for refraction or "ray-bending" of the sound waves owing to non-uniform water column characteristics such as temperature, conductivity, and pressure. A computer system processes all the data, correcting for all of the above factors as well as for the angle of each individual beam. In the end, a map is semi-automatically generated from this massive trove of data. Satellites are also used to measure bathymetry. Satellite radar maps deep-sea topography by detecting the subtle variations in sea level caused by the gravitational pull of undersea mountains, ridges, and other masses. On average, sea level is higher over mountains and ridges than abyssal plains and trenches.
(The sea floor topography near the Puerto Rico Trench)

Most surveys of navigable waterways in the United States are performed or commissioned by the United States Army Corps of Engineers, for inland waterways, and the National Oceanic and Atmospheric Administration for oceans. Coastal bathymetry data is available from the National Geodetic Data Center. Bathymetry data is often referenced to tidal vertical datums of MSL or MLW.
Some occupations or careers related to bathymetry is the study of oceans and rocks and minerals on the ocean floor. Also the study of underwater earthquakes or volcanology can apply. People who work with different types of terrains may also study the ocean floor, since it is such a unique area of the earth. Submarines and ships study the depths of the oceans, using sonars, and so people who work on those ships work with that area of expertise, as well.
*Terrain, or relief*, is the third or vertical dimension of land surface. When relief is described underwater, the term bathymetry is used. Topography has recently become an additional synonym, though in many parts of the world it retains its original more general meaning of description of place.
*Terrain is used as a general term in physical geography, referring to the lie of the land. *This is usually expressed in terms of the elevation, slope, and orientation of terrain features. Terrain affects surface water flow and distribution. Over a large area, it can affect weather and climate patterns.

*Geology*:
Our contour lines shown on a good chart indicate the lake bottom where the glaciers cut paths/troughs. These areas all have current flows around them and therefore temperature changes, different types of bottom and structure which attract bait which attracts predators and fish migration routes. When you study a bathymetry &#8220;map&#8221; of the area, (I said map because it is land under the water) you can find areas that you propose to likely hold fish, hit these areas and when you catch, &#8220;mark&#8221; the spots and record the temps and date/time/weather conditions etc.. Then one year later, if the conditions are the same, you probably want to go back there because the fish will highly likely be at that same spot again. An advantage of a good chart plotter takes the guess work out. It shows the contours, helps you follow them, records info in memory and so on and shows known wrecks, pilings, and navigational aids. The initial investment makes up for saved time and money/gas for going out guessing and getting skunked.

*An Excellent reference around the island area to Lorain, is Dean Cliftons &#8220;Fishing aboard the Denied&#8221; http://www.cliftond.com/
I wont post his info on here without permission.*

Here is an view of what the bottom looks like in the Atlantic Trench. Lake Erie is &#8220;cut&#8221; in it&#8217;s own manner.










Here is a geology link with pics that explain a lot.
http://www.dnr.state.oh.us/Portals/13/pdf/coastalatlas/3geologyweb.pdf 

We will start with the bathymetry around the islands:










The islands and reefs bordering and lying within the western basin have bedrock cores which are erosional remnants of the more resistant rock strata. Highest relief within western Lake Erie, about 15-20 meters, occurs on, and in waters adjacent to, the Bass Islands. The islands and reefs occur mainly in two north-south bands, the western band (Bass Islands, Catawba Island, Middle and East Sister Islands) formed on erosional remnants of resistant upper Silurian dolomites of the Put-in-Bay and Raisin River Formations, and the eastern band (Marblehead, Kelleys Island, Pelee Island) formed on erosional remnants of resistant lower Devonian limestones of the Columbus Formation. The natural channels which occur in the straits between the Bass Islands and adjacent to these islands to the west are over deepened where strong currents have eroded/corroded through the limestone and dolomite bedrock. The deepest channel depth is the 19-meter Starve Island Deep located between the southern-most Bass Island and Marblehead Peninsula.










*PELEE-LORAIN RIDGE* 
The Pelee-Lorain Ridge extends southeastward from Pelee Island almost to the Ohio shore. Previously it was assumed that this low ridge was continuous between Point Pelee and its southern terminus near the Ohio shore. This new bathymetry shows clearly, however, that the Pelee-Lorain Ridge is not continuous with Point Pelee, but is instead continuous with Pelee Island, 20 kilometers to the southwest. This ridge has been interpreted as an end moraine probably associated with a re-advance of the retreating Wisconsin Ice Sheet, and probably correlating with the pro-glacial Lake Maumee II.

*POINT PELEE RIDGE *
Point Pelee Ridge includes Point Pelee and extends offshore south- southeast for a distance of about 10 kilometers, where it ends abruptly. This ridge has 6-8 m of total relief and extends up to depths of less than 5 meters. Previous interpretations have presented Point Pelee together with the Point Pelee Ridge as moraine associated with the Pelee-Lorain Ridge on which 3500 years before present-to-recent sand deposits have been concentrated. Since 3500 years before present, the sub aerial extent of Point Pelee has diminished as a consequence of continued rising water levels. 
Sand transport and deposition were apparently more prolific in the past 3500 years than at present. Thickness of the sand is highly variable up to a maximum thickness of 10 meters. Sources for the sand include in-place sand concentrated by winnowing of glacial till deposits, and sand from eroding till deposits which lie principally to the north along the Ontario shore in both directions, with sand having been transported by longshore sediment drift converging on Point Pelee. Apparently, sand sources and the transport mechanisms have adjusted to the changing water circulation and shoreline configurations concomitant with rising water levels. It is noted particularly that depth contours converge from north to south along the western shore of Point Pelee, suggesting that Point Pelee has recently evolved into a narrower spit projecting farther south.










*POINT PELEE FAN *
Extending to the east of the Point Pelee Ridge is the Point Pelee Fan, a fan-shaped delta-like body of sediments *which crests at 11-12 meters below present lake level.* This fan is recognizable down slope to a depth of 18 meters and extends as far south as the Pelee- Lorain Ridge. Because of its crestal depth of 11-12 meters, we believe that this fan may have been principally formed at the time when the lake level was at about 10-15 meters lower than at present, prior to deposition of the shallower 3500 years before present- to- present sands on the Point Pelee Ridge. If this fan is in fact a relict shoreline feature, it may have been formed by the Detroit River when the Port Huron outlet was first opened up and the newly formed Detroit River was eroding its channel and bringing a heavy load of sediment into Lake Erie. An alternate interpretation for formation of the Point Pelee Fan is that strong west-to-east currents have swept around the end of the Point Pelee Ridge and carried sediments eastward.

SANDUSKY BASIN 
West of the Pelee-Lorain Ridge, the shallow, 12-14 meter deep Sandusky Basin, slopes gently down from west to east, and has local relief of 1-2 meters. Topographically it resembles a fan and it may have been the site of a shallow lake and/or marsh, and/or delta during early and middle Lake Erie time. In terms of basin configuration and continuity of the bounding walls, the Sandusky Basin appears as an integral part of the Central Erie Basin, except for the interposition of the Pelee-Lorain Ridge. Formation of the Pelee-Lorain Ridge may therefore have been the event which separated the Sandusky Basin from the Central Erie Basin.










*LONG POINT SPIT* 
This is one of the most prominent topographic features in Lake Erie, extending about 35 kilometers east-southeastward from the Ontario shore out into the Eastern Erie Basin. The spit is a late Holocene-to-recent depositional feature constructed of sand eroded from the Ontario shore cliffs to the west and brought eastward and deposited by long shore drift. Steep slopes and 55 meters of relief, the highest lake floor relief in Lake Erie, separate the Spit from the floor of the Eastern Erie Basin, the direct physical manifestation of its recent depositional origin.

*PENNSYLVANIA CHANNEL *
A ridge extending westward along the north wall of the Pennsylvania Channel suggests a "natural levee" in which sediments eroded from the southern end of the Long Point-Erie Ridge are carried westward and deposited as over bank deposits. *This channel is the location of strong return flow from the Eastern Erie Basin to the Central Erie Basin,* which is set up during and following periods of strong frontal winds blowing from west to east longitudinally down the length of the lake surface. Such winds transport surface water eastward, raising lake levels in eastern Lake Erie and requiring a compensating westward flow at depth once equilibrium is reached, or following relaxation of the strong winds.

*CLEAR CREEK RIDGE *
A narrow ridge of 4-5 meters relief and a crestal depth ranging from 14-17 meters, the Clear Creek Ridge extends in a SSE direction from the Ontario shore to the Pennsylvania Channel near Erie, Pennsylvania. This ridge lies 10-30 km west of the Long Point-Erie Ridge, with the distance between the two ridges closing toward the southeast. Both ridges are convex to the west, with the Clear Creek Ridge following a broader arc and having greater linearity. Clear Creek Ridge was not known to exist until the advent of the bathymetry described here. Origin of the Ridge is not precisely determined, but our hypothesis is that it formed in early to middle Lake Erie time, when water level had risen sufficiently (probably about 18 meters below present lake level) to create a large shallow lake in the Central Erie Basin. Once wave energy was focused on the western shore of the Long Point-Erie Ridge, an offshore bar or barrier island formed.










*LONG POINT-ERIE RIDGE *
The Long Point- Erie Ridge is a broad (14-22 kilometers) arcuate ridge of 5-10 meters overall relief, capped by complex topography, extending upward to minimum depths of 10-15 meters, and extending across the lake floor from near the inshore end of the Long Point Spit, almost to the Presque Isle Spit at Erie, Pennsylvania. This feature has been interpreted as an end moraine formed during the last major re-advance of glacial ice into the Eastern Erie Basin. Overall shape of the Eastern Erie Basin, and the arcuate shape and topography of the Long Point-Erie Ridge, as seen in this new bathymetry, strengthens the interpretation that this feature is an end moraine. 

*PRESQUE ISLE SPIT* 
In morphology, the Presque Isle Spit has the form of a recurved spit or hook. It coincides with a zone of convergence of net longshore drift, the position of which is a consequence of predominant patterns of large-scale wind-driven lake water circulation set up by the overall shape of the Lake basin and predominant wind fields. The inferred main source of sediments moving via longshore drift is from the west. Sand deposits, which are potential sediment sources occur in the near shore zone off Conneaut, Ohio and between Cleveland and Fairport Ohio. Adjacent to the Presque Isle Spit to the west lies a shallow bank (7-10 meters depth) which is roughly 5 x 10 kilometers in a real extent. Atop this bank is an arc-shaped bar which resembles in size, shape, and orientation the main, recurved portion of the Presque Isle Spit. Its position suggests that there may have occurred an eastward shift in the locus of the zone of net longshore convergence which is now centered about Presque Isle Spit.










This north-facing escarpment is surrounded by irregular topography which has a relief of 1-5 meters and a dominant NE-SW lineation running at a diagonal to the escarpment. Possibly, the escarpment lies along the boundary separating gently southward dipping, more resistant upper Devonian deltaic sands and silts, or upper Devonian limestone beds, which are more resistant than the marine shales to the north. Alternately, the escarpment could have been formed along a preexisting fault, which had juxtaposed more resistant and less resistant strata. The escarpment is parallel to the inferred direction of flow of glacial ice advancing down the axis of the lake floor. Lack of large-scale irregularities along the edge of the escarpment reflects the likelihood that in the sub glacial regime of erosion, any northward projections of the resistant eroding strata were sheared off by the eroding power of the ice.

Now, this and other factors combined is what makes the 3 basins seem like 3 different lakes. You have the guys that only fish the western end and realize all the nice days to get out and guys that only fish the eastern basin that have very few "flat" days in a summer that have utmost respect for the lake especially after the prevailing westerly winds build because of the fetch we discussed and the bathymetry along with the currents. 

Oh ya, don't go buying bathymetry cd's, a lil research and you can get the same info free online.

So with this understanding of the lake, we will dissect it more next time in "currents".


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## Fishers of Men

*Current: The horizontal movement of water?*

*But the men marveled, saying, what manner if man is this, that even the winds and sea obey him! Matt 8:27*

I dont want anyone to get discouraged here, be patient, this is not as hard as you may think. Remember, ask questions any time. I would prefer a classroom setting so we could do this and plotting hands on but since we dont have that, just make do. There is plenty of time, and I know I am probably going too fast for some but thats ok, read thru, hear the terms and go back, when you come up to them again they will be more familiar. These effects are on Lake Erie as anywhere else. You will see abbreviations here used on your gps and lorans and this will explain what they are and used for.

*Current Sailing* (This is everyone, not sailboats)
Examples taken from 283 DUTTONS NAVIGATION AND PILOTING
Introduction 1201 
Several previous chapters have laid a foundation for the consideration here of current sailing which is the determination the effect of currents on the movement of a vessel with respect to the earth. It has been mentioned that a dead reckoning plot ignored the effect of current and made use only of ordered courses and speeds.
In many areas there are horizontal flows of water of sufficient magnitude as to cause the path of a vessel with respect to the earth to differ significantly from its path through the water; often these currents can be predicted.
Presented methods by which the ships position could be fixed, and the DR plot verified or the need for correction seen will come next and hopefully clarify some of this.
*This chapter carries the process one step further showing how the net effect of current can be determined from the difference between DR positions and actual fixes and how allowances can be made in advance for the anticipated effect of currents. This is current sailing.*
In actuality, the term used in this chapter should be stated as currentin quotation marksfor more is to be considered than the horizontal movement of the waters. In navigation, especially in current sailing which may cause a ship to depart from its intended course and DR are termed current. Among the factors included in the term are:
*Ocean current 
Tidal current
Wind current
Windage on the ship
Heavy seas
Inaccurate steering
Undetermined compass error
Inaccurate determination of speed
Error in engine calibration 
Error in log calibration
Excessively fouled bottom
Unusual conditions of trim*

From the foregoing, it can be seen that current, unfortunately has two meanings as commonly used in marine navigation. First it refers to the horizontal movement of water due to ocean currents, tidal currents, or wind currents. Second, in common usage it refers to the combined effect of all the factors listed above.
Thus the term current, as used in navigation, may or may not solely involve the motion of the water through which the ship passing; in most cases, however, if it exists, will have the greatest effect on the ships course.
*Current sailing defined*
Current sailing is the art of determining course and speed through the water, making due allowance for the effect of a predicted or estimated current, so that upon completion of travel, the intended track and the actual track will coincide.
Current sailing may also be interpreted to include the determination of an existing current. Primarily, however, current sailing is the application of the best available current information to the intended track to determine what course and speed to order. Conversely, similar techniques are used to determine the actual current which has acted upon the ship.
*Types of currents*
Three types of currents are of interest to the navigator:
*Ocean current *is a well-defined current, extending over a considerable oceanic area.
*Tidal current* is one resulting from tidal action. It will normally be of a reversing nature in harbors and estuaries, etc.; velocities are often enough to be significant in navigation. Along coasts, tidal cur rents are usually rotary in nature, with weak strengths, but these must still be taken into consideration in some navigational situations.
*Wind current* is one which affects a limited area and is created by the action of a strong wind blowing for twelve hours or more; it usually does not flow in the direction of the wind, as it tends to be deflected by Coriolis force. Details of this deflection have not been covered yet.
*Estimated current* is determined by evaluating all the known forces which will contribute to make up the sum total of current effects in a given area.
*Actual current* is determined by the displacement of the ship from the DR position to a fix. It is determined only when an accurate fix can be obtained; the direction and distance between the actual fix and the DR position for the time of the fix establish the actual current. 
*Estimated position* (EP) is the most probable position of a vessel, determined from all available data, when a fix or running fix is unobtainable; it includes the effect of the estimated current.
*Current triangle *is a graphic vector diagram, in which one side represents the set and drift of the current, one side represents the ships course and speed, and the third side represents the actual track. If any two sides are known, the third can be determined by measurement or calculation.
*The terms heading, course, and speed were employed in the discussion of dead reckoning.*
Some additional terms to be introduced here include:
*Track (TR)* The intended (anticipated, desired) horizontal direction of travel with respect to the earth, taking into consideration known or predicted offsetting effects such as current, wind, and seas.
*Speed of Advance (SOA):* The intended (anticipated, desired) speed with respect to the earth, taking into consideration the effect of known or predicted current. SOA is also used to designate the average speed that must be made good to arrive at a destination at a specified time.
*Set: *The direction toward which the current is flowing; if the broad definition of current is used, the resultant direction of all offsetting influences. Note carefully that the description of the set of a current is directly opposite from the naming of a winda westerly current sets toward the west, a westerly wind blows from the west.
*Drift:* The speed of a current (or the speed of the resultant of all offsetting influences), usually stated in knots. Some publications, how ever, notably pilot charts and atlases, express drift in terms of nautical miles per day.
*Course Made Good (CMG): *The resultant direction from a given point of departure to a subsequent position; the direction of the net movement from one point to another, disregarding any intermediate course changes en route. This will differ from the Track if the correct allowance for current was not made.
*Speed Made Good (SMG):* The net speed based on distance and time of passage directly from one point to another, disregarding any intermediate speed change; speed along the Course Made Good.
*Course Over the Ground (COG): *The actual path of the vessel with respect to the earth; this may differ from CMG if there are intermediate course changes, steering inaccuracies, varying offsetting influences, etc. (Not used in current sailing triangles CMG is used.)
*Speed Over the Ground (SOG):* The actual ships speed with respect to the earth along the COG. (Not used in current sailing; SMG is used.)

*The two current Triangles*
*It should be carefully noted* that there are two triangles: before and after movement--anticipated and actual conditions. Track and speed of Advance are used with the before triangle. Course Made Good and Speed Made Good are the corresponding components of the after triangle. Set and Drift are used with both triangles, al though, of course, in one case it is estimated current and in the other, actual current. Course and Speed can be components of either the anticipated or the actual triangle.

*Practical current sailing*
Point D (Figure 1204) bears 090° distant 20 miles from Point A.
A current with an estimated set of 180 degrees, and drift of 4 knots flows
between the two points. If a ship were ordered to steam from A to D in
a total elasped time of two hours, the navigator would be faced with a 










typical problem in current sailing. It is obvious that the direction of the TR is 090°, and the SOA is 10.0 knots. It is equally obvious that if course 090°, and speed 10.0 knots were ordered, the ship two hours later would be some eight miles south of D. To allow for the estimated current on this two-hour trip, the ship should be steered on a course somewhat into the current in the direction of Point C some eight miles to the north of D, and at a speed slightly greater than 10 knots. Provided the estimate of the current was correct, the ship would arrive at D in two hours, the current effects having exactly countered the course and speed offset from the intended track.
Figure 1204 illustrates what has occurred. The ship beaded for Point C, on course 070°, but actually made good 090°, constantly crabbing into the current, as shown, At the end of the first hour she reached D, rather than C, and at the end of the second hour she reached Point D rather than C. The track, AD, is the resultant of the vector sum of the velocity of the ship with respect to the water (AC) and the velocity of the current with respect to the earth, (CD), both of which were in action for the same length of time.
Point C represents the ships DR position at the end of two hours,
and Point D represents the estimated position, EP, which is the most
probable position, short of a fix or running fix.
*The EP plot *
It has been pointed out that in the absence of a fix or running fix, the navigator, on the basis of available information, may often estimate the ships position to a greater accuracy that indicated by the DR. For instance, if a navigator has good reason to believe that a current of well-determined set and drift exists, he can find the EP for a given time by plotting the predicted movement of the ship away from the DR position for a given time, due to the effect of the current. To do this, he plots the set and measures off along this line the drift multiplied by the number of hours it has been or will be acting. An alternate method, used chiefly when the ship steams on a single course at a constant speed, is to solve graphically a current triangle.
Example: (Figure 1205) The 0500 fix of a ship is as shown. The ship is on course 300°, speed 6 knots. A current has been estimated with a
set of 250°, drift 1.0 knot.










Required: Plot and label the hourly DR positions and hourly EPs from 0500 to 0800.
Solution: Plot the course and the hourly DR positions up to 0800. From each DR position plot a line in the direction 250° and measure off 1 mile from the 0600 DR, 2 miles from the 0700 DR, and 3 miles from the 0800 DR. Enclose the points so obtained in small squares and label as shown in Figure 1205.
The accuracy of an estimated position depends on the accuracy with which the current is estimated. It is not safe to assume that a current determined by the last fix will continue, unless there is evidence to indicate that this is so. Unless there is information available to permit a reasonably accurate estimate of the current, it is best to assume zero current. It is especially unwise to expect a current to be regular and uniform near a coast, for local conditions are likely to cause irregularity, and tidal currents have greater effects here than on the open sea. When approaching pilot waters, it is often desirable to maintain two plots, allowing for anticipated current in one (the EP plot) and not in the other (the DR plot), and to consider both plots when laying a course to avoid danger.
*Three problems frequently arise *in connection with currents of estimated set and drift:
To find the anticipated track and speed of advance of a vessel steaming an ordered course at a specified speed through an estimated current.
To find what course a ship steaming at a given speed through an estimated current
should take to make good an intended track.
To find what course and speed must be ordered to steam through an estimated current to arrive at the destination on time.
If a current is setting the same direction as the course, or its reciprocal, the track is the same as the course through the water. The effect on speed can be found by addition or subtraction; if in the same direction the speeds are added, and if in opposite directions, the smaller is subtracted from the larger. This situation happens frequently when a ship encounters tidal currents upon entering or leaving a port. If a ship is crossing a current, either at right angles or at a lesser or greater angle, the solution can be found graphically by a vector diagram since the velocity over the ground is the vector sum of the ships velocity through the water and the current effects over the ground.
Such vector solution can be made to any convenient scale and at any convenient place, such as the center of a compass rose, on a separate sheet, or directly on the plot. The following examples will show the method of graphic solution:










Example 1: (Figure 1206a) Given the course and speed of the ship, and the estimated set and drift of the current, find the anticipated track (TR) and the anticipated speed (SOA) along this track. This example illustrates how the navigator not only finds the TR and SOA, but also, and perhaps more importantly, how he establishes an estimated position (D). It illustrates the first of the three cases of current sailing stated at the beginning of this article.
A ship will steam at 12 knots on a course of 211&#9702; true, through a current estimated to be setting 075° at drift of 3 knots. Find the anticipated track and speed of advance along that track.
Solution: In Figure 1206a, let point A be the location of the ship. From A, lay off the vector AC in the direction of the set of the current, 075°, for a length equal to the drift, 3 knots, at the scale selected (this represents motion of the ship due to current alone). From C, lay off a vector in the direction of the course, 211°, with length to scale of the speed, 12 knots, (this represents the travel of the vessel through the water with no consideration of current). Complete the current sailing vector diagram by drawing AD. The direction of AD is the direction of the anticipated track while its length represents, to the established scale, the speed that is anticipated along this track, if the current was predicted or estimated correctly. D is an estimated position only and must be used with caution until a fix can be obtained. The navigator is now able to apply this solution to the DR track from his last fix to obtain an estimated position.










Example 2: (Figure 1206b) Given the estimated set and drift of the current and the ordered speed of the ship, find what course must be steered to make good a given intended track (find also what the expected SOA will be along this TR).
Let the estimated set of the current be 075°, drift 3 knots. The ship will steam at 12 knots. The direction of the desired (intended) track is 195°, the speed of advance along that track is not specified and can be any value.
Solution: In Figure 1206b, from point A, the position of the ship, lay off the line AD of indefinite length in the direction 195°. Plot the current vector, AC, in the direction of the set, 07 5°, for a distance equal to the velocity of the drift, 3 knots. With C as a center, swing an arc of radius equal to the ships speed through the water, 12 knots, intersecting AD at D. The direction, CD, 207.5°, is the course to order and the length AD, 10.2 knots, is the estimated SOA. Notice that vectors AD and AC, representing intended track and current respectively, have been plotted with respect to the earth (point A), while vector CD has been plotted with respect to the water.










Example 3: (Figure 1 206c) Given the set and drift of the estimated
current, and the direction of the desired track and the required speed
of advance, find the course and speed to be ordered.
A ship at 1300 is 100 miles due west of her desired destination. If
the ship is to arrive at her destination at 1800, find the course and
speed to order if a 2-knot current setting southeast (135°) is predicted.
Solution: In Figure 1206c, the ship is located at point A with point D as its destination, 100 miles due east. With five hours to reach this destination, the ship obviously must maintain a speed of advance of 20 knots. Lay off AD in the direction 090° to represent the intended track and of a length equal to the intended SOA, 20 knots. Lay off the current vector, AC, in the direction of its set, 135°, from Point A and of a length equal to the drift, 2 knots. Complete the current sailing vector diagram by drawing CD. The direction of CD, 08 50, is the course to order while its length, 18.7 knots, is the speed to order to make the passage. Again notice that vectors AD and A C, representing intended track and current respectively, have been plotted with respect to the earth while vector CD has been plotted with respect to the water.
*Determining actual current*
The preceding three examples have all included the use of estimated currents. Another use of a current sailing triangle is the determination of actual current from a comparison of a DR position with a fix for the same time. If a course line is laid down from a fix (not a running fix) and at a later time a new fix is obtained which does not agree with the corresponding DR position, the difference between these two positions can be assumed to represent the actual current encountered during passage. It is immediately apparent that current so determined will include all of the factors mentioned in Article 1201 and, in addition, any errors in the fixes. (If the course line of the DR plot was last started from a running fix, actual current can still be deter mined but special procedures are needed; see Example 2 below.)
It should also be apparent that if the estimated position on the intended track coincides with the fix on the actual track, the estimated current computed prior to departure was exactly equal to the actual current encountered during passage. If the two positions are not identical, then the estimated current was in error by an amount directly proportional to the rate and direction of separation of the two positions.
*Three problems most frequently arise* in determining the set and drift of an actual current:
*To find set and drift of an actual current,* given the DR position based on a plot run from an earlier fix, and a new fix for the same time as the DR position.
To find set and drift of an actual current, given a DR position and an estimated position, both based on an earlier fix, and a new fix for the same time as the DR position and EP.
Example 1: (Figure 1207a) Given the DR position based on an earlier fix and a new fix for the same time, find the set and drift of the actual current.










The 1815 DR position has been run forward from a fix obtained at
0545 the same day. At 1815 a fix is obtained and when plotted, is located 7.5 miles from the 1815 DR.
Required: The set and drift of the actual current.
Solution: The set is the direction from the DR position to the fix for the same time. Drift is determined by measuring the distance between the DR position and the fix for the same time, and dividing it by the number of hours since the last fix. This is true regardless of the number of changes of course and speed since the last fix. Since the 1815 DR position represents the position the ship would have occupied had there been no current, and the 1815 fix represents the actual position of the ship, the line DB joining them is the direction and distance the ship has been moved by current. The direction of this line from the DR to the fix, 099°, is the set of the current. The drift is its distance, 7.5 miles, divided by the time between the fixes, 12.5 hours, or 7.5/12.5 = 0.6 knots.
Answer: Set 099°, drift 0.6 knots.










Example 2: (Figure 1207b) Given the DR position based on an earlier running fix, and a fix for the same time, find the set and drift of the actual current.
Two methods may be used to determine the actual current when the DR position has been run forward from a running fix. Each method is explained below. At 0700 the navigator obtained a fix as shown. At 1152 a running fix is obtained from two LOPs, one at 0919, and the other at 1152, and a new DR plot is begun. At 1710 another fix is obtained as shown.
Required: The set and drift of the current..
Solution: (Method 1). The plotted DR position at 1710 (point D has been run forward from a running fix, and therefore cannot be used to obtain the set and drift of the current. Ignore the 1152 running fix, and continue the original DR course from point C until the DR position for time 1710 (point D) is determined. The set of the current is the direction from point D, to the 1710 fix (point B), 357°, and the drift is this distance, 12.7 miles, divided by the time since the last fix, 10.2 hours, or 1.2 knots. (In this example the extension of the original course from C to D is shown as a broken line for clarity.)
Solution: (Method 2). Measure the direction and distance CC from the original 1152 DR to the 1152 running fix. By applying the reciprocal of this direction and the same distance to the 1710 DR position, point D is established. It is noted that this is the same position as determined in method 1. The set of 357° and drift of 1.2 knots are obtained as before.
Answer: Set 357°, drift 1.2 knots.










Example 3: (Figure 1207c) Given a DR position and an estimated position based on an earlier fix, and a fix for the same time, find the set and drift of the actual current.
At 0900, a navigator fixed his position at A as shown. While proceeding to Point D bearing 090°, 20 miles from A, the navigator estimated that the current would be 135°, 6 knots, and therefore he set course 075° speed 16.3 knots to make good the intended track to Point D. At 1000, the navigator fixed his position at Point B.
Required: The set and drift of the actual current.
Solution: Since the 1000 DR represents the position the ship would have occupied had there been no current, and the 1000 Fix represents the actual position of the ship, the line CB joining them is the direction and distance the ship has been moved by the actual current. The direction of this line from the DR to the fix, 180°, is the set of the current. The drift is its distance, 8.0 miles, divided by the time between fixes, 1 hour, or drift = 8.0 knots.
As is evident from an inspection of the figure, the navigators estimate of current was in error by the vector difference of CD and CB.

To be continued I ran out of gas. This post will finish in the AM!


----------



## Fishers of Men

Current sailing cont.










*Labeling the current triangle*
1208 Many times it is desirable to construct a current sailing vector triangle to assist in the graphic solution of the problem. However, as has been demonstrated, the solution of the unknown parts of the triangle must be in terms of the given information of the known parts.
A complete current triangle equally applicable to the solutions of the current problem prior to departure, as well as to its solution after arrival, is illustrated in Figure 1208. A tabulation of the respective parts of each triangle is given in the accompanying table.
Although the normal method of solving current sailing triangles is the graphic procedure described above, solutions are also possible by mathematics. In any of these triangles, there are six components, three sides and three angles (derived from the three directions): four of these factors will be known, two unknown. Solutions by plane trigonometry are unduly laborious if attempted by use of tables, but they can be quickly and easily found using a small electronic calculator, particularly a programmable model.
Advancing an LOP with current 
Article 1207 considered the fact that a running fix could not be used in the determination of current, as the earlier LOP used to obtain the running fix had in fact been acted upon by current during the tune intervening between it and the second LOP. It follows, there fore, that if the navigator be1ieve he knows the set and drift of the current within reasonable limits, he can increase the accuracy of the running fix by allowing for them when he advances the earlier LOP.
The following example illustrates the technique of plotting a running fix with a known current.
Example 1: (Figure 1210) The navigator of a ship on course 012°, speed 12 knots, observes Light E bearing 3110 at 1500. He has reason to believe that a current exists with set 030°, drift 3.0 knots. Light E is subsequently observed bearing 245° at 1520.










Required: Plot the 1520 running fix, allowing for current.
Solution: In the twenty minutes between LOPs, the ship advanced 4.0 miles in the direction 012°, so the navigator advances the 1500 LOP as shown by line AA. During this time the current has also moved the ship 1.0 mile in the direction 0 30°. The navigator must further advance the 1500 LOP to represent the additional travel of the ship caused by the current, or to the 15001520 LOP shown in the figure. The intersection of the 1500 LOP so advanced and the 1520 LOP marks the 1520 running fix. Had current not been taken into consideration, the running fix (see Article 1111) would have been located at the dotted circle, over one mile from the established running fix.
Errors inherent in running fixes
1211 In working with current, an inexperienced navigator may well make one of two errors, both about equally dangerous for his ship. He may either allow for too little or no current or he may assume that a current is continuing without change when he is not justified in so doing.
Judgment born of experience is the best guide. However there are some considerations that even the beginner can learn to apply. The estimates of current given in current tables, pilot charts, etc., are usually quite accurate and should not be ignored. When there is a strong steady wind, its effect both in forming a temporary wind-driven current and in blowing the ship to leeward should be considered. The effect of wind on a ship differs with the type of ship, her draft, and the relative direction of the wind. The current acting on a ship is generally changing because of the tide cycle, changes in wind, changes of geo graphical position, etc. The error in steering usually changes with a change of helmsman. Hence it is generally unwise to assume that the current that has acted since the last fix will continue. All the factors mentioned above go into the estimate of the current. In estimating current, the most unfavorable conditions possible should be assumed. It must be remembered that a running fix obtained by two bearings not taken simultaneously will be in error unless the course and the distance over the ground being required. Difficulty will occur in estimating the exact course when there is bad steering, a cross current, or when the ship is making leeway; errors in the estimated run will arise when the vessel is being set ahead or back by a current or when the logging is inaccurate. Since the current is rarely known, the run between two bearings will often be in error, and therefore the running fix will give a false position, the amount and direction of the error depending upon the current that has not been taken into consideration during the run.










Some indication of the current may be obtained by taking more than two successive bearings the same object and plotting a series of running fixes, each using the three most recent lines of position. If the current actually is parallel the course, its presence will be revealed by this method since the fix will be a point either too far in toward the light or to far out, depending on whether the current is with or against ship respectively , and successive fixes will show a course parallel to that steered (Figure 1211 a). If there is a cross current, however, the fix will result in a triangle, the size of which depends upon the cross component of the current; and the line through the mean points of the successive fixes will show a track oblique to the course steered, to the right or left depending upon whether the current is setting to the right or left, and it will plot between the course steered and the actual track (Figure 1211b).










Obviously, the presence of a current acting against the ship presents a hazard, since in this case the ships positions as plotted by running fixes indicate a greater margin of safety to shoals, rocks, etc. extending out from the shore than actually exists. Hence, when there is a possibility that a head current exists all dangers to navigation should be given a wider berth than indicated by running fixes.
A better plan when possible is to obtain frequent fixes by simultaneous bearings of two or more fixed objects.
Summary 1212 
This discussion on current sailing has involved aspects of DR and of pi1oting which are inseparable. Examples as pure or simple shown in this chapter are not normally encountered in actual navigation, but the ones shown serve to illustrate the vector analysis involved. Solutions are also possible using the considerable mathematical capabilities of small hand-held electronic calculators.
*A DR plot must always be maintained. *If data on current are not available, or cannot be trusted, the course and anticipated track are considered one and the same. If data of acceptable reliability are available, they should be used and an EP plot maintained. If in waters containing hazards, both plots should be maintained, at least to the extent of determining any possible danger to the ship. All possible data should be evaluated to give an estimated position, as it is a rare occasion when a fix is obtained that coincides precisely with the DR position, indicating no current effect whatsoever.


----------



## Fishers of Men

Man, I'm way off course. I was thinking I already did safety and weather. No one is reminding me of over sites! *So, lets go Safety 1st.* lol pun intended.

Keep the boat organized, a place for everything. Keep the aft deck clear at all times to avoid tripping on something or breaking a rod!

We live on the water planet earth which is over 70 &#37; water. As professional mariners, pleasure boaters or if you&#8217;re just along for the ride, the waters can and are a dangerous place that can and do take lives without excuse or reprisal. The waters themselves are beautiful and intriguing. Place a vessel on these waters and the hazards magnify. As with most everything, knowledge, forethought, anticipation and preparation can at least partially eliminate or surely reduce these dangers.

Safety on a vessel on our seas, lakes and rivers is as important if not more important than anything else in our quest for professionalism and enjoyment on these gifts of nature. We will, step by step, review and emphasize the necessities to be safe on a vessel and in fact to stay alive.

*Fueling:*

The magnitude of putting fuel in a vessel is evidenced by the statistics of accidents occurring at the fuel dock.

I just left a fuel dock down in Florida and witnessed 2 guys in about a 20 footer (fiberglass) with an outboard get into the channel and burst into flames not far astern of us. Don&#8217;t know what they did to start the fire, but it had to be something simple. They bailed out and swam to shore, the marine patrol and fire dept was right there at the marina where we got fuel and they said it was safer to just leave it alone and let her burn since they saw the occupants swim to shore. Ruined there day. 

The procedure is to close all doors, hatches and windows. The nozzle must then be grounded to the metal base around the fuel cap opening and then slowly begin fueling until the required amount is dispensed. DO NOT OVERFLOW. Should there be any spillage, it is to be wiped up and the rags, paper towels, etc. disposed of immediately. After fueling, you should open hatches, ventilate the bildges with the blower and leave the dock.

*Cold Water Survival *Water absorbs body heat much faster than air and when body heat becomes to low, your body freezes to death. The loss of body heat in water is called hyperthermia. Should something go wrong and you do go down, survival is dependent on equipment that you have at hand, ingenuity, common sense, crew and TIME. You must get the victim(s) out of the cold water and restore body heat and circulation. Life floats, life rafts, line ring buoys and anything available must be used with time being of the essence. Survival suits are a necessary tool in many commercial operations. Equipment should be readily available and the crew trained in the use of equipment and survival. Remember, overboard disasters do not always happen to everyone else. It can happen to any vessel and crew on the water. This is why the Coast Guard flies over 65,000 survival missions each year.

An insurance of falling overboard in situations where there is such a strong possibility, (high winds, storms, high waves, etc.) is to wear a safety harness consisting of a belt and suspender-like straps. A stout line attached to the belt is made fast to a life line.
Note: Good boating shoes with nonskid soles are a necessity.

*Vessel Inspection:*

Accidents and injuries including drowning can occur from faulty equipment and a defective vessel itself.

*Inspect all* through hull fittings, discharge pipes and seams. Bilge pump and spare bilge pump should be tested to make sure it (they) can discharge all unwanted bilge water.

*Batteries and spare battery* must be at full charge and connections secured and cleaned. Start the engine(s) with battery power in place of shore power before leaving the dock.

*Check radio(s)* to insure a range of at least 20 miles from shore or dock area. The wise mariner will always have a spare radio.
Distress signals are inevitable and must be stored in a water-proof container and be available at all times.

*Recognition Of Sudden Illness : *

When a crew member or passenger becomes suddenly ill on the vessel, it is the Captain&#8217;s responsibility for the welfare of all on board and he or she must recognize symptoms and signals Common signals include: nausea and/or vomiting, diarrhea, feeling lightheaded, dizzy, confused , or weak. Severe sweating and/or a change in skin color such as turning pale can also be a sign. Besides the physical symptoms that you see, evaluate the conditions such as heat, cold, medication taken or which way be required. Ask questions. Sometimes the signals come and go. If there is doubt about the severity of the illness, get help. Get on the radio telephone and seek professional help or call a local emergency number. It&#8217;s better to be safe than sorry. Until you get help you can do the following: Reassure the victim, help the victim rest, keep the victim from getting chilled or overheated, watch for changes in breathing and consciousness and do not give anything to eat or drink unless the victim is fully conscious.

*Rescue Breathing: *

To begin rescue breathing follow the following prescribed method by breathing slowly into the victim:
1. Pinch the victim&#8217;s nose shut and make a tight seal around the victim&#8217;s mouth with your mouth.
2. Breathe slowly and gently into the victim until you see the chest rise. Give two breaths each lasting about 1 to 2 seconds. Pause between breaths to let the air flow out.
3. Check for a pulse after giving 2 Initial breaths. If victim is not breathing, give one breath every 5 seconds.
4. Recheck pulse and breathing about every minute.
5. Continue rescue breathing as long as person is not breathing and professional help is available.
Possible Heart Attack Every Captain should be able to identify a heart attack condition or at least recognize the signals associated with a heart attack. Unfortunately, it isn&#8217;t always cut and dry that the victim is having a heart attack. It can be confused with pains of indigestion or muscle spasms. However, IF the possibility exists that it could be a heart attack, then it must be accepted as such, since it would be life threatening and action must be taken.

*Signals of a possible heat attack include:*

1. The victim has persistent pain and or pressure in the chest area that is not relieved by resting, changing position or oral medication. Pain may range from discomfort to an unbearable crushing sensation.
2. Breathing will be faster than normal.
3. Breathing could be noisy.
4. The victim will be short of breath.
5. Pulse may be faster or slower than normal or may be Irregular.
6. Victim&#8217;s face may be moist, or victim may sweat profusely and the skin may be pale or bluish in color. 
When the heart stops beating or beats too poorly to circulate blood properly, it is called cardiac arrest. When cardiac arrest happens breathing soon stops. Whenever you suspect a passenger or crew member of having this condition, have the person stop whatever they arc doing and rest Ask the person if they have a history of heart disease and if they have heart medication. Call for help by radio telephone or cell phone and get professional help as soon as possible. Since the victim may go into cardiac arrest be prepared to give CPR until professional help arrives.
If you feel you must use MAYDAY for a person aboard who may be having a heart attack, but are in doubt, then please do so. Yes, the symptoms may not be clear, but if there is that grey area, remember there is a human life at stake.... You could save it.

*Burns:*

On board and around the vessel: Burns can occur on the vessel, in the galley in the bilge and on the deck. The care for burns involves the following three basic steps:
1. Stop the Burning &#8212; Put out the flames or remove the victim from the source of the burn.
2. Cool the Burn &#8212; Use large amounts of cool water to cool the burned area. Do not use ice or ice water other than on a small superficial burns. Ice causes body heat loss. Use whatever resources are available &#8212; water hoses, shower, wet clothes, etc. Be sure to keep the clothes cool by adding more water.
3. Cover the Burn. &#8212; Use dry, sterile dressings or a clean cloth. Covering the burn helps keep out air and reduces pain and helps to prevent infection.

*Sunburn : *

The nautical atmosphere is one conducive of shorts, bathing suits and exposure to the sun for that nautical appearance of a suntan. However, long exposure can cause severe sunburn, skin cancer and early ageing. The classic case of too much of a good thing turned bad. You should apply the proper sunscreen 15 to 30 minutes before being in the sun and reapply it often. When combined with the glare of water surface at sea, or any boating condition, the situation magnifies. Mariners should use sunscreens labeled water resistant and reapply every 30 minutes or as described on the label.
It is equally important to protect your eyes from sun damage. Be sure your sunglasses provide protection from ultraviolet rays. Before leaving the dock or spending the day on your boat, make sure you have protection with sunscreen and sunglasses. Another thing Captain, advise your crew and passengers of the hazards of over exposure to the sun and the necessity of proper protection.

*Bleeding: *

Bleeding occurs when a blood vessel is torn. With any open wound, bleeding can be severe enough to be life-threading. An open wound means that blood flows through a tear in the skin. Normally bleeding usually stops in a matter of a few minutes. If the damage is to large or the pressure to great to have the blood clot, the excessive bleeding could cause death.
On board a vessel scrapes are a common kind of open wound. It is important to clean scrapes to prevent infection. Punctures are also common on or around boats. A splinter is an example and which usually can be removed with, a pair of tweezers.
Open wounds need some type of covering to help control bleeding and prevent infection. Assorted sizes and shapes of dressings should be stocked in an up to date readily available first aid kit. You can buy small adhesive compresses such as Band Aids and roller bandages. Gauze comes in widths from 15 to 6 inches, Although an elastic bandage(s) is very effective, it can cause problems in that it restrict blood flow.

*Control Bleeding:*

1. Cover wound with dressing and press firmly.
2. Elevate the arm above the heart.
3. Cover dressing with a roller bandage.
4. If necessary, apply additional dressings.
5. Squeeze artery against bone.
6. Never ( unless absolutely necessary), use a tourniquet.
A good well stocked First Aid Kit is an absolute necessity.

*Man Overboard:*

The presence of novices to expert seaman aboard a vessel on all types of waters and water conditions results in vulnerable situations of having a passenger go over the side. &#8220;Man Overboard&#8221;. Here the astute Captain and the necessary lookout can save a life. Numerous occasions are on record of having a person go overboard without witnesses and the vessel proceeds along it&#8217;s course without recognition of the lost passenger. Periodic head count is important along with the always necessary communications.

*Speaking of this,* I was coming in off the ocean and had 2 other adults onboard, remember those _huge ground swells_ I was talking about in the St Lucie inlet? Full moon, strong outgoing tide, wind pushing inland from sea. Well I had another guys 22&#8217; aquasport, 175hp outboard, we had to get back in a hurry because the marina where it was kept, in /out storage would be closing for the night. We messed up, spent too much time catching :B , knowing that the tide was going to be going out, knowing that the wind was going to add to the swells of the ocean coming in but did it anyways, and knowing that we would have to haul a$$ to get to the marina on time. I sat at the sea bouy a long time and timed 3 to 5 sets on the swells,  I told them to remain seated and hang on. I then commenced to ride a swell in, knew about when it was going to disappear from under me like an inverted pyramid,  hit the throttle, jumped on the next one and surfed it like a surfer in behind the break wall and came in.  Now, to get back in that_ dog leg channel_ I showed you on the chart, with little room for mistake, I am powered up and coming in. About a 65 foot Hatteras is going out and I had to take his wake. Joe decided  that he needed to see what was going on and stood up at the same time I jumped this wake. I am straightened out now and flyin across the ICW, make the turn into the St Lucie (you saw the bend on the chart)
*and Red says* &#8220; Hey, Joes back there&#8221; 
*I go:* &#8220;I know Joes back there&#8221; and keep going.  
*Red says: &#8220;I MEAN JOES WAY BACK THERE&#8221; *  
Same time I hear Man Overboard from other vessels and decide to look behind me&#8230;NO Joe. The tide was taking him out to sea, Joe weighed 300+ a big man, I spun around and went to pick him up while other vessels were watching him. Red said that he catapulted out of there when I crossed that wake and flew about 20&#8217; in the air. His pockets turned inside out when he hit the water, lost his wallet and all his money and looked like a big sponge bob :C bobbing up and down. We had one hell of a time getting his big a$$ back in the boat. Then it was if it wasn&#8217;t bad enough for him, I was pee- O&#8217;ed  and commenced the A$$ chewing. We made it to the marina with 5 min to spare by the way.

Should a person go overboard, a method of observation and pick-up is the Williamson Turn planned to get the person back on board as soon as possible and without harm to the victim. The very first thing is to SHOUT : Man Overboard. Someone must keep the victim(s) in sight constantly without taking there eyes from him or her or them. A life ring must be thrown to them ASAP. DO NOT JUMP-IN AFTER THEM. Immediate the rudder hard over to the side in order to swing the stern away from the overboard person. Don&#8217;t chop him up in the prop! 

*Here&#8217;s a tip *for your first aid kit that I learned back in dive school:

Keep a bottle of Adolfs meat tenderizer on board or in your tackle box at all times. Reason being, coral cuts, hook points, fish fins, bee stings and such are all protein poisoning, the immediate application of the tenderizer will draw the poisoning out immediately. This came in handy for a friend of mine who&#8217;s 6 yr old son was allergic to bees and got stung all over in my back yard, he didn&#8217;t have his shots with him and went into shock right away. The dad was loosing it because he wouldn&#8217;t have made it to the hospital in time. I quickly went to the tackle box, moistened the areas of the stings and put the tenderizer on. The lad settled down in about 2 minutes.


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## Fishers of Men

B]A little bit on Boat Handling[/B]
Most if you have been there and know this but here it is anyways for the newbees.

Competence in boat handling from small boats to large crafts is completely satisfying and a must for the Captain. It is a coordination of thought to action and response. Skills in boat handling are honed by constant and continuous practice. Docking for example can be mastered by placing well positioned floats such as small buoy type objects in open non traveled water and continually angling and maneuvering between the floats as if it were a dock space until expertise is attained. Then the Skipper is ready to face the dock and docking the vessel. It is a continual challenge since conditions change and can change rapidly. All factors can become essential including wind, current, dock conditions and traffic, equipment and weather. Not Just one but all combined are necessary for safety and security of crew and vessel. A large gouge in the hull (yours or theirs) is not only embarrassing, but expensive. 

*Docking techniques include:*

 Long before the vessel arrives, fenders go out. Note: On the correct side.
 Approach SLOWLY against wind and current.
 Sail boaters approach under power.
 Assign tasks to your crew
*Alert passengers to keep bodies inside the craft.*
Have dock lines ready at all times.
Use wind and current, either/ or, from ahead or astern, as required.
*Go slow, slow and most important  slow-.*
 Secure bow and stern lines before shutting down engine(s).
Undocking or leaving the dock can be equally important and certain
techniques can again *show talent and control.* The essentials remain the same as
with docking, except the vessel is now leaving a confined area. Undocking
techniques include:
 Remove shore power cord.
 *Warm up engine(s) before releasing dock lines. * (How many times you seen someone out there drifting and trying to get an engine started?)
 Use great care to avoid striking the stern against the dock.
 Cast off bow and/or stern lines depending on wind and current and as *always, go slow.*
 Use forward or after spring lines, if required and then release or have released as necessary.
 Secure all lines.
 Retrieve all fenders (called fenders not bumpers) and secure in the boat.
Cruising under power away from the dock, the skipper must watch the vessels wake and *maneuver with bare steerage *until in unrestricted waters. The wise helmsman soon realizes that driving a power boat is not like driving a car. The boat never comes to a complete stop until it is again tied up to the dock. There are no brakes on a boat. The one way to slow down is to throw the engine(s) in reverse, however this will slow the boat, but it may still continue in the forward direction.
Another difference to a car is that a boat steers from the rear, because water is forced against the rudder. In response the boat steers in the opposite direction. Each boat has a different turning radius so one must allow for numerous variations and allow room for lateral swing. A vessel with twin engines and operated by the experienced helmsman can swing the boat in its own length. All of this takes time and practice and in many cases it is prudent to ask assistance or even hire an experienced Captain to take the helm and teach and advise the new boat owner of the many actions and reactions that can occur.
A sailboat is an obviously different vessel from a power boat. The new sailor should have a basic knowledge of sail principles. He must know where the wind is coming from, in a certain direction and know how to adjust his sails. A firm hand on the tiller is the means for steering the boat. Pushing the tiller to starboard turns the rudder to the left and swings the boat to port. and vice versa.
A sailboat is sailing on a port when the wind blows against the left, or port side of the sails. On a starboard tack the wind strikes the sails on the starboard side. Head up means to turn the boat more into the wind. Head down, fall off and fall away means to turn the boat further away from the wind. On each different heading the sails need adjusted. Every shift of the winds force affects the balance of the boat and the helmsman must move the tiller and adjust his weight.
Common sense in boat handling is the most important tool, regardless of the type of boat and its size. Care, confidence, and experience are the means and utensils for proper boat handling. There are however certain terms that must be understood:
*Broaching* is yawing out of control until the vessel lies parallel to the waves.
*Pitch polling *is for the vessel to go end for end (bow over stern) in rough seas Squat is the puffing of the stern toward the bottom of a shallow channel by the speed of the vessel and the suction of the propellers.
Bank cushion is the pushing of the bow away from the bank by the vessels bow wave.
*Bank suction* is the pulling of the stern toward the bank by the suction of the propellers.
*Trough* is the most dangerous part of the wave and can cause crafts to capsize.
*Single right hand turning screw* will when backing down have the stern go to port.
*Twin Screws* are engines turning in different directions ; one right hand and one left hand.
Boat handling would not be complete without stating the importance of a *Sea Anchor.* A vessel caught in heavy seas can be hove to by setting a sea anchor off the bow with a bridle and long hawser. This conical nylon device fills with water, and the resulting drag keeps the bow into the sea. A trip line at the sea anchors apex is used for hauling the device back aboard. It should be noted that in emergencies a make shift sea anchor can be made from a bundle of tied up clothes, a number of life
jackets or a bucket with holes in the base of the bucket. If a bucket is used, it should for obvious reason, have a good sturdy handle. (A bucket should be mandatory on the boat for any purpose)
*Tying up at the dock *can be essential for the security of the boat. Many a vessel has broken loose and gone to open water without the benefit of anyone on board. Also one must ask, particularly at unfamiliar dockage if the docks are floating docks or stationary. Will the vessel rise and fall with flood waters or tides or be swamped by having it tied to a permanent dock. Periodic checking and weather forecasts are a necessity to protect a substantial investment.

*Lets tie these boats up RIGHT *and look like professionals at the dock. No need for 10,000 half hitches and granny knots either. You see this kind of crap all the time. Learn some basics and if you know the basics then learn how to apply them, for instance, 2 half hitches is plenty. THINK...you should be able to untie and be underway quickly in case of an emergency. More on knots next time.


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## Fishers of Men

*A touch on Marlinespike Seamanship*

Marlinespike in name comes from the expression or use of a pointed tool used in splicing to open the strands of a rope or cable. All kinds of marlinespikes are used, from a ground-down sharp wooden handle to a sophisticated rigging tool. Any pointed object (pencil, nail file, knife, etc) will do well, provided it will fit between the strands of rope and open them. The everyday boater may call it rope, but when the mariner takes it on board for the many necessary tasks, it becomes line. Again just as: chart verses map, fender verses bumper, line verses rope, we speak our own nautical language in our own nautical world. - *On a vessel, its line.*

The lines aboard a boat are of great importance, but just as significant to the mariner, is to know where, when and how to use these lines in the many applications. The good skipper needs the fundamental abilities to tie and use basic knots and hitches and to make splices. Sailors, in particular take pride and pleasure in doing fancy work with their lines on their sailboats.
*A variety of rope* is available in local marine stores, but selecting the type and size for certain usage can be a key factor in boating competence. There is hemp, sisal and manila, but in todays nautical world, synthetic materials are better suited for use in our modern marine environment.
*Nylon *was the first synthetic and is still the most popular with a widespread use. It has a tremendous strength and is known for its elasticity. This makes it adaptable for docking, towing and use as anchor rodes. *Nylon stretches *and academically is supposed to stretch up to 26 %, however the critical elongation stretch is 40 % and being the *strongest of all lines*, it has the greatest breaking strength. It is the best line for shock situations such as anchoring and better than manila for towing astern. *ultraviolet rays destroy nylon* but is the most resistance to mildew and rot. Because it stretches too much, and is dangerous, *nylon should never be used for hip towing *When it does break and it can break, it is dangerous because of the *whipping effect*. It can be purchased in an assortment of colors so that color code can be identified for a variety of tasks for which the nylon can be used. white for anchoring, blue for docking, red for tying up buoys, etc... Also, it should be noted that nylon as well as other synthetic line are measured by their circumference and not by their diameter. 

Now, go into a marine supply store and ask for ½ inch nylon line. Certainly, you *will be sold line measured by diameter*, since this is a little known fact. Professionally, wire braided hawsers and cable are measured by diameter.

_In The real world, just as on a craft, we cannot direct the wind, but we can adjust the sails The Old Salt_

*Dacron* is about 10-15 % weaker than nylon and does not stretch. It is used primarily in sailing for sheets and halyards and is a lot smoother than nylon.

*Polypropylene* is a lightweight line that will float. Used primarily for water skiing, it is difficult to knot and splice. It is also slippery and used where buoyancy is required.

*Natural fiber *is least resistance to mildew and rot, but must be washed and dried after use in salt water environment. Natural fiber shrinks when wet and cannot be lubricated. After continued use or age, and to detect rot in manila lines, open the strands and examine the inner fibers.

*Wire rope* is extremely difficult to work with and should be left to commercial venders and towing professionals, while the power boaters and sailors should be content with the ease of using fiber and in particular, synthetics.

*Knots:*
A knot is a universal term for securing a line to anything, Even though the spelling and sound of the word is the same, we are talking cordage and not the speed of one nautical mile per hour.
The difference between a knot, bend and hitch is unclear, yet there is a difference. *A bend* is also a knot to secure a line to another line, such as a sheet bend whether the lines are the same size or not.* A hitch* is a line or rope that secures to an object, *the most common of which is the clove hitch,* commonly used to hang fenders or tie a boat temporarily to a piling. The *term bight *is applied to an open or closed loop in a line or rope. An eye in the end of a rope is a *becket* and it could also be an eye in the end of a block used for securing an end of a line.

A *strand *is one of the lays of a rope or the yarns/ fibers that are woven together with other strands to make the rope.

*The standing part* or working end of a line or (rope) is that part that is made fast to something.

*The bitter end* or inboard end is the end made last to the vessel. It received the name bitter end from bitt. (perpendicular hardware on deck for securing lines.)

Even though the novice or the seasoned mariner feel they dont have the time or need the skill to become an old salt type of cordage specialist, a few fundamental knots, bends and hitches should be mastered. These following basic knots will serve nearly all common needs aboard a boat and they are easy to learn and enjoyable to use. I had one student who vowed he couldnt make an eye splice, and after some simple instruction created a perfect splice. He takes pleasure in doing many of them now, perhaps even showing off a little and has them in use and hanging all over his boat.

*Useful Knots:*

*Square Knot or Reef Knot* - Called a reef knot because it is used on a sail boat to tie off excess sail material during reefing. Very easy to tie. With the working end in the right hand, place the working end over the standing part. Then, do it over again working end over the standing section. You now have a square knot and if it slips back and forth your fine. If not, you have a granny.










*The king of knots is the Bowline,* used for forming a loop, in the end of a line. It is a valuable knot to know and is the best substitute for an eye splice. The bowline will not jam under heavy loads, again, it is easy to tie and is easily cast off. Steps In tying a bowline are that you make an overhand loop. You then pass the bitter end through the loop and pass it around the back end of the standing end. Continue to pass the bitter (working) end back down through the same loop and pull.










Remember - Overhand loop, and then the working end is the rabbit. We now give due credit to the poetic Captain, Master or whoever it was that said:
_The rabbit comes out of the hole, goes around the tree and goes back into the hole _

Some other useful mentions include:

Flemishing is the method of coiling the line on the deck..
Faking is the method of arranging line on the deck in long bights.
To pay out enough line to ease the tension is known as - easing a line.
Warp is a term used when a vessel is moved with lines at the dock.
Bitts are hardware on the boat. The same hardware on the dock are bollards.
Protecting the ends of a line from unlaylng by coiling or wrapping twine around the ends is known as whipping. This term does not include taping.
The eye splice is forming a permanent loop in the end of a line. In usually a 3 strand line. Unlay the 3 strands at the end of a rope a form an eye by laying the opened strands on top of the standing part of the line. Hold the middle end and tuck this strand from right to left underneath the nearest strand of the standing part. Take up the next end 9"+ and tuck it again from right to left, under the next strand to the left and under which the first strand is tucked. Now, turn the whole splice over and take the third and final strand and lead it over to the right so that the last tuck can again be made from right to left. We now have 1 end coming out from under each strand which can be pulled tight This finishes only the first sequence of tucks. Now for the second series repeat taking each end over one strand and under the next strand. Repeat this again for the third sequence. The splice can be tapered by cutting off the first strand and tucking only 2 strands for the same procedure as above and then cutting off the second strand and completing the splice by tucking only the third and remaining strand in the final sequence.


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## Fishers of Men

How to measure distance on the longitude scale:


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## ezbite

i know alot of gps units have a "man overboard" button. i like to make sure everyone onboard knows where it at. if your doesn't instruct everyone how to enter a waypoint. you might have covered this and i missed it.


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## Fishers of Men

*Weather*
As mariners, we depend on nature in order to enjoy our waters and practice our profession. Weather is a great part of that nature which can control our maritime surroundings. It can and does enhance or eliminate a day&#8217;s activities for the skipper of small crafts. Our waters can freeze, winds can blow beyond hurricane force and violent thunderstorms can churn our waters to waves incapable of floating our vessels. Visibility may be curtailed to blind barriers, lightning can strike, vessels can be swamped and sank, and all within a short period of time. In short, the Captain must respect and perhaps even fear the forces of weather.
Our armaments against these forces are first and foremost our knowledge to understand the sources of the many types of weather along with the many tools at our disposal to interpret and understand the workings of nature&#8217;s weather.
Some of these tools are at our fingertips, with accurate forecasts broadcast on marine radios, access to weather maps, meteorological instruments and the ability to read clouds, winds and the water itself. We live in a world of high-tech and we can use this relatively inexpensive technology to predict severe as well as calm and pleasant forecasts. One cardinal rule for the prudent Captain is never to leave the dock, regardless of current conditions, without first checking the forecast for the immediate and surrounding area for that day.
All weather exists in our earth&#8217;s atmosphere. This planet&#8217;s atmosphere is no more than a thin covering of gas consisting of water vapor and air with of course miscellaneous pollutants. This layer is approximately ten miles deep at the equator and diminishes to about five miles at the north and south poles. The sun heats different parts of this shell around the earth unevenly causing the different weather patterns that we experience. The areas around the equator receiving greater sunlight are much warmer than the cooler (cold) areas around the poles getting much less sunlight.

*Temperature* is a measure of the presence or absence of heat. It is measured using a thermometer. There are several different scales used to measure temperature. The most commonly used scales are the Fahrenheit Scale and the Centigrade or Celsius Scale. Heat is transferred from one place to another using one of the following methods.
*Heat Transfer Methods*
*Conduction*&#8212;the transfer of heat between two bodies in contact with each other
*Convection&#8212;*the vertical rising of hot air
*Radiation*&#8212;heat transferred through space without help of any material (heat and light radiates from the sun to the earth)

Air flowing through our atmosphere with the rotation of the earth causes atmospheric pressure. Cool air is heavy and dense and creates high pressure. On the other hand, warm air is light and rises causing low pressure.
Atmospheric pressure is the force exerted on the earth&#8217;s surface by the weight of the air above us. Consider a column of air one-inch square sitting on a balance. The force would be equal to 14.7 lbs. Normal atmospheric pressure at sea level is expressed in any one of the following units.
14.7 tb/in 2 29.92 inches of Hg = 760mm of Hg = 1013.2 millibars	Hg is Mercury.

On a weather map, lines *called isobars* connect areas of equal barometric pressure. These lines delineate the areas of high and low pressure similar to the* contour lines on a topographic map.*
This flow of air from high pressure areas to low pressure areas results in air circulation in our atmosphere. Prevailing winds around the earth flow from high pressure belts in the polar regions towards the low pressure belts at and near the equator. This same phenomenon occurs in both the northern and southern hemisphere. The prevailing winds *do not blow north and south*, but shift from left to right in the northern hemisphere and right to left in the southern hemisphere. These prevailing winds are caused by the rotation of the earth and is known as the *Coriolis Effect.*
The Coriolis Effect was first introduced in 1853 by a scientist Gustave Coriolis and the force now bears his name. Description of the Coriolis Effect has had long standing confusion because of some misguided theories that the earths rotation causes water in a sink or toilet to rotate one way in one hemisphere and another way in another hemisphere. *The Coriolis Effect is ONLY for large scale motions such as the wind.* The scientist Gus Coriolis simplified this theory as such:

Pressure differences tend to *push winds in a straight* path. However, winds aloft follow curved paths across the earth. As air begins to flow from high to low pressure and with the earth rotating under it, this makes the wind follow this curved path. *The Coriolis Effect is zero at the equator *and it further follows that in the northern hemisphere the winds bend to the right while in the southern hemisphere the wind turns to the left.
Let&#8217;s take a look at the wind direction in *North America and in particular the United States.* If the earth were not spinning, the air would move from high to low pressures and north to south. Wind Blows From, so this would be a north wind. The Coriolis Effect resulting from the earth&#8217;s, rotation causes the wind to bend from left to right and is a westerly or northwesterly wind. Below the equator, it would be an easterly or southeasterly wind.
*Thus, our weather patterns move in the same direction.* Check the weather in the afternoon in *Chicago today*, and more than likely, that will be the weather in *Cleveland tomorrow *afternoon, and in Pittsburgh tomorrow evening. In the U. S. and Canada, this is referred to as the prevailing westerlies. The Captain is concerned with basic forecasting using the prevailing westerlies in that knowing that there is stormy weather existing in Detroit, Michigan, and depending on how fast the storm is moving available from marine forecasts , he knows when to expect stormy weather in Erie, Pa. because the storm is moving west to east.
*Around the equator we have a region known as the doldrums *where there is little or no general circulation. Sailboats can get "stuck here for days/weeks. North of the doldrums are the Northeast Trades which accounted for much of the commerce for the Americas from the days of the sailing ships. Above the Northeast Trades are the Prevailing Westerlies that encompass latitudes 300 North to 60&#176; North. *This is the area that we live in* and the reason why most of our weather systems come from the west. Finally there are the Northeasterlies in the Polar Regions of the Northern Hemisphere. Similar cells exist in the Southern Hemisphere.

Before leaving atmosphere, and as general maritime information, regarding atmospheric properties, the fixed components of pure dry air are: Nitrogen 78&#37;, Oxygen 21%, Argon .09%, Carbon Dioxide .03% and miscellaneous gases .07%. The variable component is water vapor along with some very little smoke, salt particles and dust. From the weather viewpoint, this water component is the factor from which we get our moisture: rain, snow, ice, fog and dew.
Also, as we gain in altitude, there is less weight above us. Pressure increases as altitude above sea level decreases. Over one half the weight of the atmosphere is restricted in the first four miles above sea level. It then follows that the density of the atmosphere becomes less with increasing altitude and the air is thin. This is due because it is less compressed. It must then also follow that air is heavier in approaching closer to earth. This high and low pressure along with the winds following a natural bending pattern has a decided influence on the earth&#8217;s weather.
*Air masses, Frontal Systems and Fronts*
An air mass is a large body of air over the surface of the earth which takes on the characteristics of that surface such as the temperature and moisture. An air mass over cold dry air will contain that air which is dense and heavy. Such *high pressure will have cool dry weather* while a low pressure frontal system over warm water will contain cloudy, rainy weather.
With the circulation of the atmosphere the air masses move, retaining their own characteristics and overlapping other air masses. These are known as *frontal systems* and as they approach closer to the earths surface they are called fronts.
*A front *is a boundary between two air masses or frontal systems and can be experienced as a moving line with rapidly changing temperature, wind direction, barometric pressure and all types of weather conditions. It is important for the mariner to understand that the front can extent to the full height and width of the entire frontal system and *can be very devastating *or enjoyable depending on the characteristics of the air mass and the speed with which it is moving. Fronts are named for those air mass characteristics that prevail with this moving boundary.

*A warm front* marks the arrival of a moving warm air mass and it&#8217;s displacement of a cold air mass as the cold mass recedes. It must be realized that the warm air being lighter cannot displace the heavier dense cold air by under or over running it, so it rises above the cold air and remains aloft until the cold air at the surface has receded. As the warm front takes over, the temperature rises. Since the warm air can hold more moisture than cold air, the warm front is generally accompanied by an increase in relative humidity and usually rain showers or snow. The duration of precipitation that can be expected could be anywhere from 6 to 24 hours.

*A cold front* is a cold air mass overtaking a warm air mass with both of them moving and marks the approach of colder weather with a drop in temperature. Colder air has less moisture capacity and is therefore associated with low relative humidity. However, such a frontal system may extend for hundreds of miles on the earth&#8217;s surface and the winds accompanying it will blow from west or northwest. It must also be noted that even though it normally will have low humidity this type of frontal system could generate squall and thunderstorm activity depending on the speed of movement and unstable condensation will cause vertical development of clouds. The duration may be as much as 4 hours.

*A stationary front* is one where both the warm front and cold front have stopped temporarily and a stalemate exists. It may begin to move again or just dissipate. This condition is usually experienced in late summer, with hot sticky weather, although not confined to that time of year, and the same weather remains on for days. The warm air usually flows over the surface of the cold air chilling it to it&#8217;s dew point and the result is rain.
An occluded front is one front overtaking another front and with rare exceptions it is a cold front overtaking a warm front and moving in the same direction. The result is a lifting of the warmer air. Two types can occur and are referred to as warm front occlusion and a cold front occlusion. In both cases the warm front has been forced aloft. In the case of the warm front occlusion the warm moist air is forced aloft and the mariner will see high clouds followed by low clouds and then can expect some rain showers.
With a cold front occlusion, the cold air mass is heavier and the warm air is not only forced aloft rapidly, the steeper frontal system forms a line of *CUMULOMIMBUS clouds that result in thunder storms* with possible violent rain, hail, heavy winds and squalls When *the knowledgeable Captain sees these thunderheads, he knows that weather can get dangerous and with little warning. *The only good part about these cold front occlusions is that they don&#8217;t last long. It is again emphasized that the cumulomimbus cloud (thunderhead) can get hazardous and t*he prudent skipper recognizing this, will seek safe harbor.*



















*Wind barbs *are simply a convenient way to represent both wind speed and direction in a compact graphical form. Vectors also work to some degree but it is more difficult to discern the magnitude when viewing vectors. For this reason, meteorologists prefer the use of wind barbs. The graphic here clearly shows how to read a wind barb. Meteorologists are also accustomed to nautical miles per hour (knots) for the magnitude of the wind. Convert to statute miles per hour (mph) by adding 15% to the value in knots. Example: 60 knots = 60 + 9 mph. [Just remember to figure it the same way you would figure a 15% tip at a restaurant by taking 10% and then halve that value.


















The U. S. Government weather service accumulates and then provides weather information taken at various observation stations throughout the entire country. This constant observed data includes, but is not limited to, wind speed direction, temperature, pressures, fronts, systems and related data plotted on weather charts for different regions of the nation. These charts are called synoptic charts and can show weather conditions at any area at any given time.
One of the more essential features of these charts are lines with connecting points *resembling a contour map* even though the lines have nothing to due with the contour of the earth&#8217;s surface. There are points which connect equal meteorological readings and show patterns which are valuable in predicting forecasts. The lines connecting points having the same atmospheric pressure are called *isobars*. Lines that connect points having the same temperature are called* isotherms.* The patterns of greatest value are the isobars since they can predict both the relative strength and direction of the wind. *The wind will blow harder in those areas where the isobars* are closer together and since isobars represent pressure, an area of high pressure extending into a lower pressure area is called a ridge of high pressure. The slope of the isobar or gradient also signifies that it is picking up speed.
Isobars can form closed loops around a low pressure area. This is called a *cyclone*, which is not, in any way related to a cyclone that is commonly associated with a tornado. This type of low pressure cyclone does not necessarily mean problem weather and can be many miles across in it&#8217;s pattern. If this ridge were extended along a line of the lowest pressure it would be a trough or depression. Isobars which form closed loops around a high pressure are called an anticyclone.

*In the northern hemisphere*, the wind patterns around the low pressure closed loops blow counterclockwise and inward towards the center of the low pressure. It follows then, that the *wind will blow clockwise and outward from a high pressure.*
In the southern hemisphere, the wind still blows into a low pressure and outward from a high pressure. The difference is that the clockwise and counterclockwise directions are in reverse.

*The mariner can do reasonable forecasting of local weather by remembering that &#8216;highs&#8221; usually bring fair weather and &#8220;lows&#8221; bring foul weather.

Clouds are formed when warm moist air rises and cooled to the dew point. There are many kinds of clouds but the major ones include HIGH CLOUDS which are named cirrus, cirrocumulus, and cirrostratus. Cumulomimbus has already been explained and emphasized as real danger. They occur above 20,000 feet. Middle clouds between 6,500 and 20,000 feet are altocumulus, and altostratus. Low clouds below 6,500 feet are called nimbostratus, stratus and cumulus.
Fog is a cloud at the earth&#8217;s surface. Physically a cloud and fog are the same&#8212;minute water droplets suspended in air. There are different types of fog. (dew point + air pressure the same = FOG)
We have all seen and experienced fog. Fog is formed when warm moist air near a surface is chilled to the dew point. This causes the water vapor to condense into very tiny droplets there are all kinds of fog, but the most common types are:
Radiation Fog which is created in calm weather and is also called &#8220;ground fog&#8221; formed when moist air nears a cold surface and chilled to the dew point. It is usually seen over land and almost never occurs at sea. Radiation fog diminishes when the sun comes up and warms the air to the point of absorbing moisture. Winds can also blow the fog away. 
Another view of Radiation Fog, forms when the night sky is clear and low, wet areas cool by radiational cooling.
Gentle mixing is required so that wind of 3-5 knots is usually associated with Radiation Fog.
Radiation Fog will be dissipated by daytime warming of the ground that warms the air through conduction and mixing to re-evaporate the fog.

The most significant fog to the mariner is Advection Fog. This forms when warm moist air flows over a cooler surface. This happens frequently along coastlines and is also referred to as coastal fog. This is a frequent type of fog on the Great lakes and the North Atlantic. Advection means movement. The cooler surface over which the warm moist air moves can be land, or a cooler body of water. The fog banks that occur where the warm moist air from the Gulf Stream encounter the cold water of the Labrador Current is an example of Advection Fog. Wind of 4 to15 knots is required to get the warm moist air moving. Advection Fog will only be dissipated by a change in wind direction, not by the warming of the Sun. Advection fog can sneej up on you before you know it and there you are out on Lake erie and cant see the front of the boat or anything, it normally lasts a long time...all night.
Sea Smoke is a form of Advection fog. 

A rare type of fog which is also of a short period of time is Rain Fog and is where a cold rain falls through warm air. When the mariner encounters this type, it is best to anchor or wait it out.  This is Precipitation Fog and forms when rain from warm air ahead of a warm front falls through a cold air wedge at the earth&#8217;s surface. Stable cold air is saturated by the evaporation from the warm rain. No wind is required for this type of fog. Precipitation fog will dissipate when the front passes.

Humidity is best described as the amount of water vapor that the air contains. It is often referred to in forecasting as relative humidity which means the percentage of moisture in the air. The percentage of moisture or water vapor that the air can hold such, as fog, rain or clouds, etc. varies with temperature. As temperature is reduced and it gets colder, the air is less capable of holding moisture, and thus relative humidity increases.
Another take on Humidity and Condensation--Dew Point
Air holds water vapor (the gaseous form of water) like a sponge holds liquid water. When air holds all that it can hold 100% relative humidity&#8212;any excess will be forced out as liquid water. Humidity is measured using a hygrometer or Sling Psychrometer. The amount of water vapor that air can hold is temperature dependent. As air cools, the amount of water vapor that air can hold decreases. An example of this phenomenon is demonstrated when moist air comes in contact with a container holding a cold drink. As the air is cooled at the drink container surface, condensation droplets form on the surface. The temperature at which these droplets appear is known as the dew point This is what happens when warm humid air cools and the excess water vapor is squeezed out. The tiny water droplets can cling to a surface and form dew. They can also be suspended in air as fog. Dew point spread is the difference between the present temperature in an air mass and the dew point for the-humidity present in the air.

Wind is caused by the movement of air from a high pressure area to a low pressure area. When a high or low pressure system move through a region it is obvious that the wind changes direction. A wind which changes and shifts in a clockwise direction is called a veering wind. When the wind changes direction in a counterclockwise direction, it is called a backing wind.
To assist the Captain to evaluate all types of wind and weather conditions, coastal displays are established at Coast Guard Stations and some significant harbor stations to show day time flags and lights to illustrate winds and weather. The succeeding pic shows the National Weather Service Coastal Warning displays.










One of the very useful instruments available to the amateur weatherman and very valuable to the mariner is the barometer. Approaching frontal systems can be predicted by measuring air pressure with either a mercurial or the popular aneroid barometer. Predictions of weather is made possible only by the analysis of the size, shape and motions of air masses. It must be accomplished by continuous barometric readings throughout the course of the day. A singular reading will only indicate the barometric pressure at any one time. It is not necessary to have an expensive barometer. The K-Mart /Walmart variety is very adequate for the Captain to place on an outside wall of the vessel. Again it is useless, unless observed regularly.
The mercurial barometer indicates air pressure by the height of a column of mercury in a tube of glass, with standard atmospheric pressure being 29.92 inches of mercury. It is also expressed as 1013 millibars. A glass tube of mercury is not very convenient on board a boat.
The aneroid barometer can be read using the outside scale to read pressure in inches and the inside scale to read millibars. It is small, portable and not affected by the motion of the vessel. The manner of reading the aneroid is to set the movable needle known as the keeper with the initial reading of the barometer&#8217;s indicating hand. As the indicating hand changes with pressure, the keeper serves as the reference point from which the indicating hand has moved from it&#8217;s reference point and measures the amount and direction of change. The emphasis again is not only on change but the rate of change and it&#8217;s direction. If the barometer [pressure] drops sharply and rapidly terrible weather is not only predicted but imminent. Again it is incumbent and necessary for the knowledgeable Captain to take action for safety of passengers and vessel. 







*


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## Fishers of Men

I just didn't get there yet Tom. If you want to post it, go ahead. It will give my eyeballs a break! Then i'll go to how they work and loran then radar.
Thanks


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## Fishers of Men

ezbite said:


> i know alot of gps units have a "man overboard" button. i like to make sure everyone onboard knows where it at. if your doesn't instruct everyone how to enter a waypoint. you might have covered this and i missed it.


Well that story about Joe flyin out of the boat, it wouldn't have helped because the other guy didn't holler "man overboard" and didn/t really say anything for a while, I was a mile and a half up the river before I knew it. 
If someone hollers man overboard, you should push your MOB button right away so that when you turn around the way point to your last known position is marked. It is very easy:

Creating a Man Over Board (MOB) Route
The MOB route is useful when you want to instantly
create and activate a route to the last computed
position.

MOB way points will be created and titled MOB001,
MOB002 and so on. If a MOB already exists, the receiver
will give you the option of replacing the MOB.
Most unit work basically the same:
ENTER
While in MOB
screen MENU
Select
CLEAR MOB
MENU
Select
ROUTES ENTER MENU
Select
BACKTRACK
ENTER
GOTO Select

MOB ENTER
To clear a MOB. The CLEAR MOB function allows you to
delete an active MOB route.

We will get into some information on how these things work and benefit us but not so much user detail, READ your manual because there are variations between brands/models.


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## Fishers of Men

I know most fishermen on this site have smaller boats without radar capabilities but there are probably some others with a arch or hardtop that have a way to install radar. 

*I am briefly going to touch on it right now, it&#8217;s a good read for all. 
With all due respect for our other charter captains out there, besides myself, I WONT tell you how to snipe another persons fishing spot with this technology.  (Probably going to get feed for even mentioning it!) As a charter goes and you are providing the professional service to your clients you don&#8217;t need to be invaded. The crew is paying for the treatment they are receiving. Please take the time to study the diagrams and follow along. Meanwhile, enjoy the post.
*
The navigational aid *Radar *will only reach so far because of the curvature of the earth. I showed that in a previous "sight distances" post. It depends on the height of the vessel and the angle the radar is mounted for maximum efficiency. So if you put a 72 mile radar on a smaller craft, it does you no good. I have a 16 mile on mine and wish it was a 24 or a 36 but for now thats what I have. I watch the weather coming across the lake on it and figure out if I want to stay and fish thru it, leave, go around the front, how fast it is moving and so on. They are very handy for avoiding collision, restricted visability, plotting, knowing distances, spotting other vessels and much more.










*Bearing: *As the radio energy has been transmitted in a narrow directional beam controlled by the rotation of the scanner, and as the sweeping electron beam of the tube is synchronized with the same rotation, the reflected images appear on the screen at their actual bearing from the ship.
As in Figs. 1318b and 1318c, an azimuth scale surrounds the scope. A heading marker indicates the course of the ship. Sighting lines, ex tending from the center to the azimuth scale, can be directed toward any image and its bearing then read on the azimuth circle.

Some sets provide a choice of true or relative bearing presentation. If the switch is set at TRUE, the heading marker will appear on the ship&#8217;s true course, and true North will appear at the top of the scope (O on the circle), the picture being oriented by the gyro compass. All other bearings will be read from the azimuth scale as true bearings.

*When turned to REL, the heading marker of the ship points to 0&#176;, and &#8220;dead ahead&#8221; will always be at the top of the scope. All other bearings will be relative to the ship&#8217;s heading. (Are we all clear on "relative bearings?)
*









The pattern on Fig. 1318b presents the true bearing position. The heading marker shows the ship&#8217;s course of 169&#176; as it leaves the harbor. One of the adjustable sighting lines is directed toward Hoffman Island, showing a true bearing of 198&#176; (or 029&#176; to the right of the ship&#8217;s heading).

The pattern on Fig. 1318c presents the relative bearing position. The heading marker points to 0&#176; at the top of the scope, or *&#8220;dead ahead.&#8221; *The sighting line toward Hoffman Island shows a relative bearing of 029&#176; to the right of the ship&#8217;s heading.










*Range* is determined by measuring the distance from the center of the scope to the particular image of the reflecting object. The concentric range marker circles appear on the scope at definite known intervals, representing specific ranges. A comparison of the position of the image to the range circles approximates its range.

Radar sets provide a selection of over-all range scales. Since all range scales use the same effective viewing area on the scope, the shorter the range scale selected the larger each image will appear, with resulting improvement in definition. A typical set provides a selection of 1, 2, 6, 15, and 30-mile over-all range scales. Choice depends on the requirements of the navigator, for clarity or distance. The space between the fixed range marker circles on such a radar would be &#189; mile for the 1 and 2-mile ranges, 2 miles for the 6-mile range, and 5 miles for the 15 and 30-mile ranges.

Look at Figs. 1318a and 1318b. From the chart of The Narrows locate the image of Hoffman Island on the radar pattern. Estimate the range of Hoffman Island from the ship. The instrument in this Figure was set for an over-all range of 2 miles, and the distance between marker circles is &#189; mile. Hoffman Island is seen to be about 15 miles away from the ship.

On some radars a variable range marker circle measures ranges with more accuracy than can be estimated from the fixed range circles. The variable circle can be manually changed in radius to intersect any target image for which range is to be measured. This range measurement is read from a meter on the instrument panel, showing the distance in miles and tenths of miles. Figs. 1318b and 1318c show the variable range marker line touching the image of Hoffman Island.

Radar scope *interpretation* requires considerable training and practice. The operator must know how to use the controls, varying in type and arrangement with each make of instrument, in *such a way as to obtain a clear pattern on the scope under varying conditions of weather and sea.* He must select the most practical scale for his requirements as well as the true or relative pattern presentation.

*He must become familiar* with the capabilities of the particular radar he uses, such as its minimum and maximum ranges, also the distances indicated between the fixed range marker circles of his set, at each over all range setting. *The obstruction* of his ship&#8217;s own mast or stack in the path of the transmitted energy will reduce the maximum range or may entirely obscure small targets in that particular direction.

*The operator must understand the general limitations of radar.* A high shore line or large reflecting object will prevent the radar beam from traveling further in that direction and will create a shadow obscuring the area beyond it. A low coastline with hills in the immediate background may only present the reflection of the hills on the scope, and give a false impression of the distance off shore. The echo from a ship near shore may be masked out by the larger and stronger echo from the shore line itself. Vessels or other objects located on the same bearing, or at the same distance from the antenna, may appear on the screen as only one echo, if the reflecting objects are close together. Choppy seas. may cause sufficient interference to obscure some targets. Several other conditions can exist where reflections may cause false echoes to appear on the scope.

*Radar fixes* can be obtained when the bearing and range of one or more objects, having known fixed positions, is determined from the pattern on the radar scope. You can look at your chart and find water towers, radio towers, high rises and such then identify them on the radar, see the distances off and acquire a fix on your position.

Piloting, which we will cover shortly discusses plotting fixes from cross bearings, as well as bearing and distance, of fixed known objects.

Radar plotting. To utilize fully the great potentialities of radar, a plot of successive ranges and bearings is required. 

A GPS is only one of many navigational aids, a mariner should have as many as possible. Remember the chart, keep a up to date one on board whether you think you need it or not. If you lose your satellite positions or that GPS dies on you for some reason, then what?


----------



## Fishers of Men

*PILOTING *
This part uses terms we have spoke of and should clarify any questions on 
bearings, fixes, DR, LOP, and introduce some new terms and procedures. This concentrates on *in site of land* so dont over look this post. There is a demonstration at the end of the next post, I have to put this in two because of so many attachments.

*METHODS discussed* in this section are those used to conduct a ship or boat in strange waters along any coast and when within or near the land. The principles apply in all cases, but with different classes of vessels and under differing circumstances their practice may vary widely. The work is generally more difficult on sailing vessels, often of lesser draft and close in on a dangerous coast, but a relatively fast deep-draft ship may face problems seldom met with by smaller craft. Even on large ships practice differs. The following sections are arranged to give a general knowledge of the subject to be applied as experience dictates.
*Terms. *
Dr. Worth, a distinguished English yachtsman, described piloting as plotting everything on the chart and taking every opportunity of verifying the positions thus found. *An experienced navigator may not* record as many details in the log book and on the chart as should the beginner, but in any case the record must serve *to plot the position of the ship at any time.*

*A line of position*, however determined, is a series of possible positions of the ship/boat. It may be a straight line or a circle and should be considered as a series of points some one of which, not yet identified, is the ships position. Every mariner uses lines of position although the term may be unknown to him.

*A fix *is an accurately known point which marks the ships/boats position at a given time. It is generally determined by the intersection of two lines of position. By definition, the ship could be on each line and therefore is *probably* at the point where they intersect. A fix is not always available, but, as circumstances permit, may be had by one or another theoretically correct method. The navigator must keep in mind the possible magnitude and direction of errors in the fix due to inaccurate observations or instruments.

(Most of the time, you will not be where you think you are.)

*The dead reckoning position*, as the term is here used, is the position found by plotting courses steered and distances run *from the last fix* or other well determined position. Such a position should be regarded as *inaccurate*, for reasons presently developed. When two lines of position give a fix,* plotting the D.R. is started new from that point.*

*The course line* (Rumb line) is drawn in the direction of the course steered or to be steered, positions thereon being corrected, when necessary, for current and leeway. Sometimes the course is so drawn as to *compensate* for these errors. The direction of the desired course may be determined in two ways:
(1) For a power vessel or sailing craft that can lay the course, mark the ships position on the chart. From that point draw a line to the point toward which it is desired to steer. With parallel rulers determine the direction of this line from a compass rose. When read from the 360° rose, it *must be corrected* to a compass course by applying variation and deviation, each in the opposite direction of its sign. *Only deviation need be applied if the course is from the magnetic rose.*
(2) A sailing vessel close-hauled on the wind sails the best course possible under the circumstances. This course is plotted either in the direction steered or in that believed made good. Such a course *must be corrected* to magnetic or true before plotting.

The D.R. at any time may be plotted on the course line by laying off the distance from the point of departure. The D.R*. must be plotted whenever the course is changed *and a new course line must be drawn from the D.R. at that time. Because of its *uncertainties,* it is not customary to regard the course line as a line of position, but in thick weather, without radio bearings, it is the only line available.

*The estimated position* is the point which represents the navigators best judgment of the ships position at a given time,* no fix being available.* It is found by applying corrections for tidal or ocean current, leeway, etc., to a D.R. position. The term is peculiar to Navy teaching. Many mariners call such a position the Corr. D.R. or simply the D.R.

Before going further, the subject of plotting should have attention. The habit of accurate plotting,* neatly labeled in a consistent manner*, is not only of value to the pilot, but is an essential of present-day celestial navigation. To avoid repetition in various posts, plotting, labels and lettering have been discussed. Study this discussion now, as a part of this chapter.

*Graphic methods.* The following sections deal with the simpler methods of checking or fixing a ships position when near the coast. Landmarks on the drawings are lighthouses. Any mark identifiable on the chart may be used, such as water towers, spires, beacons, bold head lands, or light vessels and buoys. A Coast Guard station is useful provided it can be identified with certainty. This is sometimes difficult, as, for example, along the south shore of Long Island where a dozen or more stations are strung along the low lying beach. Tangents to the left and right sides (or ends) of an island often provide useful bearings. Bearings of radio stations obtained by a radio direction finder serve the same purpose as other bearings.

*Ranges.* When two fixed objects appear in line, one beyond the other, the ship must lie somewhere on the line of sight, or range line, which passes through both objects. If the marks observed can be identified and are shown on the chart,* a line drawn through the two objects gives a line of position.*

Such lines are especially *reliable*, because observing when the ship is on the line involves neither taking compass bearings nor any possible compass errors. A range line may be had from lights, beacons, towers, bold headlands, and buoys. Two ranges are seldom available at the same time, but a single range line *may be crossed with any other line of position for a fix*. Two marks often are placed to guide vessels through important channels. In Fig. 903 the line across the red light to the higher green light on the Brooklyn shore gives a range along the center of the deep water channel from the Hudson River to the East River.










*Bearings of fixed known objects* are the most common source of lines of position when on the coast. If the direction of a light be observed, the ship must be at some point on the line drawn through the light in the observed direction. *A single bearing line does not give a fix* but often gives valuable information which, in the case illustrated by Fig. 904, serves principally to correct the run.

*Bearings measured by a magnetic compass* either by sighting across the compass or with the aid of a pelorus, when corrected for deviation, may be plotted by the magnetic rose on the chart. Magnetic bearings are sometimes stated in quarter points. (I will give points of the compass later.) When so expressed in a Coast Pilot or in other publications, consider the bearing as magnetic unless otherwise stated.










*A bearing by magnetic compass** when corrected* both for deviation and variation *is a true bearing *to be plotted by the 360° true rose. Bearings stated in terms of degrees in a Coast Pilot, on charts, or in a Light List *are true bearings* as are those observed by gyro compass.
*Unless otherwise noted all bearings are stated as from the sea.* For example, if a light bears northeast from the ship, its bearing is N E. although the ship lies southwest from the light. Bearings of radio beacons are also as from the ship.* However,* bearings transmitted in code from a radio direction-finder station ashore to a ship at sea, are as* from the shore station.*

*Cross bearings.* If two objects be observed at approximately *the same time,* the intersection of the resulting bearing lines gives a fix as in Fig. 905a. The* minimum error* in the position so found results from lines intersecting *at a right angle*. *Sixty degrees* is a good intersection, *but with 30°* or less, a slight error in either or both bearings *may cause a serious error in position.*










*Three bearing lines,* as in Fig. 905b, probably will not intersect in a point because the bearings are seldom exact, but whenever available a third bearing should be used as a check and the center of the resulting triangle used as a fix.










*Advancing a bearing line. *When bearings of two objects cannot be obtained simultaneously to cross for a fix, it is often possible to get a *running fix *from bearings of *two objects observed at different times*. In Fig. 906 a vessel from the eastward for Portland picks up Monhegan Light at 1:30 A.M. bearing NE 3/4 N magnetic or 190 true. The D.R. is brought up to a point on the bearing line and labeled 0130 Corr. D.R., the distance of this point from Monhegan being unknown. The ship continues its course until 3:10 A.M. when the bearing of Seguin is observed and plotted.










To find the ships position from the two bearings, consider the Monhegan line as a series of dots any one of which may have been the ships position at 1:30 A.M. If each of these points be advanced by course and distance from 1:30 A.M. to 3:10 A.M a new series of dots results which forms the line labeled 0130-0310 which is parallel to the 0130 line. In practice, only one point is advanced, the 0130-0310 line being drawn through the point so found parallel to the original line. Provided that course and distance used are exactly what has been made good over the ground, this advanced line *is as accurate *as its original and when crossed with the Seguin line gives what is known as a running fix.

*Advancing a line of position is useful * when near the coast and is a regular practice with navigators at sea, *especially when working with the sun.*

*Distance off.*
*If the distance from an object be determined, the ship must be somewhere on a circle of position as in Fig. 907a. *










If the bearing of the same object be observed, the intersection of its bearing line with the circle gives a fix, as in Fig. 907b. This is the geometry of defining a position by the eye. At a short distance off, such a procedure is generally sufficiently accurate. For example, position (1) in Fig. 1402 may be defined as 1 mile true south of Race Rock. *A circle of position is of little value* when far off a mark, unless the distance be determined accurately as by radar, or otherwise.

If the height of an object is known and the angle subtended by its height be measured with a sextant, the distance from the observer to the object may be taken from Bowditch (refer to Table 9). A small book by Captain Lecky, The Danger Angle and Off-Shore Distance Tables, presents a complete discussion of this subject.










*Two bearings of same object *give information *especially useful* *for determining distance off* at which a single light or landmark will be or has been passed. The process is to observe a bearing of the mark and at the same moment read the log. After running a convenient distance, take a second bearing and again read the log. If the first bearing line be advanced by course and distance over the bottom, its intersection with the second line gives a running fix, as in Fig. 908. A line through this point in the direction of the course is the ships track as it will pass or has passed this mark. The *effect of the procedure is to correct the distance off.*









*
Bow and beam bearings* This method for determining distance off *is known to all navigators.* It is a special case of two bearings of one object that gives the distance at which the mark is passed abeam *without plotting* or mathematical solution. In Fig. 909 observer notes when Shinnecock bears 4 points or 45° off the bow and reads the log.










When the light comes abeam, at 90° to the course, he again reads the log. The distance run between the two observations is the distance off the light. This is evident on inspection of the isosceles right triangle formed by the course and the two bearing lines.

Fig. 910. *Danger bearings* warn the navigator by a compass bearing when the course is leading into danger. Suppose a vessel to be steering 71° true, as in Fig. 910.










Let the navigator draw a line through Little Gull Light clear of the rocks and shoals north of Plum Island and between that island and Little Gull, and *note *its direction, *in this case 79°*. Then if frequent bearings of the light, taken as the ship proceeds toward the Race, *are greater* or to the right of 79°,* the ship is safe on the left side of the danger line*. *If, however, the bearing of the light is less than 79°, the ship is being drawn into trouble and the course must be altered at once. *
*Danger bearings are of greatest value* in cases similar to the above where, with only one mark visible nearly ahead, *it would be difficult to get precise positions if no radar is available. In any case, the method is more convenient than plotting several fixes.*

Continued next post.


----------



## Fishers of Men

Piloting continued from last post:

*Position by soundings.* A single depth sounding may indicate that the ship is in danger. Even on a clear day there is* no excuse* for not knowing the depth when in unfamiliar waters near the land or in narrow channels. It is an important safeguard against blunders with buoys, bearings, and tidal currents known only to local watermen.

A series of soundings at regular intervals may serve to provide useful information as to the ship&#8217;s position in a period of low visibility by chart comparison. These soundings are usually taken with the echo sounder if it is available. A lead and line can also be used and has the added advantage of bringing up a sample of the bottom which can be compared with the chart.
Advance the D.R. position along the course line on the chart for the run of the ship in regular intervals of, say, ten minutes depending upon the speed of the ship and the steepness of the bottom. Lay a strip of thin paper or tracing material over the course line, and with a pencil mark the D.R. position and the course line on the paper. At the times chosen for the advanced D.R. positions, obtain soundings and mark the depths and character of the bottom (if available) along the line.
Now, keeping the line on the paper parallel to the course line on the chart, move the paper over the chart until it is found that the series of soundings along the line agrees with the soundings at corresponding positions on the chart. Practical agreement between the tracing on the paper and the chart tends to confirm the D.R. Otherwise, it is probable that the ship is not on the D.R. line but is nearer to the position indicated by the tracing.
This method is most useful when approaching from off-soundings. I*t is dangerous over short distances in shoal water, *especially when the rise and fall of the tide is important, and also in unfrequented areas where the chart may not show all variations in depth.

*Plan in advance.* Experience shows that the more thorough the preparation, the less hazardous the passage. *Captain Dutton pointed out that the navigator, especially when piloting, deals not only with the present but with the future,* _( Actually this is the only time I know of that you deal with all 3, The present, being your decisions, will involve your future and the past!)_ and that preparation must be made in advance when at anchor. The navigator is always busy in pilot waters.

Courses should be laid out starting from the anchorage to some position favorable for fixing the point of departure from which to plot the D.R. From point plot the desired courses to destination and see that they run clear of danger. *Distances to be made good* on the various courses may be stepped off from the chart. Assume the time of departure, estimate the times of arrival at various positions, and consult the Tide Tables and the Tidal Current Tables. It is possible that the time of departure or proposed courses *should be reconsidered to avoid unfavorable conditions.*
*The general plan being determined,* first study every detail of the harbor chart. Note depths of water, lights, landmarks, ranges, bearings, and buoys to be passed. Go on deck and identify every mark or aid to navigation that can be seen from the anchorage, especially those you propose to use when leaving the harbor. Then consider the various marks by which the ship&#8217;s position may be checked or fixed after leaving port. Study the Light List and visualize not only the characteristics of the lights, but also the appearance of the lighthouses by day. These matters should be *studied with the greatest of care when about to traverse strange waters.*
Before setting forth see that the* essential instruments* and tools are available and in good order. The compass, or compasses, should be examined and their deviations should be known with reasonable accuracy. If in doubt, check the deviation card before leaving port or immediately thereafter. If the ship be so equipped, start the gyro compass four hours before sailing. When a portable pelorus is to be used, see that it is properly placed with its lubber&#8217;s line axis parallel to the keel. Have necessary charts and data at hand. A pilot&#8217;s notebook is convenient for recording courses, soundings, and bearings which later may be transcribed in the log book. Also check the radio direction finder and other equipment.

On a yacht (Or any boat) with a numerous Corinthian crew, it should be *definitely understood who is responsible for the piloting.* Others may assist but *what&#8217;s everybody&#8217;s business is nobody&#8217;s business, a condition which sooner or later will put the ship aground.*

Preliminary arrangements having been completed, note nearby buoys and landmarks, and have the 1 ready for action when the hook comes up.

*En route *
Preferably, even within harbor limits, *steer exact courses *taken from the chart. *This is not only good practice but serves to train the personnel in methods which must be used in thick weather.* (And a sign of your professionalism) In a narrow, buoyed channel, however, with transverse tidal currents, steer by the buoys unless there be a range line for the center of a straight channel. *If low visibility prevents taking bearings, courses should be laid from buoy to buoy*. In either of these situations, every buoy should be identified by its number and if there be any question of depths or position, soundings should be taken continuously. (looking at your chart and the #'s on the bouys will affirm your position)

Having left port and having attained sufficient offing, define the vessel&#8217;s position by the best available method. Mark this point of departure on the chart and label it with the time, stream the log, and record its reading and the time in the log book. Plot some miles of the course on the chart. Label this course line and record the course to steer. (If you have GPS, clear your track and start a new one)
Proceed and whenever the course is changed, note the time and read the log. On the course line, lay off the distance from point of departure and label this D.R. with the time. Draw the new course line and label it. In the log book, note time, log reading, distance from last reading, and new course.
Check the D.R. position frequently by the best means at hand. In clear weather, identification on the chart of every buoy, light, or land mark which can be seen gives a rough check at all times. *At night, particular care should be taken to identify every visible light. When you cannot see a light that should be seen, find out why.*

*A single line of position*, whether a range or a bearing, *serves to correct* the D.R. in the direction of a perpendicular from that point to the line. Well crossed lines of position give a fix which is use as a new point of departure from which to plot succeeding D.R. positions and thus carry on the reckoning to destination.
The student seeking to acquire skill as a pilot should spend all his spare time observing and plotting bearings. *An experienced man will take and record more bearings than he plots, but will not omit plotting a fix *sufficiently often to check the errors which may affect the D.R.

*Tidal currents,* within the general line of the coast where the rise and fall of the tide is material, differ not only in velocity and direction at each hour of the tide but also because of wind and weather and the varying flow of rivers into bays and harbors. Often only local fishermen can judge the effect of such currents. If the average direction and velocity of a current be known for the time elapsed between two D.R. positions, the second D.R. may be corrected by plotting the current effect as a course and distance there from. Or the course from the first D.R. may be adjusted in advance to provide for the expected set.
Current tables and tidal current charts give accurate information when the weather is normal. It is just when one is in some out of the way spot and the weather is anything but normal that exact information is needed. In such cases, *the navigator must use his wits and keep in mind the vagaries of tidal currents.*

*When approaching harbor, the look of the land seldom gives indication of the opening. * The ship&#8217;s position must be determined by a buoy identified by its number or some other fix. Then, with anchor cleared, steer predetermined courses and distances, watch the buoys, and keep the lead handy. *Entering a strange harbor is more difficult* than leaving a harbor where one has had time to look about while at anchor. Therefore, examine every detail of the harbor chart before making port. It is some times difficult to sense the change to the large scale of a harbor chart, which may be from four to twenty times that of the chart used outside, with the result that the *&#8220;next buoy comes quicker.&#8221;*

*Fog or loss of visibility *from snow or rain puts a coastwise navigator to *the supreme test *and requires precautions at sea that are all * too often neglected. It fills the most experienced seaman with uneasiness and may paralyze a beginner with unwarranted panic. * A timorous navigator, confronted with a dirty situation, should remember that centuries of mariners have found their way through fog to safety and that he can and must do likewise. It is in fog that the radio direction finder and other *electronic equipment pays off.* The reader may judge for himself what parts of the text apply to regular runs along the coast or to ships at sea.

*Fog may thicken gradually but it is more likely to approach as a low, gray bank of clouds which may blot out landmarks or other vessels before it envelops the ship. Sometimes foghorns are heard before the fog itself comes down, and at night the unexpected disappearance of previously visible lights may mean fog.*

If oncoming fog be suspected, *the first precaution* is to check or fix the vessel&#8217;s position by the best means available. This applies especially to yachtsmen who may be wandering about with no exact knowledge of where they are. Meanwhile, check the foghorn, have lead and line ready for action, and if anywhere near shoal water or the shore, clear an anchor. On a sailing yacht, consideration should be given to sending down such light sails as reduce ability to maneuver quickly.

*When in the fog, place the lookout or lookouts where they can both see and hear.* On a small vessel with one lookout, the best station may be a bit aft where *the sound of the bow wave interferes less with the hearing*. Sometimes a man at the masthead can both hear and see better than can those on deck. Cut out social chatter, sound the foghorn regularly, use the lead, keep the reckoning with the utmost care, and check it by any available radio bearings.

*At first opportunity* examine the chart for bell or whistle buoys that may be encountered and note the fog signals that may be heard from lighthouses or lightships. Mark on the chart their time characteristics, taken from the Light List, and have a stop watch handy. If with out a watch and unaccustomed to counting seconds, tie a string to a small weight such as the nut off a bolt. Hold the string between the fingers so that the center of the weight is 93/4 inches below the point of suspension. The pendulum will then beat seconds.
*Decision now must be made as to whether to continue the voyage,* seek a nearby harbor, or anchor. Circumstances may dictate the answer but, if a choice be possible, almost innumerable conditions must be weighed. *Fog involves grave risks and the safety of the ship must be the skipper&#8217;s first consideration. Forget questions of convenience or of economy, and remember that the anchor is part of the navigator&#8217;s equipment.*
Danger of collision in fog is always present. When the whistle or horn of a vessel is heard, try to judge its bearing. *If the bearings of successive blasts *seem to change, you will *probably pass in safety*. If no change takes place, *collision should be considered as imminent. *The *most dangerous situation* is that of a small craft with a weak-voiced foghorn, which is unheard or unheeded by a fast-moving steamer. Lacking a good steam or compressed-air whistle, *the best protection* is a motor-driven horn that will make even a noisy steamer take notice. Gun fire may serve in an emergency or lights flashed on a yacht&#8217;s sails may avoid a crash. *When possible, small craft should keep clear of steamer lanes. *One long and two short blasts indicate a tow; the barges and the hawsers between them *are a danger *to be guarded against. If no other vessels are heard, *do not let a false sense of security lead to a violation of the rules *which require sounding your foghorn at regular intervals. *So doing is a deliberate neglect of the safety of your ship and the lives she carries.* (Among serious court issues)

*Piloting in fog is a combination of careful dead reckoning,* a variety of more or less inexact tricks for estimating one&#8217;s position, and using the lead to keep out of trouble. When possible, it is better to *make short runs* from one buoy to another than to attempt long courses which offer less frequent checks. Make certain to identify each mark and observe any indications of current around it.










*The beginner who sometimes develops false ideas of direction when fearful of being lost, must learn to believe in his compass.* The compass points in one direction while the ship revolves about the card. The compass card does not turn as the ship swings its head on different courses. It is the ship that swings and not the card (Fig. 914). In fact, with a well-adjusted magnetic compass, the card is equivalent to a magnetic rose fixed on the chart at the ship&#8217;s position.

It is a good practice in fog near shoal water to take soundings at regular intervals even though the course is supposed to lead clear of danger. The transducer (sound generator and receiver) of an echo sounder is usually near the keel; hence, the actual depth of water is somewhat greater than the indicator reading. If the ship has almost no motion through the water; with the lead on bottom, the action of the lead line will indicate the current. Near shore or shoals, or when entering harbor, soundings must be taken continuously while the navigator watches the chart as depths are reported.

Locating the ship by soundings is another discussion, it involves constant readings, chart comparison to depth, bottom type i.e. sand, mud, rock and a lot of common sense.
*When seeking harbor in fog *on a difficult coast, select some outlying mark which, once found, will give an accurate point of departure for port. This may be a lightship, an island without surrounding reefs, or a bold headland which can be approached until one sees the loom of the cliffs or hears the breakers. (if you hear the breakers, your too close!)
Fog signals on or near lighthouses, which sound accurately timed blasts, and bells and whistles on buoys have been described.
7. Sound signals at light stations can be identified by their timing as given in the Light Lists and by the character of the sound. The irregular sounds from whistle, bell, and gong buoys operated by the action of the sea *do not *positively identify such buoys and sometimes a great whistle buoy to leeward *cannot be heard* until almost aboard.
*Signals through the air are uncertain,* therefore remember:
(1) Distance at which a signal may be heard varies.
(2) Do not judge distance by the power of the sound.
(3) Occasionally there are areas near a fog signal where it is in audible.
(4) Fog may exist nearby a station and not be seen by the keeper, so that the fog signal may not be put in operation.
(5) After fog has been observed there may be delay in starting a signal.
(6) Under certain atmospheric conditions, one tone of a two-tone signal may be inaudible.

Examples and problems combining the many details of piloting discussed in this and preceding posts require the use of one or more NOS charts, an appropriate Light List, and the necessary Tide and Tidal Current Tables. The nature of such problems and the details of their solution vary according to the draft of the vessel, the local experience of the master or pilot in charge, and the availability of radar and R.DY. equipment. If we do tides, I&#8217;ll post charts and how to read them and make corrections. I don&#8217;t have a light list. Maybe some one else does.

Follow the following on the chart, good example. 
http://i202.photobucket.com/albums/aa305/FishersofMen/915portlandharbor.png (a direct link so you can have another window.)

Consider the problem of entering the harbor of Portland, Maine. A strange vessel, from off shore, especially in fog, will first pick up Port land Lightship which lies about 8 miles S S E from Portland Head. The skipper of a craft of 10 feet draft, coming up from Cape Ann, will probably try for the whistle buoy on Willard Rock, which is buoy &#8220;7&#8221; at the lower right of Fig. 915.









From there he steers to clear Portland Head, warned by the sound of the breakers when close in. 
To Spring Point Ledge, weather thick, it is easy to follow the shore by sounding.
At night, in clear weather, the red sectors of Spring Point Ledge Light keep him out of trouble.
The pilot of a coastwise steamer, making Portland every other day, may also pick up Willard Rock. In such service it is common practice to keep a record of the course, as actually steered by the ship&#8217;s steering or gyro compass, which has proved correct for each leg of the trip under various tidal conditions. Such a pilot, with Willard Rock close on the port beam, gives the quartermaster 338&#176; but adds &#8220;and crack the light to port,&#8221; orders which will surely take the vessel into the deep water off Portland Head.
Navy teaching necessarily approaches the problem from a different point of view. *The navigator must be able* to take a large deep draft vessel into a strange harbor without the aid of a local pilot. The methods used are illustrated, in part, by the work plotted in Fig. 915.

The ship is for Portland on a course of 295&#176; true. Charts and the U. S Coast Pilot must be studied. Courses into the harbor are plotted and each leg is labeled with true course, compass course, and distance to run. The navigator also studies the lights, landmarks, ranges and buoys he proposes to use, and notes the tidal conditions.*

As the coast is approached, *assistants are placed at the bearing repeaters,* (each assistant has only one job to do, keep track of his assigned bearing) and the navigator takes over the plotting. Cross bearings give the ship&#8217;s position at (1), (2), and (3). Leadsmen are at their stations. Off buoy &#8220;2,&#8221; at, the south end of Cushing Island, the rudder is put over, and the ship is steadied on course 335&#176; with Spring Point Light in range with the flagstaff on the U. S. Marine Hospital, near Martin Point, at upper left of Fig. 915.
Off buoy S4 the course is changed to 351&#176; true, with the west end of Fort Georges dead ahead and Diamond Ledge Light about 5&#176; off the port bow. As Spring Point Light comes abeam, the position is checked by vertical danger angles of the light, to assure clearing a 29 foot spot to the eastward.
The anchorage area is clear, and it is decided to anchor about 900 yards north of buoy &#8220;3&#8221; off Portland Breakwater, between that buoy and buoy N4. *The proper approach* to the proposed anchorage is from the south against the ebbing tide. Allowing for distance from the stern to the bridge of the vessel, the position of the anchor is plotted so that the bridge will be on the range between Diamond Ledge Light and buoy &#8216;7&#8221; off Fish Point when letting go. As a guide to this position, the bearings of Diamond Ledge Light and Portland Breakwater Light from the proposed anchorage point are noted.
* We are indebted to Capt. Theo. Nelson, U.S.N.R., for the details of this problem. Aids to navigation shown in Fig. 915 are illustrative only and may not conform to the current Light List.
When Spring Point Light is broad on the quarter, the ship is put on 308&#176; true toward buoy &#8220;C&#8221; until it is swung to the right on the range between buoys &#8220;3&#8221; and N4. Speed having been reduced, the anchor is let go when on the predetermined bearings of Diamond Ledge and Portland Breakwater.

*Piloting with radar. *
While the availability of radar has greatly eased the burden of the pilot, it has not invalidated the principles of navigation discussed in this chapter; it has *simply increased their importance.* As already described radar provides bearing and distance of prominent objects from the ship. This is the language of piloting, and information derived from radar is applied in the same manner as other piloting information. A radar bearing gives the direction of a line of position, and a radar range is the distance along that line as shown in Fig. 907b. *With radar, the pilot obtains directly a succession of fixes without having to derive each fix by the manipulation of lines of position.* The principles are the same, but the emphasis is changed.

Practice! 
Knowledge of all the matters discussed in this and preceding posts is not sufficient to make a navigator competent as a coastwise pilot or to keep the reckoning when at sea. *The beginner should navigate by rule and not sail by the look of the land.* Then, whenever he can check his position, he may think out for himself the probable reason or reasons for the error therein, and *learn to guard against similar errors when in thick weather.* Exact practice is the only way to develop the necessary skill and judgment whereby to cope with difficult conditions when they arise.

*WHERE AM I???*


----------



## Fishers of Men

*Errors in the D.R.* 
The difference between a fix and the dead reckoning position at the time of the fix is the error of the D.R. called current. *The term is misleading because the error may have been caused by anything but current.*
When determined as in the preceding section a D.R. position may be in error because of:
(1)	Error in point of departure	(4)	Errors in distance
(2)	Deviation errors (5)	Leeway
(3)	Bad steering (6)	Current

The navigator *cannot estimate the effect of the first three possibilities.* Errors in distance plotted may be due to errors of the patent log readings (When distance is predicated on engine revolutions, *a foul bottom *or a list of a few degrees may cause errors. Proper allowance for these errors in distance may be made after a few days experience with the ship/boat. Estimating the effect either of leeway or of currents that may move the ship hither and yon is more difficult.

The error called current as defined above is *the error accumulated during the time interval between fixes.* The set of this &#8220;current&#8221; is the direction toward which it alters the ship&#8217;s position, i.e. from the D.R. toward the fix. Its drift is its velocity in knots, i.e. the error of the D.R. in miles divided by the interval between fixes in hours. *Where am I?*

After a fix, it is seldom safe to assume that the &#8220;current&#8221; just determined will continue until the next fix. If such an assumption *leads the ship into danger,* it must be considered, but ordinarily it is not taken into account in future plotting.
*Leeway* is the leeward drift of the ship due to the pressure of the wind and the heave of the sea. It is not a fixed quantity but varies with the wind and sea and with the ship. Leeway, if any,* is measured by the angle *between the course steered and the direction made good through the water. If the wind is on the left, the ship will be set to the right of the course. Correction for estimated leeway to the right may be made by applying it as an easterly compass error. If the wind is on the right, the set will be to the left and leeway may be applied as a westerly compass error. 

Or the drift estimated to have taken place may be applied as a course and distance. _We all go through this every time we go out, and make these corrections, that&#8217;s why your &#8220;trail&#8221; through the water is not and cannot be straight._

*Estimating leeway is more difficult than applying the correction. * 

A ship driving straight into wind and sea or with wind dead aft makes no leeway; wind abeam normally causes maximum leeway. A long, low, deep-laden ship will drift to leeward less than will a short, shallow craft. A *motor boat may slip off like a balloon. *The angle between the ship&#8217;s wake or the log line and the line of the keel indicates the leeway, but in wild water and at slow speed such indications are of little value.
_These are things to think about when purchasing a craft for the waters you will be navigating mainly&#8230;Lake Erie, reservoirs, rivers and such._

*There are no rules for computing leeway.* When conditions permit accurate observations, the navigator should observe the drift of his particular ship/boat under various circumstances. He can then estimate leeway with *reasonable accuracy* during long periods of dead reckoning.

Dr. Worth, a cruising sailor man of rare judgment, considered that a yacht in ordinary weather will make little or no leeway unless the wind is well forward of the beam. Also that, when close-hauled in smooth water, the leeway will probably not exceed a quarter point. To windward under short canvas in rough weather, the leeway will be much greater. If a yachtsman fails to find any leeway when it might be expected, it is because the ship goes to windward in the puffs and because of the natural tendency of the helmsman to point high of the course when he can.

Ocean currents, clear of the land, flow continuously in more or less the same direction in contrast to the reversing characteristic of tidal currents. The principal causes of ocean currents are two fold, (1) the wind and (2) the tendency of heavier cold water to flow toward the lighter warm water of the equatorial areas.* Of these two causes, the wind predominates.* The direction of a current is that toward which it flows and is termed the set of the current. *Its speed is the drift of the current.*
Given its set and drift during an interval of time, the effect of an ocean current may be plotted as a course and distance from the D.R. to the estimated position. Or it may be plotted in advance and the navigator may adjust his course to meet the current effect. All this is simple enough if the average set and drift are known, a situation seldom encountered in strange waters, especially when near the land.

We have our contour lines as shown on the Lake Erie charts and the bathymetry we covered causing different currents in Lake Erie and the water flowing toward Niagra and the winds which create a different current. The perch fishermen notice this when they move and anchor, either the bait is straight down or to the side. And the experienced fishermen keep track of these areas and the depth, productivity rate, size, times, weather, dates, water clarity and such for future knowledge.

These same areas when trolling dipsey divers can make you productive or not. It depends if you recognize whats happening and control your baits accordingly. A lot of people get tangles trying to make a turn in these current areas. Learn how to "read" the water. And those with only a boat speedometer, you may not be going anywhere and it says 3 mph. The current will give you an inaccurate speed. It must be taken by SOG (speed over ground with the GPS to maintain bait and boat control. Other than dipseys, the same applies to the boards, down riggers, outriggers, kites, what ever. IT'S called controlled depth fishing. (whole 'nuther subject)

The following example illustrates a situation but ocean currents are another whole topic in it's self.

The velocity or drift varies with the wind and with some currents it varies greatly, according to the season of the year. Often, when far at sea, the direction and velocity of a current along its axis or center may be estimated with some accuracy. Observe, however, that the proper allowance for drift when crossing a current is less than its velocity along its axis. For example, as the Gulf Stream flows through the Straits of Florida _(picture a river running in the middle of the Ocean)_ its velocity near the middle of the stream may be almost 4 knots, but the average drift to be allowed when crossing the Straits at that point is little more than 2 knots. *(can be 12 or 14 knots during a full moon)*
The flow of an ocean current cannot be observed by the eye except as it may change the character of the sea, _(the Gulf stream will change the characteristics, and will be seen by eye. I have seen it flowing feet above the Ocean height and it is most definitely rougher out there and crossing the stream has to be well planned, the current picks up as tides flow out to it and depending what part you are going to cross it could be 8 to 14 miles and changes constantly.) _
but its motions are not unlike the motions of the water in a river. On the straight reaches of a river the fastest water runs down the center, but on a curve the velocity is greatest along the outer shore of the curve. There may be a reverse current on the inside of the curve, and an eddy in a reverse direction is almost certain to be found in a cove. Below a rock there is a quiet spot where the big fish lie. The velocity of the current increases as the river narrows, but is hardly to be observed in the wide quiet reaches below some wild rapid.

When influenced by the land and possibly combined with coastwise tidal currents, both the set and drift of any current are most uncertain. Or a countercurrent at one side or the other of the principal current may be encountered. When dealing with such conditions the navigator plotting his D.R. by courses steered and distances run through the water *must take special precautions.* Plot broken lines to represent your best estimate of the movements of the ship over the bottom and proceed on the assumption that the ship is in the estimated position of the greatest dangers.

The ocean currents of the world are exceptionally well described in Bowditch. Specific information, essential for navigating the ship, may be had from a number of sources. Many charts show the set and drift of currents. Pilot Charts are often the most valuable because they are published for various seasons of the year. All Coast Pilots, and the Sailing Directions (Pilots) for foreign waters give information about currents, and the Tidal Current Tables include valuable chapters on the ocean currents touching the shores of the United States.

The sailings (we covered some of this in current sailing. I&#8217;ll keep this short for general knowledge if you feel you want to pursue this.) are the mathematical methods formerly used by all navigators for keeping the reckoning at sea. *They are used to compute the changes in the dead reckoning position *resulting from courses and distances sailed. Some of these methods continue to be used in the Merchant Marine. 
Traverse Tables, like Bowditch&#8217;s Table 3, are the tables generally used when working the sailings by inspection. They are the tabulated solution for any right triangle like the one formed by the rhumb line, a meridian, and a parallel. Bowditch&#8217;s Table 5, which gives the increase of the latitude scale on a Mercator chart, is also used.

The sailings as commonly listed include five methods, *all dealing with *rhumb line courses. The general problem is, given the course and distance, to find the change in latitude and the change in longitude. Or any two of these four quantities may be given to find the other two.
(1) Plane sailing is nothing more than the solution of a right triangle taken by inspection.
(2) Traverse sailing. This is a relic of the days of sail. A traverse is an irregular track made by a vessel on several different courses. Working a traverse means to combine the results of the various legs of the track so that a single solution by plane sailing gives the answer.
(3) Parallel sailing applies when the course is E or W, i.e. on a parallel of latitude. Miles may be converted into longitude by inspection of Bowditch&#8217;s Table 3.
(4) Middle latitude sailing. When sailing between two points of different latitude, the mean of the latitudes is determined. With this middle latitude substituted for the single latitude, the solution is identical with that of parallel sailing.
(5)* Mercator sailing.* _(what we are involved in and do) _Used principally to find the course and distances between two points on a Mercator chart by taking into account the expansion of the latitude scale which is characteristic of such charts. The method is important in high latitudes or when the differences in latitude and longitude are so large that neither of the preceding methods is sufficiently exact. For this method a table of Meridional Parts or Increased Latitudes like Bowditch&#8217;s Table 5 must be at hand, and Table 3 is required for solutions by inspection.
*Great circle sailing,* in practice, is composite sailing carried on graphically. However, the simplest way for a celestial navigator to find the total great circle distance between two points is to compute it. On a ship/boat with a sonic depth finder or a Kelvin sounding machine, *depth of water generally gives definite warning of approaching land before any lights or landmarks can be seen.* Sometimes a hundred- fathom lead will serve to warn a yacht navigator. Even so, review the possible errors in your position, the character of the coast and its currents, and the weather conditions. *If the weather be thick, hesitate to attempt a dangerous landfall until the weather clears.*
*The young navigator, seeking to develop his judgment in these matters, must study the sea itself. So to do, determine with care your estimate of the ship&#8217;s position at the time of every fix. Then consider the possible reasons for the error in the E.P. so found.
*


----------



## Fishers of Men

*PLOTTING HINTS*
Plotting Hints...Navigation by Chart and Problem Data
Locations/Fixes...may be one of or combination of
 LAT/LONG, LORAN-C or Range(s) and/or Bearing(s) to known object(s).
 If by three bearings...may get cocked hat; assume position in center of the triangle.
 Bearings to Stbd or Port beam 90° relative or 270°, respectively.
Unless the problem dictates you do otherwise
 Headings, bearings	Use TRUE degrees
 Distances	Are in NAUTICAL miles
 Speeds	Are KNOTS (nautical miles per hour)
 Time	HOURS/MINUTES (take care in additions/subtractions)
Relationships between Speed. Distance and Elapsed Time
Memory Relationship	Distance=Speed X Time	D/ S X T
Speed= Distance/Time	S = D/T
Time= Distance/Speed	T = D/S
Develop Plotting Disciplines
 Use a fine line, sharp pencil for plotting on chart;
 Indicate Fix by circle, DR and EP by half circle with 24 hour times
 Indicate directions of bearings, headings, sets by line with arrow head for direction; always put your abbreviations properly above and below the course line. See the examples.
 Use appropriate abbreviations (see below);
 Exercise care in walking headings or bearings from the compass rose and measuring distances with dividers. Slight miscues can mean trouble!
Measuring Distances
 Always on the VERTICAL scale of the chart, i.e., between parallels of latitude.
Typical Abbreviations for use on the chart plot
 FIX known location PTA Point to Aim	 DR Dead Reckoned Pos.
 C Course or Heading CTS Course To Steer  EP Estimated Pos.
 S Speed thru water ETA Est. Time of Arrival  PSC Per Ships (or std.) Compass
 CMG Course Made Good SMG Speed Made Good
Compass Corrections
 Deviations can change with vessels heading... take note if the problem alters deviation with different headings (normally with multiple leg problems only);
 if necessary, make corrections with: TVMDC ÷ W (fall down) after completing problem.
Speeds / Direction
 RPM or Prop Speeds are speeds of vessel thru water not SMG;
 Set/Drift... Direction/Speed vessel is carried due to water currents. (* make sure you understand the nature of the vessel speed given.)
Ships Movement... Resultant of several effects
 Vessels propulsion system (oars, sails, engines, etc.,); PLUS
 Water currents. i.e., a set (direction) at a drift (current speed) ; PLUS
 Wind effects known as leeway; (normally NOT taken into account) but if problem requires, it will typically be given as westerly (or easterly) leeway degrees; simply add (or subtract) to compass corrections as with westerly (or easterly) deviations.


----------



## Fishers of Men

I found this while cleaning out my e-mail.
Here's a chart of some reefs by the islands, made by and thanks to our good friend Exexec who passed away last summer. John had bought the software from: (shoot, I just looked because he said it cost him about 99$ a few years ago, must have went down, it's only 49 bucks for the software)

http://www.lakemap.com/

I'll give a direct link so maybe it can be copied. you should be able to zoom it.
http://i202.photobucket.com/albums/aa305/FishersofMen/islandreefs.png










If you really zoom in, it shows some nice spots for this spring.


----------



## Fishers of Men

*More depth on Compass points and degrees*

*It all started *with the Babylonians who, for reasons which may have looked good to them, used mathematics based on the number 12. This may sound pretty clumsy to us, but it actually seems not so awkward in practice (no doubt you get used to it after a while).

Anyway, as these guys were the first astronomers worth the name, this explains why our days are 2 times 12 hours long; and also why the earth is divided by 2 x 180 degree meridians. It's a fair guess it also may have to do with the fact that it's easy to construct angles of 30, 60, 45 and 90 degrees and bisect them; but nobody has been able to construct a 100 degree angle. Which again may have influenced their, then after all not so odd, base 12 choice. And vice versa. I'll freely admit getting confused when having to figure in radians, not degrees.

*This is the measuring system* that will hold its own longest versus metric. For example, 1 nautical mile at the equator equals 1 minute on the map; rather easy, except that, when you're navigating. Anyway, a year inconveniently does have 365.25 days; while the moon, embarrassingly, *insists *on turning round the earth more than 12 times a year, wreaking havoc on tide tables.

*Now for the compass rose.* 

It points North after a not even very old convention; in building and civil engineering drawings it's still quite usual to find it pointing away in any old direction, as long as it fits the paper. The rose points North because a magnetic needle points there; figures. The rose is then divided in 4 quarters (North, East, South, West - we're talking clockwise, (Cardinal compass) these are bisected again (NE, SE, SW, NW).










Remember this?
Cardinal bouyage system:










Further, *we do not have* sections of 30 degrees, but of 45/2=22.5 degrees. These are called NNE, ENE etc. And finally, these are bisected once again, and all those resulting marks at 11.25 degrees are the so-called *"compass points"*. 

Still later, *when the efficiency of sail ships improved, they used "half-points" *but, wisely, refrained from giving them names.

*Compass Degree Headings*










These are given by specifying a compass point (north, south, east, or west), a number of degrees, and then another compass point. For example, N23E is a heading.

This picture shows examples of *various headings at ten degree intervals.* Any of the lines leaving the center of the diagram has its heading shown at the end of the line. Surveyors use this system today, and it can be as precise as the surveyor wants.

*Compass Point Headings.* In some parts of the country, the Compass Point system of headings was used. It used the 32 "points of the compass" shown in this compass rose diagram.










You've heard of North, and Northeast, and North-Northeast? Well, how about "North by East one quarter point North"? That, too, is a compass point. (In the diagram you'll see a small 'x' is used to represent the word 'by'.) In some areas the phrase "and by" was used to signify one half point, so, for example, "North and by East" meant "North one half point East.

With the needle pointing to 30 degrees, your ship, boat or bike is moving in the (360-30=) 330 degrees direction (where the needle points to: N).
To take a reading, adjust the graduated circle until 0 coincides with the needle, and there you are - or go.

To sum it all up: 
N	NbyE	NNE	NEbyN	NE	NEbyE	ENE	EbyN
0	11.25	22.5	33.75	45	56.25	67.5	78.75

E	EbyS	ESE	SEbyE	SE	SEbyE	SSE	SbyE
90	101.25	112.5	123.75	135	146.25	157.5	168.75

S	SbyW	SSW	SWbyS	SW	SWbyW	WSW	WbyS
180	191.25	202.5	213.75	225	236.25	247.5	258.75

W	WbyN	WNW	NWbyW	NW	NWbyN	NNW	NbyW
270	281.25	292.5	303.75	315	326.25	337.5	348.75


If you feel degrees are easier, so does everybody. They tell me it's as good as impossible to actually navigate a sailing ship with any greater accuracy than 1 point, which explains why it took to the end of the 18th century before compass roses with 360 degrees intersections came into use. A halfway decent DC-3 pilot took corrective action long before his aircraft had wandered off course for 5 degrees. Not that 1, 2 or 3 degrees made any difference, except for maybe? surveyors. If anyone can hold there vessel within these parameters I want to meet them, especially when we are considering that "currents" are involved!

Dig this quote from Ernest K. Gann's The High and the Mighty: The navigator of a DC-4 remarks: "Us amateurs don't really know the way to San Francisco. Now some experts might go so far as to pick forty-nine degrees for a course and get there eventually. But it just so happens I'm fifty-one years of age this month and I can't think of any other number."

*The compass rose was overlaid,* after the compass had come in use, *on the wind rose,* earlier developed in the Mediterranean by the Phoenicians. The wind rose points pointed in the general direction of *eight kinds of winds usual in that area.* It seems obvious that, to be of any use, navigators had to be able to distinguish between those winds somehow; at least, that's the story.

Humidity? Temperature? Mind boggling. Hard to believe. Maybe this is the solution: Their sailing ships, at night, navigated by the stars. It would be the most accurate solution available to keep steering, in daytime, *in the same direction relative to wind direction as at sunrise, for which a wind rose is a pretty good instrument.*

*The North star* being the *Only *accurate fix at night, you wonder how the old sailors even got anywhere let alone back home. Sure we have spoken of longitude sailing, they could go E and W and know about where they are, but what about the ocean currents changing their longitude all day?
They are N or S of where they think they are. Then get a fix at night and correct the course. Look at a globe and see how the currents are marked with arrows, they finally figured out to sail down the coast of Africa to somewhere, with the current and come back another way clean across the big pond on a different prevailing wind and current. These guys had some HUGE Balls. They also had a weighted length of rope that they threw overboard with knots equally spaced and timed it going out to know there speed. How would you like that full time job? So, guess where the term knots came from?

For those who wonder why it's called a rose: look at the way the flower's leaves intersect&#8212;or think of rosette, like of an agave plant.









Remember this?










*What is North?*
No, this is not a silly question, there are two types of north. 
*True North: *(also known as Geographic North or Map North - marked as N on a topographic map is the geographic north pole where all longitude lines meet. All maps are laid out with true north directly at the top. Unfortunately for the wilderness traveler, true north is not at the same point on the earth as the magnetic north Pole which is where your compass points.

*Magnetic North:* 
Think of the earth as a giant magnet (it is actually). The shape of the earth's magnetic field is roughly the same shape as the field of a bar magnet. However, the earth's magnetic field is inclined at about 11&#176; from the axis of rotation of the earth, so this means that the earth's magnetic pole doesn't correspond to the Geographic North Pole and because the earth's core is molten, *the magnetic field is always shifting slightly.* The red end of your compass needle is magnetized and wherever you are, the earth's magnetic field causes the needle to rotate until it lies in the same direction as the earth's magnetic field. This is magnetic north (marked as MN on a topographic map). The next pic shows the magnetic lines for the United States (as of 1985). If you locate yourself at any point in the U.S., your compass will orient itself parallel to the lines of magnetic force in that area.










*And this?*









*Declination*

You can see that location makes a *great deal of difference* in where the compass points. The angular difference between true north and magnetic north is known as the declination and is marked in degrees.
*Depending on where you are,* the angle between true north and magnetic north i*s different.* In the U.S., the *angle of declination varies* from about 20 degrees west in Maine to about 21 degrees east in Washington. The magnetic field lines of the earth are constantly changing, moving slowly westward (&#189; to 1 degree every five years). *This is why it is important to have a recent map/ chart* An old map will show a declination that is no longer accurate, and all your calculations using that declination angle *will be incorrect*. As you will see, understanding this distinction becomes important when navigating with a map or chart and a compass.

*TIP*
*Buy Your Compass for the Right Area:* As well as the magnetic deviation east or west, compasses also show a vertical *"dip" up and down. *This dip varies in different parts of the world and compasses are specially calibrated for that dip. *So you can't take a compass* made for North America and use it in South America *and get accurate readings.
*
compass point - any of 32 horizontal directions indicated on the card of a compass; "he checked the point on his compass" 
direction - the spatial relation between something and the course along which it points or moves; "he checked the direction and velocity of the wind"
cardinal compass point - one of the four main compass points
NbE, north by east - the compass point that is one point east (clockwise) of due north
NNE, nor'-nor'-east, north northeast - the compass point that is midway between north and northeast
NEbN, northeast by north - the compass point that is one point north of northeast
nor'-east, northeast, northeastward, NE - the compass point midway between north and east; at 45 degrees
NEbE, northeast by east - the compass point that is one point east of northeast
east northeast, ENE - the compass point midway between northeast and east
east by north, EbN - the compass point that is one point north of due east
east by south, EbS - the compass point that is one point south of due east
east southeast, ESE - the compass point midway between east and southeast
SEbE, southeast by east - the compass point that is one point east of southeast
sou'-east, southeast, southeastward, SE - the compass point midway between south and east; at 135 degrees
SEbS, southeast by south - the compass point that is one point south of southeast
sou'-sou'-east, south southeast, SSE - the compass point midway between south and southeast
SbE, south by east - the compass point that is one point east of due south
SbW, south by west - the compass point that is one point west of due south
sou'-sou'-west, south southwest, SSW - the compass point midway between south and southwest
southwest by south, SWbS - the compass point that is one point south of southwest
sou'-west, southwest, southwestward, SW - the compass point midway between south and west; at 225 degrees
southwest by west, SWbW - the compass point that is one point west of southwest
west southwest, WSW - the compass point midway between west and southwest
WbS, west by south - the compass point that is one point south of due west
WbN, west by north - the compass point that is one point north of due west
west northwest, WNW - the compass point midway between west and northwest
northwest by west, NWbW - the compass point that is one point west of northwest
nor'-west, northwestward, NW, northwest - the compass point midway between north and west; at 315 degrees
northwest by north, NWbN - the compass point that is one point north of northwest
NNW, nor'-nor'-west, north northwest - the compass point that is midway between north and northwest
NbW, north by west - the compass point that is one point west of due north

And yes there are places *it just wont work,* remember this pic below? * Study the magnetic fields.* Ever wonder why they claim in areas like the Bermuda Triangle the compass goes nuts spinning real fast, stopping and such? I have only witnessed it spinning like crazy then hesitating and spinning again when running to the Bahamas and back a few times, kinda scary. I also had an old airplane compass that my dad had from WWll that I kept for a hand held on board and for some reason when my good one on the helm pulled that crap, the old hand held kept true. I don't know why.










*Prov 3:6 &#8220;In all thy ways acknowledge him, and he shall direct thy paths.&#8221;*


----------



## Fishers of Men

Okay, ready to test yourself?

AIDS TO NAVIGATION
1) The abbreviation on a chart for a fixed light is?

A) FL
B) Fl
C) F
D) FX

2) The height of a light on a chart is usually given from:

A) Height of your eye 
B) Mean high water
C) Fifteen feet 
D) Mean low water

3) Junctions and obstructions (preferred channel markers) are marked by:

A) Black and red horizontal bands
B) Black can buoys with a bell or a whistle
C) Green and red horizontal bands
D) Black and white vertically striped buoys

4) In the U.S. aids to navigation system, red and green horizontally banded buoys mark:

A) Channels for shallow draft vessels
B) General anchorage area
C) Fishing grounds
D) Junctions or bifurcations

5) Navigational marks used for warning or regulatory purpose are:

A) Solid yellow
B) Orange and white horizontally striped
C) Red and white only
D) Green and red horizontally striped

6) Mid-channel buoys (safe water) are marked with:

A) Spherical Buoy	
B) A white light
C) An octagon day shape	
D) All of the above

7) Buoys which mark dredged areas are painted:

A)	Black	
B) Green
C). Yellow	
D) Red

8) Day beacons marking a channel would be:

A) Numbered in the same sequence as the respective buoys
B) The same shape as the respective buoys
C) Day beacons do not mark channels
D) Day beacons are only used to mark a bend

9) Which of the following is the characteristic of an isophase light?

A) Off and flashes on	
B) On and flashes on
C) Flashes every second	
D) Is on 6 seconds and off for 6 seconds

10) A triangle on a buoy means:

A) Danger area
B) You are on the intracoastal waterway
C) Its near an anchorage
D) Tow boats are operating in the area

11) A flashing light is:

A) Off and flashes on
B) Lighted and blinks off
C) Flashes twice and then once
D) Marks a junction or obstruction

12) A quick flashing light may mark:

A) Bend in the channel
B) Widening or narrowing of the channel
C) A place to attract attention
D) All of the above

13) What is true of buoys marking a channel returning from the sea?

A) Red nun with red light may mark the starboard side
B) Green can with green light may mark the port
C) Red and green banded may mark an obstruction
D) All of the above


----------



## Fishers of Men

Here's a knot conversion table:


----------



## Fishers of Men

Aids to Nav answers:
C,B,C,D,B,D,C,A,D,B,A,D,D.

Rules of the Road:
b,a,a,d,b,c,b,b,a,d,c,b,a,d,a,a,d,b,d,c,b,a,a,c,b,d,a,d,b,d.

Well, how did everybody do?


----------



## Fishers of Men

No questions so far? Any requests for a topic? Want more chart info? Want moons/tides? Prop data? How to read tide charts? How Loran works? Let's have some input.

Prov 3:6 In all thy ways acknowledge him, and he shall direct thy paths.


----------



## Fishers of Men

All right, no questions, then we will get into *more extensive chart info*.
You can start a folder if you follow all this info.

_It is established for a custom of the sea that if

a ship is lost by default of the lodesman, the mariners
may, if they please, bring the lodesman to the
windlass and cut off his head without the mariners
being bound to answer before any judge, because
the lodesman had committed high treason against
the undertaking of the pilotage, and this is the judgement.
_
Twenty-Third Article of the Laws of Oleron 1190
Quoted in Schofield

*General Information and Overview*

This chapter provides additional general information about nautical charts together with specific information about the schematic layout of a nautical chart, the chart title block, chart projections, types (and scale) of charts, chart overlap (and related matters), latitude and longitude axes, vertical and horizontal datums, isogonic lines and the compass rose, chart colors, chart lettering, and other miscellaneous charting conventions. Where appropriate, comments on the utility of this information are included, as are practical tips on how to use this information. Many specialized terms used in this chapter are defined in the Glossary in appendix A. Abbreviations are included in appendix B. Names enclosed in parentheses (e.g., Bowditch) refer to sources listed at the end of this chapter that contain additional relevant detail or useful general discussions. It is recommended that the reader have a nautical chart and Chart No. 1 at hand when studying the contents of this and subsequent chapters.

Chart No. 1 (print this out) for reference.










Chart No. 1, Nautical Chart Symbols, Abbreviations, and Terms (9th ed.), provides an indispensable description of the symbols (both national and international) and many of the conventions used on the nautical chart. Chart No. 1 should be carried aboard all vessels. The contents of Chart No. 1 provide a useful framework for organizing this manual. Although space constraints do not permit inclusion of Chart No. 1 in its entirety in this manual, many illustrative excerpts are provided.

Chart No. 1 is organized into various sections, each providing information on one or more groups or classes of symbols and conventions used on the nautical chart. 

For example, general information is included in Section A (Chart Number, Title, Marginal Notes); information on positions, distances, directions, and the compass is presented in Section B; topographic features in Sections C through G; hydrographic information in Sections H through O; aids and services in Sections P through U; and alphabetical indices in Sections V through X. Within each Section of Chart No. 1 there are several subsections, and numerous individual symbols are presented within each subsection. For example, Section F contains port information, which is further subdivided into hydraulic structures, harbor installations, canals, transshipment facilities, and public buildings. Within the subsection on harbor installations F14 is the specific symbol used to depict a pier or jetty. Where appropriate, these sections and symbols are provided (e.g., F14) in the text or headings of this manual to refer the reader to the relevant section or symbol listed in Chart No. 1. Charts published in the United States include those produced by NOAA, NOS, for U.S. waters and NIMA, for other areas of the world. Symbols used by each agency are depicted in Chart No. 1.

Because of the importance of Chart No. 1, it is worthwhile to summarize briefly the schematic layout of this chart. Figure 2.1 illustrates this layout. Item 1 in this figure is the section *(Rocks, Wrecks, Obstructions), *and item 2 the section designation (K in this illustration). Item 3 denotes the subsection (*Wrecks)*, and item 4 (*Supplementary National Symbols*) provides a reference to any supplementary national symbols given at the end of each section. As the name implies, supplementary national symbols are unique to each country (e.g., those listed in Carte No. 1, Chart 5011) and do not conform to the standard symbols authorized by the IHO. Although not officially listed by the IHO, these supplementary national symbols have been retained for the convenience of chart users in each country. *Standardized symbols *facilitate chart use by mariners from different countries, while supplementary national symbols provide the flexibility to describe country specific features and reflect historical charting practices.

Item 5 in figure 2.1 provides a cross-reference to terms contained in other relevant sections of Chart No. 1. In this illustration, the Plane of Reference for Depths, found in Section H, is relevant to information given in Section K.
Print this out:










Item 6 (column 1) identifies the standard number.
Item 7a in figure 2.1 is the symbol or representation as used on charts produced by NOAA. In many cases, the identical symbol is also used by NIMA. If not, as in this example, the NIMA symbol is provided in an additional column (item 7b). Item 8 (*Stumps of posts or piles, fully submerged*) is a written description of the various terms or abbreviations associated with this symbol. Item 9 presents the chart symbol as prescribed/recommended by the IHO. Finally, item 10 presents the corresponding symbols that may appear on NIMA reproductions of foreign charts. The reader interested principally in using NOAA charts should focus on items 1, 2, 3, 4, 5, 6, 7a, and 8 as shown in this excerpt from Chart No. 1.
*Schematic Layout of a Nautical Chart*
To begin, it is useful to examine the schematic layout of the nautical chart and to review the overall format, including the textual material given in the chart. According to the Desk Reference Guide.

The chart format is the general plan of organization or arrangement of a nautical chart including the layout of the margin notes, border, title block, and insets. Figure 2.2 presents the overall format of a nautical chart, and figure 2.3 provides additional explanatory information. The most important items shown in figures 2.2 and 2.3 are summarized in this chapter.
Number, Title, and Marginal Notes (A)
Print this out:










Item 1 in figure 2.2 is the chart number (412 in this illustration) in the (U.S.) National Chart Series, and item 3 is the corresponding chart number in the International Chart Series (if any). The system used for charts produced by both NOAA and NIMA assigns numbers to charts based upon the scale and the geographic area of coverage of the chart. One- to five-digit chart numbers are used. Details of the numbering convention can be found in several sources (e.g., Bowditch). For the most part, mariners using NOAA charts will be concerned with five-digit chart identification numbers, which are drawn
to a scale (see below) of 1:2,000,000 and larger.
Chart numbers and their respective areas of coverage are presented in the nautical chart catalog.

*Latticed Charts *(A)
Item 2 in figure 2.2 indicates whether or not a navigational lattice is overprinted on the chart and, if so, the type of lattice. For example, the legend LORAN C OVERPRINTED informs the mariner that Loran C TD data are superimposed on the chart, the legend D that Decca information is included, and the legend OMEGA OVERPRINTED indicates that Omega information is provided. Although Decca and Omega navigation systems are used extensively in other parts of the world, Loran C is of particular importance to mariners in U.S. waters. In view of the importance of this system, many NOAA charts are overprinted with Loran C TD data. Most modern Loran C receivers are able to convert from TDs to latitude and longitude, but use of TDs is still recommended for highest accuracy (Loran C User Handbook) so a TD lattice is handy. Nautical charts overprinted with a Loran C lattice are identified in the nautical chart catalog with the letter C enclosed with a circle in front of the chart number. Loran C TDs are usually provided on charts with 1:80,000 scale (see below) and smaller upon request of the USCG.
Loran C lattices *are not shown* on harbor or harbor entrance charts at scales of 1:50,000 or larger and over most inshore areas or inland waters because the navigational accuracy is adversely impacted by interference caused by land and/or building structures.

Edition (A)
*The chart edition*, shown as item 6 in figure 2.2, is one of the *most important items of information* given on the chart. The original date of issue (not shown in figure 2.2) of a new chart is printed at the top center margin. The edition number (e.g., 5th ed. May 17/89 in figure 2.2) is printed in the lower left-hand corner of the chart. New editions are published when, at the time of printing, the corrections from previous editions are too numerous or too extensive to be reported in the NM. Criteria for allocation of survey and chart compilation effort are given in table 2.1. A new chart edition supersedes all earlier editions. The date shown is the same as that of the latest NM to which the chart has been corrected. In this illustration, the 5th edition has been corrected through May 17, 1989. (Mariners sometimes overlook this important point, charts are corrected to the date shown, not to the date of purchase. *Therefore, it is generally necessary to make corrections on a newly purchased chart.) *A revised print published by NOAA may contain corrections which have been published in NM but does not supersede the current edition of the chart. The date of the revision is shown to the right of the edition date. Thus, for example, 5th ed. May 17/ 89; Revised June 20/94, indicates that this chart was revised in June 1994. A reprint, issued to replace depleted stocks, is an exact duplicate of the current issue with no changes in printing or publication dates.

A study by the NRC, indicated that nominal print cycles for NOAA charts range from 6 months to 12 years. In practice, new editions are initiated by the cumulative number of chart corrections, significant format or regulation changes, new basic data (e.g., survey data), low shelf stock, and available resources. Not all chart corrections are critical; critical chart corrections include changes in aid to navigation, obstructions, shoaling, and certain cultural and facility changes. According to NRC, *30 to 70 changes trigger a new edition.*

Reconstructed, Provisional, and Preliminary Charts
Three other types of charts, reconstructed charts, provisional charts, and preliminary charts, are worthy of mention. According to the Nautical Chart Manual:

A reconstructed chart, is one that is completely recompiled on a new projection. This is issued when the accumulation of new information is sufficiently extensive to affect most of an existing chart, or if there are changes to the chart limits, or the chart is produced using computer supported compilation and scribing techniques. A reconstructed chart is issued as a new edition.
Chart reconstruction is used to improve the quality of the chart and to incorporate any new symbols and conventions developed over the years. Changes in type style, particular symbols, and cartographic philosophy accumulate and
evolve over the years with the result that older charts contain a mixture of type styles and may include outdated symbols (e.g., symbolized depth use of road symbols rather than urban tint, etc.) and conventions. Moreover, the chart reproduction
process may cause a gradual deterioration of the image (e.g., line thickening, symbols becoming less distinct, etc.) to the point that certain symbols are difficult to recognize. When a chart is reconstructed, the symbology and chart conventions are updated along with the necessary revisions (e.g., relocated buoys, new wrecks, shoaling, etc.) typically noted in the NM or the
LNM.

A provisional chart is a special chart for which there is an urgent need. The chart is labeled PROVISIONAL CHART in the upper and lower margin or at a prominent location inside the upper and lower border.

A preliminary chart is one for which there is an urgent requirement that covers a region where some or all of the
survey data fail to meet modern standards. Survey deficiencies might include small scale, outmoded or nonstandard survey techniques, obsolete, unprocessed, or unapproved data, or other factors which cause the survey data to be below customary standards for the scale of the chart. Not all preliminary charts are published in full color. Additionally, the source diagram (see Chapter 4) alerts the mariner to the provisional nature of the data, and a separate warning note is included.An illustrative warning note is shown below.

WARNING PRELIMINARY CHART
All of the data on this preliminary chart is considered to be of marginal quality for modern charts. Many of the depths were taken by leadline in the early 1900s, so uncharted shoals are likely in this area. Navigators should use this chart with extreme caution and report discrepancies or hazards to..
From the above, it is clear that preliminary charts should be used with particular care. However, the fact that the chart may include some data of marginal quality does not mean that all data are suspect.
If the preliminary chart has a source diagram, this diagram should be consulted to determine which areas of the chart may contain data of marginal or unverified quality. Mariners may be able to select routes which avoid these areas. Alternatively, the mariner might choose a greater safety margin. (e.g., depth allowance) in selecting routes, navigate with especial vigilance, navigate at reduced vessel speeds, and employ other appropriate measures to reduce risk.









Importance of Current and Corrected Charts One opinion on the use of current charts:
In 1950 I joined Fandango for the Santender
Race returning via a race to Belle Ile and cruising home. I looked over the charts [provided by the owner] and found that they had all been bought. in June 1934. The suggestion that sixteen years and a World War might have outdated some of the musty old charts was brushed aside. by the owner [with the statement] .I believe that the rocks dont move, so whats the matter with you...

This idiosyncratic view is colorful but foolhardy; most mariners agree that it is essential to use the current edition/revision of the chart, updated to include all corrections given in the NM or LNM. Use of obsolete editions for navigation could be dangerous; buoys are moved, other ATONs may have changed location or characteristics, new hazards (e.g., obstructions, wrecks) may have been identified, natural changes to hydrography may have occurred, and areas and limits (see Chapter 7) may have been changed. Indeed, as noted above, the accumulated number of chart corrections is one of the principal determinants of NOAA.s decision to prepare a new edition.

If prudence alone is not sufficient motivation to ensure that a vessel is equipped with appropriate and corrected charts, mariners should be aware that carriage of such charts is a legal requirement for certain classes of vessels. According to 33 Code of Federal Regulations (CFR) Part 164, self-propelled vessels of 1,600 or more gross tons (when operating in the navigable waters of the United States except the St. Lawrence Seaway) are obligated (Section 164.33(a), et seq.) to carry (among other things) corrected marine charts of the area which are of a large enough scale and have enough detail to make safe navigation of the area possible.

The NOAA publication, Dates of Latest Editions (issued quarterly), provides a list of the current editions of each chart. Techniques for making chart corrections are discussed in several sources (e.g., Bowditch, Farrell, Maloney, Markel).
Source Diagram (A)
A source diagram (item 7 in figure 2.2) indicates the scale and date of *hydrographic surveys* upon which the nautical chart is based. Source diagrams and their utility are discussed in more detail in Chapter 4.
*Neat Line Dimensions* (A)
The size of a nautical chart is related to the chart scale (see below) which is dependent upon the amount of detail (geographic and cultural features, hydrography, etc.) that is charted to provide a concise, legible, graphic representation of the necessary data. The chart dimensions also reflect the sizes of printing presses found in nations around the world which reprint and reissue NOAA charts. The internationally accepted size A0. paper has outside dimensions of 841 mm x 1189 mm and is one of the standard sizes used by NOAA.
The neat line is the inner border of the chart. The dimensions of the neat line (item 8 of figure 2.2 or 740.9 mm x 1103.9 mm for this particular chart) are printed at the base of the chart. Neat line dimensions, in concert with the chart scale, enable calculation of the geographic area covered by the chart.
Chart Title, Authorities Note, and Seal (A)
Item 10 of figure 2.2 is the chart title (Cook Inlet in this illustration). Although charts are generally ordered by chart number, the chart title serves as an additional identifier. The nautical chart catalog shows the area covered by each NOAA chart, and the corresponding chart number and title. *Chart titles cannot be used alone (in lieu of chart numbers) because many place
names (and chart names) are common throughout throughout the world. *

According to one source (Coote), for example, there is a St. John in Newfoundland, New Brunswick, Antigua, the Red Sea, Florida, the Virgin Islands, Liberia, and near Hong Kong! Item 11 of figure 2.2 contains the AUTHORITIES note. This note identifies the sources of data (e.g., NOAA, USACE, U.S. Navy, etc.) used in the compilation of the chart, explanatory notes on chart construction, and related material. 
Item 12 is the *chart seal.* In the example shown in figure 2.2, the NOAA and IHO seals show this to be an international as well as national chart. Purely national charts have the national seal *only*. 
Reproductions of charts of other nations (facsimile) have the seals of the original producer (left), publisher (center), and IHO (right).
*Projection and Scale* (A)
Item 13 in figure 2.2 (located just below the chart title) identifies the type of chart projection (e.g., Mercator) and the chart scale. Projections and their relevance are discussed below.
*Projections*
From earliest times, cartographers have been faced with the theoretically impossible task of accurately representing a spheroid (the earth) on a flat plane, a task referred to as projection. As the science of cartography evolved, numerous projections were developed, each with advantages and disadvantages. A complete discussion of these various projections is beyond the scope of this manual, but can be found in several of the references given at the end of this chapter (Air Navigation, Bowditch, Brown, Maloney, Naval Training Command, Snyder, and Voxland). 

For nautical charts of other than high-latitude or polar regions, the Mercator projection is favored. T*his is because meridians of longitude are parallel straight lines, as are parallels of latitude.*
These straight lines intersect at right angles, making a convenient rectangular grid. *Directions and geographic coordinates*
are easily read on this grid. A straight course line (rhumb line or loxodromic curve) drawn on the Mercator chart can actually be run; the rhumb line track *will pass all features along that line exactly as they are charted.* This is a great advantage in coastal navigation because the straight line represents a *planned course and readily indicates the distance at which dangers will be passed abeam if this course is maintained.*
*
The rhumb line is not the shortest distance* between two points (a great circle), and either calculation or an auxiliary chart is required to determine great circle courses if a Mercator chart is used. However, the difference in distance between the rhumb line and the shorter great circle is *very small for all but the longest voyages. *
*Radio waves and light travel *along great circles, which means that radio bearings taken some distance from the transmitter *need to be corrected.* Radio bearing corrections are tabulated on some nautical charts and can also be found in the U.S. Coast Pilot and other references (Bowditch).

In a more general context, *the chief disadvantage *of the Mercator projection is that it distorts the relative size of land areas, particularly for land masses located near the poles. Other projections are superior in this regard. Indeed, one author (Monmonier) has argued (presumably tongue in-cheek) that the Mercator projection has served the aims of political propagandists seeking to magnify the Communist threat, because this projection exaggerates the relative size of the former Soviet Union relative to countries situated at lower latitudes. (One can only marvel at the political prescience of Gerhard Mercator in anticipating this application when he developed the projection in the year 1569!) Whatever its other merits or faults, the utility and convenience of the *Mercator projection for most marine navigation applications are unequalled.*
For this reason, nearly all NOAA nautical charts are based upon the Mercator projection. *The polyconic projection is used on some NOAA Great Lakes charts, but these charts are being converted to Mercator projections as resources permit.*
*
Relevant attributes of Mercator and polyconic charts* are summarized in table 2.2. 
As a practical matter, differences between these projections are *only *apparent on small-scale charts (see below). On large-scale charts, virtually identical plotting techniques are used.
*The chief differences between small-scale Mercator and polyconic charts are:*
*Distance *is most accurately measured at or near the mid-latitude of the course on the Mercator chart. Distance scales (see below) are shown in nautical miles on Mercator charts, *and in statute miles on polyconic Great Lakes charts.*

For all intents and purposes, great circles *plot as straight lines* on the polyconic chart. However, *true directions *from any point on the polyconic chart should be measured from the *nearest meridian or nearest compass rose *(see below). As noted, great circles *do not plot *as straight lines on Mercator charts. Instead, great circle courses must be calculated (or read from a polyconic or Gnomonic projection) as a series of points and transferred to the Mercator chart. Details of plotting great circle courses on Mercator charts are given in the references (Bowditch, Maloney).
True directions (rhumb lines) can be measured with respect to any meridian or parallel (or any compass rose) on the Mercator chart, although in practice the *nearest compass rose is used if magnetic courses are desired*, because the *magnetic variation* varies with location on the chart.
*Plotting geographic positions *is somewhat simpler on the Mercator chart, because meridians and parallels intersect at right angles. *Great Lakes polyconic charts include a graphic plotting interpolator for the most accurate measurements of latitude and longitude.*










*Chart Scale*

The scale of the chart is the ratio of a given distance on the chart to the actual distance that it represents on the earth. Scale is expressed in various ways. The most common expression is a simple ratio or fraction known as the representative fraction. For example, a scale of 1:40,000 or 1/40,000 means that one unit (e.g., one inch) on the chart represents 40,000 of the same unit(s) on the surface of the earth. This scale is also termed the natural or fractional scale. *A chart covering a relatively large area is called a small-scale chart,. and one covering a relatively small area is termed a large scale chart.. *

To remember the difference between small scale and large scale, it is helpful to think of a small-scale chart as presenting only a small amount of detail and a large-scale chart as presenting a large amount of detail. On a chart based upon the Mercator projection (the type shown in figure 2.2), the scale varies with the latitude. This variation is only noticeable on a chart covering a relatively large distance in a north/south direction. On such a chart, the scale at the latitude in question should be used for measuring distances.

Table 2.3 provides relevant scale information for various scales used in the preparation of nautical charts. For each chart scale, table 2.3 shows the number of nautical miles represented by 1 inch in length and its reciprocal, the length of 1 nautical mile in inches. This table also shows the area covered (in square nautical
miles) by the chart, assuming neat line dimensions of 750 mm x 1,100 mm (one of the standard chart sizes). Thus, for example, on a chart with a scale of 1:10,000 (a large-scale chart), the area covered by the chart is approximately 24 square nautical miles, 1 inch on the chart is approximately equal to 0.14 nautical miles, and 1 nautical mile is approximately 7.3 inches in length.










*Chart Types*
*No one chart scale is adequate to serve all purposes.*
*Nautical charts vary in scale with the importance of the geographic area,* the purpose for which the chart is designed, and the necessity for clearly showing all dangers within that area. NOAA charts include small-craft charts, conventional charts, ICW, and marine facilities charts.
*
Small-craft charts, identified by the letters SC i*n the nautical chart catalog, are described below:
Small-craft charts, published at scales ranging from 1:10,000 to 1:80,000, are designed for easy reference and plotting in limited spaces. Although normally used by operators of small craft, these charts provide the only chart coverage for all other marine users in some areas. These charts include the items normally depicted on other nautical charts together with details of special interest to small-craft operators, such as enlargements of harbors; tide, current, and weather data; rules of the road information; locations of marine facilities and anchorages; courses and distances.

Types of small-craft charts include:
folio charts (consisting of two to four sheets printed front and back, folded, and bound in a protective cardboard jacket); area charts (versions of conventional charts overprinted with additional small craft information); route charts (published in a single long, narrow sheet printed front and back and folded); modified route charts; recreational charts; and canoe charts (a chart series of the Minnesota Ontario border lakes providing information relevant to those who use canoes, kayaks, and similar craft).

TO BE CONTINUED


----------



## Fishers of Men

Continuation from previous post:

*Conventional charts* are flat (rather than folded) and depict the nature and shape of the coast (see Chapter 3), depth of the water (see Chapter 4), general configuration and character of the bottom (see Chapter 4), prominent landmarks (see Chapter 6), (gettin to it!) port facilities (see Chapter 3), cultural details, dredged channels, ATONs (see Chapter 5), marine hazards, magnetics (described below), areas and limits (see Chapter 7), and seaward boundaries (see Chapter 7). *The five classifications* of conventional nautical charts include:

International charts (such as that illustrated in figure 2.2) include a series of five small-scale charts covering the Northeastern Pacific Ocean and the Bering Sea at scales of 1:3,500,000 or 1:10,000,000 compiled to internationally standardized cartographic specifications. The navigational information presented on these charts includes depth curves, soundings, nautical symbols, and related data.

Sailing charts, published at scales smaller than 1:600,000, are intended for planning voyages and for fixing the mariners position as the coast is approached from the open ocean or for sailing along the coast between distant ports. The shoreline and topography are generalized, and only offshore soundings, principal navigational lights and buoys, and landmarks visible at considerable distances are shown. Figure 2.4 contains an excerpt from NOS Chart No. 13003 (Cape Sable to Cape Hatteras). This sailing chart is drawn to a scale of 1:1,200,000. In the right-hand corner, some depth and ATON information is depicted at the entrance to the Delaware Bay. No soundings, depth contours (see Chapter 4), or ATONs (see Chapter 5) are given for the Chesapeake Bay, and the city of Annapolis is depicted with only a city symbol (see Chapter 7).

*General charts*, published at scales ranging from 1:150,000 to 1:600,000, are intended for coastal navigation when a course is well offshore but can be fixed by landmarks, lights, buoys, and characteristic soundings. Figure 2.5 contains an excerpt from NOS Chart No. 12260 (Chesapeake Bay, Northern Part) showing a portion of the area covered in figure 2.4. This general chart is drawn to a scale of 1:197,250. Soundings and ATONs in the Chesapeake Bay are shown, but Annapolis is still depicted with only a city symbol, and very little detail is presented in the vicinity of the Severn River.
Coast charts, published at scales ranging from 1:50,000 to 1:150,000, are intended for nearshore navigation, entering or leaving bays and harbors, and in navigating the larger inland waterways. *Some coast charts omit detail* in areas that are covered by larger scale charts. For example (Chapman), Narragansett Bay appears on NOS Chart 13218, but no hydrography, ATONs, etc., are depicted. A small note refers the user to a larger scale chart. Figure 2.6 contains an excerpt from NOS Chart No. 12270 (Eastern Bay and South River) depicting a portion of the area covered in the preceding two figures. This chart is drawn to a scale of 1:40,000, slightly larger than a coast chart scale. Much more detail is presented on this chart. City streets, landmarks for position fixing, ATONs, soundings, and some harbor detail (e.g., piers, etc.) are clearly shown.

*Harbor charts*, published at scales of
1:50,000 and larger, are intended for navigating in harbors and smaller waterways and for anchorage. Harbor charts present more numerous soundings than are shown on smaller scale charts and all ATONs to maximize the accuracy of positions determined from plotted bearings. Figure 2.7 contains an excerpt from NOS Chart No. 12283 (Annapolis Harbor). This harbor chart is drawn to a scale of 1:10,000. Individual buildings at the U.S. Naval Academy are shown as are details important to the mariner intending to anchor in this area.

NOAA publishes ICW (inside route) charts at a scale of 1:40,000, which depict the inside route from Miami, FL, to Key West, FL, and from Tampa, FL, to Anclote Anchorage, FL.

Finally, NOAA publishes marine facilities charts. According to the Nautical Chart Manual, [Marine facilities charts] .are conventional charts with small-craft marine facility information overprinted on the chart and presented in tabular form on the back. These are produced for major port areas where facility information for a wide area, such as Narragansett Bay or Galveston harbor, is useful for the mariner.

Marine facility charts are identified with the letters MF in the nautical chart catalog.
*A Mix of Charts Necessary * 
The prudent navigator carries a mix of sailing or general charts for overall voyage planning (if a long distance voyage is contemplated), coast charts for actual use (e.g., intended tracks and DR plots) for the longer runs, and harbor charts for entering ports and trips up smaller rivers and creeks. For example, on a hypothetical voyage from Bermuda to Annapolis, sailing and general charts would be used for offshore navigation, coast charts for the trip up the Delaware Bay, through the C & D Canal (although a large-scale chart of this canal is published), and down the Chesapeake Bay, and the Annapolis Harbor chart for final approach and anchoring or docking. Continuing the example (Chapman), the best overall route up or down the Chesapeake Bay is more easily plotted on two general charts (NOS Charts 12220 and 12260), rather than on a series of five coast charts (NOS Charts 12221 to 12273) covering the same area. The coast and harbor charts are appropriate for the actual trip.










As a general matter, the mariner is well advised to use the largest scale chart of the area, as this chart presents the greatest amount of detail. Many mariners carry harbor charts for other harbors along the intended route as insurance against the possibility that mechanical malfunctions, weather, fuel shortages, medical emergencies, or other unforeseen events make a diversion to an alternate harbor advisable (Blewitt).

*Failure* to carry sufficient charts to accommodate possible diversions can have serious consequences from both safety and legal standpoints, as numerous case studies of commercial vessel strandings (Cahill) illustrate. In retrospect, it is virtually impossible to justify the loss of a multimillion dollar tanker (or even a $50,000 cabin cruiser) or even a small boat, for the lack of a $14-$20 chart! Although todays civil penalties for a lack of prudence are less draconian than that listed in the opening quotation of this chapter, these are harsh enough to command attention.










*A Brief Aside, Chart Storage and Care.*
Rollers versus Folders
As noted, conventional charts are sold as flat sheets, and typically shipped rolled in cardboard tubes, whereas small-craft charts are prefolded to simplify stowage problems on small craft. Most mariners would agree that, ideally, conventional charts should be stored flat in a draftsmans cabinet provided adequate space exists. However, many vessels (and, indeed, most recreational vessels) do not have sufficient space to accommodate flat storage of conventional charts.

There is no general consensus on how best to store conventional charts in cramped quarters.

Rather, the world of navigators (or, at least, the world of navigation textbook writers) appears to be fundamentally divided on whether to roll or fold these charts.
*Rollers* (see Chapman, Graves) argue that conventional charts should be rolled if possible, claiming that the disadvantage of the ends curling is more than out weighed by the longer life of a chart if it is not creased. *Folders.* (Campbell) argue that it is difficult to plot on a rolled chart and offer numerous suggestions on how best to fold charts (e.g., in four sections, each about the size of an average navigation desk on a yacht, with the printed side facing out). In the end, this reduces to a matter of personal preference.










If there is controversy between rollers and folders, there is unanimity that charts should be stored in a convenient but dry area in the vessel. Damp storage areas often result in mildew damage, and water spray creates bubbles, folds, and resulting distortions when the chart finally dries out. Durable as it is, the paper on which nautical charts are printed cannot stand repeated cycles of water spray, let alone water immersion.
*Linear and Logarithmic Speed Scales* (A) Item 14 on figure 2.2 is a linear scale, often provided on chart insets (see below) and larger scale charts. The linear scale (also termed a bar scale) is found on Mercator charts (or insets) with chart scale of 1:80,000 and larger (1:120,000 and larger for *polyconic projections)*. Bar scales enable the user to measure distances (in nautical miles, *statute miles (on Great Lakes charts)*, yards, and meters) quickly with a pair of dividers. The linear scale is used in lieu of the latitude scale at the side of the chart. Figure 2.8 (top) shows an example of a bar scale.

Logarithmic speed scales, shown in figure 2.8 (bottom), are also printed on these charts. *The logarithmic speed scale *is an ingenious nomograph to solve time-speed-distance (TSD) computations. It is used to calculate speed, based upon the distance and time run. T*o find the speed, one point of a pair of dividers is placed on the distance run (in any unit) and the other on minutes run. Without changing the divider spread, the right point of the divider is placed on the number 60; the left point of the dividers will then indicate the speed in units per hour. Thus, for example, if a vessel travels 4 nautical miles in 15 minutes, the calculated speed is 16 knots.*
*Notes and Cautions*
Item 16 on figures 2.2 and 2.3 refers to cautionary notes (if any) depicted on the nautical chart. These notes, which should be read before using the chart, present a variety of general and particular information. Specific notes and their meaning are discussed throughout this manual. Table 2.4 provides a sample of notes taken from various nautical charts which illustrates the type of information provided.

Notes may be located at or near the title block as shown in figure 2.2, but may also be located anywhere on the chart where they do not obscure navigationally relevant data or information. Chart Overlap, Insets, and Related Matters.

There is an old military adage (Heinl) to the effect that battle is a process which always takes place at the junction of two maps. Many navigators believe that this maxim applies equally to nautical charts. Before a vessel crosses from waters described by one chart to those covered by another, it is necessary to extend the course to the adjoining chart. Moreover, the course has to be selected so as to maintain a safe distance from charted hazards and take advantage of ATONs and landmarks depicted on the adjoining chart. As the vessel crosses into waters depicted on the adjoining chart, the navigator must be able to plot fixes rapidly on the next chart in sequence. If *electronic fixes are available (e.g., from a GPS or Loran.C receiver),* the fixes are easily plotted on the appropriate chart. However, if visual bearings are used, plotting fixes may be more difficult if the vessels position is near a chart border.

*Measures to Minimize Confusion:*
The Chartmakers Perspective
NOAA uses four methods to minimize problems associated with the transition from one chart to another.

First, nautical charts are sized and aligned (insofar as possible) to ensure that dangerous passages are not located near the chart borders. This lowers the likelihood of a vessel entering a hazardous area when it is necessary to shift from one chart to the next.

Second, nautical charts are deliberately drawn so as to overlap slightly.
Adjoining charts of the same scale, particularly coastal charts, generally have an inch or two of overlapping coverage. The amount of overlap varies from chart to chart and is sufficient to include enough common prominent features, important aids to navigation, etc., to facilitate the quick transfer of a plotted course and position from one chart to the next in sequence.



















The detail presented on overlapping charts of the same scale is identical or nearly so.

Third, if (despite efficient location and overlap) there are still important features located just outside the chart border, a border break (sometimes also called an extrusion, extension, or blister) is used. The border break, as the name implies, is an extension of the charted area outside of the chart neat lines to depict particularly important feature(s). Figure 2.9 presents an excerpt from NOS Chart No. 11445 (Sugarloaf Key to Key West), an ICW chart, which includes a border break. Note in the lower right-hand corner of this illustration that the American Shoal light is actually located *outside* the chart border. Because this light is deemed important to navigation, a border break is used to show it on this chart. Border breaks are also used to eliminate the need for printing an additional chart. For example, figure 2.
10 contains an excerpt from NIMA Chart No. 28160 (Tela to Pelican Keys). The border break in this metric chart avoids the necessity of printing another chart just to depict the small portion of the Bahia De Amatique (Honduras Bay) near the Temash River.

Fourth, notes (and sometimes diagrams) are provided on the nautical chart to identify the adjoining chart(s) so that the user can quickly identify the appropriate chart. This is done in various ways. For example, notes (e.g., JOINS CHART 12214, if the adjoining chart is to the same scale, or CONTINUED ON CHART 12311 if the adjoining chart is of a different scale) printed in black *italic capital letters outside *the neat line of the nautical chart identify the adjoining chart. Refer to item 17 in figure 2.2. (Cross-reference to join points on small craft and ICW charts is facilitated by a dashed magenta section line, e.g., line AP - - - AP in figure 2.9, which is also displayed on the adjoining chart.) In cases where a larger scale chart of the same area is available a note (e.g., chart 12284) is printed in lower case italic magenta type at or near the boundary of the larger scale chart on the smaller scale chart. (Hydrographic detail may be suppressed on the smaller scale chart in this case.)










In some cases the larger scale information may be presented in an inset (see, for example, item 15 in figure 2.2), in which case the inset will be printed somewhere on the chart so as not to obscure navigationally relevant information.

Finally, chart outlines and diagrams are also used to display larger scale overlapping or adjoining chart coverage on smaller scale charts. The intent is to provide the user with a complete reference to larger scale chart coverage.

This is done either by providing an outline of boundaries of the larger scale chart on the smaller scale chart (as shown by item 15 in figure 2. 2) or by providing a convenient chart index diagram which shows the available larger scale charts. Figure 2.11 contains a chart diagram found on NOS Chart No. 12260 which shows the boundaries of the larger scale charts available for this area.


TO BE CONTINUED


----------



## Fishers of Men

Cont. from last post

*Measures to Minimize Confusion:*
The Navigator's Role

The navigator should also take steps to minimize any confusion that might occur when shifting from one chart to another. . First, the proper adjoining (or larger scale) chart should be selected from the storage area so that it is readily at hand well before the chart is actually required. This is particularly important if the mariner is single-handing (traveling alone) or if the chart storage compartment is located some distance from the helm or plotting area. Indeed, it is a good idea to lay out all the required charts for a voyage prior to getting underway, labeling each with a removable gummed label with an attached sequence number. This procedure not only facilitates selection of the right chart, but also ensures that any missing charts are identified at the dock, rather than while underway. Few things are more frustrating than having to divert to an alternate harbor because the required chart is not aboard! (The alternative of pressing on without the missing chart in hopes that the channel is well-marked is so hazardous as to be unthinkable.)


























Second, the vessels intended track should be plotted on the adjoining (or larger scale) chart before this chart is required. The DR plot should be drawn in while underway, but the intended track can be plotted beforehand. Where possible, the intended track should be laid out so as to minimize the necessity for accurate navigation in the immediate vicinity of a chart junction.

Third, if using landmarks or ATONs for position fixing, the navigator should plan ahead to avoid selecting objects that are not shown on the same chart. For example, visual bearings on two objects not shown on the same chart cannot readily be plotted to obtain a fix. Alternatively, the navigator can designate a checkpoint or waypoint that is located in the overlap area common to both charts. Arrival at the waypoint signals the need to change charts. *This is particularly convenient if a navigational receiver (e.g., GPS or Loran.C) with a waypoint alarm is used.* 

Fourth, the navigator should fix the position of the vessel more frequently when in the vicinity of the chart junction.

Fifth, the navigator should be particularly alert to any change in scale whenever shifting to another chart as, for example, when shifting from a coast chart to a harbor chart. Although adjoining charts are often drawn to the same scale, *this is not always the case*. Moreover, larger scale charts and chart insets always involve a change in scale. Attention to scale changes is particularly important if an external distance scale (e.g., a paraline plotter) is used. These instruments often have several distance scales scribed along the straight edge. It is a common error to use the wrong distance scale, particularly when transitioning to a chart with a different scale from that used previously. *Use of the wrong distance scale* translates into an *incorrect DR plot with attendant hazards.* To avoid this error, many navigators disregard the scribed distance scales on plotters and *always measure distances with dividers using the latitude scales *or the linear scale printed on the chart. (Separate latitude scales or linear scales are always printed on insets of a different scale.)

Navigators using commercial reproductions of portions of NOAA charts, especially those printed in relatively small booklets, soon learn that chart changes are more frequent and that it is often difficult to find the adjoining chart in the booklet.

[/B] Latitude, Longitude, Regular, and Skewed Projections.[/B] 

Each nautical chart will have lines marking parallels of latitude and meridians of longitude. (In the Mercator projection, as shown in table 2.2, latitudes are parallel straight lines, and meridians of longitude are likewise parallel straight lines.) These are used to measure the geographic location of any point on the chart in terms of latitude and longitude. The latitude scale is also used to measure distance; 1 nautical mile is equal to 1 minute of latitude. (Drive this in enough?) The interval between adjacent parallels and meridians depends upon the scale of the chart. Latitude and longitude scales are marked with degrees and minutes. NOAA charts with a scale larger than 1:50,000 subdivide minutes into seconds or multiples of seconds. Small-scale charts subdivide minutes into tenths, fifths, or halves. Read these scales carefully. It is also important for the mariner to note the units of latitude/longitude readout of an electronic navigation receiver (e.g., *GPS or LORAN-C) as these may differ from those used on the chart. *For example, most electronic receivers measure latitude or longitude to degrees, minutes, and tenths (or hundreths) of minutes, *rather than degrees, minutes, seconds. *

Most conventional charts are oriented north up with latitude scales at the sides of the chart and longitude scales at the top and bottom. Some conventional charts and many small-craft charts are printed as a skewed projection so as to make the most efficient use of space. In these skewed (non-north up) projections, l*ines of latitude and longitude are not parallel to the borders of the chart. *A skewed projection is illustrated in figure 2.9.
*Depth Units and Vertical Datum*

The units of depth (e.g., feet, fathoms, fathoms and feet, meters) employed on the chart are shown in the title block and in capital magenta letters at the top and bottom of the chart. 

As discussed in Chapter 4, NOAA charts are now published in both, traditional. (feet, fathoms, fathoms and feet) and metric units. *In the future,* charts with traditional units are being replaced by those charted in metric units. 

Kals offers an interesting anecdote on misreading depth units:
&#8220;In Montreal I once conned the craft of a friend who had urgent business below. Avoiding the ship channel, I headed straight for our destination over soundings of 2, 3, and 4 fathoms. [Note 1 fathom is 6 feet.] No problem; his schooner drew only 5 feet. The river must have been well above datum level or I would have run her hard aground.&#8221;
The soundings were in feet!. Not all such stories have such a happy ending.

*It is essential *to check the depth units on the chart. This is especially important during the present transition period from conventional units to metric units.

The chart note regarding depth units also defines the vertical datum (typically mean lower low water for soundings and mean high water for heights) used on the chart, as discussed in more detail in Chapter 4.

To provide a ready source of unit conversion information, NOAA charts also include a depth conversion scale. This scale shows the correspondence between fathoms, feet, and meters. 

Figure 2.12 illustrates the depth conversion scale designed for horizontal placement. A similar scale has been designed for vertical placement. These scales are typically placed near the chart borders.

*Horizontal Datum*

The horizontal datum is shown just below the title block of the chart. The horizontal datum *is a set of constants *specifying the coordinate system used for geodetic control, that is, for calculating coordinates of points on the earth. Different horizontal datums use different ellipsoids to represent the earth&#8217;s shape. Prior to widespread use of satellite systems for surveying and navigation, most countries developed an ellipsoid that fitted the curvature of the earth for the particular areas charted. In consequence, numerous datums were employed because the datum providing the best fit for one area might not provide the best fit for another. Most NOAA charts are based upon the North American Datum of 1983 (NAD 83), the current standard for U.S. nautical charts. This datum is quite close to the World Geodetic System of 1984 (WGS 84). Other datums presently used on NOAA charts include the:
North American Datum of 1927
North American Datum of 1902 (found only on some Great Lakes charts),
Old Hawaiian Datum,
Puerto Rico Datum,
Local Astronomic Datums, and the Guam 1963 Datum.
With the exception of the charts of the Hawaiian Islands and other western Pacific islands (which will be compiled on WGS 84) all new charts and reconstructed NOAA charts are based on NAD 83.

*Relevance of Horizontal Datum*

*For navigators using radar  or visual means for position fixing,  the particular datum used is merely an academic curiosity. However, for those using electronic navigation systems, such as GPS or LORAN-C, the chart datum is potentially more relevant. This is because the mathematical conversion routines employed in these receivers to convert the received signals (e.g., LORAN-C TDs) to latitude and longitude depend upon the assumed datum. A shift from one datum to another could shift the position of the apparent fix by an amount ranging from meters to miles. One source (Brogden) notes that, outside the United States, it is commonplace to find differences of half a mile to a mile between GPS fixes and a local chart.










Most modern makes and models of GPS and LORAN-C receivers have the capability of shifting from one datum to another (Dahl, Brogden), often offering a wide selection (as many as 50 to 100) of alternate datums. If the vessel&#8217;s navigation receiver is so equipped, it should be set to match the datum used on the nautical chart of the area.

Guess what???
TO BE CONTINUED!*


----------



## Fishers of Men

Cont. from last post

*Direction and Magnetics (B)*

True and magnetic information is provided on nautical charts to enable mariners to measure direction and determine magnetic courses. This information is provided in various ways. Latitude and longitude lines provide north/south and east/west orientation. The mariner can determine true direction from either parallels of latitude or meridians of longitude with the aid of various commercially available course plotters.

*True and magnetic directions are provided with one or more compass roses (B70) located on the chart.* Magnetic information is also displayed by the use of isogonic (lines of equal magnetic variation) lines (B71) shown on the chart.

*Compass Roses (B70)*

A compass rose, as illustrated in figure 2.13 (top), is placed on nautical charts to help mariners *plot bearings and lay out courses.* As a point of interest, the use of the compass rose to indicate true and magnetic directions is a tradition dating back several centuries. As noted by Brown, The earliest known rose to indicate compass variation appeared on a map in the Cosmographiae Introduction of Apianus printed at Ingolstadt in 1529.

On the modern nautical chart, the compass rose consists of two concentric graduated circles:

*The outer circle (true rose)*, graduated in increments from 0&#176; through 360&#176;, is aligned with true north. (Depending upon the scale of the chart, the increments may be 1&#176;, 2&#176;, or 5&#176;.) The star symbol atop the 0&#176; mark presumably denotes *Polaris, the north star.*

*The inner circle (magnetic rose),* also graduated in increments of 1&#176;, 2&#176;, or 5&#176; and labeled MAGNETIC, *is aligned with magnetic north. The arrow * atop the magnetic scale points to magnetic north. A second set of graduations within the inner (magnetic rose) circle is graduated in the older 32-point system (1 point = 11.25&#176. Half points and quarter points are also given.
Another label (e.g., VAR 4&#176; 15&#8217;W (1985)

*ANNUAL DECREASE 8&#8217;*, in figure 2. 13), shows the magnetic variation (4&#176;15&#8217;W) for the charted area as of a specified date (January 1, 1985), and the annual increase or decrease to permit adjustment to the current date. *This is necessary* because magnetic variation is not constant, but rather changes due to the fluctuations of the earth&#8217;s magnetic fields.

Use of the compass rose for measuring courses or bearings is explained in numerous texts (e.g., Bowditch, Dutton) and is not discussed here. Compass roses are positioned on a chart *so as to be convenient to the most important *navigational areas, and at sufficiently frequent intervals so that all water areas are within the reach of the parallel ruler. If the compass rose is positioned on a land area, some topographic detail may be removed to reduce chart clutter. Compass roses *are not placed* in water areas at the entrance to a harbor, at or near hazards to navigation in the water, nor do the graduations obscure relevant soundings.

*Compass roses are printed in magenta *on all new charts and new editions. Some existing charts, especially those with magenta Loran.C lines, have compass roses printed in black. These will be converted to magenta when new editions are published.










*Local Magnetic Disturbance Notes*

*Local magnetic disturbances*, which may cause substantial deflections of the compass, occur quite commonly in shallow water near mountain masses. Notes, printed in magenta, alert the mariner to these areas wherever deviations of 2&#176; or more (3&#176; in Alaska) exist.

Here are two examples:
LOCAL MAGNETIC DISTURBANCE
Differences from normal variation of as much as 5&#176; have been observed in Gastineau Channel in the vicinity of Lat. 58&#176;15&#8217;.
LOCAL MAGNETIC DISTURBANCE
Differences of 12&#176; or more from normal variation may be expected in X Channel in the vicinity of Z point.

If space constraints prevent inclusion of the entire note, the full note is placed elsewhere on the chart and *the following reference note (in magenta) *is placed in the area of the disturbance:
LOCAL MAGNETIC DISTURBANCE (SEE NOTE) Isogonic Lines (B 71)
*Magnetic variation is shown by isogonic lines *on smaller scale charts. Isogonic lines are lines connecting points of *equal magnetic variation. * *The line passing through points having zero variation is termed the agonic line.*
Isogonic lines are shown on those charts drawn to scale at which a variation of 1&#176; will result in a distance between adjacent lines of less than 12 inches. Each isogonic line is labeled with the amount and direction of variation, and the date of the variation. As shown in the example given below, charts with isogonic lines carry a magenta note stating the name of the mathematical model used for computation, the year the model was computed, and the year the charted isogonic lines represent.

*MAGNETIC VARIATION*

Magnetic variation curves are for 1992 derived from 1990 World Magnetic Model and accompanying secular change.
*If additional change is in the same direction as variation it is additive and the variation is increasing. If annual change is opposite in direction to the variation it is subtractive and the variation is decreasing. *

*Additional Information*

Certain charts (e.g., small-craft and marine facilities charts) provide a variety of additional relevant information in the form of notes, tables, and pictures of harbors, landmarks, or ATONs. Examples of additional information found on small-craft charts include:
A tide note (H 30) which provides information on tide heights, and daily tide tables are often printed on the jacket of small-craft charts.
Marine facility tabulations (U 32), such as that illustrated in figure 2.14, provide information on tides, depth, services, and supplies found at various locations shown on the chart.

Several charts include additional technical tables, such as a radio bearing conversion table, to correct measured bearings to Mercator bearings, a table of distances to the horizon as a function of the height of eye of the observer, a conversion table from degrees to compass points and vice versa, or a table for determination of wind speed from observed sea conditions.

Several charts provide tables of port-to-port distances which are useful for voyage planning.










Although this same information is available in a variety of companion publications, such as the U.S. Coast Pilot or the Tide Tables, *recreational boaters typically appreciate its inclusion on the nautical chart (NRC). *

Interestingly, many professional mariners, who normally have these other reference publications, would prefer less cluttered. charts (NRC), an illustration of the trade-offs made by NOAA in deciding what to include.
Lettering Styles
(Vertical versus Slant Type)

*Chart features depicted in vertical type *include the names of topographic features and fixed objects which extend above high water. Slant (italic) type is used for names of hydrographic features, including names of water areas, underwater features, and floating aids.

*Use of Color on Charts*

Color is used on nautical charts to call the mariner&#8217;s attention to key features and to facilitate chart interpretation. NOAA uses five colors (some with different shades) to depict chart features and other information: black, blue, gold, green, and magenta. *The general color conventions on NOAA charts are as follows:*

black is used for most symbols, printed
information (e.g., notes, titles, certain Loran.C TDs, etc.), to outline shores, topographic features, and depth contours;

blue (in one or more tints) is used to depict shallow water areas, the boundaries of certain regulated areas (see Chapter 7), and Loran.C TDs;

gold (buff) is used to show land areas, and a darker screened tint is used to show built-up areas, such as cities (on charts published by NIMA, land area are shown in a screened black that appears to be gray);

green is used to depict areas that cover and uncover depending upon the stage of the tide (e.g., marches, mud flats, sand bars, etc.), another shade of green is used to depict green buoys and daybeacons;

magenta is used to depict red buoys and daybeacons, lighted buoys, and important caution and danger symbols, compass
roses, and recommended course (if given), Loran.C TDs; 

and finally white (the natural color of the chart paper) is used to depict deep-water areas, dredged channels, etc.

Symbols and Abbreviations
As noted, a standardized set of symbols is used to represent the various features depicted on nautical charts. These symbols are shown in Chart No. 1 and discussed throughout this manual. Numerous standardized abbreviations are used on nautical charts to conserve space. These abbreviations, together with others used in this manual, are shown in appendix B.
*Use of Charts

Throughout this manual the proper use of nautical charts is explored at length. 
Two concluding comments are relevant here.*

First, the mariner should keep in mind that, aesthetics aside, the modern-day nautical chart is a working tool. In earlier times,
charts were highly valuable documents printed on animal skins, parchment, and other valuable materials. The navigator&#8217;s determinations of course and distance measurements, plots of dead reckoning positions, fixes, etc., were typically made on separate pieces of paper. Distances and courses (the sailings) were determined by calculation, not actual plotting. Technical progress and economies of scale have changed the chart from an object of veneration to a working tool. Intended tracks, DR plots, bearings, fixes, distance measurement, ranges of visibility of lights, etc., are now plotted on the chart, rather than laborious calculation. So don&#8217;t be afraid to use the chart, and annotate it appropriately for the voyages you plan to take.

Second, the chart should be studied carefully before it is actually put to use. The legends should be read, scale determined (particularly if the scale changes from chart to chart), and all notes and symbols read and understood. On an actual voyage, particularly in congested and potentially dangerous waters, there may be little time to consult additional documents to determine the significance of a particular chart symbol, note, or legends. The horizontal datum should be noted and the GPS or LORAN-C receiver checked to ensure that this datum is being used. Latitude and longitude scales should be reviewed as these differ from chart to chart. Depth units should be checked and a realistic danger sounding selected (see Chapter 4) and marked on the chart. The navigator might wish to annotate the chart with additional relevant information, such as arcs of visibility of lights, prominent ranges, landmarks, facilities, danger bearings, and other relevant information from the chart or other sources such as the tide or tidal current tables, Light List, or U.S. Coast Pilot. As noted earlier, the charts should be laid out and sequenced to ensure that all necessary charts are aboard and that they can be retrieved expeditiously and in the correct order.

&#8220;Part of the responsibility for the continuing accuracy of charts lies with the user. If charts are to remain reliable, they must be corrected as indicated by the Notice to Mariners. In addition, the user's reports of errors and changes and his suggestions often are useful to the publishing agencies in correcting and improving their charts. Navigators and maritime activities have contributed much to the reliability and usefulness of the modern nautical chart. If a chart becomes wet, the expansion and subsequent shrinkage when the chart dries are likely to cause distortion..&#8221; Bowditch

*GUESS WHAT??? End of this segment, whew,... you think?*
Next I will elaborate on the Topography and related information to the charts. So you think there&#8217;s enough info on/in them yet? How about some feedback?

*Give me now wisdom and knowledge, that I may go out and come in before this people&#8230;Wisdom and knowledge is granted to thee;&#8230;2 Chr: 10-12*

References

Admiralty Charts and Publications. Symbols and Abbreviations Used on Admiralty Charts, Chart 5011, Edition 1, Hydrographic Office, Taunton, Somerset, TA 1 2DN, United Kingdom, 1991.
Blewitt, M., Navigation for Yachtsmen, David McKay Company, Inc., New York, NY, 1976.
Brogden, B., .Defining Terms, Since All
Chart Datums Are Not Interchangeable, Electronic Positions Should Be Used Carefully,. Ocean Voyager, 1994, pp. 16, et seq. Brown, L. A., The Story of Maps, Dover Publications, Inc., New York, NY, 1979.
Cahill, R. A., Strandings and Their Causes, Fairplay Publications, London, UK, 1985. Campbell, S., The Yachting Book of Practical Navigation, Dodd, Mead and Company, New York, NY, 1985.
Canadian Hydrographic Service. Chart No. 1/Carte No. 1 Symbols Abbreviations Terms, Minister of Fisheries and Oceans Canada, January 1992.
Coote, J. O., Yacht Navigation.My Way, W.
W. Norton & Company, New York, NY, 1987. Dahl, B., The User&#8217;s Guide to GPS, The Global Positioning System, Richardson&#8217;s Marine Publishing, Evanston, IL, 1993.
Defense Mapping Agency, Hydrographic/ Topographic Center. American Practical Navigator, An Epitome of Navigation (Bowditch), Publication No. 9, NIMA Stock No. NV PUB 9 V1, Bethesda, MD, 1995.
Departments of the Air Force and the Navy. Air Navigation, AMF 51.40, NAVAIR 00.80V.49, Washington, DC, 1983. Eyges, L., The Practical Pilot, Coastal Navigation by Eye, Intuition, and Common Sense, International Marine Publishing, Camden, ME, 1989. Farrell, C., Fell.s Official Guide to Small Boat Navigation, Frederick Fell Inc., New York, NY, 1962.
Graves, F., Piloting, International Marine Company, Camden, ME, 1981.
Hobbs, R. R., Marine Navigation, Piloting and Celestial and Electronic Navigation, Third Edition, Naval Institute Press, Annapolis, MD, 1990.
Human Technology, Inc. Desk Reference Guide: Specifications Unit, Chart and Map, Feature: Format. Report developed for National Ocean Service, Charting and Geodetic Services, Marine Chart Branch, Under Contract OPM-85-77, McLean, VA, October 1985.
..: Graphics.
..: Specifications.
Heinl, R. D., Dictionary of Military and Naval Quotations, Naval Institutes Press, Annapolis, MD, 1966.
Kals, W. S., Practical Navigation,
Doubleday & Company, Garden City, New York, NY, 1972.
Larkin, F. J., Basic Coastal Navigation, Sheridan House, Dobbs Ferry, New York, NY, 1993.
Maloney, E. S., Chapman Piloting, 60th Edition, Hearst Marine Books, New York, NY, 1991.
.... Dutton.s Navigation and Piloting,
Fourteenth Edition, Naval Institute Press, Annapolis, MD, 1985.
Markell, J., Coastal Navigation for the
Small Boat Sailor, Tab Books, Blue Ridge Summit, PA, 1984.
Monmonier, M., How to Lie with Maps, The University of Chicago Press, Chicago, IL, 1991.
National Research Council. Charting a Course Into the Digital Era, Guidance for NOAA&#8217;s Nautical Charting Mission, National Academy Press, Washington, DC 1994. Naval Training Command. A Navigation Compendium, NAVTRA 10494.A, U. S. Government Printing Office, Washington, DC, 1972.
Schofield, B. B., Navigation and Direction, The Story of HMS Dryad, Kenneth Mason, Homewell, UK, 1977.
Snyder, J. P. and P. M. Voxland, An Album of Map Projections, U.S. Geological Paper 1453, U.S. Government Printing Office, Washington, DC, 1989.
Toghill, J., Coastal Navigation, W. W.
Norton & Company, New York, NY, 1987. U.S. Department of Commerce, Coast and Geodetic Survey. Nautical Chart Manual, Volume One: Policies and Procedures, Seventh Edition, Washington, DC, 1992.
U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service, and Department of Defense, National Imagery and Mapping Agency. Chart No. 1 United States of America Nautical Chart Symbols Abbreviations and Terms, Ninth Edition, Washington, DC, January 1990.
U.S. Department of Commerce, National Oceanic and Atmospheric Administration, The Boat Show Briefing Book, External and Cooperative Affairs Group, Mapping and Charting Branch, Riverdale, MD, 1993.
U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service. Dates of Latest Editions, Nautical Charts & Misc. Maps, Silver Spring, MD, October 1, 1994 (issued quarterly).
U.S. Department of Transportation, United States Coast Guard, LORAN-C User Handbook, COMDTPUB P16562.6, Washington, DC, 1992.


----------



## Fishers of Men

*Changed my mind, were going to discuss:* Learn about these, The current follows them, the bait follows them, the walleye follow them...Get to identify them on the water.

CHAPTER 4
Hydrography and
Related Information
Introduction and Overview

The scope of this chapter includes hydrography (e.g., depth curves, soundings, nature of the bottom) and various specific hazards to navigation. Hazards can be either natural (e.g., rocks, reefs, shoals, tide rips, breakers) or artificial (e.g., wrecks, marine structures, unexploded ordnance, cable, and pipeline areas). This chapter provides essential background (e.g., definitions, historical asides), summarizes the utility of this information, describes the charting conventions used to depict hydrographic information (e.g., symbols and notes), highlights possible limits to the accuracy of this information (some made explicit in chart information), identifies other relevant sources (e.g., the U.S. Coast Pilot, the Tide Tables and Tidal Current Tables, NM, and LNM), and contains practical pointers on how hydrography and related information can be used by the prudent mariner.

_&#8220;Any ship can be a survey ship,. once..&#8221;_
Richards

In broad terms, the chapter *addresses hydrographic features *(e.g., soundings, depth curves, channels, nature of the bottom) and the cartographic depiction of several specific hazards to navigation (e.g., rocks, shoals, obstructions, wrecks). Because the scope of this material is so broad and *the information so important,* this chapter is long and detailed.

Many specialized terms used in this chapter are defined in the Glossary in appendix A. Names enclosed in parentheses (e.g., Bowditch) denote references listed at the end of this chapter that contain additional relevant detail or useful general discussions.

A Brief Aside: *Dual Units*
As of this writing, NOAA is in the process of converting charts from traditional or English. units (e.g., feet, fathoms) to metric units (e.g., meters). The Metric System has been established by the Metric Conversion Act of 1975 and the Omnibus Trade Act of 1988 as the preferred system of weights and measures in the United States. For U.S. nautical charts, the conversion to metric units is a multiyear effort with full implementation expected after the year 2000. Admiralty charts *will be fully converted to metric units by the year 2010 *(Bunyon). In the interim, charts in both systems of units will be available, so this manual treats both systems. The changeover to metric units is complex for many reasons, but users should have no difficulty converting from one system of units to the other. Illustrations provided in conventional units (e.g., soundings) can be mentally converted to metric units (meters and tenths) so no particular emphasis has been placed on the use of metric illustrations in this manual.

Utility of Hydrographic and Related Information Approximately 71percent of the surface of the earth is covered with water (Kember), and it is reasonable to believe that (on an overall basis) water would encompass at least this percentage of the area of the average nautical chart (excluding harbor charts). Regardless of the accuracy of this assertion, it is certainly true that the depiction of hydrographic and related information is one of the defining characteristics of the nautical chart as opposed to the landbound map.
In a sense, any question relating to the utility of hydrographic and related information on the nautical chart is almost rhetorical.

Nonetheless, it is instructive to set forth some of the uses of hydrographic and related information.
Table 4.1 outlines both general and specific uses of this information to the mariner.
*Simply put, this information is essential to effecting a safe and efficient voyage determining a relatively direct course from origin
to destination while avoiding hazards to navigation.
*

*Depth information *(particularly in areas of substantial gradient) can often be valuable as *an aid in fixing the vessels position.* And following a *depth contour* (using the vessels depth sounder) can be a useful technique in circumstances of restricted visibility. Charted islets (rocks which are above water) can also be used for position fixing rather like a landmark
(see Chapter 6) in the water.

*Some of the features normally classified as hazards to navigation, such as fish havens, wrecks, and offshore drilling platforms, are of interest to particular chart users. The recreational or charter fisherman, for example, is vitally interested in the accurate location of fish havens and wrecks (where fish often congregate). *Vessels or aircraft that service
offshore rigs need to know where these are located not to avoid them but to travel to these structures.

Yet other features, such as foul areas, areas where unexploded depth charges lie, and cable or pipeline crossings do not necessarily present hazards to transiting vessels, but rather mark areas where certain activities may be restricted or ill-advised. For example, foul grounds may snag fishing nets or lines, anchoring is prohibited in the vicinity of submerged pipelines and cables, and anchoring is unwise in areas where unexploded ordnance is reported.
Finally, the bottom characteristics are relevant for several reasons. Bottom samples, drawn with tallow attached to a leadline, were used in bygone times as an aid in determining the vessels position (Cohen). Nowadays, knowledge of the nature of the bottom is chiefly important in selecting a suitable place to anchor and the type of anchor to use (Hinz). As noted above, hydrographic information is first discussed, followed by specific h*azards to navigation.*

Specific Illustrations:
&#8226;	To voyage expeditiously without running aground (e.g., depth information, limits to channels, presence of shoals, reefs, submerged rocks, etc.).
&#8226;	To ascertain whether anchoring is possible (e.g., depth, type of bottom, absence of restrictions, absence of unexploded depth charges, etc.) or desirable (e.g., designated anchorage areas1) and aid in the determination of the proper amount of anchor line to deploy (depth) or even type of anchor to deploy (type of bottom).
&#8226;	To identify which slips/piers are suitable for berthing (depth, nearby hazards).
&#8226;	To be used as an aid in fixing the vessel&#8217;s position (e.g., depth curves, bare rocks, stranded wrecks, etc.).
&#8226;	To facilitate tracking during times of reduced visibility and/or when operating in areas with few ATONs or distinguishing topography/landmarks (e.g., depth). For example, in waters with a relatively steep depth profile, a depth sounder can be used to track along a depth curve.
&#8226;	To provide information relevant to fishing activities (e.g., locating wrecks or fish havens). Also, to
avoid areas where fishing nets or other equipment might be damaged.
&#8226;	To avoid possible hazards to operation (e.g., fish trap or stake areas, log booms, pilings, wrecks,
deadheads, stumps, snags, tide rips, etc.).
&#8226;	To identify areas of special interest to various user-community segments (e.g., drilling platforms, artificial islands, hunting and fishing structures, etc.).

*Hydrographic information,* as portrayed on the nautical chart, consists of depth soundings, depth contours or curves, depth-dependent color designations (blue tints), notes showing the controlling depth of improved channels, and descriptions of the nature of the bottom. Taken together, this information enables the mariner to navigate safely and efficiently.
*Common Plane of Reference and Survey Scales*

Hydrographic surveys are the basic source of soundings and related information. These surveys, conducted by NOAA and other vessels, utilize information derived from a wire drag apparatus (earlier technology), echo sounding, and side-scan sonar. Sounding data derived from these surveys are adjusted to reflect a common horizontal plane of reference, mean lower low water (MLLW), as shown in figure 4.1.










By definition MLLW is an average (generally over a 19-year epoch) of all lowest water levels for tidal days. Viewed from this perspective, charted soundings are conservative, in the sense that depths are typically greater than shown by soundings data. Even though the datum is based on averages of low water (lower low water in cases where there are two low-water periods in a day), the actual water level at any time can be lower than this average which means that the actual water depth can be less than the charted depth. On days with spring tides (tides having a greater range than normal), prolonged winds from certain directions, or persistent extremes of barometric pressure, the actual depth of water can be less than the charted depth.

The basic scale for hydrographic surveys performed by NOAA is 1:20,000.other scales are multiples or fractions of this basic scale.
As noted in the NOS Hydrographic Manual,

The criteria used for scale selection are based on the area to be covered and the amount of hydrographic detail necessary to depict adequately the bottom topography and portray the least depths over critical features. A cardinal rule of nautical chart construction is data from a hydrographic survey should always be plotted at a scale ratio larger than that of the chart to be
compiled. The survey scale is generally at least twice as large as that of the largest scale chart published or proposed for the area.

*Inshore surveys, *defined as those conducted adjacent to the shoreline and in general depths of 20 fathoms or less shall be plotted at scales of 1:20,000 or larger . . . In contrast, *offshore surveys *are those conducted in waters of general depths between 20 and 110 fathoms not adjacent to the shoreline.

Basic hydrographic and navigable area surveys of all important harbors, anchorages, restricted navigable waterways, and areas where dangers to navigation are numerous shall be plotted at scales of 1:10,000 or larger..
Cartographers, therefore, always have hydrographic information available at a larger scale than are plotted on the nautical chart.









*A source diagram* is included in all new editions (after November 20, 1992) of NOAA nautical charts at a scale of 1:500,000 or larger. (A source diagram is included on similar Admiralty charts.) It provides information on the source, date, and scale of the survey(s) used in the preparation of a given chart. The source diagram provides an indirect indication of the quality of the data (older surveys used less modern equipment, may not have been as complete, and the depth profile of the bottom may have altered over time as a result of suspension and deposition processes). This information allows users to make their own judgments of the datas fitness for a particular purpose.

The date of the survey may prove useful in selecting a route.transiting areas more recently surveyed in preference to others. Large-scale charts compiled exclusively from a single survey do not contain a source diagram. Instead, this information is provided in a parenthetical expression (e.g., from surveys of 1982 to 1984) to the AUTHORITIES note shown on each chart.

Figure 4.2 provides an illustrative source diagram, taken from NOS Chart No. 13218 (Martha.s Vineyard to Block Island). The Queen Elizabeth II (QE II) ran aground (Brogden, Sabellico, Walsh, Ocean Navigator) in August 1992 on an uncharted rock in area .d. (plotted with soundings from a 1939 survey) on this source diagram. The QE II, drawing 32 feet, went aground in an area having a shoalest charted depth of 39 feet. A full discussion of the incident is beyond the scope of this manual, but it does serve as a cautionary tale and illustrates the wisdom of providing an ample margin of safety beyond the minimum depth required to accommodate the vessel.s dynamic draft.

The master of the QE II might have selected a route which provided a greater margin of safety had a source diagram been available. Inspection of this source diagram and the chart itself indicates that, in general, the shallower areas have been the subject of more recent (and larger scale) surveys by NOAA.

*Soundings*
As noted, the inclusion of individual soundings is one of the ways in which hydrographic information is represented on the nautical chart. Individual soundings are expressed in meters and tenths (decimeters) on new charts, and in feet and fathoms on older charts, measured relative to MLLW. The source of the soundings data is the hydrographic survey(s) of the area to be charted.

As noted above, surveys are normally conducted at a scale larger than the largest scale chart of the area. Depicting all of the survey soundings on the chart particularly at a smaller scale would be difficult or impossible.
Recall all the other features, such as ATONs, hazards, and areas and limits (Chapter 7) that compete for space on the nautical chart (Kember). Even if physically possible to prepare, a plot showing all hydrographic survey data would be very cluttered and difficult for the mariner to interpret.at least for the well-surveyed coastal areas. Figure 4.3 illustrates the differences between detailed hydrographic survey soundings (on the left side) and those generalized and plotted on a typical nautical chart (on the right side).










As a practical matter, therefore, the cartographer is faced with the important task of selecting a subset of the available soundings for depiction on the chart (e.g., Zoraster, Ekblom). The objectives of the selection process are to ensure that the overall presentation of depth data is accurate, as complete as feasible, and is easily understood by mariners. 

*The Soundings Selection Challenge *

To explain the particular selection rules and guidance followed by cartographers, it is well to remember that the primary function of soundings and depth curves on nautical charts is to present an accurate portrayal of the bottom configuration. Key bottom features that are charted include shallow areas, shoals, banks, and bars, irregular bottoms, smooth bottoms, deeps, and navigable natural channels and passages. These features are defined in table 4.2. (Additional material can be found in appendix A.) Briefly, these features serve to define preferred routes (e.g., navigable channels or passages), areas to be avoided (e.g., shoals, ledges), opportunities for position fixing (e.g., deeps, irregular bottoms), or other relevant detail (e.g., smooth bottoms).

The aim of the selection process, therefore, is to reduce the total number of soundings (so as to improve chart clarity) yet still provide a sufficient number of soundings to identify and locate the features described in table 4-2. 

The selection process does not operate by merely deleting a certain number of survey soundings e.g., by deleting every second point. Rather, the process takes cognizance of the information content of each sounding, and preferentially retains significant. soundings. A sufficient sounding density is retained to depict natural channels, shoals, or other hazardous areas to highlight these features for quick recognition by the mariner. Additional (but fewer) supportive soundings are selected to complete the bottom description. 

The spacing of soundings on the nautical chart is also relevant. Fill soundings (see below) over flat bottom areas are relatively widely spaced. Soundings in shoal areas are provided in greater density, which serves to draw the *attention of the mariner to these potentially dangerous areas* (Magee)

In general, cartographers *first select soundings from shoal areas *and natural channels and work toward deeper water so as to identify all shoal areas that might impede surface navigation, provide information about natural channels between or through shoal areas, and portray the configuration of the bottom (Nautical Chart Manual, Kember). As of this writing, the selection of soundings is still a manual process, although computer models (Zoraster) show promise.

*Selection Criteria for Soundings to be Charted. *
The above discussion summarizes the objectives and overall importance of the selection of appropriate soundings for depiction on nautical charts. This section summarizes the specific criteria and guidance used by cartographers for selection of soundings.

These criteria, and supporting guidance, are summarized in table 4.3. In brief, the emphasis is on selection of soundings which present information on least depths, critical soundings, deep soundings, supportive soundings, and fill soundings. Additional specific guidance is also given in table 4.3 for selection of channel range soundings, non junction soundings, changeable soundings, soundings in slips and around piers, depths over rocks, areas where the survey has not been able to detect the bottom, and river depths. Broadly, the criteria offered in table 4.3 identify soundings to be emphasized (e.g., least depths, critical soundings, deeps), soundings of lesser importance (e.g., supportive soundings, fill soundings), and circumstances where the depiction of soundings is ill-advised (e.g., depiction of soundings in changeable areas).
Skippers of recreational craft often express puzzlement at some of the deeper soundings included on the nautical chart. *After all, most recreational power boats draw 4 feet or less, and most recreational sailboats probably draw 6 feet or less.*










TABLE 4-2
*Bottom Features Depicted on Nautical Charts*

*Shallow areas* are large expanses of shoals or of shallow water where the changes in depth are relatively slight. Some bays fed by river systems are shallow throughout.

*Shoals, Banks, and Bars:*

Shoals are shallows that constitute offshore* hazards to navigation.* They are defined as having a depth of 10 fathoms or less and may be composed of *any material except rock or coral. *A shoal may be an isolated feature or part of a shoal area composed of two or more shoals. A bank is an area of relatively shallow water which is, however, of sufficient depth for safe navigation. Bars are ridges of sand or gravel, often at the mouth of a river, which may obstruct navigation. Note that shallow areas of *rock and coral are charted as ledges and reefs and labeled,* rather than being delineated solely by depth indicators.

*Irregular bottom* areas may consist of shoals, shallows, passages, deeps, etc., and are characterized by relatively large and abrupt depth differences throughout the region.

*Smooth bottom* areas are expanses where variations in depth are gradual and are relatively small compared to the size and depth of the area as a whole. Smooth areas in relatively deep water are the least important feature shown on charts. Generally, they pose no navigational hazard. These are depicted to provide &#8220;bottom detail&#8221; to navigators, rather than to enhance boater&#8217;s &#8220;safety.&#8221;

*Navigable Channels and Passages:*
A channel or passage is a relatively deeper navigable route through an otherwise shallow area. Natural channels or passages are important features which contribute to the navigational value of a chart. Natural channels may constitute routes from deep water into shore or harbor areas, or routes between deep water areas through shoals or bordering shallow areas.

*Deeps:*
Deeps are local deformations in the bottom configuration characterized by a significant increase in depth when compared to the surrounding areas. The boundary of a deep is the zone which separates the deep area from the surrounding shallower water. The size of the zone depends on how well the deep can be distinguished from the surrounding area.

Why, they ask, include chart depths much greater than this? There are several reasons for inclusion of deeper soundings but two are particularly relevant. First, as noted in Chapter 1, the nautical chart is prepared for several types of users. Although recreational vessels may draw 6 feet or less, large commercial vessels draw much more.

Super tankers, for example, draw 40 feet or more (the ultra-large crude carrier, Seawise Giant, built in 1979 reportedly draws almost 100 feet!), and a submarine at periscope depth draws 100 feet (submarines operate at depths considerably greater). Second, operators of all types of vessels can use depth information as an aid in position fixing and for tracking along a depth curve (see below). 8-41

*Least Depths:*
Least depth soundings over features (e.g., pinnacles, domes, ridges), which are delineated by depth curves *should be identified because* they are typically associated with hazardous shoal areas. When applying hydrography from larger to progressively smaller scales, a series of shoals may have to be generalized into a single-shoal feature. In this case, the most shallow sounding is selected to represent the least depth over the generalized shoal. *The least depth *of a natural channel (also termed the controlling depth) is also charted. Every natural channel has *at least one* controlling sounding, which identifies the minimum depth of the channel.

*Critical Soundings:*
Within each isolated feature bound by a depth curve, the shallowest seaward sounding must be selected. By definition this is a critical sounding and is given even if the same as the depth curve. Critical soundings represent least depths in proximity to known or potential *navigational routes. *Note that while a critical sounding is almost always a least depth, *a least depth is not always a critical sounding; *the location of the sounding is also an important factor.

*Deep Soundings:*
Deeps, like shoals, are local deformations of the bottom shape. Soundings which are approximately 10&#37; to 20% deeper than their surroundings are considered important soundings and will usually be selected by cartographers. If chart space is constrained, however, a deep sounding does not normally take precedence over an adjacent critical shoal sounding.

*Supportive soundings *(also termed developmental soundings) supply additional information to the user about the shape of the bottom. These are also used to provide periodic identifiers for depth curves and to show changes in bottom slope away from shoals or deeps.

*Fill soundings *are used to portray smooth bottoms or deep areas between shoals that are not adequately defined by supportive soundings. Normally, fill soundings provide information about large, gradually sloping depressions that are not deep enough to be enclosed by a depth curve. Ideally fill soundings radiate away from the deep sounding.

*Channel Range Soundings:*
When a range is charted to show the centerline of a channel, a line of soundings is selected on the range. This policy does not apply to improved (dredged) channels.

*Nonjunction Soundings:*
When the application of a recent survey to a chart reveals conditions so changed that a satisfactory junction cannot be made with the hydrography of former surveys, a blank band of approximately 5mm shall be left beyond the limits of the more recent survey and a note added, such as: &#8220;Hydrography to (eastward) from surveys of 1984.&#8221;

*Changeable Areas:*
All hydrographic detail, including soundings and floating aids, may be omitted from all areas known to undergo continual and rapid change, such as ocean inlets and openings between barrier islands. (See figure 5-7 in chapter 5.)
*Soundings in Slips and Around Piers:*
Soundings in docks, slips, and around piers should be shown where space allows. The cartographer should select soundings far enough off piers to provide depths at the keel lines of vessels which use these piers.

*Depths over Rocks:*
A sounding over an isolated rock shall have the label &#8220;Rk&#8221; placed next to it. 
*No Bottom Soundings:*
When no bottom is reported in the survey, the measured depth shall be shown under a bar with a small dot over it. (This type of fill sounding shall be avoided whenever possible.)

*River Depths:*
The shoreline shall be broken to accommodate soundings for narrow rivers where the sounding units would touch the shoreline because of the size of the feature at chart size. When portraying hydrography in navigable tributaries, the cartographer must select soundings that indicate controlling depths in conjunction with those that portray the best navigational channel. Where feature size or chart scale do not allow for the representation of both controlling depths and channel depths, the controlling depths take precedence.

Soundings information is shown on the chart by many small printed figures, each denoting a particular sounding. Soundings in traditional units (fathoms, feet) are shown in conventional (vertical) type, soundings in metric units (meters and tenths) are charted in italic type.

Soundings are charted in their exact geographic location, and oriented parallel to the base of the chart, even if the chart projection is skewed.

All hydrographic detail and floating ATONs are removed from certain areas undergoing continual and rapid change, such as ocean inlets and openings between barrier islands if inclusion of this information might present an unreasonable risk to mariners. The area of omitted soundings is tinted in blue, and an explanatory note charted, as shown in figure 5.7 in the following chapter. 

Normally, only small-draft vessels would consider using such areas, but some of these areas are frequented by larger draft commercial vessels sometimes *with unpleasant consequences* (see Walsh, Professional Mariner, Issue No. 5). The safest course of action is to imagine these areas have *&#8220;Keep Out&#8221;* signs posted. 

*On small scale nautical charts, soundings within a group of rocks or coral heads through which there is no well-defined channel are also omitted.*

*Depth Curves* (Section I of Chart No. 1)
In addition to sounding data, depth information on nautical charts is summarized by charted depth curves and labels. According to the Desk Reference Manual, a depth curve.....is a line connecting points of equal
water depth which is sometimes significantly displaced outside of soundings, symbols, and other chart detail for clarity as well as safety. Depth curves, therefore, often represent an approximate location of the line of equal depth
[a depth contour] as related to the surveyed line delineated on the source.
The term curve is often used collectively for both depth curves and depth contours. [Material in brackets added for clarity].

Depth curves complement the sounding data and enable the mariner to form a better mental image of the shape of the ocean bottom. Griffin and Lock, writing in the Cartographic Journal, offer the following comments on contours:
&#8220;The origins of the contour may remain indistinct, but in its earliest known (submarine) form it manifested two major advances from the earlier sporadic use of spot heights (soundings). Firstly, it provided spatial continuity of information, developing a statistical surface from a set of discrete control point data, thereby introducing additional information by the process of interpolation. Secondly, it simplified the symbol array and stressed the need for visual integration of the contours to form a mental image of the configuration of the surface of the lithosphere.&#8221; 

*Depth curves (or contours)* resemble elevation curves used to depict topographic relief (see Chapter 3), but there are subtle conceptual differences between these terms. Kember, also writing in The Cartographic Journal, offers these colorful insights on the use and interpretation of depth contours on Admiralty nautical charts; comments equally applicable to NOAA charts.

Depth contours also receive treatment that may surprise topographic cartographers. For years, in hydrographic departments all over the world, these were hardly regarded as contours at all *but as danger lines *meaning precisely keep out. Each depth contour said keep out to a particular type of vessel.

The 1-fathom line warned small river and fishing vessels; 2 fathoms, many coasters, colliers, small oceangoing ships; 3 fathoms the majority of ocean-going ships. For the mighty few, the largest battleships and the proudest ocean liners, the 5-fathom line was specially provided. As keep out lines they were drawn to embrace all depths that might possibly offer danger to a vessel of the appropriate type.

Caught in the contours net were often a large number of depths greater in value than the contour itself, but nobody minded the ninety and nine greater depths caught inside so long as there was not one lesser depth left in outer darkness. 

Today marine cartographers are more inclined to treat contours in the manner of our topographic colleagues and to allow contours to play their part in revealing underwater topography. But when it comes to the crunch and we must simplify or generalize we do, deliberately and knowingly, and on behalf of the navigator, include all lesser depths within a contour even if it means that our catch includes many deep ones as well.

&#8220;So on the Admiralty Chart the depiction of depth is a curious mixture of the exact (high accuracy of spot soundings for example) coupled with this danger fixation which gives great prominence to lesser depths. *The result is a navigators bathymetry a very different thing from a bathymetrists bathymetry. *

In spite of appearances the chart is not a navigational document of the superimposition type. It has something of the underground maps ruthless selectivity and single minded user orientation.&#8221;

Depth curves are used on charts to illustrate shallow areas, shoals and banks, irregular bottoms, navigable channels and passages, and deeps much the same information as that identified in table 4.2 for soundings.

*Depth curves are particularly relevant to navigators using electronic depth sounders. *Of course, the mariner must make adjustments for the placement of the echo sounder with respect to the surface of the water and for the state of the tide in order to compare the observed depth with the charted depth. For example, assume that the observed reading on the echo sounder is 15 feet of water under the keel, the position of the transducer is 3 feet beneath the vessels water line, and that the calculated height of tide is 7 feet (relative to chart datum). To reduce these data to a figure comparable to the charted depth, it is first necessary to add the difference between the location of the transducer and sea level, and then subtract the calculated height of tide, so the comparable figure would be 15 + 3 - 7 = 11 ft. 

Guidelines for charting depth curves abstracted from the Nautical Chart Manual include:
*The development of curves varies* according to the particular bottom feature being charted. Large shallow areas are generally represented by a sparsity of depth curves, while banks and bars and isolated shoals are represented by a series of *closely spaced contour closures.
*

In areas with irregular bottoms, contours are selected for each isolated shoals least depth. Supportive soundings and curves are then selected to reinforce this least depth as well as to define the zones between the shoals. This helps to convey to the user the large depth variations in the area.

Smooth bottom areas are characterized by smoothly flowing and relatively widely spaced contours with only occasional closures identifying shoals.
Depth contours are particularly useful in *showing natural channels* from deep water into shore or harbor areas and routes between deep-water areas through shoals. If the chart scale is too small to illustrate all the channels shown on the survey, the most important routes are retained in preference to less important routes.

Depth curves *are not typically shown *around charted isolated deeps in shallow areas, unless the deep is part of a natural channel. Depth curves will usually be shown with charted deeps in deeper water. Isolated deep curves are always supported with a sounding inside. Depth curves around depressions are of little value, and are not typically charted. However, these are shown if they reveal features which may have some navigational value, or if they indicate the *deepest side of a river.*

*Very steep slopes *would entail numerous closely spaced depth curves and create a problem in terms of chart clutter. In this case the shallowest and the deepest curves are retained in lieu of less important intermediate curves. A series of standardized values for depth curves is employed. For example, the standardized curve intervals when depth is given in feet includes (in feet), 6,3 12, 18, 24, 36, 60, 120, 180, 240, 300, etc. For metric charts the standard intervals (in meters) are, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, etc.

(TIP) _The difference in type face serves to alert mariners to the difference in depth units._

GUESS WHAT?...TO BE CONTINUED


----------



## Fishers of Men

Map Coordinates - Lake Erie 
Name	Location	Latitude	Longitude	Aprox Depth
Airport Reef	E. Kelleys Island	41.35.92	82.39.92	22
Airport Reef South Bump	E. Kelleys Island	41.35.58	82.39.70	24
American Eagle Shoals	South Passage	41.36.00	82.46.00	10
Ballist Island Reef	East of Middle Bass	41.40.75	82.46.47	23
Big Pickerel Reef	Davis-Besse	41.40.08	83.03.82	14
Buckeye Reef	S. Ballist Island	41.40.27	82.47.18	2
Clinton Reef	W. Cataba Island	41.33.75	82.52.97	11
Cone Reef	W. Niagara Reef	41.40.00	83.02.85	10
Crane Reef	S. of West Sister	41.40.65	83.06.37	15
Crib Reef (7 Buoy)	S.W. of Niagara Reef	41.38.83	83.00.35	2
Doo Dah's Reef	N.W. of North Bass	41.45.10	82.55.70	26
Flat Rock Reef	W. of Niagara	41.39.49	83.01.20	13
Gull Island Shoal	Gull Island	41.39.55	82.41.37	0
Kelleys Island Shoal, (center)	N. of Kelleys Island	41.38.33	82.38.87	2
Kelleys Island Shoal, (east side)	N. of Kelleys Island	41.38.03	82.38.65	6
Lake Side Reef	N. of Lake Side	41.33.13	82.45.15	12
Little Pickerel Reef	W. of Niagara	41.40.15	83.01.24	15
Locust Point Reef	N. of Davis-Besse	41.38.70	83.04.05	5
Marble Head Reef	E. of Marble Head	41.31.82	83.40.50	22
Middle Harbor Reef	N. of Middle Harbor	41.34.12	82.47.70	2
Middle Passage Reef	E. of Gull Reef	41.39.28	82.40.32	23
Middle Passage Reef S Bump	S.E. of Gull Reef	41.38.90	82.39.77	25
Mouse Island Reef	N. of Mouse Island	41.36.38	82.50.05	9
Niagara Reef	West of Green Island	41.39.85	82.58.40	3
Northwest Reef	N.W. of North Bass	41.44.77	82.53.50	30
Round Reef	S. of Niagara Reef	41.37.03	82.59.65	9
School House Reef	S. of North Bass	41.42.20	82.49.63	9
Starve Island Reef	S.E. of Starve Island	41.36.78	82.48.87	7
Starve Island Shoal	S. of Starve Island	41.37.28	82.49.12	8
Sugar Island	S. of North Bass	41.41.87	82.49.07	10
Toussaint Reef, S.W. Crest	S.W. of Niagara Reef	41.37.75	83.01.20	3
Turtle Reef	N. of Davis-Besse	41.38.93	83.05.93	11






West Harbor Reef	N.E. of West Harbor	41.34.71	82.48.15	9
West Reef	West of North Bass	41.42.70	82.50.82	5
West North Bass	West of North Bass	41.43.13	82.50.53	6
West Reef, North Bump	West of North Bass	41.43.98	82.50.05	24
West Sister Reef	S.W. of West Sister	41.43.40	83.07.68	22

Range A Can	West End of North Line	41.41.49	83.07.55 
Range B Can	Center, North Line	41.41.48	83.03.76 
Range C Can	East End of North Line	41.41.48	83.00.00 
Range D Can	S.E. of Niagara Reef	41.38.57	82.57.39 
Range E Can	West of Mouse	41.37.09	82.56.13 
Range F Can 41.35.66	82.54.83 
Range G Can 41.34.60	82.56.73 
Range H Can 41.33.62	82.58.68 
Range J Can 41.36.02	83.03.40 
Range K Can 41.37.86	83.04.88 
Range L Can 41.39.90	83.06.30 

C Can-Bell Buoy-Can Border	East of Middle Island	41.40.59	82.35.05 
D Can-Canadian Border	Middle Island	41.40.59	82.40.79 
E Can-Canadian Border	East of North Bass	41.42.92	82.45.62 
F Can-Canadian Border	North West of North Bass	41.47.00	82.54.12 
G Can-Canadian Border	South East of Middle Sis.	41.49.33	82.58.92 
H Can-Lighted Bell	West of Middle Sister	41.51.83	83.04.18 

NOAA Weather Buoy	North off Vermillion	41.40.57	82.23.88


----------



## Fishers of Men

*Lake Erie Fishing & Landmark Nic Names*
*Actual Name Nic Name 1 Nic Name 2 Nic name 3 * 
Round Reef---	The Hoop 
Niagara Reef---	Big Green One---	Parking Meter 
West Sister Island---	Big Trees 
Middle Sister Island---	Little Trees 
East Sister Island 
Camp Perry---	Checker Board---	Picket Fence 
Starve Island--	-Hungry One 
Mouse---	Squeky One 
N.E. Corner, Middle Bass Island--	Luci's Point 
Rattle Snake Island---	Snake 
Cedar Point---	Needle 
Ruggles Beach---	Castle 
West of Catawba Island State Park---	Fish Bowl---	Bath Tub 
Kelley's Island, S.W. Corner---	Carpenters Point 
Kelley's Island, East Side---	Sunrise Point


----------



## Fishers of Men

*Continued from prior post:*

*Charting Practices*

On earlier charts, depth curves were depicted using a variety of symbols (see Section I 30 in Chart No. 1), line weights, and colors. This section details present charting practices. Charting conventions for the depiction of depth curves include lines or curves, labels, and a blue tint.

*Symbol*

Depth curves are charted with a solid black (blue on some charts) line of 0.10 mm thickness. Approximate depth curves are charted with a dashed line. These curves may be broken for curve labels (the depth) and chart notes. However, curves do not overprint any other charted feature.
Depth curves are charted to scale as depicted on source documents, but may be generalized. (Where generalization is necessary, a curve is always displaced toward deeper water, unless this closes or seriously reduces the width of a navigable channel. The minimum width between depth curves identifying a natural channel is 0.3 mm.).

*Labels*
Depth contour/curve labels are shown in italic type for charts where depths are given in feet/ fathoms. Labels for depth contours and curves on metric charts with italic soundings are printed in conventional type. The convention of printing soundings and curve labels in different type (e.g., vertical if soundings printed in italic) prevents any confusion between the estimated contour level and actual soundings. The contour or curve line is broken for the labels with the label centered on the line. As a general rule, labels are placed along the lines at 10 cm to 15 cm intervals so as not to interfere with soundings and other charted data. In congested areas, labels may be staggered along the lines if this improves the legibility of the chart. All depth contours and curves are labeled in the same unit as the soundings shown on the chart (e.g., in meters for metric charts, in feet if soundings are given in feet, etc.).

*Shallow Water Tint(s)*
A blue tint (Blue Tint No. 1) is shown on the chart to emphasize shallow water areas considered dangerous to navigation. The depth contour selected as the boundary for the tinted area is not a constant for all charts, but rather determined by the chart scale, prevailing depths available, and the draft of the vessels expected to navigate within the charted area. The limit value for the tint for any chart can be determined by noting the soundings on either side of the tinted area (see Kals).

Having said this, the limit of the blue-tinted area is typically the 6-foot curve on harbor charts, and the 12-, 18-, or 30-foot curves on coastal charts (Dutton, Chapman).
For some charts two separate tints are used, Blue Tint No. 1 and a lighter Blue Tint No. 2. 
The use of two tints enables two depth zones to be delineated; the second depth zone (deeper and tinted in a lighter blue) expands the usefulness of the blue-tinted danger area to another group of chart users.

Figure 4.4 provides an excerpt from NOS Chart No. 13218 (Martha.s Vineyard to Block Island) which illustrates many of the chart conventions discussed above. In this case, the limit of the blue tinted area is the 30-foot curve. Depth curves are shown at 30, 60, 90, 120, and 150 feet. Note that the soundings density is greatest in shoal areas and where necessary to characterize the shape of the depth curves.

*Improved (Artificial) Channels*

Unlike natural channels, improved (artificial) channels are those which are dredged to establish and maintain project depths. The side limits of improved channels are shown on charts by dashed lines (I 22 of Chart No. 1). Depth curves are not shown for improved channels. Channel depth information is either tabulated or shown within or adjacent to the channel.

*Controlling depths* are charted in feet on non metric charts (including those with soundings in fathoms) and meters and decimeters on metric charts.

Channels for which graphic surveys are received by NOAA and which are 400 feet or more in width (Type 1) for their major portion provide depth information tabulated by quarters; channels 100 feet to 400 feet (Type 2) are tabulated by outside quarters and middle half; and channels *less than 100 feet (Type 3) are tabulated by full width. *On charts where dredged
channel legends and tabulations are adequately covered by larger scale charts, the legend and tabulation are omitted, a placed in the channel, and a note (preferably on a land area of the chart) is added, as illustrated by the following example:










*BEAUFORT INLET*
The project depth is 30 feet to Morehead City. For controlling depths, use chart 11547.

If the reported depth is less than the charted depth, an additional notation such as Reported shoaling in channel 1986 is added.

*Symbols*

*Dashed lines* are used to show channel limits for improved channels. The line thickness, length of dash, and space vary with the type of channel. Blue tint is charted inside the limits of improved channels when the project depth or controlling depth is equal to or less than the value of the charted blue tint curve or when the seaward end of an improved channel terminates in a blue tint area, regardless of channel depth. Figure 4.5 presents an excerpt from NOS Chart No. 12314 (Delaware River, Philadelphia to Trenton), which shows how improved channels are depicted on the nautical chart. A table of channel depths is included elsewhere on this chart. Controlling depths in this area are between 16 and 18 feet according to surveys of 1-91. There is actually a power plant located near the two stacks to the right of the Duck Island Range. Barges laden with coal are unloaded at the overhead conveyor. Note that barges coming from seaward (the south) cannot travel directly to the conveyor from the main channel. Rather, they must be pushed north to the Perriwig Channel to avoid shoals and rocks. *Here is indisputable evidence of the benefits of a chart!*

*Bottom Characteristics*

The character of the bottom is identified on all nautical charts, particularly in harbors, designated anchorages, and all other areas where vessels may anchor. Bottom characteristics determine the suitability of the area for anchoring, and the type of anchor best suited to the area (see Hinz, or the introduction to appendix A).

Bottom characteristics are of interest for other reasons. According to the Nautical Chart Manual, bottom characteristics are charted to provide the following information;
1. They assist fishermen in selecting areas where fish may be found and in avoiding places where nets and equipment may be damaged.

2. In tidal areas, they show where vessels may safely take the ground at low water.
3. In shoal areas, they help navigators to assess the stability of shoals and to distinguish rocky areas from areas of unconsolidated materials.. Descriptors used for bottom characteristics are shown in Section J of Chart No. 1. The most commonly used bottom characteristics on nautical charts are provided in table 4.4. Definitions of these terms are given in appendix A. Nouns and their abbreviations begin with a capital letter; adjectives or qualifying words and their abbreviations are composed of lowercase letters only. Bottom characteristics are charted in black italic type.

Figure 4.4 also shows the use of bottom descriptors. In the area around Block Island, the bottom is described in various places as hrd (hard), rky, (rocky), Blds (boulders), yl S Sh G (yellow sand, shells, and gravel), and M S G (mud, sand, and gravel).

*Specific Hazards to Navigation*

The balance of this chapter addresses specific hazards to navigation, including danger curves, rocks, shoals, ledges and reefs, foul areas, wrecks, obstructions, marine structures, unexploded ordnance, and dangerous water conditions. Many of these objects/areas have special symbols described in Chart No. 1. Specific references to section of Chart No. 1 are shown in parentheses. Thus, for example, the symbol used to represent the danger curve or danger line is shown in Section K, item 1, of Chart No.
1. It is noted in what follows as danger curve (K 1). Although pertinent excerpts of Chart No. 1 are included in this and other chapters, space constraints do not permit inclusion of the entire chart in this manual. Users should read this manual with a copy of Chart No. 1 at hand for ready reference.
2.	









As a point of general interest, it is useful to note the type convention used to depict these objects/features. Vertical type is used for names of topographic features and fixed objects, which extend above high water i.e., bare features are shown in conventional type. Slant *(italic) type* is used for names of hydrographic features, including names of water areas, underwater features, and floating ATONs (see Chapter 5). Because this convention is common to all charted items discussed below, a discussion on type styles is not repeated in each of the subsections, except where necessary for clarity.

*The various specific dangers *to navigation are charted principally to alert the mariner to submerged artificial and natural hazards. However, it should be noted that certain types of vessels may congregate in these areas, and present an additional collision hazard. Thus, for example, private and charter fishing vessels may be found in the vicinity of fish havens and
wrecks, dive boats may be found in the area of charted wrecks, and service vessels of various types may be found in the area of artificial platforms.










*Rule 5 *of the Navigation Rules specifies: Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.

Particular vigilance is appropriate in areas of greatest vessel density.
Figure 4.6 provides an excerpt of Section K from Chart No. 1, which illustrates many of the symbols referenced in what follows. Danger Curve (K 1)
According to the Desk Reference Guide, a danger curve.
....is a dotted curve used to draw the navigators attention to a danger which would not stand out clearly enough if it were represented on the chart solely by other specific symbols. This dotted curve is also used to delimit areas containing numerous dangers, through which it is useful to navigate.

Danger curves are used to outline areas or emphasize discrete features (e.g., rocks, shoals, submerged structures) that are known or potential hazards to navigation. As with depth curves generally, the limiting line is always charted on the side of safety that is, the danger curve is either drawn to scale or slightly larger, to help ensure that any errors are conservative. Submerged structures covered by 66 feet, or 11 fathoms (20 meters) or less are indicated by a dotted danger curve enclosing the symbol for the particular danger. If the structure is covered by depths greater than 11 fathoms (20 meters), the danger curve is charted only if the structure is considered hazardous to navigation.

*Charting Practices*

The danger curve is charted with a black dotted line. Insofar as possible, the danger curve is charted in its exact geographic position. This curve is an integral part of other symbols used to depict hazards. If chart space presents a problem for inclusion of a specific symbol within a danger curve, the symbol may be omitted and only the depth included. Areas enclosed by a danger curve that are less than 2.5 mm in diameter at chart scale are charted with the minimum size circle 2.5 mm in diameter. Adjacent features individually enclosed with a danger curve may be enclosed with a common generalized curve on small-scale charts. *A blue tint* is used within a danger curve to mark depths of *66 feet or 11 fathoms or less*. The blue tint can be used in areas of greater depths if the object is considered a hazard to navigation.

*Labels and Notes*

Appropriate labels are included to describe the danger being enclosed with the danger curve.
Rocks (K 10-17, a, b, f)
According to the Desk Reference Guide, a rock.
....is an isolated large mass of stone, usually one constituting a danger to navigation. Rock is a collective term for masses of hard material generally not smaller than 256 mm.

Rocks are classified as bare, awash, rocks awash at the sounding datum only, or sunken. Bare rocks are those extending above the plane of mean high water [MHW see figure 4.1]; rocks awash are those exposed at some stage of the tide; .sunken rocks are those covered at the chart datum. A sunken rock is potentially the most dangerous natural hazard to navigation. 

When selecting rocks for [charting], the character of the area, whether exposed or protected; the proximity to shore; the range of tide; and the probable visibility of the rock at some stage of the tide are factors to be considered.

Special care shall be used in charting dangerous rocks. Isolated and
dangerous rocks, whether bare, awash, or sunken, shall be emphasized by a danger curve encircling the symbol.. [Material in brackets has been inserted for clarity.] Rocks are particular hazards to navigation. Running into a rock not only grounds the vessel, problem enough, but also may severely damage the hull of the vessel. Attempts to free the vessel may only make matters worse if the hull was damaged by the grounding (Cahill, Minnoch).

Bare rocks, however, can serve as useful landmarks for fixing a vessels position. A sufficiently prominent bare rock at or near a sunken rock or other danger may be an excellent natural marker for the sunken hazard a natural wreck marker. In cases where the bare rock is in the general vicinity of invisible hazards to navigation, this rock can be used by the mariner to establish a danger bearing or danger circle (see Bowditch, Dutton).










*Charting Practices*
Charting conventions consist of a symbol, and various labels or notes, which could include the height of the rock, depth of water over the rock, and the name of the rock. Names and labels or rocks covered or periodically covered at certain tide levels or that refer to the sounding datum are charted in black italic type. Corresponding labels for bare rocks are shown in vertical type. Symbols and labels are discussed below.










*Rocks Symbols and Labels*

*The classification of rocks *shown on NOAA charts *varies *according to the geographic location of the charted area Atlantic and gulf coasts, Pacific coast, *and Great Lakes.* For this reason, separate remarks are included for each region.

*Bare Rock (K 10)*
A bare rock (islet) is defined as one with an *elevation at least 2 feet *above MHW for the Atlantic and gulf coasts, at least 3 feet above MHW for the Pacific coast, and *at least 5 feet or more above low-water datum for charts of the Great Lakes.* An islet is charted in its exact geographic location. Islets are drawn to scale (if possible at the chart scale). If not, the bare rock symbol (K 10) is used. On small-scale charts, the minimum size (0.5 mm by 0.65 mm) symbol may exaggerate the size of the rock. If known, the elevation (in feet or meters above the chart datum) is shown in vertical type enclosed in parentheses.

In some cases, fixed ATONs are located on a rock. The light or daybeacon symbol (see Chapter 5) takes precedence over the rock symbol. (Cartographers take particular care to restore the rock symbol if the light or daybeacon is moved.)

*Rocks Which Cover and Uncover *(K 11) A rock which covers and uncovers (rock awash) is defined as a rock with an elevation 1 foot above MLLW to less than 1 foot above MHW for the Atlantic and gulf coasts, 2 feet above MLLW to less than 2 feet above MHW for the Pacific coast, and 2 feet above low-water datum to 4 feet above low-water datum for the Great Lakes. A rock awash is charted in its exact geographic location and shown to scale if possible. If not, the symbol (K 11) for this type of rock is used. If known, the elevation (in feet or meters above the chart datum) is given in vertical type. For these rocks, the elevation is charted in vertical type enclosed in parentheses and underlined.










*Rocks Awash at the Level of Chart Datum (K 12)*
A rock awash at the level of chart datum is defined as a rock with an elevation 1 foot below MLLW to less than 1 foot above MLLW for the Atlantic and gulf coasts, 2 feet above MLLW to less than 2 feet above MLLW for the Pacific coast, and 2 feet below low-water datum *to less than 2 feet above low-water datum for the Great Lakes.* This rock is charted in its exact geographic location and shown to scale if possible. If not, the symbol (K 12) for this type of rock is used. 
*Sunken Rocks (K 2, 13)*
A sunken or submerged rock is defined as a rock covered more than 1 foot at MLLW for the Atlantic and gulf coasts, more than 2 feet at MLLW for the Pacific coast, and covered *more than 2 feet at low-water datum for the Great
Lakes.* If the depth is unknown, a special symbol (K 13) is charted. If the depth is known, it is given (in feet or meters relative to chart datum). A depth determined by a wire-drag survey is denoted by a special symbol (K 2). The maximum wire-drag cleared depth over a rock is charted.

Critical dangers to navigation, including rocks, located under bridges are charted in their position on the largest scale chart coverage. The bridge symbol is broken when such dangers are charted beneath the bridge structure, a policy that reflects the potential importance of the hazard.

Figure 4.7 provides illustrations of chart conventions for numerous hazards to navigation.

GUESS WHAT?...TO BE CONTINUED


----------



## Fishers of Men

Chapter 4 continued:

*Doubtful Danger Labels*
In some cases information regarding rocks or other specific hazards is uncertain or incomplete.

*A series of labels *(and associated definitions) has been developed and may be appended to the symbol. According to the Desk Reference Guide, these labels include:
*SD (Sounding Doubtful)*. Of uncertain depth. This shall be used when a depth shown on a chart over a rock is strongly suspected of being less than that stated. The position is not in doubt.

*Rep. (Reported)* The .Rep. label shall be attached to a charted rock because it is considered dangerous to navigation, but which has not been confirmed by an authoritative field observation party. The year the feature is reported shall be included as part of the label (e.g., Rep (1985)) and shall be enclosed with parentheses. Rep may be combined with the other labels in these groups. 

*ED (Existence Doubtful) *Of uncertain existence. The expression shall be charted to indicate the possible existence of a rock, the actual existence of which has not been established.

*PA. (Position Approximate)* Of inexact position. The expression shall be charted to state that the position of a rock has not been accurately determined.

The plotting of an object from preliminary data is not of the desired accuracy [10 feet, see Chapter 6] . . ., but it is acceptable for interim charting until an accurate position is available.

*PD. (Position Doubtful)* Of uncertain position. This expression shall be charted to indicate that a submerged rock has been reported in various positions but no one position has been definitely verified. The existence of the feature is not in question, only its correct position.

Similar labels are used to depict other hazards, so these labels are not repeated in each of the following sections. As a practical matter, mariners would do well to resolve the cartographers&#8217; uncertainty by assuming that the feature exists.
Where adequate safe water exists adjacent to the feature, mariners should simply avoid the potentially hazardous area.

*Shoals (K b, O 25)*
According to the Desk Reference Guide, a shoal is an offshore hazard to navigation on which there is a depth of 16 fathoms (30 meters) or less, and is composed of any material except rock or coral.

Although not all shoals are hazards to navigation for all vessels note that shoals can have charted depths as great as 30 meters shoals certainly represent a hazard for deep-draft vessels. Moreover, water over a shoal may be disturbed and present other hazards to recreational vessels even if there is sufficient depth over the shoal. Finally, the prudent mariner should remember that shoals can shift location particularly after storms or in areas of strong currents.
Where these conditions are known, these are noted as changeable areas and hydrography is not reported. However, care is always required when navigating shoal areas (e.g., Professional Mariner, Issue No. 1).










*Charting Practices*
Shoals are depicted by soundings, danger curves, and blue tint as appropriate (see above). Shoals are charted in their exact geographic positions. Shoals carry the primary label Shoal. (or abbreviation Shl where space is limited) in black italic type. The label may include the name of the shoal (e.g., Nebraska Shoal.) If the danger is doubtful or its position approximate, the appropriate qualifiers (i.e., .SD,. .PD,. .ED,. or .PA.) are included. 
*Ledges and Reefs (Various)*
According to the Desk Reference Guide, ledges and reefs are defined as follows:
A ledge is a rock formation connecting and fringing the shore of an island or large land mass; it is generally characterized by a steep sheer in the submarine topography.

A reef is a rocky or coral formation dangerous to surface navigation which may or may not uncover at the sounding datum. A rocky reef is always detached from shore; a coral reef may or may not be connected with the shore.

Reefs and ledges are further subdivided into uncovering ledges and reefs (J 21, J 22, K h), submerged ledges and reefs (K 16, K g), and oyster reefs (K 1, K 47). Obviously, reefs and ledges represent a major hazard to navigation.
Running aground on ledges and reefs, as with rocks, entails the ever present danger of structural damage. Moreover, these are (at least at some part of the tidal cycle) invisible dangers to navigation. Their depiction on the nautical chart is, therefore, particularly important.

*Charting Practices*
Charting conventions consist of a symbol and various explanatory labels and notes. For uncovering ledges and reefs standard symbols (J 21, J 22, and K h) are charted. A label is added when scale permits to identify the feature, e.g., .Rock. or Coral.. Names may be incorporated into the label.

Submerged ledges and reefs are shown by a danger curve (black dotted line), and blue tint to delineate the limits of the feature. A label is added to further identify submerged ledges and reefs, e.g., Subm ledge or Subm reef. Depths over rocks and coral heads within submerged ledge or reef limits are charted using soundings and labels, e.g., 5 Rk or 5 Co Hd. If the depth over these features is unknown, the submerged rock symbol (K 13) is used with the appropriate label.

On small-scale charts where space constraints limit the amount of detail that can be included, the most shallow depth over the submerged ledge or reef is included in the label. As with other underwater features, labels are shown in italic type, e.g., Subm ledge (cov 5 feet at MLLW).

Oyster reefs are charted using the same charting conventions. If oyster reefs bare at the chart sounding datum, green tint is added to the dotted danger curve. A label is added to identify oyster reefs, e.g., Oyster Bar, or Oyster Reef in italic type. Oyster reefs and bars are charted if these present a hazard to navigation or upon request or recommendation of state or local agencies for informational purposes. 
*Foul Area (K 31)*
According to the Desk Reference Guide, a foul area is an area of numerous uncharted dangers to navigation. (not the mallard ducks!) The area charted serves as a warning to the mariner that all dangers are not charted individually and that navigation through the area may be hazardous.
A foul area is an area where the bottom is known to be strewn with rocks, reefs, boulders, coral, obstructions, heavy concentrations of kelp, or other debris that could impede navigation.

Foul grounds should be avoided by vessels intending to anchor or engage in activities, such as trawling, which could be adversely affected by the presence of hazards in the foul area (e.g., nets could snag). The term foul *does not apply* to areas where the bottom is soft (e.g., mud or sand) or composed of other bottom materials not likely to cause damage to a vessel or otherwise restrict activities.

*Charting Practices*
A foul area is charted with a limiting danger curve (see above) and label(s) A blue tint and soundings data may also be included. Symbol (K 31)

The symbol for a foul area (K 31) may be shown in isolation, but may also be combined with other symbols, e.g., those for rocks, to provide a more complete description to the mariner. Important visible objects located in foul areas, which are useful as landmarks (see Chapter 6 for chart conventions for landmarks), are also charted. These landmarks can alert the mariner to the presence of the foul area and be used for danger bearings, etc. (see Bowditch, Dutton).

Foul areas are charted in their exact geographic positions as provided in the source material available to cartographers. Where possible, foul areas are charted to scale to show the actual size and shape of the actual foul area. Foul areas less than 2.5 mm in diameter at chart scale are charted with the minimum size (2.5 mm) symbol. A blue tint is added to foul areas dangerous to navigation, generally those having depths of 66 feet or 11 fathoms (20 meters) or less, when enclosed with a danger curve and not supported by depth contours and soundings.

*Label(s) and Notes*
Descriptive labels, including Foul, Foul Area, Boulders, Blds, Kelp, Danger line, Reef line, are included to indicate the type of danger present. Labels are printed in black italic type.

*Wrecks and Hulks (K 20-31)*
According to the Desk Reference Guide, A WRECK is the ruined remains of a vessel which has been rendered useless, usually by violent action, such as the action of the sea and weather. In hydrography the term is limited to a wrecked vessel, either submerged or visible, which is attached to or foul of the bottom or cast upon the shore.

*A HULK *is generally defined as the remnants of an abandoned wrecked/ stranded vessel, the actual shape of which is shown on large-scale charts. May also be used to define stored or permanently berthed vessels where actual shape is shown on large-scale charts. Wrecks depicted on nautical charts are classified as either stranded or sunken (Nautical Chart Manual) A stranded (visible) wreck is defined as one which has any portion of the hull or superstructure above the sounding datum. Submerged wrecks are located below the sounding datum or have only the masts visible. Wrecks are continually subject to the effects of current and weather. As a result, wrecks can change in physical form and in location. Particularly if not visible and at depths at or near the draft of the vessel, wrecks present a hazard to navigation. Important information received on new wrecks or changes in the status of existing wrecks are published in the NM and LNM.

Wreck locations are not only of interest to mariners seeking to avoid potential dangers, but also to *divers and charter captains.* Fishing vessels using nets generally avoid areas with wrecks because of the potential for wrecks to snag or damage nets.

*Charting Practices*
All stranded and sunken wrecks are charted on the largest scale chart nautical chart of the area. Wrecks not classified as dangerous (see below) are omitted on charts smaller than 1:150,000 scale in areas covered by larger scale charts. Charting conventions for wrecks/hulks consist of a symbol, labels and notes, and blue or yellow tint. Additionally, doubtful or questionable wrecks are so noted by appropriate label (e.g., PA, .PD, ED, etc).

*Symbols, Labels, and Tints*
Stranded wrecks are charted with a standard black symbol (K 24) which may face either left or right. The baseline of the symbol is shown parallel to the bottom of the chart, and the small .circle. at the base of the symbol (look closely at the symbol) marks the published position of the wreck. If the scale of the chart is sufficiently large, the true outline of a stranded wreck is shown with a solid line, land (gold) tint, and labeled. If a significant portion of the wreck is determined to be bare at the SPOR, it is considered a topographic feature and labeled with vertical, rather than italic, type.

Sunken wrecks are considered dangerous to navigation if any part of the wreck lies at 66 feet or 11 fathoms (20 meters) or less below the sounding datum. Wrecks deeper than 66 feet or 11 fathoms may also be considered dangerous in areas expected to be traveled by deeper draft vessels. Wrecks in areas where water depths and submerged features have been removed (changeable areas) are not charted as this information could be misleading.

*Dangerous sunken wrecks* are denoted by one of several symbols (K 25-28) as noted below:
Dangerous wrecks lacking precise depth information and those where the depth over the wreck is unknown are charted with the center cross lines of the dangerous wreck symbol (K 28) marking the published position of the wreck. The symbol *is rotated *so that it is coincident with the known alignment of the wreck. If the alignment of the wreck is unknown, the symbol is aligned with the baseline of the chart. A blue tint is added for emphasis within the enclosing danger curve.

Sunken wrecks with only their masts visible at the sounding datum are charted using symbol (K 25) with the added label Masts.

A dangerous wreck over which a precise least depth has been determined is charted with a sounding surrounded by a dotted danger curve, blue tint, and a label (K 26). A cleared depth obtained by a wire drag survey over a dangerous wreck is shown with a sounding surrounded by a dotted danger curve, blue tint, a wire-drag symbol outside the danger curve below the sounding, and the label .Wk. (K 27). The label Wreckage and a dotted danger curve (K 31) is used to identify areas where numerous dangerous wrecks are located or where the wreckage is scattered. Blue tint is added within the danger curve. Sunken wrecks that are not deemed to be dangerous to surface vessels expected to frequent the area are charted with a sunken wreck symbol only (K 29).

*Wrecks Marked by Buoys*
Buoys used to mark dangerous wrecks are charted in their exact position if possible (see Chapter 5). However, if the chart scale does not permit showing both symbols in their exact locations, the wreck is charted in its exact location, and the buoy is moved slightly.

Can you get a general idea of what kind of wreck your looking at on the chart now?

GUESS WHAT?...TO BE CONTINUED


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## Fishers of Men

*Cont. from previous post:*

*Obstructions (K 40-42)*
According to the Desk Reference Guide, an obstruction is anything that might hinder marine navigation. An obstruction on a nautical chart is usually considered to be a hard, unyielding isolated object, such as a sunken rock or man made article commonly located in deeper depths, that would endanger or prevent the safe passage of vessels. The term obstruction is often used as a preliminary label for reported dangers until they can be identified and properly labeled, and includes such objects as submerged piles, sunken wrecks, uncharted rocks, etc..

From the mariners perspective, obstructions have the same significance as rocks or wrecks---obstructions are objects that may present a hazard to navigation. The majority of items charted as obstructions are reported to NOAA through the NM and LNM and from USCG AUX and USPS reports.

*Charting Practices*
The guidelines for classifying an obstruction as dangerous to surface navigation are the same as those used for sunken wrecks and rocks e.g., those covered by 66 feet or 11 fathoms (20 meters) or less of water, unless in an area frequented by deeper draft vessels. An unidentified submerged object that is not considered to be the remains of a submerged wreck and is not considered a danger to surface navigation is termed a Snag rather than an obstruction.

Obstructions are charted with symbols, labels, and a *blue tint.* Appropriate qualifiers (e.g., .ED,), discussed above, are included if the obstruction is questionable or uncertain.

*Symbols and Labels*
Three symbols are used to depict obstructions (K 40-42), depending upon the available depth information. These objects are charted to scale in the exact position of the obstruction and enclosed with a danger curve filled with blue tint. If the chart scale does not permit a rendition to scale, the minimum size (2.5 mm) circle is used. All obstructions carry the label abbreviation Obstn in *black italic type.*

*Snags* are charted with a 1 mm circle and labeled Snag.
The depth over the obstruction is charted if known. In cases where a cleared depth over the charted position has been obtained from a wire-drag survey, the label cleared __ ft 19__. is added.
*
Natural Dangers (K 43.2)*
Natural dangers include deadheads, logs, snags, and stumps. Running into any of these dangers can cause structural problems and/or damage propellers. (It is generally agreed by most mariners that propellers are not the depth sounding apparatus of choice!) Definitions and charting practices for these natural dangers are described briefly below. A deadhead is a grounded log or tree trunk often floating free at one end or below the surface of the water. A deadhead is usually charted with a 1 mm circle and labeled Snag.. Logs that are grounded with some parts visible above the surface of the water are charted in some cases. These logs are charted with a 1 mm circle and labeled Snag.

A tree or branch embedded in a river or lake bottom and not visible on the surface is charted as a snag. Stumps are the stationary remains of trees, often submerged. These are labeled Stumps.

*Fish Havens *Regulated by State and Federal Permits (K 46.1, K 46.2) Fish havens are artificial shelters constructed of rocks, concrete, car bodies, and other debris and put on the sea floor to attract fish. Fish havens are often found in the vicinity of fishing ports or major coastal inlets and are usually considered hazards to navigation (and certainly to anchoring). Some fish havens are periodically altered, which increases the potential hazard.

*Charting Practices*
Fish havens are denoted with a symbol (K 46.1, K 46.2), labels/notes, soundings, and blue tint (if considered a danger to navigation). Fish havens are charted in their exact position and to scale subject to a minimum dimension of 2 mm to ensure that the chart feature is readily recognizable. Fish havens with authorized minimum depths of 66 feet or 11 fathoms (20 meters) or less are charted with a dotted limiting danger curve and* blue tint.* Those greater than 66 feet or 11 fathoms are charted with a dashed limiting danger curve and *no tint,* unless the fish haven is considered to be a danger to navigation, in which case the blue tint is used. The label Fish Haven is appended.

Fish havens are often marked with privately maintained buoys. These are charted if published in the LNM but omitted otherwise.

*Miscellaneous Hazards*
Other hazards that are charted when considered dangerous to navigation include marine structures (e.g., platforms and cribs, fishing and hunting structures, drilling platforms), fishing structures (e.g., fish/crab pens, fish stakes, and fish traps, weirs, tunny nets), floating structures (e.g., floats, floating breakwaters, and floating piers), logging structures (log booms), mineral development structures (e.g., wells, wellheads, platforms, and artificial islands). Charting practices are similar to those identified above. Space constraints do not permit an exhaustive discussion of each of these hazards in this manual. A brief sampling of the chart symbols used to depict these hazards includes:
Platforms and Cribs; charted as topographic features if at or above the shoreline plane of reference, charted as hydrographic features if below the shoreline plane of reference. Fish Stakes (K 44.1)
Fish Traps, Weirs, Tunny Nets (K 44.2, K 45)
Floating Breakwaters (F 4.1)
Log Booms (N 61)
Wells (L 20)
Wellheads (L 21.1-21.3, L 13)
Artificial Islands (L 15)
Dolphins (F 20), Piles (F 22, K 43.1, K 43.2)

*Unexploded Ordnance*
According to the Desk Reference Guide, the term unexploded ordnance.....refers to any undetonated explosive material which is reported to be outside the charted limits of established regulated explosives dumping areas.
(Unexploded bombs, depth charges, torpedoes, ammunition, pyrotechnics, etc.). Unexploded ordnance generally does not pose a hazard for transiting vessels, but anchoring in these areas could be risky. Other activities, such as diving, or use of fishing nets would also be imprudent. (Disentangling a torpedo or depth charge from a fouled net would present an unwelcome challenge!) Unexploded ordnance is charted when reported in LNM or by reliable sources. Sunken wrecks containing unexploded ordnance are considered dangerous wrecks and so charted.
*
Charting Practices*
Charting conventions for unexploded ordnance consist of a symbol and explanatory labels.
*Symbols*
Unexploded ordnance areas are outlined *with a dashed line. *The ordnance is charted in its *exact* geographic positions. The dashed limit lines are charted to scale. If the area is less than 2.5 mm in diameter at chart scale, the minimum size 2.5 mm symbol is used. The size of the unexploded ordnance area includes an allowance for the uncertainty of the reported position. Sunken wrecks containing unexploded ordnance are charted with the *dangerous sunken wreck symbol *(see above).

*Labels and Notes*
Unexploded ordnance areas are labeled (in black italic type) Unexploded Ordnance, followed by the year the hazard was reported, (Reported 19__), in parentheses beneath the area label. Sunken wrecks carrying unexploded ordnance are labeled Wk (Unexploded Ordnance). The type of ordnance (e.g., bombs, depth charges, etc.) may be charted if known.
*
Unsurveyed Area (I 25)*
According to the Desk Reference Guide, an unsurveyed area ....is an area on a nautical chart where hydrographic surveys are unavailable or limited. These areas are usually labeled Unsurveyed.

Unsurveyed areas are charted to alert the mariner to areas where depth information is unknown. In general, hydrographic detail is not charted in areas of continual and rapid change. If a recent survey reveals conditions so different that a satisfactory match (junction) cannot be made with the hydrography of former surveys, a blank band is charted beyond the limits of the more recent survey.

*Charting Practices*
Unsurveyed area limit lines are charted with a dashed line (I 25). 
A blank space approximately 5.0 mm wide is charted between the limits of hydrographic surveys that fail to match satisfactorily.

The label Unsurveyed Area is charted in black italic type. In constantly changing areas, an appropriate note explaining the lack of hydrography is charted in black. Where surveys do not junction satisfactorily, a note (e.g., Hydrography to (eastward) from surveys of 1934) is charted in black italic type.

*Dangerous Water Conditions* (Various) According to the Desk Reference Guide, dangerous water conditions.
....are physical characteristics of water including visible movement, coloring, and the presence of marine vegetation that constitute a hazard to navigation or indicate the presence of submerged obstructions or shoal areas.
Illustrative dangerous water conditions include rapids/waterfalls (C 22), breakers (C d, K 17), overfalls/tide rips/races (H 44), eddies (H 45), kelp (J 13.2), discolored water (K e), and currents (H 40, 41, H m, t). Their relevance to safe navigation is so obvious as not to require further explanation.

*Charting Practices*
Extensive dangerous water conditions are outlined and labeled to identify the condition. Small areas are charted with symbols or labels only. On conventional and small-craft nautical charts or areas where significant tidal currents exist, tidal current arrows (H 40, 41, H m, t) are charted at locations selected from the Current Differences listed in the latest edition of the Tidal Current Tables.

*Symbols*
As noted, limits to dangerous water areas are charted in their exact geographic positions with a dashed line or (for small areas) with various symbols.

*Labels and Notes*
A label describing the nature of the conditions is charted to provide further information. Labels are charted with capital and lower case letters in black italic type; e.g., Tide Rips. Discolored water often an indication of shoals is abbreviated *Discol Water, or Discol* if space is at a premium.
Where particularly strong currents exist, a label and a note may be charted in addition to a current arrow and velocity label. The following note provides an illustrative example;

*CURRENTS AT SERGIUS NARROWS*
At times the velocity reaches 8 knots. On an average, the current turns from North to South about 2 hours before the time of high water at Sitka and from South to North about 1-3/4 hours before the time of low water at Sitka. For more precise information consult the Pacific Coast Current Tables of the National Ocean Service which includes predictions of the times of slack and times and velocities of strength for every day of the year.

Additional information on currents may be provided in the form of a current diagram (H t) or limits to major currents, such as the Gulf Stream. Although not necessarily considered a dangerous water condition, tidal information is relevant to the mariner, and presented in summary form on the nautical chart. Information on the height of the water is presented in two forms, tide notes for areas with appreciable tidal range, and hydrographs (diagrams showing seasonal variability in water levels) for charts of the Great Lakes. In either case, these data are averages of water levels only, and not specific predictions. The notes alert the mariner to the presence of large variations in water level, and the need to consult other references for tidal predictions.

*GUESS WHAT?...TO BE CONTINUED *


----------



## Fishers of Men

Here is the table of contents for the

*NAUTICAL
CHART USER&#8217;S
MANUAL*

This is what we have to accomplish before I move on to other items of iinterest.

U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration (NOAA)
National Ocean Service
Washington, DC, 1997
Table of Contents i
TABLE OF
CONTENTS
Preface and Acknowledgments...................................................................................... ix
Chapter 1 Introduction
Background ............................................................................................................ 1-1
The Nautical Chart User&#8217;s Manual ..................................................................... 1-3
Organization of this Manual ................................................................................. 1-4
Relevant Facts, Statistics, and Products ............................................................. 1-5
Purpose of the Nautical Chart .............................................................................. 1-7
How Does a Nautical Chart Differ from a Map? ................................................. 1-8
.An Illustrative Chart .................................................................................... 1-8
.An Illustrative Map .................................................................................... 1-10
User Groups ......................................................................................................... 1-10
Efficiency of Chart Compared to Text ................................................................ 1-12
Chart Distribution.Where to Purchase Charts .............................................. 1-13
.Mail Order Sales ......................................................................................... 1-13
.Authorized Chart Agents ............................................................................ 1-13
.The Nautical Chart Catalog ...................................................................... 1-13
Chart Prices and Related Matters...................................................................... 1-13
Chart Demand ..................................................................................................... 1-15
ECDIS, The End of the Paper Era? .................................................................... 1-16
Chart-Related Publications ................................................................................. 1-17
.Chart No. 1 .................................................................................................. 1-17
.Chart Catalogs ............................................................................................ 1-17
.Dates of Latest Editions ............................................................................. 1-17
.Notice to Mariners ...................................................................................... 1-17
.Local Notice to Mariners ............................................................................ 1-19
.U. S. Coast Pilot ......................................................................................... 1-20
.Light List .................................................................................................... 1-20
.Tide Tables and Tidal Current Tables ...................................................... 1-21
The Track Ahead ................................................................................................. 1-21
Chapter 2 General Information and Overview
Introduction ............................................................................................................ 2-1
Chart No. 1 ............................................................................................................ 2-1
Schematic Layout of a Nautical Chart ................................................................ 2-2
Number, Title, and Marginal Notes (A) .............................................................. 2-2
Latticed Charts (A) ................................................................................................ 2-6
Edition (A) .............................................................................................................. 2-6
Reconstructed, Provisional, and Preliminary Charts......................................... 2-6
.Importance of Current and Corrected Charts ............................................ 2-8
Source Diagram (A) ............................................................................................... 2-9
Neatline Dimensions (A) ....................................................................................... 2-9
ii NOAA Chart User&#8217;s Manual
Chapter 2 General Information and Overview (cont&#8217;d.)
Chart Title, Authorities Note, and Seal (A) ......................................................... 2-9
Projection and Scale (A) ........................................................................................ 2-9
.Projections ..................................................................................................... 2-9
.Chart Scale .................................................................................................. 2-11
.Chart Types ................................................................................................. 2-13
.A Mix of Charts Necessary ........................................................................ 2-14
A Brief Aside, Chart Storage and Care.Rollers versus Folders ..................... 2-16
Linear and Logarithmic Speed Scales (A) ......................................................... 2-17
Notes and Cautions ............................................................................................. 2-18
Chart Overlap, Insets, and Related Matters ..................................................... 2-19
Measures to Minimize Confusion: The Chartmaker&#8217;s Perspective ........... 2-19
Measures to Minimize Confusion: The Navigator&#8217;s Role ........................... 2-21
Latitude, Longitude, Regular, and Skewed Projections ................................... 2-25
Depth Units and Vertical Datum ....................................................................... 2-25
Horizontal Datum................................................................................................ 2-26
Relevance of Horizontal Datum ................................................................... 2-26
Direction and Magnetics (B) ............................................................................... 2-27
Compass Roses (B70) .................................................................................... 2-27
Local Magnetic Disturbance Notes ............................................................. 2-27
Isogonic Lines (B 71) ..................................................................................... 2-29
Additional Information ........................................................................................ 2-29
Lettering Styles (Vertical versus Slant Type) ................................................... 2-31
Use of Color on Charts ........................................................................................ 2-31
Symbols and Abbreviations ................................................................................. 2-31
Use of Charts ....................................................................................................... 2-31
Chapter 3 Topography and Related Information
Introduction and Overview ................................................................................... 3-1
Utility of this Information and Implications for Chart Design.......................... 3-2
Coastline/Shoreline (C 1 - C 8) .............................................................................. 3-3
.Shoreline Plane of Reference ........................................................................ 3-4
.Apparent Shoreline (C 32, C 33) .................................................................. 3-4
.Approximate or Unsurveyed Shoreline (C 2) .............................................. 3-4
.Flat Coast (C 5) ............................................................................................. 3-4
.Steep Coast.Bluff; Cliff (C 3)........................................................................ 3-4
.Surveyed Coastline (C 1) .............................................................................. 3-5
.Other Shoreline Types .................................................................................. 3-5
.Foreshore ....................................................................................................... 3-5
.Chart Sounding Datum Line (C a) .............................................................. 3-5
.Approximate Sounding Datum Line (C b) .................................................. 3-5
.Breakers ........................................................................................................ 3-5
.Grass .............................................................................................................. 3-5
.Mud/Sand/Stone or Gravel/Sand and
Mud/Sand and Gravel/Rock/Coral/Rubble.............................................. 3-5
.Illustration..................................................................................................... 3-6
Elevation and Relief Data...................................................................................... 3-6
.Land Contours C 10)..................................................................................... 3-6
.Approximate Contour Lines (C 12) .............................................................. 3-9
.Peaks (C 10, C 11) and Treetop Elevations (C 14)...................................... 3-9
.Hachures ....................................................................................................... 3-9
.Height of Object .......................................................................................... 3-10
.An Aside: Indirect Use of Terrain Information ........................................ 3-10
Table of Contents iii
Chapter 3 Topography and Related Information (cont&#8217;d.)
Inland Waters ...................................................................................................... 3-12
.Glaciers (C 25) ............................................................................................. 3-12
.Intermittent Rivers and Streams (C 21) ................................................... 3-12
.Lakes and Ponds (C 23); Lagoons (C h) .................................................... 3-12
.Rapids and Waterfalls (C 22) ..................................................................... 3-12
.Rivers and Streams (C 20) ......................................................................... 3-12
.Salt Pan (C 24) ............................................................................................ 3-12
Trees ................................................................................................................. 3-12
Lava Flow (C 26) .................................................................................................. 3-12
Vegetation (C o, C j, C l, C i, C m, C n, C k, C 30) ........................................... 3-12
Marshes and Swamps (C 32, C 33)..................................................................... 3-13
Ports and Harbors ............................................................................................... 3-13
.Berthing Structures.................................................................................... 3-13
.Additional Sources ...................................................................................... 3-16
Erosion.Control Structures ................................................................................ 3-17
.Breakwater (F 4.1) ...................................................................................... 3-17
.Groins (F 6.1, F 6.2, F 6.3) ........................................................................ 3-17
.Jetties (F a, F b, F c) .................................................................................. 3-17
.Seawall (F 2.1, F 2.2).................................................................................. 3-17
.Dikes and Levees (F 1) ............................................................................... 3-17
.Additional Sources ...................................................................................... 3-18
Docks and Tidal Basins....................................................................................... 3-18
.Dry Dock, Graving Dock (F 25) ................................................................. 3-18
.Tidal Basin (F 28) ....................................................................................... 3-18
.Wet Dock (F 27) .......................................................................................... 3-18
.Additional Sources ...................................................................................... 3-18
Bridges (D 22 . D 24, D d, D e) .......................................................................... 3-18
.Bridge Symbols (D 22 - D 24, D d, D e) and Related ................................ 3-19
.Hazards Under Bridges .............................................................................. 3-20
.Bridge Clearances (D 20, D 21) .................................................................. 3-21
.Names .......................................................................................................... 3-22
.VHF Radio Capability ................................................................................. 3-22
.Additional Sources ...................................................................................... 3-22
.Illustration................................................................................................... 3-22
Locks and Other Barriers ................................................................................... 3-23
.Locks (F 41.1, F 41.2) ................................................................................. 3-23
.Floodgates, Sills, and Miscellaneous Other .............................................. 3-24
Landing and Launching Sites ............................................................................ 3-24
.Marine Railway (F 23) ................................................................................ 3-24
.Ramps (F 23) ............................................................................................... 3-24
Artificial Features ............................................................................................... 3-24
.Roads and Related ....................................................................................... 3-24
.Cable Ferry (M 51) ...................................................................................... 3-24
.Canal (F 40) ................................................................................................. 3-25
.Dam (F 44)................................................................................................... 3-25
.Ditch (F 40) ................................................................................................. 3-25
.Pipelines on Land (D 29) ............................................................................ 3-25
.Railroads (D b)............................................................................................. 3-25
.Roads and Road Patterns (D 1, D 2, D 10, D 11, D a) ............................. 3-25
.Trails (D 12) ................................................................................................ 3-25
.Tunnel Entrances (D 16) ............................................................................ 3-26
iv NOAA Chart User&#8217;s Manual
Chapter 3 Topography and Related Information (cont&#8217;d.)
Buildings and Structures .................................................................................... 3-26
.Airports (D 17, N e) .................................................................................... 3-26
.Buildings (D 5, D 6, E d, F 61, F 62.2, F 63) and Tanks (E 32) ............. 3-26
.Illustration................................................................................................... 3-27
.Cemeteries (E 19) ........................................................................................ 3-27
.Church Buildings (E 10.1 - E 18)............................................................... 3-27
.Hospitals (F 62.2) ........................................................................................ 3-27
.Urban Screen .............................................................................................. 3-27
Miscellaneous Stations ........................................................................................ 3-27
.USCG Stations (T 10, T 11) ....................................................................... 3-28
.Fireboat Station (T d) ................................................................................. 3-29
.Marine Police Stations (T c) ....................................................................... 3-29
.Pilot Stations (T 3) ...................................................................................... 3-30
Overhead Cables and Crossings (D 26, D 27) .................................................... 3-30
.Overhead Cable Cars (D 26) ....................................................................... 3-30
Land Boundaries and Limits .............................................................................. 3-30
Key Points and Miscellaneous Comments ......................................................... 3-30
Concluding Comments ........................................................................................ 3-32
Chapter 4 Hydrography and Related Information
Introduction and Overview ................................................................................... 4-1
.A Brief Aside: Dual Units ............................................................................ 4-1
Utility of Hydrographic and Related Information ............................................... 4-2
Hydrographic Information .................................................................................... 4-3
.Common Plane of Reference and Survey Scales ......................................... 4-3
.Source Diagrams ........................................................................................... 4-5
Soundings ............................................................................................................... 4-5
.The Soundings Selection Challenge ............................................................. 4-6
.Selection Criteria for Soundings to be Charted .......................................... 4-7
.Charting Practices ...................................................................................... 4-10
Depth curves (Section I of Chart No. 1) ............................................................. 4-10
.Charting Practices ...................................................................................... 4-12
.Symbol ......................................................................................................... 4-13
.Labels ........................................................................................................... 4-13
.Shallow Water Tint(s) ................................................................................ 4-13
.Improved (Artificial) Channels................................................................... 4-13
.Symbols........................................................................................................ 4-15
Bottom Characteristics ....................................................................................... 4-15
Specific Hazards to Navigation .......................................................................... 4-15
Danger Curve (K 1) ............................................................................................. 4-18
.Charting Practices ...................................................................................... 4-18
.Labels and Notes ......................................................................................... 4-18
Rocks (K 10-17, a, b, f) ........................................................................................ 4-18
.Charting Practices ...................................................................................... 4-23
.Rocks Symbols and Labels ......................................................................... 4-23
.Bare Rock ( 10) ............................................................................................ 4-23
.Rocks Which Cover and Uncover (K 11) ................................................... 4-23
.Rocks Awash at the Level of Chart Datum (K 12) ................................... 4-23
.Sunken Rocks (K 2, 13) .............................................................................. 4-23
.Doubtful Danger Labels ............................................................................. 4-24
Shoals (K b, O 25) ................................................................................................ 4-24
.Charting Practices ...................................................................................... 4-26
Table of Contents v
Chapter 4 Hydrography and Related Information (cont&#8217;d.)
Ledges and Reefs (Various) ................................................................................. 4-26
.Charting Practices ...................................................................................... 4-26
Foul Area (K 31)................................................................................................... 4-26
.Charting Practices ...................................................................................... 4-27
.Symbol (K 31) .............................................................................................. 4-27
.Label(s) and Notes ...................................................................................... 4-27
Wrecks and Hulks (K 20-31) .............................................................................. 4-27
.Charting Practices ...................................................................................... 4-27
.Symbols, Labels, and Tints ........................................................................ 4-27
.Wrecks Marked by Buoys .......................................................................... 4-28
Obstructions (K 40-42) ........................................................................................ 4-28
.Charting Practices ...................................................................................... 4-29
.Symbols and Labels .................................................................................... 4-29
Natural Dangers (K 43.2) ................................................................................... 4-29
Fish Havens Regulated by State and Federal Permits (K 46.1, K 46.2)......... 4-29
.Charting Practices ...................................................................................... 4-29
Miscellaneous Hazards ........................................................................................ 4-30
Unexploded Ordnance ......................................................................................... 4-30
.Charting Practices ...................................................................................... 4-30
.Symbols........................................................................................................ 4-30
.Labels and Notes ......................................................................................... 4-30
Unsurveyed Area (I 25) ....................................................................................... 4-30
.Charting Practices ...................................................................................... 4-31
Dangerous Water Conditions (Various) ............................................................. 4-31
.Charting Practices ...................................................................................... 4-31
.Symbols........................................................................................................ 4-31
.Labels and Notes ......................................................................................... 4-31
Submarine Pipeline and Cables (L 30.1.44 ..................................................... 4-32
.Submarine Pipelines (L 40.1, 40.2, 41.1, 41.2, 43, 44) ............................ 4-32
.Individual Pipelines .................................................................................... 4-32
.Pipeline Areas ............................................................................................. 4-33
.Submarine Cables (L 30.1, 30.2, L 31.1, L 32) ........................................ 4-33
.Individual Cables ........................................................................................ 4-33
.Cable Areas .................................................................................................. 4-34
Other Relevant Sources of Information ............................................................. 4-34
U.S. Coast Pilot................................................................................................... 4-34
Tide Tables and Tidal Current Tables ............................................................... 4-35
Notice to Mariners ............................................................................................... 4-35
Local Notice to Mariners ..................................................................................... 4-35
Concluding Remarks ........................................................................................... 4-35
Chapter 5 Aids to Navigation
Introduction and Overview ................................................................................... 5-1
Brief Historical Asides ........................................................................................... 5-2
Importance of ATONs in Coastal Navigation...................................................... 5-2
Importance of Positive Identification and Related Matters ................................ 5-2
ATONs and Related Chart Information (General) .............................................. 5-4
vi NOAA Chart User&#8217;s Manual
Chapter 5 Aids to Navigation (cont&#8217;d.)
Lights ................................................................................................................... 5-6
.Charting Practices ........................................................................................ 5-7
.Symbol (P) ..................................................................................................... 5-7
.Labels and Notes ........................................................................................... 5-7
.Sectors and Related Matters ...................................................................... 5-11
.Directional Lights ....................................................................................... 5-11
.Leading Light .............................................................................................. 5-14
.Aeronautical Lights .................................................................................... 5-14
.Articulated Lights....................................................................................... 5-14
.Strobe Lights ............................................................................................... 5-14
.Riprap .......................................................................................................... 5-15
Supplemental Information Regarding Lights and Other ATONs ................... 5-15
.The U.S. Coast Guard Light List .............................................................. 5-15
.The U.S. Coast Pilot .................................................................................. 5-16
.Published Guides and Other Books ........................................................... 5-16
Buoys ................................................................................................................. 5-17
.A Brief Digression: Position Fixing with Buoys ....................................... 5-18
.Charting Practices ...................................................................................... 5-20
.Symbols (Q) ................................................................................................. 5-20
.Charted Characteristics ............................................................................. 5-23
.Channel Buoys ............................................................................................ 5-25
.Junction Buoys ............................................................................................ 5-26
.Midchannel Buoys....................................................................................... 5-26
Fog Signals &#174; ..................................................................................................... 5-26
.Charting Practices ...................................................................................... 5-27
.Labels and Notes ......................................................................................... 5-27
Daybeacons (Q) .................................................................................................... 5-28
.Charting Practices ...................................................................................... 5-29
.Daybeacon Symbols .................................................................................... 5-29
.Daybeacon Labels ....................................................................................... 5-29
Ranges (M)............................................................................................................ 5-31
.Charting Practices ...................................................................................... 5-32
.Symbol (M 1) ............................................................................................... 5-32
.Range Labels ............................................................................................... 5-32
.Dredging Ranges ......................................................................................... 5-32
.Natural Ranges ........................................................................................... 5-32
Radiobeacons and Related Aids (S) ..................................................................... 5-32
.Charting Practices ...................................................................................... 5-34
.Symbol (S 1)................................................................................................. 5-34
.Labels ........................................................................................................... 5-34
.Aeronautical Radiobeacons ......................................................................... 5-35
Miscellaneous Related Information .................................................................... 5-35
.Measured Course (Q 122) ........................................................................... 5-35
Concluding Remarks ........................................................................................... 5-36
Chapter 6 Landmarks
Introduction and Overview ................................................................................... 6-1
Importance of Landmarks in Coastal Navigation .............................................. 6-1
Types of Landmark ............................................................................................... 6-3
Objects Not Normally Depicted as Landmarks .................................................. 6-6
Table of Contents vii
Chapter 6 Landmarks (cont&#8217;d.)
How Landmarks Are Depicted on the Chart....................................................... 6-7
.Symbols.......................................................................................................... 6-7
.Labels ............................................................................................................. 6-9
.Other Sources of Landmark Information ................................................. 6-11
Practical Pointers and Limitations Relevant to Landmarks........................... 6-12
.Pointers........................................................................................................ 6-12
.Selecting Landmarks For Use ................................................................... 6-12
.Limitations .................................................................................................. 6-15
Concluding Comments ........................................................................................ 6-19
Chapter 7 Areas, Limits, Tracks, and Routes
Introduction and Overview ................................................................................... 7-1
Utility of This Information ................................................................................... 7-1
Federally Regulated Areas (N 1.2, N 2.2, N 31) ................................................. 7-2
.Regulated Navigation Areas ........................................................................ 7-2
.Danger Area .................................................................................................. 7-2
.Seaplane Restricted Areas/Seaplane Operating Areas (N 13, N 14) ......... 7-2
.Restricted Area (N 20) .................................................................................. 7-3
.Safety Zones/Defense Areas/Security Zones ................................................ 7-3
.Relevance to the Mariner ............................................................................. 7-5
.Charting Practices ........................................................................................ 7-5
.Symbol (e.g., N 1.2, N 2.2, N 31) ................................................................ 7-5
.Labels and Notes ........................................................................................... 7-5
.Examples ....................................................................................................... 7-7
.Illustrative Regulations ................................................................................ 7-8
.Summary..................................................................................................... 7-10
Civil Reservations ................................................................................................ 7-10
.Charting Practices ...................................................................................... 7-10
.Symbol (N 22) .............................................................................................. 7-10
.Labels and Notes ......................................................................................... 7-10
.Relevance to the Mariner ........................................................................... 7-10
Federally Regulated Anchorage Areas/Grounds................................................ 7-11
.Anchorage Grounds .................................................................................... 7-11
.Special Anchorage Areas ............................................................................ 7-12
.Fairway Anchorages ................................................................................... 7-12
.Relevance to the Mariner ........................................................................... 7-12
.Charting Practices ...................................................................................... 7-14
.Symbol (e.g., N 11.1 - N 20) ....................................................................... 7-14
.Label ............................................................................................................ 7-14
.Notes ............................................................................................................ 7-14
Nonfederally Regulated Anchorages (N 12.1) .................................................... 7-15
Harbors of Refuge (N 10) ..................................................................................... 7-16
Dumping/Disposal Areas ..................................................................................... 7-16
.EPA.Established Dumping Areas (N 24, N c, N d, N g) ........................ 7-17
.Navy.Established Dumping Areas ........................................................... 7-17
.U.S. Army Corps of Engineers Areas ........................................................ 7-17
.Dumping Grounds (N c) ............................................................................. 7-18
.Relevance to the Mariner ........................................................................... 7-18
.Illustration................................................................................................... 7-18
viii NOAA Chart User&#8217;s Manual
Chapter 7 Areas, Limits, Tracks, and Routes (cont&#8217;d.)
COLREGS Demarcation Line (N a) ................................................................... 7-20
.Charting Practices ...................................................................................... 7-20
.Symbol (N a)................................................................................................ 7-20
.Label ............................................................................................................ 7-20
Degaussing Range (N 25) .................................................................................... 7-21
Maritime Boundaries........................................................................................... 7-21
.International Boundaries (N 40, N 41) ..................................................... 7-21
.Exclusive Economic Zone (N 47) ................................................................ 7-21
.Closing Line/Three Nautical Mile Line/
Territorial Sea and Contiguous Zone (N 42, N 43, N 44) ................... 7-22
Traffic Separation Schemes and Related Matters ............................................. 7-24
.Notes ............................................................................................................ 7-29
.Additional Information ............................................................................... 7-29
.Relevance to the Mariner ........................................................................... 7-30
.Smaller Vessels ........................................................................................... 7-30
Course Lines ........................................................................................................ 7-31
Courses7-32
Concluding Comments ........................................................................................ 7-32
Appendix A Glossary .................................................................................................... A-1
Appendix B Abbreviations
Part I Index of Abbreviations (Section V of Chart No. 1) .......................... B-1
Part II Index of Abbreviations.Supplementary National
Abbreviations (Section V of Chart No. 1)......................................... B-6
Part III International Abbreviations (Section W of Chart No. 1) ................ B-9
Part IV Abbreviations used this Manual, NM, LNM,
Light List, Broadcast Notice To Mariners,
Nautical Chart Catalog, or Dates of Latest Editions ...................B-11
PREFACE AND
ACKNOWLEDGMENTS
Many products are sold with users manuals.
Some, such as those for an aircraft, automobiles, or pieces of electronic equipment, are quite voluminous and complex. Others are more modest. A patented insect destruction novelty device sold several years ago consisted of only two small wooden blocks. Even this novelty device came with a users manual; it consisted of a single sheet of paper with the following instruction, place insect on face of one block and firmly place second block on top of first block.. Generally speaking, the more sophisticated and important the item, the more elaborate the users manual. The modern nautical chart is reasonably complex and certainly an essential tool for the mariner. Yet, aside from passing mention in textbooks on navigation and the publication of Chart No. 1, no users manual had been published for the nautical chart. Arguably, such a publication is long overdue.

This manual explains what is presented on the nautical chart, highlights the utility of this information, describes the charting conventions used to depict features and items of interest, and provides some practical pointers on how this information is used. It is written to serve many types of users, ranging from operators of recreational vessels to those who drive heavy iron.

Abundant photographs and chart excerpts illustrate key points made in the text. All chart excerpts were current as of spring 1995.
Since this manual was published, some charts may have been revised. Even if these specific charts have been revised, the general points remain valid. It almost goes without saying that these chart excerpts should not be used for navigational purposes.

This manual also identifies other publications, such as the U.S. Coast Pilot, Tide Tables, Tidal Current Tables, Notices to Mariners, and the U.S. Coast Guard&#8217;s Light List which give additional relevant information to chart users. 

Excerpts from these publications are also provided in the manual. As with chart excerpts, these may also have been revised.
The writing style is less formal than that employed in many government publications designed to make the manual more user friendly in todays vernacular. The manual is authoritative, but not encyclopedic. To keep the manual to a manageable size, only the most important topics are included.

This is a chart users manual, and not a textbook on seamanship or navigation. Nonetheless, nautical charts are used principally
for navigational purposes and, therefore some basic elements of the theory and practice of navigation are included in this manual.

References that provide additional and more detailed discussions of relevant aspects of navigation are included at the end of each chapter. 
Inclusion of these references in this manual does not mean that the National Oceanic and Atmospheric Administration (NOAA) or any other agency of the U.S. government agrees with any findings, conclusions, or opinions contained in these references. Likewise, inclusion of any trade names or photographs of specific equipment does not constitute a product endorsement.
The creation of this manual was a cooperative project between NOAA and the United States Coast Guard Auxiliary (USCGAUX), the volunteer civilian component of the U.S. Coast Guard. Dr. L. Daniel Maxim (DVC.ER,
USCGAUX) wrote the manual. Mrs. Virginia L. Knudsen (DC.EX, USCGAUX) ably handled the layout and graphics. Many NOAA personnel made important contributions, notably CAPT Thomas Richards, NOAA, Messrs. Harold Schantz and Jeff Stuart who shared a common vision of excellence, always responded patiently to questions and provided constructive criticism and guidance throughout the project. A Committee consisting of CAPT David MacFarland, NOAA, Mark Friese, Robert Rodkey, Erich Frey, Nelson Garber, Jason Rolff, John Ondrejko, Ronald Stuckey, Thomas Dade, Stanley Weiss, Ken O&#8217;Dell, Eric Johnston, and LCDR Marlene Mozgala, NOAA, provided direction and expertise in developing and reviewing the Chart User&#8217;s Manual. In addition, Ira Dolich and Andrew Ritzie (both USCGAUX) made helpful comments and suggestions which improved the quality of this manual. Credit, therefore, should be shared among many. The responsibility for errors and omissions rests solely with the author. Special thanks to Dottie Brown for her attention to detail on the final edit of this manuscript.
Cranbury, NJ
December 1997

With 7 chapters to cover on charts, we SHOULD know a little something! So, grab a cold one, kick back and Hang in there  *THIS IS THE ONLY PLACE YOU ARE GOING TO GET ALL THIS INFO...and MORE.*


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## Fishers of Men

If anyone wants any particular file or the glossary let me know on here and I'll e-mail you the file. Save you a lot of copy paste issues.


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## Fishers of Men

*Hope everyone had a very merry Christmas. Final part of chapter 4:

Don't over look this page, you will find out why they call it "the Crib" and plenty more. We are not talking about "submarines here!"

Submarine Pipelines and Cables*
(L 30.1.44)
Submarine pipelines and cables can be damaged as a result of vessel groundings. Anchors can also damage these objects, and anchoring restrictions are in effect in these areas. Moreover, submarine pipelines may present significant hazards to navigation, similar to a submerged wreck, rock, or other hazards discussed above.

Submarine cables include those used for power transmission and those used for communications. Damage to either can have significant adverse consequences (e.g., loss of power, disruption of communications) as well as causing damage to the vessel and/or its propellers.

Submarine Pipelines (L 40.1, 40.2, 41.1, 41.2, 43, 44)
*Submarine pipelines are partitioned into four classes;* those used for nonvolatile material transport, *potable water intakes, *volatile material transport, and abandoned (or unused) pipelines.

*Nonvolatile material transport pipelines are conduits for the intake of non potable water (e.g., for cooling* (CEI plants, Perrys Nuclear bubble etc..)or irrigation purposes) and for discharge of wastes (e.g., cooling water). 

Potable water intakes are structures designed for the intake of drinking water. These are usually elevated above the bottom and supported and protected by a debris-screening structure (a crib), which is separately charted. These are charted in the Great Lakes and other freshwater inland lakes.[/B]

Volatile material transport pipelines are used to convey liquids and gases, usually petroleum or other mineral products of a hazardous nature. Collisions with, or dragging an anchor on, these pipelines also entail the risk of pollution incidents, explosions, and fires.

Abandoned (unused) pipelines are no longer in service, but still present a hazard to navigation.

Chart symbols and conventions differ among these pipeline classes. All pipelines may be charted either as an individual pipeline, or included in a pipeline area.

*Individual pipelines* are charted using several symbols, labels, and notes.
Intake and discharge pipes (nonvolatile material transport) are charted in *black using a unique symbol (L 41.1).* This symbol is directional the ball part of the symbol being placed *at the end furthest* from the assumed source of flow. No label is added. Conduits for discharging effluents; e.g., industrial, chemical, sanitary, and storm water discharge, are charted with the *same black symbol* (L 41.1) *and labeled Sewer in italic type *on the largest scale chart and on smaller scales as space permits.

Potable water intakes are charted using one of two black symbols (L 41.1, L 43), and * labeled PWI in italic type.*

Abandoned pipelines are charted in black using a unique symbol (L 44) without any label.

Pipelines used for liquids and gasses are depicted by a unique *magenta symbol* (L 40.1) without any label. In addition, the following caution note *(in magenta vertical type)* is added to all charts containing submarine oil and gas pipelines and submarine cable areas:
CAUTION
SUBMARINE PIPELINES AND CABLES Charted submarine pipelines and submarine cables and submarine pipeline and cable areas are shown as:
Symbols (L 40.2, L 30.2)

Additional uncharted submarine pipelines and submarine cables may exist within the area of this chart.* Not all *submarine pipelines and submarine *cables are required to be buried,* and those that were originally buried may have become exposed. Mariners should use extreme caution when operating vessels in depths of water comparable to their draft in areas where pipelines and cables may exist, and when anchoring, dragging, or trawling.

*Covered wells may be marked by lighted or unlighted buoys.*

Pipeline Areas (These are structure out there guys)

As noted above, pipelines can be charted individually or in areas. Pipeline areas are shown *in magenta by dashed area limits * (L 41.2) and labeled Pipeline Area.

According to the Nautical Chart Manual:
The extent of the limits of the area will be governed by local conditions (e.g., the number of pipelines or cables) but *shall in all cases *include the immediate area which overlies the pipeline or cables. The limiting lines shall be spaced 1,000 feet apart or 500 feet on each side of the pipeline or cable position or from the outer ones of a group, or a minimum of 5.0 mm at charting scale for small-scale charts. *Cable and pipeline areas shall be labeled in Newton Light Italic type, capital and lowercase letters, with type size appropriate to the size of the feature or scale of the chart.*

Submarine Cables (L 30.1, 30.2, L 31.1, L 32)
According to the Nautical Chart Manual:
Cables are classified as power cables and communication cables. Power cables are used to transmit electricity across a large expanse of water where overhead transmission is not feasible, or in areas of heavy commercial shipping where greater danger would exist by use of overhead transmission. Communication cables are used to transmit messages. Submarine cables shall be charted within protected waters such as harbors, rivers, bays, estuaries, or other inland navigable waterways to warn the mariner of possible interference with navigation and to help prevent damage to cables from anchors. Cable and pipeline areas should not be charted in large areas void of hydrography, except to show the terminus of a line.

As with pipelines, cables can be charted individually or in areas.

*Individual Cables*
Power cables are depicted by *one of two magenta symbols *(L 30.1 generic cable, or L 31.1). *Abandoned or unused cables* are depicted by a unique magenta symbol (L 32). Communications cables are depicted by a magenta symbol (L 30.1). *The continuity of the wavy-line symbol* (L 30.1) is not broken for soundings or other chart details except where legibility of the overprinted feature would be impaired. *No labels are included.*

*Cable areas* are charted in the same manner as pipeline areas, except that a unique symbol is used (L 30.2).

Other Relevant Sources of Information In addition to the nautical chart and Chart No. 1, several other sources provide information on hydrography and specific hazards to navigation. These include the U.S. Coast Pilot, Local Notices to Mariners, and the Tide Tables and Tidal Current Tables.

*U.S. Coast Pilot*
The U.S. Coast Pilot contains valuable material on hydrography and hazards to navigation that supplements the nautical chart. In particular (see the Coast Pilot Manual), this publication provides textual information on aquacultural sites, bars, basins, channels, currents, dangers depths, fish havens, fishtraps, heights, submarine features, tides, and wrecks. In general, the U. S. Coast Pilot provides narrative material that goes beyond that provided by the symbols, notes, and legends used on the nautical chart. For example, the guidance offered in the Coast Pilot Manual for a description of bars, dangers, submarine features, and wrecks is:
Bars. Where a bar is dangerous, state under what conditions it is dangerous and describe the most favorable conditions for crossing. State whether the bar breaks in ordinary weather or only in heavy weather and how far out the breakers extend. Give the least depth at the best place for crossing the bar (where there is no dredged channel).

Dangers. Give kind and extent of natural dangers; least depths over them; if they break, at what stage of the tide; and how much, if any, is bare at the chart datum. Do not list each individual danger in a group; a description of the most prominent, or the one nearest the channel, or the one farthest from shore is usually sufficient. 

Submarine features. Describe the character of the bottom slope, especially when approaching the shore. State whether soundings can be depended upon to warn of the approach to danger. Note any special submarine features, such as valleys and escarpments, that may be useful in depth curve navigation.

Wrecks. Describe dangerous wrecks in or near channels not maintained (dredged) by the Corps of Engineers and along established routes or likely passage. . . . Do not discuss wrecks lying well offshore unless they present a hazard in a normal coastal route or in the approach to port (e.g., within a safety fairway). A wreck lying amid other described dangers should not be mentioned, nor should those lying in shallows or other areas out of the way of normal navigation.

The U.S. Coast Pilot reads as though an experienced mariner, with local knowledge, were briefing the navigator. For example, here are three brief excerpts from the U.S. Coast Pilot, Volume 3, Atlantic Coast: Sandy Hook to Cape Henry (1993) applicable to waters off Cape May, N J .

The approaches to Delaware Bay have few off-lying dangers. The 100-fathom curve is 50 to 75 miles off Delaware Bay, and the 20-fathom curve is about 25 miles off. Depths inside the 20-fathom curve are irregular, and in thick weather a deep-draft vessel should not approach the coast closer than depths of 12 fathoms until sure of its position; the safest approach or passing courses would be outside Five Fathom Lighted Buoy F and Delaware Lighted Horn Buoy D.

*The shoals off Cape May are mixed clay and sand* and have the consistency of hardpan; t*he ridges run in approximately the same directions as the currents.* Cape May Channel, 1-mile southwest of the cape, is an unmarked passage between shoals, with depths from 2 to 6 feet on either side. The channel is seldom used, and then only by fishing vessels and pleasure craft; local knowledge is required for safe passage.

The channels have strong currents, and many tide rips form near Prissy Wicks Shoal, which has depths as little as 2 feet about 2 miles south of Cape May Light. In Cape May Channel, the current velocity is 1.5 knots on the flood and 2.3 knots on the ebb.

Tide Tables and Tidal Current Tables These publications, described in Chapter 1, provide information necessary to estimate the set and drift of the current, and the height of the tide at any time for numerous locations. Tide and current information provided on the nautical chart is very general, and use of the Tide Tables and Tidal Current Tables is recommended. Notice to Mariners (NM)

The NM is a bulletin in pamphlet form issued weekly by the National Imagery and Mapping Agency (NIMA). NM contains all corrections, additions, and deletions to all NIMA and NOAA charts.

Local Notice to Mariners (LNM)
The USCG Local Notice to Mariners (LNM) contains important information on changes to hydrographic features and dangers to navigation. Charts should be corrected with the LNM before being used.

With respect to hydrographic features, the LNM provides information on changes to charts for individual features; e.g., a revised depth over a charted hazard, and more general information. In some cases, the revised information can be described fully by a simple narrative statement; e.g., .Add, dangerous wreck at location. . In other cases, a chartlet is provided in the LNM showing the updated information. The chartlet is published in the exact scale of the chart being updated, so that all that is necessary is to cut out the chartlet and paste it over the corresponding area of the nautical chart. Figures 4.8 and 4.9, for example, provide an illustration from NOS Chart No. 12366 and the revised chartlet published on December 6, 1993. This chartlet was included to amend the published soundings and depth curve data in the East River, near the Throgs Neck Bridge, NY. As can be seen in this example, the changes are substantial, and chart correction is particularly easy.

Concluding Remarks
No attempt is made to summarize this extensive chapter. Rather, it is fitting to conclude with some general remarks on chart accuracy and tips for using the hydrographic information provided on charts. Some of the suggestions are identical to those furnished in other chapters. These points are also made here for emphasis.

The Admiralty Manual of Navigation offers the following comments on the reliability of nautical charts:
.. no chart is infallible;[/B] every chart is liable to be incomplete in some way or another. Charts based on lead-line surveys are particularly fallible; a single lead-line sounding, which surveyed at best a few centimeters on the sea bed, may be reflected by a figure occupying several hectares of ground depending on the scale of the chart. Any such chart being used for pilotage would have to be treated with the greatest suspicion. The degree of reliance to be placed on a chart must depend upon the character and completeness of the original survey material and on the completeness of reports and subsequent changes.
Apart from any suspicious inconsistencies matters which must be taken into account are the scale of the chart, its soundings in relation to the dates of the surveys or authorities from which it has been compiled and examination of the chart itself. Even these considerations can only suggest the degree of reliance to be placed on the chart. *The chart must never be taken for granted.*



















Although NOAA produces some of the finest nautical charts in the world, even these charts have some limitations. *Depth information on nautical charts is based on soundings from the latest available hydrographic survey which, in many cases, may be quite old. The age of hydrographic surveys supporting nautical charts varies. Approximately 60 percent of inshore hydrography was acquired by leadline (pre-1940) sounding technology. The mariner should consult the source diagram to identify areas recently surveyed. Where possible, courses should be selected that pass through recently surveyed areas.
*
Always use the largest scale chart of the area to be navigated.4 Large-scale charts provide the greatest amount of hydrographic detail for a small area as well as showing more ATONs and landmarks. Ensure also that the chart has been corrected with information provided in the NM and LNM. These points are especially important if using electronic charts. I*t is very tempting to zoom out on the chart scale in an attempt to fit in the entire track in setting waypoints. However, this may obscure important information on hazards to navigation. Remember also that most electronic charts are obsolete shortly after production. There is no presently available substitute for a corrected large-scale paper chart, although this may change in the future. Remember that the general appearance of the sea bottom is likely to resemble the adjacent land features, even if the chart soundings do not show this pattern. For example, if the adjacent land mass has steep hills, is strewn with boulders and rocks, and rocky islands are found offshore, the sea bottom is likely to have a similar appearance. Look carefully at the charted depths and bottom contours. Adjacent depths that differ greatly from one another (shown on the chart or observed on the depth finder) indicate boulders, pinnacles, or other natural hazards that project upwards from the sea bottom. These areas are most likely to have uncharted natural hazards. Leave an extra
marginan ample safety margin of depth under the keel in such areas. Also, where possible, travel in well-established channels in
preference to other areas.
*
Safety margins are important in the horizontal, as well as the vertical plane. Unless the vessels mission is to voyage to a charted hazard, *any hazard should be given a wide berth. *(In figuring a horizontal safety margin, it is important to consider the *probable error in the vessels position* ie., different margins are appropriate depending upon the navigation systems in use.)

Be particularly careful when voyaging in areas, such as changeable areas, for which hydrographic information is not charted. 

Natural channels in certain inlets or other areas where there are strong currents change frequently, and should be used only by mariners with local knowledge.

Amazingly, operators of even commercial craft such as the skipper of the tug Mauvilla (which ran into a railroad bridge precipitating an AMTRAK rail wreck in September 1993) sometimes venture forth without charts, let alone corrected large-scale charts (see Anon, Professional Mariner, 1994).

In another incident (Anon, Professional Mariner, Issue No. 1) the Little Gull, an offshore clam boat skippered by a hired delivery captain, ran aground off Brigantine, NJ. The vessel was found to have no fixed compass and no charts of the area of the grounding. The captain was quoted as saying that he never plots anything on a chart and rarely refers to them. I don&#8217;t have to plot; I just know it all by heart. My brain is so impregnated with loran bearings (sic) that I can figure out where to go without charts.



*Fix the vessels position at frequent intervals. This reduces the likelihood of straying from the intended track into more hazardous areas. If the vessels position is appreciably off course, plot a revised track to ensure that it is safe to return to the original course.*

The U.S. Coast Pilot and other sources, such as commercial cruising guides, should be consulted for additional information. Other mariners with local knowledge are also useful sources. (However, *do not blindly follow other vessels in the belief that they know where they are going,* unless their draft is considerably greater than yours!)

Finally, mariners should *make it a point to report chart discrepancies/update.* In order-of-magnitude terms, there are approximately 2,000 employees involved in one aspect or another of chart production including hydrographic survey crews but nearly 16 million recreational boats owned. Even if only a small fraction of these boaters were to send chart updates to NOAA, the quality of nautical charts would improve significantly.

*The sound navigator never trusts entirely to the obvious. The price of good navigation is constant vigilance.*

*The unusual is always to be guarded against and when the expected has not eventualized, a doubtful situation always arises which must be guarded against by every precaution known to navigators. It is always the captain who is sure in his own mind, without the tangible evidence of safety in his possession, who loses his ship.*

Excerpt from Report of Court Inquiry investigating the
Point Honda disaster in 1923.

*Well this ends chapter 4. If you want chapters 1 and 3 tell me and I will send the whole file to you. For some reason I cant seem to work with 1 and 3.*

References
Anon. .Fishing Vessel Hits Beach in Navigational Blunder, Professional Mariner, Issue No. 1, 1993, p. 29.

.... .Keeping a Low Profile,. Professional Mariner, Issue No. 5, 1994, p. 29

. .... .Shifting Shoals Snag Slag Ship, Professional Mariner, Issue No. 1, 1993, p. 30.

Brogdon, W., .The Limits of Charting,. Ocean Navigator, Issue No. 57, November/December 1993, pp. 75, et seq.

Bunyon, D., .The United Kingdom Hydrographic Office, The Cartographic Journal, Vol. 28, No. 1, June 1991.

Cahill, R. A., Disasters at Sea, Titanic to Exxon Valdez, American Merchant Marine Foundation,
Kings Point, NY, and Nautical Books, San Antonio, TX, 1991.

.... Strandings and Their Causes, Fairplay Publications, London, UK, 1985.

Cohen, P.M., Bathymetric Navigation and Charting, United States Naval Institute Press, Annapolis, MD, 1970.

Defense Mapping Agency, Hydrographic/Topographic Center. American Practical Navigator, An Epitome of Navigation
(Bowditch), Publication No. 9, NIMA Stock
No. NV PUB 9 V1, Bethesda, MD, 1995.

Ekblom, R., .Role of Hydrography in Marine Investigation and Litigation,. Lighthouse,
Journal of the Canadian Hydrographic Association,
Edition No. 44, Fall 1991.

Griffin, T. L. C., and B. F. Lock. .The Perceptual Problem in Contour Interpretation,
The Cartographic Journal, Vol. 16, No. 2, December 1979.

Hinz, E. The Complete Book of Anchoring and Mooring, Cornell Maritime Press, Centreville, MD, 1986.

Human Technology, Inc. Desk Reference Guide: Specifications Unit, Chart and Map, Feature: Channel. Report developed for National Ocean Service, Charting and Geodetic Services, Marine Chart Branch, Under Contract OPM-85-77, McLean, VA, October 1985.

...: Danger Curve.
...: Dangerous Curve.
...: Dangerous Water Conditions.
...: Depth Curve.
...: Feature.
...: Fish Haven.
...: Foul Area.
...: Ledge and Reef.
...: Low Water Line.
...: Natural Resources.
...: Obstruction.
...: Platform.
...: Rock.
...: Ruins.
...: Shallow.
...: Shoal.
...: Tides.
...: Unexplained Ordnance.
...: Unexploded Ordnance.
...: Unsurveyed Area.
...: Wire Drag and Swept Area.
...: Wreck.
Kals, W. S., Practical Navigation, Doubleday & Company, Gordon City, NY, 1972.

Kember, I. D., .Some Distinctive Features of Marine Cartography,. The Cartographic Journal, Vol. 8, No. 1, June 1971.

Lockwood, C. A. and H. C. Adamson., Tragedy at Honda, Chilton Company Book Division, Philadelphia, PA, 1960.

MacPhee, S. B., .How Often Should Charts Be Reissued?, Lighthouse, Journal of the Canadian Hydrographic Association, Edition No. 30, November 1984.

Magee, G. A., .The Admiralty Chart: Trends in Content and Design,. The Cartographic Journal, Vol. 5, No. 1, June 1968.

Maloney, E. S., Chapman Piloting, 60th Edition, Hearst Marine Books, New York, NY, 1991.

.... Dutton.s Navigation and Piloting, Fourteenth Edition, Naval Institute Press, Annapolis, MD, 1985.

Minnoch, J. E., Aground! Coping with Emergency Groundings, John de Graff, Inc., Clinton Corners, NY, 1985.

Ministry of Defence, Directorate of Naval Warfare. BR 45(1) Admiralty Manual of Navigation, Vol. 1, Her Majestys Stationary Office, London, UK, 1987.

Pielou, F. A., .Special Purpose Navigation Charts,. The Cartographic Journal, Vol. 8, No. 1, June 1971.

Richards, Capt. T.W., .Modernizing NOAA&#8217;s Marine Navigation Services, Sea Technology, June 1994.

Sabellico, Lt. M.S., .QE II Grounding, On Scene, COMDTPUB 16100.4, 3/92. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service, and Department of Defense, National Imagery and Mapping Agency. Chart No. 1 United States of America Nautical Chart Symbols Abbreviations and Terms, Ninth Edition, Washington, DC, January 1990.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service. Coast Pilot Manual, 5th Edition, Rockville, MD, 1994.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Survey, Hydrographic
Manual, Fourth Edition, Rockville, MD, July 4, 1976.

U.S. Department of Commerce, Coast and Geodetic Survey, Nautical Chart Manual, Volume One: Policies and Procedures, Seventh Edition, Washington, DC, 1992.

U.S. Department of Transportation, United States Coast Guard. Navigation Rules, International Inland, Commandant Instruction, M 16672.2B, 17 August 1990.

Walsh, G., .Chartroom Chatter, Ocean Navigator, Issue No. 50, November/December 1992, p. 18.

Walsh, G., .Treacherous Inlet Snags Another Ship, Professional Mariner, Issue No. 5, February 1994, pp. 24, et seq.

Zoraster, S., .The Automatic Selection of Prime Soundings for Nautical Chart Compilation, Lighthouse, Journal of the Canadian Hydrographic Association, Edition No. 41, Fall 1991.
.


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## Fishers of Men

Chapter 5

*Aids to Navigation*

_*&#8220;An incorrectly identified mark is a hazard, not an aid, to navigation..&#8221;*_
Alton B. Moody

*Introduction and Overview*

According to accepted NOAA Nautical Chart Manual nomenclature, an Aid to Navigation (ATON).

....is a man-made structure/device external to a craft designed to assist in determining the crafts position or a safe course or to warn of dangers or obstructions. When the information is transmitted by light waves, the device is a visual aid to navigation; if by sound waves, an audible aid to navigation; if by radio waves, a radio aid to navigation. Any aid to navigation using electronic equipment, whether or not radio waves are involved, may be considered an electronic aid to navigation. T*he term aid to navigation. should not be confused *with the *more general term navigational aid *which covers any instrument, device, chart, method, etc., intended to *assist *in the navigation of a craft.. A more complete list of ATONs and associated information normally found on nautical charts is provided later in this chapter. Briefly, however, ATONs include such objects as buoys, lights, fog signals, daybeacons, range markers, radiobeacons and LORAN-C and Omega lattices. *Although the GPS certainly satisfies the definition of an ATON, this system is not discussed in this chapter, because GPS information is not provided on nautical charts. Omega is also not discussed * in this manual even though Omega information is provided on certain nautical charts because small craft are not generally equipped with these receivers. Finally, charted* LORAN-C information is not included *in this manual because this is covered at length in the USCG LORAN-C User Handbook, to which the reader is referred. ATONs may be fixed (land-based or fixed structures in the water) or floating (e.g., buoys).* Landmarks* are the functional equivalent of ATONs but, because these have not been especially constructed for this purpose, *are not formally classified as ATONs. *

Landmarks are treated in a separate chapter (Chapter 6. Landmarks) of this manual.

This chapter provides information on the type and utility of ATONs and how these are depicted on nautical charts. (Because *ATONs are so important to safe navigation * and, therefore, *charted in great detail, this chapter is long and detailed.) *The chapter also identifies the sources of additional information (e.g., the Chart No. 1, U.S. Coast Pilot and the Light List) which supplement that provided on the nautical chart. As appropriate, practical comments are made throughout the chapter on the correct use of ATONs for marine navigation. (See also Chapter 6 for additional perspectives applicable
to ATONs as well as landmarks.) Numerous references are given at the end of this chapter for those interested in additional detail. Names enclosed in parentheses (e.g., Bowditch) denote particularly pertinent references. The Glossary in appendix A provides definitions of key terms related to ATONs.

*Brief Historical Asides*
As might be expected, what are now called ATONs have a long history (see, e.g., Bowditch, Naish). As the later history of ATONs may be familiar to readers of this manual, it is interesting to provide some brief asides on the early periods. Towers (used originally as landmarks, and later as lighthouses) were reportedly constructed to aid passage along the Mediterranean coast as early as 660 B.C. Between 283 and 277 B.C., Sostratus of Cnidus built a large (500 ft) structure on the island of Pharos which marked the harbor of Alexandria from the north. The Romans established a network of fire towers along the Mediterranean.

By medieval times, beacons and range markers were in use to facilitate entrance to the ports of Genoa and Pisa. In the so-called Dark Ages in Europe, hermits and monks located on remote islands and promontories displayed light signals in chapels and participated in salvage operations for wrecked vessels. (Today this might be viewed as a conflict of interest!)

The organization of the Hanseatic League not only provided for economic cooperation but also advanced the use of ATONs (and mechanisms for collecting what would now be termed user fees.) for navigation. A surviving chart of the approaches to Bruge dating from about 1500 A.D. shows buoys as well as towers. (A seamans manual of 1295 A.D. refers to buoys marking the river channels to Seville.) In England, Trinity House was established in the early 1500s as a pilotage authority charged with (among other things) the responsibility of constructing and maintaining marks on the land.

By the 1700s ATONs had become relatively sophisticated and widespread. The first recorded range marks in America were two light towers placed in line on Plumb Island to mark the channel to Newburyport, MA, on the Merrimack River.

*Importance of ATONs in Coastal Navigation*

As with landmarks, ATONs are charted objects used for determining LOP (e.g., with a hand-bearing compass or radar or by direct plotting in the case of range markers) and curves of position (e.g., circles of position with an optical range finder for ATONs with charted height information, such as certain lights or hyperbolas of position with LORAN-C) so as to determine a fix or estimated position for the vessel. ATONs also mark hazards to navigation, identify the limits to safe channels, designate special-use areas (quarantine and anchorages), and provide other relevant information. 

Table 5.1 provides both general and specific illustrations of how information derived from ATONs can be used for marine navigation. ATONs can be used to fix the vessels position, to serve as homing or tracking aids, to ensure that the vessel remains clear of dangerous waters (e.g., by using danger bearings, danger circles, or passing on the safe side of buoys) to identify turn points, and for a variety of specialized purposes such as compass calibration or (less frequently with ATONs) to determine whether or not the vessels anchor is dragging.

Importance of Positive Identification and Related Matters Before discussing the various types of ATONs, charting practices, and related matters, it is appropriate to emphasize several key points noted throughout this manual.

The mariner should be fully familiar with [/B]the charting conventions employed to depict ATONs. And important textual material (e.g., Chart No. 1, and the appropriate USCG Light List) should be readily available for reference.

Any observed ATON (or landmark) *should be positively identified *by the mariner prior to its use for navigation. Published texts (e.g., Cahill, Milligan, Maxim) and USCG accident files are replete with examples of mishaps or accidents which resulted from the incorrect identification of an ATON. Bowditch (see references) &#8220;lists failure to identify aids to navigation.&#8221; as the *second of 16 common errors in navigation. *The mere observation of an ATON (or landmark) at approximately the right position and at approximately the right time although relevant *is not sufficient proof *that the aid observed is the same as that shown on the chart. ATONs are equipped with numerous characteristics (e.g., the flash characteristics and color of a light, the Morse code identifier of a radiobeacon, the number and color of an unlighted buoy or daybeacon) to facilitate positive identification. Closely related to the above point, it is important that charts (and such publications as the Light List and U.S. Coast Pilot) be amended as described in the latest published corrections. ATONs are moved, renumbered, removed, and/or characteristics changed periodically. This can have significant consequences (see Cahill) for the uninformed mariner. Bowditch also lists failure to correct charts among the common errors in navigation.

Whenever observations are taken on any fixed ATON or landmark, this information should be plotted on the nautical chart by the mariner. Even a single LOP can be useful, and frequent fixes are typically necessary in coastal waters where ATONs are placed. Differences between the vessels dead reckoning position and the plotted fix enable currents to be estimated and/or should alert the mariner to the possibility of other errors.

Finally, *all available means* (e.g., maintenance of a dead reckoning plot, use of GPS, LORAN-C, depth sounder or other means) should be used for navigation. *Reliance on only one method is unprofessional and unwise.
*
ATONs and Related Chart Information
(General)
This chapter includes the following: ATONs: lights, buoys, fog signals, daybeacons, ranges, and radiobeacons. These are discussed in order in the following sections. Brief comments on trial courses are also included in this chapter. The symbols used in charting these aids are illustrated in Sections P, Q, R, and S of Chart No. 1, Nautical Chart Symbols, Abbreviations, and Terms (Ninth Ed.) to which the reader is referred. (Pertinent excerpts from Chart No. 1 are included in this chapter for ready reference.)

ATONs are placed in appropriate locations in harbors and inland waterways to facilitate navigation. The placement of these ATONs follow a particular pattern or convention termed the lateral system, in which the colors, shapes, and numbering of lights, buoys, and daybeacons are determined by their position in relation to safe water. (In virtually all U.S. waters the International Association of Lighthouse Authorities (IALA) System B is followed.

Therefore, the IALA-B system is discussed in this manual.) These designations are applied to navigable channels proceeding from seaward toward the head (limit) of navigation. The colors and numbers of buoys and lights along the coasts and along traffic routes not leading distinctly from seaward or toward headwaters follow the same system, but applied so that *even-numbered aids mark the starboard side when proceeding in southerly direction * along the Atlantic coast, *in a northerly and westerly direction along the gulf coast, and in a northerly direction along the Pacific coast.* Table 5.2 provides a capsule summary of the characteristics of lateral aid in most U.S. waters. Additional information on buoyage systems can be found in the Light List and other references (e.g., Coast Guard Aids to Navigation, Chapman).
Most ATONs used by mariners on a day to day basis for navigation purposes are maintained by the USCG. In 1993, there were approximately 50,500 federal ATONs in U.S. waters (Ihnat)! These aids include lights, buoys (lighted and unlighted), daybeacons, and approximately 200 marine radiobeacons. As shown in figure 5.1, the majority (51 percent) of these ATONs are buoys lights (25 percent) and daybeacons (24 percent) account for about equal portions of the remainder. (Fog signals are not included in this tabulation, as these are typically collocated with a buoy or light.) In addition to federally maintained ATONs, there are approximately the same number of privately maintained ATONs. Some privately maintained aids are useful for navigation and are tabulated in the Light List and shown on nautical charts. Charting federal aids (let alone some fraction of the private aids) and keeping charts up to date, is obviously a large undertaking.



















An ATON is charted if it is in the Light List or is assigned a Light List number when published in the LNM. Thus, any ATON found in the Light List will also be found on the chart. * (This assumes that the chart has been corrected based upon data in the LNM.)*

Additionally, some ATONs are charted which are not in the Light List, such as those established by neighboring foreign countries, aids having reliable maintenance authorities (such as those established by the military), and environmental buoys which are not included in the Light List. As well, radar reflectors, lights, and sound signals are charted for those features (e.g., floats, targets, platforms, dredging range markers, and data collection buoys) not specifically intended for use in navigation, whether the feature is listed in the Light List or not.

AND, we Will Continue...


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## Fishers of Men

*PREVIOUS POST CONTINUED*

ATON information provided on nautical charts includes a symbol unique to each class of aid and a set of characteristics such as number, height, color, and nominal range. These characteristics are provided in labels. Symbols and characteristics are placed so as to be readily identified by the chart user (not obscured by less important information) and to avoid overlap with any charted channels. These standard symbols are reserved for ATONs which appear in the Light List. Charted lights and beacons not intended as guides for normal surface navigation are shown with a landmark symbol (see Nautical Chart Manual, Chapter 6. Landmarks) and identifying label. 

Any identifying navigational light or beacon that is not established by the USCG or equivalent authority is identified on the charts either by the label Priv (for privately maintained aids) or by naming the agency that is responsible for its maintenance. Temporary aids are seldom charted unless given a Light List number. 

ATONs established (and/or aid characteristics that are changed) for the winter navigation season are considered temporary aids and these (changes) are not charted. However, specific details for important aids, such as seasonal fog signals at major aids, are charted in all areas. 

*A seasonal aid note is found on all Great Lakes charts and on east coast charts from Cape Henry, VA, northward. This note reads as follows:*

*SEASONAL AIDS*
&#8220;During some winter months or when endangered by ice, certain aids to navigation are replaced by other types or removed. For details see the U.S. Coast Guard Light List.&#8221;

*Lights*
According to official charting definitions in the Desk Reference Guide, a light is a luminous signal *emitted by a fixed structure* to aid navigation that marks channels, warns of dangers or obstructions to navigation, and assists the mariner in determining his position. Lights are identified by their characteristics at night and by the shape and color of their daymarks. Light characteristics include flash sequence, length of light and dark periods, color, and range of visibility. Lights are categorized by function (e.g., junction light, directional light, range light, leading light, sector light, passing light, and aeronautical light).. [Emphasis added.] There were approximately 12,200 federally maintained lights in U.S. waters in 1993. Most lighted ATONs (including lights and lighted buoys) are equipped with controls that automatically cause the light to operate during darkness and to be extinguished during daylight. These devices are not of equal sensitivity and, in consequence, *all lights do not* come on or go off at the same time. The lighting apparatus is serviced at periodic intervals, but there is always the possibility that the light is extinguished or *operating improperly.*

ATON information provided on nautical charts includes a symbol unique to each class of aid and a set of characteristics such as number, height, color, and nominal range. 

These characteristics are provided in labels. Symbols and characteristics are placed so as to be readily identified by the chart user (not obscured by less important information) and to avoid overlap with any charted channels. These standard symbols are reserved for ATONs which appear in the Light List. 

Charted lights and beacons not intended[/B] as guides for normal surface navigation are shown *with a landmark symbol *(see Nautical Chart Manual, Chapter 6. Landmarks) and identifying label.

Any identifying navigational light or beacon that is not established by the USCG or equivalent authority is identified on the charts either by the label *Priv* (for privately maintained aids) or by naming the agency that is responsible for its maintenance. Temporary aids are seldom charted unless given a Light List number.

ATONs established (and/or aid characteristics that are changed) for the winter navigation season are considered temporary aids and these (changes) are not charted. However, specific details for important aids, such as seasonal fog signals at major aids, are charted in all areas. *A seasonal aid *note is found on *all Great Lakes charts *and on east coast charts from Cape Henry, VA, northward. This note reads as follows:

SEASONAL AIDS
"During some winter months or when endangered by ice, certain aids to navigation are replaced by other types or removed. For details see the U.S. Coast Guard Light List."

*Lights*
According to official charting definitions in the Desk Reference Guide, a light. is a luminous signal emitted by a fixed structure to aid navigation that marks channels, warns of dangers or obstructions to navigation, and assists the mariner in determining his position. 

(Lighted buoys are classified by NOAA as buoys, rather than lights, and are discussed later in the main text.)

Lights are identified by their characteristics at night and by the shape and color of their daymarks. 

Light characteristics include flash sequence, length of light and dark periods, color, and range of visibility. Lights are categorized by function (e.g., junction light, directional light, range light, leading light, sector light, passing light, and aeronautical light). [Emphasis added.] There were approximately 12,200 federally maintained lights in U.S. waters in 1993. Most lighted ATONs (including lights and lighted buoys) are equipped with controls that automatically cause the light to operate during darkness and to be extinguished during daylight. These devices are not of equal sensitivity and, in consequence, all lights do not come on or go off at the same time. The lighting apparatus is serviced at periodic intervals, but there is always the possibility that the light is extinguished or operating improperly.

Lights can be used for navigation during the hours of daylight or darkness. During daylight, the fixed structures associated with these lights serve as landmarks for bearing or range determination. 

During daylight hours, the identification of the light is based upon the position of the light and its physical appearance. (The physical appearance of a 
light structure is not found on the chart, however, as noted below.) At night, the light is used in much the same manner except that the identification of the light is based primarily upon the characteristics of the light, such as the color, flash sequence, and position.

*Charting Practices*
This section provides information on charting practices for lights and related information. Charting conventions consist of a light symbol, associated labels and notes, and (for sectored lights or where lights have obscured sectors) information on the sector(s). Symbol (P)

Major lights, minor lights, and lighthouses are charted as shown in Section P of Chart No. 1.

In particular, the position of the light is shown by a black 0.75 mm dot (or open black circle 1.0 mm in diameter in the case of an articulated light), with a magenta flare. (3.4 mm in length with a rounded end of 0.6 mm radius) drawn about 1 mm from the light dot. This light symbol has the visual appearance of an exclamation mark (!) in print. The flare is generally oriented toward the label and is drawn to avoid obscuring other relevant chart detail. Where possible, the flare orientation is aligned with those of neighboring buoy symbols (see below). Leading lights (i.e., those arranged, similar to range lights except that only a single light is used to indicate a path to be followed) may be charted with the flare oriented seaward along the line.










The label and note(s) provide information on the name of the light and the lights characteristics, including the light number (if any). This information is very useful for identifying the light and for determining whether it can be seen from the vessels approximate position. If the name of the light appears in the Light List and space permits, the name of the light is shown in black conventional (vertical) type above the light characteristics. (These are shown in conventional, rather than italic type because italic type refers, among other things, to floating structures. See also Chapter 4.)

The name may be omitted if it is the same as the name of the geographic feature in the immediate vicinity and space is at a premium. Thus, for example, if the geographic name Pt Judith were shown in the chart, the name Pt Judith Lt would not be given.

The characteristics of the light include its flash characteristic, color, period, height, visibility (nominal range), and number.
Flash characteristics include the sequence and timing of the flashes and include fixed, occulting (single occulting, group occulting, and composite group occulting) isophase, flashing (including single flashing, group flashing, composite group flashing, quick, very quick, and ultra quick), Morse code (e.g., Morse A), fixed and flashing, and alternating.

Illustrative flash characteristics and associated chart labels are shown in Section P (10.1 to 10.11) of Chart No. 1, which is reproduced in figure 5.2. Although not particularly complex, this diagram requires some study.

Study of this illustration should be supplemented with on-the-water practice in identifying the characteristics of lights. Mariners are also cautioned that if a vessel has considerable vertical motion due to pitching in heavy seas, a light sighted on or near the horizon may alternately appear and disappear with the possible result that *its true characteristic will not be apparent.* In consequence, *the light could be misidentified.* Under these conditions, the true characteristic may not be apparent until the vessel is closer to the light. The watch stander should be placed at the highest convenient station for such observation. The color of lights is shown using standard abbreviation (e.g., R for red, G for green, W for white, etc., as shown in Sections P 11.2 through 11.8 of Chart No. 1) following the flash characteristics of the light.
*
Generally, white lights are not so labeled *(and if no color is shown, on the chart, white can be assumed) except *where a light exhibits more than one color,* in which case W is shown. *Amber lights are charted as yellow and abbreviated Y. *

Although the color of a light is important to its identification, mariners should be aware that the apparent color of the light may change with distance, because the various colored lights may have different nominal ranges (see below). Additionally, ice or snow may cover the panes of unattended lights, greatly reducing the visibility of lights (see below) and may cause colored lights to appear white.

The period of a light is defined as the time (in seconds) required to exhibit a full pattern together with the interval between patterns. Periods are shown on the nautical chart, to the nearest *tenth of a second *expressed as a decimal, after the flash characteristic. 

Mariners should time a light using a stopwatch. To increase the precision of measurement for lights with short periods, the aggregate time required to complete several cycles should be measured. Thus, for example, if 60 seconds were required for 10 cycles, the period would be 6 seconds.

*Taken together*, the flash characteristic, color, and period provide key information necessary to identify the light when it is in operation. According to both the Admiralty Manual of Navigation and Bowditch, the characteristics of a light must always be checked on sighting. As noted by Moody, *An incorrectly identified mark is a hazard, not an aid, to navigation.*

The height of the light is the vertical distance between the light source (not the top of the light!) and the shoreline reference datum. Height is shown in feet using the abbreviation ft except on metric charts, where height is shown in meters using the abbreviation m.

Height information is important for distance off calculations (see Bowditch) in daytime or for estimating the distance at which a light can be seen at night (see below). Normally, the mariner should search for the highest lights first when approaching a coast as these are likely to be seen most easily. However, the mariner should bear in mind that lights placed at high elevations are more frequently obscured by clouds, mist, or fog than those lights located at or near sea level.

*The visibility* of the light is expressed as the nominal range, and is charted except in the case of range lights or privately maintained lights. The nominal range is the maximum distance (in nautical miles on most charts, *in statute miles on most Great Lakes charts) *a light may be seen at night in clear weather (meteorological visibility of 10 nautical miles) without regard for the height of the light or the observer. (The nominal range is not given in the USCG Light List either, because these are very short-range
ATONs.)

For those lights with two or more colors (see below) either both nominal ranges are shown (e.g., 15/10M) or the lesser of the two ranges will be given. Calculation procedures for estimating the actual distance from which a light can be seen at night, considering the height of the light and observer, nominal range, and prevailing visibility, are detailed in the Light List and other references (e.g., Bowditch, Dutton, Maxim). 

Common practice for the navigator is to draw circles around these lights on the chart with radius equal to the distance at which the light is likely to be visible (see Schlereth) and to estimate the corresponding time when these should first be seen.

*Source: Chart No. 1.
Fig. 5-2. Illustrative Flash Characteristics*

These calculations are only approximate (Burch). Nonetheless, if lights are not sighted within a reasonable time after that predicted, a dangerous situation may exist and the mariner should be appropriately cautious. Finally, the assigned number or letter(s) of the light structure (if any) are shown following the visibility, and enclosed in quotation marks. The number or letter can be observed (e.g., with binoculars) during daylight hours.










On large-scale charts, the characteristics of lights are shown in the following order:
flash characteristic, color, period, height, visibility, and number. For example, an 85 foot
red light (number .2.) of nominal range 10 miles which exhibits a group of three flashes within a period of 10 seconds would include the light symbol, light name (if appropriate) and the label: Fl (3) R 10s 85ft 10M 2. 

*Small-scale charts* show complete information regarding characteristics for major seacoast lights expected to be used for coastal navigation, but may omit certain information in cases where congestion is a problem. In this event, characteristics *are omitted in the following order:* height, period, number of flashes in groups, the number or letter on the structure, and the nominal visibility.

Sectors, and Related Matters In some cases, terrain masking (e.g., a mountain or island) may limit the area over which a light may be seen.

*Knowledge of these blind areas i*s obviously useful to mariners. (There is, after all, no point in looking for something that cannot be seen. Moreover, a prudent mariner might well alter the intended track so as to avoid an obscured sector of a major light.) An obscured sector (sometimes termed dark sector.) is a portion of the light sector of a navigational light in which the light is not visible. 

Where a LNM reports its establishment, the obscured sector (see Section P 43 of Chart No. 1) is charted with dashed rays marking the limits of the obscured sector. Additionally a dashed arc in the sector centered on the light indicates the obscured sector. Directional arrows are used to mark the points where the dashed arc intersects the dashed ray line. A label, LT OBSC or DARK SECTOR, is added for clarity.

See figure 5.3 for an illustration of a light with an observed sector taken from NOS Chart No. 13218. 

In other cases, sectors are deliberately created by placing colored glass in the lanterns of lights to provide additional information to the mariner. Sector lights (see Sections P 40 and 42 of Chart No. 1 for symbology) are used primarily to warn mariners of dangerous shoals or other hazards to surface navigation.
*
The danger sectors *are usually *red* and are charted (in degrees true) from the perspective of the mariner looking toward the light.* Mariners are cautioned not to alter course* based solely on the observed sectors, but rather to note the *correct compass bearing.* *This is because it is difficult to *determine the sector boundaries with accuracy because the edges of a colored sector cannot be sharply demarcated. 

Figure 5.4 presents an excerpt from NOS Chart No. 12304 which shows a *red *sector on the Brandywine Shoals Light warning of shoals in this area.

Several types of *directional lights *are in use:
(see Section P 30 of Chart No. 1 for chart conventions). These lights have a very narrow sector designed to mark a direction to be followed. The narrow sector may be flanked by an obscured or intensified light, or by lights of a different color or characteristic. *A directional light normally shows three *adjoining sectors of red, white, and green, with the center white beam oriented to mark the channel.




























A *leading light *(see Section P 20 of Chart No. 1 for chart conventions) is similar to a range light or marker (see below) *except that it marks a channel with a single light *(with ray lines) rather than with two separate lights. It is usually a high intensity beam marking the safe channel which diminishes to much lower intensities around the remainder of the horizon. It differs from a directional light (see above) in that it shows only *one color of *light instead of the three-color sectors of the directional light.

*Aeronautical lights *(see Section P 60 of Chart No. 1 for chart conventions) are white and green navigation lights associated with airports and often found atop the control tower.

Because these are generally attended during their hours of operation, the lights are highly dependable. Moreover, these are often the most conspicuous of the nonstrobe lights and their nominal range may be greater than those established for marine navigation. 

The aeronautical light is charted by a *standard light dot with magenta flare. *The light symbol is accompanied by its characteristics and the label AERO.

An *articulated light *is a floating light, also called a buoyant beacon. It is basically a vertical pipe structure that oscillates around a universal coupling connected to a sinker. The light structure (which is typically 10 feet to 15 feet above the water surface at high tide) is kept upright by the buoyancy of a submerged floatation chamber. Unlike other buoys (see below) it has no scope of chain and the light is directly over the sinker, i.e., this structure has no watch circle. It is designed primarily to mark narrow channels with greater precision than conventional buoys in situations where the depth of water, up to 60 feet, is too great for a normal pile or dolphin light structure (see Dutton).

When first introduced, this type of ATON, which is *neither a true buoy* nor exactly a fixed light, required *a new symbol *for charting (see Section P 5 of Chart No. 1). This symbol is *a black open circle *1.0 mm in diameter *with a magenta flare.* (the approximate position symbol for a landmark explained in Chapter 6) centered on the published position. The open circle is chosen in lieu of a dot (used for other fixed lights) because the structure *may be displaced more than 10 feet of its true position.*

*The articulated light* is labeled Art. in Newton
Medium italic type (The reason italics are used (in lieu of the vertical lettering found on other lights) is that articulated
lights though classified as fixed structures are floating lights. Buoys are also labeled in italic type.)

*Strobe Lights*
Many charted features are marked with very quick-flashing high-intensity lights, called strobe lights. The light is usually a xenon gas condenser-discharge flash lamp or flash tube. Strobe lights are used on certain USCG-maintained ATONs and on aeronautical hazards, such as stacks, towers, and buildings. ATONs published in the NM and Light List as well as landmarks with a strobe light include the label Strobe as well as other label elements (see above). The flash period of a strobe light is usually (but not always) omitted because of its extremely short duration (much less than 1 second).

TO BE CONTINUED


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## ezbite

Fishers of Men said:


> If anyone wants any particular file or the glossary let me know on here and I'll e-mail you the file. Save you a lot of copy paste issues.


hey van, id like the whole thing. ive been waiting to save it and print it out when your finished. if you have a condensed version that would be great. looks like its gonna take a lot of ink just printing out the black and white version. lol . you know something without everyones avatars, the OGF headers and such.thanks


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## Fishers of Men

ezbite said:


> hey van, id like the whole thing. ive been waiting to save it and print it out when your finished. if you have a condensed version that would be great. looks like its gonna take a lot of ink just printing out the black and white version. lol . you know something without everyones avatars, the OGF headers and such.thanks


Tom, It will take all winter like I said! The beginning was just an eye opener. Now we are going into extremes. I'll send ya 1-5 and the glossary, and such, and as I go on, I'll send ya each file. Can you burn it to a cd? Let me know if you can open them ok, it's adobe.


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## Fishers of Men

CONTINUED FROM PREVIOUS POST

*Riprap* 
Riprap are mounds of broken rock, cobbles, boulders, or fragments that are often placed *around light structures* as protection against ice damage and scouring by fast-moving currents. Desirable as the use of riprap may be from the point of view of protecting the structure and helping to ensure the reliability of the light *riprap also presents a hazard to navigation for vessels* that pass too close aboard. (good fishin areas) Riprap is denoted on nautical charts by a special symbol (see Section P a of Chart No. 1).

Supplemental Information Regarding Lights and Other ATONs In addition to the nautical chart, the Light List, the U.S. Coast Pilot, and commercial cruising guides offer relevant information on ATONs. Additional information provided in these sources is briefly discussed below.

*The Light List is the authoritative source * of information on ATONs. It is published annually by the USCG in several volumes, covering various geographic areas. The Light List is a valuable complement to the nautical chart and provides specific information on ATONs. Contrary to the implication of its title, the Light List offers information on unlighted as well as lighted ATONs. In addition to general information regarding ATONs the Light List includes specific information on each ATON such as its LLNR, the name and location of the ATON, the geographic coordinates (latitude and longitude), characteristics, height, nominal range (for a wider variety of ATONs than found on the nautical chart), an identification of the structure, and pertinent remarks. The organization of the Light List is actually quite logical, but requires some study to be used effectively. When all else fails, the index at the back of each volume is helpful.

Much of the information on ATONs shown in the Light List is identical to that provided on nautical charts. However, the Light List does contain information not found on charts and, additionally, is revised more frequently than most nautical charts and, therefore, is more likely to contain up-to-date information. (However, a properly corrected chart is also up to date.)
Perhaps the most useful information contained in the Light List that does not appear in the nautical chart is a brief description of the structure and the accompanying remarks. The description of the structure is particularly useful for identifying lights during daylight conditions. For example, the route from seaward up the Delaware Bay is marked by several lighthouses, including the Brandywine Shoal Light (see figure 5.4), Fourteen Foot Bank Light, Miah Maull Shoal Light, Elbow of Cross Ledge Light, and Ship John Shoal Light. (Photographs in this chapter show two of these lights.) Mariners with local knowledge can readily identify these lights by their distinctive physical appearance. 

(In SAR cases on the Delaware Bay in which the distressed mariner reports a position near one of these lights, *Rescue authorities often ask the mariner to describe the light. *This procedure can save fruitless search hours in cases where the distressed vessel does not have an accurate position fix and misidentifies the light.)

However, those without local knowledge would certainly benefit from the following descriptions taken from the Light List, Volume II, Atlantic Coast, Toms River, New Jersey to Little River, South Carolina (1993):

Brandywine Shoal Light-Cylindrical concrete structure, adjacent to old screwpile with red sector from 151 degrees to 338 degrees covering shoal area southwest of Cape May. 

As with several other lights in the area, this light is equipped with an emergency light of lower intensity with same characteristic as main light when main light is extinguished.

Fourteen Foot Bank Light-White tower and dwelling on black cylindrical pile.
Miah Maull Shoal Light-Red conical tower, on gray conical pier; red cylindrical watch room and black lantern. 

Elbow of Cross Ledge Light-Red skeleton tower with small white house on international orange cylindrical base. 

Ship John Shoal Light-Brown octagonal dwelling with pyramidal roof; on cylindrical pier. Light has red sector from 138 degrees to 321.5 degrees covers shoals on east channel. High intensity beam down Miah Maul Range.

Additionally, the Light List provides specific information on ATONs which are seasonal information not shown on the nautical chart. For example, this same volume of the Light List notes that the Deadman Shoal Lighted Buoy IDS which is normally equipped with a flashing green light with a 4-second period is replaced by an unlighted winter marker from December 15 to April 1 of each year.

*The U.S. Coast Pilot* also provides information on lights and other ATONs. The scope of the material provided in the U.S. Coast Pilot is quite broad (see other chapters of this manual) and, as a result, coverage of ATONs is less complete than can be found in the Light List. Nonetheless, the U. S. Coast Pilot does contain useful information on selected ATONs. In particular, the U. S. Coast Pilot often provides descriptions of lights that are useful for identifying the light structure during daylight hours. For example, here are a few descriptions of lights taken from the U.S. Coast Pilot Volume 3 (1993), Atlantic Coast: Sandy Hook to Cape Henry:

The entrance to South River is between Saunders Point and Thomas Point, 1.8 miles northeastward. 

Thomas Point Shoal Light (38&#176; 53.9&#8217; N, 76&#176; 26.2&#8217; W), 43 feet above the water, is shown from a white hexagonal tower on piles, in depths of 5 feet near the outer end of the shoal 1.2 miles east-southeastward of the point; a fog signal is at the light. The light is 1.5 miles due west of a point on the bay ship channel 124.2 miles above the Capes. (p. 176)

Solomons Lump Light (38&#176; 02.9&#8217; N, 76&#176; 00.9&#8217; W), 47 feet above the water, is shown from a white octagonal dwelling, with a square tower, on a brown cylindrical base, in depths of 7 feet on the Smith Island side of Kedges Straits. (p. 190) 

Sharps Island Light (38&#176; 38.3&#8217; N, 76&#176; 22.5&#8217; W), 54 feet above the water, is shown from a leaning, brown tower on a cylindrical pier, in 10 feet at the north end of a shoal that bares at the east end. (p. 194) [This description is particularly valuable to those without local knowledge. The structure actually leans a great deal, and it is difficult to believe that this is an ATON when approaching from certain angles in daylight!]

Published Guides and Other Books Published cruising guides and other books often have descriptions and photographs which are useful to the mariner. Books on lighthouses (e.g., Caldwell, de Gast, Holland), in particular, often contain photographs which facilitate daylight identification. 

These books are not designed for navigational purposes, however, and the appearance of the light may have changed since the photograph was taken.

(As an example of this point, an attractively illustrated book (see de Gast) reprinted in 1993, contains a dramatic photograph of the Sharps Island Light referred to above. This light (correctly described in the USCG Light List) is leaning as a result of ice damage in 1977. The photograph of this light, unchanged since the original 1973 edition of this book, does not reflect this damage. No doubt the light looks better in its undamaged state, and the author did not intend to write a navigation text.)

*Buoys*
According to the somewhat lengthy official definition in the Desk Reference Guide, a buoy is a floating object, other than a lightship, moored or anchored to the bottom as an aid to navigation. Buoys may be classified according to shape, as spar, cylindrical or can, conical, nun, spherical, barrel, or pillar buoy. They may also be classified according to the color scheme, as a red, green, or checkered buoy. A buoy fitted with a characteristic shape at the top to aid in its identification is called a topmark buoy. 

A sound buoy is one equipped with a characteristic sound signal, and may be further classified according to the manner in which the sound is produced, as a bell, gong, horn, trumpet, or whistle buoy.

A lighted buoy is one with a light having definite characteristics for detection and identification during darkness. If the light is produced by gas it may be called a gas buoy.

A buoy equipped with a marker radiobeacon is called a radiobeacon buoy. A buoy with equipment for automatically transmitting a radio signal when triggered by an underwater sound signal is called a sonobuoy. 

A combination buoy has more than one means of conveying intelligence; it may be called a lighted sound buoy if it is a lighted buoy provided with a sound signal. Buoys may be classified according to location, as channel, midchannel, middle ground, turning, fairway, bifurcation, junction or sea buoy.

A bar buoy marks the location of a bar. A buoy marking a hazard to navigation may be *classified according to the nature of the hazard,* as obstruction, wreck, telegraph, cable, fish net, dredging, or spoilground buoy.

Buoys used for particular purposes may be classified according to their use, as anchor, anchorage, quarantine, mooring, warping, swinging, marker, station, watch, or position buoy. 

A light-weight buoy especially designed to withstand strong currents is called a river buoy. 

An ice buoy is a sturdy one used to replace a more easily damaged buoy during a period when heavy ice is anticipated.

The above definition also identifies some of the many navigational uses of buoys. Perhaps the most significant use of a buoy is to enable the mariner to stay in safe water and avoid unseen hazards to navigation. *As noted, buoys are the most common ATON.* Approximately 25,500 federal buoys marked U.S. waters in 1993. 

Buoys may be lighted and/or have fog signals (see below), but most (82 percent) are unlighted can or nun buoys.










Physically, buoys are floating ATONs that are moored to the seabed by concrete sinkers attached to the body of the buoy with chain or synthetic rope of various lengths. 

Buoy moorings vary in length, being sufficiently long to accommodate the water depth where the buoy is located, plus an allowance for variations in water depth. *The mooring lengths define a watch circle, and buoys move within this circle depending upon wind, current, and tidal height. The size of the watch circle is not reflected in the chart.*

Buoys vary substantially in size and physical appearance. The reader is directed to any of several references at the end of this chapter for illustrations and photographs of various types of buoys.

*A Brief Digression: Position Fixing with Buoys*

It is noted above that ATONs can be used for fixing the vessels position. Although it may be common practice to use both fixed and floating ATONs for this purpose, *the prudent mariner should try to avoid fixing the vessels position using floating aids.*

(An articulated light (see main text) is a buoyant structure tethered directly to the seabed in such a manner that it has no watch circle. Although similar to a buoy in some respects, it is regarded as a fixed ATON for charting purposes. However, these should be treated as floating aids in terms of position fixing.)

As noted in the introductory material published in each Light List:

Buoy positions represented on nautical charts are approximate positions only, due to the practical limitations of positioning and maintaining buoys and their sinkers in precise geographical locations.

Buoy positions are normally verified during periodic maintenance visits. Between visits, atmospheric and sea conditions, seabed slope and composition, and collisions or other accidents may cause buoys to shift from their charted locations, or cause buoys to be sunk or capsized.

*Prudent mariners will use bearings or angles from fixed aids to navigation and shore objects, soundings, and various methods of electronic navigation to positively fix their position.* [Emphasis added.]

Guidance on the use of buoys for position fixing offered in COMDTPUB P16502.8, U. S. Coast Guard Aids to Navigation (p. 39) is even more explicit:

In order for mariners to derive maximum use from aids to navigation, the different aids to navigation are shown on nautical charts. Thus, mariners are aware of the aids to navigation which they may expect to pass, and may plot any bearings which they take for the purpose of determining their position.
*
DO NOT USE BUOYS TO PLOT A FIX..*

Buoys could be off-station at any time, but are more likely to be off-station after storms, and in icy conditions. During the severe flooding of the Midwest in the summer of 1993, for example, it was estimated (Professional Mariner, Issue No. 3) that as many as 70 percent of the thousands of ATONs in the area needed to be replaced. Severe ice and snow storms in the Northeast in the following year also required numerous buoys to be reset in the Delaware Bay and New York harbor.

It is recognized that there are circumstances where fixed ATONs may not be available for position fixing yet numerous buoys might be present in the area. *Any position based solely on buoys should be regarded with a healthy skepticism and verified using fixed ATONs at the first opportunity.*









*
Charting Practices*
As with other ATONs, buoys are charted with a symbol and one or more labels providing capsule information about the buoy. As noted, generally only buoys listed in the Light List are charted. In most cases this presents no difficulty for the mariner. However, there are numerous buoys that are not charted. In particular, buoys marking channels along the Atlantic coast and gulf coast that shift frequently are generally omitted. (Charting these would require excessively frequent revisions.) Where these buoys are not charted, a note is added explaining that these buoys are omitted. In this case a standard note is added to the chart:

*Entrance to Inlets*

The entrance channels at the inlets not protected by jetties are subject to frequent changes. *The buoys are not charted *because they are frequently shifted in position. Buoys are removed if shoaling makes inlets unnavigable. Entries for such buoys in the Light List *do not contain latitude and longitude coordinates. * Note also that a given chart may omit buoys (and other information) which are shown on a larger scale chart of the area. Symbols (Q)
There are numerous charting symbols used to depict buoys of various types. Figure 5.5, taken from Chart No. 1, provides a sample for review. 

Chart No. 1 should be studied in some detail to ensure familiarity with the various buoy symbols. Refer to table 5.2 for guidance on the significance of lateral aids. Definitions of various types of buoys can be found in the Glossary in appendix A of this manual and the Light List. Additionally, the Light List provides an explanation of the significance of each buoy to the mariner.

The position of a buoy is shown with a small circle, the approximate position symbol (see Chapter 6) because of the practical limitations in positioning and maintaining buoys and their sinkers in accurate geographic locations. Buoys are charted, insofar as possible, in their published position on large-scale charts. In cases where a buoy position coincides with the symbol for another critical feature, such as a rock awash, the buoy may be charted slightly off position for clarity, but always on the same azimuth as the feature that it marks. If buoys are on opposite sides of a dredged channel and plot less than 0.5 mm apart, the aids may be separated to 0.5 mm.

*Channel buoy *symbols (e.g., the diamond shape) are generally shown at a 65&#176; angle from the channel lines, with the symbol pointing toward the top of the chart. 

Buoy symbols marking the limits of fish trap areas are oriented so as to fall inside the area. For other buoys the orientation of the buoy symbols is approximately 25&#176; from the vertical with the symbol inclined toward the label.

Lighted buoys, except superbuoys, are charted with a *magenta disk 2.5 mm in diameter, centered on the circle located at the base of the buoy symbol. *

The few buoys equipped with a RACON are charted with a 7.1 mm diameter *magenta circle centered on the circle located at the base of the buoy.* (The word RACON is derived from RAdar beaCON. A RACON produces a coded response (Morse) when triggered by a radar signal.)

*Superbuoys,* including single point mooring buoys, oceanographic data acquisition systems buoys (ODAS), and large automated navigation buoys (LNB or LANBY), share a unique symbol (Sections P 8 and Q 26 of Chart No. 1). See figure 5.6 for an illustration.




























As a point of interest the present LANBYs built originally to replace lightships are now nearing the end of their service life and are being replaced by smaller, solar-powered exposed location buoys (ELBs). The newer ELBs are cheaper to buy and maintain than the older diesel-powered LNBs (Walsh).

*Charted Characteristics*

*The characteristics of buoys include color and shape, and, if so equipped, the color and period of their light.* Characteristics are abbreviated as shown in Chart No. 1 (Sections Q 2 through Q 71, and a through U) and the Light List. These characteristics are important to the mariner for identification purposes. Indeed, as with lights, all mariners are cautioned to establish *positive identification *of each buoy in the vicinity of the vessels track. 

Noticeably absent from this list of characteristics are the height of the buoy and the nominal range (if lighted). (Nominal ranges for selected buoys can be found in the Light List, and typically varies from about 4- to 6-nautical miles for most lighted buoys.)










Buoy characteristics are shown in italic type. (This is consistent with the convention that floating objects are shown in italics.) These labels are placed so as not to overlap with wreck symbols, shoals, least depths, and other critical features. Buoys are identified on charts by their shape (can, nun, spherical buoy, spar buoy, or pillar buoy) and by any audible signal they emit (bell, whistle, gong). Buoys (with the exception of mooring buoys) are labeled as to their color using specified abbreviations given in Chart No. 1. (Black buoys are not discussed in this manual as these are being phased out.) For example, red buoys are shown with magenta fill, labeled R, and green buoys with green fill and labeled G.

The identifying number (or letter(s)) painted on the buoy (not the LLNR) is shown in quotation marks, e.g., 22. Light characteristics and period are also presented in the label in much the same manner as noted above for lights.

Private buoys listed in the Light List are identified with the label Priv in italic print. The service name is charted on military ATONs, e.g., Navy.

Privately maintained buoys not listed in the Light List are not generally charted.

A radar-enhancing structure or reflective material has been installed on nearly all major buoys and many minor buoys. Therefore, reference to this feature is not charted as part of the buoys characteristics.

Instead, the following note is included on the chart:

Radar reflectors have been placed on many floating aids to navigation. Individual radar reflector identification on these aids has been omitted from this chart.

On large-scale charts, the characteristics of buoys are shown in the following standardized order; color (omit if black) shape, (if unlighted), number (or letter(s)), flash character (if lighted), light color (if lighted), light period (if lighted), and fog signal (if so equipped). For example, the complete legend would be charted as follows:

Lighted Buoy = R 22 Fl R 4s BELL

Unlighted Buoy= R N 22

In congested areas and on smaller scale charts, some of these characteristics are sometimes omitted. Characteristics of lighted buoys are omitted in the following order: period, color, number, light color, and flash characteristics. *For unlighted buoys, the corresponding order is: color then number.*

Space constraints do not permit an exhaustive discussion of the many types of buoys found in U.S. waters. However, three of the most common types of buoys are briefly reviewed.

*Channel Buoys*

These buoys mark the edges of navigable channels. In the IALA-B system, red buoys mark the starboard side of the channel, and green the port side of the channel when proceeding from seaward. Unlighted red buoys have a conical shape, called a nun, and bear even numbers, increasing from seaward. These would be charted using the first symbol shown in Section Q 3 (Q 20) of Chart No. 1 and carry the label R (for red), N (for nun), and the number of the buoy (e.g., .6.) in quotation marks. If lighted, this buoy would have a somewhat different physical appearance (e.g., a larger buoy rather than the simple nun), a red light atop the buoy, and would be charted by adding the magenta disc and the characteristics of the light would be noted as discussed above.

Unlighted green buoys have a cylindrical shape, called a can, and bear odd numbers, increasing from seaward. These would be charted using the first of the symbols shown
in Section Q 2 (Q 21) of Chart No. 1, and carry the label G (for green), C (for can), and the number of the buoy (e.g., .7.) in quotation marks.

If lighted, this buoy would have a somewhat different physical appearance (e.g., a larger buoy rather than the simple can), a
green light atop the buoy, and would be charted by adding the magenta disc and the characteristics of the light would be noted as discussed above.

*Incidentally, mariners are sometimes confused by the exact meaning of the phrase returning from seaward in certain instances. * The nautical chart should always be consulted to verify the safe side for passing any buoy with lateral significance. Additionally it is worth noting that no buoy should be passed very close aboard; buoys can move throughout the watch circle (endangering the vessel). Moreover, buoys may be located outside of the channel (generally noted in the Light List) in cases where the channel is deep. A vessel that ventures too close to the buoy may no longer be in the channel.

*Junction buoys* typically mark a junction of two channels and can be passed safely on either side. As with other buoys, these can be lighted or unlighted.

If unlighted, the buoy would resemble a green can (if the preferred channel were to the right when approaching from seaward) or a red nun (if the preferred channel were to the left when approaching from seaward). The nun would have horizontal red and green bands with the topmost band red. It would be charted by the symbol shown in Section Q 4 of Chart No. 1. The diamond shape would have two fills red and green (topmost red) and the letters RG along with the letter(s) on the buoy shown in quotation marks. If lighted, these would be larger buoys, but retain the same physical color and lettering scheme. The color of the light matches the color of the topmost band. These would be charted using the same symbols as given above, except that the magenta disc would be added, along with the light characteristics as noted above.


*Midchannel buoys* (also called fairway buoys) mark safe water at or near the center of the channel and can be passed on either side. Physically these can be lighted (with a white light blinking the Morse .A.) or unlighted, with either the characteristic shape of the lighted buoy or a spherical shape. These are vertically striped red and white. These are charted by the first of the symbols shown in Section Q 5 of Chart No. 1, with or without the magenta disc depending upon whether the buoy is lighted or not. The label would contain the color code RW (for red and white), and the identifying letter on the buoy, together with the light characteristic Mo (A) if appropriate.

*Fog Signals *

According to official charting definitions in the Nautical Chart Manual, fog signals. are audible aids used to warn of danger and to provide the mariner with a means of determining a crafts position when visibility is obscured by fog, snow, rain, smoke, or thick weather. Among the devices in common use as fog signals are the following:

Diaphones produce sound by means of a slotted reciprocating piston actuated by compressed air. &#8216;Two-tone&#8217; blasts consist of two tones of different pitch, beginning with a high-pitched blast and ending on a low pitch.

Diaphragm horns produce sound by means of a disc diaphragm vibrated by compressed air or electricity. Duplex or triplex horn units of differing pitch produce a chime signal.

Sirens produce sound by means of either a disk or a cup-shaped rotor actuated by compressed air or electricity. .Whistles produce sound by compressed air emitted through a circumferential slot into a cylindrical bell chamber.

Bells produce a distinctive sound by the vibration of a hollow, cup-shaped metallic vessel which gives forth a ringing sound when struck.

Gongs produce a sound by the vibration of a resonant disc..

There were approximately 1,620 fog signals on federally maintained ATONs in 1993, the majority (75 percent) of which were installed on buoys.

These fog signals are used by the mariner in much the same manner as lights or buoys. And, indeed, these signals are often collocated with fixed or floating aids to navigation. 

Each fog signal has specific characteristics by which it can be distinguished. The signal characteristic is the phase relationship of the recurring sound emissions. Here are a few pointers to keep in mind relative to fog signals and operation in fog:

Fog signals on fixed stations and large navigational buoys produce a specific number of blasts and silent periods each minute, when operating, to facilitate positive identification. 

Fog signals on buoys are generally activated by the motion of the sea: therefore, they do not emit regular signal characteristics and, when the sea is calm, *may emit no sound signals.*

Fog signals can be activated by several means (including manually, remotely, or with a fog detector). In cases where a fog detector is employed, there may be a delay in the automatic activation of the signal. Additionally, fog detectors may not be capable of detecting patchy fog conditions.

The sound from a fog signal may not be sufficiently loud to be heard over the noise of an engine. Therefore, it may be useful to periodically reduce the engine to idle power or turn it off completely to listen for these signals.

Remember to sound the appropriate signals when operating in fog.
If visibility is so impaired to necessitate reliance on fog signals, it is sufficiently poor to require appropriate sound signals from all vessels.

*Note also that speed should also be adjusted to the prevailing circumstances.
Particular attention should be paid to positive identification of buoys in sequence. When a buoy in sequence is missed, consider running a search pattern to find the buoy.
*

Moreover, use all available means of navigation, including electronic position-finding aids, radar, and depth-sounder information.

Finally, as noted in the Light List, mariners *should not rely on sound *signals to determine their position. Distance cannot be accurately determined by sound intensity.

Occasionally, sound signals may not be heard in areas close to their location. Signals may not sound in cases where fog exists close to, but not at, the location of the sound signal.

These important caveats aside, fog signals can be very useful aids to navigation in circumstances of restricted visibility.

*Charting Practices*

Fog signals are depicted by a symbol and appropriate labels and notes. In most cases, fog signals are located on fixed or floating aids to navigation. 

Therefore, the fog signal is charted using the appropriate symbol for the light or buoy. Information on the fog signal is included in the labels associated with the ATON. In some cases, fog signals are included on structures not normally used for navigation. In this case the landmark symbol (see Chapter 6) is used, and the appropriate label appended.
*
Labels and Notes*
Fog signals are labeled as DIAPHONE, HORN, SIREN, WHISTLE, BELL, or GONG.

The appropriate designation (see Section R of Chart No. 1) is used as part of the characteristic of the aid. Refer to the Light List for a detailed presentation of the sound sequence and period.

*TO BE CONTINUED*


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## Fishers of Men

CONTINUED FROM PREVIOUS POST

*Daybeacons *(Q)
According to official charting definitions in the Desk Reference Guide, a daybeacon. ....is an unlighted fixed aid, specifically designated for navigation, placed on shore or on marine sites. They are established and maintained by the U.S. Coast Guard. They are identified by their color and the shape of the daymark. Reflective borders are placed on certain daybeacons to assist the navigator using a searchlight to more readily locate them at night. The color of the reflectors has the same significance as the color of the aid. [Emphasis added.]

*Key words in the above definition are beacon and fixed. *Contrary to the popular sense of the word beacon, *daybeacons are unlighted aids.* 

(According to Naish (see references), the word beacon comes from the German word bake. The meaning of this word in Frisia and North Germany is a signal pole or construction placed in or near the water. The pluralform, baken, is the source of the English word beacon.) 

Moreover, *these are fixed structures *and, therefore, admonitions against using floating structures (noted in the above section on buoys) for *position fixing do not apply.* Daybeacons are used by mariners in the same manner as lights and landmarks.e.g., to identify channels and to fix the vessels position.

The lack of lighting limits the utility of these aids for night navigation but, despite this limitation, daybeacons appear surprisingly bright in the reflected glare of the vessels searchlight. 

Daybeacons include lateral daybeacons (in red or green), preferred channel daybeacons, safe water daybeacons (in red and white), and special-purpose daybeacons (yellow quarantine area daybeacons, regulatory warning daybeacons).

There were approximately 11,900 federally maintained daybeacons in U.S. waters in 1993, less than one-half the number of buoys.

Daybeacons are often used in shallow inland waters, because these are less expensive to install and maintain than buoys. Additionally, these have the advantage of being fixed, rather than floating structures. Physically, these consist of one or more piles driven into the bottom, surmounted by signboards called daymarks.










*Charting Practices*
This section provides information on charting practices for daybeacons and related information. Charting conventions consist of a symbol and associated labels to describe the characteristics of the daybeacon.

*Daybeacon Symbols*
The daybeacon symbols are shown in Section Q (80 through 83) of Chart No. 1. The center of the daybeacon symbol is located at its geographic position.

Daybeacons along dredged channels are also charted in their *true positions,* unless they are on opposite sides of a channel and plot less than 0.5 mm apart. In this case, to add clarity, the aids may be separated to 0.5 mm. However, daybeacons are not moved off ranges (see below) nor natural objects.

There are two principal standard symbols used to depict daybeacons; a triangle and a square. Triangular daybeacons (starboard hand red marks with even numbers in the IALA-B system) are typically represented by an equilateral triangle 2.0 mm on each side.
(To avoid chart clutter in congested areas, a 1.5 mm triangle may be substituted.) 

Red triangular daybeacons are shown with a magenta fill, those with other colors (e.g., preferred channel daybeacons) are unfilled and the colors and identifying numbers or letters are included in the label.

Square daybeacons (port hand marks with odd numbers in the IALA-B system) are typically represented by a square 1.65 mm on each side (or a smaller 1.3 mm square). The square symbol is also used to represent rectangular, round, octagonal or diamond-shaped daybeacons). 

Green daybeacons are shown with a green fill, those with other colors (e.g., preferred channel, safe water, or special purpose daybeacons) are left unfilled, and the colors and identifying numbers or letters are included in the label.

Figure 5.7 shows daybeacons in the vicinity of Hereford Inlet, New Jersey.










http://i202.photobucket.com/albums/aa305/FishersofMen/5-7Littleeggharbortocapemay.jpg

Fig. 5-7. Excerpt from NOS Chart No. 12316 (Little Egg Harbor to Cape May, New Jersey). 
*Note that the buoys in Hereford Inlet are not charted. Note also the daymark symbols marking the Great Flat Thoro. Cupolas and a standpipe can be seen as landmarks. Lights, lighted, and unlighted buoys are also shown.
*

*Daybeacon Labels*
Labels include the color(s) of the daybeacon and the identifying numbers and letter(s), charted in black vertical type. (Note that these are depicted in *upright letters, rather than italics,* because these are fixed structures.)


Color choices include red (starboard hand markers), designated with an R, red and green (junction beacons with preferred channel to port), designated with an RG, red and white (fairway beacons), designated with an RW, green (port hand markers), designated with a G, green and red (junction beacons with preferred channel to starboard), designated with a GR, yellow (quarantine area, practice area), designated with a Y, and white (regulatory warning, state boundary), designated with a W.

Numbers and letters are charted as appropriate.
The abbreviation Bn is used to depict daybeacons which* do not have *identifying numbers or letters.

Daybeacons that have information written on the dayboards may have that information (e.g., .Rock.) charted as an optional part of the aid characteristic. 

*Private daybeacons*are labeled Priv.

Congrats to those who hung in here. At least _we_ will know what _we _are lookin at on a chart or on the water. I guarantee next spring when you get out, you will notice things you never new existed. One more post tomorrow on chapter 5 and we will proceed further. 

TO BE CONTINUED


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## Fishers of Men

CONTINUED FROM PREVIOUS POST
*Ranges (M)*
According to the Light List, ranges are non-lateral aids to navigation systems employing *dual beacons* which, when the structures appear to be in line, assist the mariner in maintaining a safe course. The appropriate nautical chart must be consulted when using ranges to determine whether the range marks the centerline of the navigation channel and also what section of the range may be safely traversed. 

Ranges display rectangular dayboards of various colors and are generally, but not always lighted. When lighted, ranges may display lights of any color. As constructed, a range consists of two beacons, one is called the front range marker and is lower in height than the other, called the rear range marker.

The rear marker is usually located some distance from the front marker. (Often the front range marker is on a fixed structure in the water, and the rear range marker is on land.) When these two markers appear directly in line (one behind the other, but both visible because the rear marker is higher) they are said to be in range, or in transit in British usage. The line defined by the range is called a range line or leading line.

Daybeacons and other charted objects forming a range are often called *leading marks.* Likewise range lights are sometimes termed *leading lights.*

*Approaching the front range marker,* if the two marks are exactly in range, the vessels position is exactly along the range line. If the lower marker is to the left (right), the vessel *must alter course *to the left (right) to rejoin the range. 

*Because of geometric* considerations, the horizontal angle between the range markers seen by a vessel a fixed distance away from the channel centerline *increases with decreasing distance *(Brogden). Thus, the sensitivity of the angle to *side-to-side excursions increases *as the vessel draws closer to the markers. 

*The range markers provide* an accurate and easily obtained line of position. Artificial ranges (lighted or unlighted) have been installed in line with channels in many ports. In cases, such as the Delaware River, where the river has many bends, separate ranges mark each of the straight sections, and navigation amounts to following a sequence of ranges throughout the voyage. 

Most ranges are aligned with the center of the channel, but in some areas more than one range is used to define the inbound and outbound ranges of the channel.

Range lights may be of any standard light color or period, the principal requirement being that these stand out from their surroundings. Thus, for example, green rather than red or white lights might be used to mark a range that would be aligned with the setting sun. Most range lights show a high intensity beam within only a very narrow arc of visibility marking the channel centerline and are obscured around the remainder of the horizon. These lights appear to lose brilliance rapidly as the vessel strays from the range line.

Range lights are often visible at distances considerably greater than the actual usable range, to ensure that they can be seen in adverse weather conditions.

After extensive research and testing, the USCG is preparing to install light pipes on many channel ranges around the country (Professional Mariner, 1994). These light pipes are fiberglass tubes, approximately 15 feet long and 6 inches in diameter with a special film on the inside and a light source at one end. The light pipe is placed directly in front of the boards of the range markers.

*The light pipes* are highly conspicuous at ranges up to several miles, and compared to conventional lights it is much easier to detect the alignment (or misalignment) of two vertical lines of light. Light pipes will be supplied with various colors and characteristics in the same manner as conventional range lights.

*Charting Practices*
Only ranges published in the Light List are charted. As with other ATONs charting conventions consist of a symbol and associated labels.

Range lights are separately charted as noted above in the section on lights. If the scale is too small to chart a pair of range lights individually, these are shown with one light dot and labeled, for example, 2F. *A passing light*, if installed, is generally placed on the front light of a range structure located in the water. The passing light serves as an extra precaution to alert mariners to the existence of the range light structure when approaching the light from its dark side at night. (Not all ranges are equipped with passing lights, however.) Because the passing light is of secondary importance to the range light, its characteristic is charted on a separate line below the range light label in the same order as shown in the Light List. If the visibility of the passing light is included in the Light List, it is also included in the chart label.
Symbol (M 1)

The range symbol is shown in Section M 1 of Chart No. 1. The usable portion of ranges is shown by a solid line to the point where the vessel should leave the range. (Defining the limits of the range is obviously of key importance for curving channels.)

From the point where the range should be left, the range is continued with a short-dashed line to the rear navigational aid.

In the event of extreme shoaling or shoaling over a large area in an improved channel, *range lines may be dashed,* or even omitted, through a shoaling area that is depicted by hydrography. 

Figure 5.8 shows ranges used to mark a section of the upper Delaware River, as shown on NOS Chart 12314 (Delaware River, Philadelphia, PA, to Trenton, NJ).










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Fig. 5-8. Excerpt from NOS Chart No. 12314 (Delaware River, Philadelphia, PA, to Trenton, NJ). Three ranges are shown on this inset. The rear range marker for the Kinkora Range is an occulting white light with a 4-second period. The front range marker for this same range is a quick-flashing white. The boundary between the Roebling Range and the Kinkora Range is close to the unlighted
red nun 70 Green buoy 71 is a lighted quick-flashing buoy. 

*The reason that the quick characteristic is used* is that two course changes are necessary over a short distance. Landmarks shown include tanks and a spire.

*Range Labels*
The range label shows the name of the range and the bearing of the range (in degrees true along the range in the direction of the front marker) if these are published in the Light List and considered useful to the mariner.

*Dredging Ranges*
The USACE has established ranges in some areas to control channel maintenance dredging. These ranges (often unlighted) are not intended for navigation and are charted only as a DREDGING RANGE. 

Structures comprising this range are charted as landmarks (see Chapter 6). If the dredging structure is listed in the Light List, the structure label provides light and fog signal information.

*Natural Ranges*
Spires, cupolas, towers, tanks, and other artificial or natural features may form natural ranges which chart users sometimes recommend for charting. These natural ranges are not charted unless recommended by the USCG and published in the LNM. Radiobeacons and Related Aids (S) A brief introduction to radiobeacons provided in the Light List states: 

As the first electronic navigation system of navigation, radiobeacons provided offshore coverage and also became the first all-weather electronic aid to navigation. The Coast Guard operates about 200 radiobeacons located on the Atlantic, Gulf, and Pacific coasts, *and on the Great Lakes.* 

These radiobeacons are located at lighthouses, on large buoys and along the coasts. All positions are charted.* In order to use this system,* the mariner needs a radio direction finder, which is a specifically designed radio receiver with a directional antenna. This antenna is used to determine the direction of the signal being emitted by the shore station, relative to the vessel.

The basic value of the radiobeacon system lies in its simplicity of operation and its relatively low user costs, even though the results obtained may be somewhat limited. The general problems and practices of navigation when using radiobeacons are very similar to those encountered when using visual bearings of lighthouses or other charted objects. *A radiobeacon is basically a short range navigational aid, with ranges from 10 to 175 nautical miles. Although bearings can be obtained at greater ranges, they will be of doubtful accuracy and should be used with caution. *

When the distance to a radiobeacon is greater than 50 miles, a correction is usually applied to the bearing before plotting on a Mercator chart. These corrections, as well as information on accuracy of bearings, plotting, and other matters are contained in Radio Navigation Aids [or the U.S. Coast Pilot].

An individual radiobeacon can be used to determine a single LOP and for tracking or homing purposes. If the vessel makes a 90&#176; dog leg of known length, the approximate distance off (Maxim) a single radiobeacon can be calculated from the length of the dog leg and the degrees of bearing change.

Radiobeacons are typically located at or near harbor entrances to maximize the utility of the homing or tracking capability of the system. The LOP from a radiobeacon can be crossed with another LOP (e.g., from a nearby radiobeacon or visual aid) to determine a fix. 

Mariners using radiobeacons for tracking or homing purposes are cautioned to keep track of the vessels position so as to avoid running aground or into hazardous waters.

Historical examples (see Maxim) of homing without distance checks abound. Additional material on radiobeacons can be found in the references listed at the end of this chapter (e.g., Bowditch, Dutton, Hobbs).

For many years, this system, also called radio direction finder (RDF), had the largest number of users of any radionavigation system. In recent years, LORAN-C and GPS have become systems of choice for marine navigation. However, many radiobeacons are being modified to broadcast differential GPS corrections, so radiobeacons will continue in service for some time to come.

Marine radiobeacons operate in the 200 to 400 kilohertz region, just beneath the AM broadcast band. These radiobeacons transmit a Morse code identifier for 50 seconds, followed by a 10-second continuous tone at the end of each operating minute:

The function of the Morse code sequence is to provide positive identification of the radiobeacon. Positive identification of radiobeacons is as important as positive identification of any ATON.

Morse code identifiers are often (but not always) an abbreviation of the facility name. Thus, for example, the two letter Morse code identifier for Cape May is CM, and that for Barnegat Inlet is BI.

*However, there are exceptions *(Cape Henry, for example, carries the identifier CB), so it is necessary to consult the Light List for authoritative information. 

The Light List provides the Morse symbols (e.g., Cape May is .... . .) so it is not necessary to know Morse code to use the system.

The function of the continuous tone is to provide the best signal for determining an aural null in rotating the antenna to determine the bearing to the station.

*Charting Practices*
All marine radiobeacons transmitting signals in areas where hydrography and other navigational information is provided are charted. The useful range of the radiobeacon, along with other pertinent information for radiobeacons in U.S. waters is provided in the Light List. On charts of scale 1:500,000 and smaller, radiobeacons are not shown if the chart does not permit navigation within their range. (Low power radiobeacons with a useful range of 10 miles or less are normally omitted from small-scale charts where larger scale charts are available.)

This section provides information on charting practices for radiobeacons and related information. Charting conventions consist of a radiobeacon symbol and associated label(s), Symbol (S 1)
Most radiobeacons are *collocated with another visual aid *to navigation. *If so, the chart symbol will include* that for the co-located aid, together with a radiobeacon symbol (see Section S 1 of Chart No. 1) consisting of a 7.1 mm diameter magenta circle centered on the position of the aid. 

For stand-alone radiobeacons, the black position accurate landmark symbol (see Chapter 6) is placed at the center of the magenta circle.

*Labels*
In addition to providing information about the host aid (e.g., buoy, light, etc.), if one exists, the label provides information about the radiobeacon. The label is given* in black vertical type if the antenna is attached to a fixed aid,* and italic type if the antenna is attached to a floating aid.

The label includes the abbreviation R Bn, the frequency (in kilohertz), and the Morse code characteristics, regardless of the chart scale.
*
Aeronautical Radiobeacons*
Aeronautical radiobeacons (which operate on similar frequencies to marine radiobeacons and can be received by the same equipment) are sometimes useful for marine navigation, particularly if located in close proximity to the coastline or if there is no rough terrain between the beacons and the coastline that might distort signal propagation. If charted, the aeronautical radiobeacon is depicted with a black position accurate landmark symbol and a 7.1 mm diameter magenta circle centered on the landmark symbol. A label in conventional black type is placed adjacent to the symbol and clear of the magenta circle. The label includes the abbreviation AERO R Bn and the frequency and characteristics of the radiobeacon.

Miscellaneous Related Information Nautical charts also include information on courses, recommended and alternate courses, routing systems, traffic schemes, and areas and limits. These are discussed in Chapter 7. 

Trial courses, however are included in this chapter. Measured Course (Q 122).
*A trial course is a course at sea, the ends of which are marked by ranges ashore and the length of which has been accurately measured. Trial courses are used by vessels to calibrate logs and other instruments that measure speed, as well as to prepare graphs or tables of engine revolutions per minute (RPM) versus speed through the water. * (See Maxim or other references for details.)

A standard symbol (see the excerpt noted in Section Q 122 from Chart No. 1 and reproduced here in figure 5.9) is used to mark the range or measured course ashore. The course and length of the trial course are indicated by a label.










http://i202.photobucket.com/albums/aa305/FishersofMen/5-9trialcourse.jpg

Well we should be good to go to chapter 6 since there was no questions. I must _assume_ everyone has a thorough understanding of chart reading by now! With all the references given you should be good to go at the library to pursue further research. If you have questions, you better get them out before we get into navigation.

"Simon Peter saith unto them, I go a fishing. They say unto him, we also go with thee. They went forth and entered into a ship immediately: and that night they caught nothing. But when the morning was now come, Jesus stood on the shore: but the disciples knew not that it was Jesus... "Cast the net on the right side of the ship and ye shall find." They cast therefore, and now they were not able to draw it for the multitude of fishes."
St. John 21:3-6[/B]

*Concluding Remarks*
As noted, this chapter is long and quite detailed. Nonetheless, the information presented is very important, and bears reading (preferably with a *nautical chart and Chart No. 1 readily at hand)* and re-reading to ensure complete familiarity with this important topic.

Unlike many of the other objects or features depicted on the chart, ATONs are deliberately placed so as to optimize information provided to the mariner. Because the cost of establishment and periodic maintenance are sufficiently high, ATONs are not casually placed.

So it is certain that if an ATON has been put in a given place, it is because this location has real significance to the mariner. Therefore, it is particularly important that the mariner be familiar with the uses, significance, and chart conventions employed to depict this aid.

_&#8220;The consequences [of poor cartography] could be dire. During the Napoleonic Wars, British losses by shipwreck, caused by bad charts as well as bad weather, *were eight times as great as those inflicted by the enemy.&#8221;*_
Wilford

*References*
Anon Charthouse Chatter, Professional Mariner, Issue No. 3, October/November,
1993, p. 7.

Anon Charthouse Chatter, Professional Mariner, Issue No. 4, December/January
1994, pp. 6.7.

Brogden, W., Inside Ranges A Look at What Makes These NAVAIDS so Useful,. Ocean
Navigator, Issue No. 60, March/April 1994, pp. 74, et seq.
Burch, D., Emergency Navigation, International Marine Publishing Company, Camden, ME, 1986.

Cahill, R. A., Strandings and Their Causes, Fairplay Publications, London, UK, 1985.

Caldwell, B., Lighthouses of Maine, Gannett Books, Portland, ME, 1986.

Dahl, N., The Yacht Navigator.s Handbook, Hearst Books, New York, NY, 1983.

National Imagery and Mapping Agency. American Practical Navigator, An Epitome of Navigation (Bowditch), Publication No. 9, NIMA Stock No. NV PUB 9 V1, Bethesda, MD,
1984.

National Imagery and Mapping Agency Radionavigation Aids, RAPUB 117, Bethesda, MD, (Annual) de Gast, R., The Lighthouses of the Chesapeake, The Johns Hopkins University Press, Baltimore, MD, 1993.

Dutton.s Navigation and Piloting, Fourteenth Edition, Naval Institute Press, Annapolis,
MD, 1985.

Eyges, L., The Practical Pilot, Coastal Navigation by Eye, Intuition, and Common Sense,
International Marine Publishing, Camden, ME, 1989.

Hobbs, R. R., Marine Navigation Piloting and Celestial and Electronic Navigation, Third
Edition, Naval Institute Press, Annapolis, MD, 1990.

Holland, F. R., Jr., America.s Lighthouses An Illustrated History, Dover Publications,
New York, NY, 1981.

Human Technology, Inc. Desk Reference Guide: Specifications Unit, Chart and Map, Feature: Buoy. Report developed for National Ocean Service, Charting and Geodetic Services, Marine Chart Branch, Under Contract OPM-85-77, McLean, VA, October
1985.

...: Daybeacon.
...: Light.
...: Marker.
...: Obscured Sector.
...: Range Line.
...: Riprap.
Ihnat, D. J., CDR, U.S. Coast Guard Quarterly Report of Short Range Aids to Navigation, Commandant (G-NSR-1), quarter ending 31 March 1993. Data updated to January 1994 with personal communication, Lt. Mike Peterson, USCG.

Maloney, E. S., Chapman Piloting, 60th Edition, Hearst Marine Books, New York, NY, 1991.

Maxim, L. D., Advanced Coastal Navigation, Second Edition, United States Coast
Guard Auxiliary, Coast Guard Auxiliary National Board, Inc., Washington, DC, 1990.

Mellor, J., The Art of Pilotage, Sheridan House, Dobbs Ferry, NY, 1990.

Milligan, J. E., The Amateur Pilot, Cornell Maritime Press, Centreville, MD, 1982.

Ministry of Defence, Directorate of Naval Warfare. BR 45(1) Admiralty Manual of Navigation, Vol. 1, Her Majesty.s Stationary Office, London, UK, 1987.

Moody, A. B., Navigation Afloat, Van Nostrand Reinhold, New York, NY, 1980.

Naish, J., Seamarks, Their History and Development, Stanford Maritime, London, UK,
1985.

Schlereth, H., Commonsense Coastal Navigation, W. W. Norton Co., New York, NY,
1982.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration,
National Ocean Service, and Department of Defense, National Imagery and Mapping Agency Chart No. 1 United States of America Nautical Chart Symbols Abbreviations and Terms, Ninth Edition, Washington, DC, January 1990.

U.S. Department of Commerce, Coast and Geodetic Survey, Nautical Chart Manual, Volume One: Policies and Procedures, Seventh Edition, Washington, DC, 1992

U.S. Department of Transportation. United States Coast Guard Aids to Navigation,
COMDTPUB P16502.8, Washington, DC, May 1988.

U.S. Department of Transportation. United States Coast Guard, Light List, Volume 1, Atlantic Coast, St. Croix River, Maine to Toms River, New Jersey, COMDTPUB P16502.1, Washington, DC, 1991.

U.S. Department of Transportation. United States Coast Guard, LORAN-C User
Handbook, COMDTPUB P16562.6, Washington, DC, 1992.

Walsh, G., Chartroom Chatter, Ocean Navigator, Issue No. 60, March/April 1994, p. 14.

Wilford, J.N., The Mapmakers: The story of the great pioneers in cartography from antiquity to the space age, Vintage Books, New York, NY 1982.


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## Fishers of Men

*Chapter 6
Landmarks
Introduction and Overview*

According to accepted NOAA Nautical Chart Manual nomenclature, a landmark. ....is any *fixed* natural or artificial object on land which is prominent from seaward and can be used in determining a direction or position. The term excludes objects expressly erected for navigational purposes such as lights or daybeacons. Prominence is the first requisite for a landmark, but ease of positive identification is also important. The unusual or unique feature may qualify as a landmark because it is easy to identify although not particularly prominent.

A more complete list of landmarks typically charted is provided later in this chapter. Briefly, however, landmarks include such objects as buildings, stacks, tanks, domes, towers of various descriptions, spires and radio antennas. (Not all of these objects in a given area would be charted as landmarks, however.)

Often, as in the examples presented in this brief list, landmarks are artificial features. But landmarks also include prominent natural features such as a mountain peak, glacier, volcano, cliffs, or other suitable natural objects.
(It is important that natural features have clearly defined reference points that can be accurately located if these are to be charted as landmarks. Mountains with rounded peaks would probably not be charted as landmarks, although the topography would be shown.)

This chapter provides information on the type and utility of landmarks and how these are depicted on nautical charts. This chapter also identifies sources of additional information (e.g., the U.S. Coast Pilot, Chart No. 1, United States of America Nautical Chart Abbreviations and Terms and the Light List) , which supplement that provided on the nautical chart. Finally, the chapter concludes with practical pointers on the selection of landmarks for navigation and why landmarks are sometimes not seen or identified when underway. Importance of Landmarks in Coastal Navigation All mariners, with varying degrees of formality, employ landmarks for navigation.

Used in conjunction with seamans eye or informal navigation, landmarks serve to determine *an approximate position,* define hazardous areas, provide directions for harbor entry, etc. 

For example, directions to a favorite anchorage *based on recent local knowledge *might be given as:

Stay in the main river channel until passing the red brick pump house on the left (when northbound) then alter course to starboard until the bow is aligned with the blue A-frame building between the flagpole and the marina and the stern with the pump house. Continue along an imaginary line joining these two landmarks until well past the small island on the right-hand side, then turn to port.

More formally, landmarks are charted objects used for determining LOP (e.g., with a hand-bearing compass or radar) and circles of position (e.g., with radar or an optical range finder for landmarks with charted height information) so as to determine a fix or estimated position for the vessel.

(Landmarks are generally selected so as to be detectable and identifiable from the sea by visual means. Some may be detectable and identifiable by radar, but charting as a landmark offers no guarantee that the object can be detected and identified by radar. In particular, landmarks in built-up areas, such as cities, are often lost among many land returns.)

Table 6.1 provides both general and specific illustrations of how information derived from landmarks can be used for marine navigation. As with ATONs, discussed in Chapter 5, landmarks can be used to fix the vessels position, to serve as the visual equivalent of radio beacons for homing or tracking purposes, to evaluate whether or not a vessel is in dangerous waters (e.g., by use of a danger bearing or danger circle), to identify turn points, and for a variety of specialized purposes such as compass calibration or to determine whether or not the vessels anchor is dragging. Included in the list of references at the end of this chapter are texts that discuss these topics in detail. Names enclosed in parentheses (e. g., Bowditch) denote particularly pertinent references.










(The landmark need not be charted for this purpose.)
In short, charted landmarks are the logical equivalent of shore-based ATONs for use in coastal waters. If accurately charted (more below), detectable, and readily identifiable, these can be superior to the use of floating ATONs (buoys)recall that fixed structures are preferable to floating structures for position determination. In some areas of high population density or numerous conspicuous natural features, charted landmarks are actually more numerous than charted ATONs.

*Types of Landmark*
Table 6.2 provides a list of the more common artificial landmarks depicted on nautical charts, together with pertinent brief remarks. Refer to the Glossary given in appendix A for more complete definitions. It is worthwhile to study these and to gain practical familiarity with landmarks by systematically comparing the chart representation of landmarks in your area with the physical appearance of the object. These training sessions can be made an enjoyable part of each cruise. An experienced navigator can often form a highly accurate mental picture of landmarks to be found in unfamiliar waters merely by studying the chart.




























For most landmarks (e.g., buildings, churches, radio towers), object definitions are familiar and the mariner should have little or no difficulty correlating the chart representation with the physical appearance of the object. In some cases (e.g., cupola, dome, chimney, stack), the definitions are more subtle and/or the objects may be less familiar so more study and on-the-water comparisons are appropriate. Objects Not Normally Depicted As Landmarks 
There are also several classes of objects that are not typically selected as landmarks on nautical charts. (These objects may be shown on certain charts in areas where suitable landmarks are few and far between.) Table 6.3 provides a list of those either intentionally or unintentionally omitted. In the main, the reasons for not selecting these objects as landmarks are obvious. For example, objects of a temporary nature, such as a construction crane, would be a poor choice for a landmark since the object would probably be moved to another location by the time that the chart was printed.










Trees are another example of an object not normally charted as a landmark. Think of the consequences, for example, if the tree were struck by lightning or chopped down. Even worse, suppose there were another tree standing one-half mile away!

The charting of movable objects as landmarks is generally avoided. A gantry crane at a shipyard may be a very prominent feature, but it would not have a fixed geographic position and, therefore, would have little utility for precise fixing of a vessels position. Signs are not typically charted as landmarks.
However, an unusually conspicuous sign, especially in an area without other suitable landmarks, may be charted. The elevation and lighting of the sign are considered in making the determination of whether or not to select the sign as a landmark. 

Signboards displaying navigational information may be considered as landmarks if they display navigationally relevant information, for example, signboards used to mark distances along a waterway. As another example, signs providing water-level information are normally charted even if not visible from a distance.

It may come as a surprise to some readers that not all items potentially suitable as landmarks are actually charted. To be sure, in sparsely populated flat land areas, nearly all suitable landmarks would be charted. But in built-up areas, only a few otherwise suitable objects would be plotted as landmarks. (Aside from the logistics and compilation problems of charting all possible landmarks, the resultant chart (with requisite labels) would be physically impossible to produce. Moreover, NOAA is actively seeking ways to reduce chart clutter and make more user-friendly products.)

For example, large cities, such as Boston, New York, and Philadelphia, have literally thousands of buildings that might be suitable landmarks.
However, in practice only a handful those believed sufficient for safe and efficient Navigation are actually depicted as landmarks on the chart. Figure 6.1 provides such an illustration for the Philadelphia, PA., Camden, NJ, area.

Indeed, one of the criteria for charting landmarks in the Desk Reference Guide, is that consideration should be given to the number and quality of other charted landmarks or reported objects of landmark value in the area. Therefore, the mariner should not expect that the nautical chart will depict all possible structures as landmarks.

Generally, this poses no particular problem to the informed mariner. But while underway this can sometimes lead to confusion and identification problems. For example, several water tanks may be visible in an area in which only one or two are charted. In this case, the mariner might be faced with the problem of which of the tanks in view are those charted?

*How Landmarks Are Depicted on the Chart*
Landmarks are charted in the exact position reported on source documents. Both a symbol and one or more labels usually accompany a charted landmark.

*Symbols*
In certain cases, the outline shape of a prominent structure may be charted to scale if it is relatively large or of particular interest and of landmark value (e.g., the Pentagon, Fort McHenry).

More typically, however, landmarks are charted with standard symbols.
Landmark symbols are shown in Section E of Chart No. 1. According to the accuracy with which the landmarks location is known, the symbols include:
An accurate landmark symbol, consisting of *a black circle* 1.18 mm (0.047) *in radius with a center dot *0.25 mm (0.010) in diameter in cases where the position of the landmark is considered to be located *within 10 feet of its correct geographic location.*

An approximate landmark symbol, consisting of a *smaller black circle* 0.5 mm (0.020) in radius *without any center dot *in cases where the landmark is less accurately located than above, but generally considered to be *within 100 feet *of its correct geographic location.

An approximate landmark symbol explained above, but with the letters PA (position approximate) as part of the label in cases where the location of the object is considered to be within 101 to 300 feet of its correct geographic location.

Such landmarks, sometimes referred to as inexact position landmarks, are only charted if they serve a critical navigation need. In some cases a landmark, such as a building, will be drawn to scale and, additionally, have some contained feature depicted with the accurate or approximate position label.

For example, the Customs House in Philadelphia, shown in figure 6.1 is drawn to scale. Additionally, the tower atop this building is shown as a landmark with the accurate position symbol.










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Identifying particular portions of structures as landmarks makes it possible to *take accurate bearings.* Excepting those landmarks which are drawn to scale, charted landmarks are shown in only one of two sizes (1.18 mm radius circle and 0.5 mm radius circle) regardless of actual dimensions. In this sense, all landmarks are alike. *Something more is clearly needed *to help the navigator identify the landmark. This additional information is provided in labels that are printed next to the landmark symbol.

*TO BE CONTINUED
*


----------



## Fishers of Men

*CONTINUED Ch 6 and conclusion of 6
Labels*
Accompanying the landmark symbol is one or more labels. Labels are used to provide additional information useful in identifying the landmark. The label also provides a redundant indication of the accuracy with which a landmark is located.
The first label depicts the primary nature or descriptive term most likely to identify the object (e.g., TOWER, STACK, CHIMNEY) set in 6 pt. Newton Medium type and placed in close proximity to the landmark symbol. Landmarks charted with the accurate landmark symbol are labeled entirely in vertical capital letters, those charted with the approximate landmark symbol are labeled with initial capitals only. Thus, for example, a tower considered to be located within 10 feet of its correct position would include the accurate landmark symbol and the label .TOWER, whereas one located to within 100 feet of its true location would have the approximate landmark symbol and the label Tower. (The lone exception to this rule is the case where an acronym is used in the primary or secondary label of an approximately determined landmark. Here the acronym would be included in capital letters, e.g. Tower (USCG). The primary label would be shown in initial capitals only.)

A tower with a location uncertainty greater than 100 feet would carry the label Tower PA A partial list of standardized labels and authorized abbreviations are shown in table 6.4.










Secondary and descriptive labels may be added for clarity and are enclosed in parentheses to the side or underneath the primary label. The capitalization convention for the secondary label(s) is the same as that for the primary label. Consider a lighthouse, for example.

If operational, this would not be considered a landmark rather it would be included as an ATON (see Chapter 5). However, if no longer used as a lighthouse, it would be classed as a tower... But, because the term tower includes many different types of structures, it is desirable to add a secondary or descriptive label, abandoned lighthouse, to supplement the primary label. Accordingly, such a landmark (if accurately located) would be labeled TOWER (ABAND LT HO).

Names of certain locally well-known buildings may be shown as secondary labels to facilitate identification. For example, DOME (STATE HOUSE) or BUILDING (RITZ TOWER) or TOWER (CUSTOM HO) might be shown on secondary labels. Well-known and unusually prominent landmarks are, on occasion, depicted using the name of the landmark as the primary label. For example, EMPIRE STATE BUILDING and WASHINGTON MONUMENT are shown on nautical charts. Descriptive labels that identify the relative size or location or other distinguishing characteristics of the landmark may also be shown in parentheses following or below the primary name. When only one object of a group of similar objects is charted, the descriptive label includes the number of objects in the group. Examples include STACK (TALLEST OF THREE), HOUSE (WEST GABLE), SIGN (LIGHTED).

A descriptive label may also relate to the shape of the object. Examples include TANK (OBLONG), TANK (BALL), or TANK (BALL ON TEE). Color is not normally noted in a label because this may be only temporary. (Color may be included, however, in U.S. Coast Pilot or Light List descriptions.)

Painted names on objects are not normally shown unless the name or abbreviation is displayed in very large and conspicuous letters that are easily identified. The material of construction is not described in a secondary label because the mariner usually cannot identify the material from a distance.
In some cases both a secondary name and descriptive label are included. For example:
STACK (FLARE)
(TALLEST OF THREE) might be found in a shore side petroleum refinery.
The height of the object is also sometimes included. Heights can be used for determining the vessels distance from the landmark (see Bowditch) and, with bearing data, to fix the vessels position. In the case of landmarks, the height is given in feet (or meters for metric charts) measured from the top of the landmark relative to mean high water except in nontidal areas where these are measured relative to the sounding datum. Height information is provided for only a minority of charted landmarks, however.

Aircraft obstruction lights are typically regarded as secondary importance as an aid to navigation. Therefore, these are not normally charted with a light dot and magenta flare unless listed in the Light List and given a Light List number. Obstruction lights on landmark objects are not labeled unless specifically requested by a reliable source. In this case, no differentiation is made between occulting and fixed lights. For example, a stack (with accurate location) with a white strobe and red obstruction lights would be labeled:
STACK (STROBE, R LTS).

An obstruction recommended for charting as a landmark that is identified only as an aircraft obstruction light is charted with the appropriate landmark symbol and labeled:
OBSTN (R LT).

Radio structures are labeled with the type of function and height (when considered of significant importance for visual sighting). AM broadcast stations will have the call letters and frequency included in the label, as will other stations known to be used for marine navigation assistance. Here are a few examples:
RADIO MAST 862 FT 
(TV) (STROBE, 
R LTS)

RADIO MAST 483 FT
WSSO
1230 KHZ
(R LTS)

RADIO TOWER 315 FT 
(FM, MICROWAVE) 
(R LTS)

In very congested areas, a list of stations may be provided elsewhere on the chart to avoid the elimination of important topography and/or hydrography as a result of labeling. The foregoing provides a useful summary of key charting conventions for landmarks.
Other Sources of Landmark Information In most cases the position and the label(s) shown on the chart will be sufficient for the navigator to use the landmark for navigation. However, other sources may offer useful information as well.

Pictures of selected landmarks are included on the back of certain conventional and small-craft nautical charts. These photographs are very useful in identifying landmarks. For example, the back of NOS Chart No. 13221 (Narragansett Bay) contains several photographs of landmarks and ATONs in the area. Commercially produced cruising guides of the area sometimes provide descriptions and/ or photographs of landmarks. An important source of collateral information on landmarks is the U.S. Coast Pilot imbedded in the general text and, in some areas, highlighted in a special section called Prominent Features, the U.S. Coast Pilot provides information on the location, appearance, and suitability of landmarks for navigation. Guidance for the preparation and revision of the U.S. Coast Pilot is provided in the Coast Pilot Manual. Here is an excerpt from this document regarding how.
*&#8220;Prominent Features&#8221; should be described:*
&#8220;Prominent Features Describe the best charted landmarks for navigation, such as land formations, lights, tanks, stacks, towers, buildings, etc. Note the color, form, and height of headlands and peaks. Streaks of color in bluffs may be useful in identifying features. If objects such as mountains, hills, cliffs, islets, or rocks are recommended as landmarks, give their measured or estimated heights.&#8221;

In highly developed areas where there are numerous charted structures, the Coast Pilot supplements the charts in two important ways: by identifying the best landmarks and by describing the structures for positive identification. Give the height, color, and painting pattern of prominent structures if available. Describe the general shape of unusual objects...
*Here are a few passages* from Volume 3, Atlantic Coast: Sandy Hook to Cape Henry (1993) that illustrate the type of information presented:
When approaching Maurice River, mariners should use care and not confuse the structure of East Point Light with a private house with a tower about 1.3 miles to the east, both landmarks are similar in appearance..

In 1967, the monument on Liston Point was reported destroyed; and in 1983, the monument on the south side of the entrance to Hope Creek was also reported destroyed.
Remains of the structure from Liston Point may exist up to 100 feet offshore and may be covered during high tide..
A large, cylindrical water tank, about 1.5 miles west of Ocean City Inlet, is prominent and is a good landmark while entering the inlet.

Assateague Light and the lookout tower on the southern tip of Assateague Island are good marks for approaching Chincoteague Inlet.

Abandoned Navesink Lighthouse is in a cleared space on the easternmost spur at a ground elevation of 180 feet; the two 73- foot brownstone towers, the north one octagonal and the south square, are connected by a dwelling.

As a final example, consider this description of the entrance to Bridgeport, CT, harbor, taken from Volume 2, Atlantic Coast: Cape Cod to Sandy Hook (1993):
*Prominent Features.*
The large red and white horizontally banded stack of a power plant on Tongue Point is the most prominent landmark in this area.
Other prominent landmarks include a group of stacks on Steel Point: the towers of a high-voltage line; several church spires; a gas tank with a red-and-white checkered band at the top, on the west side of Pequonnock River; the radio towers at Pleasure Beach; the Bridgeport Harbor Light 13A. The rays of an aerolight about 1.3 miles northwestward of Stratford Point can be seen from offshore.

The U.S. Coast Pilot is invaluable as a supplement to nautical charts for many reasons. These few examples illustrate why this is so for the identification of landmarks. Practical Pointers and Limitations Relevant to Landmarks.
The balance of this chapter provides some practical pointers relevant to the use of charted landmarks in navigation. The first part of this section presents practical ideas on the selection of charts and landmarks for navigation. The second part addresses the important topic of why some charted landmarks may not always be able to be seen (or identified) from the vessel.
*Pointers*
Perhaps the most important suggestion is to select the largest scale chart of the area for navigation. This point is made in several places in this manual, but it is worth restating here. Large-scale charts offer the greatest amount of detail for a small area, and offer the greatest number of charted landmarks hence the largest number of options for position fixing. Any landmark shown on a small(er)-scale chart will also be shown on the large(er)-scale chart of the area, but many landmarks shown on large-scale charts are not depicted on small-scale charts because it is necessary to generalize charted features from large scale to small scale. As well, the latest edition of this chart with corrections given in the NM should be used. Although landmarks are relatively permanent (recall that permanence is one of the criteria for charting a landmark), they do change on occasion. Structures are torn down, and new ones are periodically constructed, so it makes sense to have the latest information at hand.

Another important point to reemphasize is that *all sources of information *should be used to fix the vessels position *not just landmarks. * Maintenance of a dead reckoning plot, use of depth information, ATONs, and other means should all be used. Knowledge of even the vessels approximate position can be helpful in identifying landmarks that might be used for more exact fixes. Moreover, other information (e.g., the depth of water at the vessels location) can be used to increase the confidence in or rule out the tentative identification of a landmark.

*Selecting Landmarks For Use*
In low-lying land areas of low population density (e.g., portions of the Delaware and Virginia coast) landmarks may be few and far between, and the mariner may have little choice as to which landmarks to use. Selection guidelines for landmarks are not relevant in this case.

However, other coastal areas offer many more charted landmarks, and the mariner often has a choice of which to use for navigational purposes. Here are four useful selection criteria for suitable landmarks in cases where choices are available:
Objects should be selected that are detectable and readily identifiable. Many features might be used for position fixing, but objects selected by cartographers as landmarks are likely to be conspicuous (see below). Landmarks depicted with the accurate position symbols are to be preferred over those depicted with the approximate location symbol. Refer also to the U.S. Coast Pilot or commercially produced cruising guides for information on the appearance of conspicuous landmarks.
Objects selected should be in a geometrical configuration suitable to their intended navigational purpose. For example, if a landmark is to be used to establish a danger bearing, it should be appropriately positioned relative to the hazard to be avoided as illustrated in figure 6.2. If more than one landmark is to be used as, for example, to plot a two or three bearing fix the landmarks should be chosen so that the resulting crossing angles of the lines of position are best. 










http://i202.photobucket.com/albums/aa305/FishersofMen/6-2marthasvinyard.jpg

For two objects, a crossing angle of 90&#176; is optimal, and crossing angles less than 20&#176; or 30&#176; should be avoided. (Refer to figure 6.3 for an illustration.) For three objects, 60&#176; crossing angles are best. (Bowditch, Maxim.)










http://i202.photobucket.com/albums/aa305/FishersofMen/6-3marthasvinyard.jpg

Selection criteria for horizontal sextant angles are more complex, and the reader is directed to some of the references (Bowditch, Admiralty Manual of Navigation) for details.

Landmarks closer to the vessel are generally preferable to those further away. This is because errors in bearing (taken with a hand-bearing compass or radar) are nearly independent of the distance, and the position error associated with a given error in azimuth increases directly with distance. If a compass bearing is inaccurate by 5&#176; (a plausible figure, see Dahl), for example, the linear error is approximately 5,300 feet if the landmark is 10 miles distant, but only about 260 feet if the landmark is &#189; mile distant. (For more detail, see Dahl, Moody, or Brogden.)

Taller landmarks should generally be chosen in preference to shorter objects.
Other things being equal, taller objects can be seen at a greater distance than shorter objects due to the curvature of the earth. If He is the height of the observers eye (in feet) and Ho is the height of the object in the same units, then maximum distance, D (in nautical miles), at which the object can be seen (as a result of the curvature of the
earth (Bowditch)) is given by the equation, D = 1.17&#214;He + 1.17&#214;Ho.

Assuming a height of eye of 10 feet, a 20 foot object would be just visible over the horizon at 8.9 nautical miles, a 100 foot high object might be seen at 15.4 nautical miles. (See table 3-1.) Of course, use of this criterion depends upon the height of the object being known and recorded on the chart.

Height information is not provided for all landmarks and certain tall landmarks, such as radio towers, may be difficult to see (Eyges) in hazy conditions because these are generally slender objects.

Limitations
*Even experienced mariners* occasionally have trouble detecting and identifying charted landmarks (Graves, Eyges). So it is worthwhile to enumerate some of the *reasons why landmarks may not be seen.* 
These include:
The landmark may no longer be there.
Although landmarks are selected so as to be relatively permanent, artificial structures are occasionally destroyed by natural disasters or demolition activities.
Ultimately, this fact is reported to NOAA and the chart is updated to delete the landmark, but this process takes time, and even the latest corrected chart of the area may show phantom landmarks. (In cases where changes in landmarks are viewed as critical to navigation safety, landmark changes will
be reported in the NM. Such listing is relatively rare, however.)

Along with demolition, new construction may create problems regarding landmarks, because new structures (see below) may be confused with charted landmarks.

The landmark may not be visible as a result of horizon geometry (see above) or poor atmospheric visibility. Knowledge of the vessels approximate position and the prevailing visibility, as well as the landmarks height, can be helpful in determining whether or not a landmark is likely to be visible. Statistical visibility data for various locations can be found in the U.S. Coast Pilot.

These data can be useful for trip planning purposes. Table 6-5, for example, shows the average annual number of days with visibility less than or equal to &#188; mile for selected locations in the United States, ranked in descending order. In Nantucket, MA, for example, poor visibility occurs an average of 96 days out of each year approximately
one day out of four. 










St. Croix, San Juan, Hilo, and Honolulu enjoy nearly total freedom from episodes of &#188;-mile visibility. Data in the U.S. Coast Pilot also show the distribution of reduced visibility episodes by month. Figure 6-4 shows this information plotted for Nantucket,
MA. As can be seen, the worst months at this location are June, July, and August.

&#8226;	The landmark may be masked by other structures, terrain features, or vegetation.
At the time that an object is selected as a suitable object for charting as a landmark, a determination is made that it is conspicuous. However, in the years since originally charted, events may have occurred which limit the visibility of the object. For landmarks in built-up areas, such as cities, new construction may have taken place which masks the landmarks from some or all approach angles. In rural areas, trees or other vegetation may obscure the structure at least from some approach angles. (In this case, landmarks may be visible in certain seasons e.g., winter and not in others.)

Remember also that landmarks are selected to be visible from the sea, but not necessarily from all possible approach angles.[/B]
(Inspection of terrain features and elevations can sometimes help to identify terrain masking.)

The detectability of an object by visual means is a complex function of atmospheric visibility, background contrast, and lighting. Landmarks may be camouflaged as a result of limited contrast with background areas or because of lighting conditions at the time of observation. (See Eyges for several illustrations.)
The mariner may be disoriented and looking in the wrong place on the chart. It is commonplace in navigation that *it is much easier to determine your position if you already know where you are.* On reflection this statement is not as trivial as it seems. A practical tip in identifying landmarks is to plot the vessels dead reckoning position (or estimated position if one LOP is available). Then, based on this position on the chart, plot the bearings to each of the charted landmarks. Next (binoculars with a built-in compass are best) look along these plotted bearings for the landmark. If the vessels assumed position is nearly correct (and the visibility is sufficiently great and the landmarks are above the horizon), the landmarks should be visible on bearings within a few degrees of those plotted. This technique will not work if the vessels position is grossly in error, but can be very helpful otherwise. (For additional details, see Bright (1990).

The mariner may actually see the landmark, but not be able to establish positive identification. This may occur because of confusion among several possible objects (see below), but may also occur because of ambiguity over the identity or appearance of the object. For example, the term tower may be used to describe many related but different objects. Towers (not otherwise distinguished) could include structures as diverse as aircraft control towers, tall buildings (the John Hancock building in Boston, MA), and abandoned lighthouses. (In some cases a secondary label will be included to narrow down the possibilities.) The mariner should study the definitions of each of the landmark terms to maximize the possibility of correct identification.

Finally, it sometimes occurs that several objects can be seen from the vessel, but it is not immediately apparent which is the charted landmark. In other words, the landmark may be detectable but not identifiable. For example, only some of the many water tanks in the Philadelphia Camden area are charted as landmarks. Depending upon the vessels position, it is not always possible to identify which are the charted landmarks. In such cases the mariner is well advised to search for other identifiable landmarks that could be used to fix the vessels position. Even an approximate fix may be sufficient to enable correct identification of the original landmark. This technique is known as shooting up measuring the bearing of each of several candidate landmarks and choosing the one that provides a line of position that passes closest to the vessels position. (For additional details, see Mellor.)

*The competent mariner* regards each voyage as a learning experience. In cases where a landmark is missed, or misidentified, the mariner should make every attempt to determine the reason(s) why this occurred. If the reason is that the landmark was improperly charted, the mariner should bring this matter to the attention of NOAA and USCG so that appropriate corrections can be made. Every error offers the opportunity to learn a valuable lesson.

*Concluding Comments*
Landmarks are very useful for coastal navigation and serve to complement the system of
. . . . . . . . . . . . . . . . . . . . . . . . .
ATONs. Careful study of the chart conventions presented in this chapter and the definitions presented here and in the Glossary will pay dividends in improved navigational skills. Student navigators and that includes all of us would do well to take the opportunity of comparing the chart presentation of familiar areas with what is observable from aboard the vessel. Finally, prudent mariners do not rely on any one aid or technique for navigation. The navigator should use all available data (e.g., dead reckoning positions, AT0Ns, depth information, electronic position data, and visual or radar observation of landmarks) to navigate safely.

&#8220;_Exhortation to Apprentices of the Art of Navigation
When so ever any Shipmaster or Mariner shall
set forth from land out of any river or haven, diligently
to mark what buildings, castles, towers,
churches, hills, downes, windmills and other marks
are standing upon the land.all of which, or many
of them, let him portray with his pen, how they bear
and how far distant.&#8221;_
A.	Ashley, 1583, quoted in Naish

This concludes Chapter 6 we will go to ch 7 tomorrow, that will take care of the charting for a while. I am sure some new terms and such paid off. Might want to invest in a *GOOD* chartplotter now, you'll love it! And then on to...uh huh, Navigation. If any one wants chapters 1 and 3 that I couldn't post let me know and I'll send the files to you. 

*References*

Bright, C., Danger Bearings and Turning
Marks,. Ocean Navigator, Issue No. 45,
March/April 1992, pp. 69, et seq.

Bright, C., .Identifying Visual Targets,.
Ocean Navigator, Issue No. 33, June 1990,
pp. 63, et seq.

Brogden, B., .Accurate Bearings: How to Get
Better Visual Fixes for Coastal Navigation, Ocean Navigator, Issue No. 51, January/
February 1993, pp. 78, et seq.

Carr, M., .Update Charts For Coastal Piloting, Ocean Navigator, Issue No. 50, November/December 1992, p. 33.

Dahl, N., The Yacht Navigator.s Handbook, Hearst Books, New York, NY, 1983.

Defense Mapping Agency Hydrographic/Topographic Center American Practical Navigator, An Epitome of Navigation (Bowditch), Publication No. 9, DMA Stock
No. NV PUB 9 V1, Bethesda, MD, 1995.

Ellam, P., Yacht Cruising, W.W. Norton & Company, New York, NY, 1983.

Eyges, L., The Practical Pilot, Coastal Navigation by Eye, Intuition, and Common
Sense, International Marine Publishing, Camden, ME, 1989.

Graves, F., Piloting, International Marine Company, Camden, ME, 1981.

Human Technology, Inc. Desk Reference Guide: Specifications Unit, Chart and Map,
Feature: Buildings. Report developed for National Ocean Service, Charting and Geodetic Services, Marine Chart Branch, Under Contract OPM-85-77, McLean, VA, October 1985.

Human Technology, Inc. Desk Reference Guide: Specifications Unit, Chart and Map,
Feature: Landmark. Report developed for National Ocean Service, Charting and Geodetic Services, Marine Chart Branch, Under Contract OPM-85-77, McLean, VA, October 1985.

Kals, W. S., Practical Navigation, Doubleday & Company, Gordon City, NY, 1972.

Maloney, E. S., Chapman Piloting, 60th Edition, Hearst Marine Books, New York, NY, 1991.

Markell, J., Coastal Navigation for the Small Boat Sailor, Tab Books, Blue Ridge Summit, PA, 1984.

Maxim, L. D., Advanced Coastal Navigation, Second Edition, United States Coast Guard
Auxiliary, Coast Guard Auxiliary National Board, Inc., Washington, DC, 1990.

McClench, D. and D. B. Millar, Mixter.s Primer of Navigation, Sixth Edition, Van
Nostrand Reinhold, New York, NY, 1979.

Mellor, J., The Art of Pilotage, Sheridan House, Dobbs Ferry, NY, 1990.

Ministry of Defence, Directorate of Naval Warfare. BR 45(1) Admiralty Manual of Navigation, Vol. 1, Her Majesty.s Stationary Office, London, UK, 1987.

Moody, A. B., Navigation Afloat, Van Nostrand
Reinhold, New York, NY, 1980.

Naish, J., Seamarks, Their History and Development,
Stanford Maritime, London, UK, 1985.

Toghill, J., The Yachtsman.s Navigation Manual, John DeGraff, Clinton Corners,
NY, 1975.

U.S. Department of Commerce, Coast and Geodetic Survey. Nautical Chart Manual, Volume One: Policies and Procedures, Seventh Edition, Washington, DC, 1992.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service, and Department of Defense, Defense Mapping Agency 

Hydrographic/ Topographic Center. Chart No. 1
United States of America Nautical Chart
Symbols Abbreviations and Terms, Ninth Edition, Washington, DC, January 1990.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service. Coast Pilot Manual,
5th Edition, Rockville, MD, 1994.


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## Fishers of Men

*Chapter 7*

Areas, Limits, Tracks, and Routes
Introduction and Overview

This chapter addresses areas, limits, tracks, and route information provided on the nautical chart. Areas and limits (referred to in Section N of Chart No. 1) refer to a collection of charting practices (symbols, labels, and notes) used to depict certain areas and limits of importance to the mariner. All these areas have statutory or regulatory significance (e.g., the three mile limit, a COLREGS demarcation line, or a designated anchorage), but most also pertain to navigation safety (e.g., a danger area or safety zone)Track/ route information (referred to in Section M of Chart No. 1) depicted on the nautical chart contains guidance (or regulations) relevant to the selection of routes and/or procedures to be followed for safe navigation. This chapter provides background, summarizes the utility of area/limit/track/route features, describes the charting conventions (e.g., symbols, labels, and notes), identifies other relevant sources of information (e.g., the U.S. Coast Pilot), and presents practical pointers on how this information can be used by the prudent mariner. No attempt has been made to enumerate all areas/limits/tracks/routes depicted on the nautical chart nor to provide an exhaustive discussion of the many legal and policy issues relevant to each. 

Instead, the chapter focuses upon those features likely to be of greatest potential relevance to the recreational and commercial vessel operator. The omission of any charted feature in this chapter does not relieve the mariner of the responsibility of complying with any applicable regulations.

As noted above, many of the charted features discussed in this chapter have statutory or regulatory significance. This is a chart users manual, which provides general information on the charting conventions and the types of regulations that may be applicable to designated areas. It does not purport to give legal advice pertaining to any rules or regulations summarized herein.

*Mariners are advised to read carefully the general and specific regulations applicable to these areas.* If in doubt, the mariner should seek advice from competent authority or legal counsel.

(You have these areas around the Islands, power plants and such.)

Many specialized terms used in this chapter are defined in the Glossary in appendix A. Names enclosed in parentheses (e.g., Bowditch) denote references listed at the end of this chapter that contain additional relevant detail or useful general information. Letter and number designators in the subsection titles and/or text (e.g., N 1.2) refer to sections of Chart No. 1. It *is recommended *that Chart No. 1 be kept at hand when reading this chapter.

*Utility of This Information*
In most other chapters of this manual, a separate section is included on the uses of the information presented. Because of the diversity of the features treated in this chapter, this utility is best discussed on an item-by item basis. In broad terms, however, this information is charted to alert the mariner to certain dangers to navigation (e.g., danger areas, safety zones) and/or to applicable legal requirements when entering or using these waters.

*Federally Regulated Areas*
(N 1.2, N 2.2, N 31)
Certain waters are subject to general and permanent federal regulations, published in a multi-volume series termed the CFR. The most pertinent portions of the CFR for chart users are Title 33, Navigation and Navigable Waters, and Title 40, Protection of the Environment. Federally regulated areas include danger areas, seaplane operating areas, seaplane restricted areas, restricted areas, safety zones, defense areas, security zones, and regulated navigation areas (not otherwise classified). Although there are some differences among these areas or zones, it is convenient to discuss these as a group under the broad rubric of federally regulated areas.

*Regulated Navigation Areas*
A regulated navigation area is a water area within a defined boundary for which specific regulations (in addition to the Navigation Rules) have been established. Regulated navigation areas (not otherwise classified) have been established in various areas of the waters of the United States. Regulated areas are established to prevent damage or marine casualties, to protect waterfront facilities, and to safeguard ports, harbors, and the environment.

The establishment of these areas is under the jurisdiction of the USCG or the USACE. The phrase regulated navigation area is sometimes used in a more general sense to include all waters for which usage or entry restrictions have been established. In this more general sense, a regulated navigation area is an inclusive term encompassing many of the areas described below.

*Danger Area*
According to official charting definitions in the Desk Reference Guide, 
a danger area ....is a specified area above, below, or within which there may exist potential danger from military, civil, natural or manmade sources. A danger area may be categorized as a prohibited area, exercise area, firing area, or missile test area.

*An exercise area* (also called a military practice area) is an area shown on charts within which troop, ship, or aircraft exercises are carried out. A missile test area is an area restricted so that missile range and reliability tests may be conducted by the military.
When in use, missile debris may be deposited at frequent and irregular intervals. A firing area is a military target area for bombing and/ or gunnery practice. A prohibited area is a danger area shown on nautical charts within which navigation and/or anchoring is prohibited except as authorized by appropriate authority.

Danger areas are typically related to potentially hazardous military activity.
*Seaplane Restricted Areas*/Seaplane Operating Areas (N 13, N 14)
As the name implies, seaplane operating areas and seaplane restricted areas refer to designated areas containing seaplane bases. The Inland Navigation Rules normally applicable to seaplane operations are changed in designated seaplane restricted areas. *Under Rule 18 *(Responsibilities Between Vessels), paragraph (d), of the Inland Navigation Rules, which applies to the conduct of vessels in sight of one another, ....a seaplane on the water shall, in general, keep well clear of all vessels and avoid impeding their navigation. (A seaplane is last in the ROW pecking order, remember?) In circumstances, however, where risk of collision exists, she shall comply with the Rules of this Part.
Seaplanes are in last place in the normal right-of-way hierarchy. However, seaplane restricted areas have been established where the conventional right-of-way hierarchy among vessel types described in Rule 18 is altered and/or vessels are prohibited from entering.

For example, in the seaplane restricted area described in 33 CFR § 162.15 in Manhasset Bay, NY, the applicable rules (found in 33 CFR or in the U.S. Coast Pilot) read: (1) vessels shall not anchor or moor within the restricted area and (2) all vessels traversing the area shall pass directly through without unnecessary delay, and shall give seaplanes the right-of-way at all times. As a practical matter, seaplanes on the water are not highly maneuverable (they cannot operate in reverse, for example, and taxiing or sailing a single-engine seaplane is not an easy skill to acquire), a fact recognized in the navigation regulations applicable to seaplane restricted areas.

As the name implies, seaplane operating areas are areas frequented by seaplanes. The seaplane operating area designation is typically less restrictive than a seaplane restricted area warning mariners of the anticipated presence of seaplanes in the area but not necessarily prohibiting entry or anchoring.
Although the number of seaplane operating and restricted areas throughout the country is not large, it is important for the mariner to be aware of the special rules which govern vessel operations in these areas.

*Restricted Area* (N 20)
According to official charting definitions in the Desk Reference Guide, a restricted area ....is a specified area designated by an appropriate authority and shown on charts, above, below, or within which navigation is controlled in accordance with certain specified conditions. These control measures are employed to prevent or minimize danger or interference between parties using the area.
Restricted areas are typically associated with military or other federal (e.g., Federal Correctional Institutions) installations. 

Figure 7.1 provides an excerpt from NOS Chart No. 12283 (Annapolis Harbor) which shows, inter alia, a restricted area in the vicinity of the U.S. Naval Academy (Anchorage areas shown in this illustration are discussed in a later section of this chapter).

*Safety Zones/Defense Areas/Security Zones*
The Desk Reference Guide defines safety zones, defense areas, and security zones as follows:
A safety zone is a water area and/or shore area to which, for safety or environmental purposes, access is limited to authorized persons, vehicles, or vessels.

It may be stationary and described by fixed limits, or it may be described as a zone around a vessel in motion. 

A defense area is a sea area, usually including the approaches to and the waters of important ports, harbors, bays, or sounds, for the control and protection of shipping, for the safeguarding of defense installations bordering on waters of the areas, and for provision of other security measures required within the specified areas. It does not extend seaward beyond the United States territorial waters. 

A security zone is all areas of water which are so designated by the Captain of the Port for such time as he deems necessary to prevent damage or injury to any vessel or waterfront facility, to safeguard ports, harbors, territories, or waters of the United States or to secure the observance of the rights and obligations of the United States.

Safety zones are defined to minimize safety or environmental hazards associated with non-military activities. For example, safety zones are typically established around facilities (berths, moorings, gas or oil transfer areas) where hazardous materials, such as liquified natural gas (LNG) or liquified petroleum gas products, are handled or shipped. 

Safety zones are also established around certain Outer Continental Shelf (OCS) oil and gas operations (see 33 CFR Part 147). Safety zones may be either permanent or temporary but, for obvious reasons, only permanent safety zones are depicted on NOAA charts.










The purpose of a security zone is to safeguard vessels, harbors, parks, and waterfront facilities from destruction, loss, or injury from sabotage, or other subversive acts, accidents, or other causes of a similar nature. Security zones are generally established around military facilities, such as ammunition depots (e.g., the Naval Ammunition Depot in the vicinity of Sandy Hook Bay, NJ), submarine bases, and submarine construction yards (e.g., the waters of the Thames River near the Electric Boat Division). As with safety zones, security zones may be temporary or permanent .but only permanent security zones are depicted on NOAA charts.

*Relevance to the Mariner*
Knowledge of the location, dimensions, and rules and regulations applicable to these areas is important to the mariner for obvious reasons of safety. Being hit by a stray round, torpedoed, or involved in a collision with an LNG tanker is certainly no ones idea of an interesting diversion during an otherwise routine voyage. Moreover, *the penalties for unauthorized operations in federally regulated areas can be substantial, including seizure and forfeiture of the vessel, fines, and prison sentences.* 

*Charting Practices*
This section provides information on charting practices and related information for federally regulated areas. Charting conventions consist of a symbol and associated labels and notes. With few exceptions, NOAA charts show only the type of regulated area, its location, and a CFR section number. 

Specific regulations applicable to the area are provided elsewhere (e.g., 33 CFR or the U.S. Coast Pilot).
Symbol (e.g., N 1.2, N 2.2, N 31) *Danger area limits are charted with a dashed magenta line.*

To emphasize the possibility of danger in these areas, a magenta screened band may be added to highlight the dashed limit line.

Seaplane landing areas and seaplane restricted areas (N 13, N 14) are charted with* a solid magenta line.*

Restricted area limit lines are charted with a *T-dashed magenta line.*

Safety zone, defense area, and security zone limit lines are charted with a *dashed magenta line.*

A regulated area, *not otherwise classified*, is depicted by magenta dashed or T-dashed limit lines. Figure 7.2 shows a regulated area (not otherwise classified) in the vicinity of the Chesapeake Bridge Tunnel as shown on NOS Chart No. 12221 (Chesapeake Bay Entrance). These areas are charted with their exact geographic limits as defined in 33 CFR.

*Labels and notes* are printed in *magenta italic type.* Regulated areas are identified on the chart only by the primary title of the area (e.g., labeled DANGER AREA, PROHIBITED AREA, SAFETY ZONE, DEFENSE AREA, SECURITY ZONE, REGULATED AREA, etc.), an alphanumeric designator for the area (if one has been assigned), the CFR section number, and a reference to standard note A (shown below).

(1Where a defense area, safety zone, or security zone line and the three-mile-limit line coincide, the three-mile line takes precedence. The label is charted along the line.)










For example, referring to the excerpt from NOS Chart No. 13218 (Martha.s Vineyard to Block Island) presented in figure 5-3 (refer to Chapter 5), the prohibited area in the vicinity of Nomans Land is labeled as follows:
PROHIBITED AREA:

*TO BE CONTINUED*


----------



## Fishers of Men

*ch 7 CONTINUED from previous post*

The number 334.70 refers to the CFR section number which discusses this prohibited area. Note A, typically found in an uncluttered land area on the chart, contains the standard text, (On NOAA charts, Note A is reserved for the note listing the publications that contain navigation regulations relevant to that chart; other charted notes begin with Note B or some other reference label even if there is no Note A on that chart.)

*NOTE A*
Navigation regulations are published in Chapter 2, U.S. Coast Pilot ______.
Additions or revisions to Chapter 2 are published in the Notice to Mariners. Information concerning the regulations may be obtained at the Office of the Commander, ____ Coast Guard District in ______, __, or at the Office of the District Engineer, Corps of Engineers in _____, __.

Blanks in the above note are filled in with the appropriate information.
The regulations applicable to the specific regulated area are always found in Chapter 2 of the indicated volume of the U. S. Coast Pilot. (Except when specifically requested by appropriate authority, these regulations are not shown on the nautical chart, however.)

*Examples*
Here is an excerpt from the text describing the prohibited area described in Section 334.70 of 33 CFR as contained in U.S. Coast Pilot Volume 2 (1993) Atlantic Coast: Cape Cod to Sandy Hook:

334.70 Buzzards Bay, and adjacent waters, Mass.; danger zones for naval operations. (a) Atlantic Ocean in vicinity of Nomans Land-(1) The area. The waters surrounding Nomans Land within an area bounded as follows:
[geographic coordinates of area omitted in this citation]
(2) The regulations. No vessel shall at any time enter or remain within a rectangular portion of the area bounded on the north by a latitude 41&#176; 16.00&#8221;, on the west by longitude 70&#176; 47&#8217; 30&#8221;, or within the remainder of the area between 1 November and 30 April, inclusive, except by permission of the enforcing agency.
(3) The regulations in this paragraph shall be enforced by the Commandant, First Naval District, and such agencies as he may designate.. The textual description in the U.S. Coast Pilot provides information on the geographic limits of the area, applicable regulations, and the enforcing agency. The text applicable to this area in the U.S. Coast Pilot is relatively brief. Entries for other areas are often more detailed and may run to several pages. However, the above excerpt illustrates the general format.
Many of the areas discussed in this section have general as well as specific regulations that apply. For example, the general regulations pertaining to a safety zone are found in 33 CFR &#167;165.23, shown below:

Unless otherwise provided in this part:
.a. No person may enter a safety zone unless authorized by the COTP [Captain of the Port] or the District Commander [USCG];
.b. No person may bring or cause to be brought into a safety zone any vehicle, vessel, or object unless authorized by the COTP or the District Commander;
.c. No person may remain in a safety zone or allow any vehicle, vessel, or object to remain in a safety zone unless authorized by the COTP or the District Commander; and .d. Each person in a safety zone who has notice of a lawful order or direction shall obey the order or direction of the COTP or District Commander issued to carry out the purposes of this subpart.
Specific regulations may amend or extend the above general regulations, and are found in the CFR (or U.S. Coast Pilot) in a separate section. Mariners need to consult both specific and general regulations.

As an example of specific rules pertaining to a safety zone, consider this entry from the U.S. Coast Pilot Volume 3 (1993) Atlantic coast: Sandy Hook to Cape Henry describing a safety zone located in the Chesapeake Bay:
&#167;165.506 Chesapeake Bay, Hampton Roads, Elizabeth River Southern Branch Liquified Petroleum Gas Carrier Safety Zone.

.(a) The waters within 250 feet from the port and starboard sides and 300 yards from the bow and stern of a vessel that is carrying liquified petroleum gas in bulk as cargo are a safety zone while the vessel transits the Chesapeake Bay and Elizabeth River between Thimble Shoal Lighted Buoy #3 and the Atlantic Energy Terminal on the Southern Branch of the Elizabeth River.
.(b)Except as provided in paragraph (c) of this section, the general safety zone regulations in &#167;165.23 [also contained in this volume of the U.S. Coast Pilot] apply to the safety zone. Permission to enter the safety zone may be obtained from the Captain of the Port or a designated representative, including the duty officer at the Coast Guard Marine Safety Office, Hampton Roads, or the Coast Guard Patrol Commander. .&#169; A vessel that is moored at a marine, wharf, or pier or is at anchor may remain in the safety zone while a vessel carrying liquified petroleum gas passes its location if the vessel remains at its moorage or anchorage during the period when its location is within the safety zone.
.(d) A vessel that has had liquified petroleum gas in a tank is carrying the liquified petroleum gas in bulk as cargo for the purposes of paragraph (a) of this section, unless the tank has been gas free since the liquified petroleum gas was last carried as cargo.
.(e) The Captain of the Port, Hampton Roads will issue a Marine Safety Information Broadcast Notice to Mariners to notify the maritime community of the scheduled arrival and departure of a liquified petroleum gas carrier..

*Illustrative Regulations*
Table 7-1 provides an illustrative list of regulations which may be applicable to various federally regulated areas. In the example of the prohibited area near Nomans Land, entry is prohibited to all but authorized vessels only for specific months of the year. Depending upon the area, the duration of the prohibition may be only for certain times of day, certain days of the year, only when actual exercises or vessel transits are taking place (when the area is said to be hot), or at all times. Alternatively, entry may be permitted, but a requirement for expeditious passage, or a requirement to vacate the area promptly upon notification may be imposed.










In the Nomans Land example, entry is forbidden, in other areas entry may be permitted, but limits may be placed upon specific activities of vessels while in the area (e.g., no loitering, no stopping, no anchoring, no trawling, no fishing, no towing, no docking, no entry onto land, etc.). Minimum separation distances (e.g., from naval vessels or carriers of hazardous cargo) may also be mandated in these areas. In some regulated areas (e.g., that shown in figure 7.1) yet other requirements may be imposed. These include requirements that vessels drawing less than a specified draft not enter certain channels (unless the vessel is crossing the channel), a prohibition on the entry of vessels above a designated size with impaired maneuverability, technical requirements on tows, requirements for operating radar in vessels above a designated size during periods of reduced visibility, and requirements for pilots with local knowledge aboard vessels greater than a certain size (e.g., 100 gross tons).

Finally, the height of vessels permitted to operate in the regulated area may be limited. The height constraint is applicable in certain restricted areas associated with some coastal airports and is intended to lower the risk of collision with low-flying aircraft and reduce the possibility of interference with navigational equipment. For example, in the restricted area (33 CFR &#167; 162.20) contiguous to La Guardia Airport, Flushing, NY, no vessels with a height greater than 35 feet may enter whenever the prevailing visibility is less than 1 mile.

In cases where entry is prohibited only during times when the area is being used, the U.S. Coast Pilot will indicate how notification
is given, either in advance (e.g., in the Notice to Mariners), or shortly before the activity commences (e.g., by display of warning flags, the presence of patrol vessels, low aircraft passes, etc.).

*Summary*
It is a surprisingly common misconception that federally regulated areas cannot be entered at any time. In fact, many of these areas are not denied (or at least not denied at all times) and these areas can be safely used if the prescribed regulations are followed. The mariner should consult 33 CFR or the U.S. Coast Pilot to determine the restrictions to entry and other pertinent regulations. However, unless the specific regulations are consulted (e.g., as found in 33 CFR or the U.S. Coast Pilot), the prudent mariner has no alternative but to remain well clear of federally regulated areas. *Do not radio the USCG with a request for realtime information on navigation regulations applicable to, or the status of, these areas. Not all USCG units have this information readily available. The USCG will respond to written or telephone inquiries, but does not necessarily offer real time response.*

*TO BE CONTINUED*


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## Fishers of Men

*ch 7 CONTINUED from previous post*

*Civil Reservations*
Civil reservations include a variety of nonmilitary areas such as state and national parks, reservations, wildlife preserves, wildlife refuges, marine sanctuaries, Indian reservations, and similar specially designated areas. Generally, reservation areas are charted only if requested by the cognizant agency. With certain exceptions, these areas provide interesting background rather than information relevant to navigation. (These areas are charted in blue, as noted below, so as to reserve the use of magenta and black for charting features that are of greater navigational importance to the mariner.) Mariners are advised, however, to consult the CFR and other sources for any regulations applicable to these areas.

As an illustration of one type of civil reservation, figure 7.3 provides an excerpt from NOS Chart No. 12274 (Head of Chesapeake Bay) which shows, inter alia, a portion of the Susquehanna National Wildlife Refuge. Applicable rules for operating in wildlife refuges and other regulations are given in 50 CFR Parts 25, 27, and 32. These regulations include the Navigation Rules, state regulations, and several additional regulations. The additional regulations include a prohibition on leaving boats (outside of designated mooring or beaching areas) unattended for a period greater than 72 hours without the permission of the refuge manager, a ban on use of government-owned docks for loading and unloading of boats (except in emergency), special rules for water skiing, regulations applicable to marine sanitation devices, and a variety of special rules which limit or prohibit hunting and fishing activities. Some wildlife refuge regulations are site specific.

*Charting Practices*
This section provides information on charting practices and related information for civil reservations. Charting conventions consist of a symbol and associated labels and notes. Symbol (N 22)

*Civil reservations are charted with a blue long-short dashed line.* A more prominent blue screened band may be added to the inside edge of the entire outline if needed to avoid confusion. For example, where different reservations overlap, the screened band may be used to denote the reservation(s) of greater importance.

*Labels and Notes*
Labels and notes are printed in *blue type.*
If the boundary is chiefly *in the water, italic type is used; if chiefly on land, conventional type is used. *The label type should be consistent on overlapping charts. 

The label consists of the name of the reservation (e.g., SUSQUEHANNA NATIONAL WILDLIFE REFUGE) in italic capitals and a description (e.g., protected area) in lower case italic type if appropriate. The label see note A is included only when the cited federal regulations are given in the U.S. Coast Pilot. Where reference to note A is not appropriate, the label may refer to another note or the CFR.










*Relevance to the Mariner*
Generally speaking, civil reservations are of only limited interest to the mariner. This is reflected in the choice of color for their depiction on the nautical chart. Nonetheless, these features are charted to alert the mariner to possible regulations which may affect entry and/or limit activities.

The U.S. Coast Pilot provides relevant information for some, but not all, of these areas. Mariners interested in using these waters should consult appreciable sections of the CFR. (Refer to the CFR Index to find the appropriate section(s)

TO BE CONTINUED


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## Fishers of Men

*Ch 7 continued *

Federally Regulated Anchorage Areas/
Grounds Federally regulated anchorage areas and grounds are important features depicted on NOAA charts. It is convenient to group federally regulated anchorage areas into three broad classes: (i) anchorage grounds, (ii) special anchorage areas, and (iii) fairway anchorages. These are discussed below.

*Anchorage Grounds*
The USCG is authorized (under Section 7 of the River and Harbor Act of March 4, 1915) to define and establish anchorage grounds for vessels whenever it is apparent that these are required by the maritime or commercial interests of the United States for safe navigation. Further, the USCG is authorized to establish rules and regulations applicable to these designated anchorage grounds.

Several types of anchorage grounds have been established by the USCG, including (but not limited to) general anchorages, commercial anchorages, deep-draft anchorages, smallcraft anchorages, special anchorages, quarantine anchorages, temporary anchorages, dead-ship anchorages, explosive anchorages, forbidden anchorages, non anchorage grounds, and restricted anchorages. For the most part, terms used to describe these anchorage grounds (e.g., commercial anchorages) are not defined explicitly in the CFR. Rather, the definitions are implicit and made clear by the specific rules and regulations pertaining to each designated anchorage. For example, a dead-ship anchorage is designed to lay up ships for extended periods, a quarantine anchorage is designed to accommodate ships requesting quarantine inspection, a deep-draft anchorage is designed principally for deep-draft ships. Forbidden, prohibited, non anchorages, and restricted anchorages all have regulations which limit or prohibit anchoring by various types of vessels, or require special authorization for anchoring. A description of these designated anchorage grounds and the regulations applicable to each can be found in the CFR and the U.S. Coast Pilot Anchoring berths are usually circular areas located within certain established anchorage grounds as a convenience in assigning anchoring locations for both military and commercial vessels.

Information concerning anchoring berths may be published in the CFR (and U.S. Coast Pilot), but may also be developed by local users and available from the originator.

*Special Anchorage Areas*
An Act of Congress of April 22, 1940, provided for the designation of special anchorage areas wherein vessels not more than 65 feet in length, when at anchor, are not required to carry or exhibit anchor lights. These special anchorage areas (33 CFR &#167; 109.10) are well removed from fairways3 and located where general navigation will not endanger or be endangered by unlighted vessels. Special anchorage areas are established for the convenience of small (typically recreational) vessels.

*Fairway Anchorages*
According to 33 CFR &#167; 166.105, .shipping safety fairway means a lane or corridor in which no artificial island or fixed structure, whether temporary or permanent, will be permitted. These fairways are established to control the erection or structures so as to provide safe approaches through: (i) oil fields in the Gulf of Mexico to entrances to the major ports along the gulf coast (33 CFR &#167; 166.200), (ii) the coast of California (33 CFR &#167; 166.300), (iii) the coast of Alaska (33 CFR &#167; 166.400), and (iv) the Atlantic coast (33 CFR &#167; 166.500). A fairway anchorage .means an anchorage area contiguous to and associated with a fairway, in which fixed structures may be permitted within certain spacing limitations..

*Relevance to the Mariner*
Knowledge of the presence and location of designated anchorage grounds/areas are relevant to the mariner for two principal reasons:
First, and perhaps most important, charting these areas serves to inform the mariner that various rules and regulations may apply to each designated area. (Sources for these regulations are identified below.) 

3 Shipping safety fairways are also charted.

Table 7.2 provides a sampling of some of the types of rules that may apply to any of these areas. In brief, there may be outright prohibitions on anchoring, limits on the type, number, or duration of stay of vessels in an anchorage, limits or prohibitions on certain activities within an anchorage (e.g., no lightering or fishing), requirements to plot position and/or maintain a communications guard, notification requirements, and technological requirements (e.g., use of multiple anchors, requirements to have tugs present, etc.). Not all of the restrictions identified in table 7.2 are applicable to each anchorage, but each of the rules are applicable to some of these areas. Failure to follow the rules could entail significant operating risks, and may involve legal penalties as well.

Second, designated anchorage grounds should alert the mariner to areas where anchored vessels may be encountered. Therefore, these areas are generally to be avoided, except by vessels intending to use the anchorage.
(By design, these designated anchorage areas are not located in main channels, so avoidance is not particularly burdensome.) In special anchorage areas, vessels less than 65 feet in length are not required to display anchor lights, which means that vessels transiting these areas at night are well advised to exert special vigilance to avoid possible collisions with unlighted vessels at anchor.

Table 7-2
Illustrative Regulations That May Pertain to Designated Anchorages

Regulations are anchorage-specific; not all anchorages will have each of the illustrative regulations given. The current U.S. Coast Pilot should be consulted to find the specific regulations applicable to each designated anchorage.

*Controlling authority and permit requirements*

Limits to type of vessel (e.g., recreational, commercial, naval, (submarines, aircraft carriers, destroyers,etc.) explosives, vessels under the custody of the United States, dead ships)

Maximum or minimum length and/or draft of vessel

Priority among vessels (e.g., priorities accorded naval vessels, commercial vessels, or vessels awaiting quarantine inspection, etc.)

*Freedom from requirements to display anchor lights *(for vessels less than 65 feet long in designated special anchorages)

Conditions of use (e.g., during emergencies only)

Limits on navigation, transit speeds, or on certain activities (e.g., fishing, lightering, etc.)

*Cargo restrictions*

Limits on the number of vessels that can use an anchorage

Prohibition of certain types of vessels (e.g., fishing vessels, vessels being dismantled)

Minimum distances among anchored ships

Limits on placement of anchors and requirements for multiple anchors

Permission or limits on placement of moorings, floats, or buoys

Notification Requirements (e.g., when anchoring, and prior to engaging in certain operations, or getting underway).

Maximum time to get underway (e.g., warm start capability, prohibition on dead ships, or requirement that dead ships have tugs alongside)

Requirements to maintain a communications guard and/or to plot position

Requirements for wooden ships to have radar reflectors aboard

Prohibitions on use by unseaworthy ships

Time limits (e.g., 24-hours, 48-hours, 30-days)

*Charting Practices*
This section provides information on charting practices and related information for federally regulated anchorages. Charting conventions consist of a symbol and associated labels and notes. With few exceptions, *NOAA charts show only* the type of anchorage, its location, and a CFR section number.

Specific regulations applicable to the area are provided elsewhere (e.g., 33 CFR or the U.S. Coast Pilot). Symbol (e.g., N 11.1 - N 20)
Federally regulated anchorages are depicted by magenta limit lines which show the exact geographic boundaries of the anchorage. The line thickness and whether or not it is solid or dashed varies with the type of anchorage, as shown in table 7.3. A magenta screen may be added for emphasis.
Anchoring berths (N 11.1, N 11.2) are charted as solid or dashed circles of specified diameter with a small center-position circle (solid or dashed to correspond the berth limit symbol) and a designator. *Circles and designators may be shown in magenta or a screened green. *(If another color is required for clarity, berths may be printed in black.) Figure 7.4 provides an excerpt from NOS Chart No. 12221 (Chesapeake Bay Entrance) showing two naval anchorages, a commercial explosive anchorage, and an anchorage berth.

*Label*
The charted anchorage area is identified with a *magenta label in italic type *that includes the primary title of the area as given in the CFR, an alphanumeric designator (if assigned), the CFR section number, and a reference to the standard note A discussed earlier in this chapter. Examples include:

SPECIAL ANCHORAGE
110.1, 110.126a (see note A)

COMMERCIAL EXPLOSIVE ANCHORAGE
110.168 (see note A)

FAIRWAY ANCHORAGE
166.200 (see note A)

Bottom characteristics (see Chapter 4) are depicted in designated anchorage areas and other areas where vessels are expected to anchor.

*Notes*
Anchorage areas also refer to the standard note A. This note directs the mariner to the appropriate section of the U.S. Coast Pilot. Applicable regulations can be found in either the CFR or the U.S. Coast Pilot. Regulations may consist of both specific regulations applicable to the designated anchorage area and general regulations (i.e., common regulations applicable to several anchorages in the same area). For example, there are numerous general regulations applicable to Anchorage E shown in figure 7.4. But there are additional specific regulations given in the CFR and the U.S. Coast Pilot. The specific regulations (33 CFR &#167; 110.168) include:

.(4) Anchorage E. (i) A vessel may not anchor in Anchorage E without a permit issued by the Captain of the Port.
.(ii) The Captain of the Port shall give commercial vessels priority over naval and public vessels.
.(iii) The Captain of the Port may at any time revoke a permit to anchor in Anchorage E issued under the authority of paragraph (f)(4)(i) of this section. 
.(iv) A vessel may not anchor in Anchorage Berth E-1 unless it is carrying or handling dangerous cargo or military explosives.

Table 7-3.
*Charting Symbols for Federally Regulated Anchorages*
Type of Anchorage
Commercial anchorage
Dead-ship anchoragea
Deep-draft anchorage
General anchorage
Military anchorage
Small-craft anchorage
Special anchorage
Temporary anchorage
*0.2 mm solid magenta line*; anchoring berths may also be shown

*Subtype (if defined) Charting Symbol*
Explosive anchorage
Forbidden anchorage
Prohibited anchorage
Nonanchorage
Quarantine anchorage
Restricted anchorage
Commercial explosive
Emergency explosive
Naval explosive
Temporary explosive
*0.2 mm dashed magenta line*; anchoring berths may also be shown

Fairway anchorage *0.5 mm solid magenta line*; anchoring berths may also be shown.

NOTES:
a See: e.g., 33 CFR &#167; 110.158.
b Some naval anchorages are further subdivided into submarine anchorages (33 CFR &#167; 110.150), aircraft carriers, destroyers (33 CFR &#167; 110.182), small craft (33 CFR &#167; 110.159), or emergency naval anchorages (33 CFR &#167; 110.155).

.(v) A vessel may not anchor within 500 yards of Anchorage Berth E-1 without the permission of the Captain of the Port, if the berth is occupied by a vessel carrying or handling dangerous cargo or military explosives.

*Nonfederally Regulated Anchorages *(N 12.1)
State and local governments may establish anchorages in waters under their jurisdiction.
These areas may also be charted at the discretion of NOAA. Chart conventions parallel those for federally regulated anchorages, *except that a black dashed line is used rather than a magenta line.* Applicable rules and regulations for these areas are not published in the U.S. Coast Pilot, but must be obtained by the agency having jurisdiction over the anchorage area.










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*Harbors of Refuge* (N 10)
Harbors of Refuge are recognized anchorage areas without defined limits. These harbors provide passing vessels with good holding ground and temporary refuge from storms. For this reason, vessel operations *(particularly operators of small vessels)* should be familiar with the location of the various Harbors of Refuge along a proposed route. A harbor of refuge may or may not be considered a part of a shipping port. A harbor of refuge is identified with a black anchor symbol (N 10) and a label HARBOR OF REFUGE in black italic capital letters.

*TO BE CONTINUED *


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## Fishers of Men

*Ch 7 continued *
*Dumping/Disposal Areas*
Dumping/disposal areas have been established for various purposes, such as for ocean dumping of toxic wastes (now prohibited) or depositing dredged materials. These areas may constitute hazards to navigation and are charted for this reason. Three general classes (determined by the federal regulatory authority that has jurisdiction over their establishment) of dumping areas are shown on NOAA charts. 

These are briefly described below.
EPA Established Dumping Areas (N 24, N c, N d, N g)
The U.S. Environmental Protection Agency (EPA) established ocean dumping sites (40 CFR Part 227) for the purpose of disposing of toxic and nontoxic materials including dredged material, industrial waste, acid waste, municipal waste, sludge, etc. *(Isn't that just great, what a fishin hole)*These areas are charted in all cases where hydrography and other navigational detail are shown in the area. (Refer to Chapter 4 for information on areas where hydrography is omitted.)

Dumping areas designated in 40 CFR &#167; 228.12 are shown by *a black dashed limit line.* A label is added in black to identify the area in italic type, capital and lowercase letters, in a size appropriate to the charted feature.
A label refers to note S. A descriptive term such as dredged material may be added to the label to reflect the primary use of the area as identified in the regulations.

*Examples include:*
Dump Site (see note S)
Dump Site (dredged material) (see note S)
Note S is charted in the vicinity of note A and states;
NOTE S Regulations for Ocean Dumping Sites are contained in 40 CFR, Parts 220-229.
Additional information concerning the regulations and requirements for use of the sites may be obtained from Environmental Protection Agency.

Hydrography and tints (see Chapter 4) are retained in the dumping areas because these areas are not intended to interfere with navigation. The date of the hydrography is stated as follows:

Depths from survey of _____.
On small-scale charts, the dimensions of the dump site may preclude its being charted to scale. In this event, a minimum-size symbol (a 2.0 mm dashed square) is used in lieu of attempting to depict the actual size. If this symbol is used for all dump sites shown on a particular chart, these are identified by label, without reference to note S, e.g.:

Dump Site (dredged material).
Navy.Established Dumping Areas
The Navy designated certain areas, generally in deep water at a considerable distance offshore, for disposal of ammunition, chemicals, and explosives. These areas are shown on NOAA charts to inform chart users, notably trawlers, who might tangle with dangerous materials. The same chart conventions are used as for Environmental Protection Agency (EPA).established dumping areas.

*U.S. Army Corps of Engineers Areas:*
The USACE has authority to establish dumping areas with the approval of EPA.
These dumping areas are classified variously as spoil areas, disposal areas, or dumping grounds. The following note is added in black to all charts containing spoil areas, disposal areas, and dumping grounds where dumping is regulated by this agency:

Dumping dredged or fill materials in spoil areas, disposal areas, and dumping grounds is illegal without authorization from the U.S. Army Corps of Engineers. Regulations and permission for dumping in area (or areas) charted, may be obtained at the office of the District Engineer, Corps of Engineers, New Orleans, Louisiana.

*Spoil areas* (N 62.1) are established for the disposal of dredged material removed from the bottom of channels and harbors during dredging operations. If inactive, the area is still charted, but labeled in black italic capital and lower-case letters, Discontinued Spoil Area. 

These areas are generally located near and parallel to the dredged channel and are potentially dangerous to navigation. Active spoil area limits are shown by a black dashed line delineating the extent of the area, a label (in italic, capital and lowercase letters) .Spoil Area, with blue tint No. 1 added to accentuate their potentially dangerous nature. Spoil areas that uncover are tinted green. Soundings and depth curves (see Chapter 4) are omitted within spoil areas, although islets and areas bare at MLLW are charted. Disposal areas (N d) are established or approved (see 33 CFR Parts 323-324) for depositing dredged material in waters where existing depths and currents indicate that the dumping will not cause sufficient shoaling to create a danger to surface navigation. Disposal area limits are shown by a black dashed line, except that soundings, tints, and depth curves are retained inside the limits of these areas.

The following note is shown in italic type:
Disposal Area
&#8220;Depths from survey of ______.&#8221;
Dumping Grounds (N c)
Dumping grounds are areas formerly designated by the USACE (under 33 CFR Part 205, now revoked) for dumping (by permit) various types of materials. These dumping grounds are typically located well offshore in deep water.
Dumping ground area limits are shown by a black dashed line. Soundings and depth curves may be charted within the limits. A blue tint is added when justified by the charted hydrography (see Chapter 4). Finally, the label Dumping Ground in black italic type (capital and lower-case letters) is added inside the limits of the area.

*Relevance to the Mariner*
Generally speaking, these areas are depicted on nautical charts to alert the mariner to the possibility of danger when transiting the area (e.g., spoil areas) or when engaging in certain activities (e.g., trawling in the vicinity of Navy-established dumping areas). Depiction of these areas on the nautical chart also serves to alert the mariner to the types of vessels that may frequent these areas. A spoil area, for example, might be frequented by dredges, tugs, and barges.

Spoil areas are of particular concern, because of their generally shallow depths and proximity to dredged channels. There are numerous instances of vessels running aground in these spoil areas. *Avoidance is the safest course of action lest they spoil your voyage in more ways than one.*

*Illustration*
Figure 7.5 shows an excerpt from NOS Chart No. 11361 (Mississippi River Delta) showing the Southwest Pass at the mouth of the Mississippi River. Several features of this chart excerpt are of interest. Note the oil platforms, oil pipelines, and the safety fairway for vessels entering and existing the Southwest Pass. 

Note also the blue tinted spoil area on either side of the channel. The blue tint alerts mariners to the danger posed by these areas. See also the dump site to the west of the channel. The northern portion of the dump site overlays the spoil area. The cartographer elected to tint the entire dump site area blue, to emphasize the possible dangers in this area.










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However, soundings south of the southern boundary of the original spoil area were retained, as these were judged unlikely to change materially as a result of the dumping activities. This area was the site of a collision between a northbound Dutch cruise ship Noordham and a southbound freighter Mt. Ymitos in November of 1993 (see Professional Mariner, Issue No. 5). The accident investigation is still pending as of this writing, so it would be premature to speculate on the cause of the accident. 

However, one aspect of this collision is of interest here. The Captain of the southbound Mt. Ymitos reportedly claimed that he could not alter course to the right (i.e., westward) because of the proximity of the dump site. Moving westward of the buoyed channel when north of the fairway buoy SW would entail some risk of grounding. For positions south of this buoy, the soundings and the included 120-foot depth curve shown on the chart offer more comfort. Presumably, any vessel of sufficient draft to be accommodated in the channel (40 feet) could transit this area without appreciable risk of grounding. COLREGS Demarcation Line (N a)

*A COLREGS demarcation line *(see 33
CFR Part 80) divides U.S. waters into two areas. Landward of this line the Inland Navigation Rules apply, seaward of this line the International Navigation Rules apply. (The USCG publishes both sets of rules in COMDTINST M16672.2B, see references.) Although many of the navigation rules are common to both sets, some differ. For example, r*equired lights and whistle signals under the inland rules differ from those under the international rules.* For this reason it is important that the mariner be aware of the water areas where each set of navigation rules apply. The COLREGS demarcation lines are published in CFR and in COMDTINST M16672.2B in terms of the latitude and longitude of linear segments, but these coordinates are not convenient for use. For this reason, the COLREGS demarcation lines are printed on NOAA charts.

*Charting Practices*
Charting conventions for COLREGS demarcation lines consist of a symbol, label, and note, as discussed below.

*Symbol *(N a)
COLREGS demarcation lines are shown on all coastal series charts (scale 1:150,000 and larger) and on other charts as needed using a magenta dashed line (N a).

*Label*
The label COLREGS DEMARCATION LINE in magenta italic capital letters (see figure 7.2 or figure 7.5) is placed along the line, either inside or outside as space permits. If labels cannot be placed along the COLREGS line, these may be placed on land and parallel to the chart base. Labels in other locations (where space is limited) where labeling may be critical are abbreviated COLREGS. This abbreviated label may be omitted in cases where the labels would be extremely close together or where several chart lines are in close proximity. Some charts depict only areas where the international rules apply. This includes certain areas of New England, Florida, Puerto Rico, the Aleutians, and other areas. The following note is added to these charts in lieu of the addition to the Symbols and Abbreviations note:
COLREGS, 80.____ (see note A) International Regulations for Preventing Collisions at Sea, 1972&#8221; In areas where COLREGS lines are shown and space permits, the second line of the label shows the CFR section number and the reference to note A, e.g., .80.325a.

*TO BE CONTINUED*


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## sstaz

Fisher of Men, I have just started reading this thread. It is great, I have sent the link to 2 of my friends who are into sailing that will enjoy it. Thank you for all the hard work. My sister sent me this compass/sundial for Christmas which I though was just awesome, and thought you may enjoy to see. It is one of the things they used back in the day for navigation. Keep up the good work


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## Fishers of Men

sstaz, 
Thanks for sharing. That is really a nice present. There is a section on this thread that Explains compass points if you havn't already read it. The book by Mixter, Primer of Navigation is a very detailed book on it's use, including celestial. I highly recommend it:
There is a good deal on amazon I just saw the other day.
[ame]http://www.amazon.com/gp/offer-listing/0393035085/ref=dp_olp_2/105-3058898-8023639[/ame]


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## Fishers of Men

Any late comers that want the files on charting practices that are in this thread let me know and I'll send them to you. just let me know on here.


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## Fishers of Men

ch 7 continued. Duh, I ran aground, finished this chapter up and forgot to upload it. Must be the age thing.

*Degaussing Range* (N 25)
(Some degaussing ranges (e.g., 33 CFR § 334.870) are also restricted areas.)
A degaussing (demagnetizing) range is an area within which a vessels magnetic field may be measured. These measurements are used to determine the required degaussing coil current settings and other corrective action(s). Sensing instruments and cables are installed on the sea bed in the range, with the cables leading from the range to a control position ashore. This range is usually marked by distinctive buoys identifying the purpose of the range. Although there are relatively few degaussing ranges, their presence and location are relevant to the mariner because of the specific rules and regulations that may apply therein. These include (but are not limited to) a prohibition on the introduction of external magnetic field sources, anchoring, trawling, and a requirement to avoid the range when it is in use. For an interesting article on the use of the degaussing range, see Ryan.

The limits of the degaussing range are shown by a dashed line (N 25). *Submarine cables *extending from the shore are charted in their exact position and *shown in magenta.* The label DEGAUSSING RANGE is shown in black capital italic letters in a type size appropriate to the feature.

*Maritime Boundaries*
There are numerous maritime boundaries (e.g., the Three Mile Line) referred to in state or federal laws. (A description of the provisions of the various laws having maritime boundaries is beyond the scope of this manual. The reader is referred to other sources for this information.) The shoreline and the low-water line are used as baselines for determining the various maritime boundaries described by geographic coordinates in legal references. The nautical chart is the legal graphic authority for most of these boundaries.
Maritime boundaries reference to the low-water line that are found on NOAA charts include the following:

Exclusive Economic Zone (200 nautical miles)
Magnuson Fishery Conservation and
Management Act Amendments
(Alaska fishing limits)
Marine Sanctuaries
National Parks
National Seashores
Natural Resources Boundary (3 leagues or 9 nautical miles; Texas, Florida-Gulf of Mexico coast, Puerto Rico)

*Political Boundaries*
Territorial Sea and Contiguous Zone (12 miles)
Three Nautical Mile Line
State Parks.

Some of the more important of these boundaries are explained below. International Boundaries (N 40, N 41) International boundaries are charted with a solid black crossed dashed line (N 40, N 41). Exclusive Economic Zone (N 47) In 1983, a 200-mile Exclusive Economic Zone (EEZ) was established. This zone is described in the Coast Pilot Manual as follows:

The EEZ of the United States is a zone contiguous to the Territorial Sea and Contiguous Zone (12 nautical miles) of the United States, the Commonwealth of Puerto Rico, the Commonwealth of the Northern Mariana Islands (to the extent consistent with the Covenant the United Nations Trusteeship Agreement), and the United States overseas territories and possessions. The EEZ extends to a distance 200 nautical miles from the baseline from which the breadth of the territorial sea is measured.

The significance of this zone is described in the Coast Pilot Manual as follows:

Within the EEZ, the United States has asserted, to the extent permitted by international law, (a) sovereign rights for the purpose of exploring, exploiting, conserving and managing natural resources, both living and nonliving, of the seabed and subsoil and the super adjacent waters and with regard to other activities for the economic exploitation and exploration of the zone, such as the production of energy from the water, currents and winds; and (b) jurisdiction with regard to the establishment and use of artificial islands, and installations and structures having economic purposes, and the protection and preservation of the marine environment. 

Without prejudice to the sovereign rights and jurisdiction of the United States, the EEZ remains an area beyond the territory and territorial sea of the United States in which all states enjoy the high seas freedoms of navigation, overflight, the laying of submarine cables and pipelines, and other internationally lawful uses of the sea.

The seaward boundary of the EEZ is coincidental with that of the Fishery Conservation Zone (FCZ) over which the United States exercises exclusive fishery management authority over all species of fish, except tuna. The EEZ limit is shown by a black screened line interspersed at regular limits by a .fish. symbol (N 47). This line is labeled .EXCLUSIVE ECONOMIC ZONE in black italic capital letters.

Closing Line/Three Nautical Mile Line/ Territorial Sea and Contiguous Zone (N 42, N 43, N 44)
The closing line (baseline) is the dividing line between inland waters and marginal seas across the entrance of a bay. The Three Nautical Mile Line marks the boundary of the waters within a three-mile zone adjacent to the coast and seaward of the closing line. The Territorial Sea and Contiguous Zone marks the boundary of the waters within a 12-nautical mile zone adjacent to the coast and seaward of the closing line.

Each of these lines are black screened unbroken lines of 0.5 mm lineweight. These lines are labeled in black italic type as follows:
THREE NAUTICAL MILE (see note X), TERRITORIAL SEA (see note X), and TERRITORIAL SEA AND CONTIGUOUS ZONE (see note X).

The text of note X differs slightly according to whether or not the natural resources boundaries of Puerto Rico or the gulf coast are shown. One version of this note is as follows:

*NOTE X*
The 12-nautical mile territorial sea was established by Presidential Proclamation 5928, December 27, 1988, and is also the outer limit of the U.S. contiguous zone for the application of domestic law. The 3-nautical mile line, previously identified as the outer limit of the territorial sea, is retained because the proclamation states that it does not alter existing State or Federal law. The 9 nautical mile natural resources boundary off Texas, the Gulf coast of Florida, and Puerto Rico, and the 3 nautical mile line elsewhere remain the inner boundary of the Federal fisheries jurisdiction and the limit of states. jurisdiction under the Submerged Lands Act (P.L. 83-31; 67 Stat. 29, March 22, 1953). 

These maritime limits are subject to modification, as represented on future charts. The lines shown on the most recent chart edition take precedence.
Figure 7.6 provides another excerpt from NOS Chart No. 12221 (Chesapeake Bay Entrance) showing a Three-Mile Limit Line among other features of interest.









Traffic Separation Schemes and Related Matters TSS and Vessel Traffic Services (VTS) are related systems used to aid in the prevention of collisions in the approaches to many major harbors. 

(Although it is convenient to discuss TSS and VTS in the same section, as both relate to routing and employ similar charting conventions, it is important to distinguish between these two systems. A TSS is a set of paper conventions (routes) established by the host country in consultation with the International Maritime Organization (IMO) (The IMO (formerly IMCO) is an organ of the United Nations, based in London, England, established to deal with recommendations relative to maritime safety and pollution.) A TSS is the subject of Rule 10 of the International Navigation Rules. A VTS, however, is a physical entity, consisting of a control facility termed a Vessel Traffic Center (VTC), manned by personnel from the host country (principally the USCG in the United States, although a new private VTS has been commissioned in Los Angeles/Long Beach, CA, and others are planned for Tampa, FL, and Philadelphia, PA), communications facilities, and systems of observation (television cameras and radar) and operates in accord with published rules and regulations (CFR) under Rule 10 of the Inland Navigation Rules. Some major harbors and harbor approaches (e.g., New York) have a TSS and a VTS. Others (e.g., the approaches to the Chesapeake or Delaware Bays) have only a TSS. Yet others (typically those entirely within inland waters, e.g., the St Marys River) have a VTS, but no TSS (although routing regulations are published for this area). Finally, most harbors and harbor approaches have neither a TSS nor a VTS.)

Briefly, a TSS consists of a series of highways in the water that segregate traffic, while a VTS is a land-based system which provides advice and control of participating vessels in a manner similar to but less elaborate than the system employed for air traffic control. Centers for VTS have communications equipment and radar and optical systems for observation. TSS and VTS are discussed in 33 CFR Part 161 (Vessel Traffic Management) and 33 CFR Part 167 (Offshore Traffic Management Schemes).

All vessels are obliged to follow Rule 10 (International Navigation Rules) regarding TSS, and there are specific rules and regulations (including whether participation in an associated VTS is voluntary or mandatory) applicable to each area. (Refer to the U.S. Coast Pilot or 33 CFR for details.) A TSS is a routing measure designed to separate opposing streams of traffic by the establishment of traffic lanes. Vessels need not use a TSS (i.e., participation is voluntary). However, under Rule 10, paragraph (h), ....a vessel not using a traffic separation scheme shall avoid it by as wide a margin as is practicable. 
A TSS may include traffic lanes, separation zones, roundabouts, precautionary areas, inshore traffic zones, deep-water routes, areas to be avoided, and (in the case of a corresponding VTS) calling-in points. It is convenient to include pilot boarding areas in this section. Definitions and charting practices are described below. Figures 7-7 and 7-8 provide excerpts from Chart No. 1 which illustrate many of the chart symbols used to depict TSS/VTS features Figure 7-6 depicts a TSS in the vicinity of Chesapeake Bay, which includes traffic lanes, separation zones, and a precautionary area. This excerpt also shows a pilot boarding area.

A traffic lane means an area within defined limits in which one-way traffic is established. When joining or leaving a traffic lane (Rule 10 paragraph (b) (iii)) vessels are required to do so at as small an angle as possible. As far as practicable, vessels should avoid crossing traffic lanes (Rule 10 paragraph c).
However, vessels crossing a traffic lane should do so on a heading as nearly as practicable at right angles to the lane. Vessels are encouraged to navigate at or near the center of the traffic lane. Otherwise (see Cockcroft and Lameijer),
....there is danger that a vessel which sets a course near the edge of a lane will stray into the separation zone or the traffic lane designated for traffic proceeding in the opposite direction.

Vessels should also keep clear of the outer limit of the traffic lane lying on the vessels starboard side, ....particularly if this line separates the lane from an inshore zone which is likely to contain traffic moving in the opposite direction. On the edge of the lane two power-driven vessels meeting on reciprocal courses would each be required to alter course to starboard by Rule 14. Such action may cause both vessels to be involved in further meeting situations making it difficult for them to return to their correct lane or zone. 
Natural obstacles, including those forming separation zones may constitute a boundary. Traffic lanes are depicted in nautical charts by a distinctive symbol (M 13). Arrows are drawn to indicate the general direction of flow. If the traffic lane is wider than 5.0 mm at chart scale, the arrows are staggered within the lane. If not, arrows are placed in the center of the lane A label INBOUND, or OUTBOUND, may be added in magenta capital italic type as shown in figure 7-6.

A separation zone or line means a zone or line which separates the ships proceeding in opposite or nearly opposite directions; or separating a traffic lane from the adjacent sea area; or separating traffic lanes designated for particular classes of ships proceeding in the same direction. Separation lines are represented by a magenta-screened line at least 3 mm wide. Figure 7.6 shows a separation zone in the eastern inbound-outbound approach to Chesapeake Bay.

A roundabout is a routing measure comprising a separation point or circular separation zone and a circular traffic lane within defined limits. Traffic within the roundabout is separated by moving in a counterclockwise direction around the separation point or zone. A roundabout is depicted by a unique symbol (M 21, M d). As of this writing, there are no roundabouts in U.S. waters.

A precautionary area means a routing measure comprising an area within defined limits where ships must navigate with particular caution and within which the direction of traffic flow may be recommended. A precautionary area is depicted by a unique symbol (M 16, M 24), and may include a label, *PRECAUTIONARY AREA*, in magenta italic capital letters. Figure 7-6 shows a precautionary area near the entrance to the Chesapeake Bay. Note that vessels not using the TSS may enter the precautionary area. In the TSS shown in figure 7-6, many vessels (e.g., recreational, tugs with barges, etc.) entering the Bay from the north or south along the coast and not using the TSS routinely enter this precautionary area. A deep-water route is a route in a designated area within definite limits which has been accurately surveyed for clearance of sea bottom and submerged obstacles as indicated on the chart. A deep-water route may be either one-way or two-way. It is labeled, DEEP WATER ROUTE, or TWO WAY DEEP WATER ROUTE, in magenta italic capital letters. Note the two-way deep-water route in the southern approach to Chesapeake Bay shown in figure 7-6. (submarine traffic)



















An inshore traffic zone is a routing measure comprising a designated area between the landward boundary of a TSS and the adjacent coast, not normally to be used by through traffic (although under Rule 10 it may always be used by vessels under 20 meters in length and sailing vessels) and where special rules may apply. An inshore traffic zone must be explicitly designated, it is not simply the area between the boundary of the TSS and the land. It is labeled, INSHORE TRAFFIC ZONE, in magenta italics. It may have defined endpoints; if so, these are designated by T-shaped dashed magenta lines (identical to those used to depict a restricted area). Reference to figure 7.6 indicates that there is no inshore traffic zone established for this TSS, because there is no label INSHORE TRAFFIC ZONE included in the chart excerpt. (In fact, as of this writing, no inshore traffic zones have been established in U.S. waters.) An area to be avoided is an area which is not recommended for navigation because of shoal hydrography, obstructions, or local and federal regulations. These areas are denoted with a unique symbol (M 29.1, M 29.2). For example (IMO), off the coasts of the United States there are areas to be avoided in the vicinity of the Louisiana Offshore Oil Port (safety concerns near the platform pumping complex and single point mooring buoys), in the region of Nantucket Shoals (because of the great danger of strandings and for environmental protection), in the region of the Northwest Hawaiian (Sandwich) Islands (to avoid the risk of pollution in a designated wildlife refuge), off the California coast near the Channel Islands National Marine Sanctuary (pollution concerns), and throughout the Florida Keys (to avoid risk of pollution and damage to the environment).

Calling-in points, requiring participating vessels to report to a traffic control center, have been established in certain waterways and port approaches (e.g., the New York Vessel Traffic Service, the Berwick Bay Vessel Traffic Service, etc.) to assist in traffic control. (Refer to the appropriate rules and regulations published in the CFR for details.) Where established, calling-in (reporting) points are denoted on the nautical chart by a unique magenta symbol (M 40) consisting of a circle enclosing an alphanumeric designator with one or two arrowheads attached. The alphanumeric designator corresponds to a calling-in point given in the CFR. (Generally numeric or alphanumeric designators indicate mandatory calling-in points, while alphabetic designators depict voluntary calling-in points.) The arrowhead(s) indicate that position reports are required for vessels bound in one or two directions. Whenever numeric or alphanumeric designators are charted, the following note is added in light magenta type:

Vessel Traffic Services calling-in point with numbers; arrow indicates direction of vessel movement. 

Pilot boarding areas denote meeting or boarding places where vessels pick up or disembark pilots. (Discussions on pilotage regulations can be found in the Coast Pilot Manual, appendix B, and in the CFR.) The limits of pilot areas are usually charted with a 2.5 mm magenta-screened band, or a magenta symbol (T 1.1) if the chart scale is too small to show the area. These areas are labeled PILOT BOARDING AREA, or (as shown in figure 7.6), PILOTAGE AREA, in magenta italic type. A pilot boarding area is not part of a TSS, but is included in the section because pilot boarding areas are often located near elements of a TSS.

Notes
All TSS are described in the applicable U.S. Coast Pilot. But, as of this writing, not all TSS are described in the CFR. A note is added on the nautical chart which provides additional information on any TSS not described in the CFR. The exact text of the note varies with the TSS, but the following serves as an illustration.

NOTE G
TRAFFIC SEPARATION SCHEME One-way traffic lanes overprinted on this chart are RECOMMENDED for use by all vessels traveling between the points involved. They have been designed to aid in the prevention of collisions at the approaches to major harbors and along heavily traveled coastal waters, but are not intended in any way to supersede or to alter the applicable Rules of the Road. Separation zones are intended to separate inbound and outbound traffic and to be free of ship traffic. Separation zones should not be used except for crossing purposes. When crossing traffic lanes and separation zones use extreme caution. A Precautionary Area has been established at San Pedro Bay. It is recommended that vessels proceed with caution in this area.
This note is customized as appropriate to each TSS and is removed upon inclusion of the TSS in the CFR.

TO BE CONTINUED


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## Fishers of Men

ch 7 CONTINUED

*Additional Information*
Additional information regarding any TSS or VTS in U.S. waters can be found in the U.S. Coast Pilot. The following excerpt from the U.S. Coast Pilot, for example, provides information on the TSS shown in figure 7.6:

Traffic Separation Schemes (Chesapeake Bay Entrance and Smith Point) have been established for the control of maritime traffic at the entrance of Chesapeake Bay and off Smith Point Light (37&#176;52.8.N., 76&#176;11.0.W.). They have been designed to aid in the prevention of collisions, but are not intended in any way to supersede or alter the applicable Navigation Rules. (See Traffic Separation Schemes, Chapter 1, for additional information.) (30) Traffic Separation Scheme (Chesapeake Bay Entrance).

The scheme provides for inbound outbound traffic lanes to enter or depart Chesapeake Bay from the northeastward and from the southeastward. (See NOS chart 12221.)
(31) A precautionary area with a radius of 2 miles is centered on Chesapeake Bay Entrance Junction Lighted Gong Buoy CBJ (36&#176;56.1.N., 75&#176;57.5.W.) (32) The northeastern inbound/outbound traffic lanes are separated by a line of four fairway buoys on bearing 250&#176;.070&#176;. The outermost buoy in the line is 6.4 miles 313&#176; from Chesapeake Light and the innermost buoy is 4.5 miles 074&#176; from Cape Henry Light. (33) The southeastern approach is marked by Chesapeake Bay Southern Approach Lighted Whistle Buoy CB (36&#176; 49.0.N., 75&#176;45.6.W.) A RACON is on the buoy. The inbound/outbound traffic lanes are separated by a Deep-Water Route marked by lighted buoys on bearings 302&#176; .122&#176; and 317&#176; .137&#176;.

The Deep-Water Route is intended for deep draft vessels and naval aircraft carriers entering or departing Chesapeake Bay. A vessel using the Deep- Water Route is advised to announce its intentions on VHF.FM channel 16 as it approaches Lighted Whistle Buoy CB on the south end, and Lighted Gong Buoy CBJ on the north end of the route. All other vessels approaching the Chesapeake Bay Traffic Separation Scheme should use the appropriate inbound/outbound lanes of the northeasterly or southeasterly approaches. (34) 

The Coast Guard advises that upon entering the traffic lanes, all inbound vessels are encouraged to make a security broadcast on VHF FM channel 13, announcing the vessels name, location, and intentions.

(35) Exercise extreme caution where the two routes converge off Cape Henry. Mariners are also warned that vessels may be maneuvering in the pilotage area which extends into the western part of the precautionary area. Additional material on TSS can also be found in other publications (e.g., IMO).

*Relevance to the Mariner*
TSS/VTS have been established to promote the safe and expeditious flow of traffic. Whether voluntary or mandatory, participation by all vessels operating in the vicinity of a TSS is desirable. The introduction of the TSS has been hailed as a significant breakthrough. in reducing the incidence of collisions. As Cahill (Strandings and Their Causes) noted:

The most effective way of achieving a reduction in ship casualties is through reduction of the risks to which mariners are exposed. A dramatic and conclusive example of the truth of this proposition is before us in the results achieved by the introduction of traffic separation schemes; specifically that in the Dover Strait. That scheme is arguably the most significant contribution to ship safety since the introduction of steam propulsion.

For a more critical view of VTS specifically, see Young.
Including TSS information on the nautical chart certainly simplifies compliance with the routing instructions. However, participating vessels should be aware that some vessels (either because they choose not to participate or because they fail to read and understand the procedures) will not follow the charted patterns. When transiting these, as well as other areas, caution is the watchword. As noted in one of the standard reference works (Farwells):

Even with up-to-date charts there remain instances of ships proceeding contrary to the direction of traffic flow laid down for traffic separation schemes. Where collisions have occurred, the courts have been consistent in finding that, despite the rogue vessels contravention of International Regulations. The other rules of the collision regulations applied in all respects.

There have been numerous instances of collisions with rogue vessels in areas with established routes (see Cahill, Collisions and Their Causes, or Holdert and Buzek), but perhaps the most famous was the Andrea Doria-Stockholm collision in 1956 (see Marriott or Hoffer). (This did not involve a TSS per se, but rather ignoring the 1948 Safety of Life at Sea (SOLAS) recommendation on traffic separation. a precursor to today&#8217;s TSS.)

*Smaller Vessels*
In the days before the electronic revolution, some might have argued that it was a challenge for operators of smaller vessels (e.g., recreational or small fishing vessels) to comply fully with an established TSS particularly in areas sufficiently far offshore to prevent visual fixes being taken on landbased objects and/or for a TSS that is not well marked by aids to navigation (ATONs).

Opting for an inshore route might have been preferable to attempting to use the lanes without suitable means for fixing the vessels position.

Now, however, it is common for even small vessels to have LORAN-C or GPS receivers on board. Use of these electronic aids greatly simplifies compliance with the established TSS, regardless of the prevailing visibility. The traffic lanes can be identified by a sequence of waypoints (defining the center of linear portions of the lanes), and the off course alarm feature common to most of these receivers can be set so that the operator is warned if the vessel strays from the charted traffic lane. (It is recommended that the off-course alarm be set up to warn the mariner well before the limits of the traffic lane so as to allow an ample margin of safety.)

Waypoints can also be used to mark calling-in points for a VTS Rule 10, paragraph (e) (ii), permits fishing within a separation zone of a TSS. The off course alarm feature of most modern LORAN-C or GPS receivers can also be used to warn the operator if the fishing vessel wanders out of the designated separation zone.

*Some final tips relevant to use of a TSS include:*
Expect to find a significant amount of traffic in a TSS. These lanes concentrate traffic from a wide ocean area, so that traffic densities can be quite high. Vessels should maintain an alert lookout (both visual and with radar if so equipped).

Ensure that your vessel is equipped with a radio if using a TSS. This enables you to communicate with other vessels using the TSS. A radio is essential if using a VTS.

Equip your vessel with a radar reflector if operating in a TSS and your vessel is not radar conspicuous. Recreational vessels, in particular, are often difficult to see on radar.

A deep-water route is primarily intended to be used by deep-draft ships. Vessels not requiring such channel depths should avoid using these routes to limit traffic congestion.

When feasible, sailing vessels are probably well advised to remain well clear of a TSS. The slow speed and restricted maneuverability of a sailing vessel could create a collision hazard.

*Read Rule 10 of the International Navigation Rules*carefully before attempting to use a TSS, A TSS is no place for the ill-informed or na&#239;ve mariner.

*TO BE CONTINUED*


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## Fishers of Men

*Ch 7 conclusion
Course Lines*

Some Great Lakes charts show course lines that are unofficial traffic separation scheme devised by shipping interests for their own benefit. These course lines have not been established by the USCG, nor are regulations published in the CFR.

These course lines are charted with a black dashed line on charts with English units and magenta dashed line on metric charts. In either case, the labels for the course lines are shown in magenta. The labels include distance (in statute and nautical miles) and bearings along a course. The point where a course changes direction is shown with a black dashed line to a point of land or object ashore. The bearing of the line and the distance offshore of the turning point are included in a black label along the dashed line.

If course lines are shown, the following sailing directions note (in black vertical letters) is included on Great Lakes metric charts with Mercator projections:

*SAILING DIRECTIONS.*
Bearings on sailing courses are true and distances given thereon are in statute miles (St M) and nautical miles (NM) between points of departure. The true bearing between any two points on this chart may be determined by connecting the two points with a straight line and measuring the angle of the intersection with a meridian line.

This note is included in the group of notes aligned under the chart title.

*Courses*, also called tracks, are a feature included on some nautical charts. Courses/ tracks are usually shown in rivers, bays, and other inshore waters and are intended primarily to help mariners avoid shoal depths rather than to regulate shipping movement. The decision whether or not to follow a charted course is left to the discretion of the mariner rather than a matter of regulation although some courses are charted in connection with a TSS.

Bearings charted along courses are given in degrees and tenths of a degree with respect to true (not magnetic) north. 

Reciprocal bearings are charted along two-way courses. 

Distances along courses may also be charted (in statute or nautical miles). Distances may also be shown as a series of mileage ticks. These ticks are generally charted (in magenta) in statute miles at 1-mile or 5-mile intervals depending upon the scale of the chart.

Recommended courses marked by fixed or floating ATONs (M 3) are charted with a solid black line. Traffic flow directional arrows may be inserted at regular intervals along the line.

Recommended courses not marked by ATONs (M 4) are charted with a dashed magenta line.

An alternate course (M c) is a secondary course available to shallower draft vessels. Usually an alternate course will rejoin the recommended course. The alternate course is charted with a dashed magenta line whether or not it is marked by ATONs. Arrows are used to indicate the direction of traffic flow if so recommended.

*Concluding Comments*
The material in this chapter is quite detailed. Although nearly all the topics discussed have regulatory significance, knowledge of the various areas, limits, routes, and tracks, and how these are depicted on the nautical chart is also very important to the mariner to ensure safe passage.

A study of collateral information, such as the CFR or the U.S. Coast Pilot, is particularly important with respect to the charted features discussed in this chapter. Charted features, for the most part, are there to alert the mariner to applicable rules and Regulations and/or potential hazards.

_&#8220;The greatest hazard to navigation is a bored navigator..&#8221;
_Anonymous, quoted in Schlereth

I have enjoyed sharing this information with you and it keeps me up to date and reminded!

I want to thank all of you that have spent the time and effort along with print paper (lol) for taking advantage of this being made available to you. And I hope you will stick in there and troll along for the Navigation part to put all this to use.

I will close chapter 7 with one of Smallies favorites:

*&#8220;I Jesus have sent mine angel to testify unto you these things in the churches. I am the root and the offspring of David and the bright morning star.&#8221; 
&#8220;And the Spirit and the bride say Come. And let him that heareth say, Come. And let him that is athirst come. And whosoever will, let him take the water of life freely.&#8221; Rev 22: 16-17
*








So you want to go night fishing? Better pay attention and follow along.
http://www.ohiogamefishing.com/community/showthread.php?t=84125&highlight=stargazing

AND, I WILL LEAVE YOU WITH THESE THOUGHTS
What would you do if this happened to you on Erie?
Solar flares knocked out GPS systems in Dec. 2006.

Who was it that said &#8220;I don&#8217;t need a chart, I have GPS?&#8221; I SAY, what about this? http://www.news.cornell.edu/stories/Sept06/solar.flares.gps.TO.html

This was one of the arguments to keep loran-C active, and it&#8217;s a good thing. A loran back up and a good CHART on board with the knowledge and wisdom you are gaining from this thread and this site will put the confidence and respect for the water/weather/elements that everyone needs to navigate safely and have a more pleasurable, less hassle boating experience.

If the scenario came down where you lost all electronics, convection fog set in on you even a mile out on the lake, how would you get back? Your compass? Did you read it, and take 3 bearings and fix the position before you left? Forgot, huh? If you did, what about wind/currents/set and drift? Can you make the corrections? Cant get close to shore and use line of sight, there is none. What would you do?
I want to hear what some of you would do, lets share it.

http://www.ohiogamefishing.com/community/showthread.php?p=555331#post555331

References: 
The Holy Bible King James Version

Anon. Mississippi Collision Placed 1,800 Passengers
in Peril,. Professional Mariner, Issue No. 5, February 1994, pp. 44, et seq.

Anon. VTS Goes Private; New VTS System Opens in Los Angeles/Long Beach,. Professional Mariner, Issue No. 7, June/July 1994, p. 34.

Bassett, F. E. and R. A. Smith, Farwell.s Rules of the Nautical Road, Sixth Edition, Naval Institute Press, Annapolis, MD, 1982.

Brannan, L., .New VTIS On-Line at California Port,. Commandant.s Bulletin, Issue 6.94, COMDTPUB P5720.2, July 1994, p. 5.

Cahill, R. A., Collisions and Their Causes, Fairplay Publications, London, UK, 1983.

Cahill, R. A., Strandings and Their Causes, Fairplay Publications, London, UK, 1985.

Cockcroft, A. N. and J. N. F. Lameijer, A Guide to the Collision Avoidance Rules, Third Edition, Stanford Maritime, London, UK, 1982.

Heinl, R. D., Dictionary of Military and Naval Quotations, Naval Institutes Press, Annapolis, MD, 1966.

Hoffer, W., Saved! The Story of the Andrea Doria.The Greatest Sea Rescue in History,
Summit Books, New York, NY, 1979. Holdert, H. M. C. and F. J. Bozek. Collision
Cases.Judgements and Diagrams, Lloyds
of London Press, London, UK, 1984.

Human Technology, Inc. Desk Reference Guide: Specifications Unit, Chart and Map, Feature: Anchorage. Report developed for National Ocean Service, Charting and
Geodetic Services, Marine Chart Branch, Under Contract OPM-85-77, McLean, VA,
October 1985.
...: Boundary.
...: Civil Reservation.
...: COLREGS.
...: Course Lines.
...: Danger Area.
...: Explosive Economic and Fishery
Conservation Zones.
...: Pilot Areas.
...: Recreational Areas and Structures.
...: Restricted Area.
...: Safety Fairway.
...: Territorial Sea and Contiguous Zone.
...: Traffic Separation Scheme.

International Maritime Organization. Ships. Routeing, Sixth Edition, Updated with
1992 Amendments IMO924E, London, UK, 1993.

Marriott, J., Disaster at Sea, Hippocrene Books, New York, NY, 1987.

McKenna, R., .VTS Takes on a Life of Its Own,. Professional Mariner, Issue No. 3,
October/November 1993, pp. 46.50.

Nemeth, D., .Passage Through a Maritime Crossroads,. Ocean Navigator, Issue No. 42,
September/October 1991, pp. 10.16.

Office of the Federal Register, National Archives and Records Administration. 33
Code of Federal Regulations, Parts 1 to End (3 Volumes), U.S. Government Printing
Office, Washington, DC, July 1, 1993.

Ryan, T., .Naval Officer Recounts Shiphandling Incident,. Professional Mariner, Issue No. 8, August/September 1994, pp. 10.14.

Schlereth, H., Commonsense Coastal Navigation, W. W. Norton & Company, New York,
NY, 1982.

Trimmer, J. W., How to Avoid Huge Ships or I Never Met A Ship I Liked, National Writers
Press, Aurora, CO, 1982, pp. 51.60.

U.S. Department of Commerce, Coast and Geodetic Survey. Nautical Chart Manual,
Volume One: Policies and Procedures, Seventh Edition, Washington, DC, 1992.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration,
National Ocean Service. Coast Pilot Manual, 5th Edition, Rockville, MD, 1994.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration,
National Ocean Service, and Department of Defense, National Imagery and Mapping Agency. Chart No. 1 United States of America Nautical Chart Symbols Abbreviations and Terms, Ninth Edition, Washington, DC, January 1990.

U.S. Department of Transportation, United States Coast Guard. Navigation Rules, International- Inland, Commandant Instruction (COMDTINST) M 16672.2B, Washington,
DC, 1990.

Young, W., .What Are Vessel Traffic Services, and What Can They Really Do?,. Navigation, Vol. 41, No. 1, Spring 1994, pp. 31.56.


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## Fishers of Men

*Perfect example of what we have been saying.*

issue Date: Professional Mariner #110 - December/January 2008, Posted On: 11/20/2007 

160-foot tour boat with 100 guests aboard runs aground in N.Y. inlet
Dom Yanchunas 
A 160-foot tour boat with a draft of 6 1/2 feet ran aground along a marsh on Long Island, N.Y., that is marked by buoys denoting 6-foot-deep water.

The Coast Guard is investigating why Nautical Empress grounded in thick mud along Sea Dog Creek, a marshy inlet on Long Island's South Shore. The vessel's owner said a buoy was off its station, but authorities disputed that claim.

The grounding at 2300 Aug. 10 caused no hull damage or pollution, but it ruined a late-night wedding party attended by more than 100 guests, who were evacuated to another tour boat.

The vessel grounded near buoy No. 7 of the Sea Dog Creek channel, said investigator Lt. Bill Grossman of the Coast Guard Marine Safety Detachment in Coram, N.Y.

Nautical Empress re-floated as the tide rose at 0500 on Aug. 11, the Coast Guard said. Grossman said the tour boat's maximum draft was perilously close to the bottom of the channel.

"It was low tide at the time of the grounding. That had a lot to do with it," Grossman said. "The charted depth is 6 feet, and the draft of the vessel was about 6 1/2 feet."

The Coast Guard investigated whether the buoy was off its station, and issued a notice to mariners alerting them about the possibility. The Coast Guard is also looking at whether Nautical Empress traveled on the wrong side of the buoy.

Nautical Cruise Lines bills its cruise-ship-like Nautical Empress as a "tri-level super ship." The vessel accommodates as many as 475 guests for receptions, parties and corporate functions.

A former dinner boat on the Potomac River in Washington, D.C., Nautical Empress has operated off Long Island for two years. The vessel routinely uses Sea Dog Creek, even at low tide, said Anthony Gillespie, one of the owners of Nautical Cruise Lines, based in Freeport, N.Y.

The crew made "no error" and the buoy was "off its station," he said. "That's the reason why the boat touched bottom. We've been through there time after time after time, and we know where that buoy is supposed to be."

The town of Hempstead, N.Y., maintains the buoy and more than 400 other aids to navigation. Donald Toby, the town's supervisor of waterways maintenance and navigational aids, said his buoy foreman used global positioning to check the buoy on the morning after the incident and the buoy was on its station.

"There is no question. It was in the right spot," Toby said.

The Sea Dog channel is used mainly by recreational boaters and fishing charters, but occasionally large party yachts and tugboats operate there too, he said. The channel is only 60 feet wide; depth ranges from 6 feet to about 15 feet. The passage, west of the Loop Bridge, can be treacherous at night or when there is poor visibility.

The buoy has green reflector tape instead of a light. The Coast Guard said seas were 1 to 2 feet, with 10 miles of visibility, when Nautical Empress grounded.

"Sea Dog is a narrow channel, and it's borderline mud and hard black sand, and there's mussel beds that make it hard too," Toby said. "You can't let your guard down. It's a tough channel if conditions are not in your favor."

The town's buoy foreman routinely checks the bottom conditions to determine whether shoaling has occurred, requiring his crew to move buoys sometimes 2 or 3 feet. That didn't happen in this case, Toby said. The town's navigational aids leave scant margin of error for mariners, he said. "Some of the Coast Guard buoys will give you a little room, but we can't because it's such a narrow channel here," Toby said.

A mariner should never rely on any single navigation aid, including buoys, said Grossman, the Coast Guard investigator, noting that crews should use a combination of tools including the depth finder, radar and global positioning.

In this case, "it's more of a management issue" whether Nautical Cruise Lines decides it's worth the risk to continue operating in Sea Dog Creek at low tide, Grossman said.

Party hosts on Long Island prefer to cruise the back bays because the sea conditions are calm and the scenery is more interesting. Gillespie said his company plans to continue using Sea Dog Creek. 

Toby said the tri-level Nautical Empress is the largest vessel that uses the Sea Dog channel, and he confirmed that "they have gone through there before at low tide with no problem."

Drug and alcohol screenings of the crew were negative, the Coast Guard said. The wedding guests transferred safely to R&S Nautical Charters' 58-foot Miss Freeport V.


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## Fishers of Men

*No comments? Here's another good example:*

Issue Date: Professional Mariner #110 - December/January 2008, Posted On: 11/20/2007 

Tug-barge hits boat anchored in channel. 

The Coast Guard is nearing the end of its probe into a fatal barge-recreational craft collision in western Long Island Sound in June, and the chief investigator says the agency is unlikely to take any action against the pleasure boater because the tug had enough room in the channel to steer around the smaller vessel.

The 24-foot pleasure boat was anchored in the channel south of the Execution Rocks Lighthouse while its occupants were fishing. The channel is at least a quarter-mile wide at that location. The 324-foot petroleum barge Patriot, owned by Seaboats Inc., of Fall River, Mass., is 75 feet wide.

Lt. Jake Hobson, of the Marine Casualty Investigations Office at Coast Guard Sector New York, said Seaboats, which owns the barge and tugboat pushing it, or their crews, could be penalized if pending tests by the Nassau County police lab prove the barge struck the pleasure boat.

The six crew on the tug and barge told investigators they were unaware of hitting another vessel. "They said they saw the fishing boat, but they believed it was entangled with or dealing with another pleasure vessel," Hobson said.

The accident occurred June 10 when boat owner Raphael Rivera, 55, of the Bronx, was fishing with his girlfriend, Leibe Ociele Medina, 47, also of the Bronx, and brother, Efrain Rivera, 60, of Rhode Island. Raphael Rivera said he saw the tug Donald C pushing Patriot, which was en route from New York City to New Haven, Conn., when they were about 300 yards away. Rivera said he expected the barge to avoid his boat, but when it didn't change course, he waved an orange life jacket and then jumped in the water with Medina.

After the impact, Rivera surfaced and saw Medina, who was wearing a life jacket, floating face down about 50 feet away. She died a week later.

Frank Floriani, a lawyer representing Medina's family, said, "Our information is that the barge did not have a lookout."

Kirk Lyons, the attorney representing Seaboats, said, "We cannot respond because the matter is under investigation."

Hobson said, "We believe they were anchored on the southern side of the channel." He said boats are not supposed to anchor in channels, but "where they were is not necessarily a narrow channel" and "as long as they are not impeding traffic," it was not a problem. "They're not professional mariners," he added. "We hold the licensed mariner to a higher standard; they are operating a commercial vessel."

Hobson would not divulge how many crew were serving as lookouts.

De Chateauvieux compares the duty of a tug master to that of a disciplined airline pilot, who reviews an exhaustive checklist meticulously even though the pilot knows the routine by heart.

"From a technical point of view, from a management point of view, this reminds us that the most expert guy who knows what he's doing still has to go by the rules," de Chateauvieux said. "So, modestly, even though you are the expert, you have to go through the calculation -- and you have to say 'no' when you have to say 'no.'"


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## Fishers of Men

I need to know how many of you want to do the navigation part. I only have 3 "signed up". Come on, make it worth my while. You will be amazed at what you will pick up. It's all "Bowditch" that you have been hearing about and seeing in the references. Say it here, so this gets a bump.


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## Fishers of Men

*I will give you CHAPTER 1 
INTRODUCTION TO MARINE NAVIGATION This will take a few posts because it is long and detailed. Since I didn't have any response, this should help you decide. We will cover how GPS works and when it wont, how to configure waypoints etc...There will be some repetition of sections, but I feel it is necessary and important to maintain a thorough understanding for the upcoming applications and will clarify any previous topics. I purposely covered some of this before the charting course because this way you are already introduced to what is coming next. (Heard it somewhere before) lol. This section will separate the novice from the pros, or men from the boys or however you want to put it. This will incorporate and use everything you have learned already and go much further, read on.
*

DEFINITIONS
*100. The Art And Science Of Navigation*
Marine navigation blends both science and art. A good navigator gathers information from every available source, evaluates this information, determines a fix, and compares that fix with his pre-determined &#8220;dead reckoning&#8221; position. A navigator constantly evaluates the ship&#8217;s position, anticipates dangerous situations well before they arise, and always keeps &#8220;ahead of the vessel.&#8221; The modern navigator must also understand the basic concepts of the many navigation systems used today, evaluate their output&#8217;s accuracy, and arrive at the best possible navigational decisions. Navigation methods and techniques vary with the type of vessel, the conditions, and the navigator&#8217;s experience. Navigating a pleasure craft, for example, differs from navigating a container ship. Both differ from navigating a naval vessel. The navigator uses the methods and techniques best suited to the vessel and conditions at hand.
Some important elements of successful navigation cannot be acquired from any book or instructor. The science of navigation can be taught, but the art of navigation must be developed from experience.

*101. Types Of Navigation*
Methods of navigation have changed through history. Each new method has enhanced the mariner&#8217;s ability to complete his voyage safely and expeditiously. One of the most important judgments the navigator must make involves choosing the best method to use. Commonly recognized types of navigation are listed below.
&#8226;	Dead reckoning (DR) determines position by advancing a known position for courses and distances.
A position so determined is called a dead reckoning
(DR) position. It is generally accepted that only
course and speed determine the DR position. Correcting
the DR position for leeway, current effects,
and steering error result in an estimated position
(EP). An inertial navigator develops an extremely accurate EP.
&#8226;	Piloting involves navigating in restricted waters with frequent determination of position relative to geographic and hydrographic features.
&#8226;	Celestial navigation involves reducing celestial
measurements to lines of position using tables, spherical trigonometry, and almanacs. It is used primarily as a backup to satellite and other electronic systems in the open ocean.
&#8226;	Radio navigation uses radio waves to determine position
by either radio direction finding systems or
hyperbolic systems.
&#8226;	Radar navigation uses radar to determine the distance from or bearing of objects whose position is known. This process is separate from radar&#8217;s use as a collision avoidance system.
&#8226;	Satellite navigation uses artificial earth satellites for determination of position.
Electronic integrated bridge concepts are driving future navigation system planning. Integrated systems take inputs from various ship sensors, electronically display positioning information, and provide control signals required to maintain a vessel on a preset course. The navigator becomes a system manager, choosing system presets, interpreting system output, and monitoring vessel response. In practice, a navigator synthesizes different methodologies into a single integrated system. He should never feel comfortable utilizing only one method when others are available for backup. Each method has advantages and disadvantages.
The navigator must choose methods appropriate to each particular situation.
With the advent of automated position fixing and electronic charts, modern navigation is almost completely an electronic process. The mariner is constantly tempted to rely solely on electronic systems. This would be a mistake. Electronic navigation systems are always subject to failure, and the professional mariner must never forget that the safety of his ship and crew may depend on skills that differ little from those practiced generations ago. Proficiency in conventional piloting and celestial navigation remains essential.

*102. Phases Of Navigation*
Four distinct phases define the navigation process. The mariner should choose the system mix that meets the accuracy requirements of each phase.
&#8226;	Inland Waterway Phase: Piloting in narrow canals, channels, rivers, and estuaries.
&#8226;	Harbor/Harbor Approach Phase: Navigating to a harbor entrance and piloting in harbor approach channels.
&#8226;	Coastal Phase: Navigating within 50 miles of the coast or inshore of the 200 meter depth contour.
&#8226;	Ocean Phase: Navigating outside the coastal area in the open sea.
The navigator&#8217;s position accuracy requirements, his fix interval, and his systems requirements differ in each phase. The following table can be used as a general guide for selecting the proper system(s).










NAVIGATIONAL TERMS AND CONVENTIONS
*103. Important Conventions And Concepts*
Throughout the history of navigation, numerous terms and conventions have been established which enjoy worldwide recognition. The professional navigator, to gain a full understanding of his field, should understand the origin of certain terms, techniques, and conventions. The following section discusses some of the important ones.
Defining a prime meridian is a comparatively recent development. Until the beginning of the 19th century, there was little uniformity among cartographers as to the meridian from which to measure longitude. This did not lead to any problem because there was no widespread method for determining longitude accurately.
Ptolemy, in the 2nd century AD, measured longitude eastward from a reference meridian 2 degrees west of the Canary Islands. In 1493, Pope Alexander VI established a line in the Atlantic west of the Azores to divide the territories of Spain and Portugal. For many years, cartographers of these two countries used this dividing line as the prime meridian. In 1570 the Dutch cartographer Ortelius used the easternmost of the Cape Verde Islands. John Davis, in his 1594 The Seaman&#8217;s Secrets, used the Isle of Fez in the Canaries because there the variation was zero. Mariners paid little attention to these conventions and often reckoned their longitude from several different capes and ports during a voyage.
The meridian of London was used as early as 1676, and over the years its popularity grew as England&#8217;s maritime interests increased. The system of measuring longitude both east and west through 180&#61616;&#61472;may have first appeared in the middle of the 18th century. Toward the end of that century, as the Greenwich Observatory increased in prominence, English cartographers began using the meridian of that observatory as a reference. The publication by the Observatory of the first British Nautical Almanac in 1767 further entrenched Greenwich as the prime meridian. An unsuccessful attempt was made in 1810 to establish Washington, D.C. as the prime meridian for American navigators and cartographers. In 1884, the meridian of Greenwich was officially established as the prime meridian. Today, all maritime nations have designated the Greenwich meridian the prime meridian, except in a few cases where local references are used for certain harbor charts.
Charts are graphic representations of areas of the earth for use in marine or air navigation. Nautical charts depict features of particular interest to the marine navigator.
Charts have probably existed since at least 600 BC. Stereographic
and orthographic projections date from the 2nd century BC. In 1569 Gerardus Mercator published a chart using the mathematical principle which now bears his name. Some 30 years later, Edward Wright published corrected mathematical tables for this projection, enabling cartographers to produce charts on the Mercator projection. This projection is still widely in use.

Sailing directions or pilots have existed since at least the 6th century BC. Continuous accumulation of navigational data, along with increased exploration and trade, led to increased production of volumes through the Middle Ages. &#8220;Routiers&#8221; were produced in France about 1500; the English referred to them as &#8220;rutters.&#8221; In 1584 Lucas Waghenaer published the Spieghel der Zeevaerdt (The Mariner&#8217;s Mirror), which became the model for such publications for several generations of navigators. They were known as &#8220;Waggoners&#8221; by most sailors. Modern pilots and sailing directions are based on extensive data collection and compilation efforts begun by Matthew Fontaine Maury beginning in 1842.
The compass was developed about 1000 years ago. The origin of the magnetic compass is uncertain, but Norsemen used it in the 11th century. It was not until the 1870s that Lord Kelvin developed a reliable dry card marine compass. The fluid-filled compass became standard in 1906.
Variation was not understood until the 18th century, when Edmond Halley led an expedition to map lines of variation in the South Atlantic. Deviation was understood at least as early as the early 1600s, but correction of compass error was not possible until Matthew Flinders discovered that a vertical iron bar could reduce errors. After 1840, British Astronomer Royal Sir George Airy and later Lord Kelvin developed combinations of iron masses and small magnets to eliminate most magnetic compass error.
The gyrocompass was made necessary by iron and steel ships. Leon Foucault developed the basic gyroscope in 1852. An American (Elmer Sperry) and a German (Anshutz Kampfe) both developed electrical gyrocompasses in the early years of the 20th century.
The log is the mariner&#8217;s speedometer. Mariners originally measured speed by observing a chip of wood passing down the side of the vessel. Later developments included a wooden board attached to a reel of line. Mariners measured speed by noting how many knots in the line unreeled as the ship moved a measured amount of time; hence the term knot. Mechanical logs using either a small paddle wheel or a rotating spinner arrived about the middle of the 17th century. The taffrail log still in limited use today was developed in 1878. Modern logs use electronic sensors or spinning devices that induce small electric fields proportional to a vessel&#8217;s speed. An engine revolution counter or shaft log often measures speed onboard large ships. Doppler speed logs are used on some vessels for very accurate speed readings. Inertial and satellite systems also provide highly accurate speed readings.
The Metric Conversion Act of 1975 and the Omnibus Trade and Competitiveness Act of 1988 established the metric system of weights and measures in the United States. As a result, the government is converting charts to the metric format. Considerations of expense, safety of navigation, and logical sequencing will require a conversion effort spanning many years. Notwithstanding the conversion to the metric system, the common measure of distance at sea is the nautical mile.

The current policy of the Defense Mapping Agency Hydrographic/Topographic Center (DMAHTC) and the National Ocean Service (NOS) is to convert new compilations of nautical, special purpose charts, and publications to the metric system. This conversion began on January 2, 1970. Most modern maritime nations have also adopted the meter as the standard measure of depths and heights. However, older charts still on issue and the charts of some foreign countries may not conform to this standard. The fathom as a unit of length or depth is of obscure origin. Posidonius reported a sounding of more than 1,000 fathoms in the 2nd century BC. How old the unit was then is unknown. Many modern charts are still based on the fathom, as conversion to the metric system continues.

The sailings refer to various methods of mathematically determining course, distance, and position. They have a history almost as old as mathematics itself. Thales, Hipparchus, Napier, Wright, and others contributed the formulas that permit computation of course and distance by plane, traverse, parallel, middle latitude, Mercator, and great circle sailings.

*104.	The Earth*
The earth is an oblate spheroid (a sphere flattened at the poles). Measurements of its dimensions and the amount of its flattening are subjects of geodesy. However, for most navigational purposes, assuming a spherical earth introduces insignificant error. The earth&#8217;s axis of rotation is the line connecting the North Pole and the South Pole.

A great circle is the line of intersection of a sphere and a plane through its center. This is the largest circle that can be drawn on a sphere. The shortest line on the surface of a sphere between two points on the surface is part of a great circle. On the spheroidal earth the shortest line is called a geodesic. A great circle is a near enough approximation to a geodesic for most problems of navigation. A small circle is the line of intersection of a sphere and a plane which does not pass through the center. See Figure 104a.










The term meridian is usually applied to the upper branch of the half-circle from pole to pole which passes through a given point. The opposite half is called the lower branch. A parallel or parallel of latitude is a circle on the surface of the earth parallel to the plane of the equator. It connects all points of equal latitude. The equator is a great circle at latitude 0&#61616;. See Figure 104b. The poles are single points at latitude 90&#61616;. All other parallels are small circles.










*To Be Continued*


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## Fishers of Men

Take the test by George (Gju42486)

http://www.usboating.com/test.htm


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## Fishers of Men

*chapter 1 Navigation Continued*

*105.	Coordinates*
Coordinates, termed latitude and longitude, can define any position on earth. Latitude (L, lat.) is the angular distance from the equator, measured northward or southward along a meridian from 0&#61616;&#61472;at the equator to 90&#61616;&#61472;at the poles. It is designated north (N) or south (S) to indicate the direction of measurement.

The difference of latitude (l, DLat.) between two places is the angular length of arc of any meridian between their parallels. It is the numerical difference of the latitudes if the places are on the same side of the equator; it is the sum of the latitudes if the places are on opposite sides of the equator. It may be designated north (N) or south (S) when appropriate. The middle or mid-latitude (Lm) between two places on the same side of the equator is half the sum of their latitudes. Mid-latitude is labeled N or S to indicate whether it is north or south of the equator.

The expression may refer to the mid-latitude of two places on opposite sides of the equator. In this case, it is equal to half the difference between the two latitudes and takes the name of the place farthest from the equator. However, this usage is misleading because it lacks the significance usually associated with the expression. When the places are on opposite sides of the equator, two mid-latitudes are generally used. Calculate these two mid-latitudes by averaging each latitude and 0&#61616;.
Longitude (l, long.) is the angular distance between the prime meridian and the meridian of a point on the earth, measured eastward or westward from the prime meridian through 180&#61616;. It is designated east (E) or west (W) to indicate the direction of measurement.

The difference of longitude (DLo) between two places is the shorter arc of the parallel or the smaller angle at the pole between the meridians of the two places. If both places are on the same side (east or west) of Greenwich, DLo is the numerical difference of the longitudes of the two places; if on opposite sides, DLo is the numerical sum unless this exceeds 180&#61616;, when it is 360&#61616;&#61472;minus the sum. The distance between two meridians at any parallel of latitude, expressed in distance units, usually nautical miles, is called departure (p, Dep.). It represents distance made good east or west as a craft proceeds from one point to another. Its numerical value between any two meridians decreases with increased latitude, while DLo is numerically the same at any latitude. Either DLo or p may be designated east (E) or west (W) when appropriate.

*106.	Distance On The Earth*
Distance, as used by the navigator, is the length of the rhumb line connecting two places. This is a line making the same angle with all meridians. Meridians and parallels which also maintain constant true directions may be considered special cases of the rhumb line. Any other rhumb line spirals toward the pole, forming a loxodromic curve or loxodrome.










Distance along the great circle connecting two points is customarily designated great-circle distance. For most purposes, considering the nautical mile the length of one minute of latitude introduces no significant error.
Speed (S) is rate of motion, or distance per unit of time.

A knot (kn.), the unit of speed commonly used in navigation, is a rate of 1 nautical mile per hour. The expression speed of advance (SOA) is used to indicate the speed to be made along the intended track. Speed over the ground (SOG) is the actual speed of the vessel over the surface of the earth at any given time. To calculate speed made good (SMG) between two positions, divide the distance between the two positions by the time elapsed between the two positions.

*107.	Direction On The Earth*
Direction is the position of one point relative to another. Navigators express direction as the angular difference in degrees from a reference direction, usually north or the ship&#8217;s head. Course (C, Cn) is the horizontal direction in which a vessel is steered or intended to be steered, expressed as angular distance from north clockwise through 360&#61616;. Strictly used, the term applies to direction through the water, not the direction intended to be made good over the ground.

The course is often designated as true, magnetic, compass, or grid according to the reference direction. Track made good (TMG) is the single resultant direction from the point of departure to point of arrival at any given time. Course of advance (COA) is the direction intended to be made good over the ground, and course over ground (COG) is the direction between a vessel&#8217;s last fix and an EP. A course line is a line drawn on a chart extending in the direction of a course. It is sometimes convenient to express a course as an angle from either north or south, through 90&#61616;&#61472;or 180&#61616;. In this case it is designated course angle &#169; and should be properly labeled to indicate the origin (prefix) and direction of measurement (suffix). Thus, C N35&#61616;E = Cn 035&#61616;&#61472;(000&#61616;&#61472;+ 35&#61616, C N155&#61616;W = Cn 205&#61616;&#61472;(360&#61616;&#61472;- 155&#61616, C S47&#61616;E = Cn 133&#61616;&#61472;(180&#61616;&#61472;- 47&#61616. But Cn 260&#61616;&#61472;may be either C N100&#61616;W or C S80&#61616;W, depending upon the conditions of the problem.

Track (TR) is the intended horizontal direction of travel with respect to the earth. The terms intended track and trackline are used to indicate the path of intended travel. See Figure 107a. The track consists of one or a series of course lines, from the point of departure to the destination, along which it is intended to proceed. A great circle which a vessel intends to follow is called a great-circle track, though it consists of a series of straight lines approximating a great circle.










Heading (Hdg., SH) is the direction in which a vessel is pointed, expressed as angular distance from 000&#61616;&#61472;clockwise through 360&#61616;. *Do not confuse heading and course.*
Heading constantly changes as a vessel yaws back and forth across the course due to sea, wind, and steering error.

Bearing (B, Brg.) is the direction of one terrestrial
point from another, expressed as angular distance from 000&#61616;&#61472;(North) clockwise through 360&#61616;. When measured through 90&#61616;&#61472;or 180&#61616;&#61472;from either north or south, it is called bearing angle (B). Bearing and azimuth are sometimes used interchangeably, but the latter more accurately refers to the horizontal direction of a point on the celestial sphere from a point on the earth. A relative bearing is measured relative to the ship&#8217;s heading from 000&#61616;&#61472;(dead ahead) clockwise through 360&#61616;. However, it is sometimes conveniently measured right or left from 0&#61616;&#61472;at the ship&#8217;s head through 180&#61616;. This is particularly true when using the table for Distance of an Object by Two Bearings.
To convert a relative bearing to a true bearing, add the true heading:
True Bearing = Relative Bearing + True Heading.
Relative Bearing = True Bearing &#8211; True Heading.

*DEVELOPMENT OF NAVIGATION
108.	Latitude And Longitude Determination*
Navigators have made latitude observations for thousands of years. Accurate sun declination tables have been published for centuries, enabling experienced seamen to compute latitude to within 1 or 2 degrees. Mariners still use meridian observations of the sun and highly refined ex-meridian techniques. Those who today determine their latitude by measuring the altitude of Polaris are using a method well known to 15th century navigators.

*A method of finding longitude eluded mariners for centuries.* Several solutions independent of time proved too cumbersome. The lunar distance method, which determines GMT by observing the moon&#8217;s position among the stars, became popular in the 1800s. However, the mathematics required by most of these processes were far above the abilities of the average seaman. It was apparent that the solution lay in keeping accurate time at sea.
In 1714, the British Board of Longitude was formed, offering a small fortune in reward to anyone who could provide a solution to the problem.
An Englishman, John Harrison, responded to the challenge, developing four chronometers between 1735 and 1760. The most accurate of these timepieces lost only 15 seconds on a 156 day round trip between London and Barbados. The Board, however, paid him only half the promised reward. The King finally intervened on Harrison&#8217;s behalf, and Harrison received his full reward of &#163;20,000 at the advanced age of 80.

Rapid chronometer development led to the problem of determining chronometer error aboard ship. Time balls, large black spheres mounted in port in prominent locations, were dropped at the stroke of noon, enabling any ship in harbor which could see the ball to determine chronometer error. By the end of the U.S. Civil War, telegraph signals were being used to key time balls. Use of radio signals to send time ticks to ships well offshore began in 1904, and soon worldwide signals were available.










http://s202.photobucket.com/albums/aa305/FishersofMen/?action=view&current=fig107b.jpg

*109.	The Navigational Triangle*
Modern celestial navigators reduce their celestial observations by solving a navigational triangle whose points are the elevated pole, the celestial body, and the zenith of the observer. The sides of this triangle are the polar distance of the body (codeclination), its zenith distance (coaltitude), and the polar distance of the zenith (colatitude of the observer). A spherical triangle was first used at sea in solving lunar distance problems. Simultaneous observations were made of the altitudes of the moon and the sun or a star near the ecliptic and the angular distance between the moon and the other body. The zenith of the observer and the two celestial bodies formed the vertices of a triangle whose sides were the two coaltitudes and the angular distance between the bodies. Using a mathematical calculation the navigator &#8220;cleared&#8221; this distance of the effects of refraction and parallax applicable to each altitude. This corrected value was then used as an argument for entering the almanac. The almanac gave the true lunar distance from the sun and several stars at 3 hour intervals. Previously, the navigator had set his watch or checked its error and rate with the local mean time determined by celestial observations. The local mean time of the watch, properly corrected, applied to the Greenwich mean time obtained from the lunar distance observation, gave the longitude.

The calculations involved were tedious. Few mariners could solve the triangle until Nathaniel Bowditch published his simplified method in 1802 in The New American Practical Navigator.

Reliable chronometers were available in 1802, but their high cost precluded their general use aboard most ships. However, most navigators could determine their longitude using Bowditch&#8217;s method. This eliminated the need for parallel sailing and the lost time associated with it. Tables for the lunar distance solution were carried in the American nautical almanac until the second decade of the 20th century.

*110.	The Time Sight*
The theory of the time sight had been known to mathematicians since the development of spherical trigonometry, but not until the chronometer was developed could it be used by mariners.
The time sight used the modern navigational triangle. The codeclination, or polar distance, of the body could be determined from the almanac. The zenith distance (coaltitude) was determined by observation. If the colatitude were known, three sides of the triangle were available. From these the meridian angle was computed. The comparison of this with the Greenwich hour angle from the almanac yielded the longitude. The time sight was mathematically sound, but the navigator was not always aware that the longitude determined was only as accurate as the latitude, and together they merely formed a point on what is known today as a line of position. If the observed body was on the prime vertical, the line of position ran north and south and a small error in latitude generally had little effect on the longitude. But when the body was close to the meridian, a small error in latitude produced a large error in longitude. The line of position by celestial observation was unknown until discovered in 1837 by 30-year-old Captain Thomas H. Sumner, a Harvard graduate and son of a United States congressman from Massachusetts. The discovery of the &#8220;Sumner line,&#8221; as it is sometimes called, was considered by Maury &#8220;the commencement of a new era in practical navigation.&#8221; This was the turning point in the development of modern celestial navigation technique. In Sumner&#8217;s own words, the discovery took place in this manner:

Having sailed from Charleston, S. C., 25th November, 1837, bound to Greenock, a series of heavy gales from the Westward promised a quick passage; after passing the Azores, the wind prevailed from the Southward, with thick weather; after passing Longitude 21&#61616;&#61472;W, no observation was had until near the land; but soundings were had not far, as was supposed, from the edge of the Bank. The weather was now more boisterous, and very thick; and the wind still Southerly; arriving about midnight, 17th December, within 40 miles, by dead reckoning, of Tusker light; the wind hauled SE, true, making the Irish coast a lee shore; the ship was then kept close to the wind, and several tacks made to preserve her position as nearly as possible until daylight; when nothing being in sight, she was kept on ENE under short sail, with heavy gales; at about 10 AM an altitude of the sun was observed, and the Chronometer time noted; but, having run so far without any observation, it was plain the Latitude by dead reckoning was liable to error, and could not be entirely relied on. Using, however, this Latitude, in finding the Longitude by Chronometer, it was found to put the ship 15&#8217; of Longitude E from her position by dead reckoning; which in Latitude 52&#61616;&#61472;N is 9 nautical miles; this seemed to agree tolerably well with the dead reckoning; but feeling doubtful of the Latitude, the observation was tried with a Latitude 10&#8217; further N, finding this placed the ship ENE 27 nautical miles, of the former position, it was tried again with a Latitude 20&#8217; N of the dead reckoning; this also placed the ship still further ENE, and still 27 nautical miles further; these three positions were then seen to lie in the direction of Small&#8217;s light.
It then at once appeared that the observed altitude must have happened at all the three points, and at Small&#8217;s light, and at the ship, at the same instant of time; and it followed, that Small&#8217;s light must bear ENE, if the Chronometer was right. Having been convinced of this truth, the ship was kept on her course, ENE, the wind being still SE., and in less than an hour, Small&#8217;s light was made bearing ENE &#189; E, and close aboard.

In 1843 Sumner published a book, A New and Accurate Method of Finding a Ship&#8217;s Position at Sea by Projection on Mercator&#8217;s Chart. He proposed solving a single time sight twice, using latitudes somewhat greater and somewhat less than that arrived at by dead reckoning, and joining the two positions obtained to form the line of position.

The Sumner method required the solution of two time sights to obtain each line of position. Many older navigators preferred not to draw the lines on their charts, but to fix their position mathematically by a method which Sumner had also devised and included in his book. This was a tedious but popular procedure.

*To Be Continued*


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## Fishers of Men

*ch 1 nav Continued

111.	Navigational Tables*
Spherical trigonometry is the basis for solving every navigational triangle, and until about 80 years ago the navigator had no choice but to solve each triangle by tedious, manual computations.
Lord Kelvin, generally considered the father of modern navigational methods, expressed interest in a book of tables with which a navigator could avoid tedious trigonometric solutions. However, solving the many thousands of triangles involved would have made the project too costly. Computers finally provided a practical means of preparing tables. In 1936 the first volume of Pub. No. 214 was made available; later, Pub. No. 249 was provided for air navigators. Pub. No. 229, Sight Reduction Tables for Marine Navigation, has replaced Pub. No. 214. Modern calculators are gradually replacing the tables.

Scientific calculators with trigonometric functions can easily solve the navigational triangle. Navigational calculators readily solve celestial sights and perform a variety of voyage planning functions. Using a calculator generally gives more accurate lines of position because it eliminates the rounding errors inherent in tabular inspection and interpolation.

*112.	Electronics And Navigation*
Perhaps the first application of electronics to navigation involved sending telegraphic time signals in 1865 to check chronometer error. Transmitting radio time signals for at sea chronometer checks dates to 1904.










http://s202.photobucket.com/albums/aa305/FishersofMen/?action=view&current=fig110.jpg

Radio broadcasts providing navigational warnings, begun in 1907 by the U.S. Navy Hydrographic Office, helped increase the safety of navigation at sea.
By the latter part of World War I the directional properties of a loop antenna were successfully used in the radio direction finder. The first radiobeacon was installed in 1921. Early 20th century experiments by Behm and Langevin led to the U.S. Navy&#8217;s development of the first practical echo sounder in 1922.

Today, electronics touches almost every aspect of navigation. Hyperbolic systems, satellite systems, and electronic charts all require an increasingly sophisticated electronics suite. These systems&#8217; accuracy and ease of use make them invaluable assets to the navigator. Indeed, it is no exaggeration to state that, with the advent of the electronic chart and differential GPS, the mariner will soon be able to navigate from port to port using electronic navigation equipment alone.

*113.	Development Of Radar*
As early as 1904, German engineers were experimenting with reflected radio waves. In 1922 two American scientists, Dr. A. Hoyt Taylor and Leo C. Young, testing a communication system at the Naval Aircraft Radio Laboratory, noted fluctuations in the signals when ships passed between stations on opposite sides of the Potomac River. In 1935 the British began work on radar. In 1937 the USS Leary tested the first seagoing radar. In 1940 United States and British scientists combined their efforts. When the British revealed the principle of the multicavity magnetron developed by J. T. Randall and H. A. H. Boot at the University of Birmingham in 1939, microwave radar became practical. In 1945, at the close of World War II, radar became available for commercial use.

*114.	Development Of Hyperbolic Radio Aids*
Various hyperbolic systems were developed from World War II, including Loran A. This was replaced by the more accurate Loran C system in use today. Using very low frequencies, the Omega navigation system provides worldwide, though less accurate, coverage for a variety of applications including marine navigation. Various short range and regional hyperbolic systems have been developed by private industry for hydrographic surveying, offshore facilities positioning, and general navigation.

*115.	Other Electronic Systems*
The Navy Navigation Satellite System (NAVSAT) fulfilled a requirement established by the Chief of Naval Operations for an accurate worldwide navigation system for all naval surface vessels, aircraft, and submarines. The system was conceived and developed by the Applied Physics Laboratory of The Johns Hopkins University. The underlying concept that led to development of satellite navigation dates to 1957 and the first launch of an artificial satellite into orbit.

*NAVSAT has been replaced by the far more accurate and widely available Global Positioning System (GPS).*

The first inertial navigation system was developed in 1942 for use in the V2 missile by the Peenemunde group under the leadership of Dr. Wernher von Braun. This system used two 2-degree-of-freedom gyroscopes and an integrating accelerometer to determine the missile velocity. By the end of World War II, the Peenemunde group had developed a stable platform with three single-degree-of-freedom gyroscopes and an integrating accelerometer. In 1958 an inertial navigation system was used to navigate the USS Nautilus under the ice to the North Pole.

*NAVIGATION ORGANIZATIONS
116.	Governmental Roles*
Navigation only a generation ago was an independent process, carried out by the mariner without outside assistance. *With compass and charts, sextant and chronometer, he could independently travel anywhere in the world.* *The increasing use of electronic navigation systems has made the navigator dependent on many factors outside his control. * Government organizations fund, operate, and regulate satellites, Loran, and other electronic systems. Governments are increasingly involved in regulation of vessel movements through traffic control systems and regulated areas. Understanding the governmental role in supporting and regulating navigation is vitally important to the mariner. In the United States, there are a number of official organizations which support the interests of navigators. Some have a policy-making role; others build and operate navigation systems. Many maritime nations have similar organizations performing similar functions. International organizations also play a significant role.

*The U.S. Coast and Geodetic * Survey was founded in
1807 when Congress passed a resolution authorizing a survey of the coast, harbors, outlying islands, and fishing banks of the United States. President Thomas Jefferson appointed Ferdinand Hassler, a Swiss immigrant and professor of mathematics at West Point, the first Director of the &#8220;Survey of the Coast.&#8221; The survey became the &#8220;Coast Survey&#8221; in 1836.
The approaches to New York were the first sections of the coast charted, and from there the work spread northward and southward along the eastern seaboard. In 1844 the work was expanded and arrangements made to chart simultaneously the gulf and east coasts. Investigation of tidal conditions began, and in 1855 the first tables of tide predictions were published. The California gold rush necessitated a survey of the west coast. This survey began in 1850, the year California became a state. Coast Pilots, or Sailing Directions, for the Atlantic coast of the United States were privately published in the first half of the 19th century. In 1850 the Survey began accumulating data that led to federally produced Coast Pilots. The 1889 Pacific Coast Pilot was an outstanding contribution to the safety of west coast shipping.

In 1878 the survey was renamed &#8220;Coast and Geodetic Survey.&#8221; In 1970 the survey became the &#8220;National Ocean Survey,&#8221; and in 1983 it became the &#8220;National Ocean Service.&#8221; The Office of Charting and Geodetic Services accomplished all charting and geodetic functions. In 1991 the name was changed back to the original &#8220;Coast and Geodetic Survey,&#8221; organized under the National Ocean Service along with several other environmental offices. Today it provides the mariner with the charts and coast pilots of all waters of the United States and its possessions, and tide and tidal current tables for much of the world. Its administrative order requires the Coast and Geodetic Survey to plan and direct programs to produce charts and related information for safe navigation of the Nation&#8217;s waterways, territorial seas, and national airspace. This work includes all activities related to the National Geodetic Reference System; surveying, charting, and data collection; production and distribution of charts; and research and development of new technologies to enhance these missions.
*
118.	The Defense Mapping Agency*
In the first years of the newly formed United States of America, charts and instruments used by the Navy and merchant mariners were left over from colonial days or were obtained from European sources. In 1830 the U.S. Navy established a &#8220;Depot of Charts and Instruments&#8221; in Washington, D. C. It was a storehouse from which available charts, sailing directions, and navigational instruments were issued to Naval ships. Lieutenant L. M. Goldsborough and one assistant, Passed Midshipman R. B. Hitchcock, constituted the entire staff.

The first chart published by the Depot was produced from data obtained in a survey made by Lieutenant Charles Wilkes, who had succeeded Goldsborough in 1834. Wilkes later earned fame as the leader of a United States expedition to Antarctica. From 1842 until 1861 Lieutenant Matthew Fontaine Maury served as Officer in Charge. Under his command the Depot rose to international prominence. Maury decided upon an ambitious plan to increase the mariner&#8217;s knowledge of existing winds, weather, and currents. He began by making a detailed record of pertinent matter included in old log books stored at the Depot. He then inaugurated a hydrographic reporting program among shipmasters, and the thousands of reports received, along with the log book data, were compiled into the &#8220;Wind and Current Chart of the North Atlantic&#8221; in 1847. This is the ancestor of today&#8217;s Pilot Chart. The United States instigated an international conference in 1853 to interest other nations in a system of exchanging nautical information. The plan, which was Maury&#8217;s, was enthusiastically adopted by other maritime nations. In 1854 the Depot was redesignated the &#8220;U.S. Naval Observatory and Hydrographical Office.&#8221; In 1861, Maury, a native of Virginia, resigned from the U.S. Navy and accepted a commission in the Confederate Navy at the beginning of the Civil War. This effectively ended his career as a navigator, author, and oceanographer. At war&#8217;s end, he fled the country. Maury&#8217;s reputation suffered from his embracing the Confederate cause. In 1867, while Maury was still absent from the country to avoid arrest for treason, George W. Blunt, an editor of hydrographic publications, wrote:
In mentioning what our government has done towards nautical knowledge, I do not allude to the works of Lieutenant Maury, because I deem them worthless. . . . They have been suppressed since the rebellion by order of the proper authorities, Maury&#8217;s loyalty and hydrography being alike in quality.

After Maury&#8217;s return to the United States in 1868, he served as an instructor at the Virginia Military Institute. He continued at this position until his death in 1873. Since his death, his reputation as one of America&#8217;s greatest hydrographers has been restored.

In 1866 Congress separated the Observatory and the Hydrographic Office, broadly increasing the functions of the latter. The Hydrographic Office was authorized to carry out surveys, collect information, and print every kind of nautical chart and publication &#8220;for the benefit and use of navigators generally.&#8221;

The Hydrographic Office purchased the copyright of The New American Practical Navigator in 1867. The first Notice to Mariners appeared in 1869. Daily broadcast of navigational warnings was inaugurated in 1907. In 1912, following the sinking of the Titanic, the International Ice Patrol was established.

In 1962 the U.S. Navy Hydrographic Office was redesignated the U.S. Naval Oceanographic Office. In 1972 certain hydrographic functions of the latter office were transferred to the Defense Mapping Agency Hydrographic Center. In 1978 the Defense Mapping Agency Hydrographic/Topographic Center (DMAHTC) assumed hydrographic and topographic chart production functions.

DMAHTC provides support to the U.S. Department of Defense and other federal agencies on matters concerning mapping, charting, and geodesy. It continues to fulfill the old Hydrographic Office&#8217;s responsibilities to &#8220;navigators generally.&#8221;

*119.	The United States Coast Guard*
Alexander Hamilton established the U.S. Coast
Guard as the Revenue Marine, later the Revenue Cutter Service, on August 4, 1790. It was charged with enforcing the customs laws of the new nation. A revenue cutter, the Harriet Lane, fired the first shot from a naval unit in the Civil War at Fort Sumter. The Revenue Cutter Service became the U.S. Coast Guard when combined with the Lifesaving Service in 1915. The Lighthouse Service was added in 1939, and the Bureau of Marine Inspection and Navigation was added in 1942. The Coast Guard was transferred from the Treasury Department to the Department of Transportation in 1967.
The primary functions of the Coast Guard include maritime search and rescue, law enforcement, and operation of the nation&#8217;s aids to navigation system. In addition, the Coast Guard is responsible for port safety and security, merchant marine inspection, and marine pollution control. The Coast Guard operates a large and varied fleet of ships, boats, and aircraft in performing its widely ranging duties. Navigation systems operated by the Coast Guard include the system of some 40,000 lighted and unlighted beacons, buoys, and ranges in U.S. waters; the U.S. stations of the Loran C system; the Omega navigation system; radiobeacons and racons; differential GPS (DGPS) services in the U.S.; and Vessel Traffic Services (VTS) in major ports and harbors of the U.S.

*To Be Continued*


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## Fishers of Men

*Okay, this is the last part of the introduction ch 1.

120.	The United States Navy*
The U.S. Navy was officially established in 1798. Its role in the development of navigational technology has been singular. From the founding of the Naval Observatory to the development of the most advanced electronics, the U.S. Navy has been a leader in developing devices and techniques designed to make the navigators job safer and easier. The development of almost every device known to navigation science has been deeply influenced by Naval policy. Some systems are direct outgrowths of specific Naval needs; some are the result of technological improvements shared with other services and with commercial maritime industry.

*121.	The United States Naval Observatory*
One of the first observatories in the United States was built in 1831-1832 at Chapel Hill, N.C. The Depot of Charts and Instruments, established in 1830, was the agency from which the U.S. Navy Hydrographic Office and the U.S. Naval Observatory evolved 36 years later. Under Lieutenant Charles Wilkes, the second Officer in Charge, the Depot about 1835 installed a small transit instrument for rating chronometers.

The Mallory Act of 1842 provided for the establishment of a permanent observatory. The director was authorized to purchase everything necessary to continue astronomical study. The observatory was completed in 1844 and the results of its first observations were published two years later. Congress established the Naval Observatory as a separate agency in 1866. In 1873 a refracting telescope with a 26 inch aperture, then the worlds largest, was installed.
The observatory, located in Washington, D.C., has occupied its present site since 1893.
*
122.	The Royal Greenwich Observatory*
England had no early privately supported observatories such as those on the continent. The need for navigational advancement was ignored by Henry VIII and Elizabeth I, but in 1675 Charles II, at the urging of John Flamsteed, Jonas Moore, Le Sieur de Saint Pierre, and Christopher Wren, established the Greenwich Royal Observatory. Charles limited construction costs to £500, and appointed Flamsteed the first Astronomer Royal, at an annual salary of £100. The equipment available in the early years of the observatory consisted of two clocks, a sextant of 7 foot radius, a quadrant of 3 foot radius, two telescopes, and the star catalog published almost a century before by Tycho Brahe. Thirteen years passed before Flamsteed had an instrument with which he could determine his latitude accurately.

In 1690 a transit instrument equipped with a telescope and vernier was invented by Romer; he later added a vertical circle to the device. This enabled the astronomer to determine declination and right ascension at the same time. One of these instruments was added to the equipment at Greenwich in 1721, replacing the huge quadrant previously used. The development and perfection of the chronometer in the next hundred years added to the accuracy of observations. Other national observatories were constructed in the years that followed: at Berlin in 1705, St. Petersburg in 1725, Palermo in 1790, Cape of Good Hope in 1820, Parramatta in New South Wales in 1822, and Sydney in 1855.
*
The International Hydrographic Organization*
(IHO) was originally established in 1921 as the International Hydrographic Bureau (IHB). The present name was adopted in 1970 as a result of a revised international agreement among member nations. However, the former name, International Hydrographic Bureau, was retained for the IHOs administrative body of three Directors and a small staff at the organizations headquarters in Monaco. The IHO sets forth hydrographic standards to be agreed upon by the member nations. All member states are urged and encouraged to follow these standards in their surveys, nautical charts, and publications. As these standards are uniformly adopted, the products of the worlds hydrographic and oceanographic offices become more uniform.
Much has been done in the field of standardization since the Bureau was founded.
The principal work undertaken by the IHO is:
	To bring about a close and permanent association between national hydrographic offices.
	To study matters relating to hydrography and allied sciences and techniques.
	To further the exchange of nautical charts and documents between hydrographic offices of member governments.
	To circulate the appropriate documents.
	To tender guidance and advice upon request, in particular to countries engaged in setting up or expanding their hydrographic service.
	To encourage coordination of hydrographic surveys with relevant oceanographic activities.
	To extend and facilitate the application of oceanographic knowledge for the benefit of navigators.
	To cooperate with international organizations and scientific institutions which have related objectives. During the 19th century, many maritime nations established hydrographic offices to provide means for improving the navigation of naval and merchant vessels by providing nautical publications, nautical charts, and other navigational services. There were substantial differences in hydrographic procedures, charts, and publications. In 1889, an International Marine Conference was held at Washington, D. C., and it was proposed to establish a permanent international commission. Similar proposals were made at the sessions of the International Congress of Navigation held at St. Petersburg in 1908 and again in 1912.

In 1919 the hydrographers of Great Britain and France cooperated in taking the necessary steps to convene an international conference of hydrographers. London was selected as the most suitable place for this conference, and on July 24, 1919, the First International Conference opened, attended by the hydrographers of 24 nations. The object of the conference was To consider the advisability of all maritime nations adopting similar methods in the preparation, construction, and production of their charts and all hydrographic publications; of rendering the results in the most convenient form to enable them to be readily used; of instituting a prompt system of mutual exchange of hydrographic information between all countries; and of providing an opportunity to consultations and discussions to be carried out on hydrographic subjects generally by the hydrographic experts of the world. This is still the major purpose of the International Hydrographic Organization. As a result of the conference, a permanent organization was formed and statutes for its operations were prepared. The International Hydrographic Bureau, now the International Hydrographic Organization, began its activities in 1921 with 18 nations as members. The Principality of Monaco was selected because of its easy communication with the rest of the world and also because of the generous offer of Prince Albert I of Monaco to provide suitable accommodations for the Bureau in the Principality. There are currently 59 member governments. Technical assistance with hydrographic matters is available through the IHO to member states requiring it.
Many IHO publications are available to the general public, such as the International Hydrographic Review, International Hydrographic Bulletin, Chart Specifications of the IHO, Hydrographic Dictionary, and others. Inquiries should be made to the International Hydrographic Bureau, 7 Avenue President J. F. Kennedy, B.P. 445, MC98011, Monaco, CEDEX.

*124.	The International Maritime Organization*
The International Maritime Organization (IMO)
was established by United Nations Convention in 1948. The Convention actually entered into force in 1959, although an international convention on marine pollution was adopted in 1954. (Until 1982 the official name of the organization was the Inter-Governmental Maritime Consultative Organization.) It is the only permanent body of the U. N. devoted to maritime matters, and the only special U. N. agency to have its headquarters in the UK.
The governing body of the IMO is the Assembly of 137 member states, which meets every two years. Between Assembly sessions a Council, consisting of 32 member governments elected by the Assembly, governs the organization.
Its work is carried out by the following committees:
	Maritime Safety Committee, with subcommittees for:
	Safety of Navigation
	Radiocommunications
	Life-saving
	Search and Rescue
	Training and Watchkeeping
	Carriage of Dangerous Goods
	Ship Design and Equipment
	Fire Protection
	Stability and Load Lines/Fishing Vessel Safety
	Containers and Cargoes
	Bulk Chemicals
	Marine Environment Protection Committee
	Legal Committee
	Technical Cooperation Committee
	Facilitation Committee
IMO is headed by the Secretary General, appointed by the council and approved by the Assembly. He is assisted by some 300 civil servants.
To achieve its objectives of coordinating international policy on marine matters, the IMO has adopted some 30 conventions and protocols, and adopted over 700 codes and recommendations. An issue to be adopted first is brought before a committee or subcommittee, which submits a draft to a conference. When the conference adopts the final text, it is submitted to member governments for ratification. Ratification by a specified number of countries is necessary for adoption; the more important the issue, the more countries must ratify. Adopted conventions are binding on member governments.
Codes and recommendations are not binding, but in most cases are supported by domestic legislation by the governments involved.
The first and most far-reaching convention adopted by
the IMO was the Convention of Safety of Life at Sea (SOLAS)
in 1960. This convention actually came into force in 1965, replacing a version first adopted in 1948. Because of the difficult process of bringing amendments into force internationally, none of subsequent amendments became binding. To remedy this situation, a new convention was adopted in 1974, and became binding in 1980. Among the regulations is V-20, requiring the carriage of up-to-date charts and publications sufficient for the intended voyage.

Other conventions and amendments were also adopted,
such as the International Convention on Load Lines (adopted
1966, came into force 1968), a convention on the tonnage
measurement of ships (adopted 1969, came into force 1982),
The International Convention on Safe Containers (adopted
1972, came into force 1977), and the convention on International
*Regulations for Preventing Collisions at Sea*
(COLREGS) (adopted 1972, came into force 1977). The 1972 COLREGS convention contained, among other provisions, a section devoted to Traffic Separation Schemes, which became binding on member states after having been adopted as recommendations in prior years.
One of the most important conventions is the International
Convention for the Prevention of Pollution from Ships
(MARPOL 73/78), which was first adopted in 1973, amended by Protocol in 1978, and became binding in 1983. This convention built on a series of prior conventions and agreements dating from 1954, highlighted by several severe pollution disasters involving oil tankers. The MARPOL convention reduces the amount of oil discharged into the sea by ships, and bans discharges completely in certain areas. A related convention known as the London Dumping Convention regulates dumping of hazardous chemicals and other debris into the sea. IMO also develops minimum performance standards for a wide range of equipment relevant to safety at sea.
Among such standards is one for the Electronic Chart Display
and Information System (ECDIS), the digital display deemed the operational and legal equivalent of the conventional paper chart.
Texts of the various conventions and recommendations, as well as a catalog and publications on other subjects, are available from the Publications Section of the IMO at 4 Albert Embankment, London SE1 7SR, United Kingdom.

*125.	The International Association Of Lighthouse*
Authorities
The International Association of Lighthouse Authorities
(IALA) brings together representatives of the aids to navigation services of more than 80 member countries for technical coordination, information sharing, and coordination of improvements to visual aids to navigation throughout the world. It was established in 1957 to provide a permanent organization to support the goals of the Technical Lighthouse Conferences, which had been convening since 1929. The General Assembly of IALA meets about every 4 years. The Council of 20 members meets twice a year to oversee the ongoing programs.
Five technical committees maintain the permanent
programs:
	The Marine Marking Committee
	The Radionavigation Systems Committee
	The Vessel Traffic Services (VTS) Committee
	The Reliability Committee
	The Documentation Committee
IALA committees provide important documentation to the IHO and other international organizations, while the IALA Secretariat acts as a clearing house for the exchange of technical information, and organizes seminars and technical support for developing countries.
Its principle work since 1973 has been the implementation of the IALA Maritime Buoyage System, described in Chapter 5, Visual Aids to Navigation. This system replaced some 30 dissimilar buoyage systems in use throughout the world with 2 major systems.
IALA is based near Paris, France in Saint-Germaineen-Laye.

*126.	The Radio Technical Commission for Maritime*
Services
The Radio Technical Commission for Maritime
Services is a non-profit organization which serves as a focal point for the exchange of information and the development of recommendations and standards related to all aspects of maritime telecommunications.
Specifically, RTCM:
	Promotes ideas and exchanges information on maritime telecommunications.
	Facilitates the development and exchange of views among government, business, and the public.
	Conducts studies and prepares reports on maritime telecommunications issues to improve efficiency and capabilities.
	Suggests minimum essential rules and regulations for effective telecommunications.
	Makes recommendations on important issues.
	Pursues other activities as permitted by its by-laws and membership.
Both government and non-government organizations are members, including many from foreign nations. The organization consists of a Board of Directors, the Assembly consisting of all Members, Officers, staff, technical advisors, and standing and special committees.
Working committees are formed as needed to develop official RTCM recommendations regarding technical standards and policies in the maritime field. Currently committees exist for maritime safety information, electronic charts, emergency position-indicating radiobeacons (EPIRBs) and personal locator beacons, survival craft telecommunications, differential GPS, and GLONASS. Ad hoc committees address short-term concerns such as regulatory proposals.
RTCM headquarters is in Washington D.C.

*127.	The National Marine Electronic Association*
The National Marine Electronic Association
(NMEA) is a professional trade association founded in 1957 whose purpose is to coordinate the efforts of marine electronics manufacturers, technicians, government agencies, ship and boat builders, and other interested groups. In addition to certifying marine electronics technicians and professionally recognizing outstanding achievements by corporate and individual members, the NMEA sets standards for the exchange of digital data by all manufacturers of marine electronic equipment. This allows the configuration of integrated navigation system using equipment from different manufacturers.
NMEA works closely with RTCM and other private organizations and with government agencies to monitor the status of laws and regulations affecting the marine electronics industry.
It also sponsors conferences and seminars, and publishes a number of guides and periodicals for members and the general public.

This the conclusion of chapter 1 introduction. Are we going on? Let me hear it.
*Lets go navigatin!*

*"And, behold the whole city came out to meet Jesus: and when they saw him, they besought him that he would depart out of there coasts." 
St.Matt 8:34 *


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## Fishers of Men

*Okay, here we go. Don't let some of these things confuse you, it will all come together as we move along. Out of everything we have discussed in this thread, bits and pieces apply to everyone everywhere, some more than others. Thanks and congats to those of you with the ambition to study these topics; The "forces" that surround us and apply to how it effects your boating/fishing. Take your time and enjoy.
*
*CHAPTER 2
GEODESY AND DATUMS IN NAVIGATION
GEODESY, THE BASIS OF CARTOGRAPHY*

200. Definition
Geodesy is the science concerned with the exact positioning of points on the surface of the earth. It also involves the study of variations of the earths gravity, the application
of these variations to exact measurements on the earth, and the study of the exact size and shape of the earth. These factors were unimportant to early navigators because of the relative inaccuracy of their methods. The precise accuracies of todays navigation systems and the global nature of satellite and other long-range positioning methods demand a more complete understanding of geodesy than has ever before been required.

201. The Shape Of The Earth

The irregular topographic surface is that upon which actual geodetic measurements are made. The measurements, however, are reduced to the geoid. Marine navigation measurements are made on the ocean surface which approximates the geoid.

The geoid is a surface along which gravity is always equal and to which the direction of gravity is always perpendicular.
The latter is particularly significant because optical instruments containing level devices are commonly used to make geodetic measurements. When properly adjusted, the vertical axis of the instrument coincides with the direction of gravity and is, therefore, perpendicular to the geoid.

The geoid is that surface to which the oceans would conform over the entire earth if free to adjust to the combined effect of the earths mass attraction and the centrifugal force of the earths rotation. The ideal ocean surface would be free of ocean currents and salinity changes. Uneven distribution of the earths mass makes the geoidal surface irregular.

The geoid refers to the actual size and shape of the earth, but such an irregular surface has serious limitations as a mathematical earth model because:
It has no complete mathematical expression.
Small variations in surface shape over time introduce small errors in measurement.
The irregularity of the surface would necessitate a prohibitive amount of computations.
Figure 201. (You can see here, another example of what I previously spoke about the curvature of the earth and distances for radios, radars and line of sight.)










The surface of the geoid, with some exceptions, tends to rise under mountains and to dip above ocean basins.
For geodetic, mapping, and charting purposes, it is necessary to use a regular or geometric shape which closely approximates the shape of the geoid either on a local or global scale and which has a specific mathematical expression.

This shape is called the ellipsoid.
The separations of the geoid and ellipsoid are called geoidal heights, geoidal undulations, or geoidal separations.

The irregularities in density and depths of the material making up the upper crust of the earth also result in slight alterations of the direction of gravity. These alterations are reflected in the irregular shape of the geoid, the surface that is perpendicular to a plumb line.

Since the earth is in fact flattened slightly at the poles and bulges somewhat at the equator, the geometric figure used in geodesy to most nearly approximate the shape of the earth is the oblate spheroid or ellipsoid of revolution. This is the three dimensional shape obtained by rotating an ellipse about its minor axis.

202. Defining The Ellipsoid
An ellipsoid of revolution is uniquely defined by specifying two parameters. Geodesists, by convention, use the semimajor axis and flattening. The size is represented by the radius at the equator, the semimajor axis. The shape of the ellipsoid is given by the flattening, which indicates how closely an ellipsoid approaches a spherical shape. The flattening is the ratio of the difference between the semimajor and semiminor axes of the ellipsoid and the semimajor axis.

See Figure 202. If a and b represent the semimajor and semiminor axes, respectively, of the ellipsoid, and f is the flattening.
This ratio is about 1/300 for the earth.










The ellipsoidal earth model has its minor axis parallel to the earths polar axis.

203. Ellipsoids And The Geoid As Reference Surfaces

Since the surface of the geoid is irregular and the surface of the ellipsoid is regular, no one ellipsoid can provide other than an approximation of part of the geoidal surface.

Figure 203 illustrates an example. The ellipsoid that fits well in North America does not fit well in Europe; therefore, it must be positioned differently.










A number of reference ellipsoids are used in geodesy and mapping because an ellipsoid is mathematically simpler than the geoid.

204. Coordinates
The astronomic latitude is the angle between the plumb line at a station and the plane of the celestial equator.
It is the latitude which results directly from observations of celestial bodies, uncorrected for deflection of the vertical component in the meridian (north-south) direction. Astronomic latitude applies only to positions on the earth. It is reckoned from the astronomic equator (0&#61616, north and south through 90&#61616;.

The astronomic longitude is the angle between the plane of the celestial meridian at a station and the plane of the celestial meridian at Greenwich. It is the longitude which results directly from observations of celestial bodies, uncorrected for deflection of the vertical component in the prime vertical (east-west) direction. These are the coordinates observed by the celestial navigator using a sextant and a very accurate clock based on the earths rotation.

Astronomic observations by geodesists are made with optical instruments (theodolite, zenith camera, prismatic astrolabe) which all contain leveling devices. When properly adjusted, the vertical axis of the instrument coincides with the direction of gravity, and is, therefore, perpendicular to the geoid. Thus, astronomic positions are referenced to the geoid. Since the geoid is an irregular, non-mathematical surface, astronomic positions are wholly independent of each other.

The geodetic latitude is the angle which the normal to the ellipsoid at a station makes with the plane of the geodetic equator. In recording a geodetic position, it is essential that the geodetic datum on which it is based be also stated.

A geodetic latitude differs from the corresponding astronomic latitude by the amount of the meridian component of the local deflection of the vertical.

The geodetic longitude is the angle between the plane of the geodetic meridian at a station and the plane of the geodetic meridian at Greenwich. A geodetic longitude differs from the corresponding astronomic longitude by the prime vertical component of the local deflection of the vertical divided by the cosine of the latitude. The geodetic coordinates are used for mapping.

The geocentric latitude is the angle at the center of the ellipsoid (used to represent the earth) between the plane of the equator, and a straight line (or radius vector) to a point on the surface of the ellipsoid. This differs from geodetic latitude because the earth is approximated more closely by a spheroid than a sphere and the meridians are ellipses, not perfect circles.

Both geocentric and geodetic latitudes refer to the reference ellipsoid and not the earth. Since the parallels of latitude are considered to be circles, geodetic longitude is geocentric, and a separate expression is not used.
Because of the oblate shape of the ellipsoid, the length of a degree of geodetic latitude is not everywhere the same, increasing from about 59.7 nautical miles at the equator to about 60.3 nautical miles at the poles.
A horizontal geodetic datum usually consists of the astronomic and geodetic latitude, and astronomic and geodetic longitude of an initial point (origin); an azimuth of a line (direction); the parameters (radius and flattening) of the ellipsoid selected for the computations; and the geoidal separation at the origin. A change in any of these quantities affects every point on the datum.

For this reason, while positions within a given datum are directly and accurately relateable, those from different datums must be transformed to a common datum for consistency.

*"He stretcheth out the north over the empty space, and hangeth the earth upon nothing" Job 26:7 (Longitude) *

To Be Continued


----------



## Fishers of Men

*ch2 cont.

TYPES OF GEODETIC SURVEY

205. Triangulation*
The most common type of geodetic survey is known as triangulation. Triangulation consists of the measurement of the angles of a series of triangles. The principle of triangulation is based on plane trigonometry. If the distance along one side of the triangle and the angles at each end are
accurately measured, the other two sides and the remaining angle can be computed. In practice, all of the angles of every triangle are measured to provide precise measurements.

Also, the latitude and longitude of one end of the measured side along with the length and direction (azimuth) of the side provide sufficient data to compute the latitude and longitude of the other end of the side.

The measured side of the base triangle is called a baseline.
Measurements are made as carefully and accurately as possible with specially calibrated tapes or wires of Invar, an alloy highly resistant to changes in length resulting from changes in temperature. The tape or wires are checked periodically against standard measures of length.

To establish an arc of triangulation between two widely separated locations, the baseline may be measured and longitude and latitude determined for the initial points at each location. The lines are then connected by a series of
adjoining triangles forming quadrilaterals extending from each end. All angles of the triangles are measured repeatedly to reduce errors. With the longitude, latitude, and azimuth of the initial points, similar data is computed for each vertex of the triangles, thereby establishing triangulation stations, or geodetic control stations. The coordinates of each of the stations are defined as geodetic coordinates.

Triangulation is extended over large areas by connecting
and extending series of arcs to form a network or triangulation system. The network is adjusted in a manner which reduces the effect of observational errors to a minimum.

A denser distribution of geodetic control is achieved in a system by subdividing or filling in with other surveys.

There are four general classes or orders of triangulation.
First-order (primary) triangulation is the most precise and exact type. The most accurate instruments and rigorous computation methods are used. It is costly and time-consuming, and is usually used to provide the basic framework of control data for an area, and the determination of the figure
of the earth. The most accurate first-order surveys furnish control points which can be interrelated with an accuracy ranging from 1 part in 25,000 over short distances to approximately 1 part in 100,000 for long distances.

Second-order triangulation furnishes points closer together than in the primary network. While second-order surveys may cover quite extensive areas, they are usually tied to a primary system where possible. The procedures are less exacting and the proportional error is 1 part in 10,000.

Third-order triangulation is run between points in a secondary survey. It is used to densify local control nets and position the topographic and hydrographic detail of the area.

Triangle error can amount to 1 part in 5,000.
The sole accuracy requirement for fourth-order triangulation is that the positions be located without any appreciable error on maps compiled on the basis of the control.

Fourth-order control is done primarily as mapping control.

206. Trilateration, Traverse, And Vertical Surveying
Trilateration involves measuring the sides of a chain of triangles or other polygons. From them, the distance and direction from A to B can be computed. Figure 206 shows this process.










Traverse involves measuring distances and the angles between them without triangles for the purpose of computing the distance and direction from A to B. See Figure 206.

Vertical surveying is the process of determining elevations above mean sea-level. In geodetic surveys executed primarily for mapping, geodetic positions are referred to an ellipsoid, the elevations of the positions are referred to the geoid. However, for satellite geodesy the geoidal heights must
be considered to establish the correct height above the geoid.

Precise geodetic leveling is used to establish a basic network of vertical control points. From these, the height of other positions in the survey can be determined by supplementary methods. The mean sea-level surface used as a
reference (vertical datum) is determined by averaging the hourly water heights for a specified period of time at specified tide gauges.

There are three leveling techniques: differential, trigonometric, and barometric. Differential leveling is the most accurate of the three methods. With the instrument locked in position, readings are made on two calibrated
staffs held in an upright position ahead of and behind the instrument.

The difference between readings is the difference in elevation between the points.

Trigonometric leveling involves measuring a vertical angle from a known distance with a theodolite and computing the elevation of the point. With this method, vertical measurement can be made at the same time horizontal angles are measured for triangulation. It is, therefore, a somewhat more economical method but less accurate than differential leveling. It is often the only practical method of establishing accurate elevation control in mountainous areas.

In barometric leveling, differences in height are determined by measuring the differences in atmospheric pressure at various elevations. Air pressure is measured by mercurial or aneroid barometer, or a boiling point thermometer. Although the accuracy of this method is not as great as either of the other two, it obtains relative heights very rapidly at points which are fairly far apart. It is used in reconnaissance and exploratory surveys where more accurate measurements will be made later or where a high degree of accuracy is not required.










207. Definitions
A datum is defined as any numerical or geometrical quantity or set of such quantities which serves as a reference point to measure other quantities.
In geodesy, as well as in cartography and navigation, two types of datums must be considered: a horizontal datum and a vertical datum. The horizontal datum forms the basis for computations of horizontal position. The vertical datum provides the reference to measure heights. A horizontal datum may be defined at an origin point on the ellipsoid (local datum) such that the center of the ellipsoid coincides with the Earth&#8217;s center of mass (geocentric datum). The coordinates for points in specific geodetic surveys and triangulation networks are computed from certain initial quantities, or datums.

208. Preferred Datums
In areas of overlapping geodetic triangulation networks, each computed on a different datum, the coordinates of the points given with respect to one datum will differ from those given with respect to the other. The differences can be used to derive transformation formulas. Datums are connected by developing transformation formulas at common points, either between overlapping control networks or by satellite connections.

Many countries have developed national datums which differ from those of their neighbors. Accordingly, national maps and charts often do not agree along national borders.

The North American Datum, 1927 (NAD 27) has been used in the United States for about 50 years, but it is being replaced by datums based on the World Geodetic System.

NAD 27 coordinates are based on the latitude and longitude of a triangulation station (the reference point) at Mead&#8217;s Ranch in Kansas, the azimuth to a nearby triangulation station called Waldo, and the mathematical parameters of the Clarke Ellipsoid of 1866. Other datums throughout the world use different
assumptions as to origin points and ellipsoids.

The origin of the European Datum is at Potsdam, Germany. Numerous national systems have been joined into a large datum based upon the International Ellipsoid of 1924 which was oriented by a modified astrogeodetic method.

European, African, and Asian triangulation chains were connected, and African measurements from Cairo to Cape Town were completed. Thus, all of Europe, Africa, and Asia are molded into one great system. Through common survey stations, it was also possible to convert data from the Russian Pulkova, 1932 system to the European Datum, and as a result, the European Datum includes triangulation as far east as the 84th meridian. Additional ties across the
Middle East have permitted connection of the Indian and European Datums.

The Ordnance Survey of Great Britain 1936 Datum has no point of origin. The data was derived as a best fit between retriangulation and original values of 11 points of the earlier Principal Triangulation of Great Britain (1783-1853).

Tokyo Datum has its origin in Tokyo. It is defined in terms of the Bessel Ellipsoid and oriented by a single astro-nomic station. Triangulation ties through Korea connect the Japanese datum with the Manchurian datum. Unfortunately, Tokyo is situated on a steep slope on the geoid, and the singlestation orientation has resulted in large systematic geoidal separations
as the system is extended from its initial point.

The Indian Datum is the preferred datum for India and several adjacent countries in Southeast Asia. It is computed on the Everest Ellipsoid with its origin at Kalianpur, in central India. It is largely the result of the untiring work of Sir George Everest (1790-1866), Surveyor General in India from 1830 to 1843. He is best known by the mountain named after him, but by far his most important legacy was the survey of the Indian subcontinent.

MODERN GEODETIC SYSTEMS
209. Development Of The World Geodetic System
By the late 1950&#8217;s the increasing range and sophistication of weapons systems had rendered local or national datums inadequate for military purposes; these new weapons required datums at least continental in scope. In response to these requirements, the U.S. Department of Defense
generated a geocentric reference system to which different geodetic networks could be referred and established compatibility between the coordinates of sites of interest. Efforts of the Army, Navy, and Air Force were
combined leading to the development of the DoD World Geodetic System of 1960 (WGS 60).

In January 1966, a World Geodetic System Committee was charged with the responsibility for developing an improved WGS needed to satisfy mapping, charting, and geodetic requirements. Additional surface gravity observations,
results from the extension of triangulation and trilateration networks, and large amounts of Doppler and optical satellite data had become available since the development of WGS 60. Using the additional data and improved
techniques, the Committee produced WGS 66 which served DoD needs following its implementation in 1967

The same World Geodetic System Committee began work in 1970 to develop a replacement for WGS 66. Since the development of WGS 66, large quantities of additional data had become available from both Doppler and optical satellites, surface gravity surveys, triangulation and trilateration surveys,
high precision traverses, and astronomic surveys.

In addition, improved capabilities had been developed in both computers and computer software. Continued research in computational procedures and error analyses had produced better methods and an improved facility for handling
and combining data. After an extensive effort extending over a period of approximately three years, the Committee completed the development of the Department of Defense World Geodetic System 1972 (WGS 72

Further refinement of WGS 72 resulted in the new World Geodetic System of 1984 (WGS 84). As of 1990, WGS 84 is being used for chart making by DMA.

For surface navigation, WGS 60, 66, 72 and the new WGS 84 are essentially the same, so that positions computed on any WGS coordinates can be plotted directly on the others without correction.

The WGS system is not based on a single point, but many points, fixed with extreme precision by satellite fixes and statistical methods. The result is an ellipsoid which fits the real surface of the earth, or geoid, far more accurately than any other.

The WGS system is applicable worldwide. All regional datums can be referenced to WGS once a survey tie has been made.

210.	The New North American Datum Of 1983

The Coast And Geodetic Survey of the National Ocean Service (NOS), NOAA, is responsible for charting United States waters. From 1927 to 1987, U.S. charts were based on NAD 27, using the Clarke 1866 ellipsoid. In 1989, the
U.S. officially switched to NAD 83 (navigationally equivalent to WGS 84 and other WGS systems) for all mapping and charting purposes, and all new NOS chart production is based on this new standard.

The grid of interconnected surveys which criss-crosses the United States consists of some 250,000 control points, each consisting of the latitude and longitude of the point, plus additional data such as elevation. Converting the NAD 27 coordinates to NAD 83 involved recomputing the position of each point based on the new NAD 83 datum. In addition to the 250,000 U.S. control points, several thousand more were added to tie in surveys from Canada,
Mexico, and Central America.

Conversion of new edition charts to the new datums, either WGS 84 or NAD 83, involves converting reference points on each chart from the old datum to the new, and adjusting the latitude and longitude grid (known as the
graticule) so that it reflects the newly plotted positions. This adjustment of the graticule is the only difference between charts which differ only in datum. *All charted features remain in exactly the same relative positions.*

IMPACTS ON NAVIGATION

211.	Datum Shifts
One impact of different datums on navigation appears when a navigation system provides a fix based on a datum different from that used for the nautical chart. The resulting plotted position may be different from the actual location on that chart. This difference is known as a datum shift.

Another effect on navigation occurs when shifting between charts that have been made using different datums. If any position is replotted on a chart of another datum using only latitude and longitude for locating that position, the
newly plotted position will not match with respect to other charted features.

*This datum shift may be avoided by replotting using bearings and ranges to common points. If datum shift conversion notes for the applicable datums are
given on the charts, positions defined by latitude and longitude may be replotted after applying the noted correction.*

*(Got that?)*

The positions given for chart corrections in the Notice to Mariners reflect the proper datum for each specific chart and edition number. Due to conversion of charts based on old datums to more modern ones, and the use of many different datums throughout the world, chart corrections intended for one edition of a chart may not be safely plotted on any other.

*These datum shifts are not constant throughout a given area, but vary according to how the differing datums fit together.
*
For example, the NAD 27 to NAD 83 conversion results in changes in latitude of 40 meters in Miami, 11 meters in New York, and 20 meters in Seattle.

Longitude changes for this conversion are about 22 meters in Miami, 35 meters in New York, and 93 meters in Seattle.

Most charts produced by DMA and NOS show a &#8220;datum note.&#8221; This note is usually found in the title block or in the upper left margin of the chart.

According to the year of the chart edition, the scale, and policy at the time of production, the note may say &#8220;World Geodetic System 1972 (WGS-72)&#8221;, &#8220;World Geodetic System 1984 (WGS-84)&#8221;, or &#8220;World Geodetic System
(WGS).&#8221; *A datum note for a chart for which satellite positions can be plotted without correction will read: &#8220;Positions obtained from satellite navigation systems referred to (REFERENCE DATUM) can be plotted directly on this chart.&#8221;*

DMA reproductions of foreign chart&#8216;s will usually be in the datum or reference system of the producing country.

In these cases a conversion factor is given in the following format: &#8220;Positions obtained from satellite navigation systems referred to the (Reference Datum) must be moved X.XX minutes (Northward/Southward) and X.XX minutes
(Eastward/ Westward) to agree with this chart.&#8221;

Some charts cannot be tied in to WGS because of lack of recent surveys.

Currently issued charts of some areas are based on surveys or use data obtained in the age of sailing ships. The lack of surveyed control points means that they cannot be properly referenced to modern geodetic systems. In this case there may be a note that says: *&#8220;Adjustments to WGS cannot be determined for this chart.&#8221;*

A few charts may have no datum note at all, but may carry a note which says: &#8220;From various sources to (year).&#8221; In these cases there is no way for the navigator to determine the mathematical difference between the local datum and WGS positions.

*However, if a radar or visual fix can be very accurately determined, the difference between this fix and a satellite fix can determine an approximate correction factor which will be reasonably consistent for that local area.*

212.	Minimizing Errors Caused By Differing Datums
To minimize problems caused by differing datums:
Plot chart corrections only on the specific charts and editions for which they are intended. Each chart correction is specific to only one edition of a chart. When the same correction is made on two charts based on different datums, the positions for the same feature may differ slightly. This difference is equal to the datum shift between the two datums for that area.

Try to determine the source and datum of positions of temporary features, such as drill rigs. In general they are given in the datum used in the area in question. Since these are usually positioned using satellites, WGS is the normal datum. A datum correction, if needed, might be found on a chart of the area.

Remember that if the datum of a plotted feature is not known, position inaccuracies may result. It is wise to allow a margin of error if there is any doubt about the datum.

*Know how the datum of the positioning system you are using (Loran, GPS, etc.) relates to your chart. GPS and other modern positioning systems use the WGS datum. If your chart is on any other datum, you must apply a datum correction when plotting the GPS position of the chart.
*
Modern geodesy can support the goal of producing all the world&#8217;s charts on the same datum. Coupling an electronic chart with satellite positioning will eliminate the problem of differing datums because electronically derived positions and the video charts on which they are displayed are derived from one of the new worldwide datums.

*Current flow?*
*"But the land, whither ye go to possess it, is a land of hills and valleys, and drinketh water of the rain of heaven:" Deut.11:11*

Chapter 2 conclusion* Ready for ch3?*


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## Fishers of Men

*I was going to leave this chapter out since we already did charts but there is some additional info. And some repetition wouldn&#8217;t hurt anything! So please don&#8217;t over look this chapter. There is some new material and different views. If you fly through it, I am sure you will pick up something new and or clarify a lot of &#8220;things&#8221;.*

CHAPTER 3
*NAUTICAL CHARTS
CHART FUNDAMENTALS*
300. Definitions
A nautical chart represents part of the spherical earth on a plane surface. It shows water depth, the shoreline of adjacent land, topographic features, aids to navigation, and other navigational information. It is a work area on which the navigator plots courses, ascertains positions, and views the relationship of the ship to the surrounding area. It assists the navigator in avoiding dangers and arriving safely at his destination.

The actual form of a chart may vary. Traditional nautical charts have been printed on paper. Electronic charts consisting of a digital data base and a display system are in use and will eventually replace paper charts for operational use. An electronic chart is not simply a digital version of a paper chart; it introduces a new navigation methodology with capabilities and limitations very different from paper charts. The electronic chart will eventually become the legal equivalent of the paper chart when approved by the International Maritime Organization and the various governmental agencies which regulate navigation. Currently, however, mariners must maintain a paper chart on the bridge. See Chapter 14, The Integrated Bridge, for a discussion of electronic charts.

Should a marine accident occur, the nautical chart in use at the time takes on legal significance. In cases of grounding, collision, and other accidents, charts become critical records for reconstructing the event and assigning liability. Charts used in reconstructing the incident can also have tremendous training value.

*301.	Projections*
Because a cartographer cannot transfer a sphere to a flat surface without distortion, he must project the surface of a sphere onto a developable surface. A developable surface is one that can be flattened to form a plane. This process is known as chart projection. If points on the surface of the sphere are projected from a single point, the projection is said to be perspective or geometric. As the use of electronic charts becomes increasingly widespread, it is important to remember that the same cartographic principles that apply to paper charts apply to their depiction on video screens.

*302.	Selecting A Projection*
Each projection has certain preferable features. However, as the area covered by the chart becomes smaller, the differences between various projections become less noticeable. On the largest scale chart, such as of a harbor, all projections are practically identical. Some desirable properties of a projection are:
1.	True shape of physical features.
2.	Correct angular relationship. A projection with this characteristic is conformal or orthomorphic.
3.	Equal area, or the representation of areas in their correct relative proportions.
4.	Constant scale values for measuring distances.
5.	Great circles represented as straight lines.
6.	Rhumb lines represented as straight lines.
Some of these properties are mutually exclusive. For example, a single projection cannot be both conformal and equal area. Similarly, both great circles and rhumb lines cannot be represented on a single projection as straight lines.

*303.	Types Of Projections*
The type of developable surface to which the spherical surface is transferred determines the projection&#8217;s classification. Further classification depends on whether the projection is centered on the equator (equatorial), a pole (polar), or some point or line between (oblique). The name of a projection indicates its type and its principal features.
Mariners most frequently use a Mercator projection, classified as a cylindrical projection upon a plane, the cylinder tangent along the equator. Similarly, a projection based upon a cylinder tangent along a meridian is called transverse (or inverse) Mercator or transverse (or inverse) orthomorphic. The Mercator is the most common projection used in maritime navigation, primarily because rhumb lines plot as straight lines.

In a simple conic projection, points on the surface of the earth are transferred to a tangent cone. In the Lambert conformal projection, the cone intersects the earth (a secant cone) at two small circles. In a polyconic projection, a series of tangent cones is used.

In an azimuthal or zenithal projection, points on the earth are transferred directly to a plane. If the origin of the projecting rays is the center of the earth, a gnomonic projection results; if it is the point opposite the plane&#8217;s point of tangency, a stereographic projection; and if at infinity (the projecting lines being parallel to each other), an orthographic projection. The gnomonic, stereographic, and orthographic are perspective projections. In an azimuthal equidistant projection, which is not perspective, the scale of distances is constant along any radial line from the point of tangency. See Figure 303.










Cylindrical and plane projections are special conical projections, using heights infinity and zero, respectively. A graticule is the network of latitude and longitude lines laid out in accordance with the principles of any projection.

*304.	Cylindrical Projections*
If a cylinder is placed around the earth, tangent along the equator, and the planes of the meridians are extended, they intersect the cylinder in a number of vertical lines. See Figure 304. These parallel lines of projection are equidistant from each other, unlike the terrestrial meridians from which they are derived which converge as the latitude increases. On the earth, parallels of latitude are perpendicular to the meridians, forming circles of progressively smaller diameter as the latitude increases. On the cylinder they are shown perpendicular to the projected meridians, but because a cylinder is everywhere of the same diameter, the projected parallels are all the same size. If the cylinder is cut along a vertical line (a meridian) and spread out flat, the meridians appear as equally spaced vertical lines; and the parallels appear as horizontal lines. The parallels&#8217; relative spacing differs in the various types of cylindrical projections.

If the cylinder is tangent along some great circle other than the equator, the projected pattern of latitude and longitude lines appears quite different from that described above, since the line of tangency and the equator no longer coincide.

These projections are classified as oblique or transverse projections.










*305.	Mercator Projection*
Navigators most often use the plane conformal projection known as the Mercator projection. The Mercator projection is not perspective, and its parallels can be derived mathematically as well as projected geometrically. Its distinguishing feature is that both the meridians and parallels are expanded at the same ratio with increased latitude. The expansion is equal to the secant of the latitude, with a small correction for the ellipticity of the earth. Since the secant of 90&#61616; &#61472;is infinity, the projection cannot include the poles. Since the projection is conformal, expansion is the same in all directions and angles are correctly shown. Rhumb lines appear as straight lines, the directions of which can be measured directly on the chart. Distances can also be measured directly if the spread of latitude is small. Great circles, except meridians and the equator, appear as curved lines concave to the equator. Small areas appear in their correct shape but of increased size unless they are near the equator.

*306.	Meridional Parts*
At the equator a degree of longitude is approximately equal in length to a degree of latitude. As the distance from the equator increases, degrees of latitude remain approximately the same, while degrees of longitude become progressively shorter. Since degrees of longitude appear everywhere the same length in the Mercator projection, it is necessary to increase the length of the meridians if the expansion is to be equal in all directions. Thus, to maintain the correct proportions between degrees of latitude and degrees of longitude, the degrees of latitude must be progressively longer as the distance from the equator increases. This is illustrated in figure 306.










The length of a meridian, increased between the equator and any given latitude, expressed in minutes of arc at the equator as a unit, constitutes the number of meridional parts (M) corresponding to that latitude. Meridional parts, given in Table 6 for every minute of latitude from the equator to the pole, make it possible to construct a Mercator chart and to solve problems in Mercator sailing. These values are for the WGS ellipsoid of 1984.

*307. Transverse Mercator Projections*
Constructing a chart using Mercator principles, but with the cylinder tangent along a meridian, results in a transverse Mercator or transverse orthomorphic projection.

The word &#8220;inverse&#8221; is used interchangeably with &#8220;transverse.&#8221; These projections use a fictitious graticule similar to, but offset from, the familiar network of meridians and parallels. The tangent great circle is the fictitious equator. Ninety degrees from it are two fictitious poles. A group of great circles through these poles and perpendicular to the tangent great circle are the fictitious meridians, while a series of circles parallel to the plane of the tangent great circle form the fictitious parallels. The actual meridians and parallels appear as curved lines.

A straight line on the transverse or oblique Mercator projection makes the same angle with all fictitious meridians, but not with the terrestrial meridians. It is therefore a fictitious rhumb line. Near the tangent great circle, a straight line closely approximates a great circle. The projection is most useful in this area. Since the area of minimum distortion is near a meridian, this projection is useful for charts covering a large band of latitude and extending a relatively short distance on each side of the tangent meridian. It is sometimes used for star charts showing the evening sky at various seasons of the year. See Figure 307.










*308.	Universal Transverse Mercator (UTM) Grid*
The Universal Transverse Mercator (UTM) grid is a military grid superimposed upon a transverse Mercator graticule, or the representation of these grid lines upon any graticule. This grid system and these projections are often used for large-scale (harbor) nautical charts and military charts.
*
309.	Oblique Mercator Projections*
A Mercator projection in which the cylinder is tangent along a great circle other than the equator or a meridian is called an oblique Mercator or oblique orthomorphic projection. This projection is used principally to depict an area in the near vicinity of an oblique great circle. Figure 309c, for example, shows the great circle joining Washington and Moscow. Figure 309d shows an oblique Mercator map with the great circle between these two centers as the tangent great circle or fictitious equator. The limits of the chart of Figure 309c are indicated in Figure 309d. Note the large variation in scale as the latitude changes.





































*To be Continued.*


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## ezbite

im still with ya van, but i gotta admit....wow, its like going back to school. lots of info. by the way, i got the emails. thanks


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## Fishers of Men

ezbite said:


> im still with ya van, but i gotta admit....wow, its like going back to school. lots of info. by the way, i got the emails. thanks


Thanks Tom, Glad to hear someones still out there! It's going to do nothing but get better. :T


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## Fishers of Men

*ch 3 Cont.

310.	Rectangular Projection*
A cylindrical projection similar to the Mercator, but with uniform spacing of the parallels, is called a rectangular projection. It is convenient for graphically depicting information where distortion is not important. The principal navigational use of this projection is for the star chart of the Air Almanac, where positions of stars are plotted by rectangular coordinates representing declination (ordinate) and sidereal hour angle (abscissa). Since the meridians are parallel, the parallels of latitude (including the equator and the poles) are all represented by lines of equal length.
*
311.	Conic Projections*
A conic projection is produced by transferring points from the surface of the earth to a cone or series of cones. This cone is then cut along an element and spread out flat to form the chart. When the axis of the cone coincides with the axis of the earth, then the parallels appear as arcs of circles, and the meridians appear as either straight or curved lines converging toward the nearer pole. Limiting the area covered to that part of the cone near the surface of the earth limits distortion. A parallel along which there is no distortion is called a standard parallel. Neither the transverse conic projection, in which the axis of the cone is in the equatorial plane, nor the oblique conic projection, in which the axis of the cone is oblique to the plane of the equator, is ordinarily used for navigation. They are typically used for illustrative maps.

Using cones tangent at various parallels, a secant (intersecting) cone, or a series of cones varies the appearance and features of a conic projection.

*312.	Simple Conic Projection*
A conic projection using a single tangent cone is a simple conic projection (Figure 312a).










The height of the cone increases as the latitude of the tangent parallel decreases. At the equator, the height reaches infinity and the cone becomes a cylinder. At the pole, its height is zero, and the cone becomes a plane. Similar to the Mercator projection, the simple conic projection is not perspective since only the meridians are projected geometrically, each becoming an element of the cone. When this projection is spread out flat to form a map, the meridians appear as straight lines converging at the apex of the cone. The standard parallel, where the cone is tangent to the earth, appears as the arc of a circle with its center at the apex of the cone. The other parallels are concentric circles. The distance along any meridian between consecutive parallels is in correct relation to the distance on the earth, and, therefore, can be derived mathematically. The pole is represented by a circle (Figure 312b).










The scale is correct along any meridian and along the standard parallel. All other parallels are too great in length, with the error increasing with increased distance from the standard parallel. Since the scale is not the same in all directions about every point, the projection is neither a conformal nor equal-area projection. Its non-conformal nature is its principal disadvantage for navigation. Since the scale is correct along the standard parallel and varies uniformly on each side, with comparatively little distortion near the standard parallel, this projection is useful for mapping an area covering a large spread of longitude and a comparatively narrow band of latitude. It was developed by Claudius Ptolemy in the second century A.D. to map just such an area: the Mediterranean Sea.

*313.	Lambert Conformal Projection*
The useful latitude range of the simple conic projection
can be increased by using a secant cone intersecting the
earth at two standard parallels. See Figure 313. 










The area between the two standard parallels is compressed, and that beyond is expanded. Such a projection is called either a secant conic or conic projection with two standard parallels.

If in such a projection the spacing of the parallels is altered, such that the distortion is the same along them as along the meridians, the projection becomes conformal. This modification produces the Lambert conformal projection. If the chart is not carried far beyond the standard parallels, and if these are not a great distance apart, the distortion over the entire chart is small.

A straight line on this projection so nearly approximates a great circle that the two are nearly identical. Radio beacon signals travel great circles; thus, they can be plotted on this projection without correction. This feature, gained without sacrificing conformality, has made this projection popular for aeronautical charts because aircraft make wide use of radio aids to navigation. Except in high latitudes, where a slightly modified form of this projection has been used for polar charts, it has not replaced the Mercator projection for marine navigation.
*
314.	Polyconic Projection*
The latitude limitations of the secant conic projection can be minimized by using a series of cones. This results in a polyconic projection. In this projection, each parallel is the base of a tangent cone . At the edges of the chart, the area between parallels is expanded to eliminate gaps. The scale is correct along any parallel and along the central meridian of the projection. Along other meridians the scale increases with increased difference of longitude from the central meridian. Parallels appear as nonconcentric circles; meridians appear as curved lines converging toward the pole and concave to the central meridian. The polyconic projection is widely used in atlases, particularly for areas of large range in latitude and reasonably large range in longitude, such as continents. However, since it is not conformal, this projection is not customarily used in navigation.

*315.	Azimuthal Projections*
If points on the earth are projected directly to a plane surface, a map is formed at once, without cutting and flattening, or developing. This can be considered a special case of a conic projection in which the cone has zero height. The simplest case of the azimuthal projection is one in which the plane is tangent at one of the poles. The meridians are straight lines intersecting at the pole, and the parallels are concentric circles with their common center at the pole. Their spacing depends upon the method used to transfer points from the earth to the plane.

If the plane is tangent at some point other than a pole, straight lines through the point of tangency are great circles, and concentric circles with their common center at the point of tangency connect points of equal distance from that point. Distortion, which is zero at the point of tangency, increases along any great circle through this point. Along any circle whose center is the point of tangency, the distortion is constant. The bearing of any point from the point of tangency is correctly represented. It is for this reason that these projections are called azimuthal. They are also called zenithal. Several of the common azimuthal projections are perspective.
*
316.	Gnomonic Projection*
If a plane is tangent to the earth, and points are projected
geometrically from the center of the earth, the result is a gnomonic
projection. See Figure 316a.










Since the projection is perspective, it can be demonstrated by placing a light at the center of a transparent terrestrial globe and holding a flat surface tangent to the sphere.

In an oblique gnomonic projection the meridians appear as straight lines converging toward the nearer pole. The parallels, except the equator, appear as curves (Figure 316b).










As in all azimuthal projections, bearings from the point of tangency are correctly represented. The distance scale, however, changes rapidly. The projection is neither conformal nor equal area. Distortion is so great that shapes, as well as distances and areas, are very poorly represented, except near the point of tangency.

The usefulness of this projection rests upon the fact that any great circle appears on the map as a straight line, giving charts made on this projection the common name great-circle charts.

Gnomonic charts are most often used for planning the great-circle track between points. Points along the determined track are then transferred to a Mercator projection. The great circle is then followed by following the rhumb lines from one point to the next. Computer programs which automatically calculate great circle routes between points and provide latitude and longitude of corresponding rhumb line endpoints are quickly making this use of the gnomonic chart obsolete.
*
317. Stereographic Projection*
A stereographic projection results from projecting points on the surface of the earth onto a tangent plane, from a point on the surface of the earth opposite the point of tangency (Figure 317a). This projection is also called an azimuthal orthomorphic projection.










The scale of the stereographic projection increases with distance from the point of tangency, but it increases more slowly than in the gnomonic projection. The stereographic projection can show an entire hemisphere without excessive distortion (Figure 317b).










As in other azimuthal projections, great circles through the point of tangency appear as straight lines. Other circles such as meridians and parallels appear as either circles or arcs of circles.

The principal navigational use of the stereographic projection is for charts of the polar regions and devices for mechanical or graphical solution of the navigational triangle.

A Universal Polar Stereographic (UPS) grid, mathematically adjusted to the graticule, is used as a reference system.
*
To Be cont.*


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## Fishers of Men

*ch 3 Cont.

318. Orthographic Projection *
If terrestrial points are projected geometrically from infinity to a tangent plane, an orthographic projection results (Figure 318a). This projection is not conformal; nor does it result in an equal area representation. Its principal use is in navigational astronomy because it is useful for illustrating and solving the navigational triangle. It is also useful for illustrating celestial coordinates. If the plane is tangent at a point on the equator, the parallels (including the equator) appear as straight lines. The meridians would appear as ellipses, except that the meridian through the point of tangency would appear as a straight line and the one 90&#61616;&#61472; away would appear as a circle (Figure 318b).









*
319. Azimuthal Equidistant Projection*
An azimuthal equidistant projection is an azimuthal projection in which the distance scale along any great circle through the point of tangency is constant. If a pole is the point of tangency, the meridians appear as straight radial lines and the parallels as equally spaced concentric circles. If the plane is tangent at some point other than a pole, the concentric circles represent distances from the point of tangency. In this case, meridians and parallels appear as curves. The projection can be used to portray the entire earth, the point 180&#61616; &#61472;from the point of tangency appearing as the largest of the concentric circles. The projection is not conformal, equal area, or perspective. Near the point of tangency distortion is small, increasing with distance until shapes near the opposite side of the earth are unrecognizable (Figure 319).

The projection is useful because it combines the three features of being azimuthal, having a constant distance scale from the point of tangency, and permitting the entire earth to be shown on one map. Thus, if an important harbor or airport is selected as the point of tangency, the great-circle course, distance, and track from that point to any other point on the earth are quickly and accurately determined. For communication work with the station at the point of tangency, the path of an incoming signal is at once apparent if the direction of arrival has been determined and the direction to train a directional antenna can be determined easily. The projection is also used for polar charts and for the star finder, No. 2102D. Figure 318a.










*POLAR CHARTS
320. Polar Projections*
Special consideration is given to the selection of projections for polar charts because the familiar projections become special cases with unique features.

In the case of cylindrical projections in which the axis of the cylinder is parallel to the polar axis of the earth, distortion becomes excessive and the scale changes rapidly. Such projections cannot be carried to the poles. However, both the transverse and oblique Mercator projections are used.

Conic projections with their axes parallel to the earth&#8217;s polar axis are limited in their usefulness for polar charts because parallels of latitude extending through a full 360&#61616;&#61472; of longitude appear as arcs of circles rather than full circles. This is because a cone, when cut along an element and flattened, does not extend through a full 360&#61616;&#61472; without stretching or resuming its former conical shape. The usefulness of such projections is also limited by the fact that the pole appears as an arc of a circle instead of a point. However, by using a parallel very near the pole as the higher standard parallel, a conic projection with two standard parallels can be made. This requires little stretching to complete the circles of the parallels and eliminate that of the pole. Such a projection, called a modified Lambert conformal or Ney&#8217;s projection, is useful for polar charts. It is particularly familiar to those accustomed to using the ordinary Lambert conformal charts in lower latitudes.

Azimuthal projections are in their simplest form when tangent at a pole. This is because the meridians are straight lines intersecting at the pole, and parallels are concentric circles with their common center at the pole. Within a few degrees of latitude of the pole they all look similar; however, as the distance becomes greater, the spacing of the parallels becomes distinctive in each projection. In the polar azimuthal equidistant it is uniform; in the polar stereographic it increases with distance from the pole until the equator is shown at a distance from the pole equal to twice the length of the radius of the earth; in the polar gnomonic the increase is considerably greater, becoming infinity at the equator; in the polar orthographic it decreases with distance from the pole (Figure 320). All of these but the last are used for polar charts.










The principal considerations in the choice of a suitable projection for polar navigation are:
1.	Conformality: When the projection represents angles correctly, the navigator can plot directly on the chart.
2.	Great circle representation: Because great circles are more useful than rhumb lines at high altitudes, the projection should represent great circles as straight lines.
3.	Scale variation: The projection should have a constant scale over the entire chart.
4.	Meridian representation: The projection should show straight meridians to facilitate plotting and grid navigation.
5.	Limits: Wide limits reduce the number of projections needed to a minimum.

The projections commonly used for polar charts are the modified Lambert conformal, gnomonic, stereographic, and azimuthal equidistant. All of these projections are similar near the pole. All are essentially conformal, and a great circle on each is nearly a straight line.

As the distance from the pole increases, however, the distinctive features of each projection become important. The modified Lambert conformal projection is virtually conformal over its entire extent. The amount of its scale distortion is comparatively little if it is carried only to about 25&#61616;&#61472; or 30&#61616; &#61472;from the pole. Beyond this, the distortion increases rapidly. A great circle is very nearly a straight line anywhere on the chart. Distances and directions can be measured directly on the chart in the same manner as on a Lambert conformal chart. However, because this projection is not strictly conformal, and on it great circles are not exactly represented by straight lines, it is not suited for highly accurate work.

The polar gnomonic projection is the one polar projection on which great circles are exactly straight lines. However, a complete hemisphere cannot be represented upon a plane because the radius of 90&#61616; &#61472;from the center would become infinity.

The polar stereographic projection is conformal over its entire extent, and a straight line closely approximates a great circle. See Figure 321. The scale distortion is not excessive for a considerable distance from the pole, but it is greater than that of the modified Lambert conformal projection.










The polar azimuthal equidistant projection is useful for showing a large area such as a hemisphere because there is no expansion along the meridians. However, the projection is not conformal and distances cannot be measured accurately in any but a north-south direction. Great circles other than the meridians differ somewhat from straight lines. The equator is a circle centered at the pole.

The two projections most commonly used for polar charts are the modified Lambert conformal and the polar stereographic. When a directional gyro is used as a directional reference, the track of the craft is approximately a great circle. A desirable chart is one on which a great circle is represented as a straight line with a constant scale and with angles correctly represented. These requirements are not met entirely by any single projection, but they are approximated by both the modified Lambert conformal and the polar stereographic. The scale is more nearly constant on the former, but the projection is not strictly conformal. The polar stereographic is conformal, and its maximum scale variation can be reduced by using a plane which intersects the earth at some parallel intermediate between the pole and the lowest parallel. The portion within this standard parallel is compressed, and that portion outside is expanded.

The selection of a suitable projection for use in polar regions depends upon mission requirements. These requirements establish the relative importance of various features. For a relatively small area, any of several projections is suitable. For a large area, however, the choice is more difficult. If grid directions are to be used, it is important that all units in related operations use charts on the same projection, with the same standard parallels, so that a single grid direction exists between any two points. Nuclear powered submarine operations under the polar icecap have increased the need for grid directions in marine navigation.

*SPECIAL CHARTS
322.	Plotting Sheets*
Position plotting sheets are &#8220;charts&#8221; designed primarily for open ocean navigation, where land, visual aids to navigation, and depth of water are not factors in navigation. They have a latitude and longitude graticule, and they may have one or more compass roses. The meridians are usually unlabeled, so a plotting sheet can be used for any longitude. *Plotting sheets on Mercator projection are specific to latitude, and the navigator should have enough aboard for all latitudes for his voyage.* 

Plotting sheets are less expensive than charts.
One use of a plotting sheet may occur in the event of an emergency when all charts have been lost or are otherwise unavailable. Directions on how to construct plotting sheets suitable for emergency purposes are given in Chapter 26, Emergency Navigation.

*323.	Grids*
No system exists for showing the surface of the earth on a plane without distortion. Moreover, the appearance of the surface varies with the projection and with the relation of that surface area to the point of tangency. One may want to identify a location or area simply by alpha-numeric rectangular coordinates. This is accomplished with a grid. In its usual form this consists of two series of lines drawn perpendicularly on the chart, marked by suitable alpha-numeric designations.
A grid may use the rectangular graticule of the Mercator projection or a set of arbitrary lines on a particular projection. The World Geodetic Reference System (GEOREF) is a method of designating latitude and longitude by a system of letters and numbers instead of by angular measure. It is not, therefore, strictly a grid. It is useful for operations extending over a wide area. Examples of the second type of grid are the Universal Transverse Mercator (UTM) grid, the Universal Polar Stereographic (UPS) grid, and the Temporary Geographic Grid (TGG).
Since these systems are used primarily by military forces, they are sometimes called military grids.

*To Be cont.*


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## Fishers of Men

*ch 3 cont

CHART SCALES
324. Types Of Scales*
The scale of a chart is the ratio of a given distance on the chart to the actual distance which it represents on the earth. It may be expressed in various ways. The most common are:
1.	A simple ratio or fraction, known as the representative fraction. For example, 1:80,000 or 1/80,000 means that one unit (such as a meter) on the chart represents 80,000 of the same unit on the surface of the earth. This scale is sometimes called the natural or fractional scale.
2.	A statement that a given distance on the earth equals a given measure on the chart, or vice versa. For example, &#8220;30 miles to the inch&#8221; means that 1 inch on the chart represents 30 miles of the earth&#8217;s surface. Similarly, &#8220;2 inches to a mile&#8221; indicates that 2 inches on the chart represent 1 mile on the earth. This is some times called the numerical scale.
3. A line or bar called a graphic scale may be drawn at a convenient place on the chart and subdivided into nautical miles, meters, etc. All charts vary somewhat in scale from point to point, and in some projections the scale is not the same in all directions about a single point. A single subdivided line or bar for use over an entire chart is shown only when the chart is of such scale and projection that the scale varies a negligible amount over the chart, usually one of about 1:75,000 or larger. Since 1 minute of latitude is very nearly equal to 1 nautical mile, the latitude scale serves as an approximate graphic scale. On most nautical charts the east and west borders are subdivided to facilitate distance measurements.

On a Mercator chart the scale varies with the latitude.
This is noticeable on a chart covering a relatively large distance in a north-south direction. On such a chart the border scale near the latitude in question should be used for measuring distances.
Of the various methods of indicating scale, the graphical method is normally available in some form on the chart.
In addition, the scale is customarily stated on charts on which the scale does not change appreciably over the chart.
The ways of expressing the scale of a chart are readily interchangeable. For instance, in a nautical mile there are about 72,913.39 inches. If the natural scale of a chart is 1:80,000, one inch of the chart represents 80,000 inches of the earth, or a little more than a mile. To find the exact amount, divide the scale by the number of inches in a mile, or 80,000/72,913.39 = 1.097. Thus, a scale of 1:80,000 is the same as a scale of 1.097 (or approximately 1.1) miles to an inch. Stated another way, there are: 72,913.39/80,000 = 0.911 (approximately 0.9) inch to a mile. Similarly, if the scale is 60 nautical miles to an inch, the representative fraction is 1: (60 x 72,913.39) = 1:4,374,803.

A chart covering a relatively large area is called a small-scale chart and one covering a relatively small area is called a large-scale chart. Since the terms are relative, there is no sharp division between the two. Thus, a chart of scale 1:100,000 is large scale when compared with a chart of 1:1,000,000 but small scale when compared with one of 1:25,000.

As scale decreases, the amount of detail which can be shown decreases also. Cartographers selectively decrease the detail in a process called generalization when producing small scale charts using large scale charts as sources.
The amount of detail shown depends on several factors, among them the coverage of the area at larger scales and the intended use of the chart. 

*325. Chart Classification By Scale*
Charts are constructed on many different scales, ranging from about 1:2,500 to 1:14,000,000. Small-scale charts covering large areas are used for route planning and for offshore navigation. Charts of larger scale, covering smaller areas, are used as the vessel approaches land. Several methods of classifying charts according to scale are used in various nations. The following classifications of nautical charts are used by the National Ocean Service.

Sailing charts are the smallest scale charts used for planning, fixing position at sea, and for plotting the dead reckoning while proceeding on a long voyage. The scale is generally smaller than 1:600,000. The shoreline and topography are generalized and only offshore soundings, the principal navigational lights, outer buoys, and landmarks visible at considerable distances are shown.
General charts are intended for coastwise navigation outside of outlying reefs and shoals. The scales range from about 1:150,000 to 1:600,000.
Coastal charts are intended for inshore coastwise navigation, for entering or leaving bays and harbors of considerable width, and for navigating large inland waterways. The scales range from about 1:50,000 to 1:150,000.
Harbor charts are intended for navigation and anchorage in harbors and small waterways. The scale is generally larger than 1:50,000.

In the classification system used by the Defense Mapping Agency Hydrographic/Topographic Center, the sailing charts are incorporated in the general charts classification (smaller than about 1:150,000); those coast charts especially useful for approaching more confined waters (bays, harbors) are classified as approach charts. There is considerable overlap in these designations, and the classification of a chart is best determined by its use and by its relationship to other charts of the area. The use of insets complicates the placement of charts into rigid classifications.

*CHART ACCURACY
326. Factors Relating To Accuracy*
The accuracy of a chart depends upon the accuracy of the hydrographic surveys used to compile it and the suitability of its scale for its intended use.
Estimate the accuracy of a chart&#8217;s surveys from the source notes given in the title of the chart. If the chart is based upon very old surveys, use it with caution. Many early surveys were inaccurate because of the technological limitations of the surveyor.

The number of soundings and their spacing indicates the completeness of the survey. Only a small fraction of the soundings taken in a thorough survey are shown on the chart, but sparse or unevenly distributed soundings indicate that the survey was probably not made in detail. See Figure 326a and Figure 326b 



















Large blank areas or absence of depth contours generally indicate lack of soundings in the area. Operate in an area with sparse sounding data only if operationally required and then only with the most extreme caution. Run the echo sounder continuously and operate at a reduced speed. Sparse sounding information does not necessarily indicate an incomplete survey. Relatively few soundings are shown when there is a large number of depth contours, or where the bottom is flat, or gently and evenly sloping. Additional soundings are shown when they are helpful in indicating the uneven character of a rough bottom. Even a detailed survey may fail to locate every rock or pinnacle. In waters where they might be located, the best method for finding them is a wire drag survey. Areas that have been dragged may be indicated on the chart by limiting lines and green or purple tint and a note added to show the effective depth at which the drag was operated. Changes in bottom contours are relatively rapid in areas such as entrances to harbors where there are strong currents or heavy surf. Similarly, there is sometimes a tendency for dredged channels to shoal, especially if they are surrounded by sand or mud, and cross currents exist. Charts often contain notes indicating the bottom contours are known to change rapidly.
The same detail cannot be shown on a small-scale chart as on a large scale chart. On small-scale charts, detailed information is omitted or &#8220;generalized&#8221; in the areas covered by larger scale charts. The navigator should use the largest scale chart available for the area in which he is operating, especially when operating in the vicinity of hazards. Charting agencies continually evaluate both the detail and the presentation of data appearing on a chart. Development of a new navigational aid may render previous charts inadequate. The development of radar, for example, required upgrading charts which lacked the detail required for reliable identification of radar targets.
After receiving a chart, the user is responsible for keeping it updated.

Mariners reports of errors, changes, and suggestions are useful to charting agencies. Even with modern automated data collection techniques, there is no substitute for on-sight observation of hydrographic conditions by experienced mariners. This holds true especially in less frequently traveled areas of the world.

*To Be cont.*


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## Fishers of Men

*ch 3 cont.

327.	Chart Dates*
NOS charts have two dates. At the top center of the chart is the date of the first edition of the chart. In the lower left corner of the chart is the current edition number and date. This date shows the latest date through which Notice to Mariners were applied to the chart. Any subsequent change will be printed in the Notice to Mariners. Any notices which accumulate between the chart date and the announcement date in the Notice to Mariners will be given with the announcement. Comparing the dates of the first and current editions gives an indication of how often the chart is updated. Charts of busy areas are updated more frequently than those of less traveled areas. This interval may vary from 6 months to more than ten years for NOS charts. This update interval may be much longer for certain DMAHTC charts in remote areas.
New editions of charts are both demand and source driven. Receiving significant new information may or may not initiate a new edition of a chart, depending on the demand for that chart. If it is in a sparsely-traveled area, other priorities may delay a new edition for several years. Conversely, a new edition may be printed without the receipt of significant new data if demand for the chart is high and stock levels are low. Notice to Mariners corrections are always included on new editions.
DMAHTC charts have the same two dates as the NOS charts; the current chart edition number and date is given in the lower left corner. Certain DMAHTC charts are reproductions of foreign charts produced under joint agreements with a number of other countries. These charts, even though of recent date, may be based on foreign charts of considerably earlier date. Further, new editions of the foreign chart will not necessarily result in a new edition of the DMAHTC reproduction. In these cases, the foreign chart is the better chart to use.
A revised or corrected print contains corrections which have been published in Notice to Mariners. These corrected prints do not supersede a current edition. The date of the revision is given, along with the latest Notice to Mariners to which the chart has been corrected.

*328.	Title Block*
See Figure 328. The chart title block should be the first thing a navigator looks at when receiving a new edition chart. The title itself tells what area the chart covers. The charts scale and projection appear below the title. The chart will give both vertical and horizontal datums and, if necessary, a datum conversion note. Source notes or diagrams will list the date of surveys and other charts used in compilation.










*329.	Shoreline*
The shoreline shown on nautical charts represents the line of contact between the land and water at a selected vertical datum. In areas affected by tidal fluctuations, this is usually the mean high-water line. In confined coastal waters of diminished tidal influence, a mean water level line may be used. The shoreline of interior waters (rivers, lakes) is usually a line representing a specified elevation above a selected datum. A shoreline is symbolized by a heavy line. A broken line indicates that the charted position is approximate only. The nature of the shore may be indicated. If the low water line differs considerably from the high water line, then a dotted line represents the low water line. If the bottom in this area is composed of mud, sand, gravel or stones, the type of material will be indicated. If the bottom is composed of coral or rock, then the appropriate symbol will be used. The area alternately covered and uncovered may be shown by a tint which is usually a combination of the land and water tint.

The apparent shoreline shows the outer edge of marine vegetation where that limit would appear as shoreline to the mariner. It is also used to indicate where marine vegetation prevents the mariner from defining the shoreline. A light line symbolizes this shoreline. A broken line marks the inner edge when no other symbol (such as a cliff or levee) furnishes such a limit. The combined land-water tint or the land tint marks the area between inner and outer limits.

*330.	Chart Symbols*
Much of the information contained on charts is shown by symbols. These symbols are not shown to scale, but they indicate the correct position of the feature to which they refer.
The standard symbols and abbreviations used on charts published by the United States of America are shown in Chart No. 1, Nautical Chart Symbols and Abbreviations.

See Figure 330.










Electronic chart symbols are, within programming and display limits, much the same as printed ones. The less expensive electronic charts have less extensive symbol libraries, and the screens resolution may affect the presentation detail. Most of the symbols and abbreviations shown in U.S. Chart No. 1 agree with recommendations of the International Hydrographic Organization (IHO). The layout is explained in the general remarks section of Chart No. 1. The symbols and abbreviations on any given chart may differ somewhat from those shown in Chart No. 1. In addition, foreign charts may use different symbology. When using a foreign chart, the navigator should have available the Chart No. 1 from the country which produced the chart. Chart No. 1 is organized according to subject matter, with each specific subject given a letter designator. The general subject areas are General, Topography, Hydrography, Aids and Services, and Indexes. Under each heading, letter designators further define subject areas, and individual numbers refer to specific symbols.

Information in Chart No. 1 is arranged in columns. The first column contains the IHO number code for the symbol in question. The next two columns show the symbol itself, in NOS and DMA formats. If the formats are the same, the two columns are combined into one. The next column is a text description of the symbol, term, or abbreviation. The next column contains the IHO standard symbol. The last column shows certain symbols used on foreign reproduction charts produced by DMA.

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## Fishers of Men

*ch 3 Cont.
331. Lettering*
Except on some modified reproductions of foreign charts, cartographers have adopted certain lettering standards. Vertical type is used for features which are dry at high water and not affected by movement of the water; slanting type is used for underwater and floating features. There are two important exceptions to the two general rules listed above. Vertical type is not used to represent heights above the waterline, and slanting type is not used to indicate soundings, except on metric charts. Section 332 below discusses the conventions for indicating soundings. Evaluating the type of lettering used to denote a feature, one can determine whether a feature is visible at high tide. For instance, a rock might bear the title &#8220; Rock&#8221; whether or not it extends above the surface. If the name is given in vertical letters, the rock constitutes a small islet; if in slanting type, the rock constitutes a reef, covered at high water.

*332. Soundings*
Charts show soundings in several ways. Numbers denote individual soundings. These numbers may be either vertical or slanting; both may be used on the same chart, distinguishing between data based upon different U.S. and foreign surveys, different datums, or smaller scale charts.

Large block letters at the top and bottom of the chart indicate the unit of measurement used for soundings. 

SOUNDINGS IN FATHOMS indicates soundings are in fathoms or fathoms and fractions. SOUNDINGS IN FATHOMS AND FEET indicates the soundings are in fathoms and feet. A similar convention is followed when the soundings are in meters or meters and tenths. A depth conversion scale is placed outside the neatline on the chart for use in converting charted depths to feet, meters, or fathoms. &#8220;No bottom&#8221; soundings are indicated by a number with a line over the top and a dot over the line. This indicates that the spot was sounded to the depth indicated without reaching the bottom. Areas which have been wire dragged are shown by a broken limiting line, and the clear effective depth is indicated, with a characteristic symbol under the numbers. On DMAHTC charts a purple or green tint is shown within the swept area.

Soundings are supplemented by depth contours, lines connecting points of equal depth. These lines present a picture of the bottom. The types of lines used for various depths are shown in Section I of Chart No. 1. On some charts depth contours are shown in solid lines; the depth represented by each line is shown by numbers placed in breaks in the lines, as with land contours. Solid line depth contours are derived from intensively developed hydrographic surveys. A broken or indefinite contour is substituted for a solid depth contour whenever the reliability of the contour is questionable. Depth contours are labeled with numerals in the unit of measurement of the soundings. A chart presenting a more detailed indication of the bottom configuration with fewer numerical soundings is useful when bottom contour navigating.

Such a chart can be made only for areas which have undergone a detailed survey Shoal areas often are given a blue tint. Charts designed to give maximum emphasis to the configuration of the bottom show depths beyond the 100-fathom curve over the entire chart by depth contours similar to the contours shown on land areas to indicate graduations in height. These are
called bottom contour or bathymetric charts.

On electronic charts, a variety of other color schemes may be used, according to the manufacturer of the system. Color perception studies are being used to determine the best presentation. The side limits of dredged channels are indicated by broken lines. The project depth and the date of dredging, if known, are shown by a statement in or along the channel. The possibility of silting is always present. Local authorities should be consulted for the controlling depth. NOS Charts frequently show controlling depths in a table, which is kept current by the Notice to Mariners.

The chart scale is generally too small to permit all soundings to be shown. In the selection of soundings, least depths are shown first. This conservative sounding pattern provides safety and ensures an uncluttered chart appearance. Steep changes in depth may be indicated by more dense soundings in the area. The limits of shoal water indicated on the chart may be in error, and nearby areas of undetected shallow water may not be included on the chart. Given this possibility, areas where shoal water is known to exist should be avoided. If the navigator must enter an area containing shoals, he must exercise extreme caution in avoiding shallow areas which may have escaped detection. By constructing a &#8220;safety range&#8221; around known shoals and ensuring his vessel does not approach the shoal any closer than the safety range, the navigator can increase his chances of successfully navigating through shoal water. Constant use of the echo sounder is also important.

*333. Bottom Description*
Abbreviations listed in Section J of Chart No. 1 are used to indicate what substance forms the bottom. The meaning of these terms can be found in the Glossary of Marine Navigation. Knowing the characteristic of the bottom is most important when anchoring.

*334. Depths And Datums*
Depths are indicated by soundings or explanatory notes. Only a small percentage of the soundings obtained in a hydrographic survey can be shown on a nautical chart.
The least depths are generally selected first, and a pattern built around them to provide a representative indication of bottom relief. In shallow water, soundings may be spaced 0.2 to 0.4 inch apart. The spacing is gradually increased as water deepens, until a spacing of 0.8 to 1.0 inch is reached in deeper waters offshore. Where a sufficient number of soundings are available to permit adequate interpretation, depth curves are drawn in at selected intervals.
All depths indicated on charts are reckoned from a selected level of the water, called the chart sounding datum.

The various chart datums are explained in Chapter 9, Tides and Tidal Currents. On charts made from surveys conducted by the United States, the chart datum is selected with regard to the tides of the region. Depths shown are the least depths to be expected under average conditions. On charts based on foreign charts and surveys the datum is that of the original authority. When it is known, the datum used is stated on the chart. In some cases where the chart is based upon old surveys, particularly in areas where the range of tide is not great, the sounding datum may not be known.

For most National Ocean Service charts of the United States and Puerto Rico, the chart datum is mean lower low water. Most Defense Mapping Agency Hydrographic/Topographic Center charts are based upon mean low water, mean lower low water, or mean low water springs. The chart datum for charts published by other countries varies greatly, but is usually lower than mean low water. On charts of the Baltic Sea, Black Sea, the Great Lakes, and other areas where tidal effects are small or without significance, the datum adopted is an arbitrary height approximating the mean water level. The chart datum of the largest scale chart of an area is generally the same as the reference level from which height of tide is tabulated in the tide tables.

The chart datum is usually only an approximation of the actual mean value, because determination of the actual mean height usually requires a longer series of tidal observations than is usually available to the cartographer. In addition, the heights of the tide vary as a function of time. Since the chart datum is generally a computed mean or average height at some state of the tide, the depth of water at any particular moment may be less than shown on the chart. For example, if the chart datum is mean lower low water, the depth of water at lower low water will be less than the charted depth about as often as it is greater. A lower depth is indicated in the tide tables by a minus sign (&#8211.

*335.	Heights*
The shoreline shown on charts is generally mean high water. A light&#8217;s height is usually reckoned from mean sea level. The heights of overhanging obstructions (bridges, power cables, etc.) are usually reckoned from mean high water. A high water reference gives the mariner the minimum clearance expected.

Since heights are usually reckoned from high water and depths from some form of low water, the reference levels are seldom the same. Except where the range of tide is very large, this is of little practical significance.

*336.	Dangers*
Dangers are shown by appropriate symbols, as indicated in Section K of Chart No. 1.
A rock uncovered at mean high water may be shown as an islet. If an isolated, offlying rock is known to uncover at the sounding datum but to be covered at high water, the chart shows the appropriate symbol for a rock and gives the height above the sounding datum. The chart can give this height one of two ways. It can use a statement such as &#8220;Uncov 2 ft.,&#8221; or it can indicate the number of feet the rock protrudes above the sounding datum, underline this value, and enclose it in parentheses (i.e. (2)). A rock which does not uncover is shown by an enclosed figure approximating its dimensions and filled with land tint. It may be enclosed by a dotted depth curve for emphasis.

A tinted, irregular-line figure of approximately true dimensions is used to show a detached coral reef which uncovers at the chart datum. For a coral or rocky reef which is submerged at chart datum, the sunken rock symbol or an appropriate statement is used, enclosed by a dotted or broken line if the limits have been determined.

Several different symbols mark wrecks. The nature of the wreck or scale of the chart determines the correct symbol. A sunken wreck with less than 11 fathoms of water over it is considered dangerous and its symbol is surrounded by a dotted curve. The curve is omitted if the wreck is deeper than 11 fathoms.The safe clearance over a wreck, if known, is indicated by a standard sounding number placed at the wreck. If this depth was determined by a wire drag, the sounding is underscored by the wire drag symbol. An unsurveyed wreck over which the exact depth is unknown but a safe clearance depth is known is depicted with a solid line above the symbol.

Tide rips, eddies, and kelp are shown by symbol or legend. Piles, dolphins (clusters of piles), snags, and stumps are shown by small circles and a label identifying the type of obstruction. If such dangers are submerged, the letters &#8220;Subm&#8221; precede the label. Fish stakes and traps are shown when known to be permanent or hazardous to navigation.

*337.	Aids To Navigation*
Aids to navigation are shown by symbols listed in Sections P through S of Chart No. 1. Abbreviations and additional descriptive text supplement these symbols. In order to make the symbols conspicuous, the chart shows them in size greatly exaggerated relative to the scale of the chart. &#8220;Position approximate&#8221; circles are used on floating aids to indicate that they have no exact position because they move around their moorings. For most floating aids, the position circle in the symbol marks the approximate location of the anchor or sinker. The actual aid may be displaced from this location by the scope of its mooring.
The type and number of aids to navigation shown on a chart and the amount of information given in their legends varies with the scale of the chart. Smaller scale charts may have fewer aids indicated and less information than larger scale charts of the same area.

Lighthouses and other navigation lights are shown as black dots with purple disks or as black dots with purple flare symbols. The center of the dot is the position of the light. Some modified facsimile foreign charts use a small star instead of a dot.
On large-scale charts the legend elements of lights are shown in the following order:










As chart scale decreases, information in the legend is selectively deleted to avoid clutter. The order of deletion is usually height first, followed by period, group repetition interval (e.g. (2)), designation, and range. Characteristic and color will almost always be shown.

Small triangles mark red daybeacons; small squares mark all others. On DMAHTC charts, pictorial beacons are used when the IALA buoyage system has been implemented. The center of the triangle marks the position of the aid. Except on Intracoastal Waterway charts and charts of state waterways, the abbreviation &#8220;Bn&#8221; is shown beside the symbol, along with the appropriate abbreviation for color if known. For black beacons the triangle is solid black and there is no color abbreviation. All beacon abbreviations are in vertical lettering.

Radiobeacons are indicated on the chart by a purple circle accompanied by the appropriate abbreviation indicating an ordinary radiobeacon (R Bn) or a radar beacon (Ramark or Racon, for example).

A variety of symbols, determined by both the charting agency and the types of buoys, indicate navigation buoys. IALA buoys (see Chapter 5, Short Range Aids to Navigation) in foreign areas are depicted by various styles of symbols with proper topmarks and colors; the position circle which shows the approximate location of the sinker is at the base of the symbol.

A mooring buoy is shown by one of several symbols as indicated in Chart No. 1. 
It may be labeled with a berth number or other information.
A buoy symbol with a horizontal line indicates the buoy has horizontal bands. A vertical line indicates vertical stripes; crossed lines indicate a checked pattern. There is no significance to the angle at which the buoy symbol appears on the chart. The symbol is placed so as to avoid interference with other features.
Lighted buoys are indicated by a purple flare from the buoy symbol or by a small purple disk centered on the position circle.
Abbreviations for light legends, type and color of buoy, designation, and any other pertinent information given near the symbol are in slanted type. The letter C, N, or S indicates a can, nun, or spar, respectively. Other buoys are assumed to be pillar buoys, except for special buoys such as spherical, barrel, etc. The number or letter designation of the buoy is given in quotation marks on NOS charts. On other charts they may be given without quotation marks or other punctuation.

Aeronautical lights included in the light lists are shown by the lighthouse symbol, accompanied by the abbreviation &#8220;AERO.&#8221; The characteristics shown depend principally upon the effective range of other navigational lights in the vicinity and the usefulness of the light for marine navigation. Directional ranges are indicated by a broken or solid line. The solid line, indicating that part of the range intended for navigation, may be broken at irregular intervals to avoid being drawn through soundings. That part of the range line drawn only to guide the eye to the objects to be kept in range is broken at regular intervals. 

The direction, if given, is expressed in degrees, clockwise *from true north. * 
Sound signals are indicated by the appropriate word in capital letters (HORN, BELL, GONG, or WHIS) or an abbreviation indicating the type of sound. Sound signals of any type except submarine sound signals may be represented by three purple 45&#61616;&#61472;arcs of concentric circles near the top of the aid. These are not shown if the type of signal is listed. The location of a sound signal which does not accompany a visual aid, either lighted or unlighted, is shown by a small circle and the appropriate word in vertical block letters. Private aids, when shown, are marked &#8220;Priv&#8221; on NOS charts. Some privately maintained unlighted fixed aids are indicated by a small circle accompanied by the word &#8220;Marker,&#8221; or a larger circle with a dot in the center and the word &#8220;MARKER.&#8221; A privately maintained lighted aid has a light symbol and is accompanied by the characteristics and the usual indication of its private nature. Private aids should be used with caution.

A light sector is the sector or area bounded by two radii and the arc of a circle in which a light is visible or in which it has a distinctive color different from that of adjoining sectors. The limiting radii are indicated on the chart by dotted or dashed lines. Sector colors are indicated by words spelled out if space permits, or by abbreviations (W, R, etc.) if it does not. Limits of light sectors and arcs of visibility as observed from a vessel are given in the light lists, in clockwise order.

*338.	Land Areas*
The amount of detail shown on the land areas of nautical charts depends upon the scale and the intended purpose of the chart. Contours, form lines, and shading indicate relief. Contours are lines connecting points of equal elevation. Heights are usually expressed in feet (or in meters with means for conversion to feet). The interval between contours is uniform over any one chart, except that certain intermediate contours are sometimes shown by broken line. When contours are broken, their locations are approximate. Form lines are approximations of contours used for the purpose of indicating relative elevations. They are used in areas where accurate information is not available in sufficient detail to permit exact location of contours. Elevations of individual form lines are not indicated on the chart. Spot elevations are generally given only for summits or for tops of conspicuous landmarks. The heights of spot elevations and contours are given with reference to mean high water when this information is available. When there is insufficient space to show the heights of islets or rocks, they are indicated by slanting figures enclosed in parentheses in the water area nearby.

*339.	Cities And Roads*
Cities are shown in a generalized pattern that approximates their extent and shape. Street names are generally not charted except those along the waterfront on the largest scale charts. In general, only the main arteries and thoroughfares or major coastal highways are shown on smaller scale charts. Occasionally, highway numbers are given. When shown, trails are indicated by a light broken line. Buildings along the waterfront or individual ones back from the waterfront but of special interest to the mariner are shown on large-scale charts. Special symbols from Chart No. 1 are used for certain kinds of buildings. A single line with cross marks indicates both single and double track railroads. City electric railways are usually not charted. Airports are shown on small-scale charts by symbol and on large-scale charts by the shape of runways. The scale of the chart determines if single or double lines show breakwaters and jetties; broken lines show the submerged portion of these features.

*340.	Landmarks*
Landmarks are shown by symbols in Chart No. 1. A large circle with a dot at its center is used to indicate that the position is precise and may be used without reservation for plotting bearings. A small circle without a dot is used for landmarks not accurately located. Capital and lower case letters are used to identify an approximate landmark:
&#8220;Mon,&#8221; &#8220;Cup,&#8221; or &#8220;Dome.&#8221; The abbreviation &#8220;PA&#8221; (position approximate) may also appear. An accurate landmark is identified by all capital type ( &#8220;MON,&#8221; &#8220;CUP,&#8221; &#8220;DOME&#8221. When only one object of a group is charted, its name is followed by a descriptive legend in parenthesis, including the number of objects in the group, for example &#8220;(TALLEST OF FOUR)&#8221;or &#8220;(NORTHEAST OF THREE).&#8221;

*341.	Miscellaneous Chart Features*
*A measured nautical mile indicated on a chart is accurate to within 6 feet of the correct length.* Most measured miles in the United States were made before 1959, when the United States adopted the International Nautical Mile. The new value is within 6 feet of the previous standard length of 6,080.20 feet. If the measured distance differs from the standard value by more than 6 feet, the actual measured distance is stated and the words &#8220;measured mile&#8221; are omitted. Periods after abbreviations in water areas are omitted because these might be mistaken for rocks. However, a lower case i or j is dotted.

Commercial radio broadcasting stations are shown on charts when they are of value to the mariner either as landmarks or sources of direction-finding bearings. Lines of demarcation between the areas in which international and inland navigation rules apply are shown only when they cannot be adequately described in notes on the chart.

Compass roses are placed at convenient locations on Mercator charts to facilitate the plotting of bearings and courses. The outer circle is graduated in degrees with zero at true north. The inner circle indicates magnetic north. On many DMAHTC charts magnetic variation is given to the nearest 1&#8217; by notes in the centers of compass roses; the annual change is given to the nearest 1&#8217; to permit correction of the given value at a later date. On NOS charts, variation is to the nearest 15&#8217;, updated at each new edition if over three years old. The current practice of DMAHTC is to give the magnetic variation to the nearest 1&#8217;, but the magnetic information on new editions is only updated to conform with the latest five year epoch. Whenever a chart is reprinted, the magnetic information is updated to the latest epoch. On other charts, the variation is given by a series of isogonic lines connecting points of equal variation; usually a separate line represents each degree of variation. The line of zero variation is called the agonic line. Many plans and insets show neither compass roses nor isogonic lines, but indicate magnetic information by note. A local magnetic disturbance of sufficient force to cause noticeable deflection of the magnetic compass, called local attraction, is indicated by a note on the chart.

Currents are sometimes shown on charts with arrows giving the directions and figures showing speeds. The information refers to the usual or average conditions. According to tides and weather, conditions at any given time may differ considerably from those shown.

Review chart notes carefully because they provide important information. Several types of notes are used. Those in the margin give such information as chart number, publication notes, and identification of adjoining charts. Notes in connection with the chart title include information on scale, sources of data, tidal information, soundings, and cautions. Another class of notes covers such topics as local magnetic disturbance, controlling depths of channels, hazards to navigation, and anchorages.

A datum note will show the datum of the chart (See Chapter 2, Geodesy and Datums in Navigation). It may also contain instructions on plotting positions from the WGS 84 or NAD 83 datums on the chart if such a conversion is needed.

Anchorage areas are labeled with a variety of magenta, black, or green lines depending on the status of the area. Anchorage berths are shown as purple circles, with the number or letter assigned to the berth inscribed within the circle. Caution notes are sometimes shown when there are specific anchoring regulations.

Spoil areas are shown within short broken black lines.
Spoil areas are tinted blue on NOS charts and labeled.
These areas contain no soundings and should be avoided. Firing and bombing practice areas in the United States territorial and adjacent waters are shown on NOS and DMAHTC charts of the same area and comparable scale. Danger areas established for short periods of time are not charted but are announced locally. Most military commands charged with supervision of gunnery and missile firing areas promulgate a weekly schedule listing activated danger areas. This schedule is subjected to frequent change; the mariner should always ensure he has the latest schedule prior to proceeding into a gunnery or missile firing area. Danger areas in effect for longer periods are published in the Notice to Mariners. Any aid to navigation established to mark a danger area or a fixed or floating target is shown on charts. 

Traffic separation schemes are shown on standard nautical charts of scale 1:600,000 and larger and are printed in magenta. A logarithmic time-speed-distance nomogram with an explanation of its application is shown on harbor charts. Tidal information boxes are shown on charts of scales 1:200,000 and larger for NOS charts, and various scales on DMA charts, according to the source. See Figure 341a. Tabulations of controlling depths are shown on some National Ocean Service harbor and coastal charts. See Figure 341b.

Study Chart No. 1 thoroughly to become familiar with all the symbols used to depict the wide variety of features on nautical charts.










*To Be cont.*


----------



## Fishers of Men

*ch 3 Cont.

REPRODUCTIONS OF FOREIGN CHARTS
342. Modified Facsimiles*
Modified facsimile charts are modified reproductions of foreign charts produced in accordance with bilateral international agreements. These reproductions provide the mariner with up-to-date charts of foreign waters. Modified facsimile charts published by DMAHTC are, in general, reproduced with minimal changes, as listed below:
1. The original name of the chart may be removed and replaced by an anglicized version.
2. English language equivalents of names and terms on the original chart are printed in a suitable glossary on the reproduction, as appropriate.
3. All hydrographic information, except bottom characteristics, is shown as depicted on the original chart.
4. Bottom characteristics are as depicted in Chart No.
1, or as on the original with a glossary.
5. The unit of measurement used for soundings is shown in block letters outside the upper and lower neatlines.
6. A scale for converting charted depth to feet, meters, or fathoms is added.
7. Blue tint is shown from a significant depth curve to the shoreline.
8. Blue tint is added to all dangers enclosed by a dotted danger curve, dangerous wrecks, foul areas, obstructions, rocks awash, sunken rocks, and swept wrecks.
9. Caution notes are shown in purple and enclosed in a box.
10. Restricted, danger, and prohibited areas are usually outlined in purple and labeled appropriately. 11. Traffic separation schemes are shown in purple. 12. A note on traffic separation schemes, printed in black, is added to the chart.
13.Wire dragged (swept) areas are shown in purple or green.
14. Corrections are provided to shift the horizontal datum to the World Geodetic System (1984).

*INTERNATIONAL CHARTS
343.	International Chart Standards*
The need for mariners and chart makers to understand and use nautical charts of different nations became increasingly apparent as the maritime nations of the world developed their own establishments for the compilation and publication of nautical charts from hydrographic surveys. Representatives of twenty-two nations formed a Hydrographic Conference in London in 1919. That conference resulted in the establishment of the International Hydrographic Bureau (IHB) in Monaco in 1921. Today, the IHB&#8217;s successor, the International Hydrographic Organization (IHO) continues to provide international standards for the cartographers of its member nations. (See Chapter 1, Introduction to Marine Navigation, for a description of the IHO.)
Recognizing the considerable duplication of effort by member states, the IHO in 1967 moved to introduce the first international chart. It formed a committee of six member states to formulate specifications for two series of international charts. Eighty-three small-scale charts were approved; responsibility for compiling these charts has subsequently been accepted by the member states&#8217; Hydrographic Offices.
Once a Member State publishes an international chart, reproduction material is made available to any other Member State which may wish to print the chart for its own purposes.

International charts can be identified by the letters INT before the chart number and the International Hydrographic Organization seal in addition to other national seals which may appear.

*CHART NUMBERING SYSTEM
344.	Description Of The Numbering System*
DMAHTC and NOS use a system in which numbers are assigned in accordance with both the scale and geographical area of coverage of a chart. With the exception of certain charts produced for military use only, one- to five-digit numbers are used. With the exception of one-digit numbers, the first digit identifies the area; the number of digits establishes the scale range. The one-digit numbers are used for certain products in the chart system which are not actually charts.



















Two- and three-digit numbers are assigned to those small-scale charts which depict a major portion of an ocean basin or a large area. The first digit identifies the applicable ocean basin. See Figure 344a. Two-digit numbers are used for charts of scale 1:9,000,000 and smaller. Three-digit numbers are used for charts of scale 1:2,000,000 to 1:9,000,000.

Due to the limited sizes of certain ocean basins, no charts for navigational use at scales of 1:9,000,000 and smaller are published to cover these basins. The otherwise unused twodigit numbers (30 to 49 and 70 to 79) are assigned to special world charts such as chart 33, Horizontal Intensity of the Earth&#8217;s Magnetic Field, chart 42, Magnetic Variation, and chart 76, Standard Time Zone Chart of the World. One exception to the scale range criteria for three-digit numbers is the use of three-digit numbers for a series of position plotting sheets. They are of larger scale than 1:2,000,000 because they have application in ocean basins and can be used in all longitudes.

Four-digit numbers are used for non-navigational and special purpose charts, such as chart 5090, Maneuvering Board; chart 5101, Gnomonic Plotting Chart North Atlantic; and chart 7707, Omega Plotting Chart. Five-digit numbers are assigned to those charts of scale 1:2,000,000 and larger that cover portions of the coastline rather than significant portions of ocean basins. These charts are based on the regions of the nautical chart index. See Figure 344b.

The first of the five digits indicates the region; the second digit indicates the subregion; the last three digits indicate the geographical sequence of the chart within the subregion. Many numbers have been left unused so that any future charts may be placed in their proper geographical sequence.
In order to establish a logical numbering system within the geographical subregions (for the 1:2,000,000 and larger-scale charts), a worldwide skeleton framework of coastal charts was laid out at a scale 1:250,000. This series was used as basic coverage except in areas where a coordinated series at about this scale already existed (such as the coast of Norway where a coordinated series of 1:200,000 charts was available). Within each region, the geographical subregions are numbered counterclockwise around the continents, and within each subregion the basic series also is numbered counterclockwise around the continents. The basic coverage is assigned generally every 20th digit, except that the first 40 numbers in each subregion are reserved for smaller-scale coverage. Charts with scales larger than the basic coverage are assigned one of the 19 numbers following the number assigned to the sheet within which it falls. Figure 344c shows the numbering sequence in Iceland. Note the sequence of numbers around the coast, the direction of numbering, and the numbering of larger scale charts within the limits of smaller scales. Five-digit numbers are also assigned to the charts produced by other hydrographic offices. This numbering system is applied to foreign charts so that they can be filed in logical sequence with the charts produced by the Defense Mapping Agency Hydrographic/Topographic Center and the National Ocean Service.



















*345.	Exceptions To The System
Exceptions to the numbering system for military needs are as follows:*
1.	Bottom contour charts are not intended for surface navigation, and do not portray portions of a coastline. They chart parts of the ocean basins. They are identified with a letter plus four digits and are not available to civilian navigators.
2.	Combat charts have 6-digit numbers beginning with an &#8220;8.&#8221; They are not available to civilian navigators.

*346.	Chart Catalogs*
Chart catalogs provide information regarding not only chart coverage, but also a variety of special purpose charts and publications of interest. Keep a corrected chart catalog aboard ship for review by the navigator. The DMAHTC catalog is available to military navigators. It contains operating area charts and other special products not available for civilian use, but it does not contain any classified listings. The NOS catalogs contain all unclassified civilian-use NOS and DMAHTC charts. Military navigators receive their nautical charts and publications directly from DMAHTC; civilian navigators purchase them from NOS sales agents.

*347.	Stock Numbers*
The stock number and bar code are generally found in the lower left corner of a DMA chart, and in the lower right corner of an NOS chart. The first two digits of the stock number refer to the region and subregion. These are followed by three letters, the first of which refers to the portfolio to which the chart belongs; the second two denote the type of chart: CO for coastal, HA for harbor and approach, and OA for military operating area charts. The last five digits are the actual chart number.

*USING CHARTS
348.	Preliminary Steps*
Upon receiving a new paper chart, verify its announcement in the Notice to Mariners and correct it with all applicable corrections. Read all the chart&#8217;s notes; there should be no question about the meanings of symbols or the units in which depths are given. Since the latitude and longitude scales differ considerably on various charts, carefully note those on the chart to be used. Prepare piloting charts as discussed in Chapter 8 and open ocean transit charts as discussed in Chapter 25. Place additional information on the chart as required. Arcs of circles might be drawn around navigational lights to indicate the limit of visibility at the height of eye of an observer on the bridge. Notes regarding other information from the light lists, tide tables, tidal current tables, and sailing directions might prove helpful.

The preparation of electronic charts for use is determined by the operator&#8217;s manual for the system. If the electronic chart system in use is not IMO-approved, the navigator is required to maintain a concurrent plot on paper charts.

*349.	Maintaining Paper Charts*
A mariner navigating on an uncorrected chart is courting disaster. The chart&#8217;s print date reflects the latest Notice to Mariners used to update the chart; responsibility for maintaining it after this date lies with the user. The weekly Notice to Mariners contains information needed for maintaining charts. Radio broadcasts give advance notice of urgent corrections. Local Notice to Mariners should be consulted for inshore areas. The navigator must develop a system to keep track of chart corrections and to ensure that the chart he is using is updated with the latest correction. A convenient way of keeping this record is with a Chart/Publication Correction Record Card system. Using this system, the navigator does not immediately update every chart in his portfolio when he receives the Notice to Mariners. Instead, he constructs a card for every chart in his portfolio and notes the correction on this card. When the time comes to use the chart, he pulls the chart and chart&#8217;s card, and he makes the indicated corrections on the chart. This system ensures that every chart is properly corrected prior to use.

A Summary of Corrections, containing a cumulative listing of previously published Notice to Mariners corrections, is published annually in 5 volumes by DMAHTC. Thus, to fully correct a chart whose edition date is several years old, the navigator needs only the Summary of Corrections for that region and the notices from that Summary forward; he does not need to obtain notices all the way back to the edition date. See Chapter 4, Nautical Publications, for a description of the Summaries and Notice to Mariners. When a new edition of a chart is published, it is normally furnished automatically to U.S. Government vessels. It should not be used until it is announced as ready for use in the Notice to Mariners. Until that time, corrections in the Notice apply to the old edition and should not be applied to the new one. When it is announced, a new edition of a chart replaces an older one.

Commercial users and others who don&#8217;t automatically receive new editions should obtain new editions from their sales agent. Occasionally, charts may be received or purchased several weeks in advance of their announcement in the Notice to Mariners. This is usually due to extensive rescheming of a chart region and the need to announce groups of charts together to avoid lapses in coverage. The mariner bears the responsibility for ensuring that his charts are the current edition. The very fact that a new edition has been prepared indicates that there have been changes that cannot adequately be shown by hand corrections.

*350.	Use And Stowage Of Charts*
Use and stow charts carefully. This is especially true with digital charts contained on electronic media. Keep optical and magnetic media containing chart data out of the sun, inside dust covers, and away from magnetic influences. Placing a disk in an inhospitable environment will destroy important data.

Make permanent corrections to paper charts in ink so that they will not be inadvertently erased. Pencil in all other markings so that they can be easily erased without damaging the chart. Lay out and label tracks on charts of frequently-traveled ports in ink. Draw lines and labels no larger than necessary. Do not obscure sounding data or other information when labeling a chart. When a voyage is completed, carefully erase the charts unless there has been a grounding or collision. In this case, preserve the charts without change because they will play a critical role in the investigation.
When not in use, stow charts flat in their proper portfolio. Minimize their folding and properly index them for easy retrieval.

*351.	Chart Lighting*
Mariners often work in a red light environment because red light is least disturbing to night adapted vision. Such lighting seriously affects the appearance of a chart. Before using a chart in red light, test the effect red light has on its markings. Do not outline or otherwise indicate navigational hazards in red pencil because red markings disappear under red light.
The above point cannot be overemphasized; do not highlight danger areas on charts with red markers. Several ships have grounded on charted hazards simply because their conning officers were operating in a red light environment that obscured dangers highlighted on their charts in red pen. Always highlight danger areas on charts with a color that will not disappear in red light.

*352.	Small-Craft Charts*
Although the small-craft charts published by the National Ocean Service are designed primarily for boatmen, these charts at scales of 1:80,000 and larger are in some cases the only charts available of inland waters transited by large vessels. In other cases the small-craft charts may provide a better presentation of navigational hazards than the standard nautical chart because of scale and detail. Therefore, navigators should use these charts in areas where they provide the best coverage.

*Should have picked up some info here that wasn't previously mentioned in the charting segment.

"To know wisdom and instruction; to percieve the words of understanding; To receive the instruction of wisdom, justice, and judgment and equity; To give subtilty to the simple, to the young man knowledge and discretion." Prov: 2-4

Conclusion of chapter 3
*


----------



## Fishers of Men

*CHAPTER 4
NAUTICAL PUBLICATIONS
INTRODUCTION
400.	Definitions*
The navigator uses many information sources when planning and conducting a voyage. These sources include notices to mariners, sailing directions, light lists, tide tables, sight reduction tables, and almanacs. Historically, this information has been found in printed publications; increasingly, it is being integrated into computer-based electronic systems. The navigator must know what information he needs to navigate his ship safely and how to obtain it.
This chapter will refer only to printed publications. If the navigator has access to this data on an electronic database, only his method of access will differ. The publications discussed here form a basic navigation library; the navigator must also obtain all supplementary materials required to navigate his ship safely.

*401.	Types And Sources Of Publications*
While voyage planning and navigating, a mariner must refer to both texts and tables. Examples of text include sailing directions, coast pilots, and notices to mariners. Examples of tables include light lists and sight reduction tables.
Navigational publications are available from many sources. Military customers automatically receive or requisition most required publications. The civilian navigator obtains his publications from a publisher&#8217;s agent. Larger agents representing many publishers can completely supply a ship&#8217;s chart and publication library.

*NAUTICAL TEXTS
402.	Sailing Directions*
Defense Mapping Agency Hydrographic/Topographic Center Sailing Directions consist of 37 Enroutes and 10 Planning Guides. Planning Guides describe general features of ocean basins; Enroutes describe features of coastlines, ports, and harbors.

Sailing Directions are updated when new data requires extensive revision of an existing text. These data are obtained from several sources, including pilots and foreign Sailing Directions.

One book comprises the Planning Guide and Enroute for Antarctica. This consolidation allows for a more effective presentation of material on this unique area. The Planning Guides are relatively permanent; by contrast, Sailing Directions (Enroute) are frequently updated.
Between updates, both are corrected by the Notice to Mariners.
*
403.	Sailing Directions (Planning Guide)*
Planning Guides assist the navigator in planning an extensive oceanic voyage. Each of the Guides covers an area determined by an arbitrary division of the world&#8217;s seas into eight &#8220;ocean basins.&#8221; This division is shown in Figure 403. A Planning Guide&#8217;s first chapter contains information about the countries adjacent to the applicable ocean basin. It also covers pratique, pilotage, signals, and shipping regulations. Search and Rescue topics include the location of all lifesaving stations.

The second chapter contains information on the physical environment of an ocean basin. It consists of Ocean Summaries and descriptions of local coastal phenomena. This gives the mariner meteorological and oceanographic information to be considered in planning a route. The third chapter lists foreign firing danger areas not shown in other DMAHTC publications. A graphic key identifies Submarine Operating Areas. This chapter also identifies publications listing danger areas and gives pertinent navigation cautions.

The fourth chapter describes recommended steamship routes. To facilitate planning, the publication shows entire routes to foreign ports originating from all major U.S. ports. This chapter also includes all applicable Traffic Separation Schemes.

The fifth and final chapter describes available radionavigation systems and the area&#8217;s system of lights, beacons, and buoys.
Appendices contain information on buoyage systems, route charts, and area meteorological conditions.









*
404.	Sailing Directions (Enroute)*
Each volume of the Sailing Directions (Enroute) contains numbered sections along a coast or through a strait. Figure 404a illustrates this division. Each sector is discussed in turn. A preface with detailed information about authorities, references, and conventions used in each book precedes the sector discussions. Finally, each book provides conversions between feet, fathoms, and meters. The Chart Information Graphic, the first item in each chapter, is a graphic key for charts pertaining to a sector. See Figure 404b.

The graduation of the border scale of the chartlet enables navigators to identify the largest scale chart for a location and to find a feature listed in the Index-Gazetteer.

These graphics are not maintained by Notice to Mariners; one should refer to the chart catalog for updated chart listings.
Other graphics may contain special information on local winds and weather, anchorages, significant coastal features, and navigation dangers.
A foreign terms glossary, an appendix of anchorages, and a comprehensive Index-Gazetteer follow the sector discussions. The Index-Gazetteer is an alphabetical listing of described and charted features. The Index lists each feature by geographic coordinates and sector number for use with the graphic key. Features mentioned in the text are listed by page number.

*405.	Coast Pilots*
The National Ocean Service publishes nine United States Coast Pilots to supplement nautical charts of U.S. waters. Information comes from field inspections, survey vessels, and various harbor authorities. Maritime officials and pilotage associations provide additional information. Coast Pilots provide more detailed information than Sailing Directions because Sailing Directions are intended exclusively for the oceangoing mariner. 
The Notice to Mariners updates Coast Pilots.

Each volume contains comprehensive sections on local operational considerations and navigation regulations. Following chapters contain detailed discussions of coastal navigation. An appendix provides information on obtaining additional weather information, communications services, and other data. An index and additional tables complete the volume.

*406.	Other Nautical Texts*
The government publishes several other nautical texts.
The Defense Mapping Agency, for example, publishes the
Maneuvering Board Manual (Pub. 217), The Radar Navigation Manual (Pub.1310) and the American Practical Navigator (Pub. 9).
The U.S. Coast Guard publishes navigation rules for international and inland waters. This publication, officially known as Commandant Instruction M16672.2b, contains the Inland Navigation Rules enacted in December 1980 and effective on all inland waters of the United States including the Great Lakes, as well as the International Regulations for the Prevention of Collisions at Sea, enacted in 1972 (1972 COLREGS). Mariners should ensure that they have the updated issue. The Coast Guard also publishes comprehensive user&#8217;s manuals for the Omega, Loran, and GPS navigation systems; Navigation and Vessel Inspection Circulars; and the Chemical Data Guide for Bulk Shipment by Water. The Government Printing Office provides several publications on navigation, safety at sea, communications, weather, and related topics. Additionally, it publishes provisions of the Code of Federal Regulations (CFR) relating to maritime matters. A number of private publishers also provide maritime publications.

The International Maritime Organization, International Hydrographic Organization, and other governing international organizations provide information on international navigation regulations. Chapter 1 gives these organizations&#8217; addresses. Regulations for various Vessel Traffic Services (VTS), canals, lock systems, and other regulated waterways are published by the authorities which operate them.










*USING THE LIGHT LISTS
407.	Light Lists*
The United States publishes two different light lists. The U.S. Coast Guard publishes the Light List for lights in U.S. territorial waters; DMAHTC publishes the List of Lights for lights in foreign waters.
Light lists furnish complete information about navigation lights and other navigation aids. They supplement, but do not replace, charts and sailing directions. Consult the chart for the location and light characteristics of all navigation aids; consult the light lists to determine their detailed description.
The Notice to Mariners corrects both lists. Corrections which have accumulated since the print date are included in the Notice to Mariners as a Summary of Corrections. All of these summary corrections, and any corrections published subsequently, should be noted in the &#8220;Record of Corrections.&#8221; A navigator needs to know both the identity of a light and when he can expect to see it; he often plans the ship&#8217;s track to pass within a light&#8217;s range. If lights are not sighted when predicted, the vessel may be significantly off course and standing into danger.

A circle with a radius equal to the visible range of the light usually defines the area in which a light can be seen. On some bearings, however, obstructions may reduce the range. In this case, the obstructed arc might differ with height of eye and distance. Also, lights of different colors may be seen at different distances. Consider these facts both when identifying a light and predicting the range at which it can be seen.

Atmospheric conditions have a major effect on a light&#8217;s range. Fog, haze, dust, smoke, or precipitation can obscure a light. Additionally, a light can be extinguished. Always report an extinguished light so maritime authorities can issue a warning.
On a dark, clear night, the visual range is limited by either:
(1)	luminous intensity, or (2) curvature of the earth.
Regardless of the height of eye, one cannot see a weak light beyond a certain luminous range. Assuming light travels linearly, an observer located below the light&#8217;s visible horizon cannot see it. The Distance to the Horizon table gives the distance to the horizon for various heights of eye. The light lists contain a condensed version of this table. Abnormal refraction patterns might change this range; therefore, one cannot exactly predict the range at which a light will be seen.

*408.	Determining Range And Bearing Of A Light At Initial Sighting*
A light&#8217;s luminous range is the maximum range at which an observer can see a light under existing visibility conditions. This luminous range ignores the elevation of the light, the observer&#8217;s height of eye, the curvature of the earth, and interference from background lighting. It is determined from the known nominal range and the existing visibility conditions. The nominal range is the maximum distance at which a light can be seen in weather conditions where visibility is 10 nautical miles.

The U.S. Coast Guard Light List usually lists a light&#8217;s nominal range. Use the Luminous Range Diagram shown in the Light List and Figure 408a to convert this nominal range to luminous range. Remember that the luminous ranges obtained are approximate because of atmospheric or background lighting conditions. Estimate the meteorological visibility by the Meteorological Optical Range Table, Figure 408b. Next, enter the Luminous Range Diagram with the nominal range on the horizontal nominal range scale. Follow a vertical line until it intersects the curve or reaches the region on the diagram representing the meteorological visibility. Finally, follow a horizontal line from this point or region until it intersects the vertical luminous range scale.
Example 1: The nominal range of a light as extracted from the Light List is 15 nautical miles. Required: The luminous range when the meteorological visibility is (1) 11 nautical miles and (2) 1 nautical mile.
Solution: To find the luminous range when the meteorological visibility is 11 nautical miles, enter the Luminous Range Diagram with nominal range 15 nautical miles on the horizontal nominal range scale; follow a vertical line upward until it intersects the curve on the diagram representing a meteorological visibility of 11 nautical miles; from this point follow a horizontal line to the right until it intersects the vertical luminous range scale at 16 nautical miles. A similar procedure is followed to find the luminous range when the meteorological visibility is 1 nautical mile. Answers: (1) 16 nautical miles; (2) 3 nautical miles.










A light&#8217;s geographic range depends upon the height of both the light and the observer. Sum the observer&#8217;s distance to the horizon based on his height of eye and the light&#8217;s distance to the horizon based on its height to calculate a light&#8217;s geographic range. See Figure 408c. This illustration uses a light 150 feet above the water. Table 12, Distance of the Horizon, yields a value of 14.3 nautical miles for a height of 150 feet. Within this range, the light, if powerful enough and atmospheric conditions permit, is visible regardless of the height of eye of the observer. Beyond 14.3 nautical miles, the geographic range depends upon the observer&#8217;s height of eye. Thus, by the Distance of the Horizon table mentioned above, an observer with height of eye of 5 feet can see the light on his horizon if he is 2.6 miles beyond the horizon of the light. The geographic range of the light is therefore 16.9 miles. For a height of 30 feet the distance is 14.3 + 6.4 = 20.7 miles. If the height of eye is 70 feet, the geographic range is 14.3 + 9.8 = 24.1 miles. A height of eye of 15 feet is often assumed when tabulating lights&#8217; geographic ranges.










To predict the bearing and range at which a vessel will initially sight a light first determine the light&#8217;s geographic range. Compare the geographic range with the light&#8217;s luminous range. The lesser of the two ranges is the range at which the light will first be sighted. Plot a visibility arc centered on the light and with a radius equal to the lesser of the geographic or luminous ranges. Extend the vessel&#8217;s track until it intersects the visibility arc. The bearing from the intersection point to the light is the light&#8217;s predicted bearing at first sighting. If the extended track crosses the visibility arc at a small angle, a small lateral track error may result in large bearing and time prediction errors. This is particularly apparent if the vessel is farther from the light than predicted; the vessel may pass the light without sighting it. However, not sighting a light when predicted does not always indicate the vessel is farther from the light than expected. It could also mean that atmospheric conditions are affecting visibility.
Example 2: The nominal range of a navigational light 120 feet above the chart datum is 20 nautical miles. The meteorological visibility is 27 nautical miles.
Required: The distance at which an observer at a height of eye of 50 feet can expect to see the light. Solution: The maximum range at which the light may be seen is the lesser of the luminous or geographic ranges. At 120 feet the distance to the horizon, by table or formula, is 12.8 miles. Add 8.3 miles, the distance to the horizon for a height of eye of 50 feet to determine the geographic range. The geographic range, 21.1 miles, is less than the luminous range, 40 miles.
Answer: 21 nautical miles. Because of various uncertainties,
the range is rounded off to the nearest whole mile.
*This is better than the one I drew in a prior post!*










When first sighting a light, an observer can determine if it is on the horizon by immediately reducing his height of eye. If the light disappears and then reappears when the observer returns to his original height, the light is on the horizon. This process is called bobbing a light. If a vessel has considerable vertical motion due to rough seas, a light sighted on the horizon may alternately appear and disappear. Wave tops may also obstruct the light periodically. This may cause the characteristic to appear different than expected. The light&#8217;s true characteristics can be observed either by closing the range to the light or by the observer&#8217;s increasing his height of eye. If a light&#8217;s range given in a foreign publication approximates the light&#8217;s geographic range for a 15-foot observer&#8217;s height of eye, assume that the printed range is the light&#8217;s geographic range. Also assume that publication has listed the lesser of the geographic and nominal ranges. Therefore, if the light&#8217;s listed range approximates the geographic range for an observer with a height of eye of 15 feet, then assume that the light&#8217;s limiting range is the geographic range. Then, calculate the light&#8217;s true geographic range using the actual observer&#8217;s height of eye, not the assumed height of eye of 15 feet. This calculated true geographic range is the range at which the light will first be sighted.
Example 3: The range of a light as printed on a foreign chart is 17 miles. The light is 120 feet above chart datum. The meteorological visibility is 10 nautical miles. Required: The distance at which an observer at a height of eye of 50 feet can expect to see the light. Solution: Calculate the geographic range of the light assuming a 15 foot observer&#8217;s height of eye. At 120 feet the distance to the horizon is 12.8 miles. Add 4.5 miles (the distance to the horizon at a height of 15 feet) to 12.8 miles; this range is 17.3 miles. This approximates the range listed on the chart. Then assuming that the charted range is the geographic range for a 15-foot observer height of eye and that the nominal range is the greater than this charted range, the predicted range is found by calculating the true geographic range with a 50 foot height of eye for the observer.
Answer: The predicted range = 12.8 mi. + 8.3 mi. =
21.1	mi.. The distance in excess of the charted range depends on the luminous intensity of the light and the meteorological visibility.

*409.	USCG Light Lists*
The U.S. Coast Guard Light List (7 volumes) gives information on lighted navigation aids, unlighted buoys, radiobeacons, radio direction finder calibration stations, daybeacons, racons, and Loran stations.
Each volume of the Light List contains aids to navigation in geographic order from north to south along the Atlantic coast, from east to west along the Gulf coast, and from south to north along the Pacific coast. It lists seacoast aids first, followed by entrance and harbor aids listed from seaward. Intracoastal Waterway aids are listed last in geographic order in the direction from New Jersey to Florida to the Texas/ Mexico border.
The listings are preceded by a description of the aids to navigation system in the United States, luminous range diagram, geographic range tables, and other information.

*"For with thee is the fountain of life: in thy light shall we see light." Ps 36:9

To Be cont.*


----------



## Fishers of Men

*Ch 4 Cont.
410.	DMAHTC List of Lights, Radio Aids, and Fog Signals*
The Defense Mapping Agency Hydrographic/Topographic Center publishes the List of Lights, Radio Aids, and Fog Signals (usually referred to as the List of Lights, not to be confused with the Coast Guard&#8217;s Light List). In addition
to information on lighted aids to navigation and sound signals in foreign waters, the DMAHTC List of Lights provides information on storm signals, signal stations, racons, radiobeacons, and radio direction finder calibration
stations located at or near lights. For more details on radio navigational aids, consult Pub. 117, Radio Navigational Aids.

The DMAHTC List of Lights does not include information on lighted buoys inside harbors. It does include certain aeronautical lights situated near the coast; however, these lights are not designed for marine navigation and are subject to unreported changes.

Foreign notices to mariners are the main correctional information source for the DMAHTC Lists of Lights; other sources, such as ship reports, are also used. Many aids to navigation in less developed countries may not be well maintained. They are subject to damage by storms and vandalism, and repairs may be delayed for long periods.

*MISCELLANEOUS NAUTICAL PUBLICATIONS
411.	DMAHTC Radio Navigational Aids (Pub. 117)*
This publication is a selected list of worldwide radio stations which perform services to the mariner. Topics covered include radio direction finder and radar stations, radio time signals, radio navigation warnings, distress and safety communications, medical advice via radio, long-range navigation aids, the AMVER system, and interim procedures for U.S. vessels in the event of an outbreak of hostilities. Pub. 117 is corrected via the Notice to Mariners and is updated periodically with a new edition.
Though Pub. 117 is essentially a list of radio stations providing vital maritime communication and navigation services, it also contains information which explains the capabilities and limitations of the various systems.

*412. Chart No. 1*
Chart No. 1 is not actually a chart but a book containing a key to chart symbols. Most countries which produce charts also produce such a list. The U.S. Chart No. 1 contains a listing of chart symbols in four categories:
Chart symbols used by the National Ocean Service
Chart symbols used by the Defense Mapping Agency
Chart symbols recommended by the International
Hydrographic Organization Chart symbols used on foreign charts reproduced by DMAHTC.

Subjects covered include general features of charts, topography, hydrography, and aids to navigation. There is also a complete index of abbreviations and an explanation of the IALA buoyage system.

*413. DMAHTC World Port Index (Pub. 150)*
The World Port Index contains a tabular listing of thousands of ports throughout the world, describing their locations, characteristics, facilities, and services available. Information is arranged geographically; the index is arranged alphabetically.
Coded information is presented in columns and rows. This information supplements information in the Sailing Directions. The applicable volume of Sailing Directions and the number of the harbor chart are given in the World Port Index. The Notice to Mariners corrects this book.

*414. DMAHTC Distances Between Ports (Pub. 151)*
This publication lists the distances between major ports. Reciprocal distances between two ports may differ due to different routes chosen because of currents and climatic conditions. To reduce the number of listings needed, junction points along major routes are used to consolidate routes converging from different directions.

This book can be most effectively used for voyage planning in conjunction with the proper volume(s) of the Sailing Directions (Planning Guide). It is corrected via the Notice to Mariners.

*415. DMAHTC International Code Of Signals (Pub. 102)*
This book lists the signals to be employed by vessels at sea to communicate a variety of information relating to safety, distress, medical, and operational information. This publication became effective in 1969.
According to this code, each signal has a unique and complete meaning. The signals can be transmitted via Morse light and sound, flag, radio-telegraphy and -telephony, and semaphore. Since these methods of signaling are internationally recognized, differences in language between sender and receiver are immaterial; the message will be understood when decoded in the language of the receiver, regardless of the language of the sender. The Notice to Mariners corrects Pub. 102.

*416.	Almanacs*
For celestial sight reduction, the navigator needs an almanac for ephemeris data. The Nautical Almanac, produced jointly by H.M. Nautical Almanac Office and the U.S. Naval Observatory, is the most common almanac used for celestial navigation. It also contains information on sunrise, sunset, moonrise, and moonset, as well as compact sight reduction tables. The Nautical Almanac is published annually.
The Air Almanac contains slightly less accurate ephemeris data for air navigation. It can be used for marine navigation if slightly reduced accuracy is acceptable. Chapter 19 provides more detailed information on using the Nautical Almanac.

*417.	Sight Reduction Tables*
Without a calculator or computer programmed for sight reduction, the navigator needs sight reduction tables to solve the celestial triangle. Two different sets of tables are commonly used at sea. Sight Reduction Tables for Marine Navigation, Pub. 229, consists of six volumes of tables designed for use with the Nautical Almanac for solution of the celestial triangle by the Marcq Saint Hilaire or intercept method. The tabular data are the solutions of the navigational triangle of which two sides and the included angle are known and it is necessary to find the third side and adjacent angle. Each volume of Pub. 229 includes two 8 degree zones, comprising 15 degree bands from 0 to 90 degrees, with a 1&#176; degree overlap between volumes. Pub. 229 is a joint publication produced by the Defense Mapping Agency, the U.S. Naval Observatory, and the Royal Greenwich Observatory.

Sight Reduction Tables for Air Navigation, Pub. 249, is also a joint production of the three organizations above. It is issued in three volumes. Volume 1 contains the values of the altitude and true azimuth of seven selected stars chosen to provide, for any given position and time, the best observations.

A new edition is issued every 5 years for the upcoming astronomical epoch. Volumes 2 (0&#176; to 40&#176 and 3 (39&#176; to 89&#176 provide for sights of the sun, moon, and planets.

*418.	Catalogs*
A chart catalog is a valuable reference to the navigator for voyage planning, inventory control, and ordering. There are two major types of catalogs, one for the military and one for the civilian market.

The military navigator will see the DMA nautical chart catalog as part of a larger suite of catalogs including aeronautical (Part 1), hydrographic (Part 2), and topographic (Part 3) products. Each Part consists of one or more volumes. Unclassified DMA nautical charts are listed in Part 2, Volume 1. This is available only to U.S. military users, DoD contractors, and those who support them. This catalog contains comprehensive ordering instructions and information about the products listed. Also listed are addresses of all Combat Support Center field offices, information on crisis support, and other special situations. The catalog is organized by geographic region corresponding to the chart regions 1 through 9. A special section of miscellaneous charts and publications is included. This section also lists products produced by NOS, the U.S. Army Corps of Engineers, U.S. Coast Guard, U.S. Naval Oceanographic Office, and some foreign publications from the United Kingdom and Canada.

The civilian navigator should refer to catalogs produced by the National Ocean Service. For U.S. waters, NOS charts are listed in a series of single sheet &#8220;charts&#8221; showing a major region of the U.S. with individual chart graphics shown. These catalogs also list charts showing titles and scales. Finally, it lists sales agents from whom the products may be purchased.
DMA products for the civilian navigator are listed by NOS in a series of regionalized catalogs similar to Part 2 Volume 1. These catalogs are also available through authorized NOS chart agents.

*MARITIME SAFETY INFORMATION
419.	Notice To Mariners*
The Notice to Mariners is published weekly by the Defense Mapping Agency Hydrographic/Topographic Center (DMAHTC), prepared jointly with the National Ocean Service (NOS) and the U.S. Coast Guard. It advises mariners of important matters affecting navigational safety, including new hydrographic information, changes in channels and aids to navigation, and other important data. The information in the Notice to Mariners is formatted to simplify the correction of paper charts, sailing directions, light lists, and other publications produced by DMAHTC, NOS, and the U.S. Coast Guard.

It is the responsibility of users to decide which of their charts and publications require correction. Suitable records of Notice to Mariners should be maintained to facilitate the updating of charts and publications prior to use. Information for the Notice to Mariners is contributed by: the Defense Mapping Agency Hydrographic/Topographic Center (Department of Defense) for waters outside the territorial limits of the United States; National Ocean Service (National Oceanic and Atmospheric Administration, Department of Commerce), which is charged with surveying and charting the coasts and harbors of the United States and its territories; the U.S. Coast Guard (Department of Transportation) which is responsible for the safety of life at sea and the establishment and operation of aids to navigation; and the Army Corps of Engineers (Department of Defense), which is charged with the improvement of rivers and harbors of the United States. In addition, important contributions are made by foreign hydrographic offices and cooperating observers of all nationalities.

Over 60 countries which produce nautical charts also produce a notice to mariners. About one third of these are weekly, another third are bi-monthly or monthly, and the rest irregularly issued according to need. Much of the data in the U.S. Notice to Mariners is obtained from these foreign notices.

Correct U.S. charts with the U.S. Notice to Mariners. Similarly, correct foreign charts using the foreign notice because chart datums often vary according to region and geographic positions are not the same for different datums.
The Notice consists of a page of Hydrograms listing important items in the notice, a chart correction section organized by ascending chart number, a publications correction section, and a summary of broadcast navigation warnings and miscellaneous information. Mariners are requested to cooperate in the correction of charts and publications by reporting all discrepancies between published information and conditions actually observed and by recommending appropriate improvements.
A convenient reporting form is provided in the back of each Notice to Mariners.
Notice to Mariners No. 1 of each year contains important information on a variety of subjects which supplements information not usually found on charts and in navigational publications. This information is published as Special Notice to Mariners Paragraphs. Additional items considered of interest to the mariner are also included in this Notice.
*
420.	Summary Of Corrections*
A close companion to the Notice to Mariners is the Summary of Corrections. The Summary is published in five volumes. Each volume covers a major portion of the earth including several chart regions and many subregions.
Volume 5 also includes special charts and publications corrected by the Notice to Mariners. Since the Summaries contain cumulative corrections, any chart, regardless of its print date, can be corrected with the proper volume of the Summary and all subsequent Notice to Mariners.

*421.	The Navigation Information Network*
Most of the weekly Notice to Mariners production is computerized. This system is known as the Automated Notice to Mariners System (ANMS). Design work on this system began in 1975, and the first Notice produced with it was issued in 1980. This system&#8217;s software allows remote query via modem. This remote access system is known as the Navigation Information Network (NAVINFONET).

Data available through NAVINFONET includes chart corrections, DMA List of Lights corrections, Coast Guard Light List corrections, radio warnings, MARAD Advisories, DMA hydrographic product catalog corrections, drill rig locations, ship hostile action report (SHAR) files, and GPS navigation system status reports. Messages can also be left for DMAHTC staff regarding suggestions, changes, corrections or comments on any navigation products. The system does not have the capability to send graphics files, which prevents the transfer of chartlets. However, navigators can access most other significant information contained in the Notice to Mariners. Information is updated daily or weekly according to the Notice to Mariners production schedule. The system supports most internationally recognized telephone protocols and can presently transfer data at a maximum rate of 9600 baud.
NAVINFONET is not a replacement for the weekly Notice to Mariners, and in certain respects the accuracy of information cannot be verified by DMA. Certain files, for example, are entered directly into the data base without editing by DMA staff. Also, drill rig locations are furnished by the companies which operate them. They are not required to provide these positions, and they cannot be verified. However, within these limitations, the system can provide information 2 to 3 weeks sooner than the printed Notice to Mariners, because the paper Notice must be compiled, edited, printed, and mailed after the digital version is completed.
NAVINFONET access is free, but the user must pay telephone charges. All users must register and receive a password by writing or calling DMAHTC, Attn.: MCCNAVINFONET, Mail Stop D-44, 4600 Sangamore Rd., Bethesda, MD, 20816-5003; telephone (301) 227-3296.

The U.S. Coast and Geodetic Survey operates a similar free computerized marine information bulletin board containing a list of wrecks and obstructions, a nautical chart locator, a list of marine sediments samples, a datum conversion program for NAD 27 to NAD 83 datum conversions, and a list of aerial photographs available from NOAA. The modem phone number is (301) 713-4573, the voice line (301) 713-2653, and FAX (301) 713-4581. The address of the office is NOAA, NOS, C&GS, (N/CG211), 1315 East-
West Highway, Silver Spring, MD, 20910

*422.	Local Notice To Mariners*
The Local Notice to Mariners is issued by each U.S. Coast Guard District to disseminate important information affecting navigational safety within that District. This Notice reports changes and deficiencies in aids to navigation maintained by the Coast Guard. Other marine information such as new charts, channel depths, naval operations, and regattas is included. Since temporary information of short duration is not included in the weekly Notice to Mariners, the Local Notice to Mariners may be the only source of such information. Small craft using the Intracoastal Waterway and small harbors not normally used by oceangoing vessels need it to keep charts and publications up-to-date. Since correcting information for U.S. charts in the DMAHTC Notice is obtained from the Coast Guard Local Notices, it is normal to expect a lag of 1 or 2 weeks for the DMAHTC Notice to publish a correction from this source. The Local Notice to Mariners may be obtained free of charge by contacting the appropriate Coast Guard District Commander. Vessels operating in ports and waterways in several districts must obtain the Local Notice to Mariners from each district. See Figure 422 for a complete list of U.S. Coast Guard Districts.










*423.	Electronic Notice To Mariners*
Electronic chart development is proceeding rapidly. The correction of these charts will become a major issue. In the near future, the quality standards of digital charts will permit the replacement of traditional paper charts. Neither paper nor electronic charts should be used unless corrected through the latest Notice to Mariners. Chapter 14 discusses potential methods for correcting electronic charts. Until the electronic chart is recognized as being the legal equivalent of the paper chart, however, it cannot replace the paper chart on the bridge. Presently, therefore, the mariner must continue to use traditional paper charts. Their use, in turn, necessitates the continued use of the Notice to Mariners correction system.

*"Thy word is a lamp unto my feet, and a light unto my path" Ps 119:105
conclusion ch 4
*


----------



## Fishers of Men

*CHAPTER 5
SHORT RANGE AIDS TO NAVIGATION
DEFINING SHORT RANGE AIDS TO NAVIGATION
500.	Terms And Definitions*
The term &#8220;short range aids to navigation&#8221; encompasses lighted and unlighted beacons, ranges, leading lights, buoys, and their associated sound signals. Each short range aid to navigation, commonly referred to as a NAVAID, fits within a system designed to warn the mariner of dangers and direct him toward safe water. An aid&#8217;s function determines its color, shape, light characteristic, and sound. This chapter explains the U.S. Aids to Navigation System as well as the international IALA Maritime Buoyage System. The placement and maintenance of marine aids to navigation in U.S. waters is the responsibility of the United States Coast Guard. The Coast Guard maintains lighthouses, radiobeacons, racons, Loran C, sound signals, buoys, and daybeacons on the navigable waters of the United States, its territories, and possessions. Additionally, the Coast Guard exercises control over privately owned navigation aid systems.

A beacon is a stationary, visual navigation aid. Large lighthouses and small single-pile structures are both beacons. Lighted beacons are called lights; unlighted beacons are daybeacons. All beacons exhibit a daymark of some sort. In the case of a lighthouse, the color and type of structure are the daymarks. On small structures, these daymarks, consisting of colored geometric shapes called dayboards, often have lateral significance. Conversely, the markings on lighthouses and towers convey no lateral significance.

*FIXED LIGHTS
501.	Major And Minor Lights*
Lights vary from tall, high intensity coastal lights to battery-powered lanterns on single wooden piles. Immovable, highly visible, and accurately charted, fixed lights provide navigators with an excellent source for bearings. The structures are often distinctively colored to aid in identification.

*See Figure 501a.*
A major light is a high-intensity light exhibited from a fixed structure or a marine site. Major lights include primary seacoast lights and secondary lights. Primary seacoast lights are those major lights established for making landfall from sea and coastwise passages from headland to headland. Secondary lights are those major lights established at harbor entrances and other locations where high intensity and reliability are required.
A minor light usually displays a light of low to moderate intensity. Minor lights are established in harbors, along channels, rivers, and in isolated locations. They usually have numbering, coloring, and light and sound characteristics that are part of the lateral system of buoyage.
Lighthouses are placed where they will be of most use:
on prominent headlands, at harbor and port entrances, on isolated dangers, or at other points where mariners can best use them to fix their position. The lighthouse&#8217;s principal purpose is to support a light at a considerable height above the water, thereby increasing its geographic range. Support equipment is often housed near the tower.

With few exceptions, all major lights are operated automatically. There are also many automatic lights on smaller structures maintained by the Coast Guard or other attendants. Unmanned major lights may have emergency generators and automatic monitoring equipment to increase the light&#8217;s reliability.

Light structures&#8217; appearances vary. Lights in low-lying areas usually are supported by tall towers; conversely, light structures on high cliffs may be relatively short. However its support tower is constructed, almost all lights are similarly generated, focused, colored, and characterized. Some major lights use modern rotating or flashing lights, but many older lights use Fresnel lenses. These lenses consist of intricately patterned pieces of glass in a heavy brass framework. Modern Fresnel-type lenses are cast from high-grade plastic; they are much smaller and lighter than their glass counterparts.
A buoyant beacon provides nearly the positional accuracy of a light in a place where a buoy would normally be used. See Figure 501b. The buoyant beacon consists of a heavy sinker to which a pipe structure is tightly moored. A buoyancy chamber near the surface supports the pipe. The light, radar reflector, and other devices are located atop the pipe above the surface of the water. The pipe with its buoyancy chamber tends to remain upright even in severe weather and heavy currents, providing a smaller watch circle than a buoy. The buoyant beacon is most useful along narrow ship channels in relatively sheltered water.










*502. Range Lights*
Range lights are light pairs that indicate a specific line of position when they are in line. The higher rear light is placed behind the front light. When the mariner sees the lights vertically in line, he is on the range line. If the front light appears left of the rear light, the observer is to the right of the rangeline; if the front appears to the right of the rear, the observer is left of the rangeline. Range lights are sometimes equipped with high intensity lights for daylight use. These are effective for long channels in hazy conditions when dayboards might not be seen. The range light structures are usually also equipped with dayboards for ordinary daytime use. Some smaller ranges, primarily in the Intracoastal Waterway and other inland waters, have just the dayboards with no lights.

*See Figure 502.*









To enhance the visibility of range lights, the Coast Guard has developed 15-foot long lighted tubes called light pipes. They are mounted vertically, and the mariner sees them as vertical bars of light distinct from background lighting. Installation of light pipes is proceeding on several range markers throughout the country. The Coast Guard is also experimenting with long range sodium lights for areas requiring visibility greater than the light pipes can provide. The output from a low pressure sodium light is almost entirely at one wavelength. This allows the use of an inexpensive band-pass filter to make the light visible even during the daytime. This arrangement eliminates the need for high intensity lights with their large power requirements. Range lights are usually white, red, or green. They display various characteristics differentiating them from surrounding lights.

A directional light is a single light that projects a high intensity, special characteristic beam in a given direction. It is used in cases where a two-light range may not be practicable. A directional sector light is a directional light that emits two or more colored beams. The beams have a precisely oriented boundary between them. A normal application of a sector light would show three colored sections: red, white, and green.

The white sector would indicate that the vessel is on the channel centerline; the green sector would indicate that the vessel is off the channel centerline in the direction of deep water; and the red sector would indicate that the vessel is off the centerline in the direction of shoal water.
*
503.	Aeronautical Lights*
Aeronautical lights may be the first lights observed at night when approaching the coast. Those situated near the coast and visible from sea are listed in the List of Lights. These lights are not listed in the Coast Guard Light List.
They usually flash alternating white and green.

Aeronautical lights are sequenced geographically in the List of Lights along with marine navigation lights. However, since they are not maintained for marine navigation, they are subject to changes of which maritime authorities may not be informed. These changes will be published in Notice to Airmen but perhaps not in Notice To Mariners.

*504.	Bridge Lights*
Red, green, and white lights mark bridges across navigable waters of the United States. Red lights mark piers and other parts of the bridge. Red lights are also used on drawbridges to show when they are in the closed position. Green lights mark open drawbridges and mark the centerline of navigable channels through fixed bridges. The position will vary according to the type of structure. Navigational lights on bridges in the U.S. are prescribed by Coast Guard regulations.

Infrequently-used bridges may be unlighted. In foreign waters, the type and method of lighting may be different from those normally found in the United States. Drawbridges which must be opened to allow passage operate upon sound and light signals given by the vessel and acknowledged by the bridge. These required signals are detailed in the Code of Federal Regulations and the applicable Coast Pilot. Certain bridges may also be equipped with sound signals and radar reflectors.
*
505.	Shore Lights*
Shore lights usually have a shore-based power supply.
Lights on pilings, such as those found in the Intracoastal Waterway, are battery powered. Solar panels may be installed to enhance the light&#8217;s power supply. The lights consist of a power source, a flasher to determine the characteristic, a lamp changer to replace burned-out lamps, and a focusing lens.

Various types of rotating lights are in use. They do not have flashers but remain continuously lit while a lens or reflector rotates around the horizon.The whole light system is carefully engineered to provide the maximum amount of light to the mariner for the least power use. Specially designed filaments and special grades of materials are used in the light to withstand the harsh marine environment.

The flasher electronically determines the characteristic by selectively interrupting the light&#8217;s power supply according to the chosen cycle.
The lamp changer consists of several sockets arranged around a central hub. When the circuit is broken by a burned-out filament, a new lamp is rotated into position. Almost all lights have daylight switches which turn the light off at sunrise and on at dusk.
The lens for small lights may be one of several types.
The common ones in use are omni-directional lenses of 155mm, 250mm, and 300mm. In addition, lights using parabolic mirrors or focused-beam lenses are used in leading lights and ranges. The lamp filaments must be carefully aligned with the plane of the lens or mirror to provide the maximum output of light. The lens&#8217; size is chosen according to the type of platform, power source, and lamp characteristics. Additionally, environmental characteristics of the location are considered. Various types of light-condensing panels, reflex reflectors, or colored sector panels may be installed inside the lens to provide the proper characteristic.
A special heavy 200mm lantern is used in locations where ice and breaking water are a hazard.

*LIGHT CHARACTERISTICS
506.	Characteristics*
A light has distinctive characteristics which distinguish it from other lights or convey specific information. A light may show a distinctive sequence of light and dark intervals. Additionally, a light may display a distinctive color or color sequence. In the Light Lists, the dark intervals are referred to as eclipses. An occulting light is a light totally eclipsed at regular intervals, the duration of light always being greater than the duration of darkness. A flashing light is a light which flashes at regular intervals, the duration of light always being less than the duration of darkness. An isophase light flashes at regular intervals, the duration of light being equal to the duration of darkness.

Light phase characteristics (Figure 506a and Figure 506b) are the distinctive sequences of light and dark intervals or sequences in the variations of the luminous intensity of a light. The light phase characteristics of lights which change color do not differ from those of lights which do not change color. 










An Earlier post has the updated version.










A light showing different colors alternately is described as an alternating light. The alternating characteristic may be used with other light phase characteristics. Light-sensitive switches extinguish most lighted navigation aids during daylight hours. However, owing to the various sensitivity of the light switches, all lights do not come on or go off at the same time. Mariners should account for this when identifying aids to navigation during twilight periods when some lighted aids are on while others are not.

*507.	Light Sectors*
Sectors of colored glass or plastic are sometimes placed in the lanterns of certain lights to indicate dangerous waters. Lights so equipped show different colors when observed from different bearings. A sector changes the color of a light, but not its characteristic, when viewed from certain directions. For example, a four second flashing white light having a red sector will appear as a four second flashing red light when viewed from within the red sector.
Sectors may be only a few degrees in width or extend in a wide arc from deep water toward shore. Bearings referring to sectors are expressed in degrees true as observed from a vessel.

In most cases, areas covered by red sectors should be avoided. The nature of the danger can be determined from the chart. In some cases a narrow sector may mark the best water across a shoal, or a turning point in a channel. Sectors generated by shadow-casting filters do not have precise boundaries as directional sector lights do. Therefore, the transition from one color to another is not abrupt. The colors change through an arc of uncertainty of 2&#61616;&#61472;or greater, depending on the optical design of the light. Therefore determining bearings by observing the color change is less accurate than obtaining a bearing with an azimuth circle.

*508.	Factors Affecting Range And Characteristics*
The condition of the atmosphere has a considerable effect upon a light&#8217;s range. Sometimes lights are obscured by fog, haze, dust, smoke, or precipitation. On the other hand, refraction may cause a light to be seen farther than under ordinary circumstances. A light of low intensity will be easily obscured by unfavorable conditions of the atmosphere. For this reason, the intensity of a light should always be considered when looking for it in thick weather. Haze and distance may reduce the apparent duration of a light&#8217;s flash. In some conditions of the atmosphere, white lights may have a reddish hue. In clear weather green lights may have a more whitish hue. Lights placed at great elevations are more frequently obscured by clouds, mist, and fog than those near sea level. In regions where ice conditions prevail, an unattended light&#8217;s lantern panes may become covered with ice or snow. This may reduce the light&#8217;s luminous range and change the light&#8217;s observed color.
The distance from a light cannot be estimated by its apparent brightness. There are too many factors which can change the perceived intensity. Also, a powerful, distant light may sometimes be confused with a smaller, closer one with similar characteristics. Every light sighted should be carefully evaluated to determine if it is the one expected. The presence of bright shore lights may make it difficult to distinguish navigational lights from background lighting. Lights may also be obscured by various shore obstructions, natural and man-made. The Coast Guard requests mariners to report these cases to the nearest Coast Guard station.

A light&#8217;s loom is seen through haze or the reflection from low-lying clouds when the light is beyond its geographic range. Only the most powerful lights can generate a loom. The loom may sometimes be sufficiently defined to obtain a bearing. If not, an accurate bearing on a light beyond geographic range may sometimes be obtained by ascending to a higher level where the light can be seen, and noting a star directly over the light. The bearing of the star can then be obtained from the navigating bridge and the bearing to the light plotted indirectly.

At short distances, some of the brighter flashing lights may show a faint continuous light, or faint flashes, between regular flashes. This is due to reflections of a rotating lens on panes of glass in the lighthouse.
If a light is not sighted within a reasonable time after prediction, a dangerous situation may exist. Conversely, the light may simply be obscured or extinguished. The ship&#8217;s position should immediately be fixed by other means to determine any possibility of danger.
The apparent characteristic of a complex light may change with the distance of the observer. For example, a light with a characteristic of fixed white and alternating flashing white and red may initially show as a simple flashing white light. As the vessel draws nearer, the red flash will become visible and the characteristic will apparently be alternating flashing white and red. Later, the fainter fixed white light will be seen between the flashes and the true characteristic of the light finally recognized as fixed white, alternating flashing white and red (F W Al W R). This is because for a given candlepower, white is the most visible color, green less so, and red least of the three. This fact also accounts for the different ranges given in the Light Lists for some multi-color sector lights. The same lamp has different ranges according to the color imparted by the sector glass. A light may be extinguished due to weather, battery failure, vandalism, or other causes. In the case of unattended lights, this condition might not be immediately corrected. The mariner should report this condition to the nearest Coast Guard station. During periods of armed conflict, certain lights may be deliberately extinguished without notice.
Offshore light stations should always be left well off the course whenever searoom permits.

*"Therefore is judgment far from us, neither doth justice overtake us: we wait for light, but behold obscurity: for brightness, but we walk in darkness"
Ps 59:9
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## Fishers of Men

*cont.Ch 5
I know a lot of this is repetitious but thats okay, we are building to advancement.
BUOYS
509.	Definitions And Types*
Buoys are floating aids to navigation. They mark channels, indicate shoals and obstructions, and warn the mariner of dangers. Buoys are used where fixed aids would be uneconomical or impractical due to the depth of water. By their color, shape, topmark, number, and light characteristics, buoys indicate to the mariner how to avoid hazards and stay in safe water. The federal buoyage system in the U.S. is maintained by the Coast Guard.

There are many different sizes and types of buoys designed to meet a wide range of environmental conditions and user requirements. The size of a buoy is determined primarily by its location. In general, the smallest buoy which will stand up to local weather and current conditions is chosen.
There are five types of buoys maintained by the Coast Guard. They are:
1.	Lateral marks.
2.	Isolated danger marks.
3.	Safe water marks.
4.	Special marks.
5.	Information/regulatory marks.
These conform in general to the specifications of the
International Association of Lighthouse Authorities
(IALA) buoyage system.










A lighted buoy is a floating hull with a tower on which a light is mounted. Batteries for the light are in watertight pockets in the buoy hull or in watertight boxes mounted on the buoy hull. To keep the buoy in an upright position, a counterweight is attached to the hull below the water surface. A radar reflector is built into the buoy tower.

The largest of the typical U.S. Coast Guard buoys can be moored in up to 190 feet of water, limited by the weight of chain the hull can support. The focal plane of the light is 15 to 20 feet high. The designed nominal visual range is 3.8 miles, and the radar range 4 miles. Actual conditions will cause these range figures to vary considerably.

The smallest buoys are designed for protected water. Some are made of plastic and weigh only 40 pounds. Specially designed buoys are used for fast current, ice, and other environmental conditions.

A variety of special purpose buoys are owned by other governmental organizations. Examples of these organizations include the Panama Canal Commission, the St. Lawrence Seaway Development Corporation, NOAA, and the Department of Defense. These buoys are usually navigational marks or data collection buoys with traditional round, boat-shaped, or discus-shaped hulls.

A special class of buoy, the Ocean Data Acquisition System (ODAS) buoy, is moored or floats free in offshore waters. Positions are promulgated through radio warnings. These buoys are generally not large enough to cause damage in a collision, but should be given a wide berth regardless, as any loss would almost certainly result in the interruption of valuable scientific experiments. They are generally bright orange or yellow in color, with vertical stripes on moored buoys and horizontal bands on free-floating ones, and have a strobe light for night visibility.

Even in clear weather, the danger of collision with a buoy exists. If struck head-on, a large buoy can inflict severe damage to a large ship; it can sink a smaller one. Reduced visibility or heavy background lighting can contribute to the problem. The Coast Guard sometimes receives reports of buoys missing from station that were actually run down and sunk. Tugboats and towboats towing or pushing barges are particularly dangerous to buoys because of poor over-the-bow visibility when pushing or yawing during towing. The professional mariner must report any collision with a buoy to the nearest Coast Guard unit. Failure to do so may cause the next vessel to miss the channel or hit the obstruction marked by the buoy; it can also lead to fines and legal liability.

Routine on-station buoy maintenance consists of inspecting the mooring, cleaning the hull and superstructure, replacing the batteries, flasher, and lamps, checking wiring and venting systems, and verifying the buoy&#8217;s exact position. Every few years, each buoy is replaced by a similar aid and returned to a Coast Guard maintenance facility for complete refurbishment.

The placement of a buoy depends on its purpose and its position on the chart. Most buoys are placed on charted position as accurately as conditions allow. However, if a buoy&#8217;s purpose is to mark a shoal and the shoal is found to be in a different position than the chart shows, the buoy will be placed to properly mark the shoal, and not on its charted position.

*510.	Lights On Buoys*
Buoy light systems consist of a battery pack, a flasher which determines the characteristic, a lamp changer which automatically replaces burned-out bulbs, a lens to focus the light, and a housing which supports the lens and protects the electrical equipment.

The batteries consist of 12-volt lead/acid type batteries electrically connected to provide sufficient power to run the proper flash characteristic and lamp size. These battery packs are contained in pockets in the buoy hull, accessible through water-tight bolted hatches or externally mounted boxes. Careful calculations based on light characteristics determine how much battery power to install.

The flasher determines the characteristic of the lamp.
It is installed in the housing supporting the lens.
The lamp changer consists of several sockets arranged around a central hub. A new lamp rotates into position if the active one burns out.
Under normal conditions, the lenses used on buoys are 155mm in diameter at the base. 200 mm lenses are used where breaking waves or swells call for the larger lens. They are colored according to the charted characteristic of the buoy. As in shore lights, the lamp must be carefully focused so that the filament is directly in line with the focal plane of the lens. This ensures that the majority of the light produced is focused in a 360&#176; horizontal fan beam A buoy light has a relatively narrow vertical profile. Because the buoy rocks in the sea, the focal plane may only be visible for fractions of a second at great ranges. A realistic range for sighting buoy lights is 4-6 miles in good visibility.

*511.	Sound Signals On Buoys*
Lighted sound buoys have the same general configuration as lighted buoys but are equipped with either a bell, gong, whistle, or horn. Bells and gongs are sounded by tappers hanging from the tower that swing as the buoys roll in the sea. Bell buoys produce only one tone; gong buoys produce several tones. The tone-producing device is mounted between the legs of the pillar or tower.
Whistle buoys make a loud moaning sound caused by the rising and falling motions of the buoy in the sea. A sound buoy equipped with an electronic horn will produce a pure tone at regular intervals regardless of the sea state. Unlighted sound buoys have the same general appearance as lighted buoys, but their underwater shape is designed to make them lively in all sea states.

*512.	Buoy Moorings*
Buoys require moorings to hold them in position. Typically the mooring consists of chain and a large concrete or cast iron sinker. See Figure 512. Because buoys are subjected to waves, wind, and tides, the moorings must be deployed with chain lengths much greater than the water depth. The scope of chain will normally be about 3 times the water depth. The length of the mooring chain defines a watch circle within which the buoy can be expected to swing. It is for this reason that the charted buoy symbol has a &#8220;position approximate&#8221; circle to indicate its charted position, whereas a light position is shown by a dot at the exact location. Actual watch circles do not necessarily coincide with the &#8220;position approximate&#8221; circles which represent them.










Over several years, the chain gradually wears out and must be replaced with new. The worn chain is often cast into the concrete of new sinkers.

*513.	Large Navigational Buoys*
Large navigational buoys are moored in open water at approaches to major seacoast ports. These 40-foot diameter buoys (Figure 513) show lights from heights of about 36 feet above the water. Emergency lights automatically energize if the main light is extinguished. These buoys may also have a radiobeacon and sound signals. Their condition is monitored by radio from shore.










*514.	Wreck Buoys*
A wreck buoy usually cannot be placed directly over the wreck it is intended to mark because the buoy tender may not want to pass over a shallow wreck or risk fouling the buoy mooring. For this reason, a wreck buoy is usually placed as closely as possible on the seaward or channelward side of a wreck. In some situations, two buoys may be used to mark the wreck, one lying off each end. The wreck may lie directly between them or inshore of a line between them, depending on the local situation. The Local Notice To Mariners should be consulted concerning details of the placement of wreck buoys on individual wrecks. Often it will also give particulars of the wreck and what activities may be in progress to clear it.

The charted position of a wreck buoy will usually be offset from the actual geographic position so that the wreck and buoy symbols do not coincide. Only on the largest scale chart will the actual and charted positions of both wreck and buoy be the same. Where they might overlap, it is the wreck symbol which occupies the exact charted position and the buoy symbol which is offset.

Wreck buoys are required to be placed by the owner of the wreck, but they may be placed by the Coast Guard if the owner is unable to comply with this requirement. In general, privately placed aids are not as reliable as Coast Guard aids.

Sunken wrecks are sometimes moved away from their buoys by storms, currents, freshets, or other causes. Just as shoals may shift away from the buoys placed to mark them, wrecks may shift away from wreck buoys.

*515.	Fallibility Of Buoys*
Buoys cannot be relied on to maintain their charted positions consistently. They are subject to a variety of hazards including severe weather, collision, mooring casualties, and electrical failure. Report any discrepancy noted in a buoy to the U.S. Coast Guard.

The buoy symbol shown on charts indicates the approximate position of the sinker which secures the buoy to the seabed. The approximate position is used because of practical limitations in placing and keeping buoys and their sinkers in precise geographical locations. These limitations include prevailing atmospheric and sea conditions, the slope and type of material making up the seabed, the scope of the mooring chain, and the fact that the positions of the buoys and the sinkers are not under continuous surveillance. The position of the buoy shifts around the area shown by the chart symbol due to the forces of wind and current. A buoy may not be in its charted position because of changes in the feature it marks. For example, a buoy meant to mark a shoal whose boundaries are shifting might frequently be moved to mark the shoal accurately. A Local Notice To Mariners will report the change, and a Notice To Mariners chart correction may also be written. In some small channels which change often, buoys are not charted even when considered permanent; local knowledge is advised in such areas.
For these reasons, a mariner must not rely completely upon the position or operation of buoys, but should navigate using bearings of charted features, structures, and aids to navigation on shore. Further, a vessel attempting to pass too close aboard a buoy risks a collision with the buoy or the obstruction it marks.

*"To give light to them that sit in darkness and in the shadow of death, to guide our fleet into the way of peace." Luke 1:79

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## Fishers of Men

*5 cont.Ch 

BUOYAGE SYSTEMS
516.	Lateral And Cardinal Systems*
There are two major types of buoyage systems: the lateral system and the cardinal system. The lateral system is best suited for well-defined channels. The description of each buoy indicates the direction of danger relative to the course which is normally followed. In principle, the positions of marks in the lateral system are determined by the general direction taken by the mariner when approaching port from seaward. These positions may also be determined with reference to the main stream of flood current. The United States Aids to Navigation System is a lateral system.

The cardinal system is best suited for coasts with numerous isolated rocks, shoals, and islands, and for dangers in the open sea. The characteristic of each buoy indicates the approximate true bearing of the danger it marks. Thus, an eastern quadrant buoy marks a danger which lies to the west of the buoy. The following pages diagram the cardinal and lateral buoyage systems as found outside the United States.

*517.	The IALA Maritime Buoyage System*
Although most of the major maritime nations have used either the lateral or the cardinal system for many years, details such as the buoy shapes and colors have varied from country to country. With the increase in maritime commerce between countries, the need for a uniform system of buoyage became apparent.
In 1889, an International Marine Conference held in Washington, D.C., recommended that in the lateral system, starboard hand buoys be painted red and port hand buoys black. Unfortunately, when lights for buoys were introduced some years later, some European countries placed red lights on the black port hand buoys to conform with the red lights marking the port side of harbor entrances, while in North America red lights were placed on red starboard hand buoys. In 1936, a League of Nations subcommittee recommended a coloring system opposite to the 1889 proposal.
The International Association of Lighthouse Authorities
(IALA) is a non-governmental organization which consists of representatives of the worldwide community of aids to navigation services to promote information exchange and recommend improvements based on new technologies. In 1980, with the assistance of IMO and the IHO, the lighthouse authorities from 50 countries and representatives of 9 international organizations concerned with aids to navigation met and adopted the IALA Maritime Buoyage System. They established two regions, Region A and Region B, for the entire world. Region A roughly corresponds to the 1936 League of Nations system, and Region B to the older 1889 system.
Lateral marks differ between Regions A and B. Lateral marks in Region A use red and green colors by day and night to indicate port and starboard sides of channels, respectively.

In Region B, these colors are reversed with red to starboard and green to port. In both systems, the conventional direction of buoyage is considered to be returning from sea, hence the phrase &#8220;red right returning&#8221; in IALA region B.

*518.	Types Of Marks*
The IALA Maritime Buoyage System applies to all fixed and floating marks, other than lighthouses, sector lights, leading lights and daymarks, lightships and large navigational buoys, and indicates:
1.	The side and center-lines of navigable channels.
2.	Natural dangers, wrecks, and other obstructions.
3.	Regulated navigation areas.
4.	Other important features.
Most lighted and unlighted beacons other than leading marks are included in the system. In general, beacon topmarks will have the same shape and colors as those used on buoys. The system provides five types of marks which may be used in any combination:
1.	Lateral marks indicate port and starboard sides of channels.
2.	Cardinal marks, named according to the four points of the compass, indicate that the navigable water lies to the named side of the mark.
3.	Isolated danger marks erected on, or moored directly on or over, dangers of limited extent.
4.	Safe water marks, such as midchannel buoys.
5.	Special marks, the purpose of which is apparent from
reference to the chart or other nautical documents.
*Characteristics Of Marks*
The significance of a mark depends on one or more features:
1.	By day&#8212;color, shape, and topmark.
2.	By night&#8212;light color and phase characteristics.
*Colors Of Marks*
The colors red and green are reserved for lateral marks, and yellow for special marks. The other types of marks have black and yellow or black and red horizontal bands, or red and white vertical stripes.
*Shapes Of Marks*
There are five basic buoy shapes:
1.	Can.
2.	Cone.
3.	Sphere.
4.	Pillar.
5.	Spar.
In the case of can, conical, and spherical, the shapes have lateral significance because the shape indicates the correct side to pass. With pillar and spar buoys, the shape has no special significance.

The term &#8220;pillar&#8221; is used to describe any buoy which is smaller than a &#8220;large navigation buoy (LNB)&#8221; and which has a tall, central structure on a broad base; it includes beacon buoys, high focal plane buoys, and others (except spar buoys) whose body shape does not indicate the correct side to pass.

*Topmarks*
The IALA System makes use of can, conical, spherical, and X-shaped topmarks only. Topmarks on pillar and spar buoys are particularly important and will be used wherever practicable, but ice or other severe conditions may occasionally prevent their use.

*Colors Of Lights*
Where marks are lighted, red and green lights are reserved for lateral marks, and yellow for special marks. The other types of marks have a white light, distinguished one from another by phase characteristic.

*Phase Characteristics Of Lights*
Red and green lights may have any phase characteristic, as the color alone is sufficient to show on which side they should be passed. Special marks, when lighted, have a yellow light with any phase characteristic not reserved for white lights of the system. The other types of marks have clearly specified phase characteristics of white light: various quick-flashing phase characteristics for cardinal marks, group flashing (2) for isolated danger marks, and relatively long periods of light for safe water marks. Some shore lights specifically excluded from the IALA System may coincidentally have characteristics corresponding to those approved for use with the new marks. Care is needed to ensure that such lights are not misinterpreted.

*"Thy word is a lamp unto my feet, and a light unto my path." Ps 119:105

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## Fishers of Men

*cont.Ch 5

519.	IALA Lateral Marks*
Lateral marks are generally used for well-defined channels; they indicate the port and starboard hand sides of the route to be followed, and are used in conjunction with a conventional direction of buoyage.
This direction is defined in one of two ways:
1.	Local direction of buoyage is the direction taken by the mariner when approaching a harbor, river estuary, or other waterway from seaward.

2. General direction of buoyage is determined by the buoyage authorities, following a clockwise direction around continental land-masses, given in sailing directions, and, if necessary, indicated on charts by a large open arrow symbol.
In some places, particularly straits open at both ends, the local direction of buoyage may be overridden by the general direction.

Along the coasts of the United States, the characteristics assume that proceeding &#8220;from seaward&#8221; constitutes a clockwise direction: a southerly direction along the Atlantic coast, a westerly direction along the Gulf of Mexico coast, and a northerly direction along the Pacific coast. On the Great Lakes, a westerly and northerly direction is taken as being &#8220;from seaward&#8221; (except on Lake Michigan, where a southerly direction is used). On the Mississippi and Ohio Rivers and their tributaries, the characteristics of aids to navigation are determined as proceeding from sea toward the head of navigation. On the Intracoastal Waterway, proceeding in a generally southerly direction along the Atlantic coast, and in a generally westerly direction along the gulf coast, is considered as proceeding &#8220;from seaward.&#8221;

*520.	IALA Cardinal Marks*
A cardinal mark is used in conjunction with the compass to indicate where the mariner may find the best navigable water. It is placed in one of the four quadrants (north, east, south, and west), bounded by the true bearings NW-NE, NE-SE, SE-SW, and SW-NW, taken from the point of interest. A cardinal mark takes its name from the quadrant in which it is placed.
The mariner is safe if he passes north of a north mark, east of an east mark, south of a south mark, and west of a west mark.
A cardinal mark may be used to:
1.	Indicate that the deepest water in an area is on the named side of the mark.
2.	Indicate the safe side on which to pass a danger.
3.	Emphasize a feature in a channel, such as a bend, junction, bifurcation, or end of a shoal.

*Topmarks*
Black double-cone topmarks are the most important feature, by day, of cardinal marks. The cones are vertically placed, one over the other. The arrangement of the cones is very logical: North is two cones with their points up (as in &#8220;north-up&#8221. South is two cones, points down. East is two cones with bases together, and west is two cones with points together, which gives a wineglass shape. &#8220;West is a Wineglass&#8221; is a memory aid.
Cardinal marks carry topmarks whenever practicable, with the cones as large as possible and clearly separated.
*Colors*
Black and yellow horizontal bands are used to color a cardinal mark. The position of the black band, or bands, is related to the points of the black topmarks.
*Shape*
The shape of a cardinal mark is not significant, but buoys must be pillars or spars.
*Lights*
When lighted, a cardinal mark exhibits a white light; its characteristics are based on a group of quick or very quick flashes which distinguish it as a cardinal mark and indicate its quadrant. The distinguishing quick or very quick flashes are:
North&#8212;Uninterrupted
East&#8212;three flashes in a group
South&#8212;six flashes in a group followed by a long flash West&#8212;nine flashes in a group As a memory aid, the number of flashes in each group can be associated with a clock face as follows:
(3 o&#8217;clock&#8212;E, 6 o&#8217;clock&#8212;S, and 9 o&#8217;clock&#8212;W). The long flash (of not less than 2 seconds duration), immediately following the group of flashes of a south cardinal mark, is to ensure that its six flashes cannot be mistaken for three or nine.
The periods of the east, south, and west lights are, respectively, 10, 15, and 15 seconds if quick flashing; and 5, 10, and 10 seconds if very quick flashing. Quick flashing lights flash at a rate between 50 and 79 flashes per minute, usually either 50 or 60. Very quick flashing lights flash at a rate between 80 and 159 flashes per minute, usually either 100 or 120.
It is necessary to have a choice of quick flashing or very quick flashing lights in order to avoid confusion if, for example, two north buoys are placed near enough to each other for one to be mistaken for the other.

*521.	IALA Isolated Danger Marks*
An isolated danger mark is erected on, or moored on or above, an isolated danger of limited extent which has navigable water all around it. The extent of the surrounding navigable water is immaterial; such a mark can, for example, indicate either a shoal which is well offshore or an islet separated by a narrow channel from the coast.
*Position*
On a chart, the position of a danger is the center of the symbol or sounding indicating that danger; an isolated danger buoy may therefore be slightly displaced from its geographic position to avoid overprinting the two symbols. The smaller the scale, the greater this offset will be. At very large scales the symbol may be correctly charted.
*Topmark*
A black double-sphere topmark is, by day, the most important feature of an isolated danger mark. Whenever practicable, this topmark will be carried with the spheres as large as possible, disposed vertically, and clearly separated.
*Color*
Black with one or more red horizontal bands are the colors used for isolated danger marks.
*Shape*
The shape of an isolated danger mark is not significant, but a buoy will be a pillar or a spar.
*Light*
When lighted, a white flashing light showing a group of two flashes is used to denote an isolated danger mark. As a memory aid, associate two flashes with two balls in the topmark.

*522.	IALA Safe Water Marks*
A safe water mark is used to indicate that there is navigable water all around the mark. Such a mark may be used as a center line, mid-channel, or landfall buoy.
*Color*
Red and white vertical stripes are used for safe water marks, and distinguish them from the black-banded, danger-marking marks.
*Shape*
Spherical, pillar, or spar buoys may be used as safe water marks.
*Topmark*
A single red spherical topmark will be carried, whenever practicable, by a pillar or spar buoy used as a safe water mark.
*Lights*
When lighted, safe water marks exhibit a white light. This light can be occulting, isophase, a single long flash, or Morse &#8220;A.&#8221; If a long flash (i.e. a flash of not less than 2 seconds) is used, the period of the light will be 10 seconds. As a memory aid, remember a single flash and a single sphere topmark.

*523.	IALA Special Marks*
A special mark may be used to indicate a special area or feature which is apparent by referring to a chart, sailing directions, or notices to mariners. Uses include:
1.	Ocean Data Acquisition System (ODAS) buoys.
2.	Traffic separation marks.
3.	Spoil ground marks.
4.	Military exercise zone marks.
5.	Cable or pipeline marks, including outfall pipes.
6.	Recreation zone marks.
Another function of a special mark is to define a channel within a channel. For example, a channel for deep draft vessels in a wide estuary, where the limits of the channel for normal navigation are marked by red and green lateral buoys, may have its boundaries or centerline marked by yellow buoys of the appropriate lateral shapes.
*Color*
Yellow is the color used for special marks.
*Shape*
The shape of a special mark is optional, but must not conflict with that used for a lateral or a safe water mark. For example, an outfall buoy on the port hand side of a channel could be can-shaped but not conical.
*Topmark*
When a topmark is carried it takes the form of a single yellow X.
*Lights*
When a light is exhibited it is yellow. It may show any phase characteristic except those used for the white lights of cardinal, isolated danger, and safe water marks, In the case of ODAS buoys, the phase characteristic used is groupflashing with a group of five flashes every 20 seconds.

*524.	IALA New Dangers*
A newly discovered hazard to navigation not yet shown on charts, included in sailing directions, or announced by a Notice To Mariners is termed a new danger. The term covers naturally occurring and man-made obstructions.
*Marking*
A new danger is marked by one or more cardinal or lateral marks in accordance with the IALA system rules. If the danger is especially grave, at least one of the marks will be duplicated as soon as practicable by an identical mark until the danger has been sufficiently identified.
*Lights*
If a lighted mark is used for a new danger, it must exhibit a quick flashing or very quick flashing light. If a cardinal mark is used, it must exhibit a white light; if a lateral mark, a red or green light.
*Racons*
The duplicate mark may carry a Racon, Morse coded D, showing a signal length of 1 nautical mile on a radar display.

*To be cont*


----------



## Fishers of Men

*cont.Ch 5 
525.	Chart Symbols And Abbreviations*
Spar buoys and spindle buoys are represented by the same symbol; it is slanted to distinguish them from upright beacon symbols. The abbreviated description of the color of a buoy is given under the symbol. Where a buoy is colored in bands, the colors are indicated in sequence from the top. If the sequence of the bands is not known, or if the buoy is striped, the colors are indicated with the darker color first.

*Topmarks*
Topmark symbols are solid black except when the topmark is red.
*Lights*
The period of the light of a cardinal mark is determined by its quadrant and its flash characteristic (either quickflashing or a very quick-flashing). The light&#8217;s period is less important than its phase characteristic. Where space on charts is limited, the period may be omitted.
*Light flares*
Magenta light-flares are normally slanted and inserted with their points adjacent to the position circles at the base of the symbols so the flare symbols do not obscure the topmark symbols.
*Radar Reflectors*
Radar reflectors are not affected by the IALA buoyage rules. They are not charted for several reasons. It can be assumed that most major buoys are fitted with radar reflectors. It is also necessary to reduce the size and complexity of buoy symbols and associated legends. Finally, it is understood that, in the case of cardinal buoys, buoyage authorities site the reflector so that it cannot be mistaken for a topmark. For these reasons, radar reflectors are not charted under IALA rules. The symbols and abbreviations of the IALA Maritime Buoyage System may be found in U.S.. Chart No. 1, Nautical Chart Symbols and Abbreviations, and in foreign equivalents.
*
526.	Description Of The U.S. Aids to Navigation System*
In the United States, the U.S. Coast Guard has incorporated the major features of the IALA system with the existing infrastructure of buoys and lights as explained below.

*Colors*
Under this system, green buoys mark a channel&#8217;s port side and obstructions which must be passed by keeping the buoy on the port hand. Red buoys mark a channel&#8217;s starboard side and obstructions which must be passed by keeping the buoy on the starboard hand.

Red and green horizontally banded preferred channel buoys mark junctions or bifurcations in a channel or obstructions which may be passed on either side. If the topmost band is green, the preferred channel will be followed by keeping the buoy on the port hand. If the topmost band is red, the preferred channel will be followed by keeping the buoy on the starboard hand.
Red and white vertically striped safe water buoys mark a fairway or mid-channel.

Reflective material is placed on buoys to assist in their detection at night with a searchlight. The color of the reflective material agrees with the buoy color. Red or green reflective material may be placed on preferred channel (junction) buoys; red if topmost band is red or green if the topmost band is green. White reflective material is used on safe water buoys. Special purpose buoys display yellow reflective material. Warning or regulatory buoys display orange reflective horizontal bands and a warning symbol. Intracoastal Waterway buoys display a yellow reflective square, triangle, or horizontal strip along with the reflective material coincident with the buoy&#8217;s function.
*Shapes*
Certain unlighted buoys are differentiated by shape. Red buoys and red and green horizontally banded buoys with the topmost band red are cone-shaped buoys called nuns. Green buoys and green and red horizontally banded buoys with the topmost band green are cylinder-shaped buoys called cans.

Unlighted red and white vertically striped buoys may be pillar shaped or spherical. Lighted buoys, sound buoys, and spar buoys are not differentiated by shape to indicate the side on which they should be passed. Their purpose is indicated not by shape but by the color, number, or light characteristics.
*Numbers*
All solid colored buoys are numbered, red buoys bearing even numbers and green buoys bearing odd numbers. (Note that this same rule applies in IALA System A also.) The numbers increase from seaward upstream or toward land. No other colored buoys are numbered; however, any buoy may have a letter for identification.
*Light colors*
Red lights are used only on red buoys or red and green horizontally banded buoys with the topmost band red. Green lights are used only on the green buoys or green and red horizontally banded buoys with the topmost band green. White lights are used on both &#8220;safe water&#8221; aids showing a Morse A characteristic and on Information and Regulatory aids.
*Light Characteristics*
Lights on red buoys or green buoys, if not occulting or isophase, will generally be regularly flashing (Fl). For ordinary purposes, the frequency of flashes will be not more than 50 flashes per minute. Lights with a distinct cautionary significance, such as at sharp turns or marking dangerous obstructions, will flash not less than 50 flashes but not more than 80 flashes per minute (quick flashing, Q). Lights on preferred channel buoys will show a series of grouped flashes with successive groups in a period having different number of flashes&#8212;composite group flashing (or a quick light in which the sequence of flashes is interrupted by regularly repeated eclipses of constant and long duration). Lights on safe water buoys will always show a white Morse Code &#8220;A&#8221; (Short-Long) flash recurring at the rate of approximately eight times per minute.
*Daylight Controls*
Lighted buoys have a special device to energize the light when darkness falls and to de-energize the light when day breaks. These devices are not of equal sensitivity; therefore all lights do not come on or go off at the same time. Mariners should ensure correct identification of aids during twilight periods when some light aids to navigation are on while others are not.
*Special Purpose Buoys*
Buoys for special purposes are colored yellow. White buoys with orange bands are for information or regulatory purposes. The shape of special purpose buoys has no significance. They are not numbered, but they may be lettered. If lighted, special purpose buoys display a yellow light usually with fixed or slow flash characteristics. Information and regulatory buoys, if lighted, display white lights.

*BEACONS
527. Definition And Description*
Beacons are fixed aids to navigation placed on shore or on pilings in relatively shallow water. If unlighted, the beacon is referred to as a daybeacon. A daybeacon is identified by its color and the color, shape, and number of its dayboard. The simplest form of daybeacon consists of a single pile with a dayboard affixed at or near its top. See Figure 527. Daybeacons may be used to form an unlighted range. Dayboards identify aids to navigation against daylight backgrounds. The size of the dayboard required to make the aid conspicuous depends upon the aid&#8217;s intended range. Most dayboards also display numbers or letters for identification. The numbers, letters, and borders of most dayboards have reflective tape to make them visible at night.
The detection, recognition, and identification distances vary widely for any particular dayboard. They depend upon the luminance of the dayboard, the sun&#8217;s position, and the local visibility conditions. 










*SOUND SIGNALS
528.	Types Of Sound Signals*
Most lighthouses and offshore light platforms, as well as some minor light structures and buoys, are equipped with sound-producing devices to help the mariner in periods of low visibility. Charts and Light Lists contain the information required for positive identification. Buoys fitted with bells, gongs, or whistles actuated by wave motion may produce no sound when the sea is calm. Sound signals are not designed to identify the buoy or beacon for navigation purposes. Rather, they allow the mariner to pass clear of the buoy or beacon during low visibility.

*"And suddenly there came a sound from heaven as if a rushing mighty wind, and it filled all the house where they were sitting." Acts 2:2
*
Sound signals vary. The navigator must use the Light List to determine the exact length of each blast and silent interval. The various types of sound signals also differ in tone, facilitating recognition of the respective stations.

Diaphones produce sound with a slotted piston moved back and forth by compressed air. Blasts may consist of a high and low tone. These alternate-pitch signals are called &#8220;two-tone.&#8221; Diaphones are not used by the Coast Guard, but the mariner may find them on some private navigation aids. Horns produce sound by means of a disc diaphragm operated pneumatically or electrically. Duplex or triplex horn units of differing pitch produce a chime signal. Sirens produce sound with either a disc or a cupshaped rotor actuated electrically or pneumatically. Sirens are not used on U.S. navigation aids.
Whistles use compressed air emitted through a circumferential slot into a cylindrical bell chamber.
Bells and gongs are sounded with a mechanically operated hammer.
*
529.	Limitations Of Sound Signals*
As aids to navigation, sound signals have serious limitations because sound travels through the air in an unpredictable manner.
It has been clearly established that:
1.	Sound signals are heard at greatly varying distances and that the distance at which a sound signal can be heard may vary with the bearing and timing of the signal.

*"But I say, Have they not heard? Yes verily, their sound went onto all the earth, and their words unto the ends of the world" Romans 10:18*
2.	Under certain atmospheric conditions, when a sound signal has a combination high and low tone, it is not unusual for one of the tones to be inaudible. In the case of sirens, which produce a varying tone, portions of the signal may not be heard.
3.	When the sound is screened by an obstruction, there are areas where it is inaudible.
4.	Operators may not activate a remotely controlled sound aid for a condition unobserved from the controlling station.
5.	Some sound signals cannot be immediately started.
6.	The status of the vessel&#8217;s engines and the location of the observer both affect the effective range of the aid.
These considerations justify the utmost caution when navigating near land in a fog. A navigator can never rely on sound signals alone; he should continuously man both the radar and fathometer. He should place lookouts in positions where the noises in the ship are least likely to interfere with hearing a sound signal. The aid upon which a sound signal rests is usually a good radar target, but collision with the aid or the danger it marks is always a possibility.

Emergency signals are sounded at some of the light and fog signal stations when the main and stand-by sound signals are inoperative. Some of these emergency sound signals are of a different type and characteristic than the main sound signal. The characteristics of the emergency sound signals are listed in the Light List.
The mariner should never assume:
1.	That he is out of ordinary hearing distance because he fails to hear the sound signal.
2.	That because he hears a sound signal faintly, he is far from it.
3.	That because he hears it clearly, he is near it.
4.	That the distance from and the intensity of a sound on any one occasion is a guide for any future occasion.
5.	That the sound signal is not sounding because he does not hear it, even when in close proximity.
6.	That the sound signal is in the direction the sound appears to come from.

*MISCELLANEOUS U.S. SYSTEMS
530.	Intracoastal Waterway Aids To Navigation*
The Intracoastal Waterway (ICW) runs parallel to the Atlantic and Gulf of Mexico coasts from Manasquan Inlet on the New Jersey shore to the Texas/Mexican border. It follows rivers, sloughs, estuaries, tidal channels, and other natural waterways, connected with dredged channels where necessary. Some of the aids marking these waters are marked with yellow; otherwise, the marking of buoys and beacons follows the same system as that in other U.S. waterways.

Yellow symbols indicate that an aid marks the Intracoastal Waterway. Yellow triangles indicate starboard hand aids, and yellow squares indicate port hand aids when following the ICW&#8217;s conventional direction of buoyage. Nonlateral aids such as safe water, isolated danger, and front range boards are marked with a horizontal yellow band. Rear range boards do not display the yellow band. At a junction with a federally-maintained waterway, the preferred channel mark will display a yellow triangle or square as appropriate. Junctions between the ICW and privately maintained waterways are not marked with preferred channel buoys.

*To be cont
*


----------



## Fishers of Men

*cont.Ch 5 
531.	Western Rivers System*
Aids to navigation on the Mississippi River and its tributaries above Baton Rouge generally conform to the lateral system of buoyage in use in the rest of the U.S. The following differences are significant:
*1.	Buoys are not numbered.*
2.	The numbers on lights and daybeacons do not have lateral significance; *they indicate the mileage from a designated point, normally the river mouth.*
3.	Flashing lights on the left side proceeding upstream show single green or white flashes while those on the right side show group flashing red or white flashes.
4.	Diamond shaped crossing daymarks are used to indicate where the channel crosses from one side of the river to the other.
*532.	The Uniform State Waterway Marking System
(USWMS)*
This system was developed jointly by the U.S. Coast Guard and state boating administrators to assist the small craft operator in those state waters marked by participating states. The USWMS consists of two categories of aids to navigation. The first is a system of aids to navigation, generally compatible with the Federal lateral system of buoyage, supplementing the federal system in state waters. The other is a system of regulatory markers to warn small craft operator of dangers or to provide general information. On a well-defined channel, red and black buoys are established in pairs called gates; the channel lies between the buoys. The buoy which marks the left side of the channel viewed looking upstream or toward the head of navigation is black; the buoy which marks the right side of the channel is red. In an irregularly-defined channel, buoys may be staggered on alternate sides of the channel, but they are spaced at sufficiently close intervals to mark clearly the channel lying between them.

When there is no well-defined channel or when a body of water is obstructed by objects whose nature or location is such that the obstruction can be approached by a vessel from more than one direction, aids to navigation having cardinal significance may be used. The aids conforming to the cardinal system consist of three distinctly colored buoys.
1.	A white buoy with a red top must be passed to the south or west of the buoy.
2.	A white buoy with a black top must be passed to the north or east of the buoy.
3.	A buoy showing alternate vertical red and white stripes indicates that an obstruction to navigation extends from the nearest shore to the buoy and that he must not pass between the buoy and the nearest shore.
The shape of buoys has no significance under the USWMS.
Regulatory buoys are colored white with orange horizontal bands completely around them. One band is at the top of the buoy and a second band just above the waterline of the buoy so that both orange bands are clearly visible.
Geometric shapes colored orange are placed on the white portion of the buoy body. The authorized geometric shapes and meanings associated with them are as follows:
1.	A vertical open faced diamond shape means danger.
2.	A vertical open faced diamond shape with a cross centered in the diamond means that vessels are excluded from the marked area.
3.	A circular shape means that vessels in the marked area are subject to certain operating restrictions.
4.	A square or rectangular shape indicates that directions or information is written inside the shape. Regulatory markers consist of square and rectangular shaped signs displayed from fixed structures. Each sign is white with an orange border. Geometric shapes with the same meanings as those displayed on buoys are centered on the sign boards. The geometric shape displayed on a regulatory marker tells the mariner if he should stay well clear of the marker or if he may approach the marker in order to read directions.

*533.	Private Aids To Navigation*
A private navigation aid is any aid established and maintained by entities other than the Coast Guard. The Coast Guard must approve the placement of private navigation aids. In addition, the District Engineer, U.S. Army Corps of Engineers, must approve the placement of any structure, including aids to navigation, in the navigable waters of the U.S.
Private aids to navigation are similar to the aids established and maintained by the U.S. Coast Guard; they are specially designated on the chart and in the Light List. In some cases, particularly on large commercial structures, the aids are the same type of equipment used by the Coast Guard. Although the Coast Guard periodically inspects some private navigation aids, the mariner should exercise special caution when using them.

In addition to private aids to navigation, numerous types of construction and anchor buoys are used in various oil drilling operations and marine construction. These buoys are not charted, as they are temporary, and may not be lighted well or at all. Mariners should give a wide berth to drilling and construction sites to avoid the possibility of fouling moorings. This is a particular danger in offshore oil fields, where large anchors are often used to stabilize the positions of drill rigs in deep water. Up to eight anchors may be placed at various positions as much as a mile from the drill ship. These may or may not be marked by buoys.

*534. Protection By Law*
It is unlawful to impair the usefulness of any navigation aid established and maintained by the United States. If any vessel collides with an navigation aid, it is the legal duty of the person in charge of the vessel to report the accident to the nearest U.S. Coast Guard station.

*Conclusion chapter 5*


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## Fishers of Men

*CHAPTER 6
MAGNETIC COMPASS ADJUSTMENT
GENERAL PROCEDURES FOR MAGNETIC COMPASS ADJUSTMENT

&#8220;In all thy ways acknowledge him, and he shall direct thy paths&#8221; Prov 3:6
600.	Introduction*
This chapter presents information and procedures for magnetic compass adjustment. Sections 601 and 613 cover procedures designed to eliminate compass errors satisfactorily. Refer to Figure 607 for condensed information regarding the various compass errors and their correction.
The term compass adjustment refers to any change of permanent magnet or soft iron correctors to reduce normal compass errors. The term compass compensation refers to any change in the current supplied to the compass compensating coils to reduce degaussing errors.

*601.	Adjustment Check-Off List*
If the magnetic adjustment necessitates (a) movement of degaussing compensating coils, or (b) a change of Flinders bar length, check also the coil compensation per section 646.
Expeditious compass adjustment depends on the application of the various correctors in an optimum sequence designed to minimize the number of correction steps. Certain adjustments may be made conveniently at dockside, simplifying the at sea adjustment procedures. Moving the wrong corrector wastes time and upsets all previous adjustments, so be careful to make the correct adjustments. Throughout an adjustment, special care should be taken to pair off spare magnets so that the resultant field about them will be negligible. To make doubly sure that the compass is not affected by a spare magnet&#8217;s stray field, keep them at an appropriate distance until they are actually inserted into the binnacle.
A.	Dockside tests and adjustments.
1.	Physical checks on the compass and binnacle.
a.	Remove any bubbles in compass bowl (section 610).
b.	Test for moment and sensibility of compass needles (section 610).
c.	Remove any slack in gimbal arrangement.
d.	Magnetization check of spheres and Flinders bar (section 610).
e.	Alignment of compass with fore-and-aft line of ship (section 610).
f.	Alignment of magnets in binnacle.
g.	Alignment of heeling magnet tube under pivot point of compass.
h.	See that corrector magnets are available.
2.	Physical checks of gyro, azimuth circle, and peloruses.
a.	Alignment of peloruses with fore-and-aft line of ship (section 610).
b.	Synchronize gyro repeaters with master gyro.
c.	Ensure azimuth circles and peloruses are in good condition.
3.	Necessary data.
a.	Past history or log data which might establish length of Flinders bar (sections 610 and 623).
b.	Azimuths for date and observer&#8217;s position (section 633 and Chapter 17).
c.	Ranges or distant objects in vicinity if needed (local charts).
d.	Correct variation (local charts).
e.	Degaussing coil current settings for swing for residual deviations after adjustment and compensation (ship&#8217;s Degaussing Folder).
4.	Precautions.
a.	Determine transient deviations of compass from gyro repeaters, doors, guns, etc. (sections 636 and 639).
b.	Secure all effective magnetic gear in normal seagoing position before beginning adjustments.
c.	Make sure degaussing coils are secured before beginning adjustments. Use reversal sequence, if necessary.
d.	Whenever possible, correctors should be placed symmetrically with respect to the compass.
5.	Adjustments.
a.	Place Flinders bar according to best available information (sections 610, 622 through 625).
b.	Set spheres at mid-position, or as indicated by last deviation table.
c.	Adjust heeling magnet, using balanced dip needle if available (section 637).
B.	Adjustments at sea. Make these adjustments with the ship on an even keel and steady on each heading. When using the gyro, swing slowly from heading to heading and check gyro error by sun&#8217;s azimuth or ranges on each heading to ensure a greater degree of accuracy (section 631). Be sure gyro is set for the mean speed and latitude of the vessel. Note all precautions in section A-4 above. Fly the &#8220;OSCAR QUEBEC&#8221; international code signal to indicate such work is in progress. Section 631 discusses methods for placing the ship on desired headings.










http://i202.photobucket.com/albums/aa305/FishersofMen/601.jpg
1. Adjust the heeling magnet while the ship is rolling on north and south magnetic headings until the oscillations of the compass card have been reduced to an average minimum. This step is not required if prior adjustment has been made using a dip needle to indicate proper placement of the heeling magnet.
2. Come to a cardinal magnetic heading, e.g., east (090&#176. Insert fore-and-aft B magnets, or move the existing B magnets, to remove all deviation. 3. Come to a south (180&#176 magnetic heading. Insert athwartship C magnets, or move the existing C magnets, to remove all deviation. 4. Come to a west (270&#176 magnetic heading. Correct half of any observed deviation by moving the B magnets.
5. Come to a north (000&#176 magnetic heading. Correct half of any observed deviation by moving the C magnets.
The cardinal heading adjustments should now be complete.
6. Come to any intercardinal magnetic heading, e.g., northeast (045&#176. Correct any observed deviation by moving the spheres in or out.
7.	Come to the next intercardinal magnetic heading, e.g., southeast (135&#176. Correct half of any observed deviation by moving the spheres.
The intercardinal heading adjustments should now be complete, although more accurate results might be obtained by correcting the D error determined from the deviations on all four intercardinal headings, as discussed in section 615.
8.	Secure all correctors before swinging for residual deviations.
9.	Swing for residual undegaussed deviations on as many headings as desired, although the eight cardinal and intercardinal headings should be sufficient.
10.	Should there still be any large deviations, analyze the deviation curve to determine the necessary corrections and repeat as necessary steps 1
through 9 above.
11.	Record deviations and the details of corrector positions on the deviation card to be posted near the compass.
12.	Swing for residual degaussed deviations with the degaussing circuits properly energized.
13.	Record deviations for degaussed conditions on the deviation card.
The above check-off list describes a simplified method of adjusting compasses, designed to serve as a workable outline for the novice who chooses to follow a step-by-step procedure. The dockside tests and adjustments are essential as a foundation for the adjustments at sea. Neglecting the dockside procedures may lead to spurious results or needless repetition of the procedures at sea. Give careful consideration to these dockside checks prior to making the final adjustment. This will allow time to repair or replace faulty compasses, anneal or replace magnetized spheres or Flinders bars, realign the binnacle, move a gyro repeater if it is affecting the compass, or to make any other necessary preliminary repairs.

Expeditious compass adjustment depends upon the application of the various correctors in a logical sequence so as to achieve the final adjustment with a minimum number of steps. The above check-off list accomplishes this purpose. Figure 607 presents the various compass errors and their correction in condensed form. Frequent, careful observations should be made to determine the constancy of deviations, and results should be systematically recorded. Significant changes in deviation will indicate the need for readjustment.

To avoid Gaussin error (section 636) when adjusting and swinging ship for residuals, the ship should be steady on the desired heading for at least 2 minutes prior to observing the deviation.

*602.	The Magnetic Compass And Magnetism*
The principle of the present day magnetic compass is no different from that of the compasses used by ancient mariners. It consists of a magnetized needle, or an array of needles, allowed to rotate in the horizontal plane. The superiority of the present day compasses over ancient ones results from a better knowledge of the laws of magnetism which govern the behavior of the compass and from greater precision in construction.
Any piece of metal on becoming magnetized will develop regions of concentrated magnetism called poles. Any such magnet will have at least two poles of opposite polarity. Magnetic force (flux) lines connect one pole of such a magnet with the other pole. The number of such lines per unit area represents the intensity of the magnetic field in that area. If two such magnetic bars or magnets are placed close to each other, the like poles will repel each other and the unlike poles will attract each other.
Magnetism can be either permanent or induced. A bar having permanent magnetism will retain its magnetism when it is removed from the magnetizing field. A bar having induced magnetism will lose its magnetism when removed from the magnetizing field. Whether or not a bar will retain its magnetism on removal from the magnetizing field will depend on the strength of that field, the degree of hardness of the iron (retentivity), and also upon the amount of physical stress applied to the bar while in the magnetizing field. The harder the iron, the more permanent will be the magnetism acquired.

*603.	Terrestrial Magnetism*
Consider the earth as a huge magnet surrounded by magnetic flux lines connecting its two magnetic poles. These magnetic poles are near, but not coincidental with, the earth&#8217;s geographic poles. Since the north seeking end of a compass needle is conventionally called the north pole, or positive pole, it must therefore be attracted to a south pole, or negative pole.
Figure 603a illustrates the earth and its surrounding magnetic field. The flux lines enter the surface of the earth at different angles to the horizontal, at different magnetic atitudes.
This angle is called the angle of magnetic dip, q, and increases from 0&#176;, at the magnetic equator, to 90&#176; at the magnetic poles.

The total magnetic field is generally considered as having two components: H, the horizontal component; and Z, the vertical component. These components change as the angle q, changes, such that H is maximum at the magnetic equator and decreases in the direction of either pole; Z is zero at the magnetic equator and increases in the direction of either pole. The values of magnetic dip may be found on Chart 30 (shown simplified in Figure 603b). The values of H and Z may be found on charts 33 and 36.



















Since the magnetic poles of the earth do not coincide with the geographic poles, a compass needle in line with the earth&#8217;s magnetic field will not indicate true north, but magnetic north. The angular difference between the true meridian (great circle connecting the geographic poles) and the magnetic meridian (direction of the lines of magnetic flux) is called variation. This variation has different values at different locations on the earth. These values of magnetic variation may be found on Chart 42 (shown simplified in Figure 603c), on pilot charts, and, on the compass rose of navigational charts. The variation for most given areas undergoes an annual change, the amount of which is also noted on charts.

*604.	Ship&#8217;s Magnetism*
A ship under construction or major repair will acquire permanent magnetism due to hammering and jarring while sitting stationary in the earth&#8217;s magnetic field. After launching, the ship will lose some of this original magnetism as a result of vibration and pounding in varying magnetic fields, and will eventually reach a more or less stable magnetic condition. The magnetism which remains is the permanent magnetism of the ship.

*(Every boat has its own unique magnetism, even the very same two coming out of the same &#8220;mold&#8221; will differ.)*

The fact that a ship has permanent magnetism does not mean that it cannot also acquire induced magnetism when placed in the earth&#8217;s magnetic field. The magnetism induced in any given piece of soft iron is a function of the field intensity, the alignment of the soft iron in that field, and the physical properties and dimensions of the iron. This induced magnetism may add to, or subtract from, the permanent magnetism already present in the ship, depending on how the ship is aligned in the magnetic field. The softer the iron, the more readily it will be magnetized by the earth&#8217;s magnetic field, and the more readily it will give up its magnetism when removed from that field. The magnetism in the various structures of a ship, which tends to change as a result of cruising, vibration, or aging, but which does not alter immediately so as to be properly termed induced magnetism, is called subpermanent magnetism. This magnetism, at any instant, is part of the ship&#8217;s permanent magnetism, and consequently must be corrected by permanent magnet correctors. It is the principal cause of deviation changes on a magnetic compass. Subsequent reference to permanent magnetism will refer to the apparent permanent magnetism which includes the existing permanent and subpermanent magnetism. A ship, then, has a combination of permanent, subpermanent, and induced magnetism. Therefore, the ship&#8217;s apparent permanent magnetic condition is subject to change from deperming, excessive shocks, welding, and vibration. The ship&#8217;s induced magnetism will vary with the earth&#8217;s magnetic field strength and with the alignment of the ship in that field.

*605.	Magnetic Adjustment*
A rod of soft iron, in a plane parallel to the earth&#8217;s horizontal magnetic field, H, will have a north pole induced in the end toward the north geographic pole and a south pole induced in the end toward the south geographic pole. This same rod in a horizontal plane, but at right angles to the horizontal earth&#8217;s field, would have no magnetism induced in it, because its alignment in the magnetic field is such that there will be no tendency toward linear magnetization, and the rod is of negligible cross section. Should the rod be aligned in some horizontal direction between those headings which create maximum and zero induction, it would be induced by an amount which is a function of the angle of alignment. If a similar rod is placed in a vertical position in northern latitudes so as to be aligned with the vertical earth&#8217;s field Z, it will have a south pole induced at the upper end and a north pole induced at the lower end. These polarities of vertical induced magnetization will be reversed in southern latitudes. The amount of horizontal or vertical induction in such rods, or in ships whose construction is equivalent to combinations of such rods, will vary with the intensity of H and Z, heading and heel of the ship.

The magnetic compass must be corrected for the vessel&#8217;s permanent and induced magnetism so that its operation approximates that of a completely nonmagnetic vessel. Ship&#8217;s magnetic conditions create magnetic compass deviations and sectors of sluggishness and unsteadiness. Deviation is defined as deflection right or left of the magnetic meridian. Adjusting the compass consists of arranging magnetic and soft iron correctors about the binnacle so that their effects are equal and opposite to the effects of the magnetic material in the ship. The total permanent magnetic field effect at the compass may be broken into three components, mutually 90&#176; apart, as shown in Figure 605a.










The vertical permanent component tilts the compass card, and, when the ship rolls or pitches, causes oscillating deflections of the card. Oscillation effects which accompany roll are maximum on north and south compass headings, and those which accompany pitch are maximum on east and west compass headings.

The horizontal B and C components of permanent magnetism cause varying deviations of the compass as the ship swings in heading on an even keel. Plotting these deviations against compass heading yields the sine and cosine curves shown in Figure 605b. These deviation curves are called semicircular curves because they reverse direction by 180&#176;.










A vector analysis is helpful in determining deviations or the strength of deviating fields. For example, a ship as shown in Figure 605c on an east magnetic heading will subject its compass to a combination of magnetic effects; namely, the earth&#8217;s horizontal field H, and the deviating field B, at right angles to the field H. The compass needle will align itself in the resultant field which is represented by the vector sum of H and B, as shown. A similar analysis will reveal that the resulting directive force on the compass would be maximum on a north heading and minimum on a south heading because the deviations for both conditions are zero.










The magnitude of the deviation caused by the permanent B magnetic field will vary with different values of H; hence, deviations resulting from permanent magnetic fields will vary with the magnetic latitude of the ship.

Induced magnetism varies with the strength of the surrounding field, the mass of metal, and the alignment of the metal in the field. Since the intensity of the earth&#8217;s magnetic field varies over the earth&#8217;s surface, the induced magnetism in a ship will vary with latitude, heading, and heel of the ship. With the ship on an even keel, the resultant vertical induced magnetism, if not directed through the compass itself, will create deviations which plot as a semicircular deviation curve. This is true because the vertical induction changes magnitude and polarity only with magnetic latitude and heel, and not with heading of the ship. Therefore, as long as the ship is in the same magnetic latitude, its vertical induced pole swinging about the compass will produce the same effect on the compass as a permanent pole swinging about the compass.

The earth&#8217;s field induction in certain other unsymmetrical arrangements of horizontal soft iron create a constant A deviation curve. In addition to this magnetic A error, there are constant A deviations resulting from: (1) physical misalignments of the compass, pelorus, or gyro; (2) errors in calculating the sun&#8217;s azimuth, observing time, or taking bearings. The nature, magnitude, and polarity of all these induced effects are dependent upon the disposition of metal, the symmetry or asymmetry of the ship, the location of the binnacle, the strength of the earth&#8217;s magnetic field, and the angle of dip.










http://s202.photobucket.com/albums/aa305/FishersofMen/?action=view&current=607.jpg
Certain heeling errors, in addition to those resulting from permanent magnetism, are created by the presence of both horizontal and vertical soft iron which experience changing induction as the ship rolls in the earth&#8217;s magnetic field. This part of the heeling error will naturally change in magnitude with changes of magnetic latitude of the ship. Oscillation effects accompanying roll are maximum on north and south headings, just as with the permanent magnetic heeling errors.

*To be continued*


----------



## Fishers of Men

*CHAPTER 6 continued
607.	Adjustments And Correctors*
Since some magnetic effects are functions of the vessel&#8217;s magnetic latitude and others are not, each individual effect should be corrected independently. Furthermore, to make the corrections, use (1) permanent magnet correctors to compensate for permanent magnetic fields at the compass, and (2) soft iron correctors to compensate for induced magnetism. The compass binnacle provides support for both the compass and such correctors. Typical binnacles hold the following correctors:
1.	Vertical permanent heeling magnet in the central vertical tube.
2.	Fore-and-aft B permanent magnets in their trays.
3.	Athwartship C permanent magnets in their trays.
4.	Vertical soft iron Flinders bar in its external tube.
5.	Soft iron quadrantal spheres.
The heeling magnet is the only corrector which corrects for both permanent and induced effects. Therefore, it must be adjusted occasionally for changes in ship&#8217;s latitude. However, any movement of the heeling magnet will require readjustment of other correctors.

Figure 607 summarizes all the various magnetic conditions in a ship, the types of deviation curves they create, the correctors for each effect, and headings on which each corrector is adjusted. Apply the correctors symmetrically and as far away from the compass as possible. This preserves the uniformity of magnetic fields about the compass needle array.

Fortunately, each magnetic effect has a slightly different characteristic curve. This makes identification and correction convenient. Analyzing a complete deviation curve for its different components allows one to anticipate the necessary corrections.

*COMPASS OPERATION
608.	Effects Of Errors On The Compass*
An uncorrected compass suffers large deviations and sluggish, unsteady operation. These conditions may be associated with the maximum and minimum directive force acting on the compass. The maximum deviation occurs at the point of average directive force; and the zero deviations occur at the points of maximum and minimum directive force.

Applying correctors to reduce compass deviation effects compass error correction. Applying correctors to equalize the directive forces across the compass position could also effect compass correction. The deviation method is most often used because it utilizes the compass itself as the correction indicator. Equalizing the directive forces would require an additional piece of test and calibration equipment.

Occasionally, the permanent magnetic effects at the location of the compass are so large that they overcome the earth&#8217;s directive force, H. This condition will not only create sluggish and unsteady sectors, but may even freeze the compass to one reading or to one quadrant, regardless of the heading of the ship. Should the compass become so frozen, the polarity of the magnetism which must be attracting the compass needles is indicated; hence, correction may be effected simply by the application of permanent magnet correctors, in suitable quantity to neutralize this magnetism. Whenever such adjustments are made, it would be well to have the ship placed on a heading such that the unfreezing of the compass needles will be immediately evident. For example, a ship whose compass is frozen to a north reading would require fore-and-aft B corrector magnets with the positive ends forward in order to neutralize the existing negative pole which attracted the compass. If made on an east heading, such an adjustment would be practically complete when the compass card was freed to indicate an east heading.
*
609.	Reasons For Correcting Compass*
There are several reasons for correcting the errors of the magnetic compass:
1.	It is easier to use a magnetic compass if the deviations are small.
2.	Even known and compensated for deviation introduces error because the compass operates sluggishly and unsteadily when deviation is present.
3.	Even though the deviations are compensated for, they will be subject to appreciable change as a function of heel and magnetic latitude.
Once properly adjusted, the magnetic compass deviations should remain constant until there is some change in the magnetic condition of the vessel resulting from magnetic treatment, shock from gunfire, vibration, repair, or structural changes. Frequently, the movement of nearby guns, doors, gyro repeaters, or cargo affects the compass greatly.

*DETAILED PROCEDURES FOR COMPASS ADJUSTMENT
610.	Dockside Tests And Adjustments*
Section 601, the Adjustment Checkoff List, gives the physical checks required before beginning an adjustment. The adjustment procedure assumes that these checks have been completed. The navigator will avoid much delay by making these checks before starting the magnet and soft iron corrector adjustments. The most important of these checks are discussed below.
Should the compass have a small bubble, add compass fluid through the filling plug on the compass bowl. If an appreciable amount of compass liquid has leaked out, check the sealing gasket and filling plug for leaks. Take the compass to a place free from all magnetic influences except the earth&#8217;s magnetic field for tests of moment and sensibility. These tests involve measurements of the time of vibration and the ability of the compass card to return to a consistent reading after deflection. These tests will indicate the condition of the pivot, jewel, and magnetic strength of the compass needles.
Next, check the spheres and Flinders bar for residual magnetism. Move the spheres as close to the compass as possible and slowly rotate each sphere separately. Any appreciable deflection (2&#176; or more) of the compass needles resulting from this rotation indicates residual magnetism in the spheres. The Flinders bar magnetization check is preferably made with the ship on an east or west compass heading. To make this check: (a) note the compass reading with the Flinders bar in the holder; (b) invert the Flinders bar in the holder and again note the compass reading. Any appreciable difference (2&#176; or more) between these observed readings indicates residual magnetism in the Flinders bar. Spheres or Flinders bars which show signs of such residual magnetism should be annealed, i.e., heated to a dull red and allowed to cool slowly.
Correct alignment of the lubber&#8217;s line of the compass, gyro repeater, and pelorus with the fore-and-aft line of the ship is important. Any misalignment will produce a constant error in the deviation curve. All of these instruments may be aligned correctly with the fore-andaft line of the ship by using the azimuth circle and a metal tape measure. Should the instrument be located on the centerline of the ship, a sight is taken on a mast or other object on the centerline. If the instrument is not on the centerline, measure the distance from the centerline of the ship to the center of the instrument. Mark this distance off from the centerline forward or abaft the compass and place reference marks on the deck. Take sights on these marks.
Align the compass so that the compass&#8217; lubber&#8217;s line is parallel to the fore-and-aft line of the ship. Steering compasses may occasionally be deliberately misaligned in order to correct for any magnetic A error present, as discussed in section 611.

Adjust the Flinders bar first because it is subject to induction from several of the correctors and its adjustment is not dependent on any single observation. To adjust the Flinders bar, use one of the following methods:
1.	Use deviation data obtained at two different magnetic latitudes to calculate the proper length of Flinders bar for any particular compass location. Sections 622 through 624 contain details on acquiring the data and making the required calculations.
2.	If the above method is impractical, set the Flinders bar length by:
a.	Using a Flinders bar length determined by other ships of similar structure.
b.	Studying the arrangement of masts, stacks, and other vertical structures and estimating the Flinders bar length required.
If these methods are not suitable, omit the Flinders bar until the required data are acquired.

The iron sections of Flinders bar should be continuous and placed at the top of the tube with the longest section at the top. Wooden spacers are used at the bottom of the tube.
Having adjusted the length of Flinders bar, place the spheres on the bracket arms at an approximate position. If the compass has been adjusted previously, place the spheres at the position indicated by the previous deviation table. In the event the compass has never been adjusted, place the spheres at the midpoint on the bracket arms.
The next adjustment is the positioning of the heeling magnet using a properly balanced dip needle. Section 637 discusses this procedure.

These three dockside adjustments (Flinders bar, quadrantal spheres, and heeling magnet) will properly establish the conditions of mutual induction and shielding of the compass. This minimizes the steps required at sea to complete the adjustment.

*611.	Expected Errors*
Figure 607 lists six different coefficients or types of deviation errors with their causes and corresponding correctors. A discussion of these coefficients follows:
The A error is caused by the miscalculation of azimuths or by physical misalignments rather than magnetic effects of unsymmetrical arrangements of horizontal soft iron. Thus, checking the physical alignments at dockside and making careful calculations will minimize the A error. Where an azimuth or bearing circle is used on a standard compass to determine deviations, any observed A error will be solely magnetic A error because such readings are taken on the face of the compass card rather than at the lubber&#8217;s line of the compass. On a steering compass where deviations are obtained by a comparison of the compass lubber&#8217;s line reading with the ship&#8217;s magnetic heading, as determined by pelorus or gyro, any observed A error may be a combination of magnetic A and mechanical A (misalignment). These facts explain the procedure in which only mechanical A is corrected on the standard compass, by realignment of the binnacle, and both mechanical A and magnetic A errors are corrected on the steering compass by realignment of the binnacle. On the standard compass, the mechanical A error may be isolated from the magnetic A error by making the following observations simultaneously:
1.	Record a curve of deviations by using an azimuth (or bearing) circle. Any A error found will be solely magnetic A.
2.	Record a curve of deviations by comparison of the compass lubber&#8217;s line reading with the ship&#8217;s magnetic heading as determined by pelorus or by gyro.
Any A error found will be a combination of mechanical A and magnetic A.
3.	The mechanical A on the standard compass is then found by subtracting the A found in the first instance from the total A found in the second instance, and is corrected by rotating the binnacle in the proper direction by that amount. It is neither convenient nor necessary to isolate the two types of A on the steering compass and all A found by using the pelorus or gyro may be removed by rotating the binnacle in the proper direction.

The B error results from both the fore-and-aft permanent magnetic field across the compass and a resultant unsymmetrical vertical induced effect forward or aft of the compass. The former is corrected by the use of fore-and-aft B magnets, and the latter is corrected by the use of the Flinders bar forward or aft of the compass. Because the Flinders bar setting is a dockside adjustment, any remaining B error is corrected by the use of fore-and-aft B magnets. The C error results from the athwartship permanent magnetic field across the compass and a resultant unsymmetrical vertical induced effect athwartship of the compass. The former is corrected by the use of athwartship C magnets, and the latter by the use of the Flinders bar to port or starboard of the compass. Because the vertical induced effect is very rare, the C error is corrected by athwartship C magnets only.

The D error is due only to induction in the symmetrical arrangements of horizontal soft iron, and requires correction by spheres, generally athwartship of the compass. E error of appreciable magnitude is rare, since it is caused by induction in the unsymmetrical arrangements of horizontal soft iron. When this error is appreciable it may be corrected by slewing the spheres, as described in section 620. As stated previously, the heeling error is adjusted at dockside with a balanced dip needle (see section 637). As the above discussion points out, certain errors are rare and others are corrected at dockside. Therefore, for most ships, only the B, C, and D errors require at sea correction. These errors are corrected by the fore-and-aft B magnets, athwartship C magnets, and quadrantal spheres respectively.

*To be continued*


----------



## reel

In your Chapter 5 the subject of buoy light colors is discussed.
I intend to go through the New York State Erie Canal this summer (first time) and was wondering about the buoy marking system. Can I expect the state owned canal to have the same type markers as this great posting ? ?

I noticed that lock convention is not mentioned. I found this at their site:


> How to "Lock Through"
> Canal System Locks
> 
> On approaching the lock, hail the Lock Operator on Marine Channel 13 or sound three blasts on your horn to signal that you are approaching and request service. A red light indicates the lock is not ready. Stop at a safe distance and stand by for a green light. Before entering the lock, check that fenders are properly positioned.
> Entering the Lock:
> 
> A green light means come ahead. Enter the lock slowly and stay in line of approach. In the lock chamber, station vessels alongside the lock wall as directed by the Lock Operator. During the lockage, keep bow and stern close to the wall by looping line to holding apparatus (lines, ladders, cables or pipes) as provided. DO NOT TIE LINES. Serious injury can result from using hands and feet to fend a moving boat off a wall. Use a boat hook, paddle or oar. Do not wrap lines around hands or feet as lines may tighten and cause injury.


...


----------



## Fishers of Men

Reel, Yes, they will be the same. I havn't got into locks, tides and a few other things yet..but will.  

The sound signals we discussed should be known so that you can have a professional communication with the bridge tender along with ch 13 and make sure to answer him.

Where you see:
*"the wall by looping line to holding apparatus (lines, ladders, cables or pipes) as provided. DO NOT TIE LINES." *

This is very important, if you were to "tie up", when the water goes down, (very quickly) you cannot untie the strain on the lines quick enough and your boat will literally hang on the wall and/or get tore up, or flip. You would be fortunate if you even had time to cut them.

The numbers on the bouys _could _be mile markers, depending. I will try to download the latest chart for the canal for you.

You should have the 2008 Notices to Mariners before transit. Notices to Mariners provide the latest information about Canal openings/closures, water levels, construction and other elements. This will give you times and dates of operation that you need to know so you don't end up spending the night where you don't want to! 

And for notification on limited passages, of major incidents and emergencies that may affect navigation on the New York State Canal System sign up for Canal TRANSalert. http://www.nyscanals.gov/tas/index.html

Prepare for a long, slow trip. Besides no wake zones sometimes you can be delayed waiting for a lock a long time.

The entire trip can change at a moments notice and the dates of operation and hours are dependent upon weather.

For the most up-to-date information on the Canal water conditions, call 1-800-4CANAL4 and press option 3.

I'll get back with more info in detail on this. Thanks for the excellent question.


----------



## reel

OK thanks for follow up.
So far I have the NYSCS "Crusing Guide" and 
Maptech with Chart Navigator and all 78 of the NOAA Charts 14786.
And the TRANSalert.
thanks again
...


----------



## Fishers of Men

Reel, here are some of the charts by region. I don't know if it is the same as you have. Only the eastern half of the Canal is on NOS charts, from Troy to Lyons, NY. You can order a NY Canals chartbook, which covers all the Erie (and other NY canals) on line for $20 or so, very good and reasonable - go to Erie Canal or NY canal site, that should have links.

If you want to download the eastern half of the Erie, go to the maptech page from usps web site, search by region, look at region 26, and these are probably the charts you would want. I would guess 14786 is a NOS chart book, like the islands in Lake Erie, 14842. Mowhawk and Seneca rivers are part of the canal.

14786_1.KAP OSWEGO RIVER - MINETTO 
Select 1:20000 14786_10.KAP HUDSON RIVER - MECHANICVILLE 
Select 1:20000 14786_11.KAP HUDSON RIVER 
Select 1:20000 14786_12.KAP HUDSON RIVER - HOOSIC RIVER 
Select 1:20000 14786_13.KAP HUDSON RIVER 
Select 1:20000 14786_14.KAP HUDSON RIVER 
Select 1:20000 14786_15.KAP HUDSON RIVER - SCHUYLEVILLE 
Select 1:20000 14786_16.KAP CHAMPLAIN CANAL - HUDSON RIVER 
Select 1:20000 14786_17.KAP CHAMPLAIN CANAL - HUDSON RIVER 
Select 1:20000 14786_18.KAP HUDSON RIVER - FORT EDWARD 
Select 1:20000 14786_19.KAP CHAMPLAIN CANAL - HUDSON RIVER - BILLINGS ISLAND 
Select 1:20000 14786_2.KAP LAKE ONTARIO - OSWEGO RIVER 
Select 1:20000 14786_20.KAP CHAMPLAIN CANAL - BOND CREEK 
Select 1:20000 14786_21.KAP CHAMPLAIN CANAL - WOOD CREEK 
Select 1:20000 14786_22.KAP CHAMPLAIN CANAL 
Select 1:20000 14786_23.KAP CHAMPLAIN CANAL 
Select 1:20000 14786_24.KAP CHAMPLAIN CANAL - COMSTOCK 
Select 1:20000 14786_25.KAP CHAMPLAIN CANAL - METTAWEE RIVER 
Select 1:20000 14786_26.KAP SOUTH BAY 
Select 1:20000 14786_27.KAP ITHACA NEW YORK 
Select 1:25000 14786_28.KAP WATKINS GLEN NEW YORK 
Select 1:170000 14786_29.KAP CAYUGA LAKE - SENECA LAKE 
Select 1:20000 14786_3.KAP OSWEGO - BATTLE ISLAND STATE PARK 
Select 1:20000 14786_30.KAP SENECA LAKE 
Select 1:20000 14786_31.KAP CAYUGA CANAL - SENECA LAKE - WATERLOO 
Select 1:20000 14786_32.KAP CAYUGA LAKE 
Select 1:20000 14786_33.KAP CAYUGA CANAL - SENECA CANAL - ERIE CANAL 
Select 1:20000 14786_34.KAP CAYUGA CANAL - SENECA CANAL 
Select 1:20000 14786_35.KAP CLYDE RIVER 
Select 1:20000 14786_36.KAP ERIE CANAL - CLYDE RIVER 
Select 1:20000 14786_37.KAP ERIE CANAL - CLYDE RIVER 
Select 1:20000 14786_38.KAP ERIE CANAL - MONTEZUMA NATIONAL WILDLIFE REFUGE 
Select 1:20000 14786_39.KAP ERIE CANAL - HOWLAND ISLAND GAME REFUGE 
Select 1:20000 14786_4.KAP OSWEGO RIVER - FULTON 
Select 1:20000 14786_40.KAP ERIE CANAL - HICKORY ISLAND 
Select 1:20000 14786_41.KAP CHAMPLAIN CANAL - BOND CREEK 
Select 1:20000 14786_42.KAP CROSS LAKE 
Select 1:20000 14786_43.KAP SENECA RIVER - STATE DITCH CUT 
Select 1:20000 14786_44.KAP SENECA RIVER 
Select 1:20000 14786_45.KAP SENECA RIVER - BALDWINSVILLE 
Select 1:20000 14786_46.KAP ONONDAGA LAKE - SENECA RIVER 
Select 1:20000 14786_47.KAP ONONDAGA LAKE - SYRACUSE 
Select 1:30000 14786_48.KAP ONONDAGA LAKE - MAPLE BAY 
Select 1:20000 14786_49.KAP SENECA RIVER - BELGIUM 
Select 1:20000 14786_5.KAP OSWEGO RIVER - LAKE NEATAHWANTA 
Select 1:20000 14786_50.KAP OSWEGO RIVER - ONEIDA RIVER 
Select 1:20000 14786_51.KAP ONEIDA RIVER - ONEIDA LAKE 
Select 1:80000 14786_52.KAP ONEIDA LAKE 
Select 1:20000 14786_53.KAP ONEIDA LAKE - FISH CREEK 
Select 1:20000 14786_54.KAP ERIE CANAL - WOOD CREEK 
Select 1:20000 14786_55.KAP ERIE CANAL -WOOD CREEK 
Select 1:20000 14786_56.KAP MOHAWK RIVER - ERIE CANAL - ROME 
Select 1:20000 14786_57.KAP MOHAWK RIVER - ERIE CANAL 
Select 1:20000 14786_58.KAP MOHAWK RIVER - ERIE CANAL - ORISKANY CREEK 
Select 1:20000 14786_59.KAP MOHAWK RIVER - ERIE CANAL 
Select 1:20000 14786_6.KAP OSWEGO RIVER - OX CREEK 
Select 1:20000 14786_60.KAP MOHAWK RIVER - ERIE CANAL 
Select 1:20000 14786_61.KAP MOHAWK RIVER - FRANKFORT 
Select 1:20000 14786_62.KAP MOHAWK RIVER - ILION - HERKIMER 
Select 1:20000 14786_63.KAP MOHAWK RIVER - LITTLE FALLS 
Select 1:20000 14786_64.KAP MOHAWK RIVER - ERIE CANAL - LITTLE FALLS 
Select 1:20000 14786_65.KAP MOHAWK RIVER - EAST CANADA CREEK 
Select 1:20000 14786_66.KAP MOHAWK RIVER - ST. JOHNSVILLE 
Select 1:20000 14786_67.KAP MOHAWK RIVER - FORT PLAIN 
Select 1:20000 14786_68.KAP MOHAWK RIVER - CANAJOHARIE 
Select 1:20000 14786_69.KAP MOHAWK RIVER - RANDALL 
Select 1:20000 14786_7.KAP OSWEGO RIVER - ONEIDA RIVER - PHOENIX 
Select 1:20000 14786_70.KAP MOHAWK RIVER - FULTONVILLE 
Select 1:20000 14786_71.KAP MOHAWK RIVER - SCHOHARIE CREEK 
Select 1:20000 14786_72.KAP MOHAWK RIVER - AMSTERDAM 
Select 1:20000 14786_73.KAP MOHAWK RIVER 
Select 1:20000 14786_74.KAP MOHAWK RIVER - SCOTIA 
Select 1:20000 14786_75.KAP MOHAWK RIVER - ROTTERDAM JUNCTION 
Select 1:20000 14786_76.KAP MOHAWK RIVER - SCHENECTADY 
Select 1:20000 14786_77.KAP MOHAWK RIVER - MOHAWK VIEW 
Select 1:20000 14786_78.KAP MOHAWK RIVER - WATERFORD 
Select 1:20000 14786_8.KAP HUDSON RIVER - WATERFORD 
Select 1:20000 14786_9.KAP MOHAWK RIVER - HUDSON RIVER 
Select 1:40000 14788_1.KAP ONEIDA LAKE LOCK 22 TO LOCK 23 
Select 1:60000 14791_1.KAP NEW YORK STATE BARGE CANAL SYSTEM CAYUGA AND SENECA LAKES 
Select 1:10000 14791_2.KAP WATKINS GLEN NEW YORK INSET 
Select 1:10000 14791_3.KAP ITHACA NEW YORK INSET


----------



## Fishers of Men

*continued ch 6

612. Study Of Adjustment Procedure*
Inspecting the B, C, and D errors pictured in Figure 612a demonstrates a definite isolation of deviation effects on cardinal compass headings.



















For example, on 090&#176; or 270&#176; compass headings, the only deviation which is effective is that due to B. This isolation, and the fact that the B effect is greatest on these two headings, make these headings convenient for B correction. Correction of the B deviation on a 090&#176; heading will correct the B deviation on the 270&#176; heading by the same amount but in the opposite direction and naturally, it will not change the deviations on the 000&#176; and 180&#176; headings, except where B errors are large. However, the total deviation on all the intercardinal headings will be shifted in the same direction as the adjacent 090&#176; or 270&#176; deviation correction, but only by seven-tenths (0.7) of that amount, since the sine of 45&#176; equals 0.707. The same convenient isolation of effects and corrections of C error will also change the deviations on all the intercardinal headings by the seven-tenths rule. Note that only after correcting the B and C errors on the cardinal headings, and consequently their proportional values of the total curve on the intercardinal headings, can the D error be observed separately on any of the intercardinal headings. The D error may then be corrected by use of the spheres on any intercardinal heading. Correcting D error will, as a rule, change the deviations on the intercardinal headings only, and not on the cardinal headings. Only when the D error is excessive, the spheres are magnetized, or the permanent magnet correctors are so close as to create excessive induction in the spheres will there be a change in the deviations on cardinal headings as a result of sphere adjustments. Although sphere correction does not generally correct deviations on cardinal headings, it does improve compass stability on these headings.

If it were not for the occasional A or E errors, adjusting observed deviations to zero on two adjacent cardinal headings and then on the intermediate intercardinal heading would be sufficient. However, Figure 612b, showing a combination of A and B errors, illustrates why the adjusting procedure must include correcting deviations on more than the three essential headings.

Assuming no A error existed in the curve illustrated in Figure 612b, and the total deviation of 6&#176; E on the 090&#176; heading were corrected with B magnets, the error on the 270&#176; heading would be 4&#176; E due to B overcorrection. If this 4&#176; E error were taken out on the 270&#176; heading, the error on the 090&#176; heading would then be 4&#176; E due to B undercorrection. To eliminate this endlessly iterative process and correct the B error to the best possible flat curve, split this 4&#176; E difference, leaving 2&#176; E deviation on each opposite heading. This would, in effect correct the B error, leaving only the A error of 2&#176; E which must be corrected by other means. It is for this reason that, (1) splitting is done between the errors noted on opposite headings, and (2) good adjustments entail checking on all headings rather than on the fundamental three.
*
613. Adjustment Procedures At Sea*
Before proceeding with the adjustment at sea the following precautions should be observed:
1.	Secure all effective magnetic gear in the normal seagoing position.
2.	Make sure the degaussing coils are secured, using the reversal sequence, if necessary (See section 643).
The adjustments are made with the ship on an even keel, swinging from heading to heading slowly, and after steadying on each heading for at least 2 minutes to avoid Gaussin error.

Most adjustments can be made by trial and error, or by routine procedure such as the one presented in section 601. However, the procedures presented below provide analytical methods in which the adjuster is always aware of the errors&#8217; magnitude on all headings as a result of his movement of the different correctors.
Analysis Method. A complete deviation curve can be taken for any given condition, and an estimate made of all the approximate coefficients. See section 615. From this estimate,
the approximate coefficients are established and the appropriate corrections are made with reasonable accuracy on a minimum number of headings. If the original deviation curve has deviations greater than 20&#176;, rough adjustments should be made on two adjacent cardinal headings before recording curve data for such analysis. The mechanics of applying correctors are presented in Figure 601. A method of tabulating the anticipated deviations after each correction is illustrated in Figure 613a. The deviation curve used for illustration is the one which is analyzed in section 615.
Analysis revealed these coefficients:










*One-Swing Method.* More often it is desirable to begin adjustment immediately, eliminating the original swing for deviations and the estimate of approximate coefficients. In this case the above problem would be solved by tabulating data and anticipating deviation changes as the corrections are made. Figure 613b illustrates this procedure. Note that a new column of values is started after each change is made. This method of tabulation enables the adjuster to calculate the new residual deviations each time a corrector is changed, so that a record of deviations is available at all times during the swing. Arrows indicate where each change is made. Since the B error is generally greatest, it is corrected first. Therefore, on a 090&#176; heading the 11.5&#176; E deviation is corrected to approximately zero by using fore-and-aft B magnets. A lot of time need not be spent trying to reduce this deviation to exactly zero since the B coefficient may not be exactly 11.5&#176; E, and some splitting might be desirable later. After correcting on the 090&#176; heading, the swing would then be continued to 135&#176; where a 9.2&#176; W error would be observed. This deviation is recorded, but no correction is made because the quadrant error is best corrected after the deviations on all four cardinal headings have been corrected. The deviation on the 180&#176; heading would be observed as 5.5&#176; W. Since this deviation is not too large and splitting may be necessary later, it need not be corrected at this time. Continuing the swing to 225&#176; a 0.0&#176; deviation would be observed and recorded.
On the 270&#176; heading the observed error would be 1.0&#176; W, which is compared with 0.0&#176; deviation on the opposite 090&#176; heading. This could be split, leaving 0.5&#176; W deviation on both 090&#176; and 270&#176;, but since this is so small it may be left uncorrected. On 315&#176; the observed deviation would be 1.2&#176; E. At 000&#176; a deviation of 10.5&#176; E would be observed and compared with 5.5&#176; Won 180&#176;.
Analysis of the deviations on 000&#176; and 180&#176; headings reveals an 8.0&#176; E, C error, which should then be corrected with athwartship C magnets leaving 2.5&#176; E deviation on both the 000&#176; and 180&#176; headings.










All the deviations in column two are now recalculated on the basis of such an adjustment at 000&#176; heading and entered in column three. Continuing the swing, the deviation on 045&#176; would then be noted as 6.4&#176; E. Knowing the deviations on all intercardinal headings, it is now possible to estimate the approximate coefficient D. D is 5.0&#176; E so the 6.4&#176; E deviation on 045&#176; is corrected to 1.4&#176; E and new anticipated values are recorded in another column. This anticipates a fairly good curve, an estimate of which reveals, in addition to the B of 0.5&#176; E which was not considered large enough to warrant correction, an A of 1.0&#176; E and an E of 1.5&#176; E. These A and E errors may or may not be corrected, as practical. If they are corrected, the subsequent steps would be as indicated in the last two columns. Now the ship has made only one swing, all corrections have been made, and some idea of the expected curve is available.
*
614. Deviation Curves*
The last step, after completion of either of the above methods of adjustment, is to secure all correctors in position and to swing for residual deviations. These residual deviations are for undegaussed conditions of the ship, which should be recorded together with details of corrector positions. Figure 614 illustrates both sides of NAVSEA 3120/4 with proper instructions and sample deviation and Flinders bar data. Should the ship be equipped with degaussing coils, a swing for residual deviations under degaussed conditions should also be made and data recorded on NAVSEA 3120/4.

On these swings, exercise extreme care in taking bearings or azimuths and in steadying down on each heading since this swing is the basis of standard data for the particular compass. If there are any peculiar changeable errors, such as movable guns, listing of the ship, or anticipated decay from deperming, which would effect the reliability of the compass, they should also be noted on the deviation card at this time. Section 639 discusses these many sources of error in detail.










If the Flinders bar adjustment is not based on accurate data, as with a new ship, exercise particular care in recording the conventional Daily Compass Log data during the first cruise on which a considerable change of magnetic latitude occurs.
In order to have a reliable and up-to-date deviation card at all times, swing the ship to check compass deviations and to make readjustments, after:
1.	Radical changes in magnetic latitude.
2.	Deperming. (Delay adjustment for several days after treatment.)
3.	Structural changes.
4.	Long cruises or docking on the same heading, causing the permanent magnetic condition of the vessels to change.
5.	Altering magnetic equipment near the binnacle.
6.	Reaching the magnetic equator to acquire Flinders bar data.
7.	At least once annually.
8.	Changing the heeling magnet position, if Flinders bar is present.
9.	Readjusting any corrector.
10.	Changing magnetic cargo.
11.	Commissioning.










Since A is the coefficient of constant deviation, its approximate value is obtained from the above data by estimating the mean of the algebraic sum of all the deviations. Throughout these computations the sign of east deviation is considered plus, and west deviation is considered minus.



























forces, dealing with: (a) arrangements of soft iron, (b) components of permanent magnetic fields, &#169; components of the earth&#8217;s magnetic field, and (d) the shielding factor. Thus, the exact coefficients are expressions of magnetic force which produce the deviations expressed by the approximate coefficients. The exact coefficients are for mathematical considerations while the approximate coefficients are more practical for adjustment purposes. For this reason, the exact coefficients, and the associated mathematics, are not expanded further in this text.

*To be Continued*


----------



## Fishers of Men

*continued ch 6
CORRECTOR EFFECTS
617.	Compass Heading And Magnetic Heading*
When deviations are large, there is an appreciable difference in the deviation curve if it is plotted on crosssection paper against compass headings or against magnetic headings of the ship. Not only is there a difference in the shape of the curves, but if only one curve is available, navigators will find it difficult in applying deviations when converting between magnetic and compass headings. When deviations are small, no conversion is necessary. Figure 617 illustrates the differences mentioned above by presenting the deviation values used in Figure 617 plotted against both magnetic and compass headings.

*618.	Understanding Interactions Between Correctors*
Until now the principles of compass adjustment have been considered from a qualitative point of view. In general this is quite sufficient since the correctors need merely be moved until the desired amount of correction is obtained. However, it is often valuable to know the quantitative effects of different correctors as well as their qualitative effects. All the correctors are not completely independent of each other. Interaction results from the proximity of the permanent magnet correctors to the soft iron correctors. Consequently any shift in the relative position of the various correctors will change their interactive as well as their separate correction effects. Additional inductions exist in the soft iron correctors from the magnetic needles of the compass itself. The adjuster should be familiar with the nature of these interactions.

*619.	Quandrantal Sphere Correction*
Figure 619 presents the approximate quadrantal correction available with different sizes of spheres, at various positions on the sphere brackets, and with different magnetic moment compasses. These quadrantal corrections apply whether the spheres are used as D, E, or combination D and E correctors. Quadrantal correction from spheres is due partially to the earth&#8217;s field induction and partially to compass needle induction. Since compass needle induction does not change with magnetic latitude but earth&#8217;s field induction does, the sphere correction is not constant for all magnetic latitudes. A reduction in the percentage of needle induction in the spheres to the earth&#8217;s field induction in the spheres will improve the constancy of sphere correction over all magnetic latitudes. Such a reduction in the percentage of needle induction may be obtained by:
1.	Utilizing a low magnetic moment compass.
2.	Utilizing special spheroidal-shaped correctors, placed with their major axes perpendicular to their axis of position.










3. Using larger spheres farther away from the compass.


*620. Slewing Of Spheres*
Figure 620 shows a chart for determining the proper slewed position for spheres. The total values of the D and E quadrantal coefficients are used on the chart to locate a point of intersection. This point directly locates the angle and direction of slew for the spheres on the illustrated binnacle. This point will also indicate, on the radial scale, the resultant amount of quadrantal correction required from the spheres in the new slewed position to correct for both D and E coefficients. The total D and E coefficients may be calculated by an analysis of deviations on the uncorrected binnacle, or by summarizing the uncorrected coefficients with those already corrected. The data in Figure 619 and 622 will be useful in either procedure.
Example: A ship having a Navy Standard binnacle, with 7&#8221; spheres at 13&#8221; position athwartship, and a 12&#8221; Flinders bar forward, is being swung for adjustment. It is observed that 4&#176; E D error and 6&#176; E E error exist with the spheres in position. Since the spheres are athwartship, the total E coefficient for the ship is 6&#176; E, as observed. 

Figure 619 indicates that the spheres in their present position are correcting 6&#176; E D error, hence the total D coefficient of the ship and Flinders bar is 10&#176; E. Figure 620 indicates that 6&#176; E E and 10&#176; E D coefficients require slewing the spheres 15.5&#176; clockwise from their present athwartship position. The resultant quadrantal error is indicated as 11.7&#176;. Figure 619 indicates that the 7&#8221; spheres should then be moved to the 11&#8221; position after slewing 15.5&#176; clockwise so as to correct both the D and E errors. Using this chart eliminates trial-and-error adjustment methods for quadrantal errors and provides information for moving the spheres.










*621.	Corrector Magnet Inductions In Spheres*
Should a ship have both spheres and many permanent B and C magnet correctors close to the compass, induction will exist between these correctors. This induction will require some shuttling back and forth between headings while making adjustments. This situation can be improved by using larger spheres further out, by approximately setting the spheres before starting adjustments, and by using more magnets further from the spheres and compass. Magnetized spheres Flinders bars will cause difficulty during adjustment, and introduce an unstable deviation curve if they suffer a change of magnetic condition.

*622.	Flinders Bar Effects*
Figure 622 presents the approximate quadrantal error introduced by the presence of the Standard Navy Flinders bar. Since the Flinders bar is usually placed in the forward or aft position, it acts as a small minus D corrector as well as a corrector for vertical induced effects. This means that when inserting the Flinders bar, move the regular spheres closer to correct for the increased plus D error. Conversely, move the regular spheres away when removing the Flinders bar. This D error in the Flinders bar is due mostly to compass needle induction because the bar is small in crosssection and close to the compass. Such needle induction is practically constant; therefore, the deviation effects on the compass will change with magnetic latitudes because the directive force, H, changes. However, when balanced by sphere correctors, this effect tends to cancel out the variable part of the sphere correction caused by the compass needle induction.

*623.	Flinders Bar Adjustment*
One must have reliable data obtained in two widely separated magnetic latitudes to place the correct amount of Flinders bar. Placing the Flinders bar by any other method is merely an approximation. Obtaining the required magnetic data will necessitate further refinements. There are several methods of acquiring and using latitude data in order to determine the proper amount of Flinders bar:
The data required for correct Flinders bar adjustment consists of accurate tables of deviations with details of corrector conditions at two different magnetic latitudes; the farther apart the better. Should it be impossible to swing ship for a complete table of deviations, the deviations on east and west magnetic headings would be helpful. Ship&#8217;s log data is usually not reliable enough for Flinders bar calculation. Observe the following precautions when taking data. These precautions will ensure that deviation changes are due only to changes in the H and Z components of the earth&#8217;s field.










1.	Degaussing should be secured, by a reversal process if necessary, at both latitudes before data are taken.
2.	If the ship has been in dock or steaming, on one heading for several days prior to the taking of these data, the resulting temporary magnetism (Gaussin error) would create erroneous deviations. A shakedown on other headings prior to taking data will reduce such errors.
3.	Any major change in the ship&#8217;s magnetic field (caused, for example, by deperming, structural changes, heavy gunfire, shifting magnetic cargoes) between data sets will make the comparative results meaningless.
4.	Because the data will not be reliable if the ship&#8217;s permanent magnetism changes between the two latitudes, it will likewise be unreliable if any of the binnacle correctors are changed.
In the event that an approximation as to Flinders bar length cannot be made, then the deviations at the two latitudes should be taken with no Flinders bar in the holder. This procedure would also simplify the resulting calculations.
*
624. Methods Of Determining Flinders Bar Length*
Method 1. Having obtained reliable deviation data at two different magnetic latitudes, the changes in the deviations, if any, may justifiably be attributed to an incorrect Flinders bar adjustment. E/Wand N/S deviations are the ones which are subject to major changes from such an incorrect adjustment. If there is no change in any of these deviations, the Flinders bar adjustment is probably correct. A change in the E/W deviations indicates an unsymmetrical arrangement of vertical iron forward or aft of the compass, which requires correction by the Flinders bar, forward or aft of the compass. A change in the N/S deviations indicates an unsymmetrical arrangement of vertical iron to port or starboard of the compass, which requires correction by the Flinders bar to port or starboard of the compass. This latter case is very rare, but can be corrected.
Determine the B deviations on magnetic east/west headings at both latitudes. The constant c may then be calculated from the following formula:










where
&#61548;&#61472;= shielding factor (0.7 to 1.0 average).
H1 = earth&#8217;s field, H, at 1st latitude.
B1 = degrees B deviation at 1st latitude (magnetic headings).
Z1 = earth&#8217;s field, Z, at 1st latitude.
H2 = earth&#8217;s field, H, at 2nd latitude.
B2 = degrees B deviation at 2nd latitude (magnetic headings).
Z2 = earth&#8217;s field, Z, at 2nd latitude.
This constant c represents a resultant mass of vertical iron in the ship which requires Flinders bar correction. If the Flinders bar is present at the time of calculations, it must be remembered that it is already correcting an amount of c in the ship which must be added to the uncorrected c, calculated by the above formula. This total value of c is used in conjunction with Figure 624a to indicate, directly, the necessary total amount of Flinders bar. If this total c is negative, Flinders bar is required on the forward side of the binnacle; and if it is positive, a Flinders bar is required on the aft side of the binnacle. The iron sections of Flinders bar should be continuous and at the top of the tube with the longest section at the top. Wooden spacers are used at the bottom of the tube. It will be noted that the B deviations used in this formula are based on data on E/W magnetic headings rather than on compass headings, as with the approximate coefficients.










Method 2. Should the exact amount of correction required for vertical induction in the ship at some particular magnetic dip, q, be known, Figure 624a will directly indicate the correct amount of Flinders bar to be placed at the top of the holder. The exact amount of correction would be known when one of the latitudes is the magnetic equator, and the deviations there are negligible. Then the B deviation, in degrees, on magnetic headings at the other latitude, is the exact amount to correct by means of curves in Figure 624a.

Method 3. Lord Kelvin&#8217;s rule for improving the Flinders bar setting is: &#8220;Correct the deviations observed on east or west courses by the use of fore-and-aft B magnets when the ship has arrived at places of weaker vertical magnetic field, and by the use of Flinders bar when she has arrived at places of stronger vertical magnetic field, whether in the Northern or Southern Hemisphere.&#8221; After determining the correct amount of Flinders bar, by either method (1) or (2) above, the bar should then be inserted at the top of the holder, and the fore-and-aft B magnets readjusted to correct the remaining B error. Sphere adjustments should likewise be refined. It is quite possible that on inserting the Flinders bar, no visible deflection of the compass will be observed, even on an east or west heading. This should cause no concern because certain additional induction effects exist in the bar, from:
1.	The heeling magnet.
2.	The existing fore-and-aft magnets.
3.	The vertical component of the ship&#8217;s permanent magnetic field.
Figure 624b presents typical induction effects in the Flinders bar for different positions of heeling magnet. An adjuster familiar with the nature of these effects will appreciate the advantages of establishing the Flinders bar and heeling magnet combination before leaving dockside. Deviations must also be checked after adjusting the heeling magnet, if Flinders bar is present.









*
625. Slewing Of Flinders Bar*
The need for slewing the Flinders bar is much more rare than that for slewing spheres. Also, the data necessary for slewing the Flinders bar cannot be obtained on a single latitude adjustment, as with the spheres. Slewing the bar to some intermediate position is, in effect, merely using one bar to do the work of two; one forward or aft, and the other port or starboard.
Section 624 explains that a change of the E/W deviations, with changes in latitude, indicates the need for Flinders bar forward or aft of the compass; and a change of the N/S deviations, with changes in latitude, indicates the need for Flinders bar to port or starboard of the compass. A change of the B deviations on magnetic E/W headings is used, as explained in section 624, to determine the proper amount of Flinders bar forward or aft of the compass, by calculating the constant c.

If there is a change of the C deviations on magnetic N/S headings, a similar analysis may be made to determine the proper amount of Flinders bar to port or starboard of the compass by calculating the constant f from:










when l = shielding factor (0.7 to 1.0 average). H1 = earth&#8217;s field, H, at 1st latitude.
C1 = degrees C deviation at 1st latitude (magnetic headings).
Z1 = earth&#8217;s field, H, at 1st latitude.









Any value of this f constant indicates the need for Flinders bar adjustment athwartship of the compass, just as a value of the c constant indicates the need for Flinders bar adjustment forward or aft of the compass. The f constant curve in Figure 624b is used for the determination of this Flinders bar length. If f is negative, Flinders bar is required on the starboard side of the binnacle. Should both c and f exist on a ship, the angular position for a Flinders bar to correct the resultant vertical induction effects may be found by:









&#61538;&#61472;clockwise from the forward position; if c is negative and f is positive, the bar will be slewed counterclockwise from the aft position.

*To be continued*


----------



## Fishers of Men

*continued ch 6*
After determining the angle to slew the is the angle to slew the Flinders bar from the foreand-aft axis. If c and f are negative, the bar will be slewed Flinders bar from the fore-and-aft line, the total amount of Flinders bar necessary to correct the resultant vertical induction effects in this position is found by:
















The constant r is then used on the c or f constant curve in Figure 624b to determine the total amount of Flinders bar necessary in the slewed position.

*626. Compasses*
Compasses themselves play a very important part in compass adjustment, although it is common belief that the compass is only an indicating instrument, aligning itself in the resultant magnetic field. This would be essentially true if the magnetic fields were uniform about the compass; but, unfortunately, magnetism close to the compass imposes
nonuniform fields across the needles. In other words, adjustment and compensation sometimes employ nonuniform fields to correct uniform fields. Figure 626a indicates the difference between uniform and nonuniform field effects on a compass. Such unbalanced torques, arising from nonuniform magnetic fields, create deviations of the compass which have higher frequency characteristics. Compass designs include many combinations of different length needles, different numbers of needles, and different spacings and arrangements of needles all designed to minimize the higher order deviations resulting from such nonuniform magnetic fields. Although compass design is rather successful in minimizing such deviations, it is obvious that different compasses will be affected differently by the same magnetic fields. It is further stressed that, even with proper compass design, it is the responsibility of all adjusters to exercise care in applying correctors, in order to create the most uniform magnetic field possible.

This is the basis for the rule which requires the use of strong correctors symmetrically arranged, as far away from the compass as possible, instead of weak correctors very close to the compass. In general it is better to use larger spheres placed at the extremities of the brackets, equally distant from the center of the compass. B and C permanent magnet correctors should always be placed so as to have an equal number of magnets on both sides of the compass where possible. They should also be centered as indicated in Figure 626b, if regular tray arrangements are not available. The desire for symmetrical magnetic fields is one reason for maintaining a sphere of specified radius, commonly called the magnetic circle, about the magnetic compass location. This circle is kept free of any magnetic or electrical equipment.










The magnetic moment of the compass needle array, another factor in compass design, ranks in importance with the proper arrangement of needles. This magnetic moment controls the needle induction in the soft iron correctors, as discussed in section 619 and section 622, and hence governs the constancy of those corrector effects with changes in magnetic latitude. The 71/2&#8221; Navy No. 1 alcohol-water compass has a magnetic moment of approximately 4000 cgs units, whereas the 71/2&#8221; Navy No. 1 oil compass has a magnetic moment of approximately 1650 cgs units. The lower magnetic moment compass allows considerably less change in quadrantal correction, although the periods are essentially comparable, because of the difference in the compass fluid characteristics. Other factors which must be considered in compass design are period, fluid, swirl, vibration, illumination, tilt, pivot friction, fluid expansion, and others. These factors, however, are less important from an adjuster&#8217;s point of view than the magnetic moment and arrangement of needles, and are therefore not discussed further in this text.

*SHIP&#8217;S HEADING
627.	Ship&#8217;s Heading*
Ship&#8217;s heading is the angle, expressed in degrees clockwise from north, of the ship&#8217;s fore-and-aft line with respect to the true meridian or the magnetic meridian. When this angle is referred to the true meridian, it is called a true heading. When this angle is referred to the magnetic meridian, it is called a magnetic heading. Heading, as indicated on a particular compass, is termed the ship&#8217;s compass heading by that compass. It is always essential to specify heading as true heading, magnetic heading, or compass heading. In order to obtain the heading of a ship, it is essential that the line through the pivot and the forward lubber&#8217;s line of the compass be parallel to the fore-and-aft line of the ship. This applies also to the peloruses and gyro repeaters, which are used for observational purposes.
*
628.	Variation And Deviation*
Variation is the angle between the magnetic meridian and the true meridian at a given location. If the northerly part of the magnetic meridian lies to the right of the true meridian, the variation is easterly, and if this part is to the left of the true meridian, the variation is westerly. The local variation and its small annual change are noted on the compass rose of all navigational charts. Thus the true and magnetic headings of a ship differ by the local variation. Chart 42 shows approximate variation values for the world. As previously explained, a ship&#8217;s magnetic influence will generally cause the compass needle to deflect from the magnetic meridian. This angle of deflection is called deviation. If the north end of the needle points east of the magnetic meridian, the deviation is easterly; if it points west of the magnetic meridian, the deviation is westerly.
*
629.	Heading Relationships*
A summary of heading relationships follows:
1.	Deviation is the difference between the compass heading and the magnetic heading.
2.	Variation is the difference between the magnetic heading and the true heading.
3.	The algebraic sum of deviation and variation is the compass error.
Figure 629 illustrates these relationships. The following simple rules will assist in naming errors and in converting from one heading to another:
1.	Compass least, deviation east, compass best, deviation west.
2.	When correcting, add easterly errors, subtract westerly errors.
3.	When uncorrecting, subtract easterly errors, add westerly errors.
Typical heading relationships are as follows:









Use the memory aid &#8220;Can Dead Men Vote Twice at Elections&#8221; to remember the conversion process (Compass, Deviation, Magnetic, Variation, True, add east). When converting Compass Heading to True Heading, add east deviations and variations and subtract west deviations and variations.
Complete facility with conversion of heading data is essential for expeditious compass adjustment.
*
630. Use Of Compass Heading And Magnetic Heading*
For Adjustment
The primary object of adjusting compasses is to reduce deviations; that is, to minimize the difference between the magnetic and compass headings. There are two methods for accomplishing this:
Method 1. Place the ship on the desired magnetic heading (section 631) and correct the compass so that it reads the same as this magnetic heading. This is the preferred method.
Method 2. Place the ship on the desired compass heading and determine the corresponding magnetic heading of the ship. Correct the compass so that it reads the same as this known magnetic heading. Use this method whenever it is impractical to place the ship on a steady magnetic heading for direct correction.

One can easily observe compass deviation when using the first method because it is simply the difference between the compass reading and the known magnetic heading of the ship. The difficulty in using this method lies in placing the ship on the desired magnetic heading and holding the ship steady on that heading while adjustments are being made.

The difficulty in using the second method lies in the determining deviation. Further difficulty arises because the helmsman steers by an uncorrected compass whose deviations are changing while the technician is making the necessary adjustments. Therefore, as each adjustment is being made, the helmsman should hold the ship&#8217;s heading steady by some means other than the compass that is being corrected.
If the compass has no appreciable deviation, the deviation taken on compass headings will closely approximate those taken on magnetic headings. However, as the magnitude of errors increases, there will be a marked difference between the deviations taken on compass headings and those taken on magnetic headings.









*631.	Methods Of Placing Ship On Magnetic Headings*
Method 1. Bring the ship onto a magnetic heading by referencing a gyrocompass. The magnetic variation applied to true heading determines the gyro course to be steered to place the ship on the required magnetic heading. Take gyrocompass error into consideration in determining gyro course to be steered. The difference between gyro heading and magnetic heading will be constant on all headings as long as the gyrocompass error is constant and the variation does not change. Determine gyrocompass error by comparing the calculated true azimuth of the sun and the azimuth as observed on a synchronized repeater.

It should be remembered that gyrocompasses have certain errors resulting from latitude and speed changes, and these errors are not always constant on all headings. For these reasons, the gyro error must be checked constantly, especially if the gyro is being used to obtain data for determining residual deviation curves of the magnetic compass.

Method 2. Place the ship on a magnetic heading by aligning the vanes of an azimuth circle with the sun over the topside compass. The sun is a distant object whose azimuth (angle from the north) may be computed for any given time. Methods of calculating sun&#8217;s azimuths are discussed in the next section. By setting the line of sight of the vanes at an angle to the right (or left) of the fore-and-aft line of the ship equal to the difference between the computed magnetic azimuth and the desired magnetic heading of the ship, and then swinging the ship until the sun is aligned with the vanes, the ship will be on the desired magnetic heading. Simple diagrams with the ship and sun drawn in their relative positions, will aid in visualizing each problem. Always keep the azimuth circle level while making observations. This holds especially true for observing celestial bodies. 

Method 3. Use a distant object (10 or more miles away) with the azimuth circle when placing the ship on magnetic headings. This procedure is similar to that used with the sun except that the magnetic bearing of the object is constant. With an object 11.4 nautical miles distant, a change in position of 400 yards at right angles to the line of sight introduces an error of 1&#176;.

Method 4. Use a pelorus to place a ship on a magnetic heading using the sun&#8217;s azimuth in much the same manner as with the azimuth circle. Using the pelorus allows the magnetic heading of the ship to be observed continuously as the ship swings. Clamp the forward sight vane to the dial at the value of the sun&#8217;s magnetic azimuth. Then, train the sight vanes so that the sun is reflected in the mirror. As the ship turns, observe the magnetic heading under the forward lubber&#8217;s line. As the desired magnetic course is approached, the compass can be read and corrected even before that magnetic course is actually obtained.A final check can be made when the ship is on the exact course. Always keep the pelorus level while making observations, particularly of celestial bodies. 

Method 5. A distant object can be used in conjunction with the pelorus, as with the azimuth circle, in order to place the ship on magnetic headings.

*632.	Methods Of Determining Deviations On Compass*
Heading
Method 1. Determine the compass&#8217; deviation by comparing the sun&#8217;s calculated magnetic azimuth to the azimuth observed using an azimuth circle. The next section discusses methods of calculating the sun&#8217;s azimuths. Place the ship on the desired compass heading and take an azimuth of the sun on the compass card&#8217;s face. The difference between the observed azimuth and the calculated magnetic azimuth of the sun is the deviation on that compass course. 

Method 2. Use the pelorus with the sun&#8217;s azimuth to obtain deviations on compass headings. Bring the ship to the desired compass heading and set the forward sight vane on the value calculated for the sun&#8217;s magnetic azimuth. Then train the sight vanes on the sun. The pelorus indicates the ship&#8217;s magnetic heading. The difference in degrees between the compass heading and magnetic heading of the ship indicated by the pelorus is the deviation on that compass course. 

Method 3. Use the azimuth circle or pelorus in conjunction with ranges or a distant object to obtain deviations on compass courses. The procedure is similar to that used with the sun. A range consists of any two objects or markers, one in the foreground and the other in the background, which establishes a line of sight having a known magnetic bearing. Determine the range&#8217;s true bearing from a chart; then, convert this true bearing to the magnetic bearing by applying the variation listed on the chart. Bring the ship to the desired compass course and, at the instant of crossing the line of sight of the range, take a bearing to the range. With the azimuth circle, the difference between the observed range bearing and the known magnetic range bearing represents the deviation on that compass course.
If using a pelorus, set the forward sight vanes to the magnetic bearing of the range and read the ship&#8217;s magnetic heading when taking a sight on the range. The deviation is the difference between the compass heading of the ship and the known magnetic heading of the ship as indicated by pelorus.

Method 4. Obtain deviations on compass courses by using reciprocal bearings. Set up a pelorus on shore and align the dial&#8217;s south end with magnetic north. A ship then sights the pelorus on shore, using an azimuth circle or pelorus, at the same instant the observer on shore sights the ship. The ship&#8217;s bearing from shore on the reversed pelorus is the magnetic bearing of the shore position from the ship. Continuous communication between ship and shore is necessary when employing this method.
Additional methods of determining deviations are by the use of azimuths of the moon, stars, and planets.

*To be continued*


----------



## Fishers of Men

*continued ch 6
AZIMUTHS
633.	Azimuths Of The Sun*
The sun is a valuable reference point for compass adjustment because one can easily obtain accurate compass bearings of the sun and compare these bearings with the sun&#8217;s calculated true bearing (azimuth) to obtain compass error. One can use the azimuths of other celestial bodies to make this comparison; however, none are as convenient as the sun. Calculating an azimuth of the sun is covered in Chapter 17.
*
634.	Curve Of Magnetic Azimuths*
During the course of compass adjustment and swinging ship, a magnetic direction is needed many times, either to place the vessel on desired magnetic headings or to determine the deviation of the compass being adjusted. The sun&#8217;s azimuth continually changes as the earth rotates. Compensate for this by preparing a curve of magnetic azimuths. Compute true azimuths at frequent intervals. Then, apply the variation at the center of the maneuvering area to determine the equivalent magnetic azimuths. Plot the magnetic azimuths versus time and fair a curve through the points. Plotting at least three points at intervals of half an hour is usually sufficient. If the sun is near the celestial meridian and relatively high in the sky, plot additional points. Unless extreme accuracy is required, determine the Greenwich hour angle and declination for the approximate midtime. Additionally, use the same declination for all computations. Assume the Greenwich hour angle increase at 15&#176; per hour.

*TRANSIENT DEVIATIONS OF THE MAGNETIC COMPASS
635.	Stability*
So far this chapter has discussed only the principles of steady-state magnetism. However, a carefully made correction based on these steady-state phenomenon may turn out to be inaccurate due to transient magnetic effects. A compass adjuster cannot place correctors on the binnacle for such variable effects; he must recognize and handle them in the best possible manner. A good adjuster not only provides an accurate deviation curve which is reliable under steady state conditions, but he also records transient magnetic effects which cannot be eliminated.
*
636.	Sources Of Transient Error*
The magnetic circle about the magnetic compass is intended to reduce any transient conditions, but there still are many items which cause the compass to act erratically. The following is a list of some such items. If in doubt about the effect of an item on compass performance, a test can be made by swinging any movable object or energizing any electrical unit while observing the compass for deviations. This would best be tried on two different headings 90&#176; apart, since the compass might possibly be affected on one heading and not on another.
Some magnetic items which cause variable deviations if placed too close to the compass are as follows:
1.	Guns on movable mounts.
2.	Ready ammunition boxes.
3.	Variable quantities of ammunition in ready boxes.
4.	Magnetic cargo.
5.	Hoisting booms.
6.	Cable reels.
7.	Metal doors in wheelhouse.
8.	Chart table drawers.
9.	Movable gyro repeater.
10.	Windows and ports.
11.	Signal pistols racked near compass.
12.	Sound powered telephones.
13.	Magnetic wheel or rudder mechanism.
14.	Knives or tools near binnacle.
15.	Watches, wrist bands, spectacle frames.
16.	Hat grommets, belt buckles, metal pencils.
17.	Heating of smoke stack, or exhaust pipes.
18.	Landing boats.
Some electrical items which cause variable deviations if placed too close to the compass are:
1.	Electric motors.
2.	Magnetic controllers.
3.	Gyro repeaters.
4.	Nonmarried conductors.
5.	Loudspeakers.
6.	Electric indicators.
7.	Electric welding.
8.	Large power circuits.
9.	Searchlights.
10.	Electrical control panels or switches.
11.	Telephone headsets.
12.	Windshield wipers.
13.	Rudder position indicators, solenoid type.
14.	Minesweeping power circuits.
15.	Engine order telegraphs.
16.	Radar equipment.
17.	Magnetically controlled switches.
18.	Radio transmitters.
19.	Radio receivers.
20.	Voltage regulators.
Another source of transient deviation is the retentive error. This error results from the tendency of a ship&#8217;s structure to retain some of the induced magnetic effects for short periods of time. For example, a ship traveling north for several days, especially if pounding in heavy seas, will tend to retain some fore-and-aft magnetism hammered in under these induction conditions. Although this effect is transient, it may cause incorrect observations or adjustments. This same type of error occurs when ships are docked on one heading for long periods of time. A short shakedown, with the ship on other headings, will tend to remove such errors. A similar sort of residual magnetism is left in many ships if the degaussing circuits are not secured by the reversal sequence. A source of transient deviation trouble shorter in duration than retentive error is known as Gaussin error. This error is caused by eddy currents set up by a changing number of magnetic lines of force through soft iron as the ship changes heading. Due to these eddy currents, the induced magnetism on a given heading does not arrive at its normal value until about 2 minutes after changing to the heading. Deperming and other magnetic treatment will change the magnetic condition of the vessel and therefore require compass readjustment. The decaying effects of deperming are sometimes very rapid. Therefore, it is best to delay readjustment for several days after such treatment. Since the magnetic fields used for such treatments are sometimes rather large at the compass locations, the Flinders bar, compass, and related equipment are sometimes removed from the ship during these operations.
*
HEELING ADJUSTMENTS
637. Use Of The Dip Needle In Heeling Adjustments*
The heeling effects of both the permanent and induced magnetism are corrected by adjusting the position of the vertical permanent heeling magnet. This adjustment can be made in either of two ways:

Method 1. With the ship on an even keel and as close to the east or west magnetic heading as possible, adjust the heeling magnet until a dip needle inserted in the compass position is balanced at some predetermined position. 

Method 2. Adjust the heeling magnet, while the ship is rolling on north and south headings, until the oscillations of the compass card have been reduced to an average minimum.
To establish an induction condition between the heeling magnet and Flinders bar and to minimize heeling oscillations before at-sea adjustments, set the heeling magnet at dockside by the first method above. Further, position the Flinders bar and spheres before making any heeling adjustments because of the heeling correction and shielding effect they produce.
Readjust the heeling magnet when the ship changes magnetic latitude appreciably because the heeling magnet corrects for induced as well as permanent magnetic effects. Moving the heeling magnet with Flinders bar in the holder will change the induction effects in the Flinders bar and consequently change the compass deviations. Thus, the navigator is responsible for:
1.	Moving the heeling magnet up or down (invert when necessary) as the ship changes magnetic latitude, to maintain a good heeling adjustment for all latitudes.
2.	Checking his deviations and noting changes resulting from movements of the heeling magnet when Flinders bar is in the holder. Any deviation changes should be either recorded or readjusted by means of the fore-and-aft B magnets.
There are two types of dip needles. One assumes the angle of inclination for its particular location, and one uses a moveable weight to balance any magnetic torque. The latter type renders the needle&#8217;s final position more independent of the horizontal component of magnetic fields. It, therefore, is more useful on uncorrected compasses.

For ships with no shielding of the earth&#8217;s field at the compass (having no surrounding metal structure), the procedure for adjusting the heeling magnet is quite simple. Take the dip needle to a nearby area where there is no local magnetic attraction, level the instrument, and set the weight to balance the needle. It is preferable to align the instrument so that the north seeking end of the needle is pointing north. Next, level the instrument in the compass position on board ship, place the spheres in their approximate position, and adjust the heeling magnet until the needle assumes the balanced condition. This presumes that all the effects of the ship are canceled, leaving only the effect of the vertical earth&#8217;s field. Secure the degaussing circuits during this adjustment.

Some ships have shielding effects at the compass. Such would be the case for a metal enclosed wheelhouses. In this case, the procedure is essentially the same as above except that the weight on the dip needle should be moved toward the pivot to balance against some lesser value of earth&#8217;s field. The new position of the weight, expressed in centimeters from the pivot, can be approximately determined by multiplying the value of lambda, &#61548;, for the compass location by the original distance of the weight from the pivot in centimeters. Should &#61548;, for the compass location be unknown, it may generally be considered as about 0.8 for steering compass locations and 0.9 for standard compass locations. By either method, the weight on the dip needle should be moved into its new position. Next, level the instrument in the compass position on board ship and adjust the heeling magnet until the needle assumes the balanced condition. Theoretically, these methods of adjusting the heeling magnet with a dip needle should be employed only with the ship on east or west magnetic headings. This avoids heeling errors resulting from unsymmetrical induced magnetism. If it is impractical to place the ship on such a heading, make approximations on any heading and refine these approximations when convenient.

To summarize, a successful heeling magnet adjustment is one which minimizes the compass oscillations caused by the ship&#8217;s rolling. Therefore, the rolling method is a visual method of adjusting the heeling magnet or checking the accuracy of the last heeling magnet adjustment. Generally, the oscillation effects due to roll on both the north and south compass headings will be the same. However, some unsymmetrical arrangements of fore-and-aft soft iron will introduce different oscillation effects on these two headings. Such effects cannot be entirely eliminated on both headings with one setting of the heeling magnet. Therefore, the heeling magnet is generally set for the average minimum oscillation condition.


*USE OF THE HORIZONTAL FORCE INSTRUMENT
638.	Determining The Horizontal Shielding Factor*
Occasionally, the navigator must determine the magnetic field strength at some compass location for one of the following reasons:
1.	To determine the horizontal shielding factor, lambda (l), for:
a.	A complete mathematical analysis.
b.	Accurate Flinders bar adjustment.
c.	Accurate heeling adjustment.
d.	Calculations on a dockside magnetic adjustment.
e.	Determining the best compass location on board ship.
2.	To make a dockside magnetic adjustment for determining the magnitude and direction of the existing directive force at the magnetic compass. The horizontal shielding factor is the ratio of the reduced earth&#8217;s directive force, H&#8217;, on the compass to the horizontal earth&#8217;s field, H.










The navigator can determine l for a compass location by making a measurement of the reduced earth&#8217;s directive force, H&#8217;. On a corrected compass, this value H&#8217; may be measured with the ship on any heading, since this reduced earth&#8217;s directive force is the only force acting on the compass. If the compass is not corrected for the ship&#8217;s magnetism and the deviations are large, H&#8217; is determined from the several resultant directive forces observed with equally spaced headings of the ship. The Horizontal Shielding Factor should be determined for every compass location on every ship.
*
639.	Measurement Of Magnetic Fields*
Use a suitable magnetometer or a horizontal force instrument to measure magnetic fields. The magnetometer method is a direct reading method requiring no calculation. However, the force instrument method requires much less complicated test equipment so this method is discussed below. The horizontal force instrument is simply a magnetized needle pivoted in a horizontal plane, much the same as a compass. It will settle in some position which will indicate the direction of the resultant magnetic field. Determine the resulting field&#8217;s strength by comparing it with a known field. If the force needle is started swinging, it will be damped down with a certain period of oscillation dependent upon the strength of the surrounding magnetic field. The stronger the magnetic field, the shorter the period of time for each cycle of swing. The ratio is such that the squares of the period of vibration are inversely proportional to the strengths of the magnetic fields. This relationship is expressed as follows:










*To be continued*


----------



## Fishers of Men

*continued ch 6
DEGAUSSING (MAGNETIC SILENCING) COMPENSATION
640. Degaussing*
A steel vessel has a certain amount of permanent magnetism in its &#8220;hard&#8221; iron and induced magnetism in its &#8220;soft&#8221; iron. Whenever two or more magnetic fields occupy the same space, the total field is the vector sum of the individual fields. Thus, near the magnetic field of a vessel, the total field is the combined total of the earth&#8217;s field and the vessel&#8217;s field. Therefore, the earth&#8217;s magnetic field is altered slightly by the vessel.
Since certain mines are triggered by a vessel&#8217;s magnetic influence of a vessel passing near them, a vessel tries to minimize its magnetic field. One method of doing this is to neutralize each component of the field with an opposite electromagnetic field produced by electric cables coiled around the vessel. These cables, when energized, counteract the permanent magnetism of the vessel, rendering it magnetically neutral. This obviously has severe effects on magnetic compasses.
A unit sometimes used for measuring the strength of a magnetic field is the gauss. Reducing of the strength of a magnetic field decreases the number of gauss in that field. Hence, the process is called degaussing. When a vessel&#8217;s degaussing coils are energized, the magnetic field of the vessel is completely altered. This introduces large deviations in the magnetic compasses. This is removed by introducing at the magnetic compass an equal and opposite force with energized coils. This is called compass compensation. When there is a possibility of confusion with compass adjustment to neutralize the effects of the natural magnetism of the vessel, the expression degaussing compensation is used. Since compensation may not be perfect, a small amount of deviation due to degaussing may remain on certain headings. This is the reason for swinging the ship with degaussing off and with it on. This procedure leads to having two separate columns in the deviation table.
*
641.	A Vessel&#8217;s Magnetic Signature*
A simplified diagram of the distortion of the earth&#8217;s magnetic field in the vicinity of a steel vessel is shown in Figure 641a. 










The field strength is directly proportional to the line spacing density. If a vessel passes over a device for detecting and recording the strength of the magnetic field, a certain pattern is traced. Figure 641b shows this pattern. 










Since the magnetic field of each vessel is different, each produces a distinctive trace. This distinctive trace is referred to as the vessel&#8217;s magnetic signature.

Several degaussing stations have been established to determine magnetic signatures and recommend the currents needed in the various degaussing coils. Since a vessel&#8217;s induced magnetism varies with heading and magnetic latitude, the current settings of the coils may sometimes need to be changed. A degaussing folder is provided each vessel to indicate the changes and to give other pertinent information. A vessel&#8217;s permanent magnetism changes somewhat with time and the magnetic history of the vessel. Therefore, the data in the degaussing folder should be checked periodically at the magnetic station.

*642.	Degaussing Coils*
For degaussing purposes, the total field of the vessel is divided into three components: (1) vertical, (2) horizontal fore-and-aft, and (3) horizontal athwartships. The positive (+) directions are considered downward, forward, and to port, respectively. These are the normal directions for a vessel headed north or east in north latitude. Each component is opposed by a separate degaussing field just strong enough to neutralize it. Ideally, when this has been done, the earth&#8217;s field passes through the vessel smoothly and without distortion. The opposing degaussing fields are produced by direct current flowing in coils of wire. Each of the degaussing coils is placed so that the field it produces is directed to oppose one component of the ship&#8217;s field.

The number of coils installed depends upon the magnetic characteristics of the vessel, and the degree of safety desired. The ship&#8217;s permanent and induced magnetism may be neutralized separately so that control of induced magnetism can be varied as heading and latitude change, without disturbing the fields opposing the vessel&#8217;s permanent field.
The principal coils employed are the following:
Main (M) coil. TheMcoil is horizontal and completely encircles the vessel, usually at or near the waterline. Its function is to oppose the vertical component of the vessel&#8217;s permanent and induced fields combined. Generally the induced field predominates. Current in the M-coil is varied or reversed according to the change of the induced component of the vertical field with latitude.

Forecastle (F) and quarterdeck (Q) coils. The F and Q coils are placed horizontal just below the forward and after thirds (or quarters), respectively, of the weather deck.

The designation &#8220;Q&#8221; for quarterdeck is reminiscent of the days before World War II when the &#8220;quarterdeck&#8221; of naval vessels was aft along the ship&#8217;s quarter. These coils, in which current can be individually adjusted, remove much of the fore-and-aft component of the ship&#8217;s permanent and induced fields. More commonly, the combined F and Q coils consist of two parts; one part the FP and QP coils, to take care of the permanent fore-and-aft field, and the other part, the FI and QI coils, to neutralize the induced fore-and aft field. Generally, the forward and after coils of each type are connected in series, forming a split-coil installation and designated FP-QP coils and FI-QI coils. Current in the FPQP coils is generally constant, but in the FI-QI coils is varied according to the heading and magnetic latitude of the vessel. In split-coil installations, the coil designations are often called simply the P-coil and I-coil.

Longitudinal (L) coil. Better control of the fore-andaft components, but at greater installation expense, is provided by placing a series of vertical, athwartship coils along the length of the ship. It is the field, not the coils, which is longitudinal. Current in an L coil is varied as with the FI-QI coils. It is maximum on north and south headings, and zero on east and west headings.

Athwartship (A) coil. The A coil is in a vertical foreand-aft plane, thus producing a horizontal athwartship field which neutralizes the athwartship component of the vessel&#8217;s field. In most vessels, this component of the permanent field is small and can be ignored. Since the A-coil neutralizes the induced field, primarily, the current is changed with magnetic latitude and with heading, maximum on east or west headings, and zero on north or south headings.

The strength and direction of the current in each coil is indicated and adjusted at a control panel accessible to the navigator. Current may be controlled directly by rheostats at the control panel or remotely by push buttons which operate rheostats in the engine room.Appropriate values of the current in each coil are determined at a degaussing station, where the various currents are adjusted until the vessel&#8217;s magnetic signature is made as flat as possible. Recommended current values and directions for all headings and magnetic latitudes are set forth in the vessel&#8217;s degaussing folder. This document is normally kept by the navigator, whose must see that the recommended settings are maintained whenever the degaussing system is energized.

*643.	Securing The Degaussing System*
Unless the degaussing system is properly secured, residual magnetism may remain in the vessel. During degaussing compensation and at other times, as recommended in the degaussing folder, the &#8220;reversal&#8221; method is used. The steps in the reversal process are as follows:
1.	Start with maximum degaussing current used since the system was last energized.
2.	Decrease current to zero and increase it in the opposite direction to the same value as in step 1.
3.	Decrease the current to zero and increase it to threefourths maximum value in the original direction.
4.	Decrease the current to zero and increase it to onehalf maximum value in the opposite direction.
5.	Decrease the current to zero and increase it to onefourth maximum value in the original direction.
6.	Decrease the current to zero and increase it to oneeighth maximum value in the opposite direction.
7.	Decrease the current to zero and open switch.
*
644.	Magnetic Treatment Of Vessels*
In some instances, degaussing can be made more effective by changing the magnetic characteristics of the vessel by a process known as deperming. Heavy cables are wound around the vessel in an athwartship direction, forming vertical loops around the longitudinal axis of the vessel.The loops are run beneath the keel, up the sides, and over the top of the weather deck at closely spaced equal intervals along the entire length of the vessel. Predetermined values of direct current are then passed through the coils. When the desired magnetic characteristics have been acquired, the cables are removed.

A vessel which does not have degaussing coils, or which has a degaussing system which is inoperative, can be given some temporary protection by a process known as flashing.

A horizontal coil is placed around the outside of the vessel and energized with large predetermined values of direct current. When the vessel has acquired a vertical field of permanent magnetism of the correct magnitude and polarity to reduce to a minimum the resultant field below the vessel for the particular magnetic latitude involved, the cable is removed. This type protection is not as satisfactory as that provided by degaussing coils because it is not adjustable for various headings and magnetic latitudes, and also because the vessel&#8217;s magnetism slowly readjusts following treatment.

During magnetic treatment all magnetic compasses and Flinders bars should be removed from the ship. Permanent adjusting magnets and quadrantal correctors are not materially affected, and need not be removed. If it is impractical to remove a compass, the cables used for magnetic treatment should be kept as far as practical from it.
*
645.	Degaussing Effects*
The degaussing of ships for protection against magnetic mines creates additional effects upon magnetic compasses, which are somewhat different from the permanent and induced magnetic effects. The degaussing effects are electromagnetic, and depend on:
1.	Number and type of degaussing coils installed.
2.	Magnetic strength and polarity of the degaussing coils.
3.	Relative location of the different degaussing coils with respect to the binnacle.
4.	Presence of masses of steel, which would tend to concentrate or distort magnetic fields in the vicinity of the binnacle.
5.	The fact that degaussing coils are operated intermittently, with variable current values, and with different polarities, as dictated by necessary degaussing conditions.

*646.	Degaussing Compensation*
The magnetic fields created by the degaussing coils would render the vessel&#8217;s magnetic compasses useless unless compensated. This is accomplished by subjecting the compass to compensating fields along three mutually perpendicular axes. These fields are provided by small compensating coils adjacent to the compass. In nearly all installations, one of these coils, the heeling coil, is horizontal and on the same plane as the compass card, providing a vertical compensating field. Current in the heeling coil is adjusted until the vertical component of the total degaussing field is neutralized. The other compensating coils provide horizontal fields perpendicular to each other. Current is varied in these coils until their resultant field is equal and opposite to the horizontal component of the degaussing field. In early installations, these horizontal fields were directed fore-and-aft and athwartships by placing the coils around the Flinders bar and the quadrantal spheres. Compactness and other advantages are gained by placing the coils on perpendicular axes extending 045&#176;-225&#176; and 315&#176;- 135&#176; relative to the heading. 

A frequently used compensating installation, called the type K, is shown in Figure 646.
It consists of a heeling coil extending completely around the top of the binnacle, four intercardinal coils, and three control boxes. The intercardinal coils are named for their positions relative to the compass when the vessel is on a heading of north, and also for the compass headings on which the current in the coils is adjusted to the correct amount for compensation. The NE-SW coils operate together as one set, and the NW-SE coils operate as another.

One control box is provided for each set, and one for the heeling coil.
The compass compensating coils are connected to the power supply of the degaussing coils, and the currents passing through the compensating coils are adjusted by series resistances so that the compensating field is equal to the degaussing field. Thus, a change in the degaussing currents is accompanied by a proportional change in the compensating currents. Each coil has a separate winding for each degaussing circuit it compensates.

Degaussing compensation is carried out while the vessel is moored at the shipyard where the degaussing coils are installed. This is usually done by civilian professionals, using the following procedure:
Step 1. The compass is removed from its binnacle and a dip needle is installed in its place. The M coil and heeling coil are then energized, and the current in the heeling coil is adjusted until the dip needle indicates the correct value for the magnetic latitude of the vessel. The system is then secured by the reversing process.










Step 2. The compass is replaced in the binnacle. With auxiliary magnets, the compass card is deflected until the compass magnets are parallel to one of the compensating coils or set of coils used to produce a horizontal field. The compass magnets are then perpendicular to the field produced by that coil. One of the degaussing circuits producing a horizontal field, and its compensating winding, are then energized, and the current in the compensating winding is adjusted until the compass reading returns to the value it had before the degaussing circuit was energized. The system is then secured by the reversing process. The process is repeated with each additional circuit used to create a horizontal field. The auxiliary magnets are then removed.

Step 3. The auxiliary magnets are placed so that the compass magnets are parallel to the other compensating coils or set of coils used to produce a horizontal field. The procedure of step 2 is then repeated for each circuit producing a horizontal field.

When the vessel gets under way, it proceeds to a suitable maneuvering area. The vessel is then headed so that the compass magnets are parallel first to one compensating coil or set of coils and then the other, and any needed adjustment is made in the compensating circuits to reduce the error to a minimum. The vessel is then swung for residual deviation, first with degaussing off and then with degaussing on, and the correct current settings for each heading at the magnetic latitude of the vessel. From the values thus obtained, the &#8220;DG OFF&#8221; and &#8220;DG ON&#8221; columns of the deviation table are filled in. If the results indicate satisfactory compensation, a record is made of the degaussing coil settings and the resistance, voltages, and currents in the compensating coil circuits. The control boxes are then secured. 

Under normal operating conditions, the settings need not be changed unless changes are made in the degaussing system, or unless an alteration is made in the amount of Flinders bar or the setting of the quadrantal correctors. 

However, it is possible for a ground to occur in the coils or control box if the circuits are not adequately protected from moisture. If this occurs, it should be reflected by a change in deviation with degaussing on, or by a decreased installation resistance. Under these conditions, compensation should be done again. If the compass will be used with degaussing on before the ship can be returned to a shipyard where the compensation can be made by experienced personnel, the compensation should be made at sea on the actual headings needed, rather than by deflection of the compass needles by magnets. More complete information related to this process is given in the degaussing folder.

If a vessel has been given magnetic treatment, its magnetic properties have been changed. This necessitates readjustment of each magnetic compass. This is best delayed for several days to permit stabilization of the magnetic characteristics of the vessel. If compensation cannot be delayed, the vessel should be swung again for residual deviation after a few days. Degaussing compensation should not be made until after compass adjustment has been completed.

*Well, that was a handful huh? 
I know some people figure that "I don't need to know this crap". Mmmm, ya there is a lot we are covering and going to cover that will not be applicable to some but maybe parts will to others. So your going to get it all! 
Just, if you even only "brush" through the so called "unimportant crap" someday, somewhere, you will say to yourself "I heard that somewhere before" or you might run into an instance where your memory will come back into play and it might save you or someone else.

"Such knowledge is too wonderful for me; it is high, I cannot attain to it." Ps 139:6

So Hang in there we have a lot to cover and kind of quickly, because I'll have to hit the water soon.
Congratulations for finishing chapter 6. We only have 32 more chapters for this segment and 21 pages of glossarys I can give you before going into something else.

Conclusion ch 6
*


----------



## ezbite

HOLY COW, aye aye aye aye aye,,,wow. lots of info van. only chapter 6


----------



## Fishers of Men

I have to start pumping it out more in order to get this part done before April. We'll be busy!


----------



## Fishers of Men

*Okay, I am going to try to mix and match a lot of material along with the Bowditch navigation series. I think this way bits and pieces that we have discussed will fall into play.

Along this series of Bowditch I am going to incorporate GPS. I know a lot of you are chomping at the bit for this!

Basic Concepts in Coastal and Inland Navigation GPS*
By far the most popular electronic navigation system is the Global Positioning System, or GPS. The low cost and superb performance of a handheld GPS receiver make it a near-essential tool to have on a boat. GPS uses multiple satellites as artificial stars to provide precise position fixes. To be effective, a GPS receiver must have a clear view of the sky above the boat and be able to simultaneously receive signals from four or more satellites.

The resultant three- dimensional fix provides precise north-south and east-west coordinates (typically expressed as a latitude and longitude), a nominal altitude (meaningless to the boater, though not to a pilot or mountain climber), and a precise time. GPS references your fix to a horizontal datum; you must be sure the datum selected corresponds to that used on your nautical chart.

By means of its built-in navigation computer, a GPS receiver can provide other useful information in addition to your position. By comparing your current position with one from a few seconds earlier, the GPS receiver can determine your boat&#8217;s direction and speed. And by comparing your position with the coordinates of a selected waypoint, the GPS receiver can provide the bearing and distance to that waypoint, plot a course to it, provide a continuous in dictation of how close you are to that course line, and calculate a time of arrival from your present speed.

Some GPS receivers are hardwired to the boat&#8217;s power supply. If yours is not, be sure to stow extra batteries or a cigarette lighter&#8212;type adapter aboard. As with any electronic device, a GPS receiver is quire reliable but not infallible. If you use it as your primary position sensor, it&#8217;s a good idea to carry a backup GPS just in case. If all else fails, you will need to get out your plotting tools and limber up your chart-and-compass piloting skills. And remember, a GPS position is just an abstraction until you plot it on a chart.

Your GPS receiver has no inherent knowledge of the shorelines, ledges, or other hazards arrayed around your boat (unless you&#8217;ve programmed a few avoidance waypoints into its memory, as will be described. There&#8217;s just no substitute for a chart&#8217;s-eye view of your surroundings.

*Piloting*
Being near shore, you generally can use landmarks and navigation aids in piloting. Offshore navigators do not have that support structure, but they are seldom exposed to the potential underwater hazards that the coastal or inland boater will encounter. Even in relatively familiar waters near shore, the recreational boater is faced with a challenging environment that requires solid skills and a good understanding of piloting in order to boat safely.
Piloting helps to answer some basic questions, such as, &#8220;Where am I?&#8221; and &#8220;How do I get where I want to go?&#8221; Unlike mariners in past ages, today&#8217;s boaters are armed with valuable tools like GPS that answer the first question with great ease and precision. In order to answer the second question, you need to use charts to plot your current position and the intended path to your destination. Often, the straight-line path from here to there is not available, either because land blocks the way, or because underwater hazards preclude a safe passage.

This segment will explain the basic principles of navigation, including lines of motion (your course), lines of position (bearings), and fixes. It covers not only use of the GPS but also traditional methods that you also need to know.

This segment will present you with two levels of techniques you can use to navigate safely. First, you will learn the time-tested of piloting. These typically involve the use of various instruments and tools. Second under the category of &#8220;Seaman&#8217;s Eye.&#8221; you be presented with some quick tips and techniques that will teach you how to estimate your boat&#8217;s position without formal instruments or tools.

*Seaman&#8217;s Eye*
As an extension of the more formal process of piloting, you need to develop a sense of your environment. This helps to cross-check your navigation and alerts to conditions that may warrant some further action. &#8220;Seaman&#8217;s Eye&#8221; is a set of skills developed over time by experienced mariners.

This segment will highlight a number of these skills to help you. It is essential that you not rely upon them for your navigation, but use them as supplements to the more detailed process of piloting.
*
Using Basic Piloting Skills to get the most from your GPS.*
Charts are your road maps for the water, but they lack clearly defined highways. You will need to plot your paths on the water using information that you get from the charts.

Your chart is an accurately scaled depiction of the land and water area it covers. The chart scale, printed on the chart, represents a ratio (e.g., 1:n). For example, a 1:40.000 scale indicates that one unit of measure on the paper chart is equal to 40,000 of the same units in the real world. Thus one inch on the chart covers the same distance as 40,000 inches (0.6 nautical miles) on the Earth. A chart with a small value of n is called a large scale chat because one divided by a smaller n is a larger number. Generally a large scale chart covers a smaller area, but in greater detail. Each chart provides a distance scale, usually in nautical miles and statute miles and sometimes in kilometers. In addition, you can use the latitude scale on a coastal chart for measuring distance in nautical miles. This will be explained below. Mariners typically use nautical miles for distance. Each nautical mile (nm) is exactly equal to one minute of latitude and is approximately 6076 feet. For comparison, a statute mile (often used on lakes and rivers) is exactly 5280 feet.

Instead of roads, you will draw course lines. Each of these course lines will have a direction and a distance.

You will need to measure course direction in order to steer your boat. You will want to know the distance in order to estimate travel time.

Your position is indicated by a set of coordinates. Boaters generally use latitude and longitude as the frame of reference. Using these coordinates is similar to using the intersection of two streets to define a specific location. This is your frame of reference, and it is especially important if you are using a GPS to help you navigate. Your GPS provides a very precise position as a point in three-dimensional space, but it has no inherent knowledge of what is there. The GPS uses a model of the Earth to relate this point in space to a set of coordinates which include latitude, longitude and altitude. The GPS latitude and longitude values identify your location on the chart. (Altitude is not normally a factor in marine navigation.) Once you have the coordinates, you can find where you are and what is around you by plotting these coordinates on your chart. You will get a chance to do that in this session.

*Plotting Tools*
In order to work with your chart, you will use some basic plotting tools. The lines that you draw must be accurate, because any error can be reflected by a substantial difference in location when you are on the water.

In this session, I will use the USPS Rectangular Course Plotter, a clear plastic device approximately 4 inches wide by 15 inches long. It is imprinted with a series of lines parallel with the long edges and two half-circle segments similar to protractor scales for measuring directions. You will use this plotter to draw course lines and measure course directions, or to lay out a course in a specified direction.


















Other plotting tools are available, including parallel rules, rolling parallel rules, and protractors with movable arms. 
A protractor plotting tool is often included among the materials for basic plotting courses. These tools ate inexpensive and reliable. If you&#8217;re in cramped quarters or on a small charting table, protractors can be less cumbersome than parallel rules. Plus, because a protractor scale is printed directly on the plotting tool, you won&#8217;t need to access the compass rose for angles. This added flexibility is especially helpful when lack of space forces you to do your plotting on a folded chart. Murphy&#8217;s law being what it is, the compass rose is always folded underneath and therefore inaccessible. There is also a two-piece protractor with a swinging arm. For now, lets focus on the one-piece rectangular plotting tool.

This simple, rectangular, see-through-plastic template was designed by the United States Power Squadrons. Two protractor scales and parallel lines are printed on the template with one for use with latitude lines and the other (printed in reverse order) for use with longitude lines.

Course and bearing directions can be determined by using the scales on a protractor plotting tool. You need to align the bullseye with a grid line while you have the plotter aligned with the course line. You can align the top of the plotter or any of the printed parallel lines with the course line. Finally you read the course direction from the appropriate protractor scale. Which scale to use? Use common sense. This simplistic compass rose (upper right) provides you with a sense of direction. Any course or bearing toward the top right of the chart will be between 0&#176; and 90&#176;. By the same token, any course or bearing toward the bottom right will be between 90&#176; and 180&#176;. Toward the lower left will be between 180&#176; and 270&#176;. Finally toward the upper left will be between 270&#176; and 380&#176; (0).

To plot a course, align the course&#8217;s starting point (whether a navigation buoy or simply a waypoint on the plotter edge, orient the plotter&#8217;s bull&#8217;s-eye on a latitude or longitude line as appropriate, and read a direction in degrees true from one of the protractor&#8217;s scales. This device takes some practice in order to avoid reading or using the wrong scale, and it requires those pesky conversions between true and magnetic bearings and courses, which you can avoid by using parallel rules. Nevertheless, these plotting tools are the least expensive and among the easiest to use once you are comfortable with the conversion between true and magnetic, as we have discussed in TVMDC.

*Tool Kit*
You should put together an onboard kit of tools to support your navigation tasks. In addition to plotting tools and dividers, consider including a drawing compass, a calculator, a notebook for keeping waypoint information and calculations, a collection of fine tipped pencils and water proof sleeves for charts.

As you gain experience, you will find that some tools work well at home or on a chart table and others are easier to use on the boat, where space and flat surfaces are limited. On the water you will lay out the directions of sighted bearings and plot them to help identify your location. The USPS Course Plotter represents a good compromise for use in both locations.

Dividers are the second major plotting tool. They are used principally to measure distances or plot coordinates. Several types of dividers are described in the reference text. The simplest form consists of two arms ending in points and joined at the other end with a friction pivot. Once set, good dividers will not change their setting without some moderate effort; this allows you to accurately transfer a measurement from one place on the chart to another. You will mainly be using the latitude and longitude scales and possibly the distance scale as references for your dividers.
*Accuracy is important.* On a 1:80,000 scale chart, your pencil line width on the chart can represent over a hundred feet on the water. Generally, you will be asked to strive for course lines drawn with a sharp, medium-soft pencil to an accuracy of 1&#176; of angle and one- tenth of a nautical mile in distance.
*Using GPS as your Primary Position Sensor*
Much of traditional navigation is based on techniques to locate your current position. With GPS, that information is available continuously and with great precision, freeing you to concentrate on your other navigational duties. However, you need to understand and appreciate what GPS does and its limitations.

*Remember that all GPS does for you *is provide a 3-dimensional point in space that corresponds with your current location. Your GPS receiver compares this point in space with a mathematical grid that represents the surface of the Earth. Using the grid, the point is converted into a latitude and a longitude (coordinates) on the Earth , plus an altitude. For marine navigation, you are not interested in altitude, which generally is less accurate than your horizontal position.


























*It is essential to bear in mind that GPS has no inherent knowledge of what is located at that spot or in its immediate vicinity. Your charts provide that critical information.* You need to plot the coordinates reported by the GPS on the chart to gain a sense of the local terrain and features.

Your GPS receiver contains a miniature navigation computer that takes the position information and provides a great deal more information that is useful to your navigation. Specifically, GPS can compute your motion; and it can compare your current location with one that you have stored in the GPS as a way- point.

GPS computes your actual course over the Earth&#8217;s surface (or Track) by comparing your current location with your position just seconds ago. By doing this, the GPS can also compute which direction you moved and how fast you moved that way. These are reported as Course Over Ground (COG) or Track, and Speed Over Ground (SOG) or Speed.










GPS compares your current coordinates with those of a point you have stored in the unit. These points are called waypoints and are used for navigation. By making the comparison, the GPS computes the bearing from your current location to that point, and the distance between them ( Figure 4-33).
*
Skill &#8212; Plotting on a Chart*
This skill is required in order to take the GPS coordinates shown by your GPS unit and determine the position on the chart.
Refer to Figure 4-18.










You will execute the following steps:
1.	Obtain the GPS coordinates from the GPS screen in the Figure. GPS units display latitude and longitude as dd&#176; mm.mmm&#8217;.
2.	Write down the coordinates, rounding thousandths of minutes (or seconds, if used) to tenths of minutes.
3.	Examine your chart and approximate the general location of the coordinates by use of the latitude and longitude scales.
4.	Locate the position in degrees, minutes, and tenths that corresponds with the latitude position shown on the GPS screen. While you can measure these in either order, in this exercise you will start by measuring the latitude of the position.
5.	Set one point of your dividers on the position of latitude as identified on the scale and extend your dividers so that the other point is set on the nearest horizontal grid line (parallel of latitude). Preserve this setting.

6. Lift the dividers and move them to the left or right, along the same grid line, to the area you approximated the GPS position to be located.
7. Place one point on the grid line of latitude and set the other point on the chart in the direction of the coordinate. Draw a light pencil line parallel to the latitude line for reference.
8. Repeat this process for longitude using the nearest vertical grid line (meridian of longitude) for reference.
9. Place one point of the dividers on the spot determined to be the point of longitude scale and the other on the nearest vertical grid line.
10. Transfer this setting to the grid line in the area you approximated the GPS position to be located. Draw a light pencil line parallel to the longitude line for reference.
11. Mark the GPS coordinate where the two pencil lines intersect.
12. Label the GPS position with a dot surrounded by a small circle. Labeling should indicate how the position was determined (GPS) and the time the coordinates were obtained from the GPS screen (e.g., 1000 GPS).
*EXERCISE *
I can&#8217;t scan a full scale chart for us to use for exercises so I can only give examples. Wish we had a classroom setting!
GPS indicates a boat&#8217;s position by longitude and latitude, and a navigator must be able to plot GPS coordinates to determine a position on a chart. 
You will need your dividers and a chart. 
Plot and label the GPS Coordinates.
Time	Coordinates
1000	41&#176; 43.787&#8217; N; 072&#176; 02.325&#8217; W (examples)
1. Round the minutes to 43.8&#8217; and 02.3&#8217; and plot the position.
2. Approximate the location of the coordinates by looking at the latitude and longitude scales on the chart.
3. Open your dividers and on the latitude scale on the side of the chart, place one point of the dividers on the position of 41&#176; 43.8&#8217; N, and the other point on a latitude grid line.
4. Lift the dividers and move to the general area of the coordinates. Place a divider point on the same latitude grid line and set the other point down on the chart (the two points must be aligned vertically with the direction of the latitude scale) and draw a light pencil line.
5. Next, perform the same function only using the longitude coordinate and the longitude scale at the top or bottom of the chart. Open your dividers and on the longitude scale, place one point of the dividers on the position of 072&#176; 02.3&#8217; W, and the other point of a longitude grid line.
6. Lift the dividers and move to the general area of the latitude pencil line. Place the first divider point on the same longitude grid line and the other point on the chart directly to the left or right of the first point (the two points must be aligned horizon tally with the chart&#8217;s longitude scale) and draw a pencil mark. The two pencil marks should cross. If not, recheck with your dividers.
7. Mark and label the GPS coordinates with a dot surrounded by a small circle. The time of the fix is shown in the 24-hour format, followed by the letters GPS. The labeling indicates the fix was determined at 1000 by GPS.

*To be Continued*


----------



## reel

Incidentally I still have my copy of Bowditch 1966 U.S. Navy "American Practical Navigator" $7.00.

So if anyone wants to know how to read a sextant let me know. 
Ha...


----------



## Fishers of Men

reel said:


> Incidentally I still have my copy of Bowditch 1966 U.S. Navy "American Practical Navigator" $7.00.
> 
> So if anyone wants to know how to read a sextant let me know.
> Ha...


That was a good buy! Welcome to chime in anytime, thats coming about chapter 16 I believe.


----------



## Fishers of Men

Here is a contribution from Reel.
Excel Spread Sheet program to convert Degrees, Minutes and Seconds to Degrees and decimal minutes which many GPS units prefer to read.
http://www.ohiogamefishing.com/community/showthread.php?t=86221
There is also an attached spread sheet.
Thanks, Reel.


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## Fishers of Men

*This chapter will be short, just for a refresher of what we have already covered because in chapter 8 we are going to start applying what we have learned.

CHAPTER 7
DEAD RECKONING
DEFINITION AND PURPOSE
700.	The Importance Of Dead Reckoning*
Dead reckoning allows a navigator to determine his present position by projecting his past courses steered and speeds over ground from a known past position. He can also determine his future position by projecting an ordered course and speed of advance from a known present position. The DR position is only an approximate position because it does not allow for the effect of leeway, current, helmsman error, or gyro error.
Dead reckoning helps in determining sunrise and sunset; in predicting landfall, sighting lights and predicting arrival times; and in evaluating the accuracy of electronic positioning information. It also helps in predicting which celestial bodies will be available for future observation. The navigator should carefully tend his DR plot, update it when required, use it to evaluate external forces acting on his ship, and consult it to avoid potential navigation hazards.
*
CONSTRUCTING THE DEAD RECKONING PLOT*
Maintain the DR plot directly on the chart in use. DR at least two fix intervals ahead while piloting. If transiting in the open ocean, maintain the DR at least four hours ahead of the last fix position. If operating in a defined, small operating area, there is no need to extend the DR out of the operating area; extend it only to the operating area boundary. Maintaining the DR plot directly on the chart allows the navigator to evaluate a vessel&#8217;s future position in relation to charted navigation hazards. It also allows the conning officer and captain to plan course and speed changes required to meet any operational commitments. This section will discuss how to construct the DR plot.

*701.	Measuring Courses And Distances*
To measure courses, use the chart&#8217;s compass rose nearest to the chart section currently in use. Transfer course lines to and from the compass rose using parallel rulers, rolling rulers, or triangles. If using a parallel motion plotter (PMP), simply set the plotter at the desired course and plot that course directly on the chart.

The navigator can measure direction at any convenient place on a Mercator chart because the meridians are parallel to each other and a line making an angle with any one makes the same angle with all others. Measure direction on a conformal chart having nonparallel meridians at the meridian closest to the area of the chart in use. The only common nonconformal projection used is the gnomonic; a gnomonic chart usually contains instructions for measuring direction. Compass roses give both true and magnetic directions.

For most purposes, use true directions.
Measure distances using the chart&#8217;s latitude scale. Assuming that one minute of latitude equals one nautical mile introduces no significant error. Since the Mercator&#8217;s latitude scale expands as latitude increases, measure distances on the latitude scale closest to the area of interest. On large scale charts, such as harbor charts, use the distance scale provided. To measure long distances on small-scale charts, break the distance into a number of segments and measure each segment at its mid-latitude.
Navigational computers can also compute distances between two points. Because of the errors inherent in manually measuring track distances, use a navigation computer if one is available.

*702.	Plotting And Labeling The Course Line And Positions*
Draw a new course line whenever restarting the DR. Extend the course line from a fix in the direction of the ordered course. Above the course line place a capital C followed by the ordered course. Below the course line, place a capital S followed by the speed in knots. Label all course lines and fixes soon after plotting them because a conning officer or navigator can easily misinterpret an unlabeled line or position. Enclose a fix from two or more LOPs by a small circle and label it with the time to the nearest minute. Mark a DR position with a semicircle and the time. Mark an estimated position (EP) by a small square and the time. Determining an EP is covered later in this chapter.
Express the time using four digits without punctuation.
Use either zone time or GMT.
Label the plot neatly, succinctly, and clearly.

*Figure 702 illustrates this process. *
The navigator plots and labels the 0800 fix. The conning officer orders a course of 095&#176;T and a speed of 15 knots. The navigator extends the course line from the 0800 fix in a direction of 095&#176;T. He calculates that in one hour at 15 knots he will travel 15 nautical miles. He measures 15 nautical miles from the 0800 fix position along the course line and marks that point on the course line with a semicircle. He labels this DR with the time. Note that, by convention, he labels the fix time horizontally and the DR time diagonally.










*THE RULES OF DEAD RECKONING
703. Plotting The DR*
Plot the vessel&#8217;s DR position:
1.	At least every hour on the hour.
2.	After every change of course or speed.
3.	After every fix or running fix.
4.	After plotting a single line of position.
Figure 703 illustrates applying these rules. Clearing the harbor at 0900, the navigator obtains a last visual fix. This is taking departure, and the position determined is called the departure. At the 0900 departure, the conning officer orders a course of 090&#176;T and a speed of 10 knots. The navigator lays out the 090&#61616;T course line from the departure. At 1000, the navigator plots a DR position according to the rule requiring plotting a DR position at least every hour on the hour. At 1030, the conning officer orders a course change to 060&#176;T. The navigator plots the 1030 DR position in accordance with the rule requiring plotting a DR position at every course and speed change. Note that the course line changes at 1030 to 060&#176;T to conform to the new course. At 1100, the conning officer changes course back to 090&#176;T. The navigator plots an 1100 DR because of the course change, Note that, regardless of the course change, an 1100 DR would have been required because of the &#8220;every hour on the hour&#8221; rule.
At 1200, the conning officer changes course to 180&#176;T and speed to 5 knots. The navigator plots the 1200 DR. At 1300, the navigator obtains a fix. Note that the fix position is offset to the east from the DR position. The navigator determines set and drift from this offset and applies this set and drift to any DR position from 1300 until the next fix to determine an estimated position. He also resets the DR to the fix; that is, he draws the 180&#176;T course line from the 1300 fix, not the 1300 DR.










*704. Resetting The DR*
Reset the DR plot to the ship&#8217;s latest fix or running fix. In addition, consider resetting the DR to an inertial estimated position as discussed below.
If a navigator has not received a fix for a long time, the DR plot, not having been reset to a fix, will accumulate time-dependent error. Soon that error may become so significant that the DR will no longer show the ship&#8217;s position with sufficient accuracy. If his vessel is equipped with an inertial navigator, the navigator should consider resetting the DR to the inertial estimated position. Some factors to consider when making this determination are:
(1) Time since the last fix and availability of fix information. If it has been a short time since the last fix and fix information may soon become available, it may be advisable to wait for the next fix to reset the DR.
(2) Dynamics of the navigation situation. If, for example, a submerged submarine is operating in the Gulf Stream, fix information is available but operational considerations may preclude the submarine from going to periscope depth to obtain a fix. Similarly, a surface ship with an inertial navigator may be in a dynamic current and suffer a temporary loss of electronic fix equipment. In either case, the fix information will be available shortly but the dynamics of the situation call for a more accurate assessment of the vessel&#8217;s position. Plotting an inertial EP and resetting the DR to that EP may provide the navigator with a more accurate assessment of the navigation situation.
(3) Reliability and accuracy of the fix source. If a submarine is operating under the ice, for example, only the inertial EP and Omega fixes may be available for weeks at a time. Given a known inaccuracy of Omega, a high prior correlation between the inertial EP and highly accurate fix systems such as GPS, and the continued proper operation of the inertial navigator, the navigator may well decide to reset the DR to the inertial EP rather than the Omega fix.

*DEAD RECKONING AND SHIP SAFETY*
Properly maintaining a DR plot is important for ship safety. The DR allows the navigator to examine a future position in relation to a planned track. It allows him to anticipate charted hazards and plan appropriate action to avoid them. Recall that the DR position is only approximate. Using a concept called fix expansion compensates for the DR&#8217;s inaccuracy and allows the navigator to use the DR more effectively to anticipate and avoid danger.

*705. Fix Expansion*
Often a ship steams in the open ocean for extended periods without a fix. This can result from of any number of factors ranging from the inability to obtain celestial fixes to malfunctioning electronic navigation systems. Infrequent fixes are particularly common on submarines. Whatever the reason, in some instances a navigator may find himself in the position of having to steam many hours on DR alone. The navigator must take precautions to ensure that all hazards to navigation along his path are accounted for by the approximate nature of a DR position. One method which can be used is fix expansion.

Fix expansion takes into account possible errors in the DR calculation caused by factors which tend to affect the vessel&#8217;s actual course and speed over ground. The navigator considers all such factors and develops an expanding &#8220;error circle&#8221; around the DR plot. One of the basic assumptions of fix expansion is that the various individual effects of current, leeway, and steering error combine to cause a cumulative error which increases over time, hence, the concept of expansion.

Errors considered in the calculation of the fix expansion encompass all errors that can lead to DR inaccuracy. Some of the most important factors are current and wind, compass or gyro error, and steering error. Any method which attempts to determine an error circle must take these factors into account. The navigator can use the magnitude of set and drift calculated from his DR plot. See section 707 below. He can obtain the current&#8217;s magnitude from pilot charts or weather reports. He can determine wind speed from weather reports or direct measurement. He can determine compass error by comparison with an accurate standard or by obtaining an azimuth of the sun. The navigator determines the effect each of these errors has on his course and speed over ground, and applies that error to the fix expansion calculation.

As noted above, the error is a function of time; it grows as the ship proceeds down the track without a obtaining a fix. Therefore, the navigator must incorporate his calculated errors into an error circle whose radius grows with time. For example, assume the navigator calculates that all the various sources of error can create a cumulative position error of no more than 2 nm. Then his fix expansion error circle would grow at that rate; it would be 2 nm after the first hour, 4 nm after the second, and so on. At what value should the navigator start this error circle? Recall that a DR is laid out from every fix. All fix sources have a finite absolute accuracy, and the initial error circle should reflect that accuracy. Assume, for example, that a satellite navigation system has an accuracy of 0.5 nm. Then the initial error circle around that fix should be set at 0.5 nm.
Construct the error circle as follows. When the navigator obtains a fix, reset the DR to that fix. Then, enclose that DR position in a circle the radius of which is equal to the accuracy of the system used to obtain the fix. Lay out the ordered course and speed from the fix position. Then, apply the fix expansion circle to the hourly DR&#8217;s. In the example given above, the DR after one hour would be enclosed by a circle of radius 2.5 nm, after two hours 4.5 nm, and so on. Having encircled the four hour DR positions with the error circles, the navigator then draws two lines originating tangent to the original error circle and simultaneously tangent to the other error circles. The navigator then closely examines the area between the two tangent lines for hazards to navigation. This technique is illustrated in Figure 705 below.

The fix expansion encompasses all the area in which the vessel could be located (as long as all sources of error are considered). If any hazards are indicated within the cone, the navigator should be especially alert for those dangers. If, for example, the fix expansion indicates that the vessel may be standing into shoal water, continuously monitor the fathometer. Similarly, if the fix expansion indicated that the vessel might be approaching a charted obstruction, post extra lookouts.










The fix expansion may grow at such a rate that it becomes unwieldy. Obviously, if the fix expansion grows to cover too large an area, it has lost its usefulness as a tool for the navigator, and he should obtain a new fix.

*DETERMINING AN ESTIMATED POSITION*
An estimated position is a DR position corrected for the effects of leeway, steering error, and current. This section will briefly discuss the factors that cause the DR position to diverge from the vessel&#8217;s actual position. It will then discuss calculating set and drift and applying these values to the DR to obtain an estimated position. Finally, it will discuss determining the estimated course and speed made good.

*706.	Factors Affecting DR Position Accuracy*
Tidal current is the periodic horizontal movement of the water&#8217;s surface caused by the tide-affecting gravitational force of the moon. Current is the horizontal movement of the sea surface caused by meteorological, oceanographic, or topographical effects. From whatever its source, the horizontal motion of the sea&#8217;s surface is an important dynamic force acting on a vessel moving through the water.
Set refers to the current&#8217;s direction, and drift refers to the current&#8217;s speed.
Leeway is the leeward motion of a vessel due to that component of the wind vector perpendicular to the vessel&#8217;s track.
Leeway and current effects combine to produce the most pronounced natural dynamic effects on a transiting vessel. In addition to these natural forces, helmsman error and gyro error combine to produce a steering error that causes additional error in the DR.
*
707.	Calculating Set And Drift And Plotting An Estimated Position*
It is difficult to quantify the errors discussed above individually. However, the navigator can easily quantify their cumulative effect by comparing simultaneous fix and DR positions. Were there no dynamic forces acting on the vessel and no steering error, the DR position and the fix position would coincide. However, they seldom coincide. The fix is offset from the DR by a finite distance.

This offset is caused by the error factors discussed above.
Note again that this methodology provides no means to determine the magnitude of the individual errors. It simply provides the navigator with a measurable representation
of their combined effect.

When the navigator measures this combined effect, he often refers to it as the &#8220;set and drift.&#8221; Recall from above that these terms technically were restricted to describing current effects. However, even though the fix-to-DR offset is caused by effects in addition to the current, this text will follow the convention of referring to the offset as the set and drift.

The set is the direction from the DR to the fix. The drift is the distance in miles between the DR and the fix divided by the number of hours since the DR was last reset. This is true regardless of the number of changes of course or speed since the last fix.

Calculate set and drift at every fix. Calculate an EP by drawing from a DR position a vector whose direction equals the set and whose magnitude equals the product of the drift and the number of hours since the last DR reset. See Figure 707. From the 0900 DR position the navigator draws a set and drift vector. The end of that vector marks the 0900 EP. Note that the EP is enclosed in a square and labeled horizontally with the time. Plot and evaluate an EP with every DR position.










*708. Estimated Course And Speed Made Good*
The direction of a straight line from the last fix to the EP is the estimated track made good. The length of this line divided by the time between the fix and the EP is the estimated speed made good.

Solve for the estimated track and speed by using a vector diagram. See the example problems below. See. Figure 708a
Example 1: A ship on course 080&#176;, speed 10 knots, is steaming through a current having an estimated set of 140&#176; and drift of 2 knots.
Required: Estimated track and speed made good. Solution: See Figure 708a. From A, any convenient point, draw AB, the course and speed of the ship, in direction 080&#176;, for a distance of 10 miles.
From B draw BC, the set and drift of the current, in direction 140&#176;, for a distance of 2 miles. The direction and length of AC are the estimated track and speed made good.
Answers: Estimated track made good 089&#176;, estimated speed made good 11.2 knots.
To find the course to steer at a given speed to make good a desired course, plot the current vector from the origin, A, instead of from B. See Figure 708b.
Example 2: The captain desires to make good a course of 095&#176; through a current having a set of 170&#176; and a drift of 2.5 knots, using a speed of 12 knots. Required: The course to steer and the speed made good. Solution: See Figure 708b. From A, any convenient point, draw line AB extending in the direction of the course to be made good, 095&#176;.
From A draw AC, the set and drift of the current. Using C as a center, swing an arc of radius CD, the speed through the water (12 knots), intersecting line AB at D.
Measure the direction of line CD, 083.5&#176;. This is the course to steer.
Measure the length AD, 12.4 knots. This is the speed made good.
Answers: Course to steer 083.5&#176;, speed made good 12.4 knots.

To find the course to steer and the speed to use to make good a desired course and speed, proceed as follows:
See Figure 708c.










Example 3: The captain desires to make good a course of 265&#176; and a speed of 15 knots through a current having a set of 185&#176; and a drift of 3 knots.
Required: The course to steer and the speed to use. Solution: See Figure 708c. From A, any convenient point, draw AB in the direction of the course to be made good, 265&#176; and for length equal to the speed to be made good, 15 knots.
From A draw AC, the set and drift of the current. Draw a straight line from C to B. The direction of this line, 276&#176;, is the required course to steer; and the length, 14.8 knots, is the required speed.
Answers: Course to steer 276&#176;, speed to use 14.8 kn.

*Conclusion chapter 7*


----------



## Fishers of Men

*Other Electronics*
Later on we will discuss each of the following electronic navigation devices in greater detail. In the meantime, however, here&#8217;s a brief overview of what&#8217;s available for recreational boaters.

In the competition for the next electronic navigation device to consider after GPS, radar and a digital depth sounder run neck and neck. Although not essential for most boaters, radar is a powerful and versatile tool for fixing your position by means of hearings and ranges on surrounding nay aids and landmasses, and it&#8217;s the only electronic device that allows you to track the presence and movements of other boats (and even rain squalls!) in conditions of poor visibility.

Some navigators question the usefulness of a depth sounder, and they make a strong case. After all, the sounder tells you the depth of water directly beneath your boat. If it says you don&#8217;t have enough water under your hull, it&#8217;s likely that you&#8217;ve already run aground. But the depth sounder is actually a very useful navigation tool. By comparing the sounder&#8217;s reported depth against chart soundings, you can better interpret and confirm your current position. Also, when all else fails, a sounder can help you to navigate by following a depth contour or monitoring the depth trend. We will explore this in greater depth&#8212;no pun in tended.

Afluxgate compass uses electronics to sense the Earth&#8217;s magnetic field, thus eliminating potential errors caused by the friction of a compass card in a standard compass. Flux- gate compasses are also self-compensated to a high degree of accuracy&#8212;typically within one degree or better&#8212;and many can automatically correct for local magnetic variation to display true north instead of magnetic when desired. Be cause it is electronic, a fluxgate compass also has the ability to provide digital output to other devices, such as autopilot or radar. (Large ships may use a gyro compass instead, but these are larger and a lot more expensive and have found no place thus far on recreational boats.)
An autopilot is actually a mechanical (not electronic) device that controls a boats rudder in response to signals from its control unit. It needs a signal from an electronic compass (fluxgate or gyro) or a GPS to provide a direction reference. You set a heading on the control unit, and the autopilot adjusts the rudder to maintain that course until it has been shut off or altered by the crew.

Though not usually considered a navigation device, a VHF radio is a truly valuable tool&#8212;particularly in an emergency. By regulation, all new fixed VHF radios must include a function called digital selective calling (DSC). If the radio is connected to a GPS, your position is automatically radioed whenever a DSC call is made. In an emergency, all DSC-equipped radios within your immediate area will sound an alarm and automatically switch to the distress channel (16) to listen to your call. If the receiving DSC radio is connected to an appropriate chartplotter, your position will be plotted on the screen. This function helps the Coast Guard (and other nearby vessels) locate you.
Even without DSC, the Coast Guard can take a radio bearing on your VHF distress signal. Cross bearings from two or more direction finders can locate your boat within a small search area.
VHF radios also are equipped with receive-only channels that provide weather information. More than 800 transmitters cover all 50 states in the United States. The Canadian Communications Directorate provides similar transmissions in Canada, and similar services exist over much of the maritime world. Marine and standard weather reports are repeated continuously, with hourly updates.


----------



## reel

My Marine VHF radio has DSC.

About 2 years ago when I filled out the form, MMSI, boat color, width, size etc, etc, etc, at the end (half hour+ later) it asked what is your Boat USA password ? ? ?
I think the Coast Guard turned this registration process over to privatization. 

I gave up.

Is there a simple way to do this now without the hassle ?
...


----------



## Fishers of Men

reel said:


> My Marine VHF radio has DSC.
> 
> About 2 years ago when I filled out the form, MMSI, boat color, width, size etc, etc, etc, at the end (half hour+ later) it asked what is your Boat USA password ? ? ?
> I think the Coast Guard turned this registration process over to privatization.
> 
> I gave up.
> 
> Is there a simple way to do this now without the hassle ?
> ...


I am not sure, Have to check into that definitely.


----------



## Fishers of Men

*GPS Pre-Planning Plotting*


Pre-voyage Planning is the process of navigation that can be thought of in three stages&#8212;planning, navigating underway, and periodically double-checking your courses, positions, and chartwork. The planning stage&#8212;the topic of this and the following segments is essential to ensure your safety. You need to select your courses, check them for hazards, and adjust them to avoid obstacles. Even if you normally boat in an area you know well, it&#8217;s possible to be caught at sea under adverse conditions with restricted visibility. Careful planning can help you avert discomfort or even disaster in a situation such as this.
The simplest preplanning method involves working with paper charts and pushing buttons on your GPS receiver. Another method, described later in this chapter, eases some of the button pushing by using a computer to upload waypoints and routes into your GPS. A third method, planning directly on digital charts, is presented in the following chapter. Whatever method you choose, pre planning is a good off-the-boat activity that can be done in the evenings or during the off-season.

You should not say, &#8220;well lets go home now, I marked where we departed from&#8221;, and go straight there, unless you know your position and that nothing is obstructing your path home. Have a leg programmed out of your channel to head for in known deep water and then follow your departure leg back in.

*Planning and Paper Charts*
The chart is your security blanket and the navigator&#8217;s most essential tool. It provides the key information you&#8217;ll need to plan and enjoy safe boating. Of course, local knowledge and personal observations will enhance your navigation, because charts are not infallible and cannot show everything. You may know from prior experience or the advice of a local fisherman that aligning a particular red barn in front of a particular white church steeple puts you on the best course through your harbor inlet, but you won&#8217;t find the barn on your chart (though the steeple might be noted). Nevertheless, it&#8217;s amazing how much information is on a chart, and how seldom it&#8217;s wrong. It&#8217;s essential that you have the latest version of the charts for your area.

*Criteria for a Safe Course*
The fundamental premise when using GPS is that you will first pre-qualify safe paths, then follow those paths when you&#8217;re proceeding from one place to another on the water. The same principles apply to pre-qualifying an area in which to meander without fear of encountering unseen hazards. So, what is considered safe?

*DETERMINING SAFE DEPTHS* 
Obviously, you won&#8217;t go far if your boat has run aground. Thus, adequate depth is the first feature you&#8217;ll look for to pre-qualify a safe path. But what is adequate? The answer depends on two factors: the characteristics of your boat, and the characteristics of the seabed.
Each sounding shown on a chart represents a measurement of the bottom depth at a particular location. When enough soundings are assembled, a contour line of constant depth can be drawn using the soundings as a reference. All soundings are referenced to a standard datum, which for most NOAA charts is mean lower low water.
(MLLW). This means that each sounding on a printed on a chart represents nearly the shallowest you can expect to find at that location.










Isolated Hazards can be natural or man made. Outlying rocks are a common example of the former. If you drained all the water from a bay, it&#8217;s underlying topography would look much like that of the surrounding land, with hills, valleys, and rocky outcrops whose peaks might protrude above the surface or lurk just below for the unwary boater. As with wrecks and other man-made hazards, rocks are classified as exposed, covered, and covering.
In addition to wrecks, man-made hazards include old pilings. These, in fact, represent one of the greatest hazards to boats, because they can easily penetrate a hull. Lake Erie is full of them.

*SHOALS,* or circumscribed shallow areas, are in effect the tops of underwater hills. Often, shoals lie along a line, not unlike the spine of a miniature mountain range. Sometimes, though not always, they are rocky. Main channels frequently run parallel with shoals. Often, the shortest path between two points lies across intervening shoals. Be fore attempting such a path, take special care to ensure adequate water depth. (Lake Erie Island area is full of shoals and shallow reefs).

*CLEARANCE OVERHEAD *
The final consideration for pre-qualifying safe paths is vertical clearance. Will your boat fit under bridges and overhead cables? Generally, one of the manufacturer&#8217;s specifications for your boat is bridge clearance. Remember, this measurement is taken from the waterline to the highest part of the boat&#8217;s structure as it leaves the factory. You have likely added antennas, radar, outrigger poles, and so on. You will need to consider the additional heights of these objects when planning your passage. If they can be lowered, make a note on your chart as a reminder.

The clearance printed on the charts is generally referenced to mean high water (MHW), or occasionally mean higher high water (MHHW). Check your chart legend for the datum used. Just like timing a passage over shallow water, you might be able to pass beneath a low bridge by using the tides to your advantage.

In some waters on the Intracoastal Waterway along the U.S. East Coast, for example you will encounter bridges that can be raised or drawn or swung open to provide clear passage. Generally, their heights when closed are shown on the bridge itself as well as on your chart. You also may find a depth of water scale on a bridge abutment. You should be certain of your boat&#8217;s actual bridge clearance and plan carefully so as not to unnecessarily cause the operator to open the bridge or, even worse, attempt a passage you can&#8217;t clear.

When you consider vertical clearance, don&#8217;t forget about overhead cables, especially on inland waterways. Of ten, these may be low enough to present a hazard, and many carry high voltages.

*HORIZONTAL CLEARANCE *
Just as you need a safe margin between your keel or running gear and the seabed, you need to plot courses that maintain a safe horizontal margin. You need ample room to steer around obstacles. Wind and waves can cause small deviations from course, so your paths should be wide enough to allow for this. Also, typical GPS accuracy is within 50 feet of your true position. When planning, check along your intended path to ensure safe waters a little more than ten times wider than that GPS error to either side. To make planning easy, look at the latitude scale. Because one minute of latitude is a nautical mile (about 6,076 feet), one-tenth of a minute (the smallest tick mark) is roughly 600 feet. Using this handy reference for perspective, you can scan your projected path on the chart and confirm that the horizontal clearance on either side of the course is at least as wide as the smallest increment on the latitude scale.

Of course, this assumes that, when underway, you will periodically plot your GPS positions. Plan to plot your GPS position about once every hour, or more frequently if you&#8217;re traveling fast or in foul weather. While you&#8217;re at it, try to verify your GPS-derived position through independent means. In the event of a failure, this may be the only information you have.
*
Steps in Pre-voyage Planning on a Ch*art
It bears repeating: Before you do anything, you need a set of charts for your boating area. With charts in hand, study them in the comfort of your home. Preplanning waypoints, legs, routes, and avoidance waypoints will vastly simplify your navigation underway. 

FIGURE 5-10. Planning on a chart involves plotting lines between your starting point and your destination. You need to measure the coordinates of these end points to enter them as waypoints. A scan along the line indicates the potential for hazards. If potential dangers are identified, you must create intermediate waypoints to build a route that avoids the obstacles.










Here are the recommended steps for programming waypoints:
First, locate your home port and other ports you wish to visit. Buoys around these ports will become way- points.
Second, locate hazards&#8212;places where the water may be too shallow and must be avoided. This information will help you prepare safe routes or avoidance waypoints.
Third, plot a sequence of straight-line paths on your chart that will take you from your home port to other points of interest. For safe and confident navigation, these paths will ideally begin and end at prominent navigation aids&#8212;preferably ones that emit noise and/or light and are surrounded by safe water. Alternatively, you can plot waypoints just offshore from prominent landmarks fronted by safe water. Given a dearth of likely looking nay aids and landmarks, you&#8217;ll have to rely more heavily on latitude/longitude way- points in featureless waters.
Next, invent short names for each of the connecting waypoints.
Then note any landmarks you&#8217;ll be able to use for visual reference while running between waypoints. Charted towers, standpipes, tall buildings, and light houses can help you verify your position or guide you to safety if your GPS fails.
Now, using your plotting tools, measure the coordinates of each identified waypoint. Be sure to double-check each set of coordinates to avoid mistakes. To keep track of these coordinates and other useful information, create a written table with columns for waypoint name, latitude, longitude, and comments.

Finally, once the waypoint table is complete, enter the data into your GPS. This can be done manually on the GPS or by using a computer. I will discuss both approaches later on.

FIGURE 5-11. Record your waypoints on a tablet or in a log book. Waypoints should be named to reflect their location and features. The latitude and longitude for each should be recorded along with summarized details. Always double-check the accuracy of your coordinates. A simple slip of a digit can place you in peril.










GPS receivers usually allow you to enter six to nine characters for each waypoint&#8217;s name along with an accompanying symbol. You should develop a naming and symbol convention that works for you. Because there are many buoys labeled R &#8220;2&#8221; or G &#8220;1,&#8221; you will need to distinguish among them. Generally, you&#8217;ll find it easier to locate waypoints in your GPS memory if you develop regionally based nomenclature. Let&#8217;s say you&#8217;re plotting the waters around Newport, Rhode Island. You could name each waypoint with the prefix NPT&#8221; followed by an identifier such as &#8220;R2&#8221; for red buoy number &#8220;2&#8217; hence &#8220;NPTR2.&#8221;

Most GPS sets alphabetize the waypoint names, so using regional prefixes will ease the task of finding waypoints later by grouping those for a particular area. Avoid beginning a way- point name with a number. Most GPS receivers assign numbers to newly marked waypoints, and you&#8217;ll want a way to clearly distinguish your established waypoints from more transitory ones.
Next, you may wish to mark danger areas such as isolated rocks or wrecks. Use the same regional prefix (&#8220;NPT&#8221 for these locations, but also add another character such as &#8220;D,&#8221; for danger (With the &#8220;D&#8221; in place, your danger waypoints will also be alphabetically grouped within their region.) Then add identifying abbreviations such as &#8220;RKS&#8221; for rocks or &#8220;WRK&#8221; for wrecks (hence &#8220;NPTDRKS&#8221; or &#8220;NPTDWRK ). If there is more than one rock to mark near Newport, simply add a number (&#8220;NPTDRKS2&#8217;9.

Also, on most GPS receivers, you can mark locations on the Map Screen by choosing from a number of different symbols. Use these symbols to clearly differentiate between hazards and navigation aids. For instance, most GPS units offer icons such as a skull and crossbones. This sober image is perfect for marking hazards. Use a distinctly different set of symbols to mark land-based objects such as towers or buildings.

For regions of shallow water, you can add imaginary buoys at key locations if real buoys are lacking. By labeling them &#8220;R&#8221; or &#8220;G&#8221; (for &#8220;red&#8221; or &#8220;green&#8221, you will know on which side of them you need to stay. Append with something such as &#8220;I&#8221; for imaginary before any identifiers or numbers of your choice (&#8220;NPTIR3&#8221. Mark and label these points on your chart.

Many GPS models will automatically assign a route name in this construction:
name of the starting waypoint {hyphen} name of the ending waypoint.
This makes the route name clear and unambiguous. As a further convenience, many of these same GPS models can even reverse the order of the waypoints if you opt to take the route in reverse order.

*To be Continued*


----------



## reel

> When you consider vertical clearance, dont forget about overhead cables, especially on inland waterways. Of ten, these may be low enough to present a hazard, and many carry high voltages.


A friend of mine was killed when his sailboat hit (or came too close) to an overhead power line at Holiday Lakes near Willard OH.
...


----------



## Fishers of Men

*CHAPTER 8
A lot of this will refresh you on our applications we are using in the GPS section.
PILOTING	
DEFINITION AND PURPOSE*
800.	Introduction
Piloting involves navigating a vessel through restricted waters. As in all other phases of navigation, proper preparation and strict attention to detail are very important. This chapter will discuss a piloting methodology designed to ensure the procedure is carried out safely and efficiently. These procedures will vary from vessel to vessel according to the skill and composition of the piloting team. It is the responsibility of the navigator to choose the procedures applicable to his own situation.

*PREPARATION*
801.	Chart Preparation
Assemble Required Publications: 
These publications should include Coast Pilots, Sailing Directions, Light Lists, Lists of Lights, Tide Tables, Tidal Current Tables, Notice to Mariners, and Local Notice to Mariners. Often, for military vessels, a port will be under the operational direction of a particular squadron; obtain that squadron&#8217;s port Operation Order. Civilian vessels should obtain the port&#8217;s harbor regulations. These publications will cover local regulations such as speed limits and bridge-to-bridge radio frequency monitoring requirements. Assemble the broadcast Notice to Mariners file.
*
Select and Correct Charts: *
Choose the largest scale chart available for the approach. Often, the harbor approach will be too long to be represented on only one chart. For example, three charts are required to cover the waters from the Naval Station in Norfolk to the entrance of the Chesapeake Bay. Therefore, obtain all the charts required to cover the entire passage. Verify using the Notice to Mariners that the charts in use have been corrected through the latest change. Make any required changes prior to using the chart. 

Check the Local Notice to Mariners and the Broadcast Notice to Mariners file to ensure the chart is fully corrected and up to date. Annotate on the chart or a chart correction card all the corrections that have been made; this will make it easier to verify the chart&#8217;s correction status prior to its next use.

Naval ships will normally prepare three sets of charts. One set is for the primary plot, the second set is for the secondary plot, and the third set is for the conning officer and captain

*Mark the Minimum Depth Contour:* 
Determine the minimum depth of water in which the vessel can safely operate and outline that depth contour on the chart. Do this step before doing any other harbor piloting planning. Make this outline in a bright color so that it clearly stands out. Carefully examine the area inside the contour and mark the isolated shoals less than the minimum depth which fall inside the marked contour. Determine the minimum depth in which the vessel can operate as follows:
*Minimum Depth = Ship&#8217;s Draft &#8211; Height of Tide + Safety Margin + Squat. * Remember that often the fathometer&#8217;s transducer is not located at the section of the hull that extends the furthest below the waterline. Therefore, the indicated depth of water below the fathometer transducer, not the depth of water below the vessel&#8217;s deepest draft.
*
Highlight Selected Visual Navigation Aids (NAVAIDS):*
Circle, highlight, and label all NAVAIDS on the chart. Consult the applicable Coast Pilot or Sailing Directions to determine a port&#8217;s best NAVAIDS if the piloting team has not visited the port previously. These aids can be lighthouses, piers, shore features, or tanks; any prominent feature that is displayed on the chart can be used as a NAVAID. Label critical buoys, such as those marking a harbor entrance or a traffic separation scheme.
Verify charted lights against the Light List or the List of Lights to confirm the charted information is correct. This becomes most critical when attempting to identify a light at night.

Label NAVAIDS succinctly and clearly. Ensure everyone in the navigation team refers to a NAVAID using the same terminology. This will reduce confusion between the bearing taker, the bearing recorder, and plotter.

*Highlight Selected Radar NAVAIDS: *
Highlight radar NAVAIDS with a triangle instead of a circle. If the NAVAID is suitable for either visual or radar piloting, it can be highlighted with either a circle or a triangle.
*
Plot the Departure/Approach Track: *
This process is critical for ensuring safe pilotage. Consult the Fleet Guide and Sailing Directions for recommendations on the best track to use. Look for any information or regulations published by the local harbor authority. Lacking any of this information, locate a channel or safe route delineated on the chart and plot the vessel&#8217;s track through the channel. Most U.S. ports have well defined channels marked with buoys. Carefully check the intended track to ensure a sufficient depth of water under the keel will exist for the entire passage. If the scale of the chart permits, lay the track out to the starboard side of the channel to allow for any vessel traffic proceeding in the opposite direction. Many channels are marked by natural or man-made ranges. A range consists of two NAVAIDS in line with the center of a navigable channel. The navigator can determine his position relative to the track by evaluating the alignment of the NAVAIDS forming the range. These ranges should be measured to the nearest 0.1&#61616;, and this value should be marked on the chart. Not only are ranges useful in keeping a vessel on track, they are invaluable for determining gyro error.
See section 808.

*Label the Departure/Approach Track: *
Label the track course to the nearest 0.5&#176;. Similarly, label the distance of each track leg. Place these labels well off the track so they do not interfere with subsequent plotting. Highlight the track courses for easy reference while piloting. There is nothing more frustrating than approaching a turn and not being able to determine the next course from the chart quickly. Often a navigator might plan two separate tracks. One track would be for use during good visibility and the other for poor visibility. Considerations might include concern for the number of turns (fewer turns for poor visibility) or proximity to shoal water (smaller margin for error might be acceptable in good visibility). In this case, label both tracks as above and appropriately mark when to use each track. If two separate tracks are provided, the navigator must decide which one to use before the ship enters restricted waters. Never change tracks in the middle of the transit.

*Use Advance and Transfer to Determine Turning Points: *
The track determined above does not take into account advance and transfer for determining turning points.

See Figure 801a. The distance the vessel moves in the direction of the original course from when the rudder is put over until the new course is reached is called advance.










The distance the vessel moves perpendicular to the original course during the turn is called transfer. Use the advance and transfer characteristics of the vessel to determine when the vessel must put its rudder over to gain the next course. From that point, fair in a curve between the original course and the new course. Mark the point on the original course where the vessel must put its rudder over as the turning point. See Figure 801b.









*Plot Turn Bearings: *
A turn bearing is a predetermined bearing to a charted object from the track point at which the rudder must be put over in order to make a desired turn.

*Follow two rules* when selecting NAVAIDS to be used as turn bearing sources: (1) The NAVAID should be as close to the beam as possible at the turn point; and (2) The aid should be on the inside elbow of the turn. This ensures the largest rate of bearing change at the turning point, thus marking the turning point more accurately.

Plot the turn bearing to the selected NAVAID from the point on the track at which the vessel must put its rudder over to gain the new course. Label the bearing to the nearest 0.1&#176;.

Example: Figure 801b illustrates using advance and transfer to determine a turn bearing. A ship proceeding on course 100&#176; is to turn 60&#176; to the left to come on a range which will guide it up a channel. For a 60&#176; turn and the amount of rudder used, the advance is 920 yards and the transfer is 350 yards.
Required: The bearing of flagpole &#8220;FP.&#8221; when the rudder is put over.
Solution:
1.	Extend the original course line, AB.
2.	At a perpendicular distance of 350 yards, the transfer, draw a line A&#8217;B&#8217; parallel to the original course line AB. The point of intersection, C, of A&#8217;B&#8217; with the new course line is the place at which the turn is to be completed.
3.	From C draw a perpendicular, CD, to the original course line, intersecting at D.
4.	From D measure the advance, 920 yards, back along the original course line. This locates E, the point at which the turn should be started.
5.	The direction of &#8220;FP.&#8221; from E, 058&#176;, is the bearing when the turn should be started.
Answer: Bearing 058&#176;.

Plot a Slide Bar for Every Turn Bearing: To assist the navigator in quickly revising a turn bearing if the ship finds itself off track immediately prior to a turn, use a plotting technique known as the slide bar. See Figure 801c.










Draw the slide bar parallel to the new course through the turning point on the original course. The navigator can quickly determine a new turn bearing by dead reckoning ahead from the vessel&#8217;s last fix position to where the DR intersects the slide bar. The revised turn bearing is simply the bearing from that intersection point to the turn bearing NAVAID.

Draw the slide bar with a different color from that used to lay down the track. The chart gets cluttered around a turn, and the navigator must be able to see the slide bar clearly.

Label Distance to Go From Each Turn Point: At each turning point, label the distance to go until either the ship moors (inbound) or the ship clears the harbor (outbound). For an inbound transit, a vessel&#8217;s captain is more concerned about time of arrival, so assume a speed of advance and label each turn point with time to go until mooring.

*Plot Danger Bearings: *
Danger bearings warn a navigator he may be approaching a navigation hazard too closely.
See Figure 801d.










Vector AB indicates a vessel&#8217;s intended track. This track passes close to the indicated shoal. Draw a line from the NAVAID H tangent to the shoal. The bearing of that tangent line measured from the ship&#8217;s track is 074.0&#176;T. In other words, as long as NAVAID H bears less than 074&#176;T as the vessel proceeds down its track, the vessel will not ground on the shoal. Hatch the side of the bearing line on the side of the hazard and label the danger bearing NMT (no more than) 074.0&#176;T. For an added margin of safety, the line does not have to be drawn exactly tangent to the shoal. Perhaps, in this case, the navigator might want to set an error margin and draw the danger bearing at 065&#176;T from NAVAID H. Lay down a danger bearing from any appropriate NAVAID in the vicinity of any hazard to navigation. Ensure the track does not cross any danger bearing.

*Plot Danger Ranges: *
The danger range is analogous to the danger bearing. It is a standoff range from an object to prevent the vessel from approaching a hazard too closely.
Label Warning and Danger Soundings: To determine the danger sounding, examine the vessel&#8217;s proposed track and note the minimum expected sounding. The minimum expected sounding is the difference between the shallowest water expected on the transit and the vessel&#8217;s maximum draft. Set 90&#37; of this difference as the warning sounding and 80% of this difference as the danger sounding. This is not an inflexible rule. There may be peculiarities about the local conditions that will cause the navigator to choose another method of determining his warning and danger soundings. Use the above method if no other means is more suitable. For example: A vessel draws a maximum of 20 feet, and it is entering a channel dredged to a minimum depth of 50 feet. Set the warning and danger soundings at 0.9 (50ft. - 20ft) = 27ft and 0.8 (50ft. - 20ft.) = 24ft., respectively. Re-evaluate these soundings at different intervals along the track when the minimum expected sounding may change. Carefully label the points along the track between which these warning and danger soundings apply. 

*Label Demarcation Line: *
Clearly label the point on the ship&#8217;s track at which the Inland and International Rules of the Road apply. This is applicable only when piloting in U.S. ports.

*Mark Speed Limits Where Applicable:* 
Often a harbor will have a local speed limit in the vicinity of piers, other vessels, or shore facilities. Mark these speed limits and the points between which they are applicable on the chart.

*Mark the Point of Pilot Embarkation: *
Some ports require vessels over a certain size to embark a pilot. If this is the case, mark the point on the chart where the pilot is to embark.

*Mark the Tugboat Rendezvous Point: *
If the vessel requires a tug to moor, mark the tug rendezvous point on the chart.
*Mark the Chart Shift Point: *
If more than one chart will be required to complete the passage, mark the track point where the navigator should shift to the next chart.

*Harbor Communications: *
Mark the point on the chart where the vessel must contact harbor control.
Also mark the point where a vessel must contact its parent squadron to make an arrival report (military vessels only).

*Tides and Currents: *
Mark the points on the chart for which the tides and currents were calculated.

*802.	Tides And Currents*
Determining the tidal and current conditions of the port which you are entering is crucial. Determining tides and currents is covered in Chapter 9. Plot a graph of the tidal range at the appropriate port for a 24-hour period for the day of your scheduled arrival or departure. Plotting the curve for the 24-hour period will cover those contingencies that delay your arrival or departure. Depending on a vessel&#8217;s draft and the harbor&#8217;s depth, some vessels may be able to transit only at high tide. If this is this case, it is critically important to determine the time and range of the tide correctly.

The magnitude and direction of the current will give the navigator some idea of the set and drift the vessel will experience during the transit. This will allow him to plan in advance for any potential current effects in the vicinity of navigation hazards.

*803.	Weather*
The navigator should obtain a weather report covering the route which he intends to transit. This will allow him to prepare for any heavy weather by stationing extra lookouts, adjusting his speed for poor visibility, and preparing for radar navigation. If the weather is thick, he may want to consider standing off the harbor until it clears.

The navigator can receive weather information any number of ways. Military vessels receive weather reports from their parent squadrons prior to coming into port. Marine band radio carries continuous weather reports. Some vessels are equipped with weather facsimile machines.

Some navigators carry cellular phones to reach shore-side personnel and harbor control; these can be used to get weather reports. However he obtains the information, the navigator should have a good idea of the weather where he will be piloting.

*804.	The Piloting Brief*
Assemble the entire navigation team *(Gju42486 George)* for a piloting brief prior to entering or leaving port. The vessel&#8217;s captain and navigator should conduct the briefing. All navigation and bridge personnel should attend. 

The pilot, if he is already on board, should also attend. If the pilot is not onboard when the ship&#8217;s company is briefed, the navigator should immediately brief him when he embarks. The pilot must know the ship&#8217;s maneuvering characteristics before entering restricted waters. The briefing should cover, as a minimum, the following:

*Detailed Coverage of the Track Plan: *
Go over the planned route in detail. Use the prepared and approved chart as part of this brief. Concentrate especially on all the NAVAIDS and soundings which are being used to indicate danger. 

Cover the buoyage system in use and the port&#8217;s major NAVAIDS. 

Point out the radar NAVAIDS for the radar operator. Often, a Fleet Guide or Sailing Directions will have pictures of a port&#8217;s NAVAIDS. This is especially important for the piloting party that has never transited this particular port before. If no pictures are available, consider stationing a photographer to take some for submission to DMAHTC.
*
Harbor Communications:*
Discuss the bridge-to bridge radio frequencies used to raise harbor control.
Discuss what channel the vessel is supposed to monitor on its passage into port and the port&#8217;s communication protocol.
*
Duties and Responsibilities:* 
Each member of the piloting team must have a thorough understanding of his duties and responsibilities. He must also understand how his part fits into the scheme of the whole.

The radar plotter, for example, must know if radar will be the primary or secondary source of fix information.

The bearing recorder must know what fix interval the navigator is planning to use. Each person must be thoroughly briefed on his job; there is little time for questions once the vessel enters the channel.

*805.	Voyage Planning To The Harbor Entrance*
(Inbound Vessel Only)
The vessel&#8217;s planned estimated time of arrival (ETA) at its moorings determines the vessel&#8217;s course and speed to the harbor entrance. Arriving at the mooring site on time may be important in a busy port which operates its port services on a tight schedule. Therefore, it is important to conduct harbor approach voyage planning accurately. Take the ETA at the mooring and subtract from that the time it will take to navigate the harbor to the pier. The resulting time is when you must arrive at the harbor entrance. Next, measure the distance between the vessel&#8217;s present location and the harbor entrance. Determine the speed of advance (SOA) the vessel will use to make the transit to the harbor. Use the distance to the harbor and the SOA to calculate what time to leave the present position to make the mooring ETA.

*Consider these factors which might affect this decision:
Weather: *
This is the single most important factor in harbor approach planning because it directly affects the vessel&#8217;s SOA. The thicker the weather, the more slowly the vessel must proceed. Therefore, if heavy fog or rain is in the forecast, the navigator must advance the time he was planning to leave for the harbor entrance.

*Mooring Procedures: *
The navigator must take more than distance into account when calculating how long it will take him to pilot to his mooring. If the vessel needs a tug, that will significantly increase the time allotted to piloting. Similarly, picking up (inbound) or dropping off (outbound) a pilot adds time to the transit.
It is better to allow a margin for error when trying to add up all the time delays caused by these procedures. It is always easier to avoid arriving early by slowing down than it is to make up lost time by speeding up.

*Time to Find the Harbor Entrance: *
Depending on the sophistication of his vessel&#8217;s navigation suite, a navigator may require some time to find the harbor entrance. This is seldom a problem with warships and large merchant vessels, both of which carry sophisticated electronic navigation suites. However, it may be a consideration for the yachtsman relying solely on dead reckoning and celestial navigation.

*Shipping Density: *
Generally, the higher the shipping density entering and exiting the harbor, the longer it will take to proceed into the harbor entrance safely.

*TRANSITION TO PILOTING
806.	Stationing The Piloting Team*
Approximately one hour prior to leaving port or entering restricted waters, station the piloting team. The number and type of personnel available for the piloting team depend on the vessel. A Navy warship, for example, has more people available for piloting than does a merchantman. Therefore, more than one of the jobs listed below may have to be filled by a single person. The piloting team should consist of:
The Captain: The captain is ultimately responsible for the safe navigation of his vessel. His judgment regarding navigation is final. The piloting team acts to support the captain, advising him so he can make informed decisions on handling his vessel.
The Pilot: The pilot is usually the only member of the piloting team not normally a member of the ship&#8217;s company.
Many ports require a pilot, a federal or state licensed navigator who possesses extensive local knowledge of the harbor, to be on board as the vessel makes its harbor passage. The piloting team must understand the relationship between the pilot and the captain. The pilot is perhaps the captain&#8217;s most important navigation advisor; often, the captain will defer to his recommendations when navigating an unfamiliar harbor. The pilot, too, bears some responsibility for the safe passage of the vessel; he can be censured for errors of judgment which cause accidents. However, the presence of a pilot in no way relieves the captain of his ultimate responsibility for safe navigation. The piloting team works to support and advise the vessel&#8217;s captain.

*The Officer of the Deck (Conning Officer): *
In Navy piloting teams, neither the pilot or the captain usually has the conn. The officer having the conn directs the ship&#8217;s movements by rudder and engine orders. Another officer of the ship&#8217;s company usually fulfills this function. The captain can take the conn immediately simply by issuing an order to the helm should an emergency arise. The conning officer of a merchant vessel can be either the pilot, the captain, or another watch officer.

In any event, the officer having the conn must be clearly indicated in the ship&#8217;s deck log at all times. Often a single officer will have the deck and the conn.

However, sometimes a junior officer will take the conn for training. In this case, different officers will have the deck and the conn. The officer who retains the deck retains the responsibility for the vessel&#8217;s safe navigation.

*The Navigator: *
The vessel&#8217;s navigator is the officer directly responsible to the ship&#8217;s captain for the safe navigation of the ship. He is the captain&#8217;s principal navigation advisor. The piloting party works for him.

He channels the required information developed by the piloting party to the ship&#8217;s conning officer on recommended courses, speeds, and turns. He also carefully looks ahead for potential navigation hazards and makes appropriate recommendations. He is the most senior officer who devotes his effort exclusively to monitoring the navigation picture. The captain and the conning officer are concerned with all aspects of the passage, including contact avoidance and other necessary ship evolutions (making up tugs, maneuvering alongside a small boat for personnel transfers, engineering evolutions, and coordinating with harbor control via radio, for example). The navigator, on the other hand, focuses solely on safe navigation. It is his job to anticipate danger and keep himself appraised of the navigation situation at all times.

*Bearing Plotting Team: *
This team consists, ideally, of three persons. The first person measures the bearings. The second person records the bearings in an official record book. The third person plots the bearings. The more quickly and accurately this process is completed, the sooner the navigator has an accurate picture of the ship&#8217;s position. The bearing taker should be an experienced individual who has traversed the port before and who is familiar with the NAVAIDS. He should take his round of bearings as quickly as possible, minimizing any time delay errors in the resulting fix. The plotter should also be an experienced individual who can quickly and accurately lay down the required bearings. The bearing recorder can be one of the junior members of the piloting team.

*The Radar Operator: *
The radar operator has one of the more difficult jobs of the team. The radar is as important for collision avoidance as it is for navigation. Therefore, this operator must &#8220;time share&#8221; the radar between these two functions.

Determining the amount of time spent on these functions falls within the judgment of the captain and the navigator. If the day is clear and the traffic heavy, the captain may want to use the radar mostly for collision avoidance. As the weather worsens, obscuring visual NAVAIDS, the importance of radar for safe navigation increases. The radar operator must be given clear guidance on how the captain and navigator want the radar to be operated.

*Plot Supervisors: *
Ideally, the piloting team should consist of two plots: the primary plot and the secondary plot. The navigator should designate the type of navigation that will be employed on the primary plot. All other fix sources should be plotted on the secondary plot. For example, if the navigator designates visual piloting as the primary fix method, lay down only visual bearings on the primary plot. Lay down all other fix sources (radar, electronic, or satellite) on the secondary plot. The navigator can function as the primary plot supervisor. A senior, experienced individual should be employed as a secondary plot supervisor. The navigator should frequently compare the positions plotted on both plots as a check on the primary plot.
*
There are three major reasons for maintaining a primary and secondary plot. *
First, as mentioned above, the secondary fix sources provide a good check on the accuracy of visual piloting. Large discrepancies between visual and radar positions may point out a problem with the visual fixes that the navigator might not otherwise suspect. 

Secondly, the navigator often must change the primary means of navigation during the transit. He may initially designate visual bearings as the primary fix method only to have a sudden storm or fog obscure the visual NAVAIDS. If he shifts the primary fix means to radar, he has a track history of the correlation between radar and visual fixes. 

Finally, the piloting team often must shift charts several times during the transit. When the old chart is taken off the plotting table and before the new chart is secured, there is a period of time when no chart is in use. Maintaining a secondary plot eliminates this complication. Ensure the secondary plot is not shifted prior to getting the new primary plot chart down on the chart table. In this case, there will always be a chart available on which to pilot. Do not consider the primary chart shifted until the new chart is properly secured and the plotter has transferred the last fix from the original chart onto the new chart. 

*Satellite Navigation Operator: *
This operator normally works for the secondary plot supervisor. GPS absolute accuracy with SA operational is not sufficient for most piloting applications. However, the secondary plot should keep track of GPS fixes. If the teams looses visual bearings in the channel and no radar NAVAIDS are available, GPS may be the most accurate fix source available. The navigator must have some data on the comparison between satellite positions and visual positions over the history of the passage to use satellite positions effectively. The only way to obtain this data is to plot satellite positions and compare these positions to visual positions throughout the harbor passage.

*Fathometer Operator: *
Run the fathometer continuously and station an operator to monitor it. Do not rely on audible alarms to key your attention to this critically important piloting tool. The fathometer operator must know the warning and danger soundings for the area the vessel is transiting. Most fathometers can display either total depth of water or depth under the keel. Set the fathometer to display depth under the keel. The navigator must check the sounding at each fix and compare that value to the charted sounding. A discrepancy between these values is cause for immediate action to take another fix and check the ship&#8217;s position.

*807.	Plot Setup*
Once the piloting team is on station, ensure the primary and secondary plot have the following instruments:
Dividers: Dividers are used to measure distances between points on the chart.
Compasses: Compasses are used to plot range arcs for radar LOP&#8217;s. 
Beam compasses are used when the range arc exceeds the spread of a conventional compass. Both should be available at both plots.
Bearing Measuring Devices: 
Several types of bearing measuring devices are available. The preferred device is the parallel motion plotter (PMP) used in conjunction with a drafting table. Otherwise, use parallel rulers or rolling rulers with the chart&#8217;s compass rose. Finally, the plotter can use a one arm protractor. The plotter should use the device with which he can work the most quickly and accurately.
Sharpened Pencils and Erasers: Ensure an adequate supply of pencils is available. There is generally not time to sharpen one if it breaks in the middle of the transit, so have several sharpened pencils available at the plot.

*Three Arm Protractor: *
This protractor is used to plot relative bearings and sextant horizontal angles should the true bearing source fail during the transit. Fischer Radar Plotting Templates: Fischer plotting is covered in Chapter 13. The plotting templates for this technique should be stacked near the radar repeater.

*Time-Speed-Distance Calculator: *
Given two of the three unknowns (between time, speed, and distance), this calculator allows for rapid computation of the third.

*Tide and Current Graphs: *
Post the tide and current graphs near the primary plot for easy reference during the transit. Give a copy of the graphs to the conning officer and the captain.

Once the navigator verifies the above equipment is in place, he tapes down the charts on the chart table. If more than one chart is required for the transit, tape the charts in a stack such that the plotter works from the top to the bottom of the stack. This minimizes the time required to shift the chart during the transit. If the plotter is using a PMP, align the arm of the PMP with any meridian of longitude on the chart. While holding the PMP arm stationary, adjust the PMP to read 000.0&#176;T. This procedure calibrates the PMP to the chart in use. Perform this alignment every time the piloting team shifts charts.
Be careful not to fold under any important information when folding the chart on the chart table. Ensure the chart&#8217;s distance scale, the entire track, and all important warning information are visible.

Energize and test all electronic navigation equipment, if not already in operation. This includes the radar and the GPS receiver. Energize and test the fathometer. Ensure the entire electronic navigation suite is operating properly prior to entering restricted waters.

*808.	Evolutions Prior To Piloting*
The navigator should always accomplish the following evolutions prior to piloting:
*Testing the Shaft on the Main Engines in the Astern Direction: *
This ensures that the ship can answer a backing bell. If the ship is entering port, no special precautions are required prior to this test. If the ship is tied up at the pier preparing to get underway, exercise extreme caution to ensure no way is placed on the ship while testing the main engines.
*
Making the Anchor Ready for Letting Go: *
Make the anchor ready for letting go and station a watch-stander in direct communications with the bridge at the anchor windlass. Be prepared to drop anchor immediately when piloting if required to keep from drifting too close to a navigation hazard.

*Calculate Gyro Error: *
An error of greater than 1.0&#176; T indicates a gyro problem which should be investigated prior to piloting. There are several ways to determine gyro error:
1.	Compare the gyro reading with a known accurate heading reference such as an inertial navigator. The difference in the readings is the gyro error.
2.	Mark the bearing of a charted range as the range NAVAID&#8217;s come into line and compare the gyro bearing with the charted bearing. The difference is the gyro error.
3.	Prior to getting underway, plot a dockside fix using at least three lines of position. The three LOP&#8217;s should intersect at a point. Their intersecting in a &#8220;cocked hat&#8221; indicates a gyro error. Incrementally adjust each visual bearing by the same amount and in the same direction until the fix plots as a pinpoint. The total corretion required to eliminate the cocked hat is the gyro error.
4.	Measure a celestial body&#8217;s azimuth, a celestial body&#8217;s amplitude, or Polaris&#8217; azimuth with the gyro, and then compare the measured value with a value computed from the Sight Reduction tables or the Nautical Almanac. These methods are covered in detail in Chapter 17.
Report the magnitude and direction of the gyro error to the navigator and captain. The direction of the error is determined by the relative magnitude of the gyro reading and the value against which it is compared. When the compass is least, the error is east.
Conversely, when the compass is best, the error is west.

*809.	Records*
Ensure the following records are assembled and personnel assigned to complete them prior to piloting:
*Bearing Record Book: *
The bearing recorders for the primary and secondary plots should record all the bearings used on their plot during the entire transit. The books should clearly list what NAVAIDS are being used and what method of navigation was being used on their plot. In practice, the primary bearing book will contain mostly visual bearings and the secondary bearing book will contain mostly radar ranges and bearings.

*Fathometer Log: *
In restricted waters, monitor soundings continuously and record soundings every five minutes in the fathometer log. Record all fathometer settings that could affect the sounding display.

*Deck Log: *
This log is the legal record of the passage. Record all ordered course and speed changes. Record all the navigator&#8217;s recommendations and whether the navigator concurs with the actions of the conning officer. Record all buoys passed, and the shift between different Rules of the Road. Record the name and embarkation of any pilot. Record who has the conn at all times. Record any casualty or important event. The deck log combined with the bearing log should constitute a complete record of the passage.

*810.	Harbor Approach* (Inbound Vessels Only)
The piloting team must make the transition from coastal navigation to piloting smoothly as the vessel approaches restricted waters. There is no rigid demarcation between coastal navigation and piloting. Often visual NAVAIDS are visible miles from shore where hyperbolic and satellite navigation provides sufficient absolute accuracy to ensure ship safety. The navigator should take advantage of this overlap when approaching the harbor. Plot hyperbolic, satellite, and visual fixes concurrently on the primary plot, ensuring the piloting team has correctly identified NAVAIDS and is comfortably settling into a piloting routine. Once the vessel is close enough to the shore such that sufficient NAVAIDS (at least three with sufficient bearing spread) become visible, the navigator should order visual bearings only for the primary plot and shift plotting all other fixes to the secondary plot. 

Take advantage of the coastal navigation and piloting overlap to shorten the fix interval gradually. The navigator must use his judgment in adjusting these transition fix intervals. If the ship is steaming inbound directly towards the shore, set a fix interval such that two fix intervals lie between the vessel and the nearest danger. Prior to entering into restricted waters, the piloting team should be plotting visual fixes at three minute intervals.

*To be continued*


----------



## Fishers of Men

*CHAPTER 8 cont.

FIXING A VESSEL&#8217;S POSITION WHILE PILOTING*
The navigator now has his charts prepared; his team briefed, equipped, and on station; his equipment tested; and his record books distributed. He is now ready to begin piloting.

Safe navigation while piloting requires frequent fixing of the ship&#8217;s position. The next sections will discuss the three major methodologies used to fix a ship&#8217;s position when piloting: crossing lines of position, copying satellite or Loran data, or advancing a single line of position. Using one method does not exclude using other methods. The navigator must obtain as much information as possible and employ as many of these methods as practical while piloting.
*
811.	Fixing The Ship&#8217;s Position By Two Or More Lines Of Position*
The intersection of at least two LOP&#8217;s constitutes a fix.
However, always use three LOP&#8217;s if three are available. Some of the most commonly used methods of obtaining LOP&#8217;s are discussed below:
*Fix by Two Bearing Lines: *
The plotter lays down two or more bearing lines from charted NAVAIDS. This is the most common and often the most accurate way to fix a vessel&#8217;s position. The plotter can also lay down bearings to a NAVAID and a bearing to the tangent of a body of land. See Figure 811a.










The intersection of these lines constitutes a fix. Plotting bearing lines from charted buoys is the least preferred method of fixing by two bearing lines because the buoy&#8217;s charted position is only approximate. Tangent LOPs to land areas must be taken carefully to get an accurate line, particularly at long ranges; charted NAVAIDS are preferred.

*Fix by Two Ranges: *
The navigator can plot a fix consisting of the intersection of two range arcs from charted objects. He can obtain an object&#8217;s range in several ways:
1.	Radar Ranges: See Figure 811b. The plotter lays down a range arc from a small island and a range arc from a prominent point on shore. The intersection of the range arcs constitutes a fix. The navigator can plot ranges from any point on the radar scope which he can correlate on his chart. This is the most convenient and accurate way to obtain an object&#8217;s range.
If a choice is available between fixed radar NAVAIDS and low lying land, choose the fixed NAVAID. This will minimize errors caused by using low lying land subject to large tidal ranges.










2.	Stadimeter Ranges: Given a known height of a NAVAID, use a stadimeter to determine the range.
Though most often used to determine the distance to a surface contact, a stadimeter can be used to determine an object&#8217;s range. See Figure 811c for a representation of the geometry involved. Generally, stadimeters contain a height scale on which is set the height of the object. The observer then directs his line of sight through the stadimeter to the base of the object being observed. Finally, he adjusts the stadimeter&#8217;s range index until the object&#8217;s top reflection is &#8220;brought down&#8221; to the visible horizon. Read the object&#8217;s range off of the stadimeter&#8217;s range index.
3.	Sextant Vertical Angles: Measure the vertical angle from the top of the NAVAID to the waterline below the NAVAID. Enter Table 16 to determine the distance of the NAVAID. The navigator must know the height of the NAVAID above sea level
to use this table; it can be found in the light list.
4.	Sonar Ranges: If the vessel is equipped with a sonar suite, the navigator can use sonar echoes to determine ranges to charted underwater objects. It may take some trial and error to set the active signal strength at a value that will give a enough strong return and still not cause excessive reverberation. Check local harbor restrictions on energizing active sonar. Avoid active sonar transmissions in the vicinity of divers.

*Fix at Intersection of Bearing Line and Range: *
This is a hybrid fix of LOP&#8217;s from a bearing and range to a single object. The radar is the only instrument that can give simultaneous range and bearing information to the same object. (A sonar system can also provide bearing and range information, but sonar bearings are far too inaccurate to use in piloting.) Therefore, with the radar, the navigator can obtain an instantaneous fix from only one NAVAID. This unique fix is shown in Figure811d. 










This makes the radar an extremely useful tool for the piloting team. The radar&#8217;s characteristics make it much more accurate determining range than determining bearing; therefore, two radar ranges are preferable to a radar range and bearing.

*Fix by Range and Distance: *
When the vessel comes in line with a range, plot the bearing to the range and cross this LOP with a distance from another NAVAID. Figure 811e shows this fix.










*812.	Fixing The Ship&#8217;s Position By Electronics*
The stated absolute accuracy of GPS subjected to SA is insufficient to ensure ship&#8217;s safety while piloting. However, the navigator should not ignore satellite positions. If the vessel is a U.S. Navy warship, the navigator will have access to the Precise Positioning Service (PPS). Even if the navigator does not have access to the PPS, routinely comparing visual and satellite positions provides the navigator some information to use in case he loses both radar and visual piloting.

When poor visibility precludes using visual NAVAID&#8217;s and the area is not suitable for radar piloting, having a satellite position and some idea of how it has related to previous visual fixes is important. The satellite positions should be plotted periodically on the secondary plot.

If the navigator has access to Differential GPS, the absolute accuracy of his satellite positions may be high enough to provide an even more meaningful backup to visual and radar piloting.

Loran C, while generally not suitable for piloting in terms of absolute accuracy, is often accurate enough in terms of repeatable accuracy. Therefore Loran readings should be monitored in case other systems fail.

*813.	The Running Fix*
When only one NAVAID is available from which to obtain bearings, use a technique known as the running fix.
Use the following methodology:
1.	Plot a bearing to a NAVAID (LOP 1).
2.	Plot a second bearing to a NAVAID (either the same NAVAID or a different one) at a later time (LOP 2).
3.	Advance LOP 1 to the time when LOP 2 was taken.
4.	The intersection of LOP 2 and the advanced LOP 1 constitute the running fix. Figure 813a represents a ship proceeding on course 020&#176;, speed 15 knots. At 1505, the plotter plots an LOP to a lighthouse bearing 310&#176;. The ship can be at any point on this 1505 LOP. Some possible points are represented as points A, B, C, D, and E in Figure 813a. 

Ten minutes later the ship will have traveled 2.5 miles in direction 020&#176;. If the ship was at A at 1505, it will be at A&#8217; at 1515. However, if the position at 1505 was B, the position at 1515 will be B&#8217;. A similar relationship exists between C and C&#8217;, D and D&#8217;, E and E&#8217;.
Thus, if any point on the original LOP is moved a distance equal to the distance run in the direction of the motion, a line through this point parallel to the original line of position represents all possible positions of the ship at the later time. This process is called advancing a line of position. Moving a line back to an earlier time is called retiring a line of position.

When advancing a line of position, consider course changes, speed changes, and set and drift between the two bearing lines. 









*
Three methods of advancing an LOP are discussed below:*
Method 1: See Figure 813a. To advance the 1924 LOP to 1942, first apply the best estimate of set and drift to the 1942 DR position and label the resulting position point B.
Then, measure the distance between the dead reckoning position at 1924 (point A) and point B. Advance the LOP a distance equal to the distance between points A and B. Note that LOP A&#8217;B&#8217; is in the same direction as line AB.

Method 2: See Figure 813c. Advance the NAVAIDS position on the chart for the course and distance traveled by the vessel and draw the line of position from the NAVAIDS advanced position.
This is the most satisfactory method for advancing a circle of position.










Method 3: See Figure 813d. To advance the 1505 LOP to 1527, first draw a correction line from the 1505 DR position to the 1505 LOP. Next, apply a set and drift correction to the 1527 DR position. This results in a 1527 estimated position (EP). Then, draw from the 1527 EP a correction line of the same length and direction as the one drawn from the 1505 DR to the 1505 LOP. Finally, parallel the 1505 bearing to the end of the correction line as shown. Label an advanced line of position with both the time of observation and the time to which the line is adjusted.










Figure 813e through Figure 813g demonstrate three separate running fixes. Figure 813e illustrates the case of obtaining a running fix with no change in course or speed between taking two bearings on the same NAVAID.

Figure 813f illustrates a running fix with changes in a vessel&#8217;s course and speed between its taking two bearings on two different objects. 

Finally, Figure 813g illustrates a running fix obtained by advancing range circles of position using the second method discussed above.










*PILOTING PROCEDURES*
The previous section discussed the methods for fixing the ship&#8217;s position. This section discusses integrating the fix methods discussed above and the use of the fathometer into a piloting procedure. The navigator must develop his piloting procedure to meet several requirements. He must obtain all available information from as many sources as possible. He must plot and evaluate this information. Finally, he must relay his evaluations and recommendations to the vessel&#8217;s conning officer. This section examines some considerations to ensure the navigator accomplishes all these requirements quickly and effectively.

*814. Fix Type And Fix Interval*
The preferred piloting fix type is visual bearings from charted shore-based NAVAIDS. Plot visual bearings on the primary plot and plot all other fixes on the secondary plot. If poor visibility obscures visual NAVAIDS, shift to radar piloting on the primary plot. If neither visual or radar piloting is available, consider standing off until the visibility improves. The interval between fixes in restricted waters should not exceed three minutes. Setting the fix interval at three minutes optimizes the navigator&#8217;s ability to assimilate and evaluate all available information. A navigator must not only receive and plot positioning information, but he must also evaluate the information. He must relate it to charted navigation hazards and to his vessel&#8217;s intended track. It should take a well trained plotting team no more than 30 seconds to measure, record, and plot three bearings to three separate NAVAIDS. The navigator should spend the majority of the fix interval time interpreting the information, evaluating the navigation situation, and making recommendations to the conning officer.
If three minutes goes by without a fix, inform the captain and try to plot a fix as soon as possible. If the delay was caused by a loss of visibility, shift to radar piloting. If the delay was caused by plotting error, take another fix. If the navigator cannot get a fix down on the plot for several more minutes, consider slowing or stopping the ship until its position can be fixed. Never continue a passage through restricted waters if the vessel&#8217;s position is uncertain.

The secondary plot supervisor should maintain the same fix interval as the primary plot. Usually, this means he should plot a radar fix every three minutes. He should plot other fix sources (sonar ranges and satellite fixes, for example) at an interval sufficient for making meaningful comparisons between fix sources. Every third fix interval, he should pass a radar fix to the primary plot for comparison with the visual fix. He should inform the navigator how well all the fix sources plotted on the secondary plot are tracking.

*815.	The Cyclic Routine*
Following the cyclic routine ensures the timely and efficient processing of data. It yields the basic information which the navigator needs to make informed recommendations to the conning officer and captain.
Repeat this cyclic routine at each fix interval beginning when the ship gets underway until it clears the harbor (outbound) or when the ship enters the harbor until it is moored (inbound).

The cyclic routine consists of the following steps, modified as discussed below for approaching a turn:
1.	Plotting the fix.
2.	Labeling the fix.
3.	Dead Reckoning two fix intervals ahead of the fix.
4.	Calculating the set and drift from the DR and fix.

*Plotting the Fix: *
This involves coordination between the bearing taker, recorder, and plotter. The bearing taker must measure his bearings as quickly as possible.
As quickly as he takes them, however, there will be a finite amount of time between the first and last bearing measured. The navigator should advance the first and second LOP&#8217;s to the time of the last bearing taken and label the last bearings time as the fix time.
Try to have the fix completed on the even minute to allow for meaningful comparison with the DR.

*Labeling the Fix: *
The plotter should clearly mark a visual fix with a circle or an electronic fix with a triangle. Clearly label the time of each fix. A visual running fix should be circled, marked &#8220;R Fix&#8221; and labeled with the time of the second LOP. Maintain the chart neat and uncluttered when labeling fixes.

*Dead Reckoning Two Fix Intervals Ahead: *
After labeling the fix, the plotter should dead reckon the fix position ahead two fix intervals. The navigator should carefully check the area marked by this DR for any navigation hazards. If the ship is approaching a turn, update the turn bearing as discussed in section 801.Calculate Set and Drift at Every Fix: Calculating set and drift is covered in Chapter 7. Calculate these values at every fix and inform the captain and conning officer.

Compare the actual values of set and drift with the predicted values from the current graph discussed in section 802 above. Evaluate how the current is affecting the vessel&#8217;s position in relation to the track and recommend courses and speeds to regain the planned track. Because the navigator can determine set and drift only when comparing fixes and DR&#8217;s plotted for the same time, ensure that fixes are taken at the times for which a DR has been plotted. Repeat this cyclic routine at each fix interval beginning when the ship gets underway until it clears the harbor (outbound) or when the ship enters the harbor until she is moored (inbound)
*
Cyclic Routine When Turning: *
Modify the cyclic routine slightly when approaching a turn. Adjust the fix interval so that the plotting team has a fix plotted approximately one minute before a scheduled turn.
This gives the navigator *(EZBITE)* sufficient time to evaluate the position in relation to the planned track, DR ahead to the slide bar to determine a new turn bearing, relay the new turn bearing to the conning officer, and then monitor the turn bearing to mark the turn.
Approximately 30 seconds before the time to turn, train the bearing measurement instrument on the turn bearing NAVAID. The navigator should watch the bearing of the NAVAID approach the turn bearing. Approximately 1&#176; away from the turn bearing, announce to *(KAGEE)* the conning officer:
*&#8220;Stand by to turn.&#8221; *Slightly before the turn bearing is indicated, report to the conning officer: &#8220;Mark the turn.&#8221; Make this report slightly before the bearing is reached because it takes the conning officer a finite amount of time to acknowledge the report and order the helmsman to put over the rudder. Additionally, it takes a finite amount of time for the helmsman to turn the rudder and for the ship to start to turn. If the navigator waits until the turn bearing is indicated to report the turn, the ship will turn too late.
Once the ship is steady on the new course, immediately take another fix to evaluate the vessel&#8217;s position in relation to the track. If the ship is not on the track after the turn, recommend a course to the conning officer to regain track.

*816.	Using The Fathometer*
Use the fathometer to determine whether the depth of water under the keel is sufficient to prevent the ship from grounding and to check the actual water depth with the charted water depth at the fix position. The navigator must compare the charted sounding at every fix position with the fathometer reading and report to the captain any discrepancies. Continuous soundings in pilot waters are mandatory.

See the discussion of calculating the warning and danger soundings in section 801. 
If the warning sounding is received, then slow the ship, fix the ship&#8217;s position more frequently, and proceed with extreme caution. Ascertain immediately where the ship is in the channel; if the minimum expected sounding was noted correctly, the warning sounding indicates the vessel may be leaving the channel and standing into shoal water. Notify the vessel&#8217;s captain and conning officer immediately.

If the danger sounding is received, take immediate action to get the vessel back to deep water. Reverse the engines and stop the vessel&#8217;s forward movement. Turn in the direction of the deepest water before the vessel looses steerageway. Consider dropping the anchor to prevent the ship from drifting aground. The danger sounding indicates that the ship has left the channel and is standing into immediate danger. It requires immediate corrective action by the ship&#8217;s conning officer, navigator, and captain to avoid disaster.

Many underwater features are poorly surveyed. If a fathometer trace of a distinct underwater feature can be obtained along with accurate position information, send the fathometer trace and related navigation data to the Defense Mapping Agency for entry into the Digital Bathymetric Data Base. See Chapter 30 for details on recording and reporting procedures.

*To be continued*


----------



## Fishers of Men

*CHAPTER 8 cont.
ANCHORING PROCEDURES
817. Anchoring*
If a vessel is to anchor at a predetermined point, such as in an assigned berth, follow an established procedure to ensure an accurate positioning of the anchor. The following procedure is representative. See Figure 817. 










Locate the selected anchoring position on the chart. Consider limitations of land, current, shoals, other vessels when determining the direction of approach. Where conditions permit, make the approach heading into the current. Close observation of any other anchored vessels will provide clues as to which way the ship will lie to her anchor. If wind and current are strong and from different directions, ships will lie to their anchors according to the balance between these two forces and the draft and trim of each ship. Different ships may lie at different headings in the same anchorage depending on the balance of forces affecting them. Approach from a direction with a prominent NAVAID, preferably a range, available dead ahead to serve as a steering guide. If practicable, use a straight approach of at least 1200 yards to permit the vessel to steady on the required course. Draw in the approach track, allowing for advance and transfer during any turns.

In Figure 817, the chimney was selected as this steering bearing.
Next, draw a circle with the selected position of the anchor as the center, and with a radius equal to the distance between the hawsepipe and pelorus, alidade, or periscope used for measuring bearings. This circle is marked &#8220;A&#8221; in Figure 817. The intersection of this circle and the approach track is the position of the vessel&#8217;s bearing-measuring instrument at the moment of letting the anchor go. Select a NAVAID which will be on the beam when the vessel is at the point of letting go the anchor. This NAVAID is marked &#8220;FS&#8221; in Figure 817. Determine what the bearing to that object will be when the ship is at the drop point and measure this bearing to the nearest 0.1&#176;T. Label this bearing as the letting go bearing.

During the approach to the anchorage, plot fixes at frequent intervals. The navigator must advise the conning officer of any tendency of the vessel to drift from the desired track. The navigator must frequently report the conning officer of the distance to go, permitting adjustment of the speed so that the vessel will be dead in the water or have very slight sternway when the anchor is let go. To aid in determining the distance to the drop point, draw and label a number of range arcs as shown in Figure 817 representing distances to go to the drop point.

At the moment of letting the anchor go, take a fix and plot the vessel&#8217;s exact position on the chart. This is important in the construction of the swing and drag circles discussed below. To draw these circles accurately, determine the position of the vessel at the time of letting go the anchor as accurately as possible.
Veer the anchor chain to a length equal to five to seven times the depth of water at the anchorage. The exact amount to veer is a function of both vessel type and severity of weather expected at the anchorage. When calculating the scope of anchor chain to veer, take into account the maximum height of tide.

Once the ship is anchored, construct two separate circles around the ship&#8217;s position when the anchor was dropped. These circles are called the swing circle and the drag circle. Use the swing circle to check for navigation hazards and use the drag circle to ensure the anchor is holding.
The swing circle&#8217;s radius is equal to the sum of the ship&#8217;s length and the scope of the anchor chain released. This represents the maximum arc through which a ship can swing while riding at anchor if the anchor holds. Examine this swing circle carefully for navigation hazards, interfering contacts, and other anchored shipping. Use the lowest height of tide expected during the anchoring period when checking inside the swing circle for shoal water.
The drag circle&#8217;s radius equals the sum of the hawsepipe to pelorus distance and the scope of the chain released. Any bearing taken to check on the position of the ship should, if the anchor is holding, fall within the drag circle.
If a fix falls outside of that circle, then the anchor is dragging.

In some cases, the difference between the radius of the swing and drag circles will be so small that, for a given chart scale, there will be no difference between the circles when plotted. If that is the case, plot only the swing circle and treat that circle as both a swing and a drag circle. On the other hand, if there is an appreciable difference in radius between the circles when plotted, plot both on the chart.

Which method to use falls within the sound judgment of the navigator.
When determining if the anchor is holding or dragging, the most crucial period is immediately after anchoring. Fixes should be taken frequently, at least every three minutes, for the first thirty minutes after anchoring. The navigator should carefully evaluate each fix to determine if the anchor is holding. If the anchor is holding, the navigator can then increase the fix interval. What interval to set falls within the judgment of the navigator, but the interval should not exceed 30 minutes.

*818. Choosing An Anchorage*
Most U.S. Navy vessels receive instructions in their movement orders regarding the choice of anchorage. Merchant ships are often directed to specific anchorages by harbor authorities. However, lacking specific guidance, the mariner should choose his anchoring positions using the following criteria:

*Depth of Water:* 
Choose an area that will provide sufficient depth of water through an entire range of tides. Water too shallow will cause the ship to go aground, and water too deep will allow the anchor to drag.

*Type of Bottom: *
Choose the bottom that will best hold the anchor. Avoid rocky bottoms and select sandy or muddy bottoms if they are available.

*Proximity to Navigation Hazards:*
Choose an anchorage as far away as possible from known navigation hazards.

*Proximity to Adjacent Ships: *
Try to anchor as far away as possible from adjacent vessels.
Proximity to Harbor Traffic Lanes: Do not anchor in a traffic lane.

*Weather: *Choose the area with the weakest winds and currents.
*
Availability of NAVAIDS: *
Choose an anchorage with several NAVAIDS available for monitoring the ship&#8217;s position when anchored.

*NAVIGATIONAL ASPECTS OF SHIP HANDLING*
819.	Effects Of Banks, Channels, And Shallow Water
A ship moving through shallow water experiences pronounced effects from the proximity of the nearby bottom. Similarly, a ship in a channel will be affected by the proximity of the sides of the channel. These effects can easily cause errors in piloting which lead to grounding. The effects are known as squat, bank cushion, and bank suction. They are more fully explained in texts on ship-handling, but certain navigational aspects are discussed below. Squat is caused by the interaction of the hull of the ship, the bottom, and the water between. As a ship moves through shallow water, some of the water it displaces rushes under the vessel to rise again at the stern. This causes a venturi effect, decreasing upward pressure on the hull. Squat makes the ship sink deeper in the water than normal and slows the vessel. The faster the ship moves through shallow water, the greater is this effect; groundings on both charted and uncharted shoals and rocks have occurred because of this phenomenon, when at reduced speed the ship could have safely cleared the dangers. When navigating in shallow water, the navigator must reduce speed to avoid squat. If bow and stern waves nearly perpendicular the direction of travel are noticed, and the vessel slows with no change in shaft speed, squat is occurring. Immediately slow the ship to counter it. Squatting occurs in deep water also, but is more pronounced and dangerous in shoal water. The large waves generated by a squatting ship also endanger shore facilities and other craft.

Bank cushion is the effect on a ship approaching a steep underwater bank at an oblique angle. As water is forced into the narrowing gap between the ship&#8217;s bow and the shore, it tends to rise or pile up on the landward side, causing the ship to sheer away from the bank.

Bank suction occurs at the stern of a ship in a narrow channel. Water rushing past the ship on the landward side exerts less force than water on the opposite or open water side. This effect can actually be seen as a difference in draft readings from one side of the vessel to the other. The stern of the ship is forced toward the bank. If the ship gets too close to the bank, it can be forced sideways into it. The same effect occurs between two vessels passing close to each other. These effects increase as speed increases. Therefore, in shallow water and narrow channels, navigators should decrease speed to minimize these effects. Skilled pilots may use these effects to advantage in particular situations, but the average mariner&#8217;s best choice is slow speed and careful attention to piloting.

*ADVANCED PILOTING TECHNIQUES*
820.	Assuming Current Values To Set Safety Margins
When Using Running Fixes
Current affects the accuracy of a running fix. Consider, for example, the situation of an unknown head current. In Figure 820a, a ship is proceeding along a coast, on course 250&#176; speed 12 knots. At 0920 light A bears 190&#176;, and at 0930 it bears 143&#176;. If the earlier bearing line is advanced a distance of 2 miles (10 minutes at 12 knots) in the direction of the course, the running fix is as shown by the solid lines. However, if there is a head current of 2 knots, the ship is making good a speed of only 10 knots, and in 10 minutes will travel a distance of only 1 2/3 miles. If the first bearing line is advanced this distance, as shown by the broken line, the actual position of the ship is at B. This actual position is nearer the NAVAID than the running fix actually plotted. A following current, conversely, would show a position too far from the NAVAID from which the bearing was measured.










If the navigator assumes a following current when advancing his LOP, the resulting running fix will plot further from the NAVAID than the vessel&#8217;s actual position. Conversely, if he assumes a head current, the running fix will plot closer to the NAVAID than the vessel&#8217;s actual position. To ensure a margin of safety when plotting running fix bearings to a NAVAID on shore, always assume the current slows a vessel&#8217;s speed over ground. This will cause the running fix to plot closer to the shore than the ship&#8217;s actual position. When taking the second running fix bearing from a different object, maximize the speed estimate if the second object is on the same side and farther forward, or on the opposite side and farther aft, than the first object was when observed. All of these situations assume that danger is on the same side as the object observed first. If there is either a head or following current, a series of running fixes based upon a number of bearings of the same object will plot in a straight line parallel to the course line, as shown in Figure 820b.










The plotted line will be too close to the object observed if there is a head current and too far out if there is a following current. The existence of the current will not be apparent unless the actual speed over the ground is known. The position of the plotted line relative to the dead reckoning course line is not a reliable guide.

*821. Determining Track Made Good By Plotting Running Fixes*
A current oblique to a vessel&#8217;s course will also result in an incorrect running fix position. An oblique current can be detected by observing and plotting several bearings of the same object. The running fix obtained by advancing one bearing line to the time of the next one will not agree with the running fix obtained by advancing an earlier line. See Figure 821a.










If bearings A, B, and C are observed at five minute intervals, the running fix obtained by advancing B to the time of C will not be the same as that obtained by advancing A to the time of C, as shown in Figure 821a.
Whatever the current, the navigator can determine the direction of the track made good (assuming constant current and constant course and speed). Observe and plot three bearings of a charted object O. See Figure 821b. 










Through O draw XY in any direction. Using a convenient scale, determine points A and B so that OA and OB are proportional to the time intervals between the first and second bearings and the second and third bearings, respectively. From A and B draw lines parallel to the second bearing line, intersecting the first and third bearing lines at C and D, respectively. The direction of the line from C and D is the track made good.

The distance of the line CD in Figure 821b from the track is in error by an amount proportional to the ratio of the speed made good to the speed assumed for the solution. If a good fix (not a running fix) is obtained at some time before the first bearing for the running fix, and the current has not changed, the track can be determined by drawing a line from the fix, in the direction of the track made good. The intersection of the track with any of the bearing lines is an actual position.

*822. A Fix By The Distance Of An Object By Two Bearings* (Table 18)
Geometrical relationships can define a running fix. In Figure 822, the navigator takes a bearing on NAVAID D.










Express the bearing as degrees right or left of course. Later, at B, take a second bearing to D; similarly, take a bearing at C, when the landmark is broad on the beam. The navigator knows the angles at A, B, and C and the distance run between points. The various triangles can be solved using Table 18. From this table, the navigator can calculate the lengths of segments AD, BD, and CD. He knows the range and bearing; he can then plot an LOP. He can then advance these LOP&#8217;s to the time of taking the CD bearing to plot a running fix.

Enter the table with the difference between the course and first bearing (angle BAD in Figure 822) along the top of the table and the difference between the course and second bearing (angle CBD) at the left of the table. For each pair of angles listed, two numbers are given.

To find the distance from the landmark at the time of the second bearing (BD), multiply the distance run between bearings (in nautical miles) by the first number from Table 18. 

To find the distance when the object is abeam (CD), multiply the distance run between A and B by the second number from the table. If the run between bearings is exactly 1 mile, the tabulated values are the distances sought.

Example: A ship is steaming on course 050&#176;, speed 15 knots. At 1130 a lighthouse bears 024&#176;, and at 1140 it bears 359&#176;.
Required:
(1) Distance from the light at 1140.
(2) Distance form the light when it is broad on the port beam.
Solution:
(1) The difference between the course and the first bearing (050&#176; &#8211; 24&#176 is 26&#176;, and the difference between the course and the second bearing (050&#176; + 360&#176; - 359&#176 is 51&#176;.
(2) From Table 18, the two numbers (factors) are 1.04 and 0.81, found by interpolation.
(3) The distance run between bearings is 2.5 miles (10 minutes at 15 knots).
(4) The distance from the lighthouse at the time of the second bearing is 2.5 &#180; 1.04 = 2.6 miles.
(5) The distance from the lighthouse when it is broad on the beam is 2.5 &#180; 0.81 = 2.0 miles.
Answer: (1) D 2.6 mi., (2) D 2.0 mi.
This method yields accurate results only if the helmsman has steered a steady course and the navigator uses the vessel&#8217;s speed over ground.

*MINIMIZING ERRORS IN PILOTING*
823. Common Errors
Piloting requires a thorough familiarity with principles involved, constant alertness, and judgment. A study of groundings reveals that the cause of most is a failure to use or interpret available information. Among the more common errors are:
1. Failure to obtain or evaluate soundings.
2. Misidentification of aids to navigation.
3. Failure to use available navigational aids effectively.
4. Failure to correct charts.
5. Failure to adjust a magnetic compass or keep a table of corrections.
6. Failure to apply deviation.
7. Failure to apply variation.
8. Failure to check gyro and magnetic compass readings regularly.
9. Failure to keep a dead reckoning plot.
10. Failure to plot new information.
11. Failure to properly evaluate information.
12. Poor judgment.
13. Failure to use information in charts and navigation publications.
14. Poor navigation team organization.
15. Failure to &#8220;keep ahead of the vessel.&#8221;
16. Failure to have backup navigation methods in place.

Some of the errors listed above are mechanical and some are matters of judgment. Conscientiously applying the principles and procedures of this chapter will go a long way towards eliminating many of the mechanical errors. However, the navigator must guard against the feeling that in following a checklist he has eliminated all sources of error. A navigator&#8217;s judgment is just as important as his checklists.
*
824. Minimizing Errors With A Two Bearing Plot*
When measuring bearings from two NAVAIDS, the fix error resulting from an error held constant for both observations is minimized if the angle of intersection of the bearings is 90&#176;.
If the observer in Figure 824a is located at point T and the bearings of a beacon and cupola are observed and plotted without error, the intersection of the bearing lines lies on the circumference of a circle passing through the beacon, cupola, and the observer.










With constant error, the angular difference of the bearings of the beacon and the cupola is not affected. Thus, the angle formed at point F by the bearing lines plotted with constant error is equal to the angle formed at point T by the bearing lines plotted without error.

From geometry it is known that angles having their apexes on the circumference of a circle and that are subtended by the same chord are equal. Since the angles at points T and F are equal and the angles are subtended by the same chord, the intersection at point F lies on the circumference of a circle passing through the beacon, cupola, and the observer. Assuming only constant error in the plot, the direction of displacement of the two-bearing fix from the position of the observer is in accordance with the sign (or direction) of the constant error. However, a third bearing is required to determine the direction of the constant error. Assuming only constant error in the plot, the two bearing fix lies on the circumference of the circle passing through the two charted objects observed and the observer.

The fix error, the length of the chord FT in Figure 824b, depends on the magnitude of the constant error e, the distance between the charted objects, and the cosecant of the angle of cut, angle 0.

In Figure 824b, where e is the magnitude of the constant error, BC is the length of the chord BC, and &#61553;&#61472;is the angle of the LOP&#8217;s intersection.









Since the fix error is a function of the cosecant of the Figure 824a. Two-bearing plot. angle of intersection, it is least when the angle of intersection is 90&#176;.










As illustrated in Figure 824c, the error increases in accordance with the cosecant function as the angle of intersection decreases. The increase in the error becomes quite rapid after the angle of intersection has decreased to below about 30&#61616;. With an angle of intersection of 30&#61616;, the fix error is about twice that at 90&#61616;
*
825.	Adjusting A Fix For Constant Error By The Trial And Error Technique*
If several fixes obtained by bearings on three objects produce triangles of error of about the same size, suspect a constant error in observing or plotting the bearings. If applying of a constant error to all bearings results in a point, or near-point, fix, apply such a correction to all subsequent fixes. Figure 825 illustrates this technique. The solid lines indicate the original plot, and the broken lines indicate each line of position moved 3&#61616;&#61472;in a clockwise direction.










Employ this procedure carefully. Attempt to find and eliminate the error source. The error may be in the gyrocompass, the repeater, or the bearing transmission system.
Compare the resulting fix positions with a satellite position, a radar position, or the charted sounding. A high degree of correlation between these three independent positioning systems and an &#8220;adjusted&#8221; visual fix is further confirmation of a constant bearing error.
*TRAINING
826.	Piloting Simulators*
Civilian piloting training has traditionally been a function of both maritime academies and on-the-job experience.
The latter is usually more valuable, because there is no substitute for experience in developing judgment. Military piloting training consists of advanced correspondence courses and formal classroom instruction combined with duties on the bridge. U.S. Navy Quartermasters frequently attend Ship&#8217;s Piloting and Navigation (SPAN) trainers as a routine segment of shore-side training. Military vessels in general have a much clearer definition of responsibilities, as well as more people to carry them out, than civilian ships.

Computer technology has made possible the development of computerized ship simulators, which allow piloting experience to be gained without risking accidents at sea and without incurring underway expense. Simulators range from simple micro-computer-based software to a completely equipped ship&#8217;s bridge with radar, engine controls, 360&#176; horizon views, programmable sea motions, and the capability to simulate almost any navigational situation. A different type of simulator consists of scale models of ships in a pond. The models, actually small craft of about 20-30 feet, have hull forms and power-to-weight ratios similar to various types of ships, primarily supertankers, and the operator pilots the vessel from a position such that his view is from the craft&#8217;s &#8220;bridge.&#8221; These are primarily used in training pilots and masters in docking maneuvers with exceptionally large vessels.
The first computer ship simulators came into use in the late 1970s. Several years later the U.S. Coast Guard began accepting a limited amount of simulator time as &#8220;sea time&#8221; for licensing purposes. The most sophisticated simulators have a full 360&#176; horizon, visible from a completely equipped wheelhouse, which can be programmed for movement, noise, and vibration. They can simulate virtually any conditions encountered at sea or in piloting waters, including land, aids to navigation ice, wind, fog, snow, rain, and lightning. The system can also be programmed to simulate hydrodynamic effects such as shallow water, passing vessels, current, and tugs.
Virtually any type of vessel can be simulated, including tankers, bulkers, container ships, tugs and barges, yachts, and military vessels. Similarly, any given navigational situation can be modeled, including passage through any chosen harbor, river, or passage, convoy operations, meeting and passing situations at sea and in harbors.

Simulators are used not only to train mariners, but also to test feasibility of port and harbor plans and visual aids to navigation system designs. This allows pilots to &#8220;navigate&#8221; simulated ships through simulated harbors before construction begins to test the adequacy of channels, turning basins, aids to navigation, and other factors.

A full-capability simulator consists of a ship&#8217;s bridge which may have motion and noise/vibration inputs, a programmable visual display system which projects a simulated picture of the area surrounding the vessel in both daylight and night modes, image generators for the various inputs to the scenario such as video images and radar, a central data processor, a human factors monitoring system which may record and videotape bridge activities for later analysis, and a control station where instructors control the entire scenario.

Some simulators are part-task in nature, providing specific training in only one aspect of navigation such as radar navigation, collision avoidance, or night navigation.

*Guess what? Conclusion chapter 8
*


----------



## Fishers of Men

*GPS cont. 3*
Usually you will use GPS as your primary position reference as well as your navigation computer on the water, but you first need to understand what it is telling you.
Your GPS receiver makes an excellent navigation tool. GPS provides precise position on a continuous basis, and your receiver uses that information to provide a great deal of other useful information. However, it is essential that you understand what your GPS can and cannot do.

*What GPS can do*
The primary purpose of the Global Positioning System is to provide position. Your receiver converts that position into a format that is useful to the boater.
Your GPS will:
1. Provide position in latitude and longitude.
Computations within your GPS receiver will also enable it to:
2. Provide a course to steer, if waypoints are used.
3. Provide estimated arrival time at destination.
*What GPS cannot do*
GPS &#8216;s only source of information is from the constellation of satellites. Therefore, it has no inherent knowledge as to what resides at the position it provides. As a result,
GPS cannot
1. Warn of hazards.
2. Determine water depth.
3. Your source of information for the local environment must come from charts, your personal observations, and other instruments on the boat.
FIGURE 5-12. Your GPS can execute a route&#8212;a preplanned sequence of legs. To build a route, select the New Route Screen and begin by entering the departure waypoint. Then, enter each subsequent waypoint. The GPS computes the course for each leg and its distance.










*CREATING ROUTES *
To ease your tasks on the water, it makes sense to create routes or route segments using your newly entered waypoints. By accessing the route function within your GPS, you can select waypoints in a desired sequence and thus build a route. Most GPS sets allow you to enter roughly twenty waypoints for each route and can store as many as fifty routes. Usually, the GPS automatically names the route by using the first and last waypoint names. Unless you have a strong reason for changing it, the default naming scheme is preferred.

Now you have created a personal waypoint logbook for your boating area with the information stored in your GPS. By identifying and programming a substantial number of waypoints, you have constructed a frame of reference to compare with visible objects and hazards while on the water.
*
Plotting on a Chart*
Because we are using paper charts in this training exercise, it&#8217;s important to be comfortable with techniques for plotting courses and bearings on a chart. The basic tools were discussed earlier. 
It&#8217;s wise to thoroughly annotate your paper charts with the information stored in your GPS. This includes labeling the waypoints in the same manner. By the way another advantage of waterproof charts (other than the obvious) is that they usually can be written on, erased, and annotated at will without damaging the chart.

*Summary of Plotting Lines*
I have described several types of lines that you will plot on your charts&#8212;some in advance and some while you go. Here&#8217;s a quick summary:
*Ahead of Time*
Course&#8212;a solid line representing your intended path on the water, labeled with the direction and distance of the leg.
Range&#8212;a dashed line between two charted objects&#8212; generally ashore or in shoal water&#8212;that is then ex tended over navigable waters, where it switches from dashed to solid. A range is labeled with its bearing. Government-established ranges are pre plotted on charts; you can add your own ranges as desired.
*While Underway*
DR&#8212;a solid line representing your estimated progress on the water. A DR is based on the course steered; its length is the distance traveled as estimated from speed and time of travel.
*Bearing*&#8212;a solid line representing your observation of a landmark or navigation aid labeled with the time of the observation and the bearing direction in degrees.

*Plotting a Course*
In the &#8220;Planning and Paper Charts&#8221; section of this chapter, we drew straight-line segments on the chart along pre-qualified paths that avoid obstacles. We then measured the coordinates of the end points of each such leg and programmed these into the GPS as named waypoints. Finally, we programmed routes by calling up waypoints in a desired sequence.
FIGURE 5-13. 
*Plotting falls into two main categories:* 
Prevoyage plotting and plotting that&#8217;s done underway Intended courses (legs, waypoints, routes) are preplotted. Ranges are preplotted. On the water, you plot bearings to match your observations, and a DR (dead reckoning) plot to back up your electronic navigation. These courses and bearings have been measured in degrees true using the chart grid for reference.










Once a route is entered, most GPS sets provide you with the courses and distances between each of the way- points in sequence in that route. You&#8217;ll find it helpful to label the legs of the routes plotted on your chart with these values. To be consistent with navigation conventions, name the leg with the following elements: start with &#8220;C&#8221; for course, then add the three-digit direction, then finish with the letter &#8220;M&#8221; for magnetic (assuming you are using magnetic headings in your GPS). For instance, a course of 30 should be labeled &#8220;C 003 M.&#8221; Place this label near the beginning waypoint above the course line. To note the distance of a leg, start with the letter &#8220;D,&#8221; then add the GPS-derived number (usually expressed in nautical miles and tenths). This label should be placed under the course line, ideally near the center of the leg. As you add these labels, verify their accuracy with your plotting tools. Why do this if the GPS computes courses and distances for you? Well, this is another check on the accuracy of your entry for each waypoint. 

By comparing your measured course direction and distance with that computed by the GPS, you gain confidence that you&#8217;ve measured, entered, and selected waypoints properly.
(You&#8217;ll be amazed how many times you pick up an error in an entered waypoint by doing this.) Again, waypoint coordinates are just numbers until they&#8217;re plotted on a chart.

FIGURE 5-14. Most recreational boaters will want to label their plots with magnetic courses and bearings, as here. This enables them to relate to their compasses without further correction for variation. Directions labeled in magnetic should be annotated with an &#8220;M&#8221; suffix for clarity.










If you have a Maptech or other commercial chart book, you may find that some routes and legs are already labeled, along with waypoint coordinates. Most such books use magnetic headings and nautical miles. You will note that the reciprocal course heading is labeled at the other end of each line. The reciprocal is the course you steer from the opposite direction.
To determine a reciprocal, either add 1800 to a course of less than 180&#176;, or subtract 180&#176; from a course of more than 180&#176;. You can also use your GPS receiver to determine a reciprocal course simply by selecting the invert feature from its menu. Doing so will save you from entering your return trip as a separate route. Once inverted, the route will list the reciprocal course directions for each leg. Invert again to restore the original sequence.
Yet another way to find a reciprocal course is to place your parallel rules over the original course on the compass rose, then read the reciprocal from the other side of the rose.

For the most part, you probably will be working in magnetic rather than true. The language of the boat is magnetic; the language of the chart is true. You need to be comfortable with the conversion&#8212;which can be done mathematically by adding or subtracting local variation&#8212;or graphically (and more simply) using the compass rose. Let&#8217;s look at the latter first.
*
USING THE COMPASS ROSE *
As described in previously, the compass rose (which is printed in multiple locations on your chart) provides the chart&#8217;s fundamental reference for magnetic directions. It is printed in a magenta ink that is distinctive when viewed with red light at night. (Navigators use a red light at night for illuminating charts and instruments, because this color has minimal effect on night vision, which is essential for keeping watch.)

The compass rose has two rings. The outer ring aligns with the chart grid of latitude and longitude lines&#8212;that is, with true north; the inner ring aligns with magnetic north. Within the inner ring is a legend that notes the local variation used for the chart. The variation describes both the magnitude of the difference in degrees and minutes between true and magnetic north for the charted location, and the direction of that offset, either east or west. (Magnetic north is moving, albeit slowly, so variation needs to be adjusted for this movement.) In addition, the legend identifies the date used for the variation and the amount by which it will change each year, east or west. You will need to adjust the variation accordingly if your chart is several years old and the annual change is significant.

FIGURE 5-15. Charts are printed with one or more compass roses. The compass rose has two rings. The outer ring is aligned with the chart grid and true north. The inner ring is aligned with magnetic north. A legend at the center of the rose provides the local variation and its annual change. The compass rose simplifies the labeling of courses and bearings and provides instant reference between true and magnetic north.










Many mariners use the compass rose for laying out or measuring a course or bearing. Because the rose is rarely if ever located where you want to plot or measure a course, devices such as parallel rules are used to transfer the direction to or from the rose, as described and shown in Figure 5-16. Make sure you read your direction from the compass rose going the right way&#8212;that is, by imagining your boat at the center and reading toward the rose in the direction of the course or bearing.

FIGURE 5-16. The compass rose can be used to measure or plot magnetic direction. With parallel rules, you can align one rule along the bearing to be measured and extend the other rule to align with the center of the compass rose. A magnetic bearing can be read directly on the inner scale. If the distance between the compass rose and the bearing line is too great, you can walk the parallel rules.










Another type of parallel rule uses a roller (Figure 5- 17) to pick up a desired direction from the compass rose and transfer it across the chart to where you are plotting. Typically, you will need a flat, stable surface for this device to work.










FIGURE 5-17. An alternative tool uses a roller instead of two rules. The roller allows the rule to glide across the chart without changing its orientation. In the left panel, the parallel rule is aligned with a bearing. In the right panel, the parallel rule has been rolled so that the straightedge aligns with the compass rose for reading the bearing.

Using your parallel rules, confirm the GPS calculation of course direction for each pre-plotted leg on your chart as follows: Align one rule with the plotted leg, then walk the rules across the chart to the nearest compass rose and read the course in degrees magnetic from the inner ring.
Does the result agree with what your GPS is telling you? If so, the course direction calculated by the GPS is correct, and the plot can be so labeled. Now check the distance of the leg by walking it off with a pair of dividers, as de scribed previously. Does the result agree with your GPS calculation? Good; add the label and turn to the next leg of the pre-plotted route.

Are these courses now ready to steer? Yes, provided your steering compass doesn&#8217;t exhibit significant deviation errors that you can&#8217;t get rid of. See &#8220;Correcting for Deviation&#8221; later in this thread for more on this topic.

Measuring and plotting courses and bearing in degrees magnetic, as described above, is simpler than piloting by degrees true. When you confine yourself to the language of the compass, you sidestep the potential for translation errors. 

The other approach, as mentioned, is to measure and plot courses and bearings in degrees true, then steer or sight their magnetic equivalents after adding or subtracting local variation (always) and onboard deviation (if necessary), as described below.
But why do things this harder way when it&#8217;s simpler to work in degrees magnetic using the inner ring of a compass rose? The short answer is that most small-craft navigators don&#8217;t. Nevertheless, the concept of converting back and forth between true and magnetic directions is one you should understand, even if only to recognize when the difference is about to affect your navigation. We have discussed the importance for converting, in detail, way earlier in the thread.
And there are practical reasons for knowing how to measure and plot courses and bearings from a chart&#8217;s grid of latitude and longitude lines. For one thing, the grid covers the entire chart and is always available to you, whereas the nearest compass rose is often folded underneath and there fore not conveniently accessible when you&#8217;re working on a small surface. Second, those who navigate this way all the time swear that it becomes so second nature as to be faster than using a compass rose. Well, maybe.
Finally, if your ship&#8217;s compass carries deviation on some headings, as described earlier, you&#8217;ll have to add or subtract these values from your magnetic courses no matter how you obtain them, in order to get courses to steer.

Because the technique for doing this is just like adding or subtracting variation to get from true to magnetic or back, you might as well learn it now. 

If you don&#8217;t have it, go back and start reading, I can&#8217;t help a lot of things being reiterated and am not going to do them all or we will never get through this!
If you&#8217;re still not convinced, think of it like iodine on a cut&#8212;painful but good for you.

So let&#8217;s return to the routes you have pre-plotted on your local chart or charts in anticipation of a wonderful boating season, this time assuming that you&#8217;ve initialized your GPS receiver to calculate course directions in degrees true. As you call up each leg of a route in sequence, the GPS tells you its course direction and distance. As before, double check these numbers with plotting tools before labeling each leg. To do this, align one of the protractor plotting tools, (for example see prior post, Figures 4-23 and 4-24), with the plotted leg, then read its course direction in degrees true from the nearest parallel or meridian, as appropriate. Does the result agree with the GPS calculation? If so, add the label.

One kind of protractor plotting tool employs a pivoting arm (Figure 5-18). The protractor is aligned with the grid lines on the chart and the arm is set to the desired angle. Some of these plotters have an extra scale on the movable arm that allows you to adjust for the local variation between true and magnetic, making this a truly versatile tool. 
FIGURE 5-18. A very useful plotting tool has a protractor scale and a pivoting arm. Parallel lines are printed along with the pro tractor on the fixed part. This is aligned with the grid lines on the chart, with the center of the plotting tool on your current location or the object being sighted. The arm can then be rotated to a selected angle so the line can be measured or drawn. Be cause the protractor is aligned with the grid, the direction provided is in degrees true.










For the moment, however, let&#8217;s assume you&#8217;re plotting in degrees true.
You&#8217;ve pre-plotted routes on your chart and calculated the course direction for each leg in degrees true. But before you can steer that course on the water, you&#8217;ll have to convert it to degrees magnetic, which is the language of your ship&#8217;s compass. Remember, local variation is the same for all boats in an area and on all headings. Your chart will tell you what the variation was at the time the chart was created. Assuming your chart is the most recent edition (as it should be), you can safely use the charted value of variation. This is an angular correction either east or west. You will need to add a westerly variation or subtract an easterly variation from each true course to get its equivalent magnetic direction. Summarizing, the formula is:
Reminder: True = + W or &#8212; E Variation = Magnetic
Suppose, for example, your local variation is 15&#176; W and you want to convert a course of 175&#176; true to its magnetic equivalent. You add 15 to 175 and find that the magnetic course is 190&#176;. If your local variation is 15&#176;E, a course of 175&#176; T would translate to 160&#176; M. Westerly variation is added to a true course; easterly is subtracted. Some navigators find the expression &#8220;West is best; east is least&#8221; to be a helpful memory aid.

While correcting for local variation, you should correct for compass deviation too; indeed, the latter correction will apply even when your magnetic course has come from a GPS calculation or from a reading off a chart&#8217;s compass rose. Putting it all together, we get the formula TVMDC, which is the universal technique used to convert between true, magnetic, and compass directions. TVMDC was also discussed in detail in previous posts for you guys that think you can &#8220;cheat&#8221; and get away without it. lol.


Tips to remember:
1. Converting from true to magnetic
Add westerly variation (going down); subtract easterly
2. Converting from magnetic to true
Add easterly variation (going up); subtract westerly 
3. Converting from magnetic to compass
Add westerly deviation (going down); subtract easterly
4. Converting from compass to magnetic
Add easterly deviation (going up); subtract westerly
For plotting, you will use only true or magnetic directions; most navigators choose magnetic for reasons already explained. Compass courses are steered but not plotted.
*Plotting a Bearing*
While on the water, you will have occasion to take visual bearings on charted objects to help you determine your position. We discussed bearings in the past and return to their use on the water in later chapters, so here we merely discuss briefly how to plot them. Remember, a bearing is considered to be a line of position and as such represents a line on which your boat is located. Because the observed object is charted and your boat is not, you will need plot the line using the object as the reference point. Still, the line is drawn toward the object, in the direction of the bearing, from the estimated location of your boat. It is labeled with the time of the bearing in four digits (24-hourclock) above the line and the direction of the bearing in three digits below the line. These labeling conventions are the same as for courses. See past threads for details on sighting and labeling bearings, and Figures 5-13 and 5-14 for examples of labeling in degrees true and magnetic.

*Plotting a Range*
Ranges are plotted as straight dashed lines between charted objects with the line extending into the intended area of navigation. The portion of the range that is navigable is denoted by a solid line. The bearing of the range should be labeled on top of the line for ready reference on the water. If the range is charted, generally the bearing will be true. If you plot the range yourself, you can do so in degrees magnetic; just follow the bearing with the letter M Generally, the landmark to the rear will be taller, and the sight picture will be in a straight line, if you are &#8220;on&#8221; the range, the two objects will align. If you are to the left, the rear landmark will appear to the left of the one in the foreground. Plotting and labeling for true and magnetic directions are shown in Figures 5-13 and 5-14. Any charted object can be used in a range: a water tower, a church spire, a daybeacon, a bold bluff on one end of an island. With this in mind, you can plot strategically located ranges on your local chart while cruise planning. They&#8217;ll come in handy.
*
Entering Waypoints into Your GPS*
As we saw earlier, cruise planning includes a process of plotting a network of safe legs on charts covering the area in which you intend to boat. These safe legs start and end at waypoints. In turn, each waypoint is referenced by a set of coordinates, specifically a latitude and a longitude. Getting all of that into your GPS can appear to be somewhat tedious, but it&#8217;s worth the effort. This is the information that makes your GPS so useful.

You&#8217;ve learned how to measure waypoints and construct a waypoint table of latitudes and longitudes. Using this table to manually enter waypoints into the GPS is perhaps the most straightforward method; however, there are alternatives. All of the methods are summarized below.
*Manual Entry*
Enter coordinates manually by accessing the New Way- point Screen. Using the cursor button, scroll down until the coordinates field is highlighted, and press ENTER. You will be presented with a single highlighted character. Use the cursor to scroll up or down to change the character (number) until it corresponds to your desired entry. Then the cursor to scroll right or left to change the values of other characters. When you&#8217;re satisfied with the entered values for latitude and longitude, press ENTER to accept. Scroll to OK or Save and press ENTER. Your GPS will assign a number in the name field. You can change the name (or the symbol displayed with the waypoint) in this field in the same manner as entering values into the coordinates field.
*Scroll*
An easier way to store coordinates in your GPS is to scroll the cursor on the Map Screen. The cursor&#8217;s coordinates are shown on the screen. Press MARK to access and edit the New Waypoint Screen, then save. On some GPS models, this is the method by which you access the New Waypoint Screen. Usually, it is quicker and easier to scroll to the general area of the desired waypoint, press MARK, edit the details of the coordinates until your satisfied, then save.

*Bearing and Distance*
As indicated earlier, it is wise to plot your course on a paper chart and label each leg with its course directions and distances. Now you can put that information to good use. With this technique you can accurately enter all the waypoints into your GPS without entering the coordinates for each one.
Start at one of the intersections for a group of legs and enter the waypoint coordinates for just that intersection.

Many newer GPS models provide a bearing and distance readout of the cursor position in addition to its coordinates, as described above. Akin to the scroll method you can use those readouts to enter other waypoints as follows.
Set the current location of the GPS in toe simulator mode (usually found in the menu). Select the newly entered waypoint as your simulated position. Now using the cursor on the Map Screen, scroll until the displayed values for cursor bearing and distance correspond with the course direction and distance of the desired leg. Press MARK and proceed with your naming. Repeat this step for any other legs that emanate from that starting point, or reset your simulated position to another intersection and continue from there.

*To be cont.*


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## reel

Very thorough but going by the book doesn't leave much time to fish.
Seriously this is excellent reading.
Keep up the good work.
...


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## Fishers of Men

*Some of you might think that this section has nothing to do with where you boat/fish or whatever. If you take the time to research this information, you will notice similarities in what you do. Take a look at a globe and look at the water current "arrows". Pay attention to the directions, Take another look at the currents in the sky and their general patterns, take a look at the magnetic influences of the Earth that I posted in the beginning, think about individual boat magnetic characteristics that we covered, Take a good look at True vs Magnetic North, and I could go on and on. You should be able to put a LOT of pieces together. These influences definitely effect the saltwater inshore fishing. Offshore doesn't seem to matter much though. We all wonder about moon phases, effects on fishing in Lake Erie, fronts, winds, barometric pressures, and such for when the fish bite best, or where did they go? Or why? Can the fish be predicted if you know what influences them? When someone is able to do this, please let me know. There are many types of currents in Lake Erie that change. Can you keep that "stream" trail behind your boat in a straight line? You are always correcting in order to get to your destination, even if your GPS says go here. Autopilots are constantly correcting also. If you go to Florida or some other tidal area on vacation, this info could make your trip successful.

CHAPTER 9
TIDES AND TIDAL CURRENTS
ORIGINS OF TIDES
900.	Introduction*
Tides are the periodic motion of the waters of the sea due to changes in the attractive forces of the moon and sun upon the rotating earth. Tides can either help or hinder a mariner. A high tide may provide enough depth to clear a bar, while a low tide may prevent entering or leaving a harbor. Tidal current may help progress or hinder it, may set the ship toward dangers or away from them. By understanding tides, and by making intelligent use of predictions published in tide and tidal current tables and of descriptions in sailing directions, the navigator can plan an expeditious and safe passage.

*901.Tide And Current*
The rise and fall of tide is accompanied by horizontal movement of the water called tidal current. It is necessary to distinguish clearly between tide and tidal current, for the relation between them is complex and variable. For the sake of clarity mariners have adopted the following definitions: Tide is the vertical rise and fall of the water, and tidal current is the horizontal flow. The tide rises and falls, the tidal current floods and ebbs. The navigator is concerned with the amount and time of the tide, as it affects access to shallow ports. The navigator is concerned with the time, speed, and direction of the tidal current, as it will affect his ships position, speed, and course.
Tides are superimposed on nontidal rising and falling water levels, caused by weather, seismic events, or other natural forces. Similarly, tidal currents are superimposed upon non-tidal currents such as normal river flows, floods, freshets, etc.

*902.Causes Of Tides*
The principal tidal forces are generated by the moon and sun. The moon is the main tide-generating body. Due to its greater distance, the suns effect is only 46 percent of the moons. Observed tides will differ considerably from the tides predicted by equilibrium theory since size, depth, and configuration of the basin or waterway, friction, land masses, inertia of water masses, Coriolis acceleration, and other factors are neglected in this theory. Nevertheless, equilibrium theory is sufficient to describe the magnitude and distribution of the main tide-generating forces across the surface of the earth.
Newtons universal law of gravitation governs both the orbits of celestial bodies and the tide-generating forces which occur on them. The force of gravitational attraction between any two masses, m1 and m2, is given by: where d is the distance between the two masses, and G is a constant which depends upon the units employed. This law assumes that m1 and m2 are point masses.










Newton was able to show that homogeneous spheres could be treated as point masses when determining their orbits.



















However, when computing differential gravitational forces, the actual dimensions of the masses must be taken into account.

Using the law of gravitation, it is found that the orbits of two point masses are conic sections about the barycenter of the two masses. If either one or both of the masses are homogeneous spheres instead of point masses, the orbits are the same as the orbits which would result if all of the mass of the sphere were concentrated at a point at the center of the sphere. In the case of the earth-moon system, both the earth and the moon describe elliptical orbits about their barycenter if both bodies are assumed to be homogeneous spheres and the gravitational forces of the sun and other planets are neglected. The earth-moon barycenter is located 74/100 of the distance from the center of the earth to its surface, along the line connecting the earths and moons centers.

Thus the center of mass of the earth describes a very small ellipse about the earth-moon barycenter, while the center of mass of the moon describes a much larger ellipse about the same barycenter. If the gravitational forces of the other bodies of the solar system are neglected, Newtons law of gravitation also predicts that the earth-moon barycenter will describe an orbit which is approximately elliptical about the barycenter of the sun-earth-moon system. This barycentric point lies inside the sun.
*
903.	The Earth-Moon-Sun System*
The fundamental tide-generating force on the earth has two interactive but distinct components. The tide-generating forces are differential forces between the gravitational attraction of the bodies (earth-sun and earth-moon) and the centrifugal forces on the earth produced by the earths orbit around the sun and the moons orbit around the earth. Newtons Law of Gravitation and his Second Law of Motion can be combined to develop formulations for the differential force at any point on the earth, as the direction and magnitude are dependent on where you are on the earths surface. As a result of these differential forces, the tide generating forces Fdm (moon) and Fds (sun) are inversely proportional to the cube of the distance between the bodies, where:



















Where Mm is the mass of the moon and Ms is the mass of the sun, Re is the radius of the earth and d is the distance to the moon or sun. This explains why the tide-generating force of the sun is only 46/100 of the tide-generating force of the moon. Even though the sun is much more massive, it is also much farther away.

Using Newtons second law of motion, we can calculate the differential forces generated by the moon and the sun affecting any point on the earth. The easiest calculation is for the point directly below the moon, known as the sublunar point, and the point on the earth exactly opposite, known as the antipode. Similar calculations are done for the sun. If we assume that the entire surface of the earth is covered with a uniform layer of water, the differential forces may be resolved into vectors perpendicular and parallel to the surface of the earth to determine their effect. The perpendicular components change the mass on which they are acting, but do not contribute to the tidal effect. The horizontal components, parallel to the earths surface, have the effect of moving the water in a horizontal direction toward the sublunar and antipodal points until an equilibrium position is found. The horizontal components of the differential forces are the principal tide-generating forces. These are also called tractive forces. Tractive forces are zero at the sublunar and antipodal points and along the great circle halfway between these two points. Tractive forces are maximum along the small circles located 45 degrees from the sublunar point and the antipode. Figure 903b shows the tractive forces across the surface of the earth. 
Equilibrium will be reached when a bulge of water has formed at the sublunar and antipodal points such that the tractive forces due to the moons differential gravitational forces on the mass of water covering the surface of the earth are just balanced by the earths gravitational attraction (Figure 903c).

Now consider the effect of the rotation of the earth. If the declination of the moon is 0&#61616;, the bulges will lie on the equator. As the earth rotates, an observer at the equator will note that the moon transits approximately every 24 hours and 50 minutes. Since there are two bulges of water on the equator, one at the sublunar point and the other at the antipode, the observer will also see two high tides during this interval with one high tide occurring when the moon is overhead and another high tide 12 hours 25 minutes later when the observer is at the antipode. He will also experience a low tide between each high tide. The theoretical range of these equilibrium tides at the equator will be less than 1 meter.



















The heights of the two high tides should be equal at the equator. At points north or south of the equator, an observer would still experience two high and two low tides, but the heights of the high tides would not be as great as they are at the equator. The effects of the declination of the moon are shown in Figure 903d, for three cases, A, B, and C.
A.	When the moon is on the plane of the equator, the forces are equal in magnitude at the two points on the same parallel of latitude and 180&#61616;&#61472;apart in longitude.
B.	When the moon has north or south declination, the forces are unequal at such points and tend to cause an inequality in the two high waters and the two low waters each day.
C.	Observers at points X, Y, and Z experience one high tide when moon is on their meridian, then another high tide 12 hours 25 minutes later when at X, Y, and Z. The second high tide is the same at X as at X. High tides at Y and Z are lower than high tides at Y and Z.

The preceding discussion pertaining to the effects of the moon is equally valid when discussing the effects of the sun, taking into account that the magnitude of the solar effect is smaller. Hence, the tides will also vary according to the suns declination and its varying distance from the earth. A second envelope of water representing the equilibrium tides due to the sun would resemble the envelope shown in Figure 903c except that the heights of the high tides would be smaller, and the low tides correspondingly not as low.

*FEATURES OF TIDES
904.	General Features*
At most places the tidal change occurs twice daily. The tide rises until it reaches a maximum height, called high tide or high water, and then falls to a minimum level called low tide or low water.

The rate of rise and fall is not uniform. From low water, the tide begins to rise slowly at first, but at an increasing rate until it is about halfway to high water. The rate of rise then decreases until high water is reached, and the rise ceases. The falling tide behaves in a similar manner. The period at high or low water during which there is no apparent change of level is called stand. The difference in height between consecutive high and low waters is the range. Figure 904 is a graphical representation of the rise and fall of the tide at New York during a 24-hour period. The curve has the general form of a variable sine curve.










*905.	Types Of Tide*
A body of water has a natural period of oscillation, dependent upon its dimensions. None of the oceans is a single oscillating body; rather each one is made up of several separate oscillating basins. As such basins are acted upon by the tide-producing forces, some respond more readily to daily or diurnal forces, others to semidiurnal forces, and others almost equally to both. Hence, tides are classified as one of three types, semidiurnal, diurnal, or mixed, according to the characteristics of the tidal pattern.
In the semidiurnal tide, there are two high and two low waters each tidal day, with relatively small differences in the respective highs and lows. Tides on the Atlantic coast of the United States are of the semidiurnal type, which is illustrated in Figure 905a by the tide curve for Boston Harbor.










*In the diurnal tide*, only a single high and single low water occur each tidal day. Tides of the diurnal type occur along the northern shore of the Gulf of Mexico, in the Java Sea, the Gulf of Tonkin, and in a few other localities. The tide curve for Pei-Hai, China, illustrated in Figure 905b, is an example of the diurnal type.

*In the mixed tide*, the diurnal and semidiurnal oscillations are both important factors and the tide is characterized by a large inequality in the high water heights, low water heights, or in both. There are usually two high and two low waters each day, but occasionally the tide may become diurnal. Such tides are prevalent along the Pacific coast of the United States and in many other parts of the world. Examples of mixed types of tide are shown in Figure 905c. At Los Angeles, it is typical that the inequalities in the high and low waters are about the same. At Seattle the greater inequalities are typically in the low waters, while at Honolulu it is the high waters that have the greater inequalities.


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## Fishers of Men

*chap.9 cont

906.	Solar Tide*
The natural period of oscillation of a body of water may accentuate either the solar or the lunar tidal oscillations. Though as a general rule the tides follow the moon, the relative importance of the solar effect varies in different areas. There are a few places, primarily in the South Pacific and the Indonesian areas, where the solar oscillation is the more important, and at those places the high and low waters occur at about the same time each day. At Port Adelaide, Australia the solar and lunar semidiurnal oscillations are equal and nullify one another at neaps.

*907.	Special Tidal Effects*
As a wave enters shallow water, its speed is decreased. Since the trough is shallower than the crest, it is retarded more, resulting in a steepening of the wave front. In a few estuaries, the advance of the low water trough is so much retarded that the crest of the rising tide overtakes the low, and advances upstream as a breaking wave called a bore. Bores that are large and dangerous at times of large tidal ranges may be mere ripples at those times of the month when the range is small. Examples occur in the Petitcodiac River in the Bay of Fundy, and at Haining, China, in the Tsientang Kaing. The tide tables indicate where bores occur.

Other special features are the double low water (as at Hoek Van Holland) and the double high water (as at Southampton, England). At such places there is often a slight fall or rise in the middle of the high or low water period. The practical effect is to create a longer period of stand at high or low tide. The tide tables list these and other peculiarities where they occur.

*908.	Variations In Range*
Though the tide at a particular place can be classified as to type, it exhibits many variations during the month (Figure 908a). The range of the tide varies according to the intensity of the tide-producing forces, though there may be a lag of a day or two between a particular astronomic cause and the tidal effect.










The combined lunar-solar effect is obtained by adding the moon&#8217;s tractive forces vectorially to the sun&#8217;s tractive forces. The resultant tidal bulge will be predominantly lunar with modifying solar effects upon both the height of the tide and the direction of the tidal bulge. Special cases of interest occur during the times of new and full moon (Figure 908b).










With the earth, moon, and sun lying approximately on the same line, the tractive forces of the sun are acting in the same direction as the moon&#8217;s tractive forces (modified by declination effects). The resultant tides are called spring tides, whose ranges are greater than average.

Between the spring tides, the moon is at first and third quarters. At those times, the tractive forces of the sun are acting at approximately right angles to the moon&#8217;s tractive forces. The results are tides called neap tides, whose ranges are less than average.

With the moon in positions between quadrature and new or full, the effect of the sun is to cause the tidal bulge to either lag or precede the moon (Figure 908c). These effects are called priming and lagging the tides.










Thus, when the moon is at the point in its orbit nearest the earth (at perigee), the lunar semidiurnal range is increased and perigean tides occur. When the moon is farthest from the earth (at apogee), the smaller apogean tides occur. When the moon and sun are in line and pulling together, as at new and full moon, spring tides occur (the term spring has nothing to do with the season of year); when the moon and sun oppose each other, as at the quadratures, the smaller neap tides occur. When certain of these phenomena coincide, perigean spring tides and apogean neap tides occur.
These are variations in the semidiurnal portion of the tide. Variations in the diurnal portion occur as the moon and sun change declination. When the moon is at its maximum semi-monthly declination (either north or south), tropic tides occur in which the diurnal effect is at a maximum;. When it crosses the equator, the diurnal effect is a minimum and equatorial tides occur.

When the range of tide is increased, as at spring tides, there is more water available only at high tide; at low tide there is less, for the high waters rise higher and the low waters fall lower at these times. There is more water at neap low water than at spring low water. With tropic tides, there is usually more depth at one low water during the day than at the other. While it is desirable to know the meanings of these terms, the best way of determining the height of the tide at any place and time is to examine the tide predictions for the place as given in the tide tables, which take all these effects into account.

*909.	Tidal Cycles*
Tidal oscillations go through a number of cycles. The shortest cycle, completed in about 12 hours and 25 minutes for a semidiurnal tide, extends from any phase of the tide to the next recurrence of the same phase. During a lunar day (averaging 24 hours and 50 minutes) there are two highs and two lows (two of the shorter cycles) for a semidiurnal tide.

The moon revolves around the earth with respect to the sun in a synodical month of about 29 &#189; days, commonly called the lunar month. The effect of the phase variation is completed in one-half a synodical month or about 2 weeks as the moon varies from new to full or full to new. The effect of the moon&#8217;s declination is also repeated in one-half of a tropical month of 27 1/3 days or about every 2 weeks. The cycle involving the moon&#8217;s distance requires an anomalistic month of about 27 &#189; days. The sun&#8217;s declination and distance cycles are respectively a half year and a year in length. An important lunar cycle, called the nodal period, is 18.6 years (usually expressed in round figures as 19 years).
For a tidal value, particularly a range, to be considered a true mean, it must be either based upon observations extended over this period of time, or adjusted to take account of variations known to occur during the nodal period.

*910.	Time Of Tide*
Since the lunar tide-producing force has the greatest effect in producing tides at most places, the tides &#8220;follow the moon.&#8221; Because the earth rotates, high water lags behind both upper and lower meridian passage of the moon.
The tidal day, which is also the lunar day, is the time between consecutive transits of the moon, or 24 hours and 50 minutes on the average. Where the tide is largely semidiurnal in type, the lunitidal interval (the interval between the moon&#8217;s meridian transit and a particular phase of tide) is fairly constant throughout the month, varying somewhat with the tidal cycles. There are many places, however, where solar or diurnal oscillations are effective in upsetting this relationship. The interval generally given is the average elapsed time from the meridian transit (upper or lower) of the moon until the next high tide. This may be called mean high water lunitidal interval or corrected (or mean) establishment.

The common establishment is the average interval on days of full or new moon, and approximates the mean high water lunitidal interval.
In the ocean, the tide may be in the nature of a progressive wave with the crest moving forward, a stationary or standing wave which oscillates in a seesaw fashion, or a combination of the two. Consequently, caution should be used in inferring the time of tide at a place from tidal data for nearby places. In a river or estuary, the tide enters from the sea and is usually sent upstream as a progressive wave so that the tide occurs progressively later at various places upstream.
*
TIDAL DATUMS
911.	Low Water Datums*
A tidal datum is a level from which tides are measured.
There are a number of such levels of reference that are important to the mariner. See Figure 911.










The most important level of reference to the mariner is the sounding datum shown on charts. Since the tide rises and falls continually while soundings are being taken during a hydrographic survey, the tide is recorded during the survey so that soundings taken at all stages of the tide can be reduced to a common sounding datum. Soundings on charts show depths below a selected low water datum (occasionally mean sea level), and tide predictions in tide tables show heights above and below the same level. The depth of water available at any time is obtained by adding algebraically the height of the tide at the time in question to the charted depth.

By international agreement, the level used as chart datum should be low enough so that low waters do not fall very far below it. At most places, the level used is one determined from a mean of a number of low waters (usually over a 19 year period); therefore, some low waters can be expected to fall below it. The following are some of the datums in general use.

Mean low water (MLW) is the average height of all low waters at a given place. About half of the low waters fall below it, and half above.
Mean low water springs (MLWS), usually shortened to low water springs, is the average level of the low waters that occur at the times of spring tides.
Mean lower low water (MLLW) is the average height of the lower low waters of each tidal day.

Tropic lower low water (TcLLW) is the average height of the lower low waters (or of the single daily low waters if the tide becomes diurnal) that occur when the moon is near maximum declination and the diurnal effect is most pronounced. This datum is not in common use as a tidal reference.
Indian spring low water (ISLW), sometimes called Indian tide plane or harmonic tide plane, is a low water datum that includes the spring effect of the semi-diurnal portion of the tide and the tropic effect of the diurnal portion. It is about the level of lower low water of mixed tides at the time that the moon&#8217;s maximum declination coincides with the time of new or full moon. Mean lower low water springs (MLLWS) is the average level of the lower of the two low waters on the days of spring tides.
Some still lower datums used on charts are determined from tide observations and some are determined arbitrarily and later referred to the tide. Most of them fall close to one or the other of the following two datums.
Lowest normal low water is a datum that approximates the average height of monthly lowest low waters, discarding any tides disturbed by storms.

Lowest low water is an extremely low datum. It conforms generally to the lowest tide observed, or even somewhat lower. Once a tidal datum is established, it is sometimes retained for an indefinite period, even though it might differ slightly from a better determination from later observations. When this occurs, the established datum may be called low water datum, lower low water datum, etc. These datums are used in a limited area and primarily for river and harbor engineering purposes. Examples are Boston Harbor Low Water Datum and Columbia River Lower Low Water Datum.

Figure 911 illustrates variations in the ranges and heights of tides in a locality such as the Indian Ocean, where predicted and observed water levels are referenced to a chart sounding datum that will always cause them to be additive relative to the charted depth.

In some areas where there is little or no tide, such as the Baltic Sea, mean sea level (MSL) is used as chart datum. This is the average height of the surface of the sea for all stages of the tide over a 19 year period. This may differ slightly from half-tide level, which is the level midway between mean high water and mean low water.

Inconsistencies of terminology are found among charts of different countries and between charts issued at different times. Large-scale charts usually specify the datum of soundings and may contain a tide note giving mean heights of the tide at one or more places on the chart. These heights are intended merely as a rough guide to the change in depth to be expected under the specified conditions. They should not be used for the prediction of heights on any particular day, which should be obtained from tide tables.
*
912.	High Water Datums*
Heights of terrestrial features are usually referred on nautical charts to a high water datum. This gives the mariner a margin of error when passing under bridges, overhead cables, and other obstructions. The one used on charts of the United States, its territories and possessions, and widely used elsewhere, is mean high water (MHW), which is the average height of all high waters over a 19 year period. Any other high water datum in use on charts is likely to be higher than this. Other high water datums are mean high water springs (MHWS), which is the average level of the high waters that occur at the time of spring tides; mean higher high water (MHHW), which is the average height of the higher high waters of each tidal day; and tropic higher high water (TcHHW), which is the average height of the higher high waters (or the single daily high waters if the tide becomes diurnal) that occur when the moon is near maximum declination and the diurnal effect is most pronounced.
A reference merely to &#8220;high water&#8221; leaves some doubt as to the specific level referred to, for the height of high water varies from day to day. Where the range is large, the variation during a 2 week period may be considerable.
Because there are periodic and apparent secular trends in sea level, a specific 19 year cycle (the National Tidal Datum Epoch) is issued for all United States datums. The National Tidal Datum Epoch officially adopted by the National Ocean Service is presently 1960 through 1978. The Epoch is periodically reviewed for revision.

*TIDAL CURRENTS
913.	Tidal And Nontidal Currents*
Horizontal movement of water is called current. It may be either &#8220;tidal&#8221; and &#8220;nontidal.&#8221; Tidal current is the periodic horizontal flow of water accompanying the rise and fall of the tide. Nontidal current includes all currents not due to the tidal movement. Nontidal currents include the permanent currents in the general circulatory system of the oceans as well as temporary currents arising from meteorological conditions. The current experienced at any time is usually a combination of tidal and nontidal currents.

*914.	General Features*
Offshore, where the direction of flow is not restricted by any barriers, the tidal current is rotary; that is, it flows continuously, with the direction changing through all points of the compass during the tidal period. This rotation is caused by the earth&#8217;s rotation, and unless modified by local conditions, is clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The speed usually varies throughout the tidal cycle, passing through two maximums in approximately opposite directions, and two minimums about halfway between the maximums in time and direction.

Rotary currents can be depicted as in Figure 914a, by a series of arrows representing the direction and speed of the current at each hour. This is sometimes called a current rose. Because of the elliptical pattern formed by the ends of the arrows, it is also referred to as a current ellipse.










In rivers or straits, or where the direction of flow is more or less restricted to certain channels, the tidal current is reversing; that is, it flows alternately in approximately opposite directions with an instant or short period of little or no current, called slack water, at each reversal of the current. During the flow in each direction, the speed varies from zero at the time of slack water to a maximum, called strength of flood or ebb, about midway between the slacks. Reversing currents can be indicated graphically, as in Figure 914b, by arrows that represent the speed of the current at each hour.










The flood is usually depicted above the slack waterline and the ebb below it. The tidal current curve formed by the ends of the arrows has the same characteristic sine form as the tide curve. In illustrations and for certain other purposes it is convenient to omit the arrows and show only the curve.
A slight departure from the sine form is exhibited by the reversing current in a strait, such as East River, New York, that connects two tidal basins. The tides at the two ends of a strait are seldom in phase or equal in range, and the current, called hydraulic current, is generated largely by the continuously changing difference in height of water at the two ends. The speed of a hydraulic current varies nearly as the square root of the difference in height. The speed reaches a maximum more quickly and remains at strength for a longer period than shown in Figure 914b, and the period of weak current near the time of slack is considerably shortened.

The current direction, or set, is the direction toward which the current flows. The speed is sometimes called the drift. The term &#8220;velocity&#8221; is often used as the equivalent of &#8220;speed&#8221; when referring to current, although strictly speaking &#8220;velocity&#8221; implies direction as well as speed. The term &#8220;strength&#8221; is also used to refer to speed, but more often to greatest speed between consecutive slack waters. The movement toward shore or upstream is the flood, the movement away from shore or downstream is the ebb. In a purely semidiurnal current unaffected by nontidal flow, the flood and ebb each last about 6 hours and 13 minutes. But if there is either diurnal inequality or nontidal flow, the durations of flood and ebb may be quite unequal.

*915.	Types Of Tidal Current*
Tidal currents, like tides, may be of the semidiurnal, diurnal, or mixed type, corresponding to a considerable degree to the type of tide at the place, but often with a stronger semidiurnal tendency.
The tidal currents in tidal estuaries along the Atlantic coast of the United States are examples of the semidiurnal type of reversing current. Along the Gulf of Mexico coast, such as at Mobile Bay entrance, they are almost purely diurnal. At most places, however, the type is mixed to a greater or lesser degree. At Tampa and Galveston entrances there is only one flood and one ebb each day when the moon is near its maximum declination, and two floods and two ebbs each day when the moon is near the equator. Along the Pacific coast of the United States there are generally two floods and two ebbs every day, but one of the floods or ebbs has a greater speed and longer duration than the other, the inequality varying with the declination of the moon. The inequalities in the current often differ considerably from place to place even within limited areas, such as adjacent passages in Puget Sound and various passages between the Aleutian Islands. Figure 915a shows several types of reversing current. Figure 915b shows how the flood disappears as the diurnal inequality increases at one station.



















Offshore rotary currents that are purely semidiurnal repeat the elliptical pattern each tidal cycle of 12 hours and 25 minutes. If there is considerable diurnal inequality, the plotted hourly current arrows describe a set of two ellipses of different sizes during a period of 24 hours and 50 minutes, as shown in Figure 915c, and the greater the diurnal inequality, the greater the difference between the sizes of the two ellipses. In a completely diurnal rotary current, the smaller ellipse disappears and only one ellipse is produced in 24 hours and 50 minutes.










*916.	Tidal Current Periods And Cycles*
Tidal currents have periods and cycles similar to those of the tides, and are subject to similar variations, but flood and ebb of the current do not necessarily occur at the same times as the rise and fall of the tide.

The speed at strength increases and decreases during the 2 week period, month, and year along with the variations in the range of tide. Thus, the stronger spring and perigean currents occur near the times of new and full moon and near the times of the moon&#8217;s perigee, or at times of spring and perigean tides; the weaker neap and apogean currents occur at the times of neap and apogean tides; and tropic currents with increased diurnal speeds or with larger diurnal inequalities in speed occur at times of tropic tides; and equatorial currents with a minimum diurnal effect occur at times of equatorial tides.
As with the tide, a mean value represents an average obtained from a 19 year series. Since a series of current observations is usually limited to a few days, and seldom covers more than a month or two, it is necessary to adjust the observed values, usually by comparison with tides at a nearby place, to obtain such a mean.

*917.	Effect Of Nontidal Flow*
The current existing at any time is seldom purely tidal, but usually includes also a nontidal current that is due to drainage, oceanic circulation, wind, or other causes. The method in which tidal and nontidal currents combine is best explained graphically, as in Figure 917a and Figure 917b.










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## Fishers of Men

*ch 9 cont*









The pattern of the tidal current remains unchanged, but the curve is shifted from the point or line from which the currents are measured, in the direction of the nontidal current, and by an amount equal to it. It is sometimes more convenient graphically merely to move the line or point of origin in the opposite direction.
Thus, the speed of the current flowing in the direction of the nontidal current is increased by an amount equal to the magnitude of the nontidal current, and the speed of the current flowing in the opposite direction is decreased by anequal amount.

In Figure 917a, a nontidal current is represented both in direction and speed by the vector AO. Since this is greater than the speed of the tidal current in the opposite direction, the point A is outside the ellipse. The direction and speed of the combined tidal and nontidal currents at any time is represented by a vector from A to that point on the curve representing the given time, and can be scaled from the graph. 

The strongest and weakest currents may no longer be in the directions of the maximum and minimum of the tidal current. In a reversing current (Figure 917b), the effect is to advance the time of one slack, and to retard the following one. If the speed of the nontidal current exceeds that of the reversing tidal current, the resultant current flows continuously in one direction without coming to a slack. 

In this case, the speed varies from a maximum to a minimum and back to a maximum in each tidal cycle. In Figure 917b, the horizontal line A represents slack water if only tidal currents are present. Line B represents the effect of a 0.5 knot nontidal ebb, and line C the effect of a 1.0 knot nontidal ebb. With the condition shown at C there is only one flood each tidal day. If the nontidal ebb were to increase to approximately 2 knots, there would be no flood, two maximum ebbs and two minimum ebbs occurring during a tidal day.

*918. Time Of Tidal Current And Time Of Tide*
At many places where current and tide are both semidiurnal, there is a definite relationship between times of current and times of high and low water in the locality. Current atlases and notes on nautical charts often make use of this relationship by presenting for particular locations, the direction and speed of the current at each succeeding hour after high and low water, at a place for which tide predictions are available.

Where there is considerable diurnal inequality in tide or current, or where the type of current differs from the type of tide, the relationship is not constant, and it may be hazardous to try to predict the times of current from times of tide. Note the current curve for Unimak Pass in the Aleutians in Figure 915a. It shows the current as predicted in the tidal current tables. Predictions of high and low waters in the tide tables might have led one to expect the current to change from flood to ebb in the late morning, whereas actually the current continued to run flood with some strength at that time.

Since the relationship between times of tidal current and tide is not everywhere the same, and may be variable at the same place, one should exercise extreme caution in using general rules. The belief that slacks occur at local high and low tides and that the maximum flood and ebb occur when the tide is rising or falling most rapidly may be approximately true at the seaward entrance to, and in the upper reaches of, an inland tidal waterway. But generally this is not true in other parts of inland waterways. When an
inland waterway is extensive or its entrance constricted, the slacks in some parts of the waterway often occur midway between the times of high and low tide. Usually in such waterways the relationship changes from place to place as one progresses upstream, slack water getting progressively closer in time to the local tide maximum until at the head of tidewater (the inland limit of water affected by a tide) the slacks occur at about the times of high and low tide.
*
919.	Relationship Between Speed Of Current And Range Of Tide*
The speed of the tidal current is not necessarily consistent with the range of tide. It may be the reverse. For example, currents are weak in the Gulf of Maine where the tides are large, and strong near Nantucket Island and in Nantucket Sound where the tides are small. However, at any one place the speed of the current at strength of flood and ebb varies during the month in about the same proportion as the range of tide, and this relationship can be used to determine the relative strength of currents on any given day.
*
920.	Variation Across An Estuary*
In inland tidal estuaries the time of tidal current varies across the channel from shore to shore. On the average, the current turns earlier near shore than in midstream, where the speed is greater. Differences of half an hour to an hour are not uncommon, but the difference varies and the relationship may be nullified by the effect of nontidal flow.

The speed of the current also varies across the channel, usually being greater in midstream or midchannel than near shore, but in a winding river or channel the strongest currents occur near the concave shore, or the outside corner of the curve. Near the opposite (convex) shore the currents are weak or eddying.

*921.	Variation With Depth*
In tidal rivers the subsurface current acting on the lower portion of a ship&#8217;s hull may differ considerably from the surface current. An appreciable subsurface current may be present when the surface movement appears to be practically slack, and the subsurface current may even be flowing with appreciable speed in the opposite direction to the surface current.

In a tidal estuary, particularly in the lower reaches where there is considerable difference in density from top to bottom, the flood usually begins earlier near the bottom than at the surface. The difference may be an hour or two, or as little as a few minutes, depending upon the estuary, the location in the estuary, and freshet conditions. Even when the freshwater runoff becomes so great as to prevent the surface current from flooding, it may still flood below the surface. The difference in time of ebb from surface to bottom is normally small but subject to variation with time and location.

The ebb speed at strength usually decreases gradually from top to bottom, but the speed of flood at strength often is stronger at subsurface depths than at the surface.

*922.	Tidal Current Observations*
Observations of current are made with sophisticated electronic current meters. Current meters are suspended from a buoy or anchored to the bottom with no surface marker at all. Very sensitive current meters measure and record deep ocean currents; these are later recovered by triggering a release mechanism with a signal from the surface. Untended current meters either record data internally or send it by radio to a base station on ship or land. The period of observation varies from a few hours to as long as 6 months.

*TIDE AND CURRENT PREDICTION
923.	Tidal Height Predictions*
To measure tides, hydrographers select a reference level, or datum. Soundings shown on the largest scale charts are the vertical distances from this datum to the bottom. At any given time the actual depth is this charted depth plus the height of tide. In most places the reference level is some form of low water. But all low waters at a given place are not the same height, and the selected reference level is seldom the lowest tide occurring at the place. When lower tides occur, these are indicated in the tide tables by a negative sign. Thus, at a spot where the charted depth is 15 feet, the actual depth is 15 feet plus the tidal height. When the tide is three feet, the depth is 15 + 3 = 18 feet. When it is (-) 1 foot, the depth is 15 - 1 = 14 feet. The actual depth can be less than the charted depth. In an area where there is a considerable range of tide (the difference between high water and low water), the height of tide might be an important consideration when using soundings to determine if the vessel is in safe water.

The heights given in the tide tables are predictions, and when assumed conditions vary considerably, the predictions shown may be considerably in error. Heights lower than predicted can be anticipated when the atmospheric pressure is higher than normal, or when there is a persistent strong offshore wind. The greater the range of tide, the less reliable are the predictions for both height and current.

*924.	Tidal Heights*
The nature of the tide at any place can best be determined by observation. The predictions in tide tables and the tidal data on nautical charts are based upon detailed observations at specific locations, instead of theoretical predictions.

Tidal elevations are usually observed with a continuously recording gage. A year of observations is the minimum length desirable for determining the harmonic constants used in prediction. For establishing mean sea level and long-term changes in the relative elevations of land and sea, as well as for other special uses, observations have been made over periods of 20, 30, and even 120 years at important locations.

Observations for a month or less will establish the type of tide and suffice for comparison with a longer series of observations to determine tidal differences and constants.

Mathematically, the variations in the lunar and solar tide-producing forces, such as those due to changing phase, distance, and declination, are considered as separate constituent forces, and the harmonic analysis of observations reveals the response of each constituent of the tide to its corresponding force. At any one place this response remains constant and is shown for each constituent by harmonic constants which are in the form of a phase angle for the time relation and an amplitude for the height. Harmonic constants are used in making technical studies of the tide and in tidal predictions on computers. The tidal predictions in most published tide tables are produced by computer.

*925.	Meteorological Effects*
The foregoing discussion of tidal behavior assumes normal weather conditions. However, sea level is also affected by wind and atmospheric pressure. In general, onshore winds raise the level and offshore winds lower it, but the amount of change varies at different places. During periods of low atmospheric pressure, the water level tends to be higher than normal. For a stationary low, the increase in elevation can be found by the formula
R0=0.01(1010 - P), in which R0 is the increase in elevation in meters and P is the atmospheric pressure in millibars. This is equal approximately to 1 centimeter per millibar depression, or about 1 foot (13.6 inches) per inch depression. For a moving low, the increase in elevation is given by the formula 










in which R is the increase in elevation in feet, R0 is the increase in meters for a stationary low, C is the rate of motion of the low in feet per second, g is the acceleration due to gravity (32.2 feet per second per second), and h is the depth of water in feet.

Where the range of tide is very small, the meteorological effect may sometimes be greater than the normal tide.
Where a body of water is large in area but shallow, high winds can push the water from the windward to the lee shore, creating much greater local differences in water levels than occurs normally, and partially or completely masking the tides. The effect is dependent on the configuration and depth of the body of water relative to the wind direction, strength and duration.


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## Fishers of Men

*ch 9 cont.
926 Tidal Current Predictions*
Tidal currents are due primarily to tidal action, but other causes are often present. The Tidal Current Tables give the best prediction of total current. Following heavy rains or a drought, a river&#8217;s current prediction may be considerably in error. Current alters a vessel&#8217;s course and velocity. Set and drift may vary considerably over different parts of a harbor, because differences in bathymetry from place to place affect current. Since this is usually an area where small errors in a vessel&#8217;s position are crucial, a knowledge of predicted currents, particularly in reduced visibility, is important. Strong currents occur mostly in narrow passages connecting larger bodies of water. Currents of more than 5 knots are sometimes encountered in the Golden Gate at San Francisco, and currents of more than 13 knots sometimes occur at Seymour Narrows, British Columbia.

In straight portions of rivers and channels, the strongest currents usually occur in the middle of the channel. In curved portions the swiftest currents (and deepest water) usually occur near the outer edge of the curve. Countercurrents and eddies may occur on either side of the main current of a river or narrow passage, especially near obstructions and in bights.

In general, the range of tide and the velocity of tidal current are at a minimum in the open ocean or along straight coasts. The greatest tidal effects are usually encountered in estuaries, bays, and other coastal indentations. A vessel proceeding along a indented coast may encounter a set toward or away from the shore; a similar set is seldom experienced along a straight coast.

*927. Prediction Tables*
Predictions of tides and currents have been published by the National Ocean Service (NOS) since 1853. They are published annually, and are supplemented by tidal current charts. Usually, tidal information is obtained from tide and tidal current tables, or from specialized computer software or calculators. However, if these are not available, or if they do not include information at a desired place, the mariner may be able to obtain locally the mean high water lunitidal interval or the high water full and change. The approximate time of high water can be found by adding either interval to the time of transit (either upper or lower) of the moon. Low water occurs approximately &#188; tidal day (about 6h 12m) before and after the time of high water. The actual interval varies somewhat from day to day, but approximate results can be obtained in this manner. Similar information for tidal currents (lunicurrent interval) is seldom available.

*PUBLICATIONS FOR PREDICTING TIDES AND CURRENTS
928.	Tide Tables*
Tide tables for various parts of the world are published in 4 volumes by the National Ocean Service. These volumes are:
Central and Western Pacific Ocean and Indian Ocean
East Coast of North and South America (including Greenland)
Europe and West Coast of Africa
West Coast of North and South America (including Hawaiian Islands)
A small separate volume, the Alaskan Supplement, is also published.
Each volume has 5 common tables:
Table 1 contains a complete list of the predicted times and heights of the tide for each day of the year at a number of places designated as reference stations.
Table 2 gives tidal differences and ratios which can be used to modify the tidal information for the reference stations to make it applicable to a relatively large number of subordinate stations.
Table 3 provides information for finding the approximate height of the tide at any time between high water and low water.
Table 4 is a sunrise-sunset table at five-day intervals for various latitudes from 76&#61616;N to 60&#61616;S (40&#61616;S in one volume).
Table 5 provides an adjustment to convert the local mean time of table 4 to zone or standard time. For the East Coast and West Coast volumes, each contains a table 6, a moonrise and moonset table; table 7 for conversion from feet to centimeters; table 8, a table of estimated tide prediction accuracies; a glossary of terms; and an index to stations. Each table is preceded by a complete explanation. Sample problems are given where necessary. The inside back cover of each volume contains a calendar of critical astronomical data to help explain the variations of the tide during each month and throughout the year.

*929.	Tide Predictions For Reference Stations*
For each day, the date and day of week are given, and the time and height of each high and low water are listed in chronological order. Although high and low waters are not labeled as such, they can be distinguished by the relative heights given immediately to the right of the times. If two high tides and two low tides occur each tidal day, the tide is semidiurnal. Since the tidal day is longer than the civil day (because of the revolution of the moon eastward around the earth), any given tide occurs later each day. Because of later times of corresponding tides from day to day, certain days have only one high water or only one low water.
*
930.	Tide Predictions For Subordinate Stations*
For each subordinate station listed, the following information is given:
1.	Number. The stations are listed in geographical order and assigned consecutive numbers. Each volume contains an alphabetical station listing correlating the station with its consecutive number to assist in locating the entry in table 2.
2.	Place. The list of places includes both subordinate and
reference stations; the latter appear in bold type.
3.	Position. The approximate latitude and longitude are given to assist in locating the station. The latitude is north or south, and the longitude east or west, depending upon the letters (N, S, E, W) next above the entry. These may not be the same as those at the top of the column.
4.	Differences. The differences are to be applied to the predictions for the reference station, shown in capital letters above the entry. Time and height differences are given separately for high and low waters. Where differences are omitted, they are either unreliable or unknown.
5.	Ranges. Various ranges are given, as indicated in the tables.
In each case this is the difference in height between high water and low water for the tides indicated.

*Mean tide level. *This is the average between mean low and mean high water, measured from chart datum.

The time difference is the number of hours and minutes to be applied to the reference station time to find the time of the corresponding tide at the subordinate station.

This interval is added if preceded by a plus sign (+) and subtracted if preceded by a minus sign (-). The results obtained by the application of the time differences will be in the zone time of the time meridian shown directly above the difference for the subordinate station. Special conditions occurring at a few stations are indicated by footnotes on the applicable pages. In some instances, the corresponding tide falls on a different date at reference and subordinate stations.

Height differences are shown in a variety of ways. For most entries, separate height differences in feet are given for high water and low water. These are applied to the height given for the reference station. In many cases a ratio is given for either high water or low water, or both. The height at the reference station is multiplied by this ratio to find the height at the subordinate station. For a few stations, both a ratio and difference are given. In this case the height at the reference station is first multiplied by the ratio, and the difference is then applied. An example is given in each volume of tide tables. Special conditions are indicated in the table or by footnote. For example, a footnote indicates that &#8220;Values for the Hudson River above George Washington Bridge are based upon averages for the six months May to October, when the fresh-water discharge is a minimum.&#8221;

*931.	Finding Height Of Tide At Any Time*
Table 3 provides means for determining the approximate height of tide at any time. It assumes that plotting height versus time yields a sine curve. Actual values may vary from this. The explanation of the table contains directions for both mathematical and graphic solutions. Though the mathematical solution is quicker, if the vessel&#8217;s ETA changes significantly, it will have to be done for the new ETA. Therefore, if there is doubt about the ETA, the graphical solution will provide a plot of predictions for several hours and allow quick reference to the predicted height for any given time. This method will also quickly show at what time a given depth of water will occur. Figure 931a shows the OPNAV form used to calculate heights of tides. Figure 931b shows the importance of calculating tides in shallow water.



















*932.	Tidal Current Tables*
Tidal current tables are somewhat similar to tide tables, but the coverage is less extensive. NOS publishes 2 volumes on an annual basis: Atlantic Coast of North America, and Pacific Coast of North America and Asia. Each of the two volumes is arranged as follows:

Table 1 contains a complete list of predicted times of maximum currents and slack water, with the velocity (velocity) of the maximum currents, for a number of reference stations.
Table 2 gives differences, ratios, and other information related to a relatively large number of subordinate stations.
Table 3 provides information to determine the current&#8217;s velocity at any time between entries in tables 1 and 2.
Table 4 gives duration of slack, or the number of minutes the current does not exceed stated amounts, for various maximum velocities.
Table 5 (Atlantic Coast of North America only) gives information on rotary tidal currents.

Each volume also contains current diagrams and instructions for their use. Explanations and examples are given in each table.
The volumes also contain general descriptive information on wind-driven currents, combination currents, and information such as Gulf Stream currents for the east coast and coastal currents on the west coast.

*933.	Tidal Current Prediction For Reference Stations*
For each day, the date and day of week are given; current information follows. If the cycle is repeated twice each tidal day, currents are semidiurnal. On most days there are four slack waters and four maximum currents, two floods (F) and two ebbs (E). However, since the tidal day is longer than the civil day, the corresponding condition occurs later each day, and on certain days there are only three slack waters or three maximum currents. At some places, the current on some days runs maximum flood twice, but ebb only once, a minimum flood occurring in place of the second ebb. The tables show this information.

*934.	Tidal Current Predictions For Subordinate Stations*
For each subordinate station listed in table 2 of the tidal current tables, the following information is given:
1.	Number. The stations are listed in geographical order and assigned consecutive numbers, as in the tide tables. Each volume contains an alphabetical station listing correlating the station with its consecutive number to assist in locating the entry in table 2.
2.	Place. The list of places includes both subordinate and reference stations, the latter given in bold type.
3.	Position. The approximate latitude and longitude are given to assist in locating the station. The latitude is north or south and the longitude east or west as indicated by the letters (N, S, E, W) next above the entry. The current given is for the center of the channel unless another location is indicated by the station name.
4.	Time difference. Two time differences are tabulated.
One is the number of hours and minutes to be applied to the tabulated times of slack water at the reference station to find the times of slack waters at the subordinate station. The other time difference is applied to the times of maximum current at the reference station to find the times of the corresponding maximum current at the subordinate station. The intervals, which are added or subtracted in accordance with their signs, include any difference in time between the two stations, so that the answer is correct for the standard time of the subordinate station. Limited application and special conditions are indicated by footnotes.
5.	Velocity ratios. Speed of the current at the subordinate station is the product of the velocity at the reference station and the tabulated ratio. Separate ratios may be given for flood and ebb currents. Special conditions are indicated by footnotes.
6.	Average Speeds and Directions. Minimum and maximum velocities before flood and ebb are listed for each station, along with the true directions of the flow. Minimum velocity is not always 0.0 knots.
*
935.	Finding Velocity Of Tidal Current At Any Time*
Table 3 of the tidal current tables provides means for determining the approximate velocity at any time. Directions are given in an explanation preceding the table. Figure
935 shows the OPNAV form used for current prediction.










*936.	Duration Of Slack Water*
The predicted times of slack water listed in the tidal current tables indicate the instant of zero velocity. There is a period each side of slack water, however, during which the current is so weak that for practical purposes it may be considered negligible. Table 4 of the tidal current tables gives, for various maximum currents, the approximate period of time during which currents not exceeding 0.1 to 0.5 knots will be encountered. This period includes the last of the flood or ebb and the beginning of the following flood or ebb; that is, half of the duration will be before and half after the time of slack water.

When there is a difference between the velocities of the maximum flood and ebb preceding and following the slack for which the duration is desired, it will be sufficiently accurate to find a separate duration for each maximum velocity and average the two to determine the duration of the weak current. Of the two sub-tables of table 4, table A is used for all places except those listed for table B; table B is used for just the places listed and the stations in table 2 which are referred to them.

*937.	Additional Tide Prediction Publications*
NOS also publishes a special Regional Tide and Tidal Current Table for New York Harbor to Chesapeake Bay, and a Tidal Circulation and Water Level Forecast Atlas for Delaware River and Bay.
*
938.	Tidal Current Charts*
Tidal Current charts present a comprehensive view of the hourly velocity of current in different bodies of water. They also provide a means for determining the current&#8217;s velocity at various locations in these waters. The arrows show the direction of the current; the figures give the speed in knots at the time of spring tides. A weak current is defined as less than 0.1 knot. These charts depict the flow of the tidal current under normal weather conditions. Strong winds and freshets, however, may cause nontidal currents, considerably modifying the velocity indicated on the charts.

Tidal Current charts are provided (1994) for Boston Harbor, Charleston Harbor SC, Long Island Sound and Block Island Sound, Narragansett Bay, Narragansett Bay to Nantucket Sound, Puget Sound (Northern Part), Puget Sound (Southern Part), Upper Chesapeake Bay, and Tampa Bay.

The tidal current&#8217;s velocity varies from day to day as a function of the phase, distance, and declination of the moon. Therefore, to obtain the velocity for any particular day and hour, the spring velocities shown on the charts must be modified by correction factors. A correction table given in the charts can be used for this purpose. All of the charts except Narragansett Bay require the use of the annual Tidal Current Tables. Narragansett Bay requires use of the annual Tide Tables.

*939.	Current Diagrams*
A current diagram is a graph showing the velocity of the current along a channel at different stages of the tidal current cycle. The current tables include diagrams for Martha&#8217;s Vineyard and Nantucket Sounds (one diagram); East River, New York; New York Harbor; Delaware Bay and River (one diagram); and Chesapeake Bay.

On Figure 939, each vertical line represents a given instant identified by the number of hours before or after slack water at The Narrows. Each horizontal line represents a distance from Ambrose Channel entrance, measured along the usually traveled route. The names along the left margin are placed at the correct distances from Ambrose Channel entrance. The current is for the center of the channel opposite these points. The intersection of any vertical line with any horizontal line represents a given moment in the current cycle at a given place in the channel. If this intersection is in a shaded area, the current is flooding; if in an unshaded area, it is ebbing. The velocity can be found by interpolation between the numbers given in the diagram. The given values are averages. To find the value at any time, multiply the velocity found from the diagram by the ratio of maximum velocity of the current involved to the maximum shown on the diagram. If the diurnal inequality is large, the accuracy can be improved by altering the width of the shaded area to fit conditions. The diagram covers 1 &#189; current cycles, so that the right 1/3 duplicates the left 1/3.










Use table 1 or 2 to determine the current for a single station. The current diagrams are intended for use in either of two ways: to determine a favorable time for passage through the channel and to find the average current to be expected during a passage through the channel. For both of these uses, a number of &#8220;velocity lines&#8221; are provided. When the appropriate line is transferred to the correct part of the diagram, the current to be encountered during passage is indicated along the line.

If the transferred velocity line is partly in a flood current area, all ebb currents (those increasing the ship&#8217;s velocity) are given a positive sign (+), and all flood currents a negative sign (-). A separate ratio should be determined for each current (flood or ebb), and applied to the entries for that current. In the Chesapeake Bay, it is common for an outbound vessel to encounter three or even four separate currents during passage. Under the latter condition, it isgood practice to multiply each current taken from the diagram by the ratio for the current involved.

If the time of starting the passage is fixed, and the current during passage is desired, the starting time is identified in terms of the reference tidal cycle. The velocity line is then drawn through the intersection of this vertical time line and the horizontal line through the place. The average current is then determined in the same manner as when the velocity line is located as described above.

*940.	Computer Predictions*
Until recently, tidal predictions were compiled only on mainframe or minicomputers and then put into hardcopy table form for the mariner. There are several types of commercial software available now for personal computers (PC&#8217;s) that provide digital versions of the NOS tide tables and also provide the capability to graph the tidal heights. The tabular information and graphs can be printed for the desired locations for pre-voyage planning. There are also several types of specialized hand-held calculators and tide clocks that can be used to predict tides for local areas.
Newer versions of PC software use the actual harmonic constants available for locations, the prediction equation, and digital versions of table 2 in the Tide Tables to produce even more products for the navigator&#8217;s use.

Emerging applications include integration of tidal prediction with positioning systems and vessel traffic systems which are now moving towards full use of GPS. In addition, some electronic chart systems are already able to integrate tide prediction information. Many of these new systems will also use real-time water level and current information. Active research also includes providing predictions of total water level that will include not only the tidal prediction component, but also the weather-related component.

*I will post examples of the substations.*
* 
Conclusion ch 9*


----------



## Fishers of Men

reel said:


> Very thorough but going by the book doesn't leave much time to fish.
> Seriously this is excellent reading.
> Keep up the good work.
> ...


LOL, yep, no time to fish, just go cruising. We _know _that everyone is going to run right out and buy a bunch of stuff they don't need and have room on the small boats for a chart table too! 

Maybe we could get into some "do these shortcuts at your own risk" later after there is a good understanding out there of what...Naw, not a good idea.

I see a lot of people purchasing GPS-fishfinders and cant for the life of me figure out why? I think it is a marketing ploy, just like some lures are to catch fishermen. So... you have a position and see fish... big deal, one goes out, you lose 2 units of aids.  

If they wanted a combo unit, why not just purchase a chartplotter, then they can see and do *everything* that a GPS doesn't give, have better control and have their original units for a backup...until the solar flares knock out the GPS...Oh, ya, then we still have a view of the contours to follow and a chart right in front of us...   :T :T :T


----------



## Fishers of Men

okay, I didn't feel like working on this today, so, here is my daily donation, some good info:









http://i202.photobucket.com/albums/aa305/FishersofMen/geographicrange.jpg


----------



## Fishers of Men

*EVERYONE READY FOR A VIRTUAL INLAND BOAT RIDE?*
Before going further, I would like to present this in another view for the new guys to GPS. Read your manual for your particular unit. We are going to go for a virtual boat ride NOW.

Your GPS communicates data to you via a series of screens screen is intended to present a set of information in a unique way. In many models, some of the same material may appear on several screens. The summary below indicates the principal purpose of each screen and when you might consider using it.

Satellite Screen &#8212; This screen provides information about the quality of your GPS position and the operation of the receiver. Typically, a skymap showing the horizon (outer ring) and 450 above the horizon (inner ring) will pro vide the locations and identifying numbers of the satellites in view. Vertical bar graphs indicate the signal strengths from the satellites. Often a bar will be darkened to indicate that the receiver is processing information from that satellite. A hollow bar usually indicates that a satellite signal has been received but is not yet providing navigation information to the receiver. A narrative field usually indicates the status of the positioning process: Acquiring Satellites, 2-D Position, 3-D Position, or other cue. 3-D positions are best. Often an estimated position error (EPE) field will provide an estimated accuracy for the current configuration of satellites.

Position Screen &#8212; This screen may be separate or combined with another, such as the Satellite Screen. Its primary function is to provide the current position of the receiver (usually in latitude and longitude coordinates &#8212; as set up by the user). It also may show time and a variety of other data fields.

Map Screen &#8212; Often considered the most useful page, the Map Screen is only as valuable as the information stored in the unit. The Map Screen indicates your current position and direction of motion, usually via a pointer or arrow on a two- dimensional display. If other objects or places are stored in the GPS, their relative positions will be shown on the Map Screen, within the limits of the current field of view. On most GPS models, the map screen shows only stored waypoints and objects, not a map or chart. Without the chart, the Map Screen is of limited utility, but it can help you orient yourself with respect to other stored points. If a waypoint is selected for navigation, a line will be displayed on the Map Screen from the place where the way point was activated directly to the way point. In addition, if the Track feature is activated, the Map Screen will show a dotted line representing where you have been.

Highway Screen &#8212; In the absence of a real chart on the Map Screen, the Highway Screen is probably the most useful on your GPS. If a waypoint is selected for navigation, a 3-D imaginary &#8220;highway&#8221; is depicted on the screen, representing the path from the point at which you activated the waypoint directly to the waypoint. By following the path, you will be on the direct course line between those two points. The Highway Screen has good visual impact and is easy to interpret.

Compass Screen &#8212; The GPS is not a compass, so this title is a misnomer. The GPS indicates an accurate direction ONLY if you are moving. The Compass Screen shows the direction of motion, often as a simulated compass card; and if you have selected a waypoint for navigation, it will indicate the direction to that waypoint. This screen is generally considered to be more useful to hikers than to boaters.

*A lot of people make the mistake of not taking compass readings because of this.*

Menu Screen &#8212; Some GPS models omit the Menu button and use a screen instead. This screen performs the same menu functions. It is just accessed in a different way. Instead of direct access via a button, it is reached by going through the sequence of available screens.

Since the GPS is not a chart, you must plot your position, as reported by the GPS, on a chart at regular intervals in order to relate to your surroundings. Even if your Map Screen has a chart displayed directly, you still should plot your position at regular intervals, just as a backup.

Entering Waypoints into the GPS
The first step is getting the coordinates for waypoints. I have already illustrated the direct means of reading the latitude and longitude of a waypoint, using a pair of dividers. As an alternative, you can utilize your 4 x 15 plotting tool. Align the tool horizontally with the point to be measured and read the latitude on the scale to the side of the chart. Then align the plotter vertically and do the same with longitude.

Other alternatives for getting waypoint coordinates include the following:
1. Use a commercial chart with pre-printed waypoint coordinates.
2. Purchase a waypoint directory with coordinates for your area. (It pays to double-check the coordinates for accuracy.)
3. Mark waypoints while on the water.
4. Use digital charts (like those provided on the USPS Digital Chart CD. ( Join the Power Squadron for advanced classes, it&#8217;s well worth it, not counting all the benefits).

The digital chart approach will be explained in detail shortly. Using digital charts eases the navigator&#8217;s task considerably and, by transferring the coordinates of an observed waypoint directly to the GPS, reduces the tendency to make transcription errors.

Avoiding Errors
There are several opportunities to make an error in working with waypoints. It is essential to double-check and use all of your senses when navigating to a waypoint. The main problem with coordinates is that they are just a set of numbers. They have little intuitive relationship to the real world. You may avoid typical errors by:
1. Accurately transferring the waypoint position to the latitude and longitude scales on the chart.
2. Correctly reading the coordinates from the chart scales.
3. Correctly entering the coordinates into the GPS. (It&#8217;s very easy to transpose digits.)
4. Correctly selecting the correct waypoint for navigation from the list in the GPS.

Naming Waypoints
In order to avoid errors in selecting a way- point, it pays to name them carefully. Most GPS models limit to five or six the number of characters that can be applied to a waypoint name. Within those constraints, you should have names that will be easy to distinguish. It also is a good idea to note your GPS way- point names on your chart, so that you clearly understand which waypoint corresponds with which point on the chart.

TIP:
The following tip appears in GPS for Mariners.

Consider a naming convention in two parts.
The first two or three characters should reflect the locale of the waypoint. (For example, use &#8220;FH&#8221; for &#8220;Falmouth Harbor,&#8221; &#8220;SN&#8221; for &#8220;Sandy Neck,&#8221; etc.). This provides for easy identification of a group of waypoints and eliminates confusion between navigation aids in different locales that have the same name. In addition, most GPS models present waypoint lists in alphabetical order, so all the waypoints for a given locale will appear grouped together. The remaining characters should reflect what the point represents. For example, if it is a red buoy number &#8220;2&#8221;, you can use simply &#8220;R2&#8221;. With the first two characters representing the location, these latter characters unambiguously identify the aid.

Often waypoints do not relate to a particular locale. It makes sense to create artificial way points where you may wish to turn. The initials &#8220;TP&#8221; can be used for &#8220;Turning Point.&#8221;

Entering Landmarks as Waypoints
Waypoints should not be limited to places on the water. A large part of checking your navigation involves taking bearings on visible landmarks. To compare these bearing with your GPS reading, it is essential that the same landmarks be stored in your GPS. Once stored, they will appear on the Map Screen and the Highway Screen and provide visual references with which you can reinforce your comfort that you are where you should be.
Most GPS models provide for a wide range of symbols to be applied to waypoints. It&#8217;s a good idea to select a symbol other than the basic square usually applied to navigation waypoints as the default symbol.

Entering Hazards as Waypoints
In addition to landmarks and navigation waypoints your GPS can be used to store the coordinates of hazards that you wish to avoid. You can measure the coordinates of dangerous locations on your chart and enter them as you would any waypoint.

However, it is essential that you clearly identify hazard waypoints so you do not accidential1y navigate to them. Using the symbol selection option for these waypoints, choose a unique symbol for hazards. One highly appropriate option is the skull and crossbones symbol available on many units.
Also, select names that correspond with the type of hazard, such as SNRK1, for &#8220;Sandy Y Rock No. 1.

What the GPS does when you select a Waypoint
Once you have selected and activated a way- point for navigation, your GPS immediately begins the following process:
1. The GPS computes the course to the new waypoint. It also computes the bearing and distance from the current location to the waypoint.
2. It plots a line corresponding to the activated course on the Map Screen.
3. It creates a highway on the Highway Screen corresponding to the course line.

*What the GPS does not do:*
To reiterate, the GPS has no knowledge of what lies at your current position or along the computed course line. It is your job to discover that by plotting on a chart your current position and the course line to the activated waypoint. You will need to ensure that this path is clear of obstacles that could endanger your passage.

This is one of the primary reasons that you should pre-qualify paths (legs) on the water. By activating your waypoint from one end of a pre-qualified leg, you can be reasonably assured that the path is clear.

Constructing Routes
You can navigate on the water by selecting a waypoint, proceeding to that waypoint, and then selecting the next waypoint to activate. Thus you navigate from point to point to point.

Alternatively, you can use your GPS to do this for you automatically, using a route. Basically, a route is nothing more than a sequential program of stored waypoints that the GPS executes on the water.

When you construct a route on your GPS, you will be asked to insert the names of stored waypoints in the order which you wish to navigate to them.
Once the route is constructed, your GPS computes and displays the course for each leg, the length of each leg, and the cumulative distances to each waypoint. Usually, the GPS will use the names of the first and last waypoints as the route name. On many models, it is possible to make a name that reflects the route. Generally, it is better to let the GPS construct the name.

Skill &#8212; Checking Waypoints
A skill that allows the navigator to verify that the correct position coordinates have been entered into the GPS. Most errors in GPS input occur by transposing numbers in the coordinates.
1. Determine the position coordinates of a waypoint and enter the waypoint coordinates into the GPS.
2. Pre-plot the course and distance between your current position and the waypoint, using the course plotter.
3. Check the GPS by comparing the data from the pre-plotted course to the data fields in the GPS for a given waypoint.
4. Using the GoTo button on the GPS, enter the desired waypoint and verify that the GPS direction and distance to it are close to the direction and distance shown on the pre-plotted course.
5. If they are not, re-check the coordinates of the waypoint and verify that the GPS input was correct.
*
I am going to try to make a 4 part exercise work here.
I hope you can print this chart out in 2 sections and tape it together to use. I don&#8217;t know if I saved it right but it should go on 2- 8X10 sheets. Or maybe you can size it accordingly. Somebody let me know if it works, and if so, you might want to print an extra set just to have to make copies, you will need them as we go along. Also if you don&#8217;t have any plotting tool get 2 straight edges and make do. If you have access to a GPS, get it. If not just follow along. I need some participation here. Also you might want to print this cruise out for future reference.*

EXERCISE 1 Checking Waypoints
OBJECTIVE: Compare plotted waypoints on a chart to information stored in a GPS to identify errors in entering waypoints.
Note: A GPS is not required for this or any of the other exercises. Assume that the way- points identified in the exercise have been entered in your virtual GPS. If you do have a GPS, you may wish to check your work with it.

*Print these 2 charts:*

http://i202.photobucket.com/albums/aa305/FishersofMen/baychart1.jpg

http://i202.photobucket.com/albums/aa305/FishersofMen/baychart2.jpg

Establish and plot the following route and waypoints on a chart and compare them to information entered in your GPS.



















*Study the chart for the areas mentioned. You should be able to figure it out by now, if not don&#8217;t be afraid to ask right away, don&#8217;t wait until I get down the road.
*
EXERCISE 5-2 - Route Planing and Implementation
OBJECTIVE: This is the first of four sequential exercises (EXERCISES 5-2, 5-3, 6-3
and 7-2). Integrate lessons learned to select a route and to implement real time on the water decisions. You guys will create routes, pre-qualify them, plot them with course and distance, select and name waypoints, check GPS plot/entry accuracy, avoid hazards, and use hand held compass bearings and Seaman&#8217;s Eye concepts to validate bearings and fixes.

Create a qualified route from RW &#8220;OR&#8221; Mo (A) to RG &#8220;D&#8221; HR (2+ 1) GONG. Select your vessel of choice and weather options from the lists following. Identify sequence of legs on your route, course and distance of legs, reciprocal courses and waypoint names. Label all courses and waypoints properly. Be pre pared to discuss and justify your decisions. There are many correct plans. Err on the side of safety.

Vessel Options:
a. 32&#8217; sail boat, draws 4.5&#8217;, 45&#8217; mast plus radio antenna and wind instruments on top, max hull speed 6.8 knots.
b. 42&#8217; sport fisherman, draws 3.0&#8217;, 25&#8217; to top of observation tower, max speed 30 knots.
c. 26&#8217; JO, draws 2&#8217;, max speed 20 knots.

Weather Options
a. Partly cloudy, winds 10 to 12 knots from the NE, waves building 3 to 5 feet.
b. Sunny, winds variable 3 to 5 knots from the SW, a great day for boating.
c. Cloudy, winds 12 to 16 knots from the NW, visibility periodically obstructed, light drizzle.

Navigating Using GPS and Waypoints
Don&#8217;t get excited, the following is just to spur your attention for the rest of the exercises. It&#8217;s not that hard.
This section provides the sequence of steps in navigating from waypoint to waypoint using a GPS. The steps in this sequence can be summarized as follows:
I. Activating a Waypoint for Navigation
A. Where are you?
1) Current location at one end of a pre qualified path:
a. Select the waypoint at the other end.
2) Some other location:
a Plot your current location on a chart.
b. Plot the course to the desired way point.
i. Qualify the path.
B. Navigating waypoint to waypoint:
1) Select the stored waypoint of choice.
2) Activate the waypoint.
3) Observe the bearing and distance calculated and displayed by the GPS.
4) Double-check that this is reasonable vis-&#224;-vis the chart.
a. It is easy to inadvertently select the wrong waypoint.
b. Compare bearing and distance: does it match the chart?
C. Using a route
1) Same criteria regarding the current location vis-&#224;-vis the first waypoint.
2) The route activates the first way-point.
H. GPS Calculates and Presents
A. Bearing and distance to the active way point.
B. Course line on the Map Screen corresponding to the active leg.
1) Also all stored waypoints and data within the field of view.
2) If a route is selected, all legs of the route are displayed.
C. 3-D highway on the Highway Screen corresponding to the active leg.
1) Also all stored waypoints and data within the field of view.
2) If a route is selected, all legs of the route are displayed.
Steer	
A. Set heading of boat toward waypoint.
1) Compass (preferred) or GPS course (COG or Track).
2) GPS reports course (to steer) and/or bearing to waypoint.
B. GPS relies upon motion to determine course and speed.
C. GPS is not a compass.
1) Compass is attached to the boat &#8212; shows heading:
a. Direction of the bow.
2) GPS reports course over the ground (Track or COG: movement of boat):
a. Actual motion on the Earth.
D. GPS reports speed over the ground (SOG: movement of boat).
1) Not speed through the water.
a. Impact of currents
IV Intermediate Position
A. GPS Reports
1) Location &#8212; L/Lo coordinates.
2) Distance and bearing to selected way point.
3) Other data:
a. Cross-track error (or off-course):
i. Distance and direction from course line.
b. ETA, ETE
i. Based on current speed and course
B. Locating GPS Position on a Chart
1) Using coordinates
2) Using bearing and distance to active waypoint
3) Using bearing and distance to another waypoint
4) Updates; How to monitor navigation progress using the GPS and plotting position on the chart.

*Were we able to print the charts? Someone?*


----------



## reel

You mention that the GPS is not a compass. true, but
Some GPS units have a built in electronic compasses.
Not necessarily GPS controlled. Most likely magnetic ?

Such as the Garmin Rino 130
https://buy.garmin.com/shop/shop.do?pID=182&tab=rino130
...


----------



## Fishers of Men

reel said:


> You mention that the GPS is not a compass. true, but
> Some GPS units have a built in electronic compasses.
> Not necessarily GPS controlled. Most likely magnetic ?
> 
> Such as the Garmin Rino 130
> https://buy.garmin.com/shop/shop.do?pID=182&tab=rino130
> ...


Reel, trying to keep up with the electronics is unreel (no pun intended)  . By the time you get something figured out, it's up dated or obsolete or something! But I love the electronic days.

Some of the the newer/better versions like you mention would be electronic. The majority of the older or original units only give a readout while you are moving.

A GPS receiver discerns your position on the surface of the earth by measuring the length of time it takes to receive signals from satellites. It cannot, however, tell what direction you are facing while standing still (or moving slowly). So if you are navigating to a waypoint, your GPS can only point you in the correct direction once you are moving.

This is where an electronic compass added feature comes in handy. It can tell what direction you are facing, even while standing still. Not only does this make navigating easier, it also helps with projecting waypoints and orienting paper maps.

Electronic compasses will shorten battery life somewhat. They are typically paired with a barometric altimeter. 

Here is a site with plenty of info on how the electronic compass works. Some units have to be interphased with other equipment.

http://www.nxp.com/acrobat_download/applicationnotes/AN00022_COMPASS.pdf


----------



## Fishers of Men

I didn't get any response on the GPS segment so I don't know if I should move on to something else or finish the GPS exercises. Your call guys. I'm setting here dead in the water for a second.


----------



## Fishers of Men

Alright, I decided to do it anyway. Someone down the line might want the refererence.

EXERCISE 2 Route Planning and Implementation
OBJECTIVE: This is the second of four sequential exercises. Integrate lessons learned to select a route and to implement real time on the water decisions. You will create routes, pre-qualify them, plot them with course and distance, select and name waypoints, check GPS plot/entry accuracy, avoid hazards, and use handheld compass bearings and Seaman&#8217;s Eye concepts to validate bearings and fixes.

Create a qualified route from Perkins Cove to N &#8220;6&#8221; Shark River. Select your vessel of choice. Your weather is as listed. Identify sequence of legs on your route, course and distance of legs, reciprocal courses and waypoint names. Label all courses and waypoints properly. Be prepared to discuss and justify your decisions. There are many correct plans. Err on the side of safety.

Vessel Options:	
a. 32 foot sailboat, draws 4.5 feet, 45 foot mast plus radio antenna and wind instruments on top, max hull speed 6.8 knots.
b. 42 foot sport fisherman, draws 3.0 feet, 25 feet to top of observation tower, max speed 30 knots.
c. 26 foot JO, draws 2 feet, max speed 20 knots.

Weather:
Cloudy, winds 12 to 16 knots from the NW, visibility periodically obstructed to less than one mile, light drizzle.


----------



## Fishers of Men

*3rd sequence*
Monitoring Progress
You pre-qualified the path; now you need to stay on it - or be prepared to re-plan under way. You also need to stay in touch with your environment to ensure that your GPS is functioning properly.
What we will cover here:
b On course with GPS.
What to do if you get off course.
Techniques for staying on course.
Sequentially navigating waypoints.
The &#8220;Seaman&#8217;s Eye.&#8221;
Checking the GPS.
On Course with GPS

You pre-qualified the path (legs) on the water. If you remain on course, you should have little concern relative to charted obstacles. Therefore, your objective is to stay on course. This segment explains how to monitor progress to ensure that you do stay on course. The GPS is an invaluable tool to do that.

Map Screen
Once a waypoint is selected for navigation, an intended course line is drawn on the GPS
Map Screen. Your current position will be indicated by a symbol, such as a black triangle or pointer. Your actual Track (course over the ground) direction will be indicated by the orientation of the triangle, with the sharp point aligned with your current Track.
By zooming in, you will be able to determine if your position is on the intended course line.

The orientation of the pointer should parallel that of the intended course line if you are on course.
This display can make staying on course a challenging task, since the orientation of the pointer lags slightly behind your actual track on the water. The display also lacks the precise cues that you need to steer by. The Map Screen will show all other waypoints stored in your GPS that lie within the zoom level of the display.

Highway Screen
At the same time that your GPS draws a course line on the Map Screen, it also draws a highway on the Highway Screen. The center of the highway corresponds with the center of the intended course line. Your Track is straight ahead on the screen while the highway&#8217;s orientation reflects your orientation relative to the intended waypoint.

If you are on course and heading toward the waypoint, the highway display will show you in the middle of the highway with the road extending straight ahead toward the waypoint.

This display is easy to interpret and sensitive to shifts in direction.
Data Fields
A number of data fields are available to help you with your navigation tasks. The most useful displays are:
1. Course
Course usually indicates the intended course direction. It does not change with your location or orientation. It will change only if you initiate a different course.
2. Track
Track (or Course over Ground) is the actual direction in which your GPS is moving with respect to the earth (ground). It is based on changes in your latitude and longitude and is updated about once per second. Therefore, it is a short-term indicator of your motion and will change constantly to reflect any changes in the actual direction of motion for the boat.
*This is how/why you can only get a compass reading while under motion.* unless you have an electronic compass.

3. Speed
Speed (or Speed over Ground) is the actual rate of motion of the GPS (and, of course, the boat). It is based on the rate of change of your position coordinates, updated about once per second. Some GPS models offer averaging, which smooths out short-term changes to give you a more realistic value.
4. Bearing
Bearing is the direction from your current location to the active waypoint. It is a straight-line path and does not take into account the intended course, nor any barriers between your location and your destination.
5. Distance
Distance is the current straight-line distance from your current location to the active waypoint.
6. Crosstrack Error
Crosstrack Error (or Off Course) indicates the amount by which your current position is to the right (starboard) or left (port) of the intended course centerline. An alarm can be set to sound if your crosstrack error exceeds a preset limit.

Off Course
Any condition that is indicated by a mismatch of the Course, Track, and Bearing data fields means that you are off course. This can occur for a number of reasons:
1. Inattention to the helm: helmsmanship can be a tedious task requiring constant attention.
2. Cross wind or cross current: even if you are steering directly toward the waypoint, natural forces will push the boat from its intended course, requiring corrective action.
3. Avoiding obstacles: you will need to steer around other boats and obstacles in order to avoid collisions. This requires deviation from the intended course line.
4. Wave action: the natural action of the seas will tend to drive the boat off its intended course. Constant attention is required to keep the boat heading in the correct direction.

Off Course by a small amount
Usually you will have pre-qualified a path of some reasonable width to account for small errors. If you are off course within the limits of your qualified path width, simply steer back toward the centerline.

Off Course by a large amount
Sometimes, inattention can lead to your being diverted by a substantial distance from your intended course. When this happens, you are at risk. You should stop, plot your current position on a chart, and determine what path will get you safely back on course or to your destination.

SKILL &#8212; Dealing with an Off&#8212;Course Condition
EXERCISE 6-1 Off Course / Replot Safe Course
OBJECTIVE: Monitoring progress. The importance of using GPS to stay on track. Using waypoints to plot fixes. Corrective action needed to replot a safe course when you are heading into an unsafe situation.
Establish and label each Main Channel navigation aid as a waypoint:
G &#8220;3&#8221; as BBG3
R &#8220;4&#8221; as BBR4
G &#8220;5&#8221; as BBG5
R &#8220;6&#8221; as BBR6
G &#8220;7&#8221; as BBG7
R &#8220;8&#8221; as BBR8

At 1300, you depart BBR4 on a course to BBG7. Speed is 7.0 kn.
At 1335, you plot a GPS fix of 261&#176; magnetic, 5.1 nm from BBG7. What action should you take?

This is your first exercise transitioning you from DR navigation to electronic (GPS) navigation. Basic navigation rules stay the same, but you will note many new options and techniques becoming available to you.

Staying On Course
Staying on course is paramount in safely following the pre-qualified paths. When you pre qualified the paths, you determined them to be free of obstacles up to a reasonable width. For simplicity, you should make sure that these paths are clear up to about 600 ft (about 0.1&#8217; of latitude) from the course centerline on each side.

The following GPS screens and data can be used to help you stay on course:
Highway Screen
The &#8220;on-course&#8221; condition is the image described above, with your position in the center of the highway and the highway extending straight ahead.
If you are being pushed by wind or current from your intended course line, you will need to steer to counteract the effects. To do this, steer slightly into the side force to move your boat back to the center of the highway. Your objective is to steer in small increments so that you ease back onto the centerline, and then adjust your course until the active waypoint is straight ahead. Once you identify the appropriate heading that keeps you on course, you can note the reading on the ship&#8217;s com pass and then steer to that heading.

The Crosstrack Error data field can be used to fine-tune your heading. What you want is a minimal and constant error. Any continuing increase in error, either left or right, means that you are diverging from your intended course line. Fine-tune your heading to maintain a small and constant crosstrack error.

Map Screen
As indicated in the previous section, it is more difficult to stay on course using the Map Screen. You are looking for your boat symbol to be directly on the intended course line and aligned with the direction of the course line. If the Map Screen is to be useful, you will need to zoom in considerably on the map to see details. Remember that the pointer&#8217;s direction lags slightly behind your actual orientation, so don&#8217;t try to steer by the arrow.

One of the biggest difficulties in using this display for maintaining an on-course position is the high level of zoom required to see the details. When you do this, the other benefits of the Map Screen - the ability to monitor relative progress and orientation to other stored waypoints - may become lost, since these details may not show on the zoomed display.

Comparing Data Fields
If you are on course, your Track will be the same as your Course. In addition, your Bearing will match your Track. By the same token, the Crosstrack Error will be zero, indicating that you are on the original course line. This condition can only be met if your current position is precisely on the original course line.

Navigating from Waypoint to Waypoint
Your cruise will usually involve a sequence of waypoints. You can navigate manually to each in turn, activating the next waypoint as you reach your intermediate destination (waypoint).

As a note of caution, make sure that you select the proper next waypoint each time. It is easy to mistake one waypoint designation for another and find that you are navigating along an unintended (and potentially dangerous) path. Also, some danger may be caused by diverting your attention from the helm while selecting and activating the next waypoint.

Using a Route
To automate the process you can construct a mute, using stored waypoints. When building a route, your GPS will give you the opportunity to scroll through your stored inventory of waypoints. As you do so, make certain you select the correct waypoint to avoid dangerous paths on the water.
Construct your route by selecting waypoints sequentially, in the order that you intend to navigate them on the water.

When you activate the route for navigation, the GPS assumes that you are located at the first waypoint on the route list. Most GPS models will then point you toward the second waypoint on the list. If you are not located at the first waypoint, you must stop to plot your current position and check the straight-line path for safe passage from there to the first route waypoint.
You can enter a route at some intermediate point. When you do this, the GPS will make a decision as to which waypoint to aim you toward. Often it will be the second waypoint on the route list. If you enter the route at an intermediate waypoint other than the second, most GPS models will recognize what you are doing and provide bearings to subsequent waypoints from that location.

When you have reached your destination and wish to return to your starting point, you will be able to invert the route to execute the waypoints in reverse order.

Seaman&#8217;s Eye
An important part of navigating is keeping in touch with your surroundings and checking your navigation. Much of this process can be accomplished visually when you are navigating in a coastal or inland environment. There are a number of convenient, quick techniques to help you do so.

Quick Bearings
Using your boat as a reference, you can take quick visual bearings, even without instruments, to compare your position with your charts. While not precise, they can suffice to check your navigation. If any of your visual bearings call your position into question, you should be alerted to take more formal steps to verify your navigation.

Bow Bearing
The bow bearing is both reasonably accurate and quick to take. Since the bow represents the boat&#8217;s heading, you can read the bearing directly from your ship&#8217;s compass. It also is practical to turn the boat momentarily to get a bow bearing on a landmark and then return to your original heading.

Beam Bearing
While taking a bearing off the beam is not as precise as using the bow, it nonetheless can be very useful. Also, an object off your beam is likely to require an inconvenient turn in order to take a bow bearing. With another crew member steering, you can improve your accuracy by standing to face the beam. Extending your arms toward the bow and stern and then bringing them together in the middle will provide a more refined sense of the beam direction.

Beam bearings are particularly useful as you pass nearby navigation aids. These observations can be compared with your intended course to verify your progress.
You will need to add 900 to the ship&#8217;s heading to get a starboard beam bearing, or add 270&#176; to the ship&#8217;s for a port bearing. If the resulting bearing exceeds 360&#176;, subtract 360&#176; to get the appropriate compass bearing.

Stern Bearing
A stern bearing is not quite as accurate as a bow bearing because of the somewhat blunt transom. Even so, you can take a bearing by standing amidships and sighting across the midpoint of the stern, often marked by a backstay or flagpole socket. Add 180&#176; to the ship&#8217;s compass heading to get the bearing.

Other Bearings
It is possible and practical to set up your boat ahead of time for taking bearings. Using your ship&#8217;s compass, take readings from the helm at convenient increments and mark locations on the boat to use for sighting. For example, you might mark 450 on either side of the bow, using tape on the boat&#8217;s rail. You will need to add each relative angle to the ship&#8217;s heading to get the equivalent compass bearing.

Relative Bearings
The above quick bearings are called &#8220;relative&#8221; since they relate to the boat itself rather than the chart. In general, relative bearings need to be converted to be used for plotting on the chart. 

The formula for doing that is:
Magnetic Bearing = Relative Bearing + Magnetic Heading (of Boat)
Relative bearings are useful for quick visual checks. But you generally will find that the use of a hand-bearing compass is also reason- ably quick and provides the magnetic bearing directly.

You will find that other instruments, particularly radar, naturally provide relative bearings. Your visual horizon from the boat is also relative to the boat, so it&#8217;s very important to develop a feel and understanding of how relative bearings relate to your chart.

Collision Course
Another good use of the relative bearing is to determine the possibility of collision. When you are on a moving boat, everything around you appears to be moving, too. Fixed objects appear to move past you, while other moving objects, such as boats, have from your perspective relative motions that don&#8217;t necessarily reflect their true headings.

What does all of this mean relative to your safety? Simply stated, any object that maintains the same relative bearing as it approaches your boat is a risk for collision. If its relative bearing advances toward your bow, the other boat will pass in front of you. If its relative bearing falls aft toward your stem, the other boat will pass behind you.
SKILL &#8212; Checking for the Potential of Collision

EXERCISE 6-2 Collision Course
OBJECTIVE: Determine the potential of a collision course of an observed crossing boat.
&#8226; At 0940, you observe a boat at a relative bearing of 0900. At 0943, the relative bearing is 070&#176;. At 0946, the relative bearing is 050&#176;. What action should you take and why?
&#8226; At 1040, you observe a boat at a relative bearing of 280&#176;. At 1043, the relative bearing is 255&#176;. At 1046, the relative bearing is 230&#176;. What action should you take and why?
&#8226; At 1130, you observe a boat at a relative bearing of 045&#176;. At 1133, the relative bearing is 0500. At 1136, the relative bearing is 040&#176;. What action should you take and why?
&#8226; At 1530, you are on a magnetic heading of 240&#176; and you take a compass bearing of 270&#176; on a crossing boat. At 1533, the compass bearing is 290&#176;. At 1536 the compass bearing is 310&#176;. What action should you take and why?
TIP: When performing a collision course solution in a tacking sailboat, take collision course bearings with a hand-bearing compass. This will be the only constant frame of reference when the boat is tacking.
Checking the GPS
Checking your navigation is of paramount importance to your safety. While your GPS is quite reliable, it can give erroneous readings. It is important that you check your GPS navigation from time to time. In general, it is recommended that you plot your GPS position on your chart at hourly intervals. When you do that, you should also attempt to verify this position by some other means.

One reason for plotting and checking your position is so you will have a fairly recent last known good fix to fall back on in the event of a failure.

Quick GPS Check
The easiest way to check the GPS is to com pare a visual bearing with the GPS. To do that you will need to have landmarks entered into your GPS in advance. Simply sight on a selected landmark with your hand-bearing compass and compare the bearing read visually with that in the GPS to the same land mark.

You can access the bearing to the landmark of choice via the waypoint list or nearest waypoint feature in your GPS. Bring up the waypoint screen for the selected waypoint. You will find that the GPS provides the bearing and distance to that waypoint from your current location.

Compare the GPS bearing with your visual bearing. If they match (within a few degrees), your GPS appears to be functioning properly. If they differ by a significant amount, your GPS is in question. Take more bearings and develop a fix.

Multiple Bearings
Most of the time, you can perform a more rigorous check on your GPS and develop an independent position. Take two or more visual bearings on charted landmarks. Again, it is useful if these landmarks are stored as waypoints in your GPS.

If the quick check indicates a mismatch with a single bearing, your GPS position is called into question. The best thing you can do is to use two or more bearings to plot a fix on your chart. Now, you can compare this fix with your GPS reported position. If they do not match, put the GPS aside. If you have a spare GPS, turn it on and compare its position with your fix. If it too does not match, your visual fix is in error, or there is a system problem with GPS affecting its accuracy at your current location.

You will need to navigate using dead reckoning, as has been described earlier.

EXERCISE 6-3 Route Planning and Implementation
OBJECTIVE: This is the third of four sequential exercises. Integrate lessons learned to select a route and to implement real time on the water decisions. You will create routes, pre qualify them, plot them with course and distance, select and name waypoints, check GPS plot/entry accuracy, avoid hazards, and use hand held compass bearings and Seaman&#8217;s Eye concepts to validate bearings and fixes.

Using your GPS as your primary means of navigation, depart on a day cruise on the route you created in EXERCISE 5-2. Departure time is 1200. About half way along your route and half way between two GPS waypoints, you decide to take a GPS fix because your GPS screen indicates a cross track error of over one mile. This has been caused by diversions to avoid heavy boat traffic and your inattention to helmsmanship. Take the necessary action to continue on to your destination.

Vessel and weather options:
The options you selected in EXERCISE 5-2.


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## Fishers of Men

*sequence 4 GPS*

Manual Piloting
In the event that your GPS becomes unreliable, you will need to regroup and be able to proceed using manual piloting techniques.
&#8226; What we will cover in this segment:
&#8226; How to find your position if the GPS becomes unreliable.
&#8226; Using Dead Reckoning.
&#8226; Finding position using bearings.
&#8226; Navigating manually using dead reckoning.
Once the GPS has failed
Your first action is to stop your boat and regroup.

Establish Position
You will need to establish your current position and plot it on your chart before proceeding. If you are successful in taking multiple bearings as previously described, you will have a fix to work with.
If you are unable to get a fix using visual bearings or other means, you will need to duce your current position based on your last known good position. That is why you have been plotting your position at regular intervals.

Position by Dead Reckoning
You will need to go back to your last known fix on your chart and plot your progress using dead reckoning. Plot your steered course from that fix. (This is one reason to keep a good track of courses steered.)
Determine your progress along that steered by using 60D = ST: For S, take your average speed since the last fix, multiply it by the time traveled in minutes and divide by 60 to get the equivalent distance in nautical miles. Plot that along your steered course.
This is your current dead reckoning position. If you have even a single visual bearing, you can plot it as a check on the DR accuracy.

Navigate by Dead Reckoning
You will need to plot your course going for ward. Recognize that your current DR position is less accurate than with a functioning GPS. You will need to take wider legs around charted obstacles to account for this uncertainty.
Proceed using a DR plot. Maintain your course steered and speed with as much precision as you can muster, since this is your only frame of reference going forward.

Bearings
Whenever possible, take visual bearings and plot them on your chart. This will provide a sense of the accuracy of your DR plot. If you have the opportunity to get a visual fix using two or more bearings, make sure to do so. Once you have established a reason able fix, restart your DR plot from that point. Adjust your course accordingly to reach your intended destination (or next waypoint). Again, maintain your steered course, speed, and time so that you can continue your DR plot.

Estimating Time of Arrival
Even more important than when navigating with the GPS, you will need to estimate your time of arrival at buoys or landmarks. You will be using these as your principal checks for position.
You can use 60D = ST to estimate your arrival. Since you are looking to solve for time, reform the equation into:
Time (in minutes) = 60 x Distance (to landmark) / Speed (in knots)
Add the number of minutes en route to the current time and note the time that you should be seeing the landmark or buoy in question.
SKILL &#8212; Manual Navigation using Dead Reckoning
EXERCISE 7-1 GPS Malfunction &#8212; Manual Plot
OBJECTIVE: Establish a position after a GPS malfunction and proceed using dead reckoning and bearings.
&#8226; In planning a cruise on Bowditch Bay, you established and plotted the following way- points and entered them into your GPS as a route.
&#8226; R &#8220;2&#8221; Fl R 4s Oyster River as ORR2
&#8226; G &#8220;9&#8221; Fl G 4s Main Channel as BBG9
&#8226; R &#8220;10&#8221; Q R Main Channel as BBR1O
&#8226; R N &#8220;2&#8221; Shark River as SRR2
&#8226; Return to ORR2
&#8226; At 1800, you depart ORR2. GoTo BBG9. Speed is 10 kn.
&#8226; You arrive at BBG9 at 1828. Arrival is confirmed by visual sighting of G &#8220;9&#8221; Fl G 4s. GoTo BBR1O.
&#8226; You arrive at BBR1O at 1844. This is confirmed by visual sighting of R &#8220;10&#8221; Q R. GoTo SRR2.
Shortly after leaving BBR1O, your GPS screen appears intermittent and you suspect a malfunction.
Your ETA at SRR2 is 1909. At that time, there is no sign of R N &#8220;2&#8221;. It is hazy and getting dark. You continue on, looking for the buoy.
At 1914, you hear the horn and see the light Fl R 6s at a magnetic bearing of 302&#176;. What action should you take?
EXERCISE 7-2 Route Planning and Implementation
OBJECTIVE: This is the fourth of four sequential exercises. Integrate lessons learned to select a route and to implement real time on-the- water decisions. You will create routes, pre-qualify them, plot them with course and distance, select and name waypoints, check GPS plot/entry accuracy, avoid hazards, and use hand held compass bearings and Seaman&#8217;s Eye concepts to validate bearings and fixes.

Using GPS as your primary means of navigation, depart on a late afternoon voyage on the route you created in EXERCISE 5-3. About half way along your route, you determine that your GPS has experienced a major malfunction. The weather has worsened. The rain is periodically heavy and visibility is down to a few hundred feet. You can occasionally see a lighted buoy but lighthouses do show up at a significant distance. It is getting dark shortly. With the loss of your GPS and the worsening weather conditions, you decide to take what ever action necessary to get to a safe port. Choose and implement your new plan carefully.

Vessel and weather options selected/imposed on EXERCISE 5-3


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## Fishers of Men

*Using a Computer*

Manually entering information into the GPS can be a tedious task. Instead, you can use a computer keyboard to enter waypoint names and coordinates, then upload them from the computer into the GPS. Alternatively, you will likely mark waypoints into your GPS while you are on the water. The software will enable you to download those waypoints into your computer to manage or rename them.

In addition to managing waypoint names and coordinates, some software programs help you create and manage routes.

Also, by using the computer you are backing up your data. In the event that your GPS unit loses its memory; or you choose to use another GPS, you will be able to upload the same waypoints into the GPS.
GPS sets can be connected to a computer via a custom cable available from the GPS manufacturer. You will need software to work with the GPS. There are a number of freeware and shareware programs that work with the more popular GPS brands and models.



















Mark
While underway, you can enter a waypoint while passing over a point of interest. Simply press MARK, and the GPS will create a waypoint at your current location. The GPS will also automatically name the new waypoint with a unique number. You can edit the name immediately, although pushing all those buttons while simultaneously operating your boat could be cumbersome. Instead, make note of the waypoint&#8217;s number and characteristics, then edit the name while at home or at anchor.

*Planning with digital charts coming next.*


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## Fishers of Men

*Planning with Digital Charts*
If you own digital charts for your boating area, you can perform your cruise planning directly on your computer or chartplotter. When you plan on digital charts, you are far less likely to make errors. This is a distinct advantage over the manual approach, which gives you two opportunities to make a mistake: when you read the coordinates from the chart, and when you enter the coordinates into the GPS.

Using digital charts displayed on a computer screen, you can plot routes, mark waypoints, and annotate the charts by simply pointing and clicking while the computer automatically provides the latitude and longitude of each waypoint, the course and distance of each leg, and other useful information. This greatly facilitates planning, adjusting, and storing waypoints and routes for upload into a GPS.

Similar techniques can be used with a chartplotter, but a computer offers unique advantages, particularly for planning. Once you generate waypoints and routes with charting software on a computer, they can be uploaded into virtually any GPS. Then, on the water, even without the chart itself displayed on a computer screen, you can use your GPS for live navigation because you will be following the prequalified paths you generated on a digital chart. This popular approach makes navigation vastly easier for those of us who have a nonmapping handheld GPS receiver. In fact, many boaters who have a chartplotter plan their voyages on a computer at home, then upload the resulting way- points and routes into their chartplotter.

A desktop or laptop computer with charting soft ware and digital charts offers significant computing power, storage capacity, and a relatively large screen. The screen is smaller than an actual nautical chart, so you will need to zoom in and out and scroll up-down and left-right to see the entire chart.

Offsetting this inconvenience is the ability to move from chart to chart or use charts of different scales that are automatically referenced to your current location.

Digital Charts
Nautical charts are your security blanket, digital charts no less so than paper. Indeed, digital charts display all the same information. Although you don&#8217;t have easy access to the latitude and longitude scales on the edges of the chart, you have something even better: the latitude and longitude coordinates of your cursor are displayed digitally at all times on the screen.
Because you can see only a limited piece of a digital chart at a time, you scroll across the chart or zoom in and out to get a broader view. Unfortunately, when you zoom out, it&#8217;s like moving away from the chart&#8212;you get a wider view but lose detail. This calls for some techniques that will be described later.

There are two types of digital charts; which one you use probably will depend on whether you are displaying it on a computer or on a chartplotter. The latter, with its smaller memory, needs charts in a more compact form. This has prompted the development of vector charts on custom chips. Computers generally can store more data and run CD-ROMs, so they usually use scanned versions of paper charts in what is called raster format. Vector and raster charts look different but come from the same source data.

Cruise-Planning Software
You will need the appropriate software and digital charts to do navigation planning on a computer. Planning software is offered by a number of companies and may be sold for a nominal cost or bundled with digital charts. The Maptech line of Digital ChartKits is an example. These kits come by region, each with a full complement of faithfully reproduced and enhanced raster NOAA charts for that region. They also contain other chart formats for the same area, such as photographic charts, selected topographic maps, and even aeronautical charts. All of these are geo-referenced to a common grid&#8212;namely latitude and longitude. The various chart formats can even be aligned side by side so you can work simultaneously with, say, a nautical chart and a photographic version of the same area. Maptech&#8217;s Chart Navigator software is bundled with the kit along with cruising guides and aerial harbor photos. Other companies offering similar packages include Nobeltec, Softchart, and Transas. 

Software also is offered by a number of companies for live navigation on a computer connected to your GPS. This software usually does not come with digital charts, which are a separate expense. This material applies to navigation software used for planning as well as to dedicated planning software.










Because not every boater wants to use a computer for live navigation, it&#8217;s nice not to have to buy full-featured navigation software for planning. Many GPS hardware manufacturers offer proprietary software for uploading and downloading data into or from their GPS receivers. Some of these manufacturers also offer charts that can be viewed on a computer screen and in some cases selectively uploaded into the GPS, although each such chart is compatible only with that brand of GPS. The amount of cartography a GPS will store is limited, though some models offer add-on memory cards to expand the coverage area. Unless you have a mapping GPS that accepts proprietary charts, you would do better to invest in digital charts that run on a PC.

If you have a chartplotter, you may prefer to do your planning on a computer using the same chips that you use in your chartplotter. C-Map, for one, offers a software package called PC Planner, which comes with a chip reader. All you need to do is insert your chip or chips in the reader, and you can plan on your computer screen. C-Map offers writable chips that can be used to transfer your routes and waypoints to your chartplotter. Garmin offers similar features, and other companies are following.

The planning software that comes in a digital chart kit generally will not perform live navigation, but it does permit uploading waypoints and routes into your GPS as well as downloading marks and tracks from your GPS. This software also offers a host of editing features. It makes waypoint and route management easy, and it works with a wide ( range of GPS units and chartplotters. The major difference from the software described is the added ability to display and work with real charts.

Usually, the digital charts used on computers are delivered on CD-ROMs. Here we use the Maptech Chart Navigator program to demonstrate their features, although similar capabilities can be found in other packages as well. Almost all computer-based navigation and planning software accept the Maptech (BSB) charts included in the kit, with the exception of those proprietary program formats mentioned above that are designed exclusively for a particular brand (GPS. Maptech is licensed to create digital charts directly from NOAA data files, whereas other charting companies must scan the NOAA charts to construct their products. Digital charts for regions other than those covered by NOAA are drawn from charts provided by the British Admiralty and other hydrographic services.









FIGURE 6-6. Route planning on a computer is easy and accurate. You can point and click along the desired path to create the route. Each click represents a waypoint that will be saved and uploaded along with the route into your GPS. The route can be edited by adding, deleting, or moving any waypoint.

Chart-Planning Software Features
Because the main features of planning firmware and soft ware are quite similar, the tasks described in this section can be performed on either a computer or a chartplotter. As you plot your waypoints and routes on digital charts, you should annotate the corresponding information on your paper charts for backup reference on the boat. In addition, you may discover that while plotting the same courses on paper charts, you&#8217;ll find an occasional better or safer path that is not as easy to recognize on the smaller chartplotter or computer screen. As an alternative, many digital chart-planning programs provide a means of printing your own charts annotated with your routes.

The host of features at your disposal will typically include the following.
Waypoint Mark&#8212;You can scroll your cursor across the screen and mark a waypoint to be stored. From a computer, this waypoint is uploaded into your GPS receiver. On a chartplotter, this waypoint is stored directly.
Route Development&#8212;You can build a route by moving your cursor from point to point of the route on the screen. The computer automatically creates waypoints at each mouse click. The chartplotter may require you to enter the waypoints first.

Edit Waypoints&#8212;You can click on any waypoint on a computer screen and move it to a new location on the chart. Using a chartplotter, you may need to go to the way point menu to move it.

Edit Routes&#8212;You can move waypoints on a computer screen or create new ones (at the beginning, end, or middle of a route) by selecting a menu item and clicking on the screen. On a chartplotter, you may need to create the waypoints sep arately by clicking on the selected location on the screen.
FIGURE 6-7. Once the route is complete, you can bring up a route plan that provides the coordinates of each waypoint, the course for each leg, the leg distance, and total distance. You can also use the software to estimate the travel times and fuel consumption for each leg and the overall route.









FIGURE 6-8. Once you have planned on your charts at home using your computer, you can print the charts for use on the boat.









Measure Distances and Bearings&#8212;Most programs provide an A to B feature. This permits making measurements from any point (A) to any other point (B) on the screen without these being considered waypoints. This is useful for checking distances or bearings on-screen.

Route Plan&#8212;You can view the elements of a planned route to display leg course, leg distance, and total route distance. In addition, many programs permit entering an intended speed for each leg and an anticipated start time to get ETA and ETE (estimated time of arrival and estimated time en route) for each leg and the total route. Some programs permit entering a fuel consumption rate as well (GPH) and calculate total fuel consumed by leg and route.

Chart Management&#8212;You can view various charts at a given location. With a chartplotter, you can zoom to a larger scale to view greater detail. With a computer, you can view any of the nautical charts that cover a given location, or, alternatively, view photo charts, topographic maps, or bathymetric charts.

FIGURE 6-9. Chart-planning software provides a wide array of options. You can select directions as true or magnetic, distance units, and the level of symbols and in formation that will show on the chart.









FIGURE 6-10. When planning with digital charts, you can change from one scale of chart to an entirely new chart of a different scale for the same location. By scaling in, you will be presented with more refined and accurate information. By scaling out, you will be able to view a wider area.









*Navigating the Screen: coming next*


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## Fishers of Men

*Navigating the Screen:
A Quick-Start Guide*
Typical software provides a row of icons along the top of the screen that can be used to access most of the software functions. Usually, there are two other ways to access these functions: use the right-click button on your mouse to get a drop-down menu, or use the drop-down menus at the very top of the screen. These options are familiar to any user of word-processing or spreadsheet software, and the choice is a matter of personal preference.
CURSOR The usual way of navigating the screen is with a cursor, typically a small hand or an arrow. In addition, you can move the chart across the screen by pressing and holding the left mouse button while you move the mouse. Alternatively, if you move to a corner or side of the chart, the chart may scroll in that direction. On a chartplotter, you will be able to scroll across the visible portion of the chart until you reach the edges of the screen. Once there, the chart itself will scroll from under your cursor. To stop the chart from scrolling, simply move the cursor away from the screen&#8217;s edge. Then you can move the cursor across the visible portion of the chart to mark a point or read the pop up features.

SETUP You should go to the drop-down menus at the top of the screen and look for Setup or Options. This helps you to set up the chart planning for your personal preferences. On a chartplotter, setup can be found under the setup menu option.

Bearings&#8212;You can choose to have the bearings reported as magnetic or true. Generally, you will find magnetic&#8212;the language of your compass&#8212;more convenient.
Distance Units&#8212;You can set the distance units to nautical (recommended for coastal charts), statute miles (Great Lakes), or kilometers.
Lat/Lon Format&#8212;You can set latitude and longitude coordinates to read in degrees, minutes, and tenths (recommended for coastal charts); degrees, minutes, and seconds (Great Lakes); and other formats.

TOOLS The chart-planning tools or modes we use here are accessed either by icons on the top row or from drop-down menus, mentioned above. Typical options include the following.
Cursor&#8212;For navigating around the chart and scrolling, as mentioned.
Chart List&#8212;To call up a list of available charts.
Charts at this Location&#8212;This tool will list all the available chart scales and formats that cover the cursor co ordinates or the chart area on the screen.
Scale&#8212;Usually a pair of tools&#8212;one for In and one for Out. These change the presentation to a larger- or smaller-scale chart, respectively. (A larger scale means more detail for a smaller area.)
Zoom&#8212;These two tools (In and Out) do not change the scale but merely change the magnification of the current chart. This tool is useful, because many of the charts represented may be 4 feet across in their paper form, but your screen may be only a foot or so wide. Zooming on a chart does not make it more accurate, however&#8212;only bigger. Chart accuracy standards used by NOAA and other hydrographic offices are based on the scale of the chart. A small- scale chart (large area) is not as accurate as a harbor chart regarding the precise locations of charted objects. You will also notice that a chart becomes distorted and hard to read when you zoom way in, and hard to read when you zoom way out. You can have too much of a good thing!
Zooming on raster digital charts is simply a matter of magnifying the same information. No additional in formation or ac curacy is achieved, just a better view The same chart number and scale are viewed with a greater or lesser degree of magnification. 

A to B&#8212;With this tool you can measure distances and bearings without impacting any navigation tasks that also appear on the screen. (See &#8220;Working with Digital Charts,&#8221; below.)
Create Route&#8212;This tool is used to create a route on the chart. (See &#8220;Working with Digital Charts.&#8221
Create Mark&#8212;This is useful when you want to mark a spot that is uncharted. (See &#8220;Working with Digital Charts.&#8221
Annotate Chart&#8212;Many planning programs allow you to annotate your digital charts with notes. This information is not uploaded into your GPS but provides a ready reference whenever you bring up your digital charts. Many programs also allow you to print out these annotated charts to take aboard.

Chart Display&#8212;There are usually several ways to display multiple charts. The most useful is displaying two charts side by side (called tiling). For example, you can ob serve a large-scale chart, for detail, in one window and a small-scale chart covering a broader area, for context, next to it. Alternatively, you can view a nautical chart with a photo chart of the same location next to it.

Locate&#8212;Many programs help you find key information, including:
Lat/Lon&#8212;This menu takes you to a set of coordinates indicated by a bold arrow.
Routes, Marks, Named Waypoints, A to B&#8212;Highlighting any of these menu items will pop up a list of stored items corresponding to the selection.
Current, Tide Stations&#8212;These menu items provide a list of all tide and current stations on the charts by number, coordinates, and features.
Place Name, Marine Facilities&#8212;These menus provide lists of all place names and marine facilities available with the charts.
GPS&#8212;This set of drop-down menus can be used to set up your GPS and start to upload or download between the GPS and the computer.
Coordinates&#8212;The coordinates of the current cursor location are displayed in a window, usually in a panel at the bottom of the screen.

Working with Digital Charts
The real power of digital charts lies in the flexibility to create and adjust courses to suit your needs, then upload that information directly into your GPS for navigation.

The principal digital chart plotting techniques include:
A to B&#8212;point-to-point measurements
Mark&#8212;waypoints for navigation
Route&#8212;routes for navigation
Let&#8217;s look at each in turn.
A to B
This is one of the handiest navigation tools available on the software or chartplotter. This is a planning technique that is used for measurements rather than creating waypoints. The A to B marks are not uploaded into a GPS but reside on the planning software screen for reference. This tool temporarily marks two points&#8212;A and B&#8212;and provides information about the location (coordinates) and relative position of each with respect to the other (bearing and distance). It can be used to quickly measure a distance or establish a bearing.

Move the cursor to the location of the first point (A), and left-click on the mouse. Now move the cursor again, and you&#8217;ll draw a line from A like a spider trailing a thread Many programs provide the coordinates of the cursor and the bearing and distance from A to the cursor location &#8216;When you are satisfied with the cursor location, left-click again to plant point B.

Now you can access a screen or window that provides details about the line you just created. Usually, this screen provides the coordinates of points A and B as well as the distance between them and the bearings from A to B and from B to A.

This is particularly useful in checking a visual bearing or just checking the distance and direction to a point of interest. You can also measure the bearing of an impromptu range on the chart&#8212;that is, any two charted landmarks whose alignment can be used as a visual reference line on the water. With this software it&#8217;s easy to create a portfolio of ranges in nearby waters&#8212;your personal library of &#8220;local knowledge.&#8221;

FIGURE 6-12. The A to B mode can provide key in formation about any two points of your choosing. With just a few mouse clicks, you can learn the coordinates for the points, the distance between them, and the bearing from A to B, and from B to A.










Many programs impose no upper limit on the number of A to Bs you can use on your chart.


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## Fishers of Men

*Navigating the Screen cont.

Mark*
A mark is any convenient reference point you place on a chart, perhaps a wreck you&#8217;ve discovered or a favorite fishing spot. The mark tool permits you to name this mark and upload it into your GPS, choosing an appropriate symbol. This is a handy means of annotating a chart (and your GPS receiver) with features or hazards that are not otherwise charted. Each mark is shown on the chart and stored in a Mark List by name and location. You can use the mark feature to annotate your charts with updates found in the U.S. Coast Guard&#8217;s Notices to Mariners and from similar organizations throughout the world. This will keep your digital charts and your GPS information current.

FIGURE 6-13. Often, you&#8217;ll need to annotate your charts with the latest in formation from the Local Notices to Mariners, or add a new buoy or an uncharted feature. You can insert notes and symbols using the mark feature.










Route
The route tool is the most powerful tool available on digital charts. This enables you to plan your paths on the water from point to point, avoiding obstacles and moving toward and back from various destinations. When the route is complete, it consists of a sequence of waypoints representing each turn between straight-line route segments, or legs. The planning software computes the course and distance for each leg and the total route distance.
These waypoints and the route can be uploaded into your GPS and subsequently accessed by name. Once selected, the route will direct you through the preplanned sequence of waypoints.

You can move any of the waypoints in a route by clicking on the waypoint and dragging it to a new location. You can also add waypoints at the beginning of the route, at its end, or at some intermediate point. When you are finished, the route can be saved.

By accessing the list of stored routes, you can review each route&#8217;s details or edit the route with your keyboard by manually changing the waypoint coordinates. You can also assign names and symbols and provide notes relevant to the waypoints. The &#8220;short&#8221; name is usually uploaded into your GPS and appears as the waypoint name on your GPS.

ROUTE-PLANNING STRATEGY Quite often it makes sense to build route segments rather than complete routes from a common starting point to each of several frequent destinations. For example, you may need to get from your mooring or slip to some mark outside the harbor before proceeding to any of a number of destinations. This would make a logical route segment. Then the paths to each of the divergent destinations can be built as route segments from that outer mark.

FIGURE 6-14. Most GPS models limit the number of waypoints per route. An efficient technique for route development is to break a total route into segments. For example, the detailed route from your slip to the main channel or mouth of the harbor is common to most routes (shown in red). So, make that one segment and begin the remainder of your routes from there.










Because most chartplotters limit the number of way- points per route, creating route segments rather than complete end-to-end routes enables you to build more complexity into each segment. The downside is the need to sequentially call up segments as you make progress along your route. This will briefly take your attention from the helm, so you should begin and end your segments at non- challenging locations.

FIGURE 6-15. Most boaters develop a route leg by leg, starting at the beginning and working to the end of the route. Usually you will use reasonably large-scale charts, to provide adequate details about channels and hazards. You may need to work across several charts of different scales to complete your route.










FIGURE 6-16. Digital charting adds an entirely new dimension to route planning. it allows a technique called quick planning. You start by displaying a chart scale that lets you mark both your starting point and destination as a two-point route. This is a straight line between these two points, which clearly is the shortest path. However, there likely are obstacles along the path.










FIGURE 6-17. Next, you can add intermediate waypoints to modify the route around major obstacles or landmasses along the way Most digital charting programs allow you to create the routes by pointing and clicking while it generates the waypoints for you. When you add or move the waypoints, they are adjusted automatically.










There are two common ways to plan a route. Each is described below.
Linear Planning&#8212;This technique is similar to planning on paper charts with pencil and plotting tools, as discussed earlier. You start at a given spot and route leg by leg and point by point from one end other. You generally will use the largest-scale chart that shows both ends of a given leg, zooming in or out as necessary. You determine the best path for each leg as you setting waypoints accordingly. This approach is analogous to how you will navigate the course, one leg at a time.

Quick Planning&#8212;This alternative technique is rendered practical by the ease of editing afforded by digital charting. It uses the power of zooming and chart-scale Selection to its full advantage. You initiate your planning on a chart that shows both the starting and end points of a route. Selecting these two points, you create a single leg (straight line path) between them, disregarding for the moment what lies along the path.

Next, you modify this path to an acceptable level of safety by adding waypoints as necessary to avoid obstacles. By scaling in and out between harbor charts (1:10,000 or 1:20,000 scale), local charts (1:40,000), and coastal planning charts (1:80,000 or smaller scale), for example, you can address and fine-tune your route through the starting harbor, intermediate channels, and destination harbor. Finally, you should review your entire new route at the largest scale possible for a final tuning of your paths.
You then can switch to a larger-scale chart and/or zoom in for a better view of a section of your route. Because the quick route is a nearly straight line, you can be sure that the route segment that shows on your screen is close to optimum with respect to distance. With the more refined view, you can adjust the route by adding or moving waypoints to avoid obstacles. You can scroll the screen along the route and fine-tune each segment from beginning to end.

Virtually all software permits creating and moving points at will, typically by scrolling your cursor over the waypoint shown on the screen, pressing and holding the mouse button, and moving the waypoint to a new location. This, combined with the ability to zoom and scale in or out on an area of interest, makes this task quick and easy. When you start with a straight line representing the shortest distance for your trip and modify it as needed, you will likely get the most efficient route between those two original points.

&#8220;Quick planning&#8221; is quicker and easier than the linear approach, because modifying a route is actually easier than creating one. In addition, most computer software permits displaying side-by-side screens at different scales so you can view both at the same time with your route plotted on both.
FIGURE 6-19. After you have refined the main part of the route, you can use the largest-scale charts to tackle the harbors&#8212;where precision is most important.










Route, Way point, and Mark Lists
Each route, waypoint, and mark can be reviewed and edited in a list or tabular format. These lists provide extensive in formation about your routes that is handy for review and planning purposes.

Usually, you can access this information by placing the cursor over a route on the screen and right-clicking to get a menu with something like &#8220;Route Plan.&#8221; Alternatively, you can use the drop-down menu at the top of the screen under a heading such as &#8220;Routes.&#8221;

ROUTE PLAN The route plan shows all the legs of the selected route beginning with the first waypoint. The coordinates of each waypoint are shown in the same format that you selected in the setup. The following information usually can be found in the route plan.

Starting and ending waypoint coordinates
Leg distance
Cumulative route distance
Course for each leg
Speed (you can enter values for this for each leg)
Time (leg time will be computed using speed)
Time sum (cumulative time for the route will be computed)
The route can be presented in the forward or reverse sequence. It can be printed for reference, and completed routes can be uploaded into the GPS.
MARKS A list of your marks by name and coordinates usually can be found under a drop-down menu. Marks, too, can be uploaded into the GPS.
EDITING Plotting routes using digital charts is easy, and editing them is even easier. Any point that is placed on a digital chart can be moved, and points can be added at the beginning, end, or middle of an existing route by simple mouse clicks. The edited route can be uploaded into your GPS for navigation.
MOVING WAYPOINTS, MARKS, AND A TO Bs To move any waypoint or mark on the screen, simply move the cursor to the spot, hold down the button on the mouse, and drag it where you will. To move the A or B points in an A to B plot, do exactly the same thing. All associated information is automatically updated.

ADDING OR DELETING WAYPOINTS IN A ROUTE 
As mentioned, this is easy. Usually, you do it by placing the cursor over the route line or one of the waypoints of the route, then accessing a menu by a right click of the mouse. Typical menu choices include:
Insert Waypoint at Beginning (of route)&#8212;Self-explanatory.
Insert Waypoint at End&#8212;Ditto.
Insert Waypoint in Line&#8212;Simply place the cursor over the route segment where you want to add a waypoint, and click. Usually, a new waypoint is created at this point; it can be moved at will by dragging and dropping. This is particularly useful for adjusting a route around obstacles, and is the key to quick route planning.

FIGURE 6-20. Once you have completed your route, you can access and print a tabular route plan. This plan provides waypoint coordinates, course direction for each leg, leg distance, and cumulative distance. Some programs can even estimate travel times and fuel consumption.










Chartplotters
A chartplotter superimposes GPS information directly on a displayed digital chart. Most chartplotters include an integral GPS receiver, but some use the input from a remote GPS receiver. Because the chartplotter is designed for mounting at the helm, most contain a display that can be seen in direct sunlight. Digital chips contain the charts.

The limited size of most chartplotter screens makes planning a little more tedious than when using a computer, but a chartplotter is a powerful tool that can be used to plan while you are on the move. Naturally, this extra capability comes with a price, and chartplotters are generally some what more expensive than noncharting handheld GPS units. The cost of the digital chart chips is usually on a par with the cost of a digital chart package for a PC.
Both chartplotters and computers use programs to perform their intended functions. A chartplotter comes with built-in &#8220;firmware&#8221; designed to perform specific navigation tasks and controlled by the buttons on the unit.

Chartplotters generally have a limited amount of processor capability and memory They are designed primarily for live navigation; when you use one for planning, you generally do so aboard, though it is possible to buy or make interconnecting cables and power supplies so you can remove the chartplotter and work with it at home.

FIGURE 6-21. Planning on a chartplotter is fundamentally the same as working on a computer. It may not be quite as easy, because the chartplotter lacks a mouse and usually has a smaller screen. But you can perform most of the same functions with the cursor key.










Using a Chartplotter to Plan a Route
A chartplotter lacks a keyboard and mouse to speed various tasks. Because it has fewer buttons, many of its features may not be as obvious or as easy to access as when planning on a computer. Routes is usually a main menu selection, with a submenu selection for New Route.

After selecting this function, you are likely to find an associated menu that provides two ways to enter a route. One option allows you to select named waypoints already stored in your chartplotterl GPS. The other option permits you to plan your route directly on the map or chart, much as you can with a computer. After selecting this option, you are presented with a Map Screen centered on your current position (or the last active position in the absence of live GPS data). Now you can scroll to your desired route starting point and use the chartplotter&#8217;s mark feature to make a waypoint, then move sequentially from point to point to build a route. As you do so, the route course line is drawn on the chart, enabling you to scan the path for safety as you go. Once you have completed the route segment, it will be saved for future use. Generally, the chartplotter uses the first and last way- points of the route as the route name. Once entered, the route can be edited.
Personal Digital Assistants (PDAs) and Pocket PCs are among the latest platforms for navigation software and digital charts. Several GPS manufacturers produce sleeves that can be inserted into popular PDAs and Pocket PCs. Most of these PDAs have standardized interface slots for just this purpose. These self-contained units include an antenna and a receiver that provide position information to the PDA. Other GPS models interface with a PDA via a cable and connector.

Software has been created that can read digital charts on a PDA or Pocket PC and overlay GPS information&#8212; thus the PDA functions much the same way as a dedicated chartplotter. Charts and maps are available on a CD-ROM for uploading from a computer into the PDA memory Many PDAs employ removable SD (secure digital) or other memory card formats to store the substantial amount of data in a digital chart. Usually, a home computer intermediates between the data sources and the PDA.

One company, Maptech, offers an Internet subscription service to download maps and charts at will for upload into your PDA. You can plan on the PDA, or plan in the computer and upload waypoints and routes much as you do with a computer and GPS.

What&#8217;s the advantage to a PDA? First of all, many people already own one, so the incremental cost is for the software and the GPS sleeve. They are portable and hand- held. Typically, their displays have higher resolution than most mapping handheld GPS models&#8212;and they&#8217;re in color too. These devices are general purpose and permit the use of flexible software and multiple programs&#8212;so their functions are not limited by other than available memory The soft ware can be updated or substituted at will from an array commercial offerings rather than being tied to a proprietary platform.

Their disadvantages lie in their small size and general lack of marinization for the environment. Just as with handheld GPS models, many navigators use a waterproof pouch to protect their PDAs. PDAs also operate on batteries and are subject to power loss.

Nonetheless, you can expect PDAs to move into realm of handheld GPS&#8217;s to a point where the distinction blurs. Typical PDAs will be shown later.

Planning for Sailing
Preplanning for sailing is like preplanning for a passage under power, with one significant exception&#8212;tacking into wind. When you tack, you are zigzagging across rather following the direct path, or rhumb line, between points. Consequently, you need to ensure that an entire band, centered on the rhumb line, is pre-qualified, then constrain your tacks within that band&#8217;s limits to avoid having pull out the charts. To some extent you can pre-qualify area or a region, as explained in the next segment, but may not be able to predict which legs will be into the wind, so you need to plan while you navigate. This will be discussed later.


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## Fishers of Men

*CHAPTER 10 bowditch
RADIO WAVES
ELECTROMAGNETIC WAVE PROPAGATION
I put it all in one post,back to GPS coming next.*
1000.	Source Of Radio Waves
Consider electric current as a flow of electrons along a conductor between points of differing potential. A direct current flows continuously in the same direction. This would occur if the polarity of the electromotive force causing the electron flow were constant, such as is the case with a battery. If, however, the current is induced by the relative motion between a conductor and a magnetic field, such as is the case in a rotating machine called a generator, then the resulting current changes direction in the conductor as the polarity of the electromotive force changes with the rotation of the generator&#8217;s rotor. This is known as alternating current.

The energy of the current flowing through the conductor is either dissipated as heat (an energy loss proportional to both the current flowing through the conductor and the conductor&#8217;s resistance) or stored in an electromagnetic field oriented symmetrically about the conductor. The orientation of this field is a function of the polarity of the source producing the current. When the current is removed from the wire, this electromagnetic field will, after a finite time, collapse back into the wire.

What would occur should the polarity of the current source supplying the wire be reversed at a rate which greatly exceeds the finite amount of time required for the electromagnetic field to collapse back upon the wire? In the case of rapid pole reversal, another magnetic field, proportional in strength but exactly opposite in magnetic orientation to the initial field, will be formed upon the wire. The initial magnetic field, its current source gone, cannot collapse back upon the wire because of the existence of this second, oriented electromagnetic field. Instead, it &#8220;detaches&#8221; from the wire and propagates out into space. This is the basic principle of a radio antenna, which transmits a wave at a frequency proportional to the rate of pole reversal and at a speed equal to the speed of light.

1001.	Radio Wave Terminology
The magnetic field strength in the vicinity of a conductor is directly proportional to the magnitude of the current flowing through the conductor. Recall the discussion of alternating current above. A rotating generator produces current in the form of a sine wave. That is, the magnitude of the current varies as a function of the relative position of the rotating conductor and the stationary magnetic field used to induce the current. The current starts at zero, increases to a maximum as the rotor completes one quarter of its revolution, and falls to zero when the rotor completes one half of its revolution. The current then approaches a negative maximum; then it once again returns to zero. This cycle can be represented by a sine function.

The relationship between the current and the magnetic field strength induced in the conductor through which the current is flowing is shown in Figure 1001. Recall from the discussion above that this field strength is proportional to the magnitude of the current; that is, if the current is represented by a sine wave function, then so too will be the magnetic field strength resulting from that current. This characteristic shape of the field strength curve has led to the use of the term &#8220;wave&#8221; when referring to electromagnetic propagation. The maximum displacement of a peak from zero is called the amplitude.

The forward side of any wave is called the wave front. For a nondirectional antenna, each wave proceeds outward as an expanding sphere (or hemisphere).

One cycle is a complete sequence of values, as from crest to crest. The distance traveled by the energy during one cycle is the wavelength, usually expressed in metric units (meters, centimeters, etc.). The number of cycles repeated during unit time (usually 1 second) is the frequency. This is given in hertz (cycles per second). A kilohertz (kHz) is 1,000 cycles per second. A megahertz (MHz) is 1,000,000 cycles per second.
Wavelength and frequency are inversely proportional. The phase of a wave is the amount by which the cycle has progressed from a specified origin. For most purposes it 
is stated in circular measure, a complete cycle being considered 360&#176;. 









Generally, the origin is not important, principal interest being the phase relative to that of some other wave. Thus, two waves having crests &#188; cycle apart are said to be 90&#176; &#8220;out of phase.&#8221; If the crest of one wave occurs at the trough of another, the two are 180&#176; out of phase.

1002.	Electromagnetic Spectrum
The entire range of electromagnetic radiation frequencies is called the electromagnetic spectrum. The frequency range suitable for radio transmission, the radio spectrum, extends from 10 kilohertz to 300,000 megahertz. It is divided into a number of bands, as shown in Table 1002. Below the radio spectrum, but overlapping it, is the audio frequency band, extending from 20 to 20,000 hertz. Above the radio spectrum are heat and infrared, the visible spectrum (light in its various colors), ultraviolet, Xrays, gamma rays, and cosmic rays. These are included in Table 1002. Waves shorter than 30 centimeters are usually called microwaves.










1003.	Polarization
Radio waves produce both electric and magnetic fields. The direction of the electric component of the field is called the polarization of the electromagnetic field. Thus, if the electric component is vertical, the wave is said to be &#8220;vertically polarized,&#8221; and if horizontal, &#8220;horizontally polarized.&#8221; A wave traveling through space may be polarized in any direction. One traveling along the surface of the earth is always vertically polarized because the earth, a conductor, short-circuits any horizontal component. The magnetic field and the electric field are always mutually perpendicular.

1004.	Reflection
When radio waves strike a surface, the surface reflects them in the same manner as light waves. Radio waves of all frequencies are reflected by the surface of the earth. The strength of the reflected wave depends upon grazing angle (the angle between the incident ray and the horizontal), type of polarization, frequency, reflecting properties of the surface, and divergence of the reflected ray. Lower frequency results in greater penetration. At very low frequencies, usable radio signals can be received some distance below the surface of the sea.

A phase change occurs when a wave is reflected from the surface of the earth. The amount of the change varies with the conductivity of the earth and the polarization of the wave, reaching a maximum of 180&#176; for a horizontally polarized wave reflected from sea water (considered to have infinite conductivity). When direct waves (those traveling from transmitter to receiver in a relatively straight line, without reflection) and reflected waves arrive at a receiver, the total signal is the vector sum of the two. If the signals are in phase, they reinforce each other, producing a stronger signal. If there is a phase difference, the signals tend to cancel each other, the cancellation being complete if the phase difference is 180&#176; and the two signals have the same amplitude. This interaction of waves is called wave interference. A phase difference may occur because of the change of phase of a reflected wave, or because of the longer path followed by it.

The second effect decreases with greater distance between transmitter and receiver, for under these conditions the difference in path lengths is smaller. At lower frequencies there is no practical solution to interference caused in this way. For VHF and higher frequencies, the condition can be improved by elevating the antenna, by elevating the antenna, if the wave is vertically polarized. Additionally, interference at higher frequencies can be more nearly eliminated because of the greater ease of beaming the signal to avoid reflection.

Reflections may also occur from mountains, trees, and other obstacles. Such reflection is negligible for lower frequencies, but becomes more prevalent as frequency increases. In radio communication, it can be reduced by using directional antennas, but this solution is not always available for navigational systems.

Various reflecting surfaces occur in the atmosphere. At high frequencies, reflections take place from rain. At still higher frequencies, reflections are possible from clouds, particularly rain clouds. Reflections may even occur at a sharply defined boundary surface between air masses, as when warm, moist air flows over cold, dry air. When such a surface is roughly parallel to the surface of the earth, radio waves may travel for greater distances than normal The principal source of reflection in the atmosphere is the ionosphere.

1005.	Refraction
Refraction of radio waves is similar to that of light waves. Thus, as a signal passes from air of one density to that of a different density, the direction of travel is altered. The principal cause of refraction in the atmosphere is the difference in temperature and pressure occurring at various heights and in different air masses.

Refraction occurs at all frequencies, but below 30 MHz the effect is small as compared with ionospheric effects, diffraction, and absorption. At higher frequencies, refraction in the lower layer of the atmosphere extends the radio horizon to a distance about 15 percent greater than the visible horizon. The effect is the same as if the radius of the earth were about one-third greater than it is and there were no refraction.

Sometimes the lower portion of the atmosphere becomes stratified. This stratification results in nonstandard temperature and moisture changes with height. If there is a marked temperature inversion or a sharp decrease in water vapor content with increased height, a horizontal radio duct may be formed. High frequency radio waves traveling horizontally within the duct are refracted to such an extent that they remain within the duct, following the curvature of the earth for phenomenal distances. This is called super-refraction. Maximum results are obtained when both transmitting and receiving antennas are within the duct. There is a lower limit to the frequency affected by ducts. It varies from about 200 MHz to more than 1,000 MHz. At night, surface ducts may occur over land due to cooling of the surface. At sea, surface ducts about 50 feet thick may occur at any time in the trade wind belt. Surface ducts 100 feet or more in thickness may extend from land out to sea when warm air from the land flows over the cooler ocean surface. Elevated ducts from a few feet to more than 1,000 feet in thickness may occur at elevations of 1,000 to 5,000 feet, due to the settling of a large air mass. This is a frequent occurrence in Southern California and certain areas of the Pacific Ocean.

A bending in the horizontal plane occurs when a groundwave crosses a coast at an oblique angle. This is due to a marked difference in the conducting and reflecting properties of the land and water over which the wave travels. The effect is known as coastal refraction or land effect.

1006.	The Ionosphere
Since an atom normally has an equal number of negatively charged electrons and positively charged protons, it is electrically neutral. An ion is an atom or group of atoms which has become electrically charged, either positively or negatively, by the loss or gain of one or more electrons. Loss of electrons may occur in a variety of ways. In the atmosphere, ions are usually formed by collision of atoms with rapidly moving particles, or by the action of cosmic rays or ultraviolet light. In the lower portion of the atmosphere, recombination soon occurs, leaving a small percentage of ions. In thin atmosphere far above the surface of the earth, however, atoms are widely separated and a large number of ions may be present. The region of numerous positive and negative ions and unattached electrons is called the ionosphere. The extent of ionization depends upon the kinds of atoms present in the atmosphere, the density of the atmosphere, and the position relative to the sun (time of day and season). After sunset, ions and electrons recombine faster than they are separated, decreasing the ionization of the atmosphere.

An electron can be separated from its atom only by the application of greater energy than that holding the electron. Since the energy of the electron depends primarily upon the kind of an atom of which it is a part, and its position relative to the nucleus of that atom, different kinds of radiation may cause ionization of different substances.

In the outermost regions of the atmosphere, the density is so low that oxygen exists largely as separate atoms, rather than combining as molecules as it does nearer the surface of the earth. At great heights the energy level is low and ionization from solar radiation is intense. This is known as the F layer. Above this level the ionization decreases because of the lack of atoms to be ionized. Below this level it decreases because the ionizing agent of appropriate energy has already been absorbed. During daylight, two levels of maximum F ionization can be detected, the F2 layer at about 125 statute miles above the surface of the earth, and the F1 layer at about 90 statute miles. At night, these combine to form a single F layer.

At a height of about 60 statute miles, the solar radiation not absorbed by the F layer encounters, for the first time, large numbers of oxygen molecules. A new maximum ionization occurs, known as the E layer. The height of this layer is quite constant, in contrast with the fluctuating F layer. At night the E layer becomes weaker by two orders of magnitude.

Below the E layer, a weak D layer forms at a height of about 45 statute miles, where the incoming radiation encounters ozone for the first time. The D layer is the principal source of absorption of HF waves, and of reflection of LF and VLF waves during daylight.

1007.	The Ionosphere And Radio Waves
When a radio wave encounters a particle having an electric charge, it causes that particle to vibrate. The vibrating particle absorbs electromagnetic energy from the radio wave and radiates it. The net effect is a change of polarization and an alteration of the path of the wave. That portion of the wave in a more highly ionized region travels faster, causing the wave front to tilt and the wave to be directed toward a region of less intense ionization.
Refer to Figure 1007a, in which a single layer of the ionosphere is considered. Ray 1 enters the ionosphere at such an angle that its path is altered, but it passes through and proceeds outward into space. As the angle with the horizontal decreases, a critical value is reached where ray 2 is bent or reflected back toward the earth. As the angle is still further decreased, such as at 3, the return to earth occurs at a greater distance from the transmitter.

A wave reaching a receiver by way of the ionosphere is called a skywave. This expression is also appropriately applied to a wave reflected from an air mass boundary. In common usage, however, it is generally associated with the ionosphere. The wave which travels along the surface of the earth is called a groundwave. At angles greater than the critical angle, no skywave signal is received. Therefore, there is a minimum distance from the transmitter at which skywaves can be received. This is called the skip distance, shown in Figure 1007a. If the groundwave extends out for less distance than the skip distance, a skip zone occurs, in which no signal is received.










The critical radiation angle depends upon the intensity of ionization, and the frequency of the radio wave. As the frequency increases, the angle becomes smaller. At frequencies greater than about 30 MHz virtually all of the energy penetrates through or is absorbed by the ionosphere. Therefore, at any given receiver there is a maximum usable frequency if skywaves are to be utilized. The strongest signals are received at or slightly below this frequency. There is also a lower practical frequency beyond which signals are too weak to be of value. Within this band the optimum frequency can be selected to give best results. It cannot be too near the maximum usable frequency because this frequency fluctuates with changes of intensity within the ionosphere. During magnetic storms the ionosphere density decreases. The maximum usable frequency decreases, and the lower usable frequency increases. The band of usable frequencies is thus narrowed. Under extreme conditions it may be completely eliminated, isolating the receiver and causing a radio blackout.

Skywave signals reaching a given receiver may arrive by any of several paths, as shown in Figure 1007b. A signal which undergoes a single reflection is called a &#8220;one-hop&#8221; signal, one which undergoes two reflections with a ground reflection between is called a &#8220;two-hop&#8221; signal, etc. A &#8220;multihop&#8221; signal undergoes several reflections. The layer at which the reflection occurs is usually indicated, also, as &#8220;one-hop E,&#8221; &#8220;two-hop F,&#8221; etc.
Because of the different paths and phase changes occurring at each reflection, the various signals arriving at a receiver have different phase relationships. Since the density of the ionosphere is continually fluctuating, the strength and phase relationships of the various signals may undergo an almost continuous change. Thus, the various signals may reinforce each other at one moment and cancel each other at the next, resulting in fluctuations of the strength of the total signal received. This is called fading. This phenomenon may also be caused by interaction of components within a single reflected wave, or changes in its strength due to changes in the reflecting surface. Ionospheric changes are associated with fluctuations in the radiation received from the sun, since this is the principal cause of ionization. Signals from the F layer are particularly erratic because of the rapidly fluctuating conditions within the layer itself. The maximum distance at which a one-hop E signal can be received is about 1,400 miles. At this distance the signal leaves the transmitter in approximately a horizontal direction. A onehop F signal can be received out to about 2,500 miles. At low frequencies groundwaves extend out for great distances. A skywave may undergo a change of polarization during reflection from the ionosphere, accompanied by an alteration in the direction of travel of the wave. This is called polarization error. Near sunrise and sunset, when rapid changes are occurring in the ionosphere, reception may become erratic and polarization error a maximum. This is called night effect.

1008.	Diffraction
When a radio wave encounters an obstacle, its energy is reflected or absorbed, causing a shadow beyond the obstacle. However, some energy does enter the shadow area because of diffraction. This is explained by Huygens&#8217; principle, which states that every point on the surface of a wave front is a source of radiation, transmitting energy in all directions ahead of the wave. No noticeable effect of this principle is observed until the wave front encounters an obstacle, which intercepts a portion of the wave. From the edge of the obstacle, energy is radiated into the shadow area, and also outside of the area. The latter interacts with energy from other parts of the wave front, producing alternate bands in which the secondary radiation reinforces or tends to cancel the energy of the primary radiation. Thus, the practical effect of an obstacle is a greatly reduced signal strength in the shadow area, and a disturbed pattern for a short distance outside the shadow area. This is illustrated in Figure 1008.










The amount of diffraction is inversely proportional to the frequency, being greatest at very low frequencies.

1009.	Absorption And Scattering
The amplitude of a radio wave expanding outward through space varies inversely with distance, weakening with increased distance. The decrease of strength with distance is called attenuation. Under certain conditions the attenuation is greater than in free space.
A wave traveling along the surface of the earth loses a certain amount of energy to the earth. The wave is diffracted downward and absorbed by the earth. As a result of this absorption, the remainder of the wave front tilts downward, resulting in further absorption by the earth. Attenuation is greater over a surface which is a poor conductor. Relatively little absorption occurs over sea water, which is an excellent conductor at low frequencies, and low frequency groundwaves travel great distances over water.

A skywave suffers an attenuation loss in its encounter with the ionosphere. The amount depends upon the height and composition of the ionosphere as well as the frequency of the radio wave. Maximum ionospheric absorption occurs at about 1,400 kHz.

In general, atmospheric absorption increases with frequency. It is a problem only in the SHF and EHF frequency range. At these frequencies, attenuation is further increased by scattering due to reflection by oxygen, water vapor, water droplets, and rain in the atmosphere.

1010.	Noise
Unwanted signals in a receiver are called interference. The intentional production of such interference to obstruct communication is called jamming. Unintentional interference is called noise.

Noise may originate within the receiver. Hum is usually the result of induction from neighboring circuits carrying alternating current. Irregular crackling or sizzling sounds may be caused by poor contacts or faulty components within the receiver. Stray currents in normal components causes some noise. This source sets the ultimate limit of sensitivity that can be achieved in a receiver. It is the same at any frequency.

Noise originating outside the receiver may be either man-made or natural. Man-made noises originate in electrical appliances, motor and generator brushes, ignition systems, and other sources of sparks which transmit electromagnetic signals that are picked up by the receiving antenna.

Natural noise is caused principally by discharge of static electricity in the atmosphere. This is called atmospheric noise, atmospherics, or static. An extreme example is a thunderstorm. An exposed surface may acquire a considerable charge of static electricity. This may be caused by friction of water or solid particles blown against or along such a surface. It may also be caused by splitting of a water droplet which strikes the surface, one part of the droplet requiring a positive charge and the other a negative charge.

These charges may be transferred to the surface. The charge tends to gather at points and ridges of the conducting surface, and when it accumulates to a sufficient extent to overcome the insulating properties of the atmosphere, it discharges into the atmosphere. Under suitable conditions this becomes visible and is known as St. Elmo&#8217;s fire, which is sometimes seen at mastheads, the ends of yardarms, etc. Atmospheric noise occurs to some extent at all frequencies but decreases with higher frequencies. Above about 30 MHz it is not generally a problem.

1011.	Antenna Characteristics
Antenna design and orientation have a marked effect upon radio wave propagation. For a single-wire antenna, strongest signals are transmitted along the perpendicular to the wire, and virtually no signal in the direction of the wire. For a vertical antenna, the signal strength is the same in all horizontal directions. Unless the polarization undergoes a change during transit, the strongest signal received from a vertical transmitting antenna occurs when the receiving antenna is also vertical.

For lower frequencies the radiation of a radio signal takes place by interaction between the antenna and the ground. For a vertical antenna, efficiency increases with greater length of the antenna. For a horizontal antenna, efficiency increases with greater distance between antenna and ground. Near-maximum efficiency is attained when this distance is one-half wavelength. This is the reason for elevating low frequency antennas to great heights. However, at the lowest frequencies, the required height becomes prohibitively great. At 10 kHz it would be about 8 nautical miles for a half-wavelength antenna. Therefore, lower frequency antennas are inherently inefficient. This is partly offset by the greater range of a low frequency signal of the same transmitted power as one of higher frequency. At higher frequencies, the ground is not used, both conducting portions being included in a dipole antenna. Not only can such an antenna be made efficient, but it can also be made sharply directive, thus greatly increasing the strength of the signal transmitted in a desired direction. The power received is inversely proportional to the square of the distance from the transmitter, assuming there is no attenuation due to absorption or scattering.

1012.	Range
The range at which a usable signal is received depends upon the power transmitted, the sensitivity of the receiver, frequency, route of travel, noise level, and perhaps other factors. For the same transmitted power, both the groundwave and skywave ranges are greatest at the lowest frequencies, but this is somewhat offset by the lesser efficiency of antennas for these frequencies. At higher frequencies, only direct waves are useful, and the effective range is greatly reduced. Attenuation, skip distance, ground reflection, wave interference, condition of the ionosphere, atmospheric noise level, and antenna design all affect the distance at which useful signals can be received.

1013.	Radio Wave Propagation
Frequency is an important consideration in radio wave propagation. The following summary indicates the principal effects associated with the various frequency bands, starting with the lowest and progressing to the highest usable radio frequency. Very Low Frequency (VLF, 10 to 30 kHz): The VLF signals propagate between the bounds of the ionosphere and the earth and are thus guided around the curvature of the earth to great distances with low attenuation and excellent stability. Diffraction is maximum. Because of the long wavelength, large antennas are needed, and even these are inefficient, permitting radiation of relatively small amounts of power. Magnetic storms have little effect upon transmission because of the efficiency of the &#8220;earth-ionosphere waveguide.&#8221; During such storms, VLF signals may constitute the only source of radio communication over great distances. However, interference from atmospheric noise may be troublesome. Signals may be received from below the surface of the sea.

Low Frequency (LF, 30 to 300 kHz): As frequency is increased to the LF band and diffraction decreases, there is greater attenuation with distance, and range for a given power output falls off rapidly. However, this is partly offset by more efficient transmitting antennas. LF signals are most stable within groundwave distance of the transmitter. A wider bandwidth permits pulsed signals at 100 kHz. This allows separation of the stable groundwave pulse from the variable skywave pulse up to 1,500 km, and up to 2,000 km for overwater paths. The frequency for Loran C is in the LF band. This band is also useful for radio direction finding and time dissemination.

Medium Frequency (MF, 300 to 3,000 kHz): Groundwaves provide dependable service, but the range for a given power is reduced greatly. This range varies from about 400 miles at the lower portion of the band to about 15 miles at the upper end for a transmitted signal of 1 kilowatt. These values are influenced, however, by the power of the transmitter, the directivity and efficiency of the antenna, and the nature of the terrain over which signals travel. Elevating the antenna to obtain direct waves may improve the transmission. At the lower frequencies of the band, skywaves are available both day and night. As the frequency is increased, ionospheric absorption increases to a maximum at about 1,400 kHz. At higher frequencies the absorption decreases, permitting increased use of skywaves. Since the ionosphere changes with the hour, season, and sunspot cycle, the reliability of skywave signals is variable. By careful selection of frequency, ranges of as much as 8,000 miles with 1 kilowatt of transmitted power are possible, using multihop signals. However, the frequency selection is critical. If it is too high, the signals penetrate the ionosphere and are lost in space. If it is too low, signals are too weak. In general, skywave reception is equally good by day or night, but lower frequencies are needed at night. The standard broadcast band for commercial stations (535 to 1,605 kHz) is in the MF band.

High Frequency (HF, 3 to 30 MHz): As with higher medium frequencies, the groundwave range of HF signals is limited to a few miles, but the elevation of the antenna may increase the direct-wave distance of transmission. Also, the height of the antenna does have an important effect upon skywave transmission because the antenna has an &#8220;image&#8221; within the conducting earth. The distance between antenna and image is related to the height of the antenna, and this distance is as critical as the distance between elements of an antenna system. Maximum usable frequencies fall generally within the HF band. By day this may be 10 to 30 MHz, but during the night it may drop to 8 to 10 MHz. The HF band is widely used for ship-to-ship and ship-to-shore communication.

Very High Frequency (VHF, 30 to 300 MHz): Communication is limited primarily to the direct wave, or the direct wave plus a ground-reflected wave. Elevating the antenna to increase the distance at which direct waves can be used results in increased distance of reception, even though some wave interference between direct and ground-reflected waves is present. Diffraction is much less than with lower frequencies, but it is most evident when signals cross sharp mountain peaks or ridges. Under suitable conditions, reflections from the ionosphere are sufficiently strong to be useful, but generally they are unavailable. There is relatively little interference from atmospheric noise in this band. Reasonably efficient directional antennas are possible with VHF. The VHF band is much used for communication.

Ultra High Frequency (UHF, 300 to 3,000 MHz):
Skywaves are not used in the UHF band because the ionosphere is not sufficiently dense to reflect the waves, which pass through it into space. Groundwaves and ground-reflected waves are used, although there is some wave interference. Diffraction is negligible, but the radio horizon extends about 15 percent beyond the visible horizon, due principally to refraction. Reception of UHF signals is virtually free from fading and interference by atmospheric noise. Sharply directive antennas can be produced for transmission in this band, which is widely used for ship-to-ship and ship-to-shore communication.

Super High Frequency (SHF, 3,000 to 30,000 MHz):
In the SHF band, also known as the microwave or as the centimeter wave band, there are no skywaves, transmission being entirely by direct and ground-reflected waves. Diffraction and interference by atmospheric noise are virtually nonexistent. Highly efficient, sharply directive antennas can be produced. Thus, transmission in this band is similar to that of UHF, but with the effects of shorter waves being greater. Reflection by clouds, water droplets, dust particles, etc., increases, causing greater scattering, increased wave interference, and fading. The SHF band is used for marine navigational radar.

Extremely High Frequency (EHF, 30,000 to 300,000 MHz): The effects of shorter waves are more pronounced in the EHF band, transmission being free from wave interference, diffraction, fading, and interference by atmospheric noise. Only direct and ground-reflected waves are available. Scattering and absorption in the atmosphere are pronounced and may produce an upper limit to the frequency useful in radio communication.

1014.	Regulation Of Frequency Use
While the characteristics of various frequencies are important to the selection of the most suitable one for any given purpose, these are not the only considerations. Confusion and extensive interference would result if every user had complete freedom of selection. Some form of regulation is needed. The allocation of various frequency bands to particular uses is a matter of international agreement.

Within the United States, the Federal Communications Commission has responsibility for authorizing use of particular frequencies. In some cases a given frequency is allocated to several widely separated transmitters, but only under conditions which minimize interference, such as during daylight hours. Interference between stations is further reduced by the use of channels, each of a narrow band of frequencies. Assigned frequencies are separated by an arbitrary band of frequencies that are not authorized for use. In the case of radio aids to navigation and ship communications bands of several channels are allocated, permitting selection of band and channel by the user.

1015.	Types Of Radio Transmission
A series of waves transmitted at constant frequency and amplitude is called a continuous wave (CW). This cannot be heard except at the very lowest radio frequencies, when it may produce, in a receiver, an audible hum of high pitch. Although a continuous wave may be used directly, as in radiodirection finding or Decca, it is more commonly modified in some manner. This is called modulation. When this occurs, the continuous wave serves as a carrier wave for information. Any of several types of modulation may be used.

In amplitude modulation (AM) the amplitude of the carrier wave is altered in accordance with the amplitude of a modulating wave, usually of audio frequency, as shown in Figure 1015a. In the receiver the signal is demodulated by removing the modulating wave and converting it back to its original form. This form of modulation is widely used in voice radio, as in the standard broadcast band of commercial broadcasting.
If the frequency instead of the amplitude is altered in accordance with the amplitude of the impressed signal, as shown in Figure 1015a, frequency modulation (FM) occurs. This is used for commercial FM radio broadcasts and the sound portion of television broadcasts.

Pulse modulation (PM) is somewhat different, there being no impressed modulating wave. In this form of transmission, very short bursts of carrier wave are transmitted, separated by relatively long periods of &#8220;silence,&#8221; during which there is no transmission. This type of transmission, illustrated in Figure 1015b, is used in some common radio navigational aids, including radar and Loran-C.

1016.	Transmitters
A radio transmitter consists essentially of (1) a power supply to furnish direct current, (2) an oscillator to convert direct current into radio-frequency oscillations (the carrier wave), (3) a device to control the generated signal, and (4) an amplifier to increase the output of the oscillator. For some transmitters a microphone is needed with a modulator and final amplifier to modulate the carrier wave. In addition, an antenna and ground (for lower frequencies) are needed to produce electromagnetic radiation. These components are illustrated diagrammatically in Figure 1016.










1017.	Receivers
When a radio wave passes a conductor, a current is induced in that conductor. A radio receiver is a device which senses the power thus generated in an antenna, and transforms it into usable form. It is able to select signals of a single frequency (actually a narrow band of frequencies) from among the many which may reach the receiving antenna. The receiver is able to demodulate the signal and provide adequate amplification. The output of a receiver may be presented audibly by earphones or loudspeaker; or visually on a dial, cathode-ray tube, counter, or other display. Thus, the useful reception of radio signals requires three components: (1) an antenna, (2) a receiver, and (3) a display unit.

Radio receivers differ mainly in (1) frequency range, the range of frequencies to which they can be tuned; (2) selectivity, the ability to confine reception to signals of the desired frequency and avoid others of nearly the same frequency; (3) sensitivity, the ability to amplify a weak signal to usable strength against a background of noise; (4) stability, the ability to resist drift from conditions or values to which set; and (5) fidelity, the completeness with which the essential characteristics of the original signal are reproduced. 

Receivers may have additional features such as an automatic frequency control, automatic noise limiter, etc.
Some of these characteristics are interrelated. For instance, if a receiver lacks selectivity, signals of a frequency differing slightly from those to which the receiver is tuned may be received. This condition is called spillover, and the resulting interference is called crosstalk. If the selectivity is increased sufficiently to prevent spillover, it may not permit receipt of a great enough band of frequencies to obtain the full range of those of the desired signal. Thus, the fidelity may be reduced.
A transponder is a transmitter-receiver capable of accepting the challenge of an interrogator and automatically transmitting an appropriate reply.

U.S. RADIONAVIGATION POLICY
1018.	The Federal Radionavigation Plan
The Federal Radionavigation Plan (FRP) is produced by the U.S. Departments of Defense and Transportation. It establishes government policy on electronic navigation systems, ensuring consideration of national interests and efficient use of resources. It presents an integrated Federal plan for all common-use civilian and military Radionavigation systems, outlines approaches for consolidation of systems, provides information and schedules, defines and clarifies new or unresolved issues, and provides a focal point for user input. The FRP is a review of existing and planned radionavigation systems used in air, space, land, and marine navigation. It is available from the National Technical Information Service, Springfield, Virginia, 22161.

The first edition of the FRP was released in 1980 as part of a Presidential report to Congress. It marked the first time that a joint Department of Transportation/Department of Defense plan had been developed for systems used by both departments. The FRP has had international impact on navigation systems; it has been distributed to the International Maritime Organization (IMO), the International Civil Aviation Organization (ICAO), the International Association of Lighthouse Authorities (IALA), and other international organizations.

During a national emergency, any or all of the systems may be discontinued due to a decision by the National Command Authority (NCA). The NCA&#8217;s policy is to continue to operate radionavigation systems as long as the U.S. and its allies derive greater benefit than adversaries. Operating agencies may shut down systems or change signal formats and characteristics during such an emergency. The plan is reviewed continually and updated biennially. Industry, advisory groups, and other interested parties provide input. The plan considers governmental responsibilities for national security, public safety, and transportation system economy. It is the official source of radionavigation systems policy and planning for the United States. Systems covered by the FRP include, Radiobeacons, Omega, TACAN, MLS, GPS, Loran C, VOR/VOR-DME/ VORTAC, ILS, and Transit.

1019.	Individual System Plans
In order to meet both civilian and military needs, the federal government has established a number of different navigation systems. Each system utilized the latest technology available at the time of implementation and has been upgraded as technology and resources permitted. The FRP addresses the length of time each system should be part of the system mix. The 1992 FRP sets forth the following system policy guidelines:
RADIOBEACONS: Both maritime and aeronautical radiobeacons provide the civilian community with a lowcost, medium accuracy navigation system. They will remain part of the radionavigation mix at least until the year 2000. Those radiobeacons suitable for supporting Differential GPS (DGPS) will remain well into the next century. Many of the remaining maritime radiobeacons may be discontinued after the year 2000.

LORAN C: Loran C provides navigation, location, and timing services for both civil and military air, land, and sea users. It is the federally provided navigation system for the maritime Coastal Confluence Zone; it is also a supplemental air navigation system. The Loran C system serving the continental U.S., Alaska, and coastal areas with the exception of Hawaii, is expected to remain in place through the year 2015. Military requirements for Loran C ended in 1994, and U.S.-maintained stations overseas and in Hawaii will be phased out. Discussions between the U.S. and foreign governments may result in continuation of certain overseas stations after termination of the military requirements.

OMEGA: Omega serves civilian and military maritime and air navigation. The military requirement for Omega ended in 1994; the system may be maintained for civil users at least until the year 2005. Replacement of equipment at some stations may result in disruption or reduction of service in some areas. Also, the Omega system relies on support from several foreign nations whose cooperation may not be forthcoming.

TRANSIT: The Transit satellite system will end operations in December 1996.

GPS: The Global Positioning System, or GPS, will be the military&#8217;s primary radionavigation system well into the next century. It is operated by the U.S. Air Force, and it will provide two basic levels of positioning service.

Standard Positioning Service (SPS) is a positioning and timing service which will provide horizontal positioning accuracies of 100 meters (2 drms, 95&#37; probability) and 300 meters (99.99% probability). 

Precise Positioning Service (PPS) will provide extremely accurate positioning to only military users. 

DIFFERENTIAL GPS: DGPS services are planned by several DOT agencies to enhance civilian navigation without reliance on the PPS. The Coast Guard operates marine DGPS in U.S. coastal waters. DGPS is a system in which differences between observed and calculated GPS signals are broadcast to users using marine radiobeacons. The Coast Guard is implementing DGPS service in all U.S. coastal waters, beginning with important ports and harbors, to include Hawaii and the Great Lakes. It will provide 4-20 meter continuous accuracy.

A Memorandum of Agreement between DOD and DOT for radionavigation planning became effective in 1979. It was updated in 1984 and again in 1990. This agreement recognizes the joint responsibility of both agencies to provide cost-effective navigation systems for both military and civilian users, and requires the cooperation of both agencies in navigation systems planning.

Many factors influence the choice of navigation systems, which must satisfy an extremely diverse group of users. International agreements must be honored. The current investment in existing systems by both government and users must be considered. The full life-cycle cost of each system must be considered. No system will be phased out without consideration of all these factors. The FRP recognizes that-GPS may not meet the needs of all users; therefore, some systems are currently being evaluated independently of GPS. When GPS is fully implemented and evaluated, a further review will determine which systems to retain and which to phase out. The goal is to meet all military and civilian requirements with the minimum number of systems.

The Departments of Defense and Transportation continually evaluate the components which make up the federally provided and maintained radionavigation system. Several factors influence the decision on the proper mix of systems; cost, military utility, accuracy requirements, and user requirements all drive the problem of allocating scarce resources to develop and maintain marine navigation systems. The lowering cost and increasing accuracy of the Global Positioning System increase its attractiveness as the primary navigation method of the future for both military and civilian use. However, the popularity of GPS with navigation planners masks the fact that it is still much more expensive to the user than other radionavigation systems such as loran and omega, and many civilian mariners may balk at the cost of conversion. Planners&#8217; uncertainties over the future of the older navigation systems, especially in a time of shrinking resources, will contribute to the uncertainty which will mark the next five years in radionavigation planning and development.

RADIO DIRECTION FINDING
1020.	Introduction
Medium frequency radio direction finders on board vessels enable measurement of the bearings of marine radiobeacons, aeronautical radiobeacons, and some commercial radio stations. This is the simplest use of radio waves in navigation.

Depending upon the design of the radio direction finder (RDF), the bearings of the radio transmissions are measured as relative bearings, or as both relative and true bearings. In one design, the true bearing dial is manually set with respect to the relative bearing dial, in accordance with the ship&#8217;s heading. In another design, the true bearing dial is rotated electrically in accordance with a course input from the gyrocompass.

Radiobeacons established primarily for mariners are known as marine radiobeacons; beacons established primarily for airmen are known as aeronautical radiobeacons; other beacons established for both classes of user are sometimes known as aeromarine radiobeacons.

The most common type of marine radiobeacon transmits radio waves of approximately uniform strength in all directions. These omnidirectional beacons are known as
circular radiobeacons.

Except for calibration, radiobeacons operate continuously, regardless of weather conditions.

Simple combinations of dots and dashes are used for station identification. Where applicable, the Morse equivalent character or characters are shown in conjunction with the station characteristic. All radiobeacons superimpose the characteristic on a carrier wave which is on continuously during the period of transmission. This extends the usefulness of marine radiobeacons to an airborne or marine user of an automatic radio direction finder (ADF). Users of the &#8220;aural null&#8221; type radio direction finder notice no change. A 10-second dash is incorporated in the characteristic signal to enable the user of the aural null type of radio direction finder to refine the bearing.

Aeronautical radiobeacons are sometimes used by marine navigators for determining lines of position when marine radiobeacons are not available. Since it is not possible to predict the extent to which land effect may render the bearings of these beacons unreliable, they are not included in Pub. 117, Radio Navigational Aids unless they are within the marine frequency band and they are close enough to the coast to have negligible land effect. Their inclusion in Pub. 117 does not imply that the beacons have been found reliable for marine use.

176 RADIO WAVES
1021.	Using Radio Direction Finders
Direction bearing measurement at the receiver is accomplished with a directional antenna. Nearly all antennas have some directional properties, but in the usual antenna used for radio communication, these properties are not sufficiently critical for navigational use.

Simple small craft RDF units usually have a ferrite rod antenna mounted directly on a receiver, with a 360&#176; graduated scale. The rod can be rotated to the null and a reading taken off the scale, which is preset to either the boat&#8217;s course or true north, according the navigator&#8217;s wishes. Some small craft RDFs have a portable hand-held combination ferrite rod and compass, with earphones to hear the null.

Two types of loop antenna are used in larger radio direction finders. In one of these, the crossed loop type, two loops are rigidly mounted in such manner that one is placed at 90&#176; to the other. The relative output of the two antennas is related to the orientation of each with respect to the direction of travel of the radio wave, and is measured by a device called a goniometer. This is the type antenna used in an automatic direction finder. In the other variation, the rotating loop type, a single loop is kept in rapid rotation by means of a motor. The antenna output is shown on a cathode-ray tube, and the resulting display shows the direction of the signal.

1022.	Errors of Radio Bearings
Bearings obtained by radio direction finder are subject to certain errors:
Quadrantal error: When radio waves arrive at a receiver, they are influenced somewhat by the immediate environment. An erroneous bearing results from currents induced in the direction finder antenna by re-radiation from the structural features of the vessel&#8217;s superstructure and distortion of the radio wave front due to the physical dimensions and contour of the vessel&#8217;s hull. This quadrantal error is a function of the relative bearing, normally being maximum for bearings broad on the bow and broad on the quarter. Its value for various bearings can be determined, and a calibration table made.
Coastal refraction: A radio wave crossing a coastline at an oblique angle undergoes a change of direction due to differences in conducting and reflecting properties of land and water. This is sometimes called land effect. It is avoided by not using, or regarding as of doubtful accuracy, bearings of waves which cross a shoreline at an oblique angle. Bearings making an angle of less than 15&#176; to 20&#176; with a shoreline should not be trusted. If the transmitter is near the coast, negligible error is introduced because of the short distance the waves travel before undergoing refraction.

Polarization error: The direction of travel of radio waves may undergo an alteration during the confused period near sunrise or sunset, when great changes are taking place in the ionosphere. This error is sometimes called night effect. The error can be minimized by averaging several readings, but any radio bearings taken during this period should be considered of doubtful accuracy.

Reciprocal bearings: Unless a radio direction finder has a vertical sensing wire, there is a possible 180&#176; ambiguity in the reading. If such an error is discovered, one should take the reciprocal of the uncorrected reading, and apply the correction for the new direction. If there is doubt as to which of the two possible directions is the correct one, one should wait long enough for the bearing to change appreciably and take another reading. The transmitter should draw aft between readings. If the reciprocal is used, the station will appear to have drawn forward. A reciprocal bearing furnished by a direction finder station should not be used because the quadrantal error is not known, either on the given bearing or its reciprocal.

1023.	Accuracy Of Radio Bearings
In general, good radio bearings should not be in error by more than 2&#176; for distances under 150 nautical miles. However, conditions vary considerably, and skill is an important factor. By observing the technical instructions for the equipment and practicing frequently when results can be checked by visual observation or by other means, one can develop skill and learn to what extent radio bearings can be relied upon under various conditions.
Other factors affecting accuracy include range, the condition of the equipment, and the accuracy of the calibration. Errors in bearing can result if the selectivity of a radio direction finder is poor.

1024.	Factors Affecting Maximum Range
The service range of a radiobeacon is determined by the strength of the radiated signal. Field strength requirements for a given service range vary with latitude, being higher in the southern latitudes. The actual useful range may vary considerably from the service range with different types of radio direction finders and during varying atmospheric conditions. 

Sensitivity is a measure of the ability of a receiver to detect transmissions. The sensitivity of a radio direction finder determines the degree to which the full range capability of the radiobeacon system can be utilized.

Selectivity is a measure of the ability of a receiver to choose one frequency and reject all others. Selectivity varies with the type of receiver and its condition.

1025.	Using RDF Bearings
Due to the many factors which enter into the transmission and reception of radio signals, a mariner cannot practically estimate his distance from a radiobeacon either by the strength of the signals received or by the time at which the signals were first heard.
By setting the ship&#8217;s head toward the null, the navigator can steer toward the transmitter, and this is the most common use of RDFs today. In reduced visibility it is unwise to head directly toward the station unless there is certain sea room. Soundings should be watched carefully when homing, and a good lookout should be kept.
Alternatively, bearings can be taken on two or more stations and the lines plotted to determine a fix. A single RDF bearing can, of course, be crossed with any other LOP. An RDF bearing crossed with a sounding curve can give a rough position in the absence of any other systems. 

For emergency use, an ordinary transistor radio tuned to a commercial station can provide a rough bearing if the location of the transmitter is known.
Before taking bearings on a commercial broadcasting station, the mariner should consider the following, all of which lead to errors:
1.	The frequency of the commercial station may differ widely from the frequency for which the radio direction finder is calibrated.
2.	The antenna may be remote from the broadcast station.
3.	The commercial stations are usually inland.
Accordingly, the use of commercial broadcasting stations to obtain a direction finder bearing is not recommended for accurate navigation. If these stations are used, the mariner should recognize the limitations of the bearings obtained.

1026.	Radio Direction Finder Stations
Radio direction finder stations are equipped with special apparatus to determine the direction of radio signals transmitted by ships. Many are for use only in emergencies, and none are now located in the U.S. See Pub. 117, Radio Navigational Aids, for a current worldwide list of RDF stations.

*end ch 10*


----------



## Fishers of Men

*GPS Planning to Avoid Danger
This would come in REAL handy around the islands.*
There will be days on the water when your desire is not to proceed directly from point A to point B but to wander here and there, exploring coves and bays, poking among is lands, and generally enjoying a summer day. After all, freedom from goals and restraints is one of the great attractions of boating. Furthermore, sailors often need to tack back and forth into the wind rather than sailing from point to point. At times such as these, you may be more interested in knowing where you do not want to go than where you do. Now it&#8217;s time to draw on a family of avoidance techniques using GPS with paper or digital charts.

Define the Area
First, figure out how large an area you wish to pre-qualify; and the characteristics of the hazards within that area. &#8216;When an entire bay contains only a moderate number of hazards, you may be able to flag all of them in your GPS receiver&#8217;s memory. But if the waters in question are liberally sprinkled with ledges and other obstacles, you may be able to pre-qualify only a small swath across one section.

The idea is to clearly mark the hazards on your chart, then use the techniques below to enter this information into your GPS.

Mark the Obstacles
Obstacles come in various flavors, some more isolated than others. A wreck lurking just below the surface is an isolated hazard, much like an isolated rock. An outcropping of shallow rocks or a series of sandbars covers a broader area. A tightly circumscribed area is naturally easier to delimit. Shoals typically extend some distance and cover even larger areas than outcrops, requiring their own avoidance techniques and navigation tools.










Isolated Hazards
Wrecks, submerged pilings, rocks, and other isolated obstacles are easy to identify and mark. Each of these hazards represents a point on your chart. You can measure the coordinates for each, then enter them as waypoints into your GPS. You need to set a criterion as to how far you want to stay away from any of these isolated marks. Generally, a radius of 1 of a nautical mile (about 600 feet) is practical. If the hazard is marked with a navigation aid, you can use that as a supplement when you are on the water; if the object is not marked, 600 feet is a good rule of thumb. If you only need to mark a few isolated hazards, you can save them as avoidance waypoints and set an alarm at the danger radius (see below). But your GPS only permits a few avoidance waypoints; when there are many hazards to mark, you&#8217;ll have to save them as ordinary waypoints (see page 60 for naming conventions) and, when on the water, monitor their proximities using your chart and the GPS 

Map Screen.
Hazardous Regions
Outcroppings of rocks are common, often occurring over a definable region; unlike isolated hazards, they cannot be adequately reduced to a single waypoint. In this case you need to draw a circle (or other boundary) that encompasses the rocks. If you&#8217;re working with a paper chart, measure across the hazardous area at its broadest extent and set your drawing compass to half that distance. Now place the point of the compass in the center of the area and lightly swing a circle. If the circle encompasses all the hazards, make the circle darker and note the coordinates of its center, which you can mark with an X. You may need to adjust the center until you find the best fit. Measure the radius of the circle by taking your drawing compass over to the latitude or distance scale, and note this value. (All this can be done just as easily&#8212;in fact more easily&#8212;on a digital chart, designating the center of the hazard as a mark and finding its radius with an A to B plot.

Now you can enter the center point coordinates into your GPS as an avoidance waypoint. This is a special form of waypoint that allows you to set an alarm if you wander within a preset radius. When you set up the waypoint, enter both its coordinates and the alarm radius. Make sure the alarm is on and you can hear it.

FIGURE 7-2. An avoidance waypoint allows you to set an alarm radius around isolated hazards or hazardous areas. Once set, the GPS will sound an alarm if you&#8217;ve entered the danger circle.










FIGURE 7-3. Your first task is to identify what constitutes a potential hazard for your boating area. This somewhat extreme example is taken from a prominent point on Buzzards Bay The entire area is a maze of hazards. Many boats have run aground in these waters.










Using waypoints, you can create your own virtual navigation aids along the coastline that match your safe depth. A string of these waypoints makes a convenient reference. For hazardous areas, you can use a cardinal waypoint system. Place a virtual waypoint at each cardinal point marking the perimeter of the area (N-S-E-W). Make sure that you do not venture within the box. (Your GPS Map Screen will help with this.) Isolated hazards can be marked with avoidance waypoints or any standard waypoint.

As an alternative, you can mark several points that bound the region. This is analogous to the cardinal system of buoyage used in many places around the globe. Using this approach, buoys are placed at the cardinal points (north, south, east, and west) marking the edges of the hazardous area. Each buoy is distinguished by a unique pattern of black and yellow bands based on its location. You avoid the area by noting the cardinal point marked by each buoy and staying outside the imaginary boundary defined by that buoy. For example, the north buoy defines an imaginary east-west line and indicates that you should stay north of it. The net effect is an imaginary box around the hazard.

You can do the same thing using waypoints stored in your GPS. Note the location of each waypoint on the chart and the name you will assign to it. For example, HAZ1 might note the hazard, and the four waypoints would be named HAZ1N, HAZ1S, HAZ1E, and HAZ1W, respectively. Measure the coordinates of each for entry into your GPS, then you can monitor the hazard box on your GPS Map Screen.










By taking a wider view of the same region, you can qualify the regions that are safe. This is useful planning, because you can clear large portions of the bay for safe navigation.

Shoals
Shoals are likely to be far more extensive than the two categories of hazard noted above. The characteristics of a shoal determine its degree of danger. You may experience little more than aggravation if you run aground in soft mud, whereas a rocky bottom can sink your boat.

Channel edges are usually marked b buoys. Most bays and larger bodies of water are also delimited by lateral buoys to mark deeper water. If these navigation aids are available, you may wish to enter their coordinates into your GPS.










Often these buoys mark the edges of very deep channels for big ships. Recreational boaters can and do navigate closer to shore and in shallower water, cutting inside these buoys in part to stay out of ship channels. These lateral buoys may thus be of little value to you, in which case you can always create imaginary lateral buoys to mark your chosen limits. These virtual buoys will exist only in your GPS (and on your annotated chart) as waypoints to help guide you on the water. Assign them names that correspond to a buoy convention, note the names on your chart, and enter them into your GPS.
You should note your depth criterion on your chart near the line of virtual buoys. You will want to use your depth sounder along with your GPS to stay safe on the water.

FIGURE 7-6. Returning to the pre-qualified Buzzards Bay area, here is a simple technique that uses another feature on your GPS. Once you&#8217;ve identified a band of clear area along the bay, you can make a route down the middle of it. Then note the distance from the route center to the edge of the clear area on the chart. When you are on the water, activate the route segment and set the crosstrack error alarm to that measured value. You will be able to maneuver throughout the bay area within the limits of the crosstrack error and avoid the hazards that lie beyond.










Bands of Clear Area
Sometimes the techniques outlined above would lead you to define a very large number of waypoints, cluttering your GPS display and leading to confusion rather than helping. Instead, consider using other features of your GPS such as crosstrack error to help define a safe area for boating.
Crosstrack error indicates the distance left or right of your current position from an active course line. Crosstrack error can be associated with an alarm that indicates when you have wandered more than a preset distance off course. In effect, this creates a band of chosen width centered on an active course line between two waypoints.

To use the crosstrack error effectively as an avoid&#8212; ance technique, look for a band of open water crossing your region of interest. The band you want will have two parallel edges defining the limits of safe water, placed to avoid lateral hazards. You need to determine the centerline halfway between these edges, define that as the leg of an imaginary course, and use the GPS crosstrack error data field. Your choice of width for the band is virtually unlimited. This technique works for a narrow passage, for defining lateral limits for tacking a sailboat into the wind, or for outlining the safe area of an entire bay for a day of fishing.

You need to enter the waypoints of each end of the imaginary course leg. It makes sense also to enter as another waypoint your point of entry into this area, thus creating a three-point route beginning with that point. Plot the coarse leg on the chart and draw the edges of the safe band as dashed lines. Measure the distance from the course line to each edge; this becomes the crosstrack error limit, which you should mark on the dashed lines. You will want to set the GPS&#8217;s crosstrack error alarm when you boat in this region.

Mark Landmarks
Not all the waypoints you use to define safe areas need be on the water. You can also use visible, charted landmarks to help guide you in a number of ways.
Using Ranges (or Clearing Lines)

You have learned how useful a range can be in keeping you in the center of a channel. A variation of a range, called a clearing line, can help define limits. The clearing line uses two charted objects, just as with a range, the primary difference being that the clearing line defines an edge rather than the center of a channel. On the water, you want to stay on the appropriate side of the clearing line. When the two landmarks are perfectly aligned, you are on the edge of safe water. Create clearing lines for places where no navigation aids are deployed to mark edges or limits, and label each clearing line with a bearing.










Using Danger Bearings
A variation of the same technique uses only one visible charted landmark, or nay aid, from which a line is drawn across the safe side of a hazardous area you wish to avoid. Measure the direction of that bearing as seen from the water and mark it on the line. To highlight the danger bearing, crosshatch the dangerous side.

On the water, you can monitor the bearing to that landmark with a hand bearing compass or your GPS to ensure that you do not venture onto the hazardous side. For most boaters, the real challenge in this technique is determining whether the bearing on the safe side needs to be less than or more than the danger bearing. Figure this out in advance and label the danger bearing line as NMT or NLT (for &#8220;not more than&#8221; or &#8220;not less than&#8221. To make this determination, simply imagine that you are on the dangerous side. Is your bearing to the danger waypoint more or less than the danger bearing? If it is more, label the danger bearing as NMT, and vice versa.

FIGURE 7-7. lop: A danger bearing is planned using a danger waypoint (in this case a charted landmark). A bearing line is drawn from that point across the edge of the hazardous area, then it&#8217;s measured. Once you&#8217;ve drawn and labeled the danger bearing with its measurement, add crosshatches or shading to the hazardous side of the danger bearing. Then draw an &#8220;X&#8221; anywhere on the hazardous side of the line. Is the bearing to the danger waypoint from &#176;X&#8221; greater or less than the danger bearing? If it is greater, mark the danger bearing as NMT (not more than); if it is less, mark the bearing NLT (not less than). On the water, you will monitor the bearings visually to ensure that you never violate the noted values. You can do the same thing with a GPS. Below: Here, two danger bearings have been drawn to exclude an entire dangerous region. West of the danger waypoint, do not let your bearing to it exceed 118&#176; M. When north of it, do not let your bearing to it fall below 190&#176; M.










Using Danger Circles
By now you&#8217;re familiar with the concept of a line of position (LOP), which results from a visual bearing on a charted landmark or buoy, from a range, from a radar bearing, and so forth. A circle of position (COP) is similar; all you need to know to plot one is your distance from a charted object.
You will discover in that radar can be used to define a COP as well as an LOP You can also use your GPS to define a COP by observing the distance to a nearby landmark that is stored in the GPS as a waypoint. By plot ting an arc around that waypoint that you want to avoid, you can use your GPS to stay outside a hazardous area. All you need to do is measure the radius of the arc and note that on your chart, then stay outside that radius when you&#8217;re on the water. The manufacturers of GPS receivers have recognized the power of this approach and, as mentioned, have included avoidance (or proximity) waypoints that can be stored along with a danger radius set to trigger an alarm. You can use a COP to avoid dangerous areas even if your GPS does not have this feature, but it will require vigilance on the water.

FIGURE 7-8. The avoidance waypoint technique can be used to isolate most of the hazards in an area. In this example, one of the avoidance waypoints uses a charted landmark, and the other uses a virtual waypoint. The locations of the waypoints are optimized to encompass as many of the hazards as possible.










*Coming next- Underway with GPS*


----------



## reel

Yep. This chapter would have saved me a prop just off Johnson Island Sandusky Bay.
...


----------



## Fishers of Men

*Underway with GPS Charts and Paper *
We discussed navigation planning. By pre-qualifying courses and routes in your boating area, you have established paths that are free of underwater obstacles and identified areas to avoid. Now it&#8217;s time to get underway.

Steps in Waypoint Navigation
We first introduced the concept of navigating to a GPS waypoint. The process is quite simple. To recap, here are the steps.
1. Select and activate the waypoint.
Use the GoTo function of your GPS receiver:
This function is accessed via the buttons. Some GPS models have a button labeled GoTo. Others place the GoTo function on a submenu accessed via another button such as NAV.
Scan until you find the desired waypoint from the stored list.
Select and activate that waypoint.
The GPS receiver:
Calculates the bearing and distance to the activated waypoint
Plots the course line on the Map Screen from your current position to the waypoint
Draws a highway on the Highway Screen from your current position to the way- point
2. Double-check that this is a pre-qualified path.
Are you following a pre-qualified path&#8212;that is, one that you have plotted on your chart and used to define the starting and destination waypoints you are using for this leg of your route?
If not, plot your current position (as reported by the GPS) on a chart and draw the course line from there to the active waypoint. Is it safe?
Let&#8217;s say you are starting a cruise from the entrance to Oak Bluffs Harbor on Martha&#8217;s Vineyard. Your ultimate destination is Waquoit Bay, across Nantucket Sound on the mainland of Cape Cod. You previously have created an intermediate waypoint, which you have stored in your GPS as &#8220;WPT.&#8221; So, to get started, you use the GoTo function on your GPS and scroll through the way- point list until you find WPT. Pressing ENTER brings up the corresponding way- point screen for this selection, It&#8217;s the correct one, so you select OK. Your GPS computes the course and distance and puts a highway on your Highway Screen, which you are planning to use for this cruise.










Just to make sure, you decide to pull out your chart and plot the course from Oak Bluffs to WPT before you set out on the first leg of your cruise. All looks good, so let&#8217;s go.

FIGURE 8-2. It is your responsibility to ensure that the path to the waypoint is clear of obstructions. You should plot your current position and the waypoint, then draw the course line between them. Scan the intended course for hazards.









3. Steer to the bearing direction indicated on the GPS.
Note the &#8220;Bearing to Waypoint&#8221; reported by the GPS. Steer a heading corresponding to that initial bearing.
(The initial bearing will be the same as the course, but the bearing will change if your actual track deviates from the rhumb-line course, whereas the course between the two waypoints in question is a fixed value in GPS memory. Some GPS models offer a &#8220;course&#8221; readout that presents the course direction corresponding to the line plotted on the Map Screen.)

Be sure that the initial track matches the bearing to waypoint.
Look at your compass. It, too, matches the initial GPS bearing within the accuracy of the compass, assuming you&#8217;ve set up the GPS to report courses and bearings in degrees magnetic.

Your GPS indicates that the bearing from Oak Bluffs Harbor to WPT is 054&#176; magnetic (which is the same as your course to steer), and the distance is 2.17 nautical miles. Because your ship&#8217;s compass has been properly compensated, you will steer to 054&#176; M on your compass. You&#8217;re underway.










FIGURE 8-3. You can use the Highway Screen to navigate to your next waypoint. The course field pro vides the desired course to steer. When you start, the bearing to the waypoint is the same as the course. Steer the boat until the highway extends straight ahead to the waypoint, as shown.
4. Monitor your progress.

Monitor distance to waypoint.
Monitor track (the direction of your progress &#8220;over the ground&#8221 and compare it with the bearing, If your track does not match the active course from the waypoint you just left to the one ahead, it will not match the present bearing to the active waypoint either&#8212;a sign that you are getting off course.
The bearing is continually updated from your current position. If you&#8217;re off course, the bearing will diverge from the original course line.

Monitor your Map and Highway Screens.
Are you on the original course line? Monitor your crosstrack error and observe your Map Screen or, preferably, your Highway Screen; your boat will appear to be on the original course line on the Map Screen if you are still on course. You will also appear to be in the center of the highway on the Highway Screen, and the highway will be ex tended straight ahead to the active waypoint.

Does the bearing to the waypoint match your track? If yes, you are on course. It no, you are off course. If you are close to the original course line, make adjustments to return. If you have wandered significantly from the course line (by more than your pre-qualified path width), plot your current position (as reported by the GPS) on your chart, and plot a line directly from your location to the active waypoint. Is it safe?

If yes, proceed. If not, plot a safe path back to your original course line.
As you proceed from Oak Bluffs toward WPT, you&#8217;re operating under the principle &#8220;make your plan, follow your plan.&#8221; You want to stay on course. You&#8217;re in the middle of the highway, and WPT is dead ahead. You can use the Off-Course data window on your GPS for more refined details. That&#8217;s what this model uses for crosstrack error. You&#8217;re now only 1.38 nm from the destination, and you are off course by only 26.3 feet&#8212;that&#8217;s really close. So far, so good.
FIGURE 8-4. As you proceed along the course, check to make sure that you are still in the center of the highway, and the highway continues to extend straight ahead toward the waypoint. Note that the distance to the waypoint continues to diminish as you make progress. When you started, you were 2.17 nm from the waypoint. In this example, you are now only 1.38 nm away.










5. Be alert as you approach your destination.
Many GPS receivers sound an arrival alarm when you are approaching the active waypoint.










Prepare your next step before you arrive.
As you approach WPT, an alarm sounds and an information box pops up to say you are &#8220;Arriving at Destination.&#8221; This is your cue to get ready to enter the next waypoint. You&#8217;re still on plan.
6. Select and activate the next waypoint (as appropriate). 
If you are planning to go to another waypoint immediately, initiate a GoTo and select the next active waypoint, repeating the steps above,	
Now it&#8217;s time to enter the next waypoint, called &#8220;DEST,&#8221; repeating all the steps that successfully got you to WPT. As soon as DEST is entered and activated, your GPS indicates your new bearing and course to be 013&#176; and the new distance as 3.31 nm. You steer in that direction and get underway.
FIGURE 8-6. To complete this cruise, activate the next waypoint and repeat the process.





































FIGURE 8-10. The Highway Screen is possibly the most valuable screen on a handheld GPS. At a glance, you can tell whether you are on your intended course line and are headed in the proper direction. The screen depicts a 3-D view of a virtual highway. In this example, you are on the center of the highway, and thus on the center of your course line. You are heading directly toward your active waypoint. A route has been activated, so you see not only the active leg but the next leg as well. The data fields are user-selectable. In this case, you have chosen course, off course, track, speed, bearing, and distance as your data fields. Course is the direction of the active leg (what you intended). Off Course is your current distance from the center of the highway Track is the direction of your actual motion over ground. Speed is your speed over ground. Bearing is the direction to the active waypoint, and distance is your current distance from it. You can change the perspective of this screen by zooming out (it currently is shown at maximum zoom). The name of the active waypoint is indicated in a data field.










If you have not selected an active waypoint, there will be no highway on this screen. As soon as you activate a waypoint, the highway is drawn. It stays on the screen, providing you with a frame of reference to your originally selected course, until you activate another waypoint. If you select a route, all legs of the route will be shown on the Highway Screen sequentially, with the appropriate turns between each leg.
The &#8220;highway&#8221; is what you would expect to see from a vantage point above your boat, looking in the direction you are moving. You steer to stay in the center If you get off the highway, you steer to get back on it.
Newer GPS models have sufficient resolution on their displays that other waypoints can also be displayed relative to the highway, and you can zoom in or out to get a more or less detailed view.

In the absence of a chart on your Map Screen, the Highway Screen is perhaps the most useful screen on your GPS.

To be cont.


----------



## Fishers of Men

*Underway cont.
*
FIGURE 8-11. 
The Compass Screen is not as useful for marine navigation. Remember, this is not a compass. The light bar at the top indicates your direction of motion. The black arrow indicates the direction to your waypoint. This GPS also shows the bearings of the sun and the moon to provide additional visual references.










COMPASS SCREEN
The Compass Screen shows a circular representation of a compass card. Your current heading is at the top. Usually, the bearing to your active waypoint is shown by a separate indicator and you steer to line up the two. The Compass Screen is more useful for hiking than boating. The Highway Screen presents more useful information.

Staying On Course
If you wander from your intended course line, you need to get out the charts, plot your present position, and decide on a new path from there to your destination waypoint. It is better, obviously, to stay on the original course line, but there are a number of reasons why you may get off course:
(1) steering to avoid visible obstacles, (2) a crosswind, (3) a crosscurrent, (4) your boat yawing in waves, or (5) inattention to the helm.

Recovering from Off Course
If the waters you&#8217;ve strayed into are relatively free of obstacles, you may be able to approximate your position, see that the path from your current location directly to the waypoint is clear, then simply steer to the bearing of the waypoint as shown on your GPS. Be aware that whatever environmental influence moved you off course (often a tidal current) is still likely to be operating on you, so compensate.

If there are hazards nearby, however, take the time to plot your position on the chart and pre-qualify the direct path to the waypoint. You may well find that you should return to your original course line, still showing on your Map and Highway Screens, before turning toward the waypoint. Just be sure that the path you take back to the course line also is clear of obstacles.










FIGURE 8-12. Even with GPS, you may find yourself off your intended course line. You began the leg steering toward your destination (1), but some time later you find that you no longer are on the intended course line (2). Now you&#8217;ll need to consult the chart (see Figure 8-13).

Note that there is no GPS data readout for your heading, which is the compass course you are steering. *GPS doesn&#8217;t know or care where your boat is pointing&#8212;only where it&#8217;s actually going.*










FIGURE 8-13. As soon as you discover that you&#8217;re off course, you need to plot your current position (2) on a chart and draw the direct path to your destination waypoint to determine whether it is safe to proceed. In this example, it is clear that you are facing dangerous shoals. Your best choice is to plan a direct path back to your intended course line (3), then proceed from there.










FIGURE 8-14. In this example, you have returned to the original course line and aligned yourself so your position is in the center of the highway and the destination waypoint is straight ahead.










How CAN I TELL WHERE I AM WITH A GPS? If you have a handheld GPS without built-in charts, you probably will need to pinpoint your location on a paper chart using plotting tools. GPS units provide all the information you need to do that. There are two approaches: (1) latitude and longitude coordinates, and (2) bearing and distance to a waypoint.

FIGURE 8-15. Whenever your location relative to pre-planned courses is in question, you should plot your GPS position on the chart.










PLOTTING LATITUDE AND LONGITUDE Plot your GPS latitude and longitude coordinates on the chart as described in Chapter 4 to get your current position. This sounds simple and straightforward, and in principle it is; however, it may not be so easy to perform on a moving, bouncing boat at sea.

TIP&#8212;A quick way to plot an approximate latitude and longitude is to slide a rectangular plotting tool across the chart by eye. First, align the tool with the chart grid and slide it so the top is next to the latitude scale at the latitude shown on the GPS screen. Next, slide it over so the left (or right) side is close to the longitude shown on the GPS, and mark the latitude with a pencil. Now slide the tool to the longitude scale and align it more carefully with the GPS longitude, then slide it back to complete the mark. This is a quick way to check your position, but it is not precise. If it places you near charted hazards, get out the dividers or use the technique below.

PLOTTING BEARING AND DISTANCE A better approach uses the bearing and distance to a waypoint that is shown on the GPS and plotted on your chart. This information is continuously updated and available on the GPS screen for the active waypoint (though any other waypoint can be selected; see below). Using parallel rules (and assuming you&#8217;re working in degrees magnetic), transfer the magnetic bearing from the inner (magnetic) ring of the chart&#8217;s compass rose to the charted location of the active waypoint, then draw the bearing line from your approximate location to the waypoint.

Next, using the GPS distance to that waypoint, mark off this distance from the waypoint along the bearing line you have just drawn. This is your current location.

This approach works well when your chart is folded. You only need to see a compass rose and the charted way- point (which is probably a navigation buoy) and have access to the distance scale or one of the latitude scales. More important, this plot has physical significance because it is the bearing and distance to your active waypoint. The bearing line coincides with the straight-line path from where you are to where you want to go.

Suppose you find that you are off course. If you used your active waypoint as the reference, the bearing line you have just drawn is also the direct path to the waypoint. Look along the path for obstacles. If it is clear, you can steer directly to the waypoint. Just remember that the wind or tidal current that pushed you off course in the first place may continue to act on the boat, moving you even farther off.

The original course line will stay on the GPS map and Highway Screens. If you prefer to restart navigation from your present location, simply use the GPS GoTo function again, selecting the same active waypoint. The original course line will disappear, and a new line from your present position to the waypoint will replace it.

If the new direct path is not free of obstructions, how ever, you will need to find a safe path back to the original course line before proceeding to the active waypoint.

TIP&#8212;If you don&#8217;t have or can&#8217;t use parallel rules conveniently on your boat, you can try a quick technique to transfer the angle. Align your plotting tool correctly on the compass rose, then slide it across the chart so it aligns with your waypoint. Even working freehand, you generally can transfer a direction to within a few degrees using this technique. But it is approximate, so if you are near hazards, use the more precise approach.

USE ANOTHER WAYPOINT FOR BEARING AND DISTANCE
You are not limited to using the active waypoint for these measurements. Often, another waypoint is closer or more convenient. Any nearby waypoint will do, provided it is charted. Using the Map Screen, you will see all the stored waypoints that lie within the current zoom level of the display.
On many GPS models, you can determine the bearing and distance to any waypoint by simply scrolling the cursor over that waypoint until it is highlighted. The GPS usually indicates the corresponding bearing and distance in a data window. You don&#8217;t want to navigate to this waypoint, just sample its bearing and distance, so use the QUIT or Esc buttons to return to the original GPS display. Your active navigation will not be interrupted.

FIGURE 8-16. A quicker way to plot position is to use a protractor plotting tool with a pivoting arm to locate your position by bearing and distance. You align the bearing of 44&#176; M opposite 15&#176; Won the variation scale (see Figure 5-19). (Remember to read 44&#176; on the reciprocal scale or turn the protractor upside-down. Then measure out 3.5 nm along the arm to mark your current position.)










Alternatively, you can go to the Waypoints or Nearest Waypoints menu and call up the desired waypoint there. The Waypoint Screen will provide the current bearing and distance to the desired waypoint. (Use QUIT or Esc to go back without causing the GPS to consider this the new active waypoint.) Using this bearing and distance, plot your position as above. If you find that you are off course, how ever, you will need to draw a line from your plotted location to the active waypoint before attempting to steer to its bearing.
Waypoints off to one side of your course often provide greater precision and convenience for this bearing-and- distance measurement. You can get a quick sense of whether you are off course simply by looking at the distance from the reference waypoint.

*TIP&#8212;Your chart has several built-in bearing protractors&#8212;namely, its compass roses.* Simply enter the center point of each printed compass rose as a waypoint in your GPS. Anytime on the water, look up the bearing and distance of a given compass rose, then plot that bearing using the rose without a protractor. All you need to mark your position is a straightedge and some means of measuring the distance. Just remember either to use the reciprocal of the bearing or to plot using the angle on the far side of the rose from the center point. That&#8217;s because the bearing your GPS gives you is from your boat to the rose, not from the rose to you.

*to be cont.*


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## Fishers of Men

reel said:


> Yep. This chapter would have saved me a prop just off Johnson Island Sandusky Bay.
> ...


Yep, there is a lot of messups on the west end. It deserves some studying.


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## Fishers of Men

*Underway cont.*

FIGURE 8-17. It&#8217;s possible that your destination waypoint is some distance away, or another waypoint may simply be more convenient. In this example, a waypoint to the side of the in tended course line has been used for bearing-and-distance plots at 1010, 1030, and 1050 hours. Each plot was done as shown in Figure 8-16.










TIP&#8212;As an alternative to plotting a bearing from a compass rose, you can place a protractor plotting tool over the waypoint to which you wish to plot a bearing and distance. Some plotting tools come with distance scales already printed on the straightedge. But because the scales of to day&#8217;s commercial charts may not be standard, it is recommended that you first align the straightedge with the latitude scale and mark the nautical miles (minutes of latitude) and half miles directly on the straightedge using a pencil. Now align the straightedge with the bearing using the pro tractor and read outward to the distance provided by the GPS. This is your current location. This approach is ideal for a folded chart, because you do not need access to either the latitude/longitude scales or the compass rose to mark your position.

There is one complication: because the plotting tool aligns with the chart&#8217;s latitude/longitude grid instead of magnetic directions, you will need to correct for variation if your GPS is set to magnetic headings. Some tools provide a correcting scale on the straightedge (as shown in Figure 8- 16). Otherwise, you will need to convert mathematically.

If you want to monitor your progress along a route, you can use a single waypoint along the side of your route and periodically plot successive bearings and distances, as shown in Figure 8-17. Also note that this technique will work with a standard protractor if you don&#8217;t have a protractor plotting tool at hand, but it should be placed with 1800 pointed north, so the scale reads the reciprocal course. This is harder to describe than to do; if you try it, you&#8217;ll see.

FIGURE 8-18. Another tip is to use the center of the chart&#8217;s compass rose as a virtual waypoint. If you do this, you don&#8217;t even need a protractor scale; the compass rose provides that for you. All you need is a straightedge calibrated to distance. Enter the compass rose coordinates as a waypoint, then call up that waypoint to determine its bearing and distance from your current position. Mark the bearing directly using the inner ring of the rose for magnetic direction. Remember that you are reading the bearing from you to the rose, so read the bearing on the far side of the compass rose center.










Effects of Wind or Current
It&#8217;s natural to head your boat directly toward your next way- point, but in the presence of an oblique tidal current or a strong crosswind, which will push you away from your planned course line, it&#8217;s a mistake. As you&#8217;re pushed off course, your GPS shows a new bearing to the waypoint. If you then steer to that new bearing, you will be pushed even farther off course. Finally, you will approach the waypoint not from your direction of origin but from the side. The result is called a hooked course&#8212;a curved path instead of the intended straight line to your waypoint. When a hooked track takes you far enough off your intended course, you can easily encounter hazards that you had planned to give a wide berth. Clearly, steering to a waypoint without checking your position relative to the course line can be dangerous. More information about winds and currents later.










FIGURE 8-19. A natural tendency while boating is to head toward your destination or waypoint. This is fine when you start, but it&#8217;s not so good if you&#8217;ve been pushed off course by wind or current. In this example, you have adjusted your heading to correct for the bearing to the waypoint at several points along your path. Instead of heading directly to the waypoint, you will reach it from the side. Unfortunately, hazards lurk to the side of the intended course line.

This is the same thing that happens when you visually steer directly toward the next buoy in a tight channel with a crosscurrent. By focusing on the buoy and not your course line, you can be pushed out of the channel.

This occurs on a regular basis in Woods Hole, Massachusetts, for example, even to experienced mariners. The &#8220;Hole,&#8221; as it is called, has a shortcut called &#8220;Broadway,&#8221; which takes boaters through a narrow channel between two substantial outcroppings of shallow rocks. Adding insult to injury, at certain phases of the tide, very strong cross currents develop in Woods Hole as Buzzards Bay empties into Nantucket Sound. This current cuts across Broadway. Those who steer by eye to the next buoy may find that the resultant hooked course has taken them onto the rocks, as shown in Figure 8-20.










Figure 8-21 shows graphically what happens. You steer directly toward your destination, but the wind or current pushes you to the right. You still are pointed in the original heading, but your position is shifted to the right. Your actual track is at an angle downwind or &#8220;downcurrent.&#8221;










The solution is to steer into the wind or current as shown in Figure 8-22. Your heading is upwind or &#8220;upcurrent&#8221; of your destination, but the actual track of your boat is along your intended course line. In effect you are proceeding &#8220;crabwise&#8221; along your course line. The big question is, how much to compensate&#8212; how far do you have to turn into the wind or current? GPS provides a ready answer.

The Highway Screen, as shown in Figure 8-23, provides the ideal solution. All you need to do is stay in the center of the highway with the highway extending straight up in the center of the display. This is the position that represents an on-course orientation.










FIGURE 8-23. You can use the Highway Screen on your GPS to determine the course to steer. Adjust your heading in small increments until the off-course data field becomes stable and stops increasing. If you are still away from the center of the course line, temporarily overcompensate until you have returned to the center. When properly aligned, you will find that your boat heading does not match your course direction or your actual motion (track). You can still use your compass to steer. Simply maintain the heading shown on the compass, in this case about 340&#176;.

FIGURE 8-24. In this example, you found your location to be off course (2) and decided to return to the original course line (3), because going directly to your destination would have put you in danger. You can see on the Map Screen that your location is somewhat to the right of the intended course line. However, there is no way to tell from the GPS Map Screen of the potential peril along the path. The Highway Screen (see Figure 8-25) will show the high way off to the left, but you are pointed toward your destination.










Initially, you will head the boat directly toward the active waypoint. In a crosswind or current, however, you may soon notice that you are moving to one side of the highway or the other, a signal that you need to adjust your course into the wind or current. To get back on course, you need to &#8220;oversteer&#8221; a bit to return to the centerline, which means that the highway shown on the screen will be at a slight angle. You will be heading temporarily toward the center of the highway rather than the waypoint.

Once back in the center of the highway, by adjusting your course into the wind or current in small increments you will find the steering angle that keeps you in the middle of the display with the high way extending straight ahead toward the active waypoint. This is the steering angle to maintain until such time as the wind or current change, necessitating a further adjustment. As an alternative, display the course and track data windows on your GPS and steer to keep these values equal to each other. This is easier if you begin when you are on course, simply adjusting your steering so that they match. If you are already off course by some distance, using these two data fields can be more confusing than simply observing the highway.

FIGURE 8-25A. A/though somewhat intuitive, the Highway Screen may take a little experience to use It effectively Going back to the example shown in Figure 8-24, these screens provide a step-by-step view of how to return to the original course line. Left: Your high way view from Position 2 in Figure 8-24. Middle: You have decided to head back to the original course line. Now the highway appears to cut across your screen. Your destination waypoint no longer appears within the field of view In the real world, this is the view that you would have returning to a roadway Note that the off-course data field has been reduced to 0.49 nm from 0.71 nm. Right: You are closer to the highway Note that off course is now down to 0.20 nm.










FIGURE 8-25B. Left: Off course is now only 371 feet. Time to begin your turn toward your destination. Middle: Now you are nearly aligned with your destination waypoint. Off course is down to 91 feet. Right: You continue to close on the centerline by small steering increments. The off course is now down to 9 feet (on course). Because the wind or current that moved you away from your intended course may still be acting on you, your heading may not correspond with your boat&#8217;s track. You will continue to adjust the steering until the off-course indicator remains steady If you are close to the center of the highway simply maintain this heading.










If your GPS does not display the intended course as a data field, you can use the bearing data field instead. You will need to make a note of the intended course when you first activate the waypoint. The bearing from that spot is exactly the same as your intended course. Just make sure that the bearing does not change from that value as you move toward your waypoint, and be sure the bearing and track readouts continue to match.
But again, studies and experience have shown that a graphical display is easier to monitor than a numerical one. With even a quick glance at the Highway Screen, you can tell if you are on course as shown in Figure 8-26.










FIGURE 8-26. Most of us prefer graphical displays, which the Highway Screen provides. But this display also provides data fields that can be used to accomplish the same tasks. With only a glance, you can tell whether you are on course and determine your direction with respect to the waypoint and intended course. In the screen on the left, you can see that, in order to reach your waypoint, you&#8217;ll need to steer to the right (yellow arrow) as you return to the highway. In the screen on the right, you can see that you need to adjust slightly to the left (yellow arrow) to get back to the center of the highway (intended course). All of the same information is shown numerically (orange boxes), but it&#8217;s less straightforward than the graphics.

*to be cont.*


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## Fishers of Men

*Underway cont.*

If you use the ship&#8217;s compass to steer, all you need to do is note the compass reading for the heading that keeps you on course and stay on that heading. As shown in Figure 8-23, you will see that the compass heading and the boat&#8217;s track, or course over ground, no longer match. The difference is the amount by which you have had to &#8220;crab&#8221; the boat into the wind or current to compensate for leeway or set. Remember, by holding your position in the center of the highway with the highway straight ahead toward your destination waypoint, you guarantee that your track will follow the planned course line. The GPS track readout is an accurate reflection of your true motion over ground, whereas the compass shows the boat&#8217;s heading through the water.

Crosstrack Error
Another very useful data field displayed on the Highway Screen is crosstrack error (sometimes labeled as &#8220;XTK,&#8221; or &#8220;off course&#8221. Crosstrack error is the distance that you are off course, either L (to port) or R (to star board). When you are close to your intended course line, the distance is usually presented in feet. If you venture farther from your course line, the distance is usually presented in nautical miles (assuming you have your GPS set up in nautical units). &#8216;Whether you&#8217;re off course due to wind, tide, or simple inattention, crosstrack error tells you by how much. You can program your GPS to sound an alarm at a preset distance in case it&#8217;s needed to bring your attention back to navigating.

FIGURE 8-27. Navigating from point to point is the most com mon form of GPS navigation, even by experienced boaters. In this example, the direct path is unsafe, so an intermediate way- point was added. The GPS offers a route function that sequen tially navigates to selected waypoints. This two-leg path can be conveniently automated.










FIGURE 8-28. This typical GPS Route Screen is used to build a route. In this example, you access the field with the cursor and scroll through your stored waypoints until you find &#8220;START&#8221; Next, you do the same for &#8220;WP7&#8221; then &#8220;DEST&#8221; (If you intended to add another waypoint, you would highlight the dashed data field at the bottom and select another waypoint.) Note that the total distance for the route is displayed on the screen. By scroll ing to the right, you will find the course and distance for each leg. In this example, the route name has been provided by the GPS. The default mode will name the route using the names of the first and last waypoints in the sequence. This is easy to use and easy to remember.










Navigating a Route with GPS
Manually navigating your route from waypoint to waypoint is simple, but you&#8217;ll need to activate the next waypoint as you complete each leg. Unfortunately, this usually occurs at the same time your attention is needed to execute a course change. The GPS route function simplifies the process by automatically activating the next leg as soon as you reach a waypoint. As explained in Chapter 2 and elsewhere, a route is a sequence of legs defined by starting and ending way- points. Your GPS navigates each leg using the beginning waypoint as the &#8220;active from&#8221; waypoint and the leg destination as the &#8220;active to&#8221; waypoint, and calculates the intended leg course, distance, and other functions such as time or fuel consumption.
FIGURE 8-29. There are a few cautions to consider when you use a route. When you activate a route, most GPS receivers compute the course from your current location to the second waypoint (in this case, WPT). The GPS assumes that you are starting at the first waypoint on the route list. If you are not, as shown in the figure, you need to plot your position and a safe course to the waypoint.










Selecting a Route
Routes should be preplanned, at least in segments; you activate the desired route from the Routes menu. Most GPS units automatically store route names in a format that lists the first and last waypoint names of each route. This is the preferred naming convention, though you can name routes as you choose. Just make absolutely certain you are activating the correct route. On the water, when there are other boats to avoid, passengers to watch and converse with, weather to observe, waves, and countless other stimuli clamoring for your attention, it is easy to make a mistake even with a simple task. This is where the first and last way- point names help, and one of the reasons why you should clearly label your waypoints during the planning process in a way that makes it easy to distinguish one from another. These same labels should appear on the charts that you carry with you.
Using the carpenter&#8217;s maxim &#8220;Measure twice, cut once,&#8221; you need to double- check your selection. In addition to checking the name twice, you should look at the bearing and direction to the initial waypoint of the Selected route as displayed on your GPS to make sure it makes sense.

Your choices when you select a route are to activate, invert, or edit. Activating the route starts the navigation process from your current location, which may or may not correspond with the first way- point on the route list.
If it doesn&#8217;t, you must ensure that your path to the newly active waypoint is safe, which means pulling out your chart, locating your current position on the chart, and establishing the safety of the direct path to the route&#8217;s starting point.

Alternatively, you may be at the route destination and wish to return to the initial waypoint. In this event you will select &#8220;invert&#8221; from the Routes menu, which reverses the order of the waypoints. Often, the route name will invert as well.










FIGURE 8-30. As soon as you select and activate the route, your Route Screen indicates the active leg and waypoint (see arrow on Active Route Screen). Your GPS can now also display a corresponding highway on the Highway Screen and a course on the Map Screen. Note that the entire route is displayed on both screens.

Following a Route
On the GPS Highway Screen, the imaginary highway of the route you&#8217;ve selected extends not only from your starting point to the active waypoint, but to all the subsequent waypoints as well. In addition, most GPS models display all other waypoints within the field of view, including those that are not part of the active route. Danger waypoints will appear relative to the highway, to alert you as you approach them. Seeing the entire route plotted also helps you to pre pare in advance for each turn.

The Map Screen also is useful, but unless you have a chartplotter it may appear rather vacant of detail. Your position will be indicated by a symbol, typically a triangle that points in the direction of your boat&#8217;s motion (usually with a few seconds&#8217; lag). Also shown are the route&#8217;s course line and all programmed waypoints within the field of view at the selected zoom level. A track line showing where you have been will be displayed if you activate that feature. You can monitor your track or position relative to the intended course line as you navigate, but to use this display to stay on course, you may need to zoom well in, at which point you will see only a small segment of the route. Monitoring your position using the Map Screen takes quite a bit more visual attention than using the more intuitive Highway Screen. Most GPS models also let you select which data readouts are displayed on the Map Screen.










FIGURE 8-31. Underway, you can monitor your progress on the Map and Highway Screens. The black arrow shows your position on the map. Your position is also shown on the highway. As you approach your first waypoint, an alarm and message indicate that you&#8217;re Approaching Turn.&#8221; As you get within an arrival radius of the first waypoint, the GPS activates the next waypoint and provides the course and bearing to that waypoint. You need to steer in that new direction and monitor your progress.

Entering a Route at a Midway Point
You may wish to enter a route at some midway point, as opposed to one of its ends. Simply activate the route, and some GPS models give you the bearing and distance to the nearest waypoint in that route. Others point you to the route&#8217;s initial waypoint. but assuming you have checked your planned action on a chart, you can set out toward the place where you wish to join the route. Most GPS models interpret this move and switch to the next logical waypoint so you can join the route from there.

Navigating in a Region
We described methods for preplanning a cruise in a region, avoiding obstacles and hazards marked in your GPS. Having identified critical hazards, you can meander more or less freely around the region in question, as long as you regularly monitor your GPS to make sure you are not encroaching upon any of the danger areas. Danger or proximity waypoints and crosstrack error are useful functions for this, because they are associated with an audible alarm. You may not hear the alarm, however; most handheld GPS units have limited audio volume.

Generally, you will find it convenient to use the Map Screen when you navigate casually in a region. By monitoring the screen, you can see when you are encroaching on one of the hazard areas. You will need to set the zoom level to correspond with your speed. If you are fishing or puttering, you can zoom in; when moving fast, you will need to zoom out far enough see the entire area of operation. Recognize that at high speeds, it is possible to &#8220;outrun&#8221; your GPS. That is, your reported position will be behind you.
Also, you may find that setting the GPS screen to its Course-Up option helps with your orientation. In this mode the track of your boat is always up, so your visual surroundings match the GPS screen.
You will not need to select an active waypoint. Rather, the display will show all waypoints within your Map Screen&#8217;s field of view. Having selected special symbols for hazard waypoints during the planning process, such as a skull and crossbones, you will know which points to avoid.

Marking Objects
On the water, you will inevitably find objects whose locations you want to record. Locally maintained buoys are often not listed on charts, and you may find clusters of lobster pots or uncharted hazards you want to add to your GPS memory.

Usually, you can mark a location on a handheld GPS simply by pressing the designated button, often twice. The GPS will store the waypoint coordinates with a number rather than a name. Jot the number on your chart or a notepad with a notation of its significance; then you can create a name for the new waypoint and edit its information later, on your mooring or at home.
You may also see landmarks that can be useful for position finding or for checking the GPS, including potential ranges. You may not be able to mark these at the time, but you should identify them on your chart and make a note to enter them into your GPS upon your return home.

Keeping Track
In traditional navigation, you maintain a plot of your progress on your chart using dead reckoning, then verify this &#8220;guesstimate&#8221; of your current position with a position fix (from a navigation aid, crossed bearings, et cetera) at every opportunity. By telling you your precise coordinates, GPS obviates the need for dead reckoning. But what do you do if the GPS quits? As you will see coming up, you will need to resort to dead reckoning based on your last known position. *But if you didn&#8217;t plot it, you won&#8217;t know what it was. Then, if you don&#8217;t have charted navigation aids or landmarks in view, you&#8217;re lost&#8212;literally.*

*It took me 18 pages to make this clear! 

" I have gone astray like a lost sheep; seek thy servant; for I do not forget thy commandments" Ps. 119:176 *

The solution is simple: plot your GPS position on your chart from time to time. On an extended cruise in open waters, an hourly interval is okay. At high speed, in dangerous waters, or in poor weather, consider doing so more frequently. We&#8217;ll revisit this in a while.
*
"My people hath been lost sheep: their shepherds have caused them to go astray, they have turned them away in the mountains: they have gone from mountain to hill, they have forgotten their resting place." Jer 50:6 * 

FIGURE 8-32. Plotting with GPS is somewhat different from traditional navigation. You are encouraged to plot your GPS position at intervals nominally an hour apart (depending upon the area and type of boat). Each time you plot your GPS position, you should make an attempt to verify its accuracy by taking a bearing and comparing it with the GPS. In this example, the OPS fixes have been plotted more frequently They are close to the planned course line but deviate a bit to port or starboard. This could be due to winds or currents or just inattention at the helm.










Underway with digital charts next


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## Fishers of Men

*Changed course for a minute
CHAPTER 11 BOWDITCH
SATELLITE NAVIGATION
INTRODUCTION	*
1100.	Early Developments In Satellite Navigation
The idea that led to development of the satellite navigation systems dates back to 1957 and the first launch of an artificial satellite into orbit, Russia&#8217;s Sputnik I. Dr. William H. Guier and Dr. George C. Wieffenbach at the Applied Physics Laboratory of the Johns Hopkins University were monitoring the famous &#8220;beeps&#8221; transmitted by the passing satellite. They plotted the received signals at precise intervals, and noticed that a characteristic Doppler curve emerged. Since celestial bodies followed fixed orbits, they reasoned that this curve could be used to describe the satellite orbit. Later, they demonstrated that they could determine all of the orbital parameters for a passing satellite by doppler observation of a single pass from a single fixed station. The doppler shift apparent while receiving a transmission from a passing satellite proved to be an effective measuring device for establishing the satellite orbit. Dr. Frank T. McClure, also of the Applied Physics Laboratory, reasoned that if the satellite orbit was known, doppler shift measurements could be used to determine one&#8217;s position on earth. His studies in support of this hypothesis earned him the first National Aeronautics and Space Administration award for important contributions to space development.

In 1958, the Applied Physics Laboratory proposed exploring the possibility of an operational satellite doppler navigation system. The Chief of Naval Operations then set forth requirements for such a system. The first successful launching of a prototype system satellite in April 1960 demonstrated the doppler system&#8217;s operational feasibility.

1101.	NAVSAT, The First Satellite Navigation System
The Navy Navigation Satellite System (NAVSAT, also known as TRANSIT) was the first operational satellite navigation system. The system&#8217;s accuracy was better than 0.1 nautical mile anywhere in the world. It was used primarily for the navigation of surface ships and submarines; but it also had some applications in air navigation. It was also used in hydrographic surveying and geodetic position determination.

NAVSAT uses the doppler shift of radio signals transmitted from a satellite to measure the relative velocity between the satellite and the navigator. Knowing the satellite orbit precisely, the navigator&#8217;s absolute position can be accurately determined from the time rate of change of range to the satellite.

The Johns Hopkins University Applied Physics Laboratory developed NAVSAT for the U. S. Navy. The operation of the system is under the control of the U. S. Navy Astronautics Group with headquarters at Point Mugu, California.

1102. System Configuration, Operation, And Termination
The NAVSAT consists of 10 orbiting satellites and 3 orbiting spares; a network of tracking stations continuously monitoring the satellites and updating the information they transmit; and the receivers and computers for processing signals.

Each satellite is in a nominally circular polar orbit at an approximate altitude of 600 nautical miles. There are usually five satellites operating in the system. Five satellites in orbit provide redundancy; the minimum constellation for system operation is four. This redundancy allows for an unexpected failure of a satellite and the relatively long period of time required to schedule, prepare, and launch a replacement satellite. This redundancy also provides for turning off a satellite when (on rare occasions) its orbital plane precesses near another satellite&#8217;s plane, or when the timing (phasing) of several satellites in their orbits are temporarily such that many satellites pass nearly simultaneously near one of the poles.

Each satellite contains: (1) receiver equipment to accept injection data and operational commands from the ground, (2) a decoder for digitizing the data, (3) switching logic and memory banks for sorting and storing the digital data, (4) control circuits to cause the data to be read out at specific times in the proper format, (5) an encoder to translate the digital data to phase modulation, (6) ultra stable 5 MHz oscillators, and (7) 1.5-watt transmitters to broadcast the 150- and 400-MHz oscillator-regulated frequencies that carry the data to earth.

The transit launch program ended in 1988. According to the Federal Radionavigation Plan, the Navy will cease operation of NAVSAT by the end of 1996, as the new Global Positioning System (GPS) comes into operation.

180 SATELLITE NAVIGATION
THE GLOBAL POSITIONING SYSTEM
1103. Basic System Description
The Federal Radionavigation Plan has designated the Navigation System using Timing and Ranging (NAVSTAR) Global Positioning System (GPS) as the primary navigation system of the U.S. government. GPS is a spaced-based radio positioning system which provides suitably equipped users with highly accurate position, velocity, and time data. It consists of three major segments: a space segment, a control segment, and a user segment.

The space segment contains 24 satellites. Precise spacing of the satellites in orbit is arranged such that a minimum of four satellites are in view to a user at any time on a worldwide basis. Each satellite transmits signals on two radio frequencies, superimposed on which are navigation and system data. Included in this data is predicted satellite ephemeris, atmospheric propagation correction data, satellite clock error information, and satellite health data. This segment consists of 21 operational satellites with three satellites orbiting as active spares. The satellites orbit in six separate orbital planes. The orbital planes have an inclination relative to the equator of 55&#176; and an orbital height of 20,200 km. The satellites complete an orbit approximately once every 12 hours.

GPS satellites transmit pseudorandom noise (PRN) sequence-modulated radio frequencies, designated L1 (1575.42 MHz) and L2 (1227.60 MHz). The satellite transmits both a Coarse Acquisition Code (C/A code) and a Precision Code (P code). Both the P and C/A codes are transmitted on the L1 carrier; only the P code is transmitted on the L2 carrier. Superimposed on both the C/A and P codes is the Navigation message. This message contains satellite ephemeris data, atmospheric propagation correction data, and satellite clock bias.

GPS assigns a unique C/A code and a unique P code to each satellite. This practice, known as code division multiple access (CDMA), allows all satellites the use of a common carrier frequency while still allowing the receiver to determine which satellite is transmitting. CDMA also allows for easy user identification of each GPS satellite.

Since each satellite broadcasts using its own unique C/A and P code combination, it can be assigned a unique PRN sequence number. This number is how a satellite is identified when the GPS control system communicates with users about a particular GPS satellite.

The control segment includes a master control station (MCS), a number of monitor stations, and ground antennas located throughout the world. The master control station, located in Colorado Springs, Colorado, consists of equipment and facilities required for satellite monitoring, telemetry, tracking, commanding, control, uploading, and navigation message generation. The monitor stations, located in Hawaii, Colorado Springs, Kwajalein, Diego Garcia, and Ascension Island, passively track the satellites, accumulating ranging data from the satellites&#8217; signals and relaying them to the MCS. 

The MCS processes this information to determine satellite position and signal data accuracy, updates the navigation message of each satellite and relays this information to the ground antennas. The ground antennas then transmit this information to the satellites. The ground antennas, located at Ascension Island, Diego Garcia, and Kwajalein, are also used for transmitting and receiving satellite control information.

The user segment is designed for different requirements of various users. These receivers can be used in high, medium, and low dynamic applications. An example of a low dynamic application would be a fixed antenna or slowly drifting marine craft. An example of a medium dynamic application would be a marine or land vehicle traveling at a constant controlled speed.

Finally, an example of a high dynamic application would be a high performance aircraft or a spacecraft. The user equipment is designed to receive and process signals from four or more orbiting satellites either simultaneously or sequentially. The processor in the receiver then converts these signals to three-dimensional navigation information based on the World Geodetic System 1984 reference ellipsoid. The user segment can consist of stand-alone receivers or equipment that is integrated into another navigation system. Since GPS is used in a wide variety of applications, from marine navigation to land surveying, these receivers can vary greatly in function and design.

1104. System Capabilities
GPS provides multiple users with accurate, continuous, worldwide, all-weather, common-grid, three dimensional positioning and navigation information.
To obtain a navigation solution of position (latitude, longitude, and altitude) and time (four unknowns), four satellites must be selected. The GPS user measures pseudorange and pseudorange rate by synchronizing and tracking the navigation signal from each of the four selected satellites. Pseudorange is the true distance between the satellite and the user plus an offset due to the user&#8217;s clock bias. Pseudorange rate is the true slant range rate plus an offset due to the frequency error of the user&#8217;s clock. By decoding the ephemeris data and system timing information on each satellite&#8217;s signal, the user&#8217;s receiver/processor can convert the pseudorange and pseudorange rate to three-dimensional position and velocity. Four measurements are necessary to solve for the three unknown components of position (or velocity) and the unknown user time (or frequency) bias.

SATELLITE NAVIGATION 
The navigation accuracy that can be achieved by any user depends primarily on the variability of the errors in making pseudorange measurements, the instantaneous geometry of the satellites as seen from the user&#8217;s location on Earth, and the presence of Selective Avaliability (SA). Selective Availability is discussed further below.

1105. Global Positioning System Basic Concepts
As discussed above, GPS measures distances between satellites in orbit and a receiver on or above the earth and computes spheres of position from those distances. The intersections of those spheres of position then determine the receiver&#8217;s position.
The distance measurements described above are done by comparing timing signals generated simultaneously by the satellites&#8217; and receiver&#8217;s internal clocks. These signals, characterized by a special wave form known as the pseudorandom code, are generated in phase with each other. The signal from the satellite arrives at the receiver following a time delay proportional to its distance traveled. This time delay is detected by the phase shift between the received pseudo-random code and the code generated by the receiver. Knowing the time required for the signal to reach the receiver from the satellite allows the receiver to calculate the distance from the satellite. The receiver, therefore, must be located on a sphere centered at the satellite with a radius equal to this distance measurement. The intersection of three spheres of position yields two possible points of receiver position. One of these points can be disregarded since it is hundreds of miles from the surface of the earth. Theoretically, then, only three time measurements are required to obtain a fix from GPS. In practice, however, a fourth measurement is required to obtain an accurate position from GPS. This is due to receiver clock error. Timing signals travel from the satellite to the receiver at the speed of light; even extremely slight timing errors between the clocks on the satellite and in the receiver will lead to tremendous range errors. The satellite&#8217;s atomic clock is accurate to 10-9 seconds; installing a clock that accurate on a receiver would make the receiver prohibitively expensive. Therefore, receiver clock accuracy is sacrificed, and an additional satellite timing measurement is made. The fix error caused by the inaccuracies in the receiver clock is reduced by simultaneously subtracting a constant timing error from four satellite timing measurements until a pinpoint fix is reached. This process is analogous to the navigator&#8217;s plotting of a visual fix when bearing transmission error is present in his bearing repeater system. With that bearing error present, two visual LOP&#8217;s will not intersect at a vessel&#8217;s true position; there will be an error introduced due to the fixed, constant error in the bearing transmission process. There are two ways to overcome such an error. The navigator can buy extremely accurate (and expensive) bearing transmission and display equipment, or he can simply take a bearing to a third visual navigation aid. The resulting fix will not plot as a pinpoint (as it would were there no transmission error present); rather, it will plot as a triangle. The navigator can then apply a constant bearing correction to each LOP until the correction applied equals the bearing transmission error. When the correction applied equals the original transmission error, the resultant fix should plot as a pinpoint. The situation with GPS receiver timing inaccuracies is analogous; time measurement error simply replaces bearing measurement error in the analysis. Assuming that the satellite clocks are perfectly synchronized and the receiver clock&#8217;s error is constant, the subtraction of that constant error from the resulting distance determinations will reduce the fix error until a &#8220;pinpoint&#8221; position is obtained. It is important to note here that the number of lines of position required to employ this technique is a function of the number of lines of position required to obtain a fix. In the two dimensional visual plotting scenario described above, only two LOP&#8217;s were required to constitute a fix. The bearing error introduced another unknown into the process, resulting in three total unknowns (the x coordinate of position, the y coordinate of position, and the bearing error). Because of the three unknowns, three LOP&#8217;s were required to employ this correction technique. GPS determines position in three dimensions; the presence of receiver clock error adds an additional unknown. Therefore, four timing measurements are required to solve for the resulting four unknowns.

1106. GPS Signal Coding
Two separate carrier frequencies carry the signal transmitted by a GPS satellite. The first carrier frequency (L1) transmits on 1575.42 MHz; the second (L2) transmits on 1227.60 MHz. The GPS signal consists of three separate messages: the P-code, transmitted on both L1 and L2; the C/ A code, transmitted on L1 only; and a navigation data message. The P code and C/A code messages are divided into individual bits known as chips. The frequency at which bits are sent for each type of signal is known as the chipping rate. The chipping rate for the P-code is 10.23 MHz (10.23 &#180; 106 bits per second); for the C/A code, 1.023 MHz (1.023 &#180; 106 bits per second); and for the data message, 50 Hz (50 bits per second). The P and C/A codes phase modulate the carriers; the C/A code is transmitted at a phase angle of 90&#176; from the P code. The periods of repetition for the C/A and P codes differ. The C/A code repeats once every millisecond; the P-code sequence repeats every seven days.

As stated above the GPS carrier frequencies are phase modulated. This is simply another way of saying that the digital &#8220;1&#8217;s&#8221; and &#8220;0&#8217;s&#8221; contained in the P and C/A codes are indicated along the carrier by a shift in the carrier phase. This is analogous to sending the same data along a carrier by varying its amplitude (amplitude modulation, or AM) or its frequency (frequency modulation, or FM). See Figure 1106a. In phase modulation, the frequency and the amplitude of the carrier are unchanged by the &#8220;information signal,&#8221; and the digital information is transmitted by shifting the carrier&#8217;s phase. The phase modulation employed by GPS is known as bi-phase shift keying (BPSK).

Figure 1106a. Digital data transmission with amplitude, frequency and phase modulation. 










Figure 1106b. Modulation of the L1 and L2 carrier frequencies with the C/A and P code signals.










Figure 1106c. GPS signal spreading and recovery from satellite to receiver.










Due to this BPSK, the carrier frequency is &#8220;spread&#8221; about its center frequency by an amount equal to twice the &#8220;chipping rate&#8221; of the modulating signal. In the case of the P code, this spreading is equal to (2 &#180; 10.23 MHz) = 20.46 MHz. For the C/A code, the spreading is equal to (2 &#180; 1.023 MHz) = 2.046 MHz. See Figure 1106b. Note that the L1 carrier signal, modulated with both the P code and C/A code, is shaped differently from the L2 carrier, modulated with only the P code. This spreading of the carrier signal lowers the total signal strength below the thermal noise threshold present at the receiver. This effect is demonstrated in Figure 1106c. When the satellite signal is multiplied with the C/A and P codes generated by the receiver, the satellite signal will be collapsed into the original carrier frequency band. The signal power is then raised above the thermal noise level.

The navigation message is superimposed on both the P code and C/A code with a data rate of 50 bits per second (50 Hz.) The navigation message consists of 25 data frames, each frame consisting of 1500 bits. Each frame is divided into five subframes of 300 bits each. It will, therefore, take 30 seconds to receive one data frame and 12.5 minutes to receive all 25 frames. The navigation message contains GPS system time of transmission; a hand over word (HOW), allowing the transition between tracking the C/A code to the P code; ephemeris and clock data for the satellite being tracked; and almanac data for the satellites in orbit. It also contains coefficients for ionospheric delay models used by C/A receivers and coefficients used to calculate Universal Coordinated Time (UTC).

1107. The Correlation Process
The correlation process compares the signal received with the signal generated internal to the receiver. It does this by comparing the square wave function of the received signal with the square wave function generated by the receiver. The computer logic of the receiver recognizes the square wave signals as either a +1 or a 0 depending on whether the signal is &#8220;on&#8221; or &#8220;off.&#8221; The signals are processed and matched by using an autocorrelation function. This process defines the necessity for a &#8220;pseudo-random code.&#8221; The code must be repeatable (i.e., non-random) because it is in comparing the two signals that the receiver makes its distance calculations. At the same time, the code must be random for the correlation process to work; the randomness of the signals must be such that the matching process excludes all possible combinations except the combination that occurs when the generated signal is shifted a distance proportional to the received signal&#8217;s time delay. These simultaneous requirements to be both repeatable (non-random) and random give rise to the description of &#8220;pseudo-random&#8221;; the signal has enough repeatability to enable the receiver to make the required measurement while simultaneously retaining enough randomness to ensure incorrect calculations are excluded.

1108. Precise Positioning Service And Standard Positioning Service
Two levels of navigational accuracy are provided by the GPS: the Precise Positioning Service (PPS) and the Standard Positioning Service (SPS). GPS was designed, first and foremost, by the U.S. Department of Defense as a United States military asset; its extremely accurate positioning capability is an asset access to which the U.S. military would like to limit during time of war. Therefore, the PPS is available only to authorized users, mainly the U.S. military and authorized allies. SPS, on the other hand, is available worldwide to anyone possessing a GPS receiver. PPS, therefore, provides a more accurate position than does SPS.

Two cryptographic methods are employed to deny the PPS accuracy to civilian users: selective availability (SA) and anti-spoofing (A-S). SA operates by introducing controlled errors into both the C/A and P code signals. SA can be programmed to degrade the signals&#8217; accuracy even further during time of war, denying a potential adversary the ability to use GPS to nominal SPS accuracy. SA introduces two errors into the satellite signal: (1) The epsilon error: an error in satellite ephemeris data in the navigation message; and (2) clock dither: error introduced in the satellite atomic clocks&#8217; timing. The presence of SA is the largest source of error present in an SPS GPS position measurement. 










Anti-spoofing is designed to negate any hostile imitation of GPS signals. The technique alters the P code into another code, designated the Y code. The C/A code remains unaffected. The U.S. employs this technique to the satellite signals at random times and without warning; therefore, civilian users are unaware when this P code transformation takes place. Since anti-spoofing is applied only to the P code, the C/A code is not protected and can be spoofed. Only users employing the proper cryptographic devices can defeat both SA and anti-spoofing. Without these devices, the user will be subject to the accuracy degradation of SA and will be unable to track the Y code.

GPS PPS receivers can use either the P code or the C/ A code, or both, in determining position. Maximum accuracy is obtained by using the P code on both L1 and L2. The difference in propagation delay is then used to calculate ionospheric corrections. The C/A code is normally used to acquire the satellite signal and determine the approximate P code phase. Then, the receiver locks on the P code for precise positioning (subject to SA if not cryptographically equipped). Some PPS receivers possess a clock accurate enough to track and lock on the P code signal without initially tracking the C/A code. Some PPS receivers can track only the C/A code and disregard the P code entirely. Since the C/A code is transmitted on only one frequency, the dual frequency ionosphere correction methodology is unavailable and a ionospheric modeling procedure is required to calculate the required corrections.

SPS receivers, as mentioned above, provide positions with a degraded accuracy. The A-S feature denies SPS users access to the P code when transformed to the Y code. Therefore, the SPS user cannot rely on access to the P code to measure propagation delays between L1 and L2 and compute ionospheric delay corrections. Consequently, the typical SPS receiver uses only the C/A code because it is unaffected by A-S. Since C/A is transmitted only on L1, the dual frequency method of calculating ionospheric corrections is unavailable; an ionospheric modeling technique must be used. This is less accurate than the dual frequency method; this degradation in accuracy is accounted for in the 100 meter accuracy calculation.

Figure 1108 presents the effect on SA and A-S on different types of GPS measurements.

1109. GPS Receiver Operations
In order for the GPS receiver to navigate, it has to track satellite signals, make pseudorange measurements, and collect navigation data.
A typical satellite tracking sequence begins with the receiver determining which satellites are available for it to track. Satellite visibility is determined by user-entered predictions of position, velocity, and time, and by almanac information stored internal to the receiver. If no stored almanac information exists, then the receiver must attempt to locate and lock onto the signal from any satellite in view. When the receiver is locked onto a satellite, it can demodulate the navigation message and read the almanac information about all the other satellites in the constellation. A carrier tracking loop tracks the carrier frequency while a code tracking loop tracks the C/A and P code signals. The two tracking loops operate together in an iterative process to acquire and track satellite signals.

The receiver&#8217;s carrier tracking loop will locally generate an L1 carrier frequency which differs from the satellite produced L1 frequency due to a doppler shift in the received frequency. This doppler offset is proportional to the relative velocity along the line of sight between the satellite and the receiver, subject to a receiver frequency bias. The carrier tracking loop adjusts the frequency of the receiver generated frequency until it matches the incoming frequency. This determines the relative velocity between the satellite and the receiver. The GPS receiver uses this relative velocity to calculate the velocity of the receiver. This velocity is then used to aid the code tracking loop.

The code tracking loop is used to make pseudorange measurements between the GPS receiver and the satellites. The receiver&#8217;s tracking loop will generate a replica of the targeted satellite&#8217;s C/A code with estimated ranging delay. In order to match the received signal with the internally generated replica, two things must be done: 1) The center frequency of the replica must be adjusted to be the same as the center frequency of the received signal; and 2) the phase of the replica code must be lined up with the phase of the received code. The center frequency of the replica is set by using the doppler-estimated output of the carrier tracking loop. The receiver will then slew the code loop generated C/ A code though a millisecond search window to correlate with the received C/A code and obtain C/A tracking. Once the carrier tracking loop and the code tracking loop have locked onto the received signal and the C/A code has been stripped from the carrier, the navigation message is demodulated and read. This gives the receiver other information crucial to a pseudorange measurement. The navigation message also gives the receiver the handover word, the code that allows a GPS receiver to shift from C/ A code tracking to P code tracking.

The handover word is required due to the long phase (seven days) of the P code signal. The C/A code repeats every millisecond, allowing for a relatively small search window. The seven day repeat period of the P code requires that the receiver be given the approximate P code phase to narrow its search window to a manageable time. The handover word provides this P code phase information. The handover word is repeated every subframe in a 30 bit long block of data in the navigation message. It is repeated in the second 30 second data block of each subframe. For some receivers, this handover word is unnecessary; they can acquire the P code directly. This normally requires the receiver to have a clock whose accuracy approaches that of an atomic clock. Since this greatly increases the cost of the receiver, most receivers for non-military marine use do not have this capability.

Once the receiver has acquired the satellite signals from four GPS satellites, achieved carrier and code tracking, and has read the navigation message, the receiver is ready to begin making pseudorange measurements. Recall that these measurements are termed pseudorange because a receiver clock offset makes them inaccurate; that is, they do not represent the true range from the satellite, only a range biased by a receiver clock error. 

This clock bias introduces a fourth unknown into the system of equations for which the GPS receiver must solve (the other three being the x coordinate, y coordinate, and z coordinate of the receiver position). Recall from the discussion in section 1103 that the receiver solves this clock bias problem by making a fourth pseudorange measurement, resulting in a fourth equation to allow solving for the fourth unknown. Once the four equations are solved, the receiver has an estimate of the receiver&#8217;s position in three dimensions and of GPS time. The receiver then converts this position into coordinates referenced to an earth model based on the World Geodetic System (1984).

1110. User Range Errors And Geometric Dilution Of Precision
There are two formal position accuracy requirements for GPS:
1) The PPS spherical position accuracy shall be 16
meters SEP (spherical error probable) or better.
2) The SPS user two dimensional position accuracy shall be 100 meters 2 drms or better.
Assume that a universal set of GPS pseudorange measurements results in a set of GPS position measurements.

The accuracy of these measurements will conform to a normal (i.e. values symmetrically distributed around a mean of zero) probability function because the two most important factors affecting accuracy, the geometric dilution of precision (GDOP) and the user equivalent range error (UERE), are continuously variable.

The UERE is the error in the measurement of the pseudoranges from each satellite to the user. The UERE is the product of several factors, including the clock stability, the predictability of the satellite&#8217;s orbit, errors in the 50 Hz navigation message, the precision of the receiver&#8217;s correlation process, errors due to atmospheric distortion and the calculations to compensate for it, and the quality of the satellite&#8217;s signal. The UERE, therefore, is a random error which is the function of errors in both the satellites and the user&#8217;s receiver. The GDOP depends on the geometry of the satellites in relation to the user&#8217;s receiver. It is independent of the quality of the broadcast signals and the user&#8217;s receiver. Generally speaking, the GDOP measures the &#8220;spread&#8221; of the satellites around the receiver. The optimum case would be to have one satellite directly overhead and the other three spaced 120&#176; around the receiver on the horizon. The worst GDOP would occur if the satellites were spaced closely together or in a line overhead.

Figure 1110. Position and time error computations.
There are special types of DOP&#8217;s for each of the position and time solution dimensions; these particular DOP&#8217;s combine to determine the GDOP. For the vertical dimension, the vertical dilution of precision (VDOP) describes the effect of satellite geometry on altitude calculations. 

The horizontal dilution of precision (HDOP) describes satellite geometry&#8217;s effect on position (latitude and longitude) errors. These two DOP&#8217;s combine to determine the position dilution of precision (PDOP). The PDOP combined with the time dilution of precision (TDOP) results in the GDOP.

See Figure 1110. 










1111. Ionospheric Delay Errors
Section 1107 covered errors in GPS positions due to errors inherent in the satellite signal (UERE) and the geometry of the satellite constellation (GDOP). Another major cause of accuracy degradation is the effect of the ionosphere on the radio frequency signals that comprise the GPS signal. A discussion of a model of the earth&#8217;s atmosphere will be useful in understanding this concept. Consider the earth as surrounded by three layers of atmosphere. The first layer, extending from the surface of the earth to an altitude of approximately 10 km, is known as the troposphere. Above the troposphere and extending to an altitude of approximately 50 km is the stratosphere. Finally, above the stratosphere and extending to an altitude that varies as a function of the time of day is the ionosphere. Though radio signals are subjected to effects which degrade its accuracy in all three layers of this atmospheric model, the effects of the ionosphere are the most significant; therefore, they will be discussed here.

The ionosphere, as the name implies, is that region of the atmosphere which contains a large number of ionized molecules and a correspondingly high number of free electrons. These charged molecules are those which have lost one or more electrons. No atom will loose an electron without an input of energy; the energy input that causes the ions to be formed in the ionosphere comes from the ultraviolet (U-V) radiation of the sun.
Therefore, the more intense the sun&#8217;s rays, the larger the number of free electrons which will exist in this region of the atmosphere.
The largest effect that this ionospheric effect has on GPS accuracy is a phenomenon known as group time delay. As the name implies, group time delay results in a delay in the time a signal takes to travel through a given distance. Obviously, since GPS relies on extremely accurate timing measurement of these signals between satellites and ground receivers, this group time delay can have a noticeable effect on the magnitude of GPS position error.

The group time delay is a function of several elements. It is inversely proportional to the square of the frequency at which the satellite transmits, and it is directly proportional to the atmosphere&#8217;s total electron content (TEC), a measure of the degree of the atmosphere&#8217;s ionization. The general form of the equation describing the delay effect is:










Since the sun&#8217;s U-V radiation ionizes the molecules in the upper atmosphere, it stands to reason that the time delay value will be highest when the sun is shining and lowest at night. Experimental evidence has borne this out, showing that the value for TEC is highest around 1500 local time and lowest around 0500 local time. Therefore, the magnitude of the accuracy degradation caused by this effect will be highest during daylight operations. In addition to these daily variations, the magnitude of this time delay error also varies with the seasons; it is highest at the vernal equinox. Finally, this effect shows a solar cycle dependence. The greater the number of sunspots, the higher the TEC value and the greater the group time delay effect. The solar cycle typically follows an eleven year pattern. Solar cycle 22 began in 1986, peaked in 1991, and is now in decline. It should reach a minimum in 1997, at which time the effect on the group time delay from this phenomenon will also reach a minimum. Given that this ionospheric delay introduces a serious accuracy degradation into the system, how does GPS account for it? There are two methods used: (1) the dual frequency technique, and (2) the ionospheric delay method.

1112. Dual Frequency Correction Technique
As the term implies, the dual frequency technique requires the ability to acquire and track both the L1 and L2 frequency signals. Recall from the discussion in section 1105 that the C/A and P codes are transmitted on carrier frequency L1, but only the P code is transmitted on L2. Recall also from section 1105 that only authorized operators with access to DOD cryptographic material are able to copy the P code. It follows, then, that only those authorized users are able to copy the L2 carrier frequency. Therefore, only those authorized users are able to use the dual frequency correction method. The dual frequency method measures the distance between the satellite and the user based on both the L1 and L2 carrier signal. These ranges will be different because the group time delay for each signal will be different. This is because of the frequency dependence of the time delay error. The range from the satellite to the user will be the true range combined with the range error caused by the time delay, as shown by the following equation:










where R(f) is the range which differs from the actual range as a function of the carrier frequency. The dual frequency correction method takes two such range measurements, R(L1) and R(L2). Recall that the error term is a function of a constant divided by the square of the frequency. By combining the two range equations derived from the two frequency measurements, the constant term can be eliminated and one is left with an equation in which the true range is simply a function of the two carrier frequencies and the measured ranges R(L1) and R(L2). This method has two major advantages over the ionospheric model method. (1) It calculates corrections from real-time measured data; therefore, it is more accurate. (2) It alleviates the need to include ionospheric data on the navigation message. A significant portion of the data message is devoted to ionospheric correction data. If the receiver is dual frequency capable, then it does not need any of this data.

The vast majority of maritime users cannot copy dual frequency signals. For them, the ionospheric delay model provides the correction for the group time delay.

1113. The Ionospheric Delay Model
The ionospheric delay model mathematically models the diurnal ionospheric variation. The value for this time delay is determined from a cosinusoidal function into which coefficients representing the maximum value of the time delay (i.e., the amplitude of the cosine wave representing the delay function); the time of day; the period of the variation; and a minimum value of delay are introduced. This model is designed to be most accurate at the diurnal maximum. This is obviously a reasonable design consideration because it is at the time of day when the maximum diurnal time delay occurs that the largest magnitude of error appears. The coefficients for use in this delay model are transmitted to the receiver in the navigation data message. As stated in section 1112, this method of correction is not as accurate as the dual frequency method; however, for the non-military user, it is the only method of correction available.

1114. Multipath Reflection Errors
Multipath reflection errors occur when the receiver detects parts of the same signal at two different times. The first reception is the direct path reception, the signal that is received directly from the satellite. The second reception is from a reflection of that same signal from the ground or any other reflective surface. The direct path signal arrives first, the reflected signal, having had to travel a longer distance to the receiver, arrives later. The GPS signal is designed to minimize this multipath error. The L1 and L2 frequencies used demonstrate a diffuse reflection pattern, lowering the signal strength or any reflection that arrives at the receiver. In addition, the receiver&#8217;s antenna can be designed to reject a signal that it recognizes as a reflection. In addition to the properties of the carrier frequencies, the high data frequency of both the P and C/A codes and their resulting good correlation properties minimize the effect of multipath propagation.
The design features mentioned above combine to reduce the maximum error expected from multipath propagation to less than 20 feet.

1115. Differential GPS Concept
The discussions above make it clear that the Global Positioning System provides the most accurate positions available to navigators today. They should also make clear that the most accurate positioning information is available to only a small fraction of the using population: U.S. and allied military. For most open ocean navigation applications, the degraded accuracy inherent in selective availability and the inability to copy the precision code presents no serious hazard to navigation. A mariner seldom if ever needs greater than 100 meter accuracy in the middle of the ocean. It is a different situation as the mariner approaches shore. Typically for harbor approaches and piloting, the mariner will shift to visual piloting. The increase in accuracy provided by this navigational method is required to ensure ship&#8217;s safety. The 100 meter accuracy of GPS in this situation is not sufficient. Any mariner who has groped his way through a restricted channel, in a fog obscuring all visual navigation aids will certainly appreciate the fact that even a degraded GPS position is available for them to plot. However, 100 meter accuracy is not sufficient to ensure ship&#8217;s safety in most piloting situations. In this situation, the mariner needs P code accuracy. The problem then becomes how to obtain the accuracy of the Precise Positioning Service with due regard to the legitimate security concerns of the U.S. military. The answer to this seeming dilemma lies in the concept of Differential GPS (DGPS).

Differential GPS is a system in which a receiver at an accurately surveyed position utilizes GPS signals to calculate timing errors and then broadcasts a correction signal to account for these errors. This is an extremely powerful concept. The errors which contribute to GPS accuracy degradation, ionospheric time delay and selective availability, are experienced simultaneously by both the DGPS receiver and a relatively close user&#8217;s receiver. The extremely high altitude of the GPS satellites means that, as long as the DGPS receiver is within 100-200 km of the user&#8217;s receiver, the user&#8217;s receiver is close enough to take advantage of any DGPS correction signal.

The theory behind a DGPS system is straightforward. Located on an accurately surveyed site, the DGPS receiver already knows its location. It receives data which tell it where the satellite is. Knowing the two locations, it then calculates the time it should take for a satellite&#8217;s signal to reach it. It compares the time that it actually takes for the signal to arrive. This difference in time between the theoretical and the actual is the basis for the DGPS receiver&#8217;s computation of a timing error signal; this difference in time is caused by all the errors to which the GPS signal is subjected; errors, except for receiver error and multipath error, to which both the DGPS and the user&#8217;s receivers are simultaneously subject. The DGPS system then broadcasts a timing correction signal, the effect of which is to correct for selective availability, ionospheric delay, and all the other error sources the two receivers share in common.

For suitably equipped users, DGPS results in positions as accurate as if not more accurate than those obtainable by the Precise Positioning Service. For the mariner approaching a harbor or piloting in restricted waters near a site with a DGPS transmitter, the accuracy required for ship&#8217;s safety is now available from a system other than plotting visual bearings. This capability is not limited to simply displaying the correct position for the navigator to plot. The DGPS position can be used as the prime input to an electronic chart system, providing an electronic readout of position accurate enough to pilot safely in the most restricted channel. The U.S. Coast Guard presently plans to install DGPS systems to provide 100&#37; coverage along the eastern seaboard, the Gulf Coast, and the Pacific coast. Alaska and Hawaii will also be covered with a DGPS network. The DGPS signal will be broadcast using existing radiobeacons.

DGPS accuracy will revolutionize marine navigation. It is important to note, however, that, even with the development of the electronic chart and the proliferation of accurate, real-time electronic navigation systems, the mariner should not let his skills in the more traditional areas of navigation, such as celestial navigation and piloting, wane. They will become important secondary methods; any mariner who has put his faith in electronic navigation only to see the system suffer an electronic failure at sea can attest to the importance of maintaining proficiency in the more traditional methods of navigation. However, there is no doubt that the ease, convenience, and accuracy of DGPS will revolutionize the practice of marine navigation.

*End ch 11
Underway with digital charts next*


----------



## Fishers of Men

*UNDERWAY WITH DIGITAL CHARTS*
I hope that GPS questions were answered to an extent where you see that they are just another navigational aid, and that&#8217;s all. Now this is where it would &#8220;pay&#8221; you to spend a little more and go a chart plotter so you have the most you can get for your money, your GPS is included, mapping, being able to locate the nearest hospital, gas or beer store and more with a touch of a button. Safety and an excellent aid that will provide tons of information and even help your fishing tactics. There are many models out there, and a lot of good ones. Research before you buy. Ones that will let you record your own info, interphase with a home computer, be able to get proper updates, and for me, I like a fast changing screen&#8230;as with any computer, the need for speed! Some even have a Radar overlay feature. After we discuss this, you will know what to look for in a affordable unit. You definitely want one that is daylight readable, can split screens, and has night vision and options for changing colors to your specs. Some even have a split screen for a color fishfinder.

There is no question that displaying GPS information directly on a Chart Screen is ideal for ease of use and safety. You are freed from the tedious task and potential errors associated with transferring positions back and forth between your GPS and paper charts.

This ideal in no way diminishes the effectiveness of a nonmapping handheld GPS, a paper chart, and the techniques described in the previous chapters. Digital charts are just easier, though somewhat more expensive. Most boaters start with a handheld GPS and gravitate toward using a computer with the GPS at home for planning. The next step in the progression is usually either a chartplotter or an onboard computer for live navigation.

A chartplotter is specifically tailored to navigation tasks, whereas a general-purpose computer can be used with navigation software to do the same things and potentially more. Where and how you plan to use the equipment and how much you care to spend on it are the primary considerations.

At some point in the near future, the differences between chartplotters and onboard computers will blur. With improving performance and lower costs, chartplotters are already finding their way onto smaller boats, which is actually where they belong. These self-contained units are ideal for an 18-foot boat that has little room in which to lay out a paper chart.

Meanwhile, advances in onboard computer hardware and software are giving computers increasing application on the water. Today, most oceangoing commercial ships are moving to totally computerized electronic navigation suites. The power and versatility of computer-based navigation is attractive to anyone who cruises. As previously noted, many boaters use both chartplotters and computers. The computer shines for planning; for navigating longer, more complex routes; and for use in an enclosed helm station. The chartplotter, with its marinized, waterproof construction and simplified keyboard, is a better choice for an open helm. In the future, most chartplotters may in fact be general purpose computers in custom enclosures with large, touch-screen color displays. Later, we&#8217;ll glimpse into the future by taking a look at one of the high- end systems offered today.

Using a Chartplotter Underway
In essence, a chartplotter is a custom display and processing unit that is programmed to present live position information on a digital representation of a chart. It may include a GPS with a built-in antenna or a remote external antenna, or it may accept input from an external GPS receiver.

Most chartplotters are tailored to the marine environment, including some degree of waterproofing for use at open helm stations. Their grayscale displays are bright enough to be seen in sunlight, with color displays becoming more common but still somewhat more expensive as of this writing. Color adds an extra dimension that helps cue the helmsman, and the charts appear in their natural colors.

Most chartplotters use vector charts. The charts are sold on chips that can be inserted into the plotter, each chip holding a substantial portfolio of charts for a particular region. Several companies provide cartography on chartplotter chips, and manufacturers design their chartplotters to be compatible with a particular chip configuration. Chips are interchangeable among units using the same cartography, but nor more broadly.

Regardless of chip configuration, all chartplotters display your current position superimposed on a chart, your active route or leg, and all stored waypoints within the field of view of the current zoom level on the display.

There is usually a much greater amount of information available than could be displayed on the screen without overly cluttering it. When you scroll the cursor over the object in question, a pop-up box usually provides further details. It is important to note that the accuracy of the chart is limited to the accuracy of the source chart at its original scale. Overzooming can give you a false sense of security if you seem to be clear of charted objects. Actually, the locations of these objects may be charted in error, which is only exaggerated by the increased zoom. 

Some digital chartmakers such as C-Map prevent significant overzooming for this very reason.
Many chartplotters permit the user to select the amount of detail that will be displayed at a given level of zoom. Although seeing more details may appear to be an advantage, particularly for planning, details often are a distraction on the water. Underway, a simpler display is better, because you may not be able to devote a high degree of attention to the chartplotter and man the helm at the same time. This is one of the clear advantages of vector charts. They are simpler, clearer, and the chart data are sized to the level of zoom. 

Chartplotters can be operated in two modes:
Planning and navigation. You need to preplan how you want to set up and use your chartplotter while navigating.

&#8226; CHARTPLOTTER SETUP FOR NAVIGATION
Just as you would in preparing to pilot an airplane, you need to go through a preflight check of your chartplotter Here are a few things to do:
1. Fire up the chartplotter at the dock and check that it&#8217;s reporting your docked location accurately both on the chart and in the digital readout.
2. Look into the setup menu to ensure that the chart datum matches the chart chip installed in the unit. Also, double- check other settings such as &#8220;Auto Magnetic&#8221; for heading, &#8220;Nautical&#8221; for units, and &#8220;ODD MMM.MMM&#8221; for coordinates (if boating in coastal or offshore regions).
3. Make sure you have up-to-date chart chips for the regions you intend to navigate. While you&#8217;re at it, check that you have corresponding paper charts.
4. Check under the Routes menu to make sure you have stored the appropriate planned routes (and corresponding way-points) in the unit.
5. On a chart, check the intended path from your current location to the first waypoint you intend to use. Plan this first &#8220;pre -leg&#8221; before departure.
6. Make sure you have your backup strategies and equipment in place. Typically, a handheld GPS with the same waypoints and routes is a good idea, and paper charts are always an important backup.
7. As you fire up other equipment and the engine(s) on the boat, recheck the GPS to ensure that nothing has changed regarding your reported position before departure. It&#8217;s a good idea to turn off the GPS (and other programmed electronics) before starting the engine to avoid any current surge, which could scramble settings.
8. Select your first waypoint or route.
This pre-departure check will take just minutes and will add to your confidence, safety, and comfort underway. Remember navigation is but one of your tasks at the helm, so you Want it to be easy.

*To be cont.*


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## Fishers of Men

*Underway cont.*
FIGURE 9-1. Chartplotters display your GPS position overlaid on a digital representation of a chart. Typically, chartplotters are designed with 5- to 10-inch screens. Because these devices are designed for use on the water, they usually are sealed. To provide a more waterproof interface and compact data, the digital charts typically are provided on removable chips in vector format. Chartplotters may have a built-in GPS or use an external GPS. Often, they can display depth sounder and radar in formation. (Courtesy: Raymarine, Garmin, Sitex)



















Many chartplotters are fixed-mounted and cannot readily be removed from the boat for planning. The Sitex units are easily removed with a push of a button and have dual c-map slots. This is one of the reasons why many chartplotter users also use planning software on a computer at home. The resultant routes and waypoints can be uploaded from a laptop computer into the chartplotter using the standard NMEA (National Marine Electronics Association) 0183 protocol (see later in this chapter). You may need to have a cable made if your chartplotter manufacturer does not provide one as an option. With that cable, you can connect directly to the chart- plotter from the serial port on your computer.

Become familiar with the buttons and functions of your chartplotter while in port, so you can change modes quickly on the water without diverting attention from the helm. The large screen and easy&#8212;to-access buttons of a typical fixed-mount chartplotter make navigation a great deal easier than with a handheld GPS.

As with GPS, the two screens you will find most useful underway are the Map (Chart) Screen (which, unlike handheld GPS models, contains an actual chart) and the Highway Screen.

Chart Screen
Typically, you will use the Chart Screen while getting into position for a leg, while in harbors or channels, or near obstacles. When departing, you can zoom in to view the details of a channel and the approaches to your boating waters.

Local Channels Harbors are likely to show the least amount of preprinted chart detail. For these areas, you should annotate your charts with waypoints marking hazards or cues that you will use to navigate safely.

FIGURE 9-2. The boat position is indicated by the black arrow symbol on the chart. The vector chart shows navigation aids, shorelines, depth contours, and soundings.










FIGURE 9-3. You can look ahead using the cursor (cross symbol). This harbor is 9.7 nm at a bearing of 3510 from your current location. You can set the chartplotter to &#8220;Go To&#8221; this location. This will result in a course line and highway being drawn on their respective screens.










FIGURE 9-4. Just outside the same harbor, you will find a number of circled potential hazards. (The highlighting is not a feature on the chartplotter) Having the chart on the screen helps you to stay clear of the hazards.










Mark them when the weather is fair, keeping in mind what references you will need when visibility is impaired. The Chart Screen provides a rich trove of information. Just re member that if you overzoom, you may be lulled into believing that the chart is more accurate than it really is. Don&#8217;t rely on the placement of navigation aids that comes with the chart data; mark your own where maneuvering is tight and accuracy is critical. Most chartplotters today offer WAAS GPS, which can give your position to within ten feet of accuracy. In fact, your WAAS-plotted position is likely the most accurate feature on the chart.

OPEN WATER In open water the Chart Screen is useful to check for hazards and to stay on planned courses. You will be able to see depth contours and soundings in addition to wrecks, rocks, and other obstacles. Your boat will be represented by a symbol that shows its position and direction of travel. You should compare your chartplotter screen with your depth sounder, visible landmarks, and radar to ensure that they match. Then you know that the chartplotter is working properly.

Zooming in, you will see details of your surroundings, but you lose perspective on your progress toward your destination. Zooming out, you can see your position relative to your route and land features. Some chartplotters permit displaying two screens side by side or one over the other. Usually, this is limited to units with 10-inch or larger screens.

About every hour, or more frequently depending on boat speed and weather and sea conditions, you should plot your position and the time on a paper chart. This is in case the chartplotter or other electronics fails or starts providing suspect information. Then you can go back to the last known plotted point and estimate your current position from there using dead reckoning. When you use dead reckoning, try to verify the accuracy of your estimated positions by using other tools and your eyes to obtain fixes whenever possible.

PLANNING ON THE FLY A chartplotter is invaluable when you need to plan or replan on the fly. Many chartplotters provide a point-to-point measuring feature that allows for planning without disrupting ongoing active navigation.
During re-planning, your primary mission is to plot your new intended course on a chart and scan along that line for potential obstacles. You can zoom out to locate your new destination. Scroll the cursor to the intended destination, then zoom in to fine-tune the location of the new waypoint. Then you can scroll along the course line to make sure it is clear, and you can add waypoints to adjust the course around any obstacles along the way, much as you did in planning the initial routes.

Highway Screen
A chartplotter provides several screens similar to those on a GPS. Generally, however, the chartplotter screens are more feature-rich than those on a handheld GPS owing to the higher resolution and larger screen size.
FIGURE 9-5. You can construct a route using the chartplotter by simply dragging the cursor and clicking the ENTER button. In this example, you have moved a waypoint to a new location (cursor position).










FIGURE 9-6. Most chartplotters also offer the Highway Screen as an option. Because the display is larger and has higher resolution, more data can be shown.










The Highway Screen is preferable to the Chart Screen while running a leg because it is easier to navigate with less attention to the screen. The use of the GPS Highway Screen is described in the prior GPS posts; the techniques are the same with a chartplotter. But the Highway Screen on a typical chartplotter has a great deal of detail and higher definition, thanks to the larger screen. Moreover, the larger screen usually allows you to add more data windows and possibly a compass band to help with your navigation.

Staying on course using the Highway Screen takes only a glance from time to time. This allows you to concentrate most of your attention on other duties.
FIGURE 9-7. Using the full size of the larger display, many chartplotters offer large numeral data displays, which can be read from some distance. Here, one of the windows shows the readout from an interfaced depth sounder.










Under normal circumstances underway, you can concentrate on the Highway Screen and stay in the center of the highway with the active waypoint straight ahead. Periodically, you will want to switch to the chart display to ob serve details of what is around you. 
*to be cont.*


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## Fishers of Men

*Underway cont.*

Many helmsmen prefer to use the large digital readouts for navigating. Either way, if you&#8217;ve preplanned your routes, your navigation on the water is rather simple.

Celestial and Tide Data
Most new chartplotters provide access to the rising and setting times of the moon and sun and the times of high and low tide at the location of the cursor. Usually, tide and tidal current stations are identified as icons on the display. By scrolling over a nearby icon, you can bring up a tide chart.

FIGURE 9-8. Top: The Satellite Screen on a chartplotter is very similar to that found on a handheld GPS. Above: The Navigation Position Screen is similar to the Position Screen on a hand held GPS. Given the larger display size, more data fields can be presented.










Using a Computer and GPS Underway
With appropriate software, you can use a computer for on- board navigation and as an excellent planning tool. Indeed, a navigation computer offers far more capability than can be achieved with a typical chartplotter. Over time, this trend toward computer-based navigation will find its way onto progressively smaller boats.

Offshore sailors have been using computer-based navigation for years to help solve complex weather-routing problems. The major issue with using a computer on board is the hostile marine environment. When the computer is on, it generates heat, and the air inside the case expands. When it cools and the air contracts, salt-laden air can be drawn into the computer case where it will condense its corrosive salts on circuit boards and components. A number of computers have been suitably &#8220;marinized&#8221; for use on a boat: they are adequately sealed to prevent salt-air intrusions and have extra protective coating on internal circuits to combat corrosion. Marinized computers are surprisingly reasonable in price. It&#8217;s the marinized display that&#8217;s still very expensive.

FIGURE 9-9. Left: Typical chartplotters provide a great deal of in formation, such as sunrise, sunset, moonrise, nearest tide station, and times of high and low water. This display provides a handy calendar for looking ahead to other dates. All of this in formation is stored on the chart chips that you use with the chartplotter. Right: Tide charts can be displayed on the chartplotter to indicate the present tide height and the times of high and low water. You can look forward or backward to determine the predicted tide level at any time for this station. You can also select other stations.










Most recreational boaters use laptop computers on board, then take them home after a day&#8217;s sail. Laptops are convenient to handle and require only limited battery power to operate. Additional protection on board can be provided by storing the laptop in a sealed container when not in use.
Another significant issue is the display. Although chartplotters typically offer sunlight-readable displays, there are fewer options for a computer screen.

Typically, displays used above decks are shrouded so they can be seen, some what reminiscent of the cathode-ray tube radarscopes of old. Below decks, the display brightness is not a major issue. Sunlight-readable touch-screen LCD displays, which will greatly ease a navigator&#8217;s tasks, are under development as of this writing. As marinized versions become available, you can expect computers to supplant many chartplotter installations.

Computers gain favor with those who cruise considerable distances. Unlike most chartplotters, computer- based navigation software does not limit the number of waypoints in a route or, for that matter, the number of routes. Also, mariners on extended cruises need more on- board planning capability to keep up with the usual changes along the way; a computer is far more versatile for that task.

One example of an emerging trend in computer- based navigation is Maptech&#8217;s &#8220;i3&#8221; system, which includes a custom-built, marinized PC with a 12-inch color touch screen. This device offers the best of chartplotters and computers in one package. This is described at the end of the chapter in the section &#8220;The Future of Onboard Computers.&#8221; The ultimate flexibility of a PC platform means that the device can be reprogrammed and updated to stay cur rent. It also is the ideal solution for an integrated helm station.

Many boaters use both a computer and a chartplotter, with the latter mounted at the helm, the former below decks, and the two in communication.

The computer is used more for planning and routing; the chartplotter is used for steering. Ultimately, as boating technology continues to improve, there will be no discernible difference between a chartplotter and a computer.

As repeated many times, notwithstanding what electronics you have on board, it is imperative that you carry paper charts and plotting tools aboard and be prepared to use them. Even the 1,100-foot aircraft carrier George Washington, with untold computing power aboard, carries and uses paper charts.

Navigation Software
Computer navigation software generally is far more versa tile than are the fixed programs of a chartplotter. In addition to a much larger number of waypoints and routes, navigation software offers many useful tools, and its memory can be substantial. You can plan even while navigating on a route. Some software provides range rings (circles of a given radius, as on a radar screen) around the plotted location of your boat, so you get a better sense of your surroundings.










Computer screens tend to be larger than those on chartplotters, so you can make use of such features as side- by-side displays. Because even a computer screen is small compared with a paper chart, however, you will still need to zoom out from time to time to get the bigger picture. Using side-by-side displays, you can place a smaller-scale chart on one side and a larger-scale chart on the other. Your position is displayed on both screens, and both will scroll as you move.










Another two-screen combination is a nautical chart with its corresponding photo chart. The photo chart helps identify land features and gives you a visual sense of surrounding waters. Your position is indicated on the photo chart, too, because it is geo-referenced to the same set of coordinates as your chart.










Alternatively, you can use topo maps from such sources as the U.S. Geological Survey (USGS). These provide land contours and other land features, such as buildings, that are missing or heavily curtailed on nautical charts. These can be useful when you are attempting to orient yourself with respect to nearby topographic features such as hills.










FIGURE 9-15. You can also place a topographic map side by side with a nautical chart. The advantage of the topo map is its rich representation of land features, handy for identifying shore lines, hills, etc., for navigation.

NAVIGATION SOFTWARE VERSUS PLANNING SOFTWARE
The major difference between digital chart planning software and navigation software is the latter&#8217;s ability to accept and plot GPS positions on the screen. Most such programs will work with a host of different GPS models. Many offer a menu from which you select a GPS model; the software takes care of the rest. Beyond that, virtually all GPS receivers output key information in a standard format called NMEA 0183. The National Marine Electronics Association created this protocol as a sequence of &#8220;sentences,&#8221; each with specific coded information. The protocol is designed so the data-in and data-out lines from a GPS or other marine electronics devices can be connected directly to the standard serial port on a computer.
The navigation software receives and interprets these coded sentences to plot your position. Generally, most of the other functions performed in the GPS are not used by the software. Instead, these computations are performed in the computer independently. For example, you select way- points and routes for navigation in your computer, and it computes your course, bearing, and distance to the active waypoint. You can, of course, select the same waypoint in the GPS for active navigation and it, too, computes the course, bearing, and distance&#8212;independently. The GPS processor and the computer are working in parallel&#8212;like two-year-olds in a sandbox&#8212;doing the same thing using position information from the GPS. This is the way you are likely to navigate with a chartplotter at the helm and a computer below decks.

Navigation Computer Display Information
The heart of a computer navigation display is the nautical chart. When you&#8217;re using raster charts, these appear virtually identical with the paper charts you carry. The higher- resolution, larger display of a computer can be used to its full advantage. Some computers are designed to work with touch screens, so your interface becomes the display rather than a keyboard and mouse. But even if you do not have a touch screen, a keyboard and mouse are far easier to use than the limited number of buttons and the joystick cursor control of a typical chartplotter.

FIGURE 9-16. Connecting a GPS to a computer is reasonably straightforward. Usually, the GPS connectors can be obtained from the manufacturer. The connector for the PC is usually a standard 9-pin serial port connector. Most marine electronics equipment offers NMEA 0183 interfaces. That means there is one pin for data out of the GPS, one pin for data in, and a ground pin. By the same token, the serial port on the computer has one pin for data in, one for data out, and a ground pin. The units connect much like a DVD player and a TV set. Unfortunately, most new notebook computers are delivered without a serial port. There are a variety of USB adapters on the market, but not all software has been updated to deal with the virtual serial port created by these adapters.










Data windows are typically large and clear, and you can position them at will so they won&#8217;t interfere with tracking your boat&#8217;s progress across the chart. In addition, you have a wide choice of data to display in these boxes, and you can select data at will without any interruption to ongoing navigation. It&#8217;s easy to switch to a full-screen chart display for a better look, for example. Often, an inset display is available to show a wider or more detailed area.
Typical data fields (digital readouts) include the following:










FIGURE 9-17. Navigation software has special screens for on-the-water use. This screen provides large data fields that are easy to read at the helm. In addition, a small window shows a wider view of the region and marks the area shown on the full chart screen. This version also has depth contour data and presents a look at the depth contour in front of the boat (see Figure 9-19).
FIGURE 9-19. The depth contour (top) shows the variation in charted depth based on bathymetric data. An alarm can be set to a particular level; those areas are highlighted in the contour to indicate potential hazards. The corresponding chart image is shown below the contour.










If the navigation software is supplemented with depth contour data, the display can be set up to show a depth contour in front of the boat. Both Maptech and Nobeltec offer similar features in their programs.

*To be cont.*


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## Fishers of Men

*MONITORING AND PLANNING WITH NAVIGATION SOFTWARE *

Your present boat position will be displayed directly on the chart along with the current active course and track, if selected. If you choose to array chart windows side by side, your boat&#8217;s position will be shown on all open windows to facilitate comparisons between chart scales and between a nautical chart and a photo chart or topo map.

FIGURE 9-18. Bathymetric (contour) charts provide a view be low the surface of the water. In this split view, the image on the left shows the boat and the depth below it. A vertical red line shows the depth in fathoms below the boat. A red ball indicates the location of a nearby red beacon. The image on the right shows the corresponding chart. The box around the boat on the chart shows the area displayed in the contour plot.










*FIND some fish with this view, will ya?*

Using the navigation software, you will be able to call upon a wide range of alarms that can be set in advance or adjusted. These include anchor alarms, waypoint vicinity and arrival alarms, avoidance area alarms, fishing area boundary alarms, and crosstrack or off-course alarms. Unlike most chartplotters, the alarm boundaries are flexible, including custom shapes. Alarms can be audible, visual, or both and can be set to go off if you enter or, alternatively, if you leave a selected area.

FIGURE 9-20. Navigation software offers a range of alarms. In this example, two shapes have been placed over hazardous areas. On the right is an elliptical alarm area. On the left is a polygonic alarm area. A polygon can be constructed with virtually any shape. These alarms are set to go off if you enter either area.










FIGURE 9-21. As an alternative to areas that sound alarms upon entry, you can mark off a safe area and set an alarm to go off if you leave. In this example, the green represents safe area. However, within this area are two hazardous areas (red circles), which will cause an alarm to sound upon entry










The software can support planning on the fly even while plotting the current path and monitoring your navigation. You will be able to use the complete suite of tools described in previous posts. This includes the ability to plot unlimited A to B lines to measure distances and bearings. New routes can be constructed or current routes modified in real time.

You can add notes on a digital chart for future reference. Most CD-ROM chart packages include notes on marine facilities, local regulations, coast pilot information, light lists, and other tools to provide key information at your fingertips.

If your GPS receiver quits or starts to provide inaccurate information, it is possible to use the navigation soft ware to continue in dead reckoning mode. You will be able to plot bearing lines from your observations and create fixes. Once a fix is identified, you will be able to reposition the boat symbol over that spot to continue the dead reckoning navigation.

A man overboard (MOB) feature is available on most packages that immediately marks the accident location and plots a return path to effect a rescue.
Most navigation software programs output instructions to an autopilot in NMEA 0183 sentences. The soft ware provides a host of information in addition to the in tended course and track. Steering information and cross- track error are provided to let the autopilot return to a planned course line. Waypoint proximity and arrival information are also provided, in addition to advance information on changes in course.

PDAs and Pocket PCs
As mentioned, Personal Digital Assistants (PDAs) can be equipped for live navigation with a GPS. Most Palm- and Pocket PC-based PDAs are designed with an accessory sleeve capability to accept devices such as a GPS receiver. Others connect via cable, or through a wire less connection using Bluetooth technology. Garmin and Navman both offer a completely self-contained unit.

These devices are essentially programmable computers that use a GPS and digital charts for live navigation. They demonstrate the convergent evolution of computers and chartplotters. Planning can be done directly on the PDA or on a home computer and uploaded. Indeed, PDAs are designed to work closely with computers. One advantage of PDAs that is finding its way to chartplotters and on-board computers is the touch screen, which saves considerable space and makes working with charts quite easy.

Ultimately, we&#8217;ll see specialized units designed for the marine environment. In the meantime, if you use one of the earlier units available on the market, consider keeping it in a clear, waterproof pouch to protect it from the environment.

These small handheld units have sharp color displays that present clear charts. The small size of the screen, how ever, makes navigation tasks somewhat more difficult than on their larger counterparts because you can see only a small part of the chart at a time.










Look for similar devices with larger displays and waterproofing as the ultimate alternative to the chartplotter.

The Future of Onboard Computers
The Maptech i3 could represent the future of navigation. It has all the advantages of a computer, but it is smaller and less susceptible to the harsh elements.
Rugged and marinized computers are not new, but historically, you would need to buy a separate computer and then a marinized display unit. Taking a cue from the PDA market, these newest devices have incorporated an integral color touch screen. The buttons are displayed on the screen and are therefore tailored to each application.

This new system can use a wide variety of chart types and incorporates display options including radar and even weather reports. In radar mode, the radar targets are directly superimposed on nautical charts or photo charts on the dis play, making it easy for the navigator to separate fixed tar gets from boats and adding new meaning to the display. You can plan a route by simply touching the screen. Future models may even help plan the route automatically to stay in channels and avoid charted obstacles. (However, most of us will still want to check these paths ourselves. Navigators will not be obsolete any time soon!)

Some examples of displays from the i3 system are shown in Figure 9-23. While this system may be currently out of the price range for most recreational boaters, as with all new technologies, that will eventually change. At this point, most of us can just dream.





































*end of this part...for now!*


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## Fishers of Men

*CHAPTER 12 Bowditch
HYPERBOLIC SYSTEMS
INTRODUCTION TO LORAN C*
1200.	History
The theory behind the operation of hyperbolic radionavigation systems was known in the late 1930&#8217;s, but it took the urgency of World War II to speed development of the system into practical use. By early 1942, the British had an operating hyperbolic system in use designed to aid in long range bomber navigation. This system, named Gee, operated on frequencies between 30 MHz and 80 MHz and employed master and &#8220;slave&#8221; transmitters spaced approximately 100 miles apart. The Americans were not far behind the British in development of their own system. By 1943, the U. S. Coast Guard was operating a chain of hyperbolic navigation transmitters that became Loran A. By the end of the war, the network consisted of over 70 transmitters covering over 30&#37; of the earth&#8217;s surface.

In the late 1940&#8217;s and early 1950&#8217;s, experiments in low frequency Loran produced a longer range, more accurate system. Using the 90-110 kHz band, Loran developed into a 24-hour-a-day, all-weather radionavigation system. Serving both the marine and aviation communities, Loran C boasts the highest number of users of any precise radionavigation system in use. It has been designated the primary federally provided marine navigation system for the U. S. Coastal Confluence Zone (CCZ), southern Alaska, and the Great Lakes. The maritime community comprises the vast majority of Loran C users (87%), followed by civil aviation users (14%). The number of Loran users is projected to grow until well into the next century.

Notwithstanding the popularity of the system, the U. S. Department of Defense is phasing out use of Loran C in favor of the highly accurate, space-based Global Positioning System (GPS). This phase out has resulted in closing the Hawaii-based Central Pacific Loran C chain and transferring several overseas Loran C stations to host governments. The use of Loran C in the United States&#8217; radionavigation plan will undergo continuous evaluation until a final determination of the future of the system is made in 1996. At that point, a decision will be made to either continue operations or to begin to phase out the system in favor of satellite navigation. No matter what decision is reached, Loran C is expected to remain operational until at least 2015.
LORAN C DESCRIPTION

1201.	Basic Theory Of Operation
The Loran C system consists of a chain of transmitting stations, each separated by several hundred miles. Within the Loran chain, one station is designated as the master station and the others as secondary stations. There must be at least two secondary stations for one master station; therefore, every Loran transmitting chain will contain at least three transmitting stations. The master and secondary stations transmit radio pulses at precise time intervals. A Loran receiver measures the time difference (TD) in reception at the vessel between these pulses; it then displays either this difference or a computed latitude and longitude to the operator.

The signal arrival time difference between a given master-secondary pair corresponds to the difference in distance between the receiving vessel and the two stations. The locus of points having the same time difference from a specific master-secondary pair forms a hyperbolic line of position (LOP). The intersection of two or more of these LOP&#8217;s produces a fix of the vessel&#8217;s position.

There are two methods by which the navigator can convert these time differences to geographic positions. The first involves the use of a chart overprinted with a Loran time delay lattice consisting of time delay lines spaced at convenient intervals. The navigator plots the displayed time difference by interpolating between the lattice lines printed on the chart. In the second method computer algorithms in the receiver&#8217;s software convert the time delay signals to latitude and longitude for display.

Early receiver conversion algorithms were imprecise; however, modern receivers employ more precise algorithms. Their position output is usually well within the 0. 25 NM accuracy specification for Loran C. Modern receivers can also navigate by employing waypoints, directing a vessel&#8217;s course between two operator-selected points. Section 1207, section 1208, and section 1209 more fully explore questions of system employment.

1202.	Components Of The Loran System
The components of the Loran system consist of the land based transmitting stations, the Loran receiver and antenna, and the Loran charts. Land-based facilities include master transmitting stations, at least two secondary transmitters for each master transmitter, control stations, monitor sites, and a time reference. The transmitters transmit the Loran signals at precise intervals in time. The control station and associated monitor sites continually measure the characteristics of the Loran signals received to detect any anomalies or any out-of-specification condition. Some transmitters serve only one function within a chain (i.e., either master or secondary); however, in several instances, one transmitter can serve as the master of one chain and secondary in another. This dual function lowers the overall costs and operating expense for the system.

Loran receivers exhibit varying degrees of sophistication; however, their signal processing is similar. The first processing stage consists of search and acquisition, during which the receiver searches for the signal from a particular Loran chain, establishing the approximate location in time of the master and secondaries with sufficient accuracy to permit subsequent settling and tracking. After search and acquisition, the receiver enters the settling phase. In this phase, the receiver searches for and detects the front edge of the Loran pulse. After detecting the front edge of the pulse, it selects the correct cycle of the pulse to track. Having selected the correct tracking cycle, the receiver begins the tracking and lock phase, in which the receiver maintains synchronization with the selected received signals. Once this phase is reached, the receiver displays either the time difference of the signals or the computed latitude and longitude as discussed above.

*This: "&#181;" symbol is the MICRO symbol.*

1203.	Description Of Operation
The Loran signal consists of a series of 100 kHz pulses sent first by the master station and then, in turn, by the secondary stations. For the master signal, a series of nine pulses is transmitted, the first eight spaced 1000 &#181;sec apart followed by a ninth transmitted 2000 &#181;sec after the eighth. Pulsed transmission results in lower power output requirements, better signal identification properties, and more precise timing of the signals. After the time delays discussed below, secondary stations transmit a series of eight pulses, each spaced 1000 &#181;sec apart. The master and secondary stations in a chain transmit at precisely determined intervals. First, the master station transmits; then, after a specified interval, the first secondary station transmits.

Then the second secondary transmits, and so on. Secondary stations are given letter designations of W, X, Y, and Z; this letter designation indicates the order in which they transmit following the master. When the master signal reaches the next secondary in sequence, this secondary station waits an interval, defined as the secondary coding delay, (SCD) or simply coding delay (CD), and then transmits. The total elapsed time from the master transmission until the secondary emission is termed the emissions delay (ED). The ED is the sum of the time for the master signal to travel to the secondary and the CD. The time required for the master to travel to the secondary is defined as the baseline travel time (BTT) or baseline length (BLL). After the first secondary transmits, the remaining secondaries transmit in order. Each of these secondaries has its own CD/ED value. Once the last secondary has transmitted, the master transmits again, and the cycle is repeated. The time to complete this cycle of transmission defines an important characteristic for the chain: the group repetition interval (GRI). 

The group repetition interval divided by ten yields the chain&#8217;s designator. For example, the interval between successive transmissions of the master pulse group for the northeast US chain is 99,600 &#181;sec. From the definition above, the GRI designator for this chain is defined as 9960. The GRI must be sufficiently large to allow the signals from the master and secondary stations in the chain to propagate fully throughout the region covered by the chain before the next cycle of pulses begins.

Other concepts important to the understanding of the operation of Loran are the baseline and baseline extension. The geographic line connecting a master to a particular secondary station is defined as the station pair baseline. The baseline is, in other words, that part of a great circle on which lie all the points connecting the two stations. The extension of this line beyond the stations to encompass the points along this great circle not lying between the two stations defines the baseline extension. The importance of these two concepts will become apparent during the discussion of Loran accuracy considerations below.

As discussed above, Loran C relies on time differences between two or more received signals to develop LOP&#8217;s used to fix the ship&#8217;s position. This section will examine in greater detail the process by which the signals are developed, transmitted, and ultimately interpreted by the navigator.

The basic theory behind the operation of a hyperbolic system is straightforward. First, the locus of points defining a constant difference in distance between a vessel and two separate stations is described by a mathematical function that, when plotted in two dimensional space, yields a hyperbola. Second, assuming a constant speed of propagation of electromagnetic radiation in the atmosphere, the time difference in the arrival of electromagnetic radiation from the two transmitter sites to the vessel is proportional to the distance between the transmitting sites and the vessel. The following equations demonstrating this proportionality between distance and time apply:
Distance=Velocity x Time
or, using algebraic symbols
d=c x t

Therefore, if the velocity &#169; is constant, the distance between a vessel and two transmitting stations will be directly proportional to the time delay detected at the vessel between pulses of electromagnetic radiation transmitted from the two stations.

An example will better illustrate the concept. See Figure 1203a. Assume that two Loran transmitting stations, a master and a secondary, are located along with an observer in a Cartesian coordinate system whose units are in nautical miles. 










Assume further that the master station is located at coordinates (x,y) = (-200,0) and the secondary is located at (x,y) = (+200,0). Designate this secondary station as station Xray. An observer with a receiver capable of detecting electromagnetic radiation is positioned at any point A whose coordinates are defined as x(a) and y(a). The Pythagorean theorem can be used to determine the distance between the observer and the master station; similarly, one can obtain the distance between the observer and the secondary station. This methodology yields the following result for the given example:










Finally, the difference between these distances (Z) is given by the following:
After algebraic manipulation,
With a given position of the master and secondary stations, therefore, the function describing the difference in distance is reduced to one variable; i.e., the position of the observer. 

Figure 1203b. The time axis for Loran C TD for point &#8220;A.&#8221;










Figure 1203a is a conventional graphical representation of the data obtained from solving for the value (Z) using varying positions of A in the example above. The hyperbolic lines of position in the figure represent the locus of points along which the observer&#8217;s simultaneous distances from the master and secondary stations are equal; he is on the centerline. For example, if the observer above were located at the point (271. 9, 200) then the distance between that observer and the secondary station (in this case, designated &#8220;X&#8221 would be 212. 5 NM. In turn, the observer&#8217;s distance from the master station would be 512. 5 nautical miles. The function Z would simply be the difference of the two, or 300 NM. Refer again to Figure 1203a. The hyperbola marked by &#8220;300&#8221; represents the locus of points along which the observer is simultaneously 300 NM closer to the secondary transmitter than to the master. To fix his position, the observer must obtain a similar hyperbolic line of position generated by another master-secondary pair. Once this is done, the intersection of the two LOP&#8217;s can be determined, and the observer can fix his position in the plane at a discrete position in time.

The above example was evaluated in terms of differences in distance; as discussed previously, an analogous situation exists with respect to differences in signal reception time. All that is required is the assumption that the signal propagates at constant speed. Once this assumption is made, the hyperbolic LOP&#8217;s in Figure 1203a above can be re-labeled to indicate time differences instead of distances.

This principle is graphically demonstrated in Figure 1203b. Assume that electromagnetic radiation travels at the speed of light (one nautical mile traveled in 6. 18 &#181;sec) and reconsider point A from the example above. The distance from the master station to point A was 512. 5 NM. From the relationship between distance and time defined above, it would take a signal (6.18 &#181;sec/NM) X &#61472;512. 5 NM = 3,167 &#181;sec to travel from the master station to the observer at point A. At the arrival of this signal, the observer&#8217;s Loran receiver would start the time delay (TD) measurement. Recall from the general discussion above that a secondary station transmits after an emissions delay equal to the sum of the baseline travel time and the secondary coding delay. In this example, the master and the secondary are 400 NM apart; therefore, the baseline travel time is (6.18 &#181;sec/NM) X 400 NM = 2,472 &#181;sec. Assuming a secondary coding delay of 11,000 &#181;sec, the secondary station in this example would transmit (2,472 + 11,000)&#181;sec or 13,472 &#181;sec after the master station. The signal must then reach the receiver located with the observer at point A. Recall from above that this distance was 212. 5 NM. Therefore, the time associated with signal travel is: (6. 18 &#181;sec/NM) X 212. 5 NM = 1,313 &#181;sec. Therefore, the total time from transmission of the master signal to the reception of the secondary signal by the observer at point A is (13,472 + 1,313) &#181;sec = 14,785 &#181;sec.

Recall, however, that the Loran receiver measures the time delay between reception of the master signal and the reception of the secondary signal. The quantity determined above was the total time from the transmission of the master signal to the reception of the secondary signal. Therefore, the time quantity above must be corrected by subtracting the amount of time required for the signal to travel from the master transmitter to the observer at point A. This amount of time was 3,167 &#181;sec. Therefore, the time delay observed at point A in this hypothetical example is (14,785 - 3,167) &#181;sec or 11,618 &#181;sec. Once again, this time delay is a function of the simultaneous differences in distance between the observer and the two transmitting stations, and it gives rise to a hyperbolic line of position which can be crossed with another LOP to fix the observer&#8217;s position at a discrete position.

1204.	Allowances For Non-Uniform Propagation Rates
The proportionality of the time and distance differences assumes a constant speed of propagation of electromagnetic radiation. To a first approximation, this is a valid assumption; however, in practice, Loran&#8217;s accuracy criteria require a refinement of this approximation. The initial calculations above assumed the speed of light in a vacuum; however, the actual speed at which electromagnetic radiation propagates through the atmosphere is affected by both the medium through which it travels and the terrain over which it passes. The first of these concerns, the nature of the atmosphere through which the signal passes, gives rise to the first correction term: the Primary Phase Factor (PF). This correction is transparent to the operator of a Loran system because it is incorporated into the charts and receivers used with the system, and it requires no operator action.

A Secondary Phase Factor (SF) accounts for the effect traveling over seawater has on the propagated signal. This correction, like the primary phase factor above, is transparent to the operator since it is incorporated into charts and system receivers.

The third and final correction required because of nonuniform speed of electromagnetic radiation is termed the Additional Secondary Phase Factor (ASF). 

Of the three corrections mentioned in this section, this is the most important one to understand because its correct application is crucial to obtaining the most accurate results from the system. This correction is required because the SF described above assumes that the signal travels only over water when the signal travels over terrain composed of water and land. The ASF can be determined from either a mathematical model or a table constructed from empirical measurement. The latter method tends to yield more accurate results. To complicate matters further, the ASF varies seasonally. The ASF correction is important because it is required to convert Loran time delay measurements into geographic coordinates. ASF corrections must be used with care. Some Loran charts incorporate ASF corrections while others do not. One cannot manually apply ASF correction to measured time delays when using a chart that has already been corrected. In addition, the accuracy of ASF&#8217;s is much less accurate within 10 NM of the coastline. Therefore, navigators must use prudence and caution when operating with ASF corrections in this area.

One other point must be made about ASF corrections. Some commercially available Loran receivers contain preprogrammed ASF corrections for the conversion of measured time delays into latitude and longitude printouts. The internal values for ASF corrections used by these receivers may or may not be accurate, thus leading to the possibility of navigational error. Periodically, the navigator should compare his receiver&#8217;s latitude and longitude readout with either a position plotted on a chart incorporating ASF corrections for observed TD&#8217;s or a position determined from manual TD correction using official ASF published values. This procedure can act as a check on his receiver&#8217;s ASF correction accuracy. When the navigator wants to take full advantage of the navigational accuracy of the Loran system, he should use and plot the TD&#8217;s generated by the receiver, not the converted latitude and longitude. When precision navigation is not required, converted latitude and longitude may be used.

1205.	Loran Pulse Architecture
As mentioned above, Loran uses a pulsed signal rather than a continuous wave signal. This section will analyze the Loran pulse signal architecture, emphasizing design and operational considerations.

Figure 1205 represents the Loran signal. Nine of these signals are transmitted by the master station and eight are transmitted by the secondary stations every transmission cycle. 










The pulse exhibits a steep rise to its maximum amplitude within 65 &#61549;sec of emission and an exponential decay to zero within 200 to 300 &#61549;sec. The signal frequency is nominally defined as 100 kHz; in actuality, the signal is designed such that 99% of the radiated power is contained in a 20 kHz band centered on 100 kHz. The Loran receiver is programmed to detect the signal on the cycle corresponding to the carrier frequency&#8217;s third positive crossing of the x axis. This occurrence, termed the third positive zero crossing, is chosen for two reasons. First, it is late enough for the pulse to have built up sufficient signal strength for the receiver to detect it. Secondly, it is early enough in the pulse to ensure that the receiver is detecting the transmitting station&#8217;s ground wave pulse and not its sky wave pulse. Sky wave pulses are affected by atmospheric refraction and induce large errors into positions determined by the Loran system. Pulse architecture is designed to eliminate this major source of error.

Another pulse feature designed to eliminate sky wave contamination is known as phase coding. With phase coding, the phase of the carrier signal (i.e. , the 100 kHz signal) is changed systematically from pulse to pulse. Upon reaching the receiver, sky waves will be out of phase with the simultaneously received ground waves and, thus, they will not be recognized by the receiver. Although this phase coding offers several technical advantages, the one most important to the operator is this increase in accuracy due to the rejection of sky wave signals.

The final aspect of pulse architecture that is important to the operator is blink coding. When a signal from a secondary station is unreliable and should not be used for navigation, the affected secondary station will blink; that is, the first two pulses of the affected secondary station are turned off for 3. 6 seconds and on for 0. 4 seconds. This blink is detected by the Loran receiver and displayed to the operator. When the blink indication is received, the operator should not use the affected secondary station.

LORAN C ACCURACY CONSIDERATIONS
1206.	Position Uncertainty With Loran C
As discussed above, the TD&#8217;s from a given master-secondary pair form a family of hyperbolae. Each hyperbola in this family can be considered a line of position; the vessel must be somewhere along that locus of points which form the hyperbola. A typical family of hyperbolae is shown in Figure 1206a. 










Now, suppose the hyperbolic family from the master-Xray station pair shown in Figure 1203a were superimposed upon the family shown in Figure 1206a. The results would be the hyperbolic lattice shown in Figure 1206b. Loran C LOP&#8217;s for various chains and secondaries (the hyperbolic lattice formed by the families of hyperbolae for several master-secondary pairs) are printed on special nautical charts. Each of the sets of LOP&#8217;s is given a separate color and is denoted by a characteristic set of symbols. For example, an LOP might be designated 9960-X-25750. The designation is read as follows: the chain GRI designator is 9960, the TD is for the Master-Xray pair (M-X), and the time difference along this LOP is 25750 &#61549;sec. The chart only shows a limited number of LOP&#8217;s to reduce clutter on the chart. Therefore, if the observed time delay falls between two charted LOP&#8217;s, interpolate between them to obtain the precise LOP. After having interpolated (if necessary) between two TD measurements and plotted the resulting LOP&#8217;s on the chart, the navigator marks the intersection of the LOP&#8217;s and labels that intersection as his Loran fix.

A closer examination of Figure 1206b reveals two possible sources of Loran fix error. The first of these errors is a function of the LOP crossing angle. The second is a phenomenon known as fix ambiguity. Let us examine both of these in turn.

Figure 1206c shows graphically how error magnitude varies as a function of crossing angle. Assume that LOP 1 is known to contain no error, while LOP 2 has an uncertainly as shown. As the crossing angle (i.e. , the angle of intersection of the two LOP&#8217;s) approaches 90&#61616;, range of possible positions along LOP 1 (i.e., the position uncertainty or fix error) approaches a minimum; conversely, as the crossing angle decreases, the position uncertainty increases; the line defining the range of uncertainty grows longer. 










This illustration demonstrates the desirability of choosing LOP&#8217;s for which the crossing angle is as close to 90&#61616;&#61472;as possible. The relationship between crossing angle and accuracy can be expressed mathematically: 










where x is the crossing angle. Rearranging algebraically,










Assuming that LOP error is constant, then position uncertainty is inversely proportional to the sine of the crossing angle. As the crossing angle increases from 0&#61616;&#61472;to 90&#61616;, the sin of the crossing angle increases from 0 to 1. Therefore, the error is at a minimum when the crossing angle is 90&#61616;, and it increases thereafter as the crossing angle decreases. Fix ambiguity can also cause the navigator to plot an erroneous position. Fix ambiguity results when one Loran LOP crosses another LOP in two separate places. Most Loran receivers have an ambiguity alarm to alert the navigator to this occurrence. Absent other information, the navigator is unsure as to which intersection marks his true position.

Again, refer to Figure 1206b for an example. The -350 difference line from the master-Xray station pair crosses the 500 difference line from the master-Yankee station pair in two separate places. Absent a third LOP from either another station pair or a separate source, the navigator would not know which of these LOP intersections marked his position. Fix ambiguity occurs in the area known as the mastersecondary baseline extension, defined above in section 1203. Therefore, do not use a master-secondary pair while operating in the vicinity of that pair&#8217;s baseline extension if other station pairs are available.

The large gradient of the LOP when operating in the vicinity of a baseline extension is another reason to avoid using stations in the vicinity of their baseline extensions. Uncertainty error is directly proportional to the gradient of the LOP&#8217;s used to determine the fix. Therefore, to minimize possible error, the gradient of the LOP&#8217;s used should be as small as possible. Refer again to Figure 1206b. Note that the gradient is at a minimum along the station pair baseline and increases to its maximum value in the vicinity of the baseline extension.

The navigator, therefore, has several factors to consider in maximizing fix accuracy. Do not use a station pair when operating along it baseline extension because both the LOP gradient and crossing angle are unfavorable. In addition, fix ambiguity is more likely here.

LORAN C OPERATIONS
1207.	Waypoint Navigation
A Loran receiver&#8217;s major advantage is its ability to accept and store waypoints. Waypoints are sets of coordinates that describe a location of navigational interest. A navigator can enter waypoints into a receiver in one of two ways. He can either visit the area and press the appropriate receiver control key, or he can enter the waypoint coordinates manually. When manually entering the waypoint, he can express it either as a TD, a latitude and longitude, or a distance and bearing from another waypoint.
Typically, waypoints mark either points along a planned route or locations of interest. The navigator can plan his voyage as a series of waypoints, and the receiver will keep track of the vessel&#8217;s progress in relation to the track between them. In keeping track of the vessel&#8217;s progress, most receivers display the following parameters to the operator:

Cross Track Error (XTE): 
XTE is the perpendicular distance from the user&#8217;s present position to the intended track between waypoints. Steering to maintain XTE near zero corrects for cross track current, cross track wind, and compass error.

Bearing (BRG): The BRG display, sometimes called the Course to Steer display, indicates the bearing from the vessel to the destination waypoint.

Distance to Go (DTG): The DTG display indicates the great circle distance between the vessel&#8217;s present location and the destination waypoint.

Course and Speed Over Ground (COG and SOG):
The COG and the SOG refer to motion over ground rather than motion relative to the water. Thus, COG and SOG reflect the combined effects of the vessel&#8217;s progress through the water and the set and drift to which it is subject. The navigator may steer to maintain the COG equal to the intended track.
Loran navigation using waypoints was an important development because it showed the navigator his position in relation to his intended destination. Though this method of navigation is not a substitute for plotting a vessel&#8217;s position on a chart to check for navigation hazards, it does give the navigator a second check on his plot.

1208.	Using Loran&#8217;s High Repeatable Accuracy
In discussing Loran employment, one must develop a working definition of three types of accuracy: absolute accuracy, repeatable accuracy, and relative accuracy.

Absolute accuracy is the accuracy of a position with respect to the geographic coordinates of the earth. For example, if the navigator plots a position based on the Loran C latitude and longitude (or based on Loran C TD&#8217;s) the difference between the Loran C position and the actual position is a measure of the system&#8217;s absolute accuracy.

Repeatable accuracy is the accuracy with which the navigator can return to a position whose coordinates have been measured previously with the same navigational system. For example, suppose a navigator were to travel to a buoy and note the TD&#8217;s at that position. Later, suppose the navigator, wanting to return to the buoy, returns to the previously-measured TD&#8217;s. The resulting position difference between the vessel and the buoy is a measure of the system&#8217;s repeatable accuracy.

Relative accuracy is the accuracy with which a user can measure position relative to that of another user of the same navigation system at the same time. If one vessel were to travel to the TD&#8217;s determined by another vessel, the difference in position between the two vessels would be a measure of the system&#8217;s relative accuracy.

The distinction between absolute and repeatable accuracy is the most important one to understand. With the correct application of ASF&#8217;s, the absolute accuracy of the Loran system varies from between 0. 1 and 0. 25 nautical miles. However, the repeatable accuracy of the system is much greater. If the navigator has been to an area previously and noted the TD&#8217;s corresponding to different navigational aids (a buoy marking a harbor entrance, for example), the high repeatable accuracy of the system enables him to locate the buoy in under adverse weather. Similarly, selected TD data for various harbor navigational aids has been collected and recorded. These tables, if available to the navigator, provide an excellent backup navigational source to conventional harbor approach navigation. To maximize a Loran system&#8217;s utility, exploit its high repeatable accuracy by using previously-determined TD measurements that locate positions critical to a vessel&#8217;s safe passage. This statement raises an important question: Why use measured TD&#8217;s and not a receiver&#8217;s latitude and longitude output? If the navigator seeks to use the repeatable accuracy of the system, why does it matter if TD&#8217;s or coordinates are used? The following section discusses this question.

1209.	Time Delay Measurements And Repeatable Accuracy
The ASF conversion process is the reason for using TD&#8217;s and not Latitude/Longitude readings.
Recall that Loran receivers use ASF conversion factors to convert measured TD&#8217;s into coordinates. Recall also that the ASF corrections are a function of the terrain over which the signal must pass to reach the receiver. Therefore, the ASF corrections for one station pair are different from the ASF corrections for another station pair because the signals from the different pairs must travel over different terrain to reach the receiver. A Loran receiver does not always use the same pairs of stations to calculate a fix. Suppose a navigator marks the position of a channel buoy by recording its latitude and longitude as determine by his Loran receiver. If, on the return trip, the receiver tracks different station pairs, the latitude and longitude readings for the exact same buoy would be different because the new station pair would be using a different ASF correction. The same effect would occur if the navigator attempted to find the buoy with another receiver. By using previously-measured TD&#8217;s and not previously-measured latitudes and longitudes, this ASF introduced error is eliminated.










Envision the process this way. A receiver measures between measuring these TD&#8217;s and displaying a latitude and longitude, the receiver accomplishes an intermediate step: applying the ASF corrections. This intermediate step is fraught with potential error. The accuracy of the corrections is a function of the stations received, the quality of the ASF correction software used, and the type of receiver employed. Measuring and using TD&#8217;s eliminates this step, thus increasing the system&#8217;s repeatable accuracy.

Many Loran receivers store waypoints as latitude and longitude coordinates regardless of the form in which the operator entered them into the receiver&#8217;s memory. That is, the receiver applies ASF corrections prior to storing the waypoints. If, on the return visit, the same ASF&#8217;s are applied to the same TD&#8217;s, the latitude and longitude will also be the same. But a problem similar to the one discussed above will occur if different secondaries are used. Avoid this problem by recording all the TD&#8217;s of waypoints of interest, not just the ones used by the receiver at the time. Then, when returning to the waypoint, other secondaries will be available if the previously used secondaries are not. ASF correction tables were designed for first generation Loran receivers. The use of advanced propagation correction algorithms in modern receivers has eliminated the need for most mariners to refer to ASF Correction tables. Use these tables only when navigating on a chart whose TD LOP&#8217;s have not been verified by actual measurement with a receiver whose ASF correction function has been disabled.

*To be cont.*


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## reel

Chapter 1203 assume the ? mark means microseconds ?.
...


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## Fishers of Men

reel said:


> Chapter 1203 assume the ? mark means microseconds ?.
> ...


Yes, that "?" is supposed to be a µ with a tail down on the left hand side for a micro sign...µ
I will try to fox the typo, I overlooked proof reading that post in a hurry.
Thanks Reel.


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## Fishers of Men

*INFREQUENT LORAN OPERATIONS*
1210.	Use of ASF Correction Tables
The following is an example of the proper use of ASF Correction Tables.
Example: Given an estimated ship&#8217;s position of 39&#61616;N 74&#61616;&#61472;30&#8217;W, the ASF value for the Whiskey station pair of chain 9960.

Solution: Enter the Whiskey station pair table with the correct latitude and longitude. See Figure 1210. Extract a value of -0.9 &#61549;sec. This value would then be added to the observed time difference to compute the corrected time difference.

INTRODUCTION TO OMEGA
1211.	System Description
Omega is a worldwide, internationally operated radio navigation system. It operates in the Very Low Frequency (VLF) band between 10 and 14 kHz. It provides an all weather, medium-accuracy navigation service to marine navigators. The system consists of eight widely-spaced transmitters. Figure 1211 gives the location of these stations. There is no master-secondary relationship between the Omega stations as there is between Loran C stations. The navigator is free to use any station pair that provides the most accurate line of position. Additionally, Omega measures phase differences between the two signals whereas Loran C measures time delays between signal receptions.

Figure 1211. Omega stations and frequencies.










1212. Signal Format
Each Omega station transmits on the following frequencies:
10.2 kHz, 11.05 kHz, 11.3 kHz, and 13.6 kHz. In addition to these common frequencies, each station transmits on a unique frequency given in Figure 1212. No two stations transmit the same frequency at the same time, and there is no overlap of transmissions. Each transmission segment is between 0.9 and 1.2 seconds long, with a 0.2 second interval between segments. Each station continuously repeats its transmission cycle.










BASIC OMEGA OPERATION
An Omega receiver determines position in either the direct ranging mode or the hyperbolic mode. Some call the direct ranging mode the rho-rho mode. In the direct ranging mode, the receiver measures ranges from stations by measuring phase shifts between transmitted signals and an internal reference signal. In the hyperbolic mode, the receiver measures position relative to transmitter pairs by making phase comparisons between signals coming from these pairs.

1213. Direct Ranging Mode
The Omega wavelength, at 10.2 kHz, is approximately 16 miles long. The wavelength defines the width of each Omega &#8220;lane.&#8221; See Figure 1213a. This figure shows the lanes as concentric circles formed around the transmitting station. An Omega receiver measures the phase of the received signal within a known lane. This phase shift allows the receiver to determine its position&#8217;s fraction distance between lanes. Knowing which lane it is in and the fractional distance between lane boundaries, the receiver can calculate an LOP. The LOP is the line of points corresponding to the fractional distance between lanes calculated by the receiver. The schematic of Figure 1213a does not take into account that the transmitted navigation signal forming the Omega lane is not stationary. Rather, it propagates at the speed of light.










To account for this moving wave, the receiver generates a reference signal at the same frequency of the Omega navigation signal. This reference signal &#8220;freezes&#8221; the Omega signal from the receiver&#8217;s perspective in a manner analogous to the way a strobe light flashing at the same frequency of a rotating disk freezes the disk from an observer&#8217;s perspective. Comparing these &#8220;frozen&#8221; reference and navigation signals allows the receiver to measure the phase difference between the navigation signal and the reference signal. This phase difference, in turn, is proportional to the receiver&#8217;s fractional distance between two Omega lanes. See Figure 1213b for an illustration of how the direct ranging mode works. The operator initializes the Omega receiver at point 1. This initialization tells the receiver what lane it is in and the fractional distance between the lane boundaries. From this information, the receiver calculates A1 and B1, the distances between the receiver and stations A and B, respectively. The receiver then travels to point 2. 










During the trip to point 2, the receiver keeps track of how many lanes it crosses. When it stops, it determines the fractional distance between lane boundaries at point two. From the lane counting and the phase comparison at point 2, the receiver calculates A2 and B2, the distances between the receiver and stations A and B, respectively.

1214. Hyperbolic Mode
In the direct range mode discussed above, the receiver measured the distance between it and two or more transmitting stations to determine lines of position. In the hyperbolic mode, the receiver measures the difference in phase between two transmitters.

See Figure 1214. This figure shows two transmitting stations, labeled A and B. Both of these stations transmit on the same frequency. Additionally, the stations transmit such that their waves&#8217; phase is zero at precisely the same time. Because each signal&#8217;s phase is zero at each wave front, the phase difference where the wave fronts intersect is zero. Connecting the intersecting wave fronts yields a line along which the phase difference between the two signals is zero. This line forms a hyperbola called an isophase contour. At any point along this contour, the phase difference between the stations is zero. At any point between the isophase contours, there is a phase difference in the signals proportional to the fractional distance between the contours.










The set of isophase contours between station pairs forms a series of lanes, each corresponding to one complete cycle of phase difference. The hyperbolic mode lane width on the stations&#8217; baseline equals one-half the signal wavelength. For a 10.2 kHz signal, the baseline lane width is approximately 8 miles. Each of these 8 mile wide lanes is divided into 100 centilanes (cels). The receiver measures the phase difference between stations in hundredths of a cycle. These units are termed centicycles (cec).

1215. Direct Ranging And Hyperbolic Operation
Originally, the hyperbolic mode was more accurate because the direct ranging mode required a precise receiver internal oscillator to remain synchronized with the atomic oscillators used by the transmitting station. Since these oscillators would have made the receiver prohibitively expensive, the receiver carried an oscillator that was subject to clock error. In the direct ranging mode, this clock error would have been critical because this mode relies on a direct comparison between one transmitter&#8217;s signal and the clock internal oscillator. In the hyperbolic mode, the receiver measures the phase difference between two transmitted signals and the receiver&#8217;s internal oscillator. When the receiver subtracts one phase difference from another to calculate the difference, the clock error is mathematically eliminated. In other words, as long as the clock error remained constant between the two measurements, subtracting the two phase differences canceled out the error.

The microprocessing of modern receivers, however, allows the direct ranging mode to be used. The methodology used is similar to that used by the Global Positioning System to account for inaccuracies in GPS receiver clocks. See section 1105. The Omega receiver makes three ranging measurements and looks at the intersection of the three resulting LOP&#8217;s. If there were no clock error present, the LOP&#8217;s would intersect at a pinpoint. Therefore, the receiver subtracts a constant clock error from each LOP until the fix is reduced to a pinpoint. This technique allows a receiver to use the direct ranging method without a precise atomic oscillator. This technique works only if the clock error is constant for each phase difference measurement.

1216. Using Multiple Frequencies
To this point, this chapter has discussed Omega operation involving only the 10.2 kHz signal. 10.2 kHz is the primary navigation frequency because virtually all Omega receivers use this frequency. More sophisticated receivers, however, use a combination of all the available frequencies in computing a fix. Each receiver operates differently. Consult the operator&#8217;s manual for a detailed discussion on how a specific receiver operates.

The above discussion on Omega operations assumed that the 10.2 kHz measurements required to calculate a fix were measured simultaneously. However, Figure 1212 shows that no two stations transmit 10.2 kHz simultaneously. Therefore, the receiver makes the 10.2 kHz phase measurements several minutes apart. In both the direct ranging and hyperbolic modes, the receiver stores the first phase difference measurement between the received signal and the receiver&#8217;s internal oscillator in memory and then compares that stored value with a second phase difference measured later. The fix error caused by the slight delay between measuring station signals would be inconsequential for marine navigators because of the relative slowness of their craft. Receivers on aircraft, however, because of their craft&#8217;s relatively high speed, must have a technique to advance the phase difference measured first to the time of the second phase difference measurement. This technique is called rate aiding.

OMEGA UNDER ICE OPERATIONS
1217. Under Ice Operation
For most military marine navigation applications, GPS has eclipsed Omega as the primary open ocean electronic navigation system. There is one area, however, in which military navigators use Omega as the primary electronic fix source: submarine operations under the polar ice cap. Under the ice, the submarine cannot raise any antennas capable of copying GPS signals. However, VLF signals can penetrate the ice. Therefore, the submarine can deploy a floating wire antenna (FWA) that rises from the submerged submarine to the bottom of the ice overhead. The submarine then copies the Omega signals through the ice on the FWA. Even though Omega is the only external electronic fix source available under the ice, its accuracy is seldom sufficient to ensure ship safety or mission accomplishment. Submarines, for example, must accurately plot the positions of thin ice regions in the event they must return to emergency surface. Omega does not position the ship with sufficient accuracy to do this. Submarines, therefore, use the inertial navigator as the primary positioning method when operating under the ice. When sufficient sounding data is available on their charts, submarine navigators supplement the inertial navigator with bottom contour navigation. Omega does, however, provide a useful backup in the under ice environment because no navigator feels comfortable navigating with only one positioning source, even if it is as accurate as the submarine inertial navigator.

VLF SIGNAL PROPAGATION
1218. Ionosphere Effects On VLF Propagation
The propagation of very-low-frequency (VLF) electromagnetic waves in the region between the lower portion of the ionosphere and the surface of the earth may be described in much the same manner as the propagation of higher frequency waves in conventional waveguides. These waves&#8217; transmission can be described by &#8220;the natural modes of propagation,&#8221; or simply &#8220;modes.&#8221; The behavior of the VLF wave may be discussed in terms of these modes of propagation.

There are three parameters that indicate how a certain mode will propagate in the earth-ionosphere waveguide: its attenuation rate, its excitation factor, and its phase velocity. The attenuation rate defines how fast energy is lost by the mode during its travel. The excitation factor measures how strongly the source generates the mode in comparison to other modes. Phase velocity defines the mode&#8217;s speed and direction of travel. The modes are usually ordered by increasing attenuation rates, so that normally mode 1 has the lowest rate. For frequencies in the 10 kHz to 14 kHz band, the attenuation rates for the second and higher modes are so high that only the first mode is of any practical importance at very long distances. However, since mode 2 is more strongly excited than mode 1 by the type of transmitters used in the Omega system, both modes must be considered at intermediate distances.
Another consideration is that the modes have different phase velocities. Thus, as modes propagate outward from the transmitter, they move in and out of phase with one another, so that the strength of the vertical electric field of the signal displays &#8220;dips&#8221; or &#8220;nulls&#8221; at several points. These nulls gradually disappear, however, as mode 2 attenuates, so that the strength behaves in a smooth and regular manner at long distances (where mode 1 dominates).
Since the degree of modal interference is also dependent upon factors other than proximity to the transmitter, the minimum distance for reliable use is variable. For applications sensitive to spatial irregularities, such as lane resolution, the receiver should be at least 450 miles from the transmitter. Lesser separations may be adequate for daylight path propagation at 10.2 kHz. As a warning, the Omega LOPs depicted on charts are dashed within 450 nautical miles of a station.

Since the characteristics of the Omega signal are largely determined by the electromagnetic properties of the lower ionosphere and the surface of the earth, any change in these properties along a propagation path will generally affect the behavior of these signals. Of course, the changes will not all produce the same effect. Some will lead to small effects due to a relatively insensitive relationship between the signal characteristics and the corresponding properties. For Omega signals, one of the most important properties in this category is the effective height of the ionosphere. This height is about 90 kilometers (km) at night, but decreases quite rapidly to about 70 km soon after sunrise due to the ionization produced by solar radiation.

The phase velocity of mode 1 is inversely proportional to the ionosphere&#8217;s height. Therefore, the daily changing ionosphere height causes a regular diurnal phase change in mode 1. The exact magnitude of this diurnal variation depends on several factors, including the geographic position of the receiver and transmitter and the orientation of the path relative to the boundary between the day and night hemispheres. This diurnal variation in phase is the major variation in the characteristics of the Omega signal at long distances.
Finally, the presence of a boundary between the day and night hemispheres may produce an additional variation. In the night hemisphere, both mode 1 and mode 2 are usually present. In the day hemisphere, however, only mode 1 is usually present. Hence, as the signal passes from the night to the day hemisphere, mode 2 will be converted into the daytime mode 1 at the day-night boundary. This resultant mode 1 may then interfere with the nighttime mode 1 passing unchanged into the day hemisphere. Thus, some additional variation in the characteristics may be present due to such interference.

1219. Geophysical Effects On VLF Propagation
Effects less pronounced than those associated with diurnal phase shifts are produced by various geophysical parameters including:
&#8226;	Ground conductivity. Freshwater ice caps cause very high attenuation.
&#8226;	Earth&#8217;s magnetic field. Westerly propagation is attenuated more than easterly propagation.
&#8226;	Solar activity. See the discussions of Sudden
Ionospheric Disturbances and Polar Cap Absorption below.
&#8226;	Latitude. The height of the ionosphere varies
proportionally with latitude.

1220. Sudden Ionospheric Disturbances (SID&#8217;s)
These disturbances occur when there is a very sudden and large increase in X-ray flux emitted from the sun. This occurs during either a solar flare or an &#8220;X-ray flare.&#8221; An Xray flare produces a large X-ray flux without producing a corresponding visible light emission. This effect, known as a sudden phase anomaly (SPA), causes a phase advance in the VLF signal. SID effects are related to the solar zenith angle, and, consequently, occur mostly in lower latitude regions. Usually there is a phase advance over a period of 5 to 10 minutes, followed by a recovery over a period of about 30 to 60 minutes. Significant SID&#8217;s could cause position errors of about 2 to 3 miles.

1221. The Polar Cap Disturbance (PCD&#8217;s)
The polar cap disturbance results from the earth&#8217;s magnetic field focusing particles released from the sun during a solar proton event. High-energy particles concentrate in the region of the magnetic pole, disrupting normal VLF transmission.

This effect is called the polar cap disturbance (PCD). Its magnitude depends on how much of the total transmission path crosses the region near the magnetic pole. A transmission path which is entirely outside the arctic region will be unaffected by the PCD. The probability of a PCD increases during periods of high solar activity. The Omega Propagation Correction Tables make no allowances for this random phenomenon.

PCD&#8217;s may persist for a week or more, but a duration of only a few days is more common. HYDROLANT/HYDROPAC messages are originated by the Defense Mapping Agency Hydrographic/Topographic Center if significant PCD&#8217;s are detected.

The position error magnitude will depend upon the positioning mode in use and the effect of the PCD on each signal. If the navigator is using the hyperbolic mode and has chosen station pairs with similar transmission paths, the effect will largely be canceled out. If using the direct ranging mode, the navigator can expect a position error of up to 8 miles.

1222. Arctic Paths And Auroral Zones
The predicted propagation corrections include allowance for propagation over regions of very poor conductivity, such as Greenland and parts of Iceland. Little data are available for these areas, hence even the best estimates are uncertain. In particular, rather rapid attenuation of the signal with position occurs as one passes into the &#8220;shadow&#8221; of the Greenland ice cap.

The auroral zones surrounding the north and south geomagnetic poles affect the phase of VLF signals. Auroral effects are believed to arise from electron precipitation in the higher regions of the ionosphere. Although the visual auroral zone is generally oval in shape, the affected region near the geomagnetic poles may be circular. Thus, auroral effects occur in a circular band between 60&#61616;&#61472;and 80&#61616;&#61472;north and south geomagnetic latitude. This effect slows the phase velocity of the VLF signal. This effect is approximately four times as severe at night.

INFREQUENT OMEGA OPERATIONS
As the VLF signal propagates through the atmosphere, it suffers distortion from the atmospheric phenomena discussed above. Most of these phenomena can be modeled mathematically, and receiver software can automatically correct for them. After initializing the receiver with the correct position, the receiver displays the vessel&#8217;s latitude and longitude, not the measured phase differences. All modern receivers have this correction capability. Therefore, a navigator with a modern receiver will seldom need to use the Propagation Correction Tables. However, if a mariner is navigating with a first generation receiver which does not automatically make propagation corrections, then he must use these Correction Tables before plotting his LOP on the chart.

1223. Manually Correcting Omega Readings
The following is an example of the correction process.
Example: A vessel&#8217;s DR position at 1200Z on January 23 is 16&#61616;N, 40&#61616;W. The navigator, operating Omega in the hyperbolic mode, chooses stations A (Norway) and C (Hawaii) to obtain an LOP. The Omega receiver readout is 720. 12. (720 full cycles + 12 centicycles). Correct this reading for plotting on the chart.

First, examine the Omega Table Area chart to determine the area corresponding to the vessel&#8217;s DR position. A DR position of 16&#61616;N 40&#61616;W corresponds to area 12. Figure 1223a shows this chart.










Next, obtain the proper Omega Propagation Correction Tables. There will be two separate volumes in this example. There will be an area 12 volume for the Norwegian station and an area 12 volume for the Hawaiian station. Inside each volume is a Page Index to Propagation Corrections. This index consists of a chartlet of area 12 subdivided into smaller areas. Figure 1223b shows the index for the Norwegian station in area 12. 










Again using the ship&#8217;s DR position, find the section of the index corresponding to 16&#61616;N 40&#61616;W. Inspecting Figure 1223b shows that the DR position falls in section 39. That indicates that the proper correction is found on page 39 of the Correction Table. Go to page 39 of the table. The entering arguments for the table on page 39 are date and GMT. The date is January 23 and GMT is 1200. The correction corresponding to these arguments is -0.06 cec. See Figure 1223c.










Following the same process in the Area 12 Correction volume for the Hawaiian station yields a correction of &#8211;0.67 cec.

To obtain a station pair correction, subtract the correction for the station with the higher alphabetical designator from the correction for the station with the lower designator. In this example, Hawaii&#8217;s station designator &#169; is higher than Norway&#8217;s station designator (A). Therefore, the station pair correction is (&#8211;0.06 cec) &#8211; (&#8211;0.67 cec) = +0.61 cec.

1224. Lane Identification
The receiver&#8217;s lane counter, set on departure from a known position, will indicate the present lane unless it looses its lane counting capability. In that case, the navigator can determine his lane by either dead reckoning or using the procedure described below.

Using a receiver capable of tracking multiple frequencies, compute a 3.4 kHz lane by subtracting the corrected 10.2 kHz phase reading from a corrected 13.6 kHz phase reading. Since the 3.4 kHz lane is 24 miles wide, the navigator need know his position only within 12 miles to identify the correct 3.4 kHz &#8220;coarse&#8221; lane. This &#8220;coarse&#8221; lane is formed by three 10.2 kHz &#8220;fine&#8221; lanes; all 3.4 kHz coarse lanes are bounded by 10.2 kHz lanes evenly divisible by three. Determine and plot the computed 3.4 kHz phase difference in relation to the derived 3.4 kHz coarse lane to determine the correct 10.2 kHz fine lane in which the vessel is located. Having determined the correct 10.2 kHz lane, the navigator can reset his receiver to the proper lane count.

Example: A vessel&#8217;s 200700Z Jan DR position is 51&#61616;&#61472;26&#8217;N, 167&#61616;32&#8217;W. The receiver has lost the lane count but the 0700Z phase readings for pair A-C are 0.19 centicycles for 10.2 kHz and 0.99 centicycles for 13.6 kHz. Determine the correct 10.2 kHz fine lane. See Figure 1224.

To solve the problem, first plot the vessel&#8217;s DR position. Use Omega plotting sheet 7609. Then determine the 10.2 kHz lanes evenly divisible by three between which the DR position plots. Inspecting the DR position on chart 7609 shows that the position falls between lanes A-C 1017 and A-C 1020. These lanes mark the boundary of the 3.4 kHz coarse lane. Then, determine the propagation correction for both the 10.2 kHz and 13.6 kHz signals from the Propagation Correction Tables for both frequencies, and apply these corrections to the measured phase difference to obtain the corrected phase difference.

Inspecting the tables yields the following results:
Correction for Station A (13.6 kHz) = &#8211; 1.42 cec 
Correction for Station C (13.6 kHz) = &#8211; 0.89 cec 
Correction for Station A (10.2 kHz) = &#8211; 0.54 cec 
Correction for Station C (10.2 kHz) = &#8211; 0.45 cec 
Corrected 13.6 kHz reading = 0.99 cec + (&#8211; 1.42 cec) &#8211; ( &#8211; 0.89 cec) = 0.46 cec.
Corrected 10.2 kHz reading = 0.19 cec + (&#8211; 0.54 cec) &#8211; (&#8211; 0.45 cec) = 0.10 cec 
Corrected 3.4 kHz derived reading = 0.46 cec &#8211; 0.10 cec = 0.36 cec.

Therefore, the vessel&#8217;s position lies 36&#37; of the way from lane A-C 1017 to lane A-C 1020. Use this information to determine that the correct 10.2 kHz fine lane is lane A-C 1018. Combining the proper lane with the 10.2 kHz corrected reading yields the correct Omega LOP: A-C 1018.10.










*End chapter 12*


----------



## Fishers of Men

*CHAPTER 13
RADAR NAVIGATION
PRINCIPLES OF RADAR NAVIGATION
*
Introduction
Radar determines distance to an object by measuring the time required for a radio signal to travel from a transmitter to an object and return. Since most radars use directional antennae, they can also determine an object&#8217;s bearing.

However, a radar&#8217;s bearing measurement will be less accurate than its distance measurement. Understanding this concept is crucial to ensuring the optimal employment of the radar for safe navigation.

Signal Characteristics
In most marine navigation applications, the radar signal is pulse modulated. Signals are generated by a timing circuit so that energy leaves the antenna in very short pulses. When transmitting, the antenna is connected to the transmitter but not the receiver. As soon as the pulse leaves, an electronic switch disconnects the antenna from the transmitter and connects it to the receiver. Another pulse is not transmitted until after the preceding one has had time to travel to the most distant target within range and return. Since the interval between pulses is long compared with the length of a pulse, strong signals can be provided with low average power. The duration or length of a single pulse is called pulse length, pulse duration, or pulse width. This pulse emission sequence repeats a great many times, per-haps 1,000 per second. This rate defines the pulse repetition rate (PRR). The returned pulses are displayed on an indicator screen.

The Display
The most common type of radar display used in the Navy is the plan position indicator (PPI). On a PPI, the sweep starts at the center of the display and moves outward along a radial line rotating in synchronization with the antenna. A detection is indicated by a brightening of the display screen at the bearing and range of the return. Because of a luminescent tube face coating, the glow continues after the trace rotates past the target. 
Figure 1302 shows this presentation.










On a PPI, a target&#8217;s actual range is proportional to its echo&#8217;s distance from the scope&#8217;s center. A moveable cursor helps to measure ranges and bearings. In the &#8220;heading-up-ward&#8221; presentation, which indicates relative bearings, the top of the scope represents the direction of the ship&#8217;s head. In this unstabilized presentation, the orientation changes as the ship changes heading. In the stabilized &#8220;north-upward&#8221; presentation, gyro north is always at the top of the scope.

The Radar Beam
The pulses of energy comprising the radar beam would form a single lobe-shaped pattern of radiation if emitted in free space. Figure 1303a. shows this free space radiation pattern, including the undesirable minor lobes or side lobes associated with practical antenna design.
Although the radiated energy is concentrated into a relatively narrow main beam by the antenna, there is no clearly defined envelope of the energy radiated. The energy is concentrated along the axis of the beam. With the rapid decrease in the amount of radiated energy in directions away from this axis, practical power limits may be used to define the dimensions of the radar beam.

A radar beam&#8217;s horizontal and vertical beam widths are referenced to arbitrarily selected power limits. The most common convention defines beam width as the angular width between half power points. The half power point corresponds to a drop in 3 decibels from the maximum beam strength. The definition of the decibel shows this halving of power at a decrease in 3 dB from maximum power. A decibel is simply the logarithm of the ratio of a final power level to a reference power level: 








where P 1 is the final power level, and P 0 is a reference power level.
When calculating the dB drop for a 50&#37; reduction in power level, the equation becomes:









The radiation diagram shown in Figure 1303b depicts relative values of power in the same plane existing at the same distances from the antenna or the origin of the radar
beam. Maximum power is in the direction of the axis of the beam. Power values diminish rapidly in directions away from the axis. The beam width is taken as the angle between the half-power points.

The beam width depends upon the frequency or wave-length of the transmitted energy, antenna design, and the dimensions of the antenna.
For a given antenna size (antenna aperture), narrower beam widths result from using shorter wavelengths. For a given wavelength, narrower beam widths result from using larger antennas.

With radar waves being propagated in the vicinity of the surface of the sea, the main lobe of the radar beam is composed of a number of separate lobes, as opposed to the single lobe-shaped pattern of radiation as emitted in free space. This phenomenon is the result of interference between radar waves directly transmitted, and those waves which are reflected from the surface of the sea. Radar waves strike the surface of the sea, and the indirect waves reflect off the surface of the sea. See Figure 1303c. These reflected waves either constructively or destructively interfere with the direct waves depending upon the waves&#8217; phase relationship.










Diffraction And Attenuation
Diffraction is the bending of a wave as it passes an obstruction. Because of diffraction there is some illumination of the region behind an obstruction or target by the radar beam. Diffraction effects are greater at the lower frequencies. Thus, the radar beam of a lower frequency radar tends to illuminate more of the shadow region behind an obstruction than the beam of a radar of higher frequency or shorter wavelength.
Attenuation is the scattering and absorption of the energy in the radar beam as it passes through the atmosphere.
It causes a decrease in echo strength. Attenuation is greater at the higher frequencies or shorter wavelengths.
While reflected echoes are much weaker than the transmitted pulses, the characteristics of their return to the source are similar to the characteristics of propagation. The strengths of these echoes are dependent upon the amount of transmitted energy striking the targets and the size and reflecting properties of the targets.

Refraction
If the radar waves traveled in straight lines, the distance to the radar horizon would be dependent only on the power output of the transmitter and the height of the antenna. In other words, the distance to the radar horizon would be the same as that of the geometrical horizon for the antenna height. However, atmospheric density gradients bend radar rays as they travel to and from a target. This bending is called refraction.
The following formula, where h is the height of the antenna in feet, gives the distance to the radar horizon in nautical miles:








The distance to the radar horizon does not limit the distance from which echoes may be received from targets. Assuming that adequate power is transmitted, echoes may be received from targets beyond the radar horizon if their reflecting surfaces extend above it. Note that the distance to the radar horizon is the distance at which the radar rays pass tangent to the surface of the earth.

Factors Affecting Radar Interpretation
Radar&#8217;s value as a navigational aid depends on the navigator&#8217;s understanding its characteristics and limitations.
Whether measuring the range to a single reflective object or trying to discern a shoreline lost amid severe clutter, knowledge of the characteristics of the individual radar used are crucial. Some of the factors to be considered in interpretation are discussed below:

Resolution in Range. In part A of Figure 1306a, a transmitted pulse has arrived at the second of two targets of insufficient size or density to absorb or reflect all of the energy of the pulse. While the pulse has traveled from the first to the second target, the echo from the first has traveled an equal distance in the opposite direction. At B, the transmitted pulse has continued on beyond the second target, and the two echoes are returning toward the transmitter. The distance between leading edges of the two echoes is twice the distance between targets. The correct distance will be shown on the scope, which is calibrated to show half the distance traveled out and back. At C the targets are closer together and the pulse length has been increased. The two echoes merge, and on the scope they will appear as a single, large target. At D the pulse length has been decreased, and the two echoes appear separated. The ability of a radar to separate targets close together on the same bearing is called resolution in range. It is related primarily to pulse length.










The minimum distance between targets that can be distinguished as separate is half the pulse length. This (half the pulse length) is the apparent depth or thickness of a target presenting a flat perpendicular surface to the radar beam. Thus, several ships close together may appear as an island. Echoes from a number of small boats, piles, breakers, or even large ships close to the shore may blend with echoes from the shore, resulting in an incorrect indication of the position and shape of the shoreline.

Resolution in Bearing. Echoes from two or more tar-gets close together at the same range may merge to form a single, wider echo. The ability to separate targets is called resolution in bearing. Bearing resolution is a function of two variables: beam width and range between targets. A narrower beam and a shorter distance between objects both increase bearing resolution.

Height of Antenna and Target. If the radar horizon is between the transmitting vessel and the target, the lower part of the target will not be visible. A large vessel may appear as a small craft, or a shoreline may appear at some distance inland.

Reflecting Quality and Aspect of Target. Echoes from several targets of the same size may be quite different in appearance. A metal surface reflects radio waves more strongly than a wooden surface. A surface perpendicular to the beam returns a stronger echo than a non perpendicular one. For this reason, a gently sloping beach may not be visible. A vessel encountered broadside returns a stronger echo than one heading directly toward or away.

Frequency. As frequency increases, reflections occur from smaller targets.
Atmospheric noise, sea return, and precipitation complicate radar interpretation by producing clutter. Clutter is usually strongest near the vessel. Strong echoes can some-times be detected by reducing receiver gain to eliminate weaker signals. By watching the repeater during several rotations of the antenna, the operator can discriminate between clutter and a target even when the signal strengths from clutter and the target are equal. At each rotation, the signals from targets will remain relatively stationary on the display while those caused by clutter will appear at different locations.

Another major problem lies in determining which features in the vicinity of the shoreline are actually represented by echoes shown on the repeater. Particularly in cases where a low lying shore is being scanned, there may be considerable uncertainty.

A related problem is that certain features on the shore will not return echoes because they are blocked from the radar beam by other physical features or obstructions. This factor in turn causes the chart like image painted on the scope to differ from the chart of the area.

If the navigator is to be able to interpret the presentation on his radarscope, he must understand the characteristics of radar propagation, the capabilities of his radar set, the reflecting properties of different types of radar targets, and the ability to analyze his chart to determine which charted features are most likely to reflect the transmitted pulses or to be blocked. Experience gained during clear weather comparison between radar and visual images is invaluable.

Land masses are generally recognizable because of the steady brilliance of the relatively large areas painted on the PPI. Also, land should be at positions expected from the ship&#8217;s navigational position. Although land masses are readily recognizable, the primary problem is the identification of specific land features. Identification of specific features can be quite difficult because of various factors, including distortion resulting from beam width and pulse length, and uncertainty as to just which charted features are reflecting the echoes.

Sand spits and smooth, clear beaches normally do not appear on the PPI at ranges beyond 1 or 2 miles because these targets have almost no area that can reflect energy back to the radar. Ranges determined from these targets are not reliable.

If waves are breaking over a sandbar, echoes may be returned from the surf. Waves may, however, break well out from the actual shoreline, so that ranging on the surf may be
misleading.

Mud flats and marshes normally reflect radar pulses only a little better than a sand spit. The weak echoes received at low tide disappear at high tide. Mangroves and other thick growth may produce a strong echo. Areas that are indicated as swamps on a chart, therefore, may return either strong or weak echoes, depending on the density and size of the vegetation growing in the area.

When sand dunes are covered with vegetation and are well back from a low, smooth beach, the apparent shoreline determined by radar appears as the line of the dunes rather than the true shoreline. Under some conditions, sand dunes may return strong echo signals because the combination of the vertical surface of the vegetation and the horizontal beach may form a sort of corner reflector.

Lagoons and inland lakes usually appear as blank areas on a PPI because the smooth water surface returns no energy to the radar antenna. In some instances, the sandbar or reef surrounding the lagoon may not appear on the PPI be-cause it lies too low in the water.

Coral atolls and long chains of islands may produce long lines of echoes when the radar beam is directed perpendicular to the line of the islands. This indication is especially true when the islands are closely spaced. The reason is that the spreading resulting from the width of the radar beam causes the echoes to blend into continuous lines. When the chain of islands is viewed lengthwise, or obliquely, however, each island may produce a separate return.

Surf breaking on a reef around an atoll produces a ragged, variable line of echoes.
One or two rocks projecting above the surface of the water, or waves breaking over a reef, may appear on the PPI. When an object is submerged entirely and the sea is smooth over it, no indication is seen on the PPI.

If the land rises in a gradual, regular manner from the shoreline, no part of the terrain produces an echo that is stronger than the echo from any other part. As a result, a general haze of echoes appears on the PPI, and it is difficult to ascertain the range to any particular part of the land.

Blotchy signals are returned from hilly ground, because the crest of each hill returns a good echo although the valley beyond is in a shadow. If high receiver gain is used, the pat-tern may become solid except for the very deep shadows.

Low islands ordinarily produce small echoes. When thick palm trees or other foliage grow on the island, strong echoes often are produced because the horizontal surface of the water around the island forms a sort of corner reflector with the vertical surfaces of the trees. As a result, wooded islands give good echoes and can be detected at a much greater range than barren islands.

Sizable land masses may be missing from the radar display because of certain features being blocked from the radar beam by other features. A shoreline which is continuous on the PPI display when the ship is at one position, may not be continuous when the ship is at another position and scanning the same shoreline. The radar beam may be blocked from a segment of this shoreline by an obstruction such as a promontory. An indentation in the shoreline, such as a cove or bay, appearing on the PPI when the ship is at one position, may not appear when the ship is at another position nearby. Thus, radar shadow alone can cause considerable differences between the PPI display and the chart presentation. This effect in conjunction with beam width and pulse length distortion of the PPI display can cause even greater differences.

The returns of objects close to shore may merge with the shoreline image on the PPI, because of distortion effects of horizontal beam width and pulse length. Target images on the PPI always are distorted angularly by an amount equal to the effective horizontal beam width. Also, the target images always are distorted radially by an amount at least equal to one-half the pulse length (164 yards per microsecond of pulse length).

Figure 1306b illustrates the effects of ship&#8217;s position, beam width, and pulse length on the radar shoreline. Be-cause of beam width distortion, a straight, or nearly straight, shoreline often appears crescent-shaped on the PPI. This effect is greater with the wider beam widths. Note that this distortion increases as the angle between the beam axis and the shoreline decreases.










Figure 1306c illustrates the distortion effects of radar shadow, beam width, and pulse length. View A shows the actual shape of the shoreline and the land behind it. Note the steel tower on the low sand beach and the two ships at anchor close to shore. The heavy line in view B represents the shoreline on the PPI. The dotted lines represent the actual position and shape of all targets. Note in particular:
1.	The low sand beach is not detected by the radar.
2.	The tower on the low beach is detected, but it looks like a ship in a cove. At closer range the land would be detected and the cove-shaped area would begin to fill in;
then the tower could not be seen without reducing the receiver gain.
3.	The radar shadow behind both mountains. Distortion owing to radar shadows is responsible for more confusion than any other cause. The small island does not appear because it is in the radar shadow.
4.	The spreading of the land in bearing caused by beam width distortion. Look at the upper shore of the peninsula. The shoreline distortion is greater to the west because the angle between the radar beam and the shore is smaller as the beam seeks out the more westerly shore.
5.	Ship No. 1 appears as a small peninsula. Her return has merged with the land because of the beam width distortion.
6.	Ship No. 2 also merges with the shoreline and forms a bump. This bump is caused by pulse length and beam width distortion. Reducing receiver gain might cause the ship to separate from land, provided the ship is not too close to the shore. The Fast Time Constant (FTC) control could also be used to attempt to separate the ship from land.










*To be cont.*


----------



## Fishers of Men

*Ch. 13 cont.
Recognition Of Unwanted Echoes*
The navigator must be able to recognize various abnormal echoes and effects on the radarscope so as not to be confused by their presence.
Indirect or false echoes are caused by reflection of the main lobe of the radar beam off ship&#8217;s structures such as stacks and kingposts. When such reflection does occur, the echo will return from a legitimate radar contact to the antenna by the same indirect path. Consequently, the echo will appear on the PPI at the bearing of the reflecting surface. As shown in Figure 1307a, the indirect echo will appear on the PPI at the same range as the direct echo received, assuming that the additional distance by the indirect path is negligible.










Characteristics by which indirect echoes may be recognized are summarized as follows:

1.	The indirect echoes will usually occur in shadow sectors.
2.	They are received on substantially constant bearings, although the true bearing of the radar contact may change appreciably.
3.	They appear at the same ranges as the corresponding direct echoes.
4.	When plotted, their movements are usually abnormal.
5.	Their shapes may indicate that they are not direct echoes. Side-lobe effects are readily recognized in that they produce a series of echoes (Figure 1307b) on each side of the main lobe echo at the same range as the latter. Semicircles, or even complete circles, may be produced. Because of the low energy of the side-lobes, these effects will normally occur only at the shorter ranges. The effects may be minimized or eliminated, through use of the gain and anti-clutter controls. Slotted wave guide antennas have largely eliminated the side-lobe problem.










Multiple echoes may occur when a strong echo is received from another ship at close range. A second or third or more echoes may be observed on the radarscope at double, triple, or other multiples of the actual range of the radar contact (Figure 1307c).

Second-trace echoes (multiple-trace echoes) are echoes received from a contact at an actual range greater than the radar range setting. If an echo from a distant target is received after the following pulse has been transmitted, the echo will appear on the radarscope at the correct bearing but not at the true range. Second-trace echoes are unusual, except under abnormal atmospheric conditions, or conditions under which super-refraction is present. Second-trace echoes may be recognized through changes in their positions on the radarscope in changing the pulse repetition rate (PRR); their hazy, streaky, or distorted shape; and the erratic movements on plotting.

As illustrated in Figure 1307d, a target return is detected on a true bearing of 090&#176; &#61472;at a distance of 7.5 miles. On changing the PRR from 2,000 to 1,800 pulses per second, the same target is detected on a bearing of 090&#176; &#61472;at a distance of 3 miles (Figure 1307e). The change in the position of the return indicates that the return is a second-trace echo. The actual distance of the target is the distance as indicated on the PPI plus half the distance the radar wave travels between pulses. Electronic interference effects, such as may occur when near another radar operating in the same frequency band as that of the observer&#8217;s ship, is usually seen on the PPI as a large number of bright dots either scattered at random or in the form of dotted lines extending from the center to the edge of the PPI.

Interference effects are greater at the longer radar range scale settings. The interference effects can be distinguished easily from normal echoes because they do not appear in the same places on successive rotations of the antenna.

Stacks, masts, samson posts, and other structures, may cause a reduction in the intensity of the radar beam beyond these obstructions, especially if they are close to the radar antenna. If the angle at the antenna subtended by the obstruction is more than a few degrees, the reduction of the intensity of the radar beam beyond the obstruction may produce a blind sector. Less reduction in the intensity of the beam beyond the obstructions may produce shadow sectors. Within a shadow sector, small targets at close range may not be detected, while larger targets at much greater ranges will appear.
Spoking appears on the PPI as a number of spokes or radial lines. Spoking is easily distinguished from interference effects because the lines are straight on all range-scale settings, and are lines rather than a series of dots.

The spokes may appear all around the PPI, or they may be confined to a sector. If spoking is confined to a narrow sector, the effect can be distinguished from a Ramark signal of similar appearance through observation of the steady relative bearing of the spoke in a situation where the bearing of the Ramark signal should change. Spoking indicates a need for maintenance or adjustment.

The PPI display may appear as normal sectors alternating with dark sectors. This is usually due to the automatic frequency control being out of adjustment.

The appearance of serrated range rings indicates a need for maintenance.
After the radar set has been turned on, the display may not spread immediately to the whole of the PPI because of static electricity inside the CRT. Usually, the static electricity effect, which produces a distorted PPI display, lasts no longer than a few minutes.

Hour-glass effect appears as either a constriction or expansion of the display near the center of the PPI. The expansion effect is similar in appearance to the expanded center display. This effect, which can be caused by a non-linear time base or the sweep not starting on the indicator at the same instant as the transmission of the pulse, is most apparent when in narrow rivers or close to shore.

The echo from an overhead power cable appears on the PPI as a single echo always at right angles to the line of the cable. If this phenomenon is not recognized, the echo can be wrongly identified as the echo from a ship on a steady bearing. Avoiding action results in the echo remaining on a constant bearing and moving to the same side of the channel as the ship altering course. This phenomenon is particularly apparent for the power cable spanning the Straits of Messina.

Aids To Radar Navigation
Radar navigation aids help identify radar targets and in-crease echo signal strength from otherwise poor radar targets.
Buoys are particularly poor radar targets. Weak, fluctuating echoes received from these targets are easily lost in the sea clutter. To aid in the detection of these targets, radar reflectors, designated corner reflectors, may be used. These reflectors may be mounted on the tops of buoys. Additionally, the body of the buoy may be shaped as a reflector.

Each corner reflector, shown in Figure 1308a, consists of three mutually perpendicular flat metal surfaces. A radar wave striking any of the metal surfaces or plates will be reflected back in the direction of its source. Maximum energy will be reflected back to the antenna if the axis of the radar beam makes equal angles with all the metal surfaces. Frequently, corner reflectors are assembled in clusters to maximize the reflected signal.










Although radar reflectors are used to obtain stronger echoes from radar targets, other means are required for more positive identification of radar targets. Radar beacons are transmitters operating in the marine radar frequency band, which produce distinctive indications on the radarscopes of ships within range of these beacons. There are two general classes of these beacons: racons, which provide both bearing and range information to the target, and ramarks which provide bearing information only. However, if the ramark installation is detected as an echo on the radarscope, the range will be available also.

A racon is a radar transponder which emits a characteristic signal when triggered by a ship&#8217;s radar. The signal may be emitted on the same frequency as that of the triggering radar, in which case it is superimposed on the ship&#8217;s radar display automatically. The signal may be emitted on a separate frequency, in which case to receive the signal the ship&#8217;s radar receiver must be tuned to the beacon frequency, or a special receiver must be used. In either case, the PPI will be blank except for the beacon signal. However, the only racons in service are &#8220;in band&#8221; beacons which transmit in one of the marine radar bands, usually only the 3-centi-meter band.

The racon signal appears on the PPI as a radial line originating at a point just beyond the position of the radar beacon, or as a Morse code signal (Figure 1308b) displayed radially from just beyond the beacon.










A ramark is a radar beacon which transmits either continuously or at intervals. The latter method of transmission is used so that the PPI can be inspected without any clutter introduced by the ramark signal on the scope. The ramark signal as it appears on the PPI is a radial line from the center. The radial line may be a continuous narrow line, a broken line (Figure 1308c), a series of dots, or a series of dots and dashes.

RADAR PILOTING
When navigating in restricted waters, a mariner most often relies on visual piloting to provide the accuracy required to ensure ship safety. Visual piloting, however,
requires clear weather; often, mariners must navigate through fog. When conditions render visual piloting impossible and a vessel is not equipped with DGPS, radar navigation provides a method of fixing a vessel&#8217;s position with sufficient accuracy to allow safe passage. See Chapter 8 for a detailed discussion of integrating radar into a piloting procedure.

Fixing Position By Two Or More Simultaneous Ranges
The most accurate radar fixes result from measuring and plotting ranges to two or more objects. Measure objects directly ahead or astern first; measure objects closest to the beam last. This procedure is the opposite to that recommended for taking visual bearings, where objects closest to the beam are measured first; however, both recommendations rest on the same principle. When measuring objects to determine a line of position, measure first those which have the greatest rate of change in the quantity being measured; measure last those which have the least rate of change in that quantity. This minimizes measurement time delay errors. Since the range of those objects directly ahead or astern of the ship changes more rapidly than those objects located abeam, measure objects ahead or astern first.

Record the ranges to the navigation aids used and lay the resulting range arcs down on the chart. Theoretically, these lines of position should intersect at a point coincident with the ship&#8217;s position at the time of the fix. However, the inherent inaccuracy of the radar coupled with the relatively large scale of most piloting charts usually precludes such a point fix. In this case, the navigator must carefully interpret the resulting fix. Check the echo sounder with the charted depth where the fix lies. If both soundings consistently correlate, that is an indication that the fixes are accurate. If there is disparity in the sounding data, then that is an indication that either the radar ranges were inaccurate or that the piloting party has misplotted them.

This practice of checking sounding data with each fix cannot be overemphasized. Though verifying soundings is always a good practice in all navigation scenarios, its importance increases tremendously when piloting using only radar. Assuming proper operation of the fathometer, soundings give the navigator invaluable information on the reliability of his fixes. When a disparity exists between the charted depth at the fix and the recorded sounding, the navigator should assume that the disparity has been caused by fix inaccuracy. 

This is especially true if the fathometer shows the ship heading into water shallower than that anticipated. When there is a consistent disparity between charted and fathometer sounding data, the navigator should assume that he does not know the ship&#8217;s position with sufficient accuracy to proceed safely. The ship should be slowed or stopped until the navigator is confident that he can continue his passage safely.

Fixing Position By A Range And Bearing To One Object
Visual piloting requires bearings from at least two objects; radar, with its ability to determine both bearing and range from one object, allows the navigator to obtain a fix where only a single navigation aid is available. An example of using radar in this fashion occurs in approaching a harbor whose entrance is marked with a single, prominent light such as Chesapeake Light at the entrance of the Chesapeake Bay. Well beyond the range of any land-based visual navigation aid, and beyond the visual range of the light itself, a shipboard radar can detect the light and provide bearings and ranges for the ship&#8217;s piloting party.

This methodology is limited by the inherent inaccuracy associated with radar bearings; typically, a radar bearing is accurate to within 5&#176;&#61472;of the true bearing. Therefore, the navigator must carefully evaluate the resulting position, checking it particularly with the sounding obtained from the bottom sounder. If a visual bearing is available from the object, use that bearing instead of the radar bearing when laying down the fix. This illustrates the basic concept discussed above: radar ranges are inherently more accurate than radar bearings.

Prior to using this single object method, the navigator must ensure that he has correctly identified the object from which the bearing and range are to be taken. Using only one navigation aid for both lines of position can lead to disaster if the navigation aid is not properly identified.

Fixing Position With Tangent Bearings And A Range
This method combines bearings tangent to an object with a range measurement from some point on that object. The object must be large enough to provide sufficient bearing spread between the tangent bearings; often an island is used. Identify some prominent feature of the object that is displayed on both the chart and the radar display. Take a range measurement from that feature and plot it on the chart. Then determine the tangent bearings to the island and plot them on the chart.

Fixing Position By Bearings To Two Or More Objects
The inherent inaccuracy of radar bearings discussed above makes this method less accurate than fixing position by radar range. Use this method to plot a position quickly on the chart when approaching restricted waters to obtain an approximate ship&#8217;s position for evaluating radar targets to use for range measurements. Speed is the advantage of this method, as the plotter can lay bearings down more quickly than ranges on the chart. Unless no more accurate method is available, do not use this method while piloting in restricted waters.

Fischer Plotting
In Fischer plotting, the navigator adjusts the scale of the radar to match the scale of the chart in use. He then overlays the PPI screen with a clear surface such as Plexiglas and traces the shape of land and location of navigation aids from the radar scope onto the Plexiglas. He then transfers the surface from the radar scope to the chart. He matches the chart&#8217;s features with the features on the radar by adjusting the tracings on the Plexiglas to match the charts features. Once obtaining the best fit, he marks the ship&#8217;s position as the center of the Plexiglas cover.

RASTER RADARS
Basic Description
Conventional PPI-display radars use a Cathode Ray Tube (CRT) to direct an electron beam at a screen coated with phosphorus. The phosphorus glows when illuminated by an electron beam. Internal circuitry forms the beam such that a &#8220;sweep&#8221; is indicated on the face of the PPI. This sweep is timed to coincide with the sweep of the radar&#8217;s antenna. A return echo is added to the sweep signal so that the screen is more brightly illuminated at a point corresponding to the bearing and range of the target that returned the echo. The raster radar also employs a cathode ray tube; how-ever, the end of the tube upon which the picture is formed is rectangular, not circular as in the PPI display. The raster radar does not produce its picture from a circular sweep; it utilizes a liner scan in which the picture is &#8220;drawn,&#8221; line by line, horizontally across the screen. As the sweep moves across the screen, the electron beam from the CRT illuminates the pixels on the screen. A pixel is the smallest area of phosphorus that can be excited to form a picture element. In order to produce a sufficiently high resolution, some raster radars require over 1 million pixels per screen combined with an update rate of 60 scans per second.

Completing the processing for such a large number of pixel elements requires sophisticated, expensive circuitry. One way to lower cost is to slow down the required processing speed. This speed can be lowered to approximately 30 frames per second before the picture develops a noticeable flicker.

Further cost reduction can be gained by using an inter-laced display. An interlaced display does not draw the entire picture in one pass. On the first pass, it draws every other line; it draws the remaining lines on the second pass. This type of display reduces the number of screens that have to be drawn per unit time by a factor of two; however, if the two pictures are misaligned, the picture will appear to jitter.
Raster radars represent the future of radar technology, and they will be utilized in the integrated bridge systems discussed in Chapter 14.

Chapter 13 end.


----------



## Fishers of Men

I am getting e-mails from others than OGF from this thread. Seems the "blow Boats" are interested. Some are signing up, thought they didn't care for "stink pots"!   

Flotsam and Jetsam:
Traditionally, flotsam and jetsam are words that describe goods of potential value that have been thrown into the ocean. There is a technical difference between the two: jetsam has been voluntarily cast into the sea (jettisoned) by the crew of a ship, usually in order to lighten it in an emergency; while flotsam describes goods that are floating on the water without having been thrown in deliberately, often after a shipwreck. Traditionally spelled flotsom and jetsom, the "o" was replaced with "a" in the early twentieth century, and the former spellings have since been out of common usage.

In modern usage, flotsam also includes driftwood, logs and other natural debris in oceans and waterways, much of which enters waterways through the action of shore surf, rain or wind. Flotsam on beaches may increase after storms due to the debris brought there from riverbanks and drainage channels being flushed out, or marine equipment (including broken docks and piers) torn loose.

Ligan (or lagan), describes goods that have been marked by being tied to a buoy so that its owner can find and retrieve it later.

Derelict is property which has been abandoned and deserted at sea by those who were in charge without any hope of recovering it. This includes vessels and cargo.

The differences among flotsam, jetsam, and ligan are occasionally of consequence in the law of admiralty and marine salvage. On land the distinction between deliberate and accidental loss led to the concept of Treasure trove.

Now, here is some of ours floating around out there:

Donkey once posted "So you think you want to fish at night."

FishCrazy says "Dont be afraid of the dark"

Reel has been chomping at the bit to pull that sextant out.

George says ""It follows than as certain as that night succeeds the day, that without a decisive naval force we can do nothing definitive, and with it, everything honorable and glorious."
Really he stole it from this guy:
President George Washington, 15 November 1781, to Marquis de Lafayette.
[The Writings of George Washington from the Original Manuscript Sources 1745-1799. vol.23. (Washington, DC: Government Printing Office, 1937): 341.]

We are going to kick it up a notch now like Emeril says. Did I mention that the old sailors were very superstitious? 

This next chapter will take some work on both our parts.

And if you don't "toe the line" ie: The space between each pair of deck planks in a wooden ship was filled with a packing material called "oakum" and then sealed with a mixture of pitch and tar. The result, from afar, was a series of parallel lines a half-foot or so apart, running the length of the deck. Once a week, as a rule, usually on Sunday, a warship's crew was ordered to fall in at quarters -- that is, each group of men into which the crew was divided would line up in formation in a given area of the deck. To insure a neat alignment of each row, the Sailors were directed to stand with their toes just touching a particular seam. Another use for these seams was punitive. The youngsters in a ship, be they ship's boys or student officers, might be required to stand with their toes just touching a designated seam for a length of time as punishment for some minor infraction of discipline, such as talking or fidgeting at the wrong time. A tough captain might require the miscreant to stand there, not talking to anyone, in fair weather or foul, for hours at a time. Hopefully, he would learn it was easier and more pleasant to conduct himself in the required manner rather than suffer the punishment. From these two uses of deck seams comes our cautionary word to obstreperous youngsters to "toe the line."

You will be Keel hauled, ie:
A naval punishment on board ships said to have originated with the Dutch but adopted by other navies during the 15th and 16th centuries. A rope was rigged from yardarm to yardarm, passing under the bottom of the ship, and the unfortunate delinquent secured to it, sometimes with lead or iron weights attached to his legs. He was hoisted up to one yardarm and then dropped suddenly into the sea, hauled underneath the ship, and hoisted up to the opposite yardarm, the punishment being repeated after he had had time to recover his breath. While he was under water, a "great gun" was fired, "which is done as well to astonish him so much the more with the thunder of the shot, as to give warning until all others of the fleet to look out and be wary by his harms" (from Nathaniel Boteler, A Dialogicall Discourse, 1634). The U.S. Navy never practiced keel hauling.

Therefore, "It is established for a custom of the sea that if a ship is lost by default of the lodesman, the mariners may, if they please, bring the lodesman to the windlass and cut off his head without the mariners being bound to answer before any judge, because the lodesman had committed high treason against OGF and the undertaking of the pilotage, and this is the judgement.
Twenty-Third Article of the Laws of Oleron 1190
Quoted in Schofield

EZ says, "I wish to have no Connection with any Ship that does not Sail fast for I intend to go in harm's way." Really stolen from this guy:
Captain John Paul Jones, 16 November 1778, in a letter to le Ray de Chaumont.
[Morison, Samuel Eliot. John Paul Jones: A Sailor's Biography. (Boston: Little, Brown and Company, 1959): 182.]

Now with that said:
Richard Henry Dana Jr. on American merchant brig Pilgrim, 1 Oct. 1834.
Wednesday, October Ist. Crossed the equator in lon. 24 24' W. I now, for the first time, felt at liberty, according to the old usage, to call myself a son of Neptune, and was very glad to be able to claim the title without the disagreeable initiation which so many have to go through. After once crossing the line, you can never be subjected to the process, but are considered as a son of Neptune, with full powers to play tricks upon others. This ancient custom is now seldom allowed, unless there are passengers on board, in which case there is always a good deal of sport.
Source: Dana, Richard Henry. Two Years Before the Mast: A Personal Narrative by Richard Henry Dana, Jr. vol.1 (Boston: Houghton Mifflin, 1911): 22-23.

Lets get ready to navigate by the Heavens, what say ye???

&#8220;And he was afraid, and said, How dreadful is this place! This is none other but the house of God, and this is the gate of heaven&#8221; Gen 28:17


----------



## Fishers of Men

*Okay you night owls, lets go for a cruise. This one is going to cost you! Take your time and study and enjoy. This chapter will start an excursion that bewilders some people. Don't let this first part scare you, you don't need to know all of it, just understand how it works. 

&#8220;And of Joseph he said, Blessed of the Lord be his land, for the precious things of heaven, for the dew, and for the deep that coucheth beneath,
And for the precious fruits brought forth by the sun, and for the precious things brought forth by the moon,&#8221; Deut 33: 13-14

CHAPTER 15
NAVIGATIONAL ASTRONOMY
PRELIMINARY CONSIDERATIONS*

1500. Definition
Astronomy predicts the future positions and motions of celestial bodies and seeks to understand and explain their physical properties. Navigational astronomy, dealing principally with celestial coordinates, time, and the apparent motions of celestial bodies, is the branch of astronomy most important to the navigator. The symbols commonly recognized in navigational astronomy are given in Table 1500. Astronomical symbols.










The Celestial Sphere
Looking at the sky on a dark night, imagine that celestial bodies are located on the inner surface of a vast, earth-centered sphere. This model is useful since we are only interested in the relative positions and motions of celestial bodies on this imaginary surface. Understanding the concept of the celestial sphere is most important when discussing sight reduction in Chapter 20 and an earlier post.










Relative And Apparent Motion
Celestial bodies are in constant motion. There is no fixed position in space from which one can observe absolute motion. Since all motion is relative, the position of the observer must be noted when discussing planetary motion. From the earth we see apparent motions of celestial bodies on the celestial sphere. In considering how planets follow their orbits around the sun, we assume a hypothetical observer at some distant point in space. When discussing the rising or setting of a body on a local horizon, we must locate the observer at a particular point on the earth because the setting sun for one observer may be the rising sun for another.
Motion on the celestial sphere results from the motions in space of both the celestial body and the earth. Without special instruments, motions toward and away from the earth cannot be discerned.

Astronomical Distances
Consider the celestial sphere as having an infinite radius because distances between celestial bodies are remarkably vast. The difficulty of illustrating astronomical distances is indicated by the fact that if the earth were represented by a circle one inch in diameter, the moon would be a circle one-fourth inch in diameter at a distance of 30 inches, the sun would be a circle nine feet in diameter at a distance of nearly a fifth of a mile, and Pluto would be a circle half an inch in diameter at a distance of about seven miles. The nearest star would be one-fifth the actual distance to the moon.
Because of the size of celestial distances, it is inconvenient to measure them in common units such as the mile or kilometer. The mean distance to our nearest neighbor, the moon, is 238,900 miles. For convenience this distance is sometimes expressed in units of the equatorial radius of the earth: 60.27 earth radii.

Distances between the planets are usually expressed in terms of the astronomical unit (AU), the mean distance between the earth and the sun. This is approximately 92,960,000 miles. Thus the mean distance of the earth from the sun is 1 A.U. The mean distance of Pluto, the outermost known planet in our solar system, is 39.5 A.U. Expressed in astronomical units, the mean distance from the earth to the moon is 0.00257 A.U.

Distances to the stars require another leap in units. A commonly-used unit is the light-year, the distance light travels in one year. Since the speed of light is about 1.86 X 10(5 power) miles per second and there are about 3.16 X 10(7(power) seconds per year, the length of one light-year is about 5.88 X 10(12 power) miles. The nearest stars, Alpha Centauri and its neighbor
Proxima, are 4.3 light-years away. Relatively few stars are less than 100 light-years away. The nearest galaxies, the Clouds of Magellan, are 150,000 to 200,000 light years away. The most distant galaxies observed by astronomers are several billion light years away.

Magnitude
The relative brightness of celestial bodies is indicated by a scale of stellar magnitudes. Initially, astronomers divided the stars into 6 groups according to brightness. The 20 brightest were classified as of the first magnitude, and the dimmest were of the sixth magnitude. In modern times, when it became desirable to define more precisely the limits of magnitude, a first magnitude star was considered 100 times brighter than one of the sixth magnitude. Since the fifth root of 100 is 2.512, this number is considered the magnitude ratio. 

A first magnitude star is 2.512 times as bright as a second magnitude star, which is 2.512 times as bright as a third magnitude star,. A second magnitude is 2.512 &#61620;&#61472;2.512 = 6.310 times as bright as a fourth magnitude star. A first magnitude star is 2.512 20 times as bright as a star of the 21st magnitude, the dimmest that can be seen through a 200-inch telescope.

Brightness is normally tabulated to the nearest 0.1 magnitude, about the smallest change that can be detected by the unaided eye of a trained observer. All stars of magnitude 1.50 or brighter are popularly called &#8220;first magnitude&#8221; stars. Those between 1.51 and 2.50 are called &#8220;second magnitude&#8221; stars, those between 2.51 and 3.50 are called &#8220;third magnitude&#8221; stars, etc. Sirius, the brightest star, has a magnitude of &#8211;1.6. The only other star with a negative magnitude is Canopus, &#8211;0.9. At greatest brilliance Venus has a magnitude of about &#8211;4.4. Mars, Jupiter, and Saturn are sometimes of negative magnitude. The full moon has a magnitude of about &#8211;12.6, but varies somewhat. The magnitude of the sun is about &#8211;26.7.

THE UNIVERSE
1505.	The Solar System
The sun, the most conspicuous celestial object in the sky, is the central body of the solar system. Associated with it are at least nine principal planets and thousands of asteroids, comets, and meteors. Some planets like earth have satellites.

Motions Of Bodies Of The Solar System
Astronomers distinguish between two principal motions of celestial bodies. Rotation is a spinning motion about an axis within the body, whereas revolution is the motion of a body in its orbit around another body. The body around which a celestial object revolves is known as that body&#8217;s primary. For the satellites, the primary is a planet. For the planets and other bodies of the solar system, the primary is the sun. The entire solar system is held together by the gravitational force of the sun. The whole system revolves around the center of the Milky Way galaxy (section 1515), and the Milky Way is in motion relative to its neighboring galaxies.

The hierarchies of motions in the universe are caused by the force of gravity. As a result of gravity, bodies attract each other in proportion to their masses and to the inverse square of the distances between them. This force causes the planets to go around the sun in nearly circular, elliptical orbits. In each planet&#8217;s orbit, the point nearest the sun is called the perihelion. The point farthest from the sun is called the aphelion. The line joining perihelion and aphelion is called the line of apsides. In the orbit of the moon, the point nearest the earth is called the perigee, and that point farthest from the earth is called the apogee. Figure 1506 shows the orbit of the earth (with exaggerated eccentricity), and the orbit of the moon around the earth.










The Sun
The sun dominates our solar system. Its mass is nearly a thousand times that of all other bodies of the solar system combined. Its diameter is about 866,000 miles. Since it is a star, it generates its own energy through thermonuclear reactions, thereby providing heat and light for the entire solar system.
The distance from the earth to the sun varies from 91,300,000 at perihelion to 94,500,000 miles at aphelion. When the earth is at perihelion, which always occurs early in January, the sun appears largest, 32.6&#8217; in diameter. Six months later at aphelion, the sun&#8217;s apparent diameter is a minimum of 31.5&#8217;.

Observations of the sun&#8217;s surface (called the photo-sphere) reveal small dark areas called sunspots. These are areas of intense magnetic fields in which relatively cool gas (at 7000 degrees F.) appears dark in contrast to the surrounding hotter gas (10,000 degrees F.). Sunspots vary in size from perhaps 50,000 miles in diameter to the smallest spots that can be detected (a few hundred miles in diameter). They generally appear in groups. Large sunspots can be seen without a telescope if the eyes are protected, as by the shade glasses of a sextant. Surrounding the photosphere is an outer corona of very hot but tenuous gas. This can only be seen during an eclipse of the sun, when the moon blocks the light of the photosphere.










The sun is continuously emitting charged particles, which form the solar wind. As the solar wind sweeps past the earth, these particles interact with the earth&#8217;s magnetic field. If the solar wind is particularly strong, the interaction can produce magnetic storms which adversely affect radio signals on the earth. At such times the auroras are particularly brilliant and widespread.

The sun is moving approximately in the direction of Vega at about 12 miles per second, or about two-thirds as fast as the earth moves in its orbit around the sun. This is in addition to the general motion of the sun around the center of our galaxy.

Planets
The principal bodies orbiting the sun are called planets. Nine principal planets are known: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. 
*Of these, only four are commonly used for celestial navigation:
Venus, Mars, Jupiter, and Saturn.*

Except for Pluto, the orbits of the planets lie in nearly the same plane as the earth&#8217;s orbit. Therefore, as seen from the earth, the planets are confined to a strip of the celestial sphere called the ecliptic.

The two planets with orbits smaller than that of the earth are called inferior planets, and those with orbits larger than that of the earth are called superior planets. The four planets nearest the sun are sometimes called the inner planets, and the others the outer planets. Jupiter, Saturn, Uranus, and Neptune are so much larger than the others that they are sometimes classed as major planets. Uranus is barely visible to the unaided eye; Neptune and Pluto are not visible without a telescope. 

Planets can be identified in the sky because, unlike the stars, they do not twinkle. The stars are so distant that they are virtually point sources of light. Therefore the tiny stream of light from a star is easily scattered by normal motions of air in the atmosphere causing the affect of twinkling. The naked-eye planets, however, are close enough to present perceptible disks. The broader stream of light from a planet is not easily disrupted unless the planet is low on the horizon or the air is especially turbulent.
The orbits of many thousands of tiny minor planets or asteroids lie chiefly between the orbits of Mars and Jupiter. These are all too faint to be seen with the naked eye.

The Earth
In common with other planets, the earth rotates on its axis and revolves in its orbit around the sun. These motions are the principal source of the daily apparent motions of other celestial bodies. *The earth&#8217;s rotation also causes a deflection of water and air currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Because of the earth&#8217;s rotation, high tides on the open sea lag behind the meridian transit of the moon.

If you look at a globe, you will see these prevailing currents shown with arrows.*

For most navigational purposes, the earth can be considered a sphere. However, like the other planets, the earth is approximately an oblate spheroid, or ellipsoid of revolution, flattened at the poles and bulged at the equator. See Figure 1509. Therefore, the polar diameter is less than the equatorial diameter, and the meridians are slightly elliptical, rather than circular. The dimensions of the earth are recomputed from time to time, as additional and more precise measurements become available. Since the earth is not exactly an ellipsoid, results differ slightly when equally precise and extensive measurements are made on different parts of the surface.










1510.	Inferior Planets
Since Mercury and Venus are inside the earth&#8217;s orbit, they always appear in the neighborhood of the sun. Over a period of weeks or months, they appear to oscillate back and forth from one side of the sun to the other. They are seen either in the eastern sky before sunrise or in the western sky after sunset. For brief periods they disappear into the sun&#8217;s glare. At this time they are between the earth and sun (known as inferior conjunction) or on the opposite side of the sun from the earth (superior conjunction). On rare occasions at inferior conjunction, the planet will cross the face of the sun as seen from the earth. This is known as a transit of the sun.

When Mercury or Venus appears most distant from the sun in the evening sky, it is at greatest eastern elongation. (Although the planet is in the western sky, it is at its easternmost point from the sun.) From night to night the planet will approach the sun until it disappears into the glare of twilight. At this time it is moving between the earth and sun to inferior conjunction. A few days later, the planet will appear in the morning sky at dawn. It will gradually move away from the sun to western elongation, then move back toward the sun. After disappearing in the morning twilight, it will move behind the sun to superior conjunction. After this it will reappear in the evening sky, heading toward eastern elongation.

*You have seen this, maybe didn't know why?
*
Mercury is never seen more than about 28 degrees&#61472; from the sun. For this reason it is not commonly used for navigation. Near greatest elongation it appears near the western horizon after sunset, or the eastern horizon before sunrise. At these times it resembles a first magnitude star and is sometimes reported as a new or strange object in the sky. The interval during which it appears as a morning or evening star can vary from about 30 to 50 days. Around inferior conjunction, Mercury disappears for about 5 days; near superior conjunction, it disappears for about 35 days. Observed with a telescope, Mercury is seen to go through phases similar to those of the moon.
Venus can reach a distance of 47 degrees &#61472;from the sun, allowing it to dominate the morning or evening sky. At maximum brilliance, about five weeks before and after inferior conjunction, it has a magnitude of about &#8211;4.4 and is brighter than any other object in the sky except the sun and moon.










At these times it can be seen during the day and is sometimes observed for a celestial line of position. It appears as a morning or evening star for approximately 263 days in succession. Near inferior conjunction Venus disappears for 8 days; around superior conjunction it disappears for 50 days. When it transits the sun, Venus can be seen to the naked eye as a small dot about the size of a group of sunspots. Through binoculars, Venus can be seen to go through a full set of phases.

1511. Superior Planets
As planets outside the earth&#8217;s orbit, the superior planets are not confined to the proximity of the sun as seen from the earth. They can pass behind the sun (conjunction), but they cannot pass between the sun and the earth. Instead we see them move away from the sun until they are opposite the sun in the sky (opposition). When a superior planet is near conjunction, it rises and sets approximately with the sun and is thus lost in the sun&#8217;s glare. Gradually it becomes visible in the early morning sky before sunrise. From day to day, it rises and sets earlier, becoming increasingly visible through the late night hours until dawn. Approaching opposition, the planet will rise in the late evening, until at opposition, it will rise when the sun sets, be visible through-out the night, and set when the sun rises.

Observed against the background stars, the planets normally move eastward in what is called direct motion. Approaching opposition, however, a planet will slow down, pause (at a stationary point), and begin moving westward (retrograde motion), until it reaches the next stationary point and resumes its direct motion. This is not because the planet is moving strangely in space. This relative, observed motion results because the faster moving earth is catching up with and passing by the slower moving superior planet. The superior planets are brightest and closest to the earth at opposition. The interval between oppositions is known as the synodic period. This period is longest for the closest planet, Mars, and becomes increasingly shorter for the outer planets.

Unlike Mercury and Venus, the superior planets do not go through a full cycle of phases. They are always full or highly gibbous.
Mars can usually be identified by its orange color. It can become as bright as magnitude &#8211;2.8 but is more often between &#8211;1.0 and &#8211;2.0 at opposition. Oppositions occur at intervals of about 780 days. The planet is visible for about 330 days on either side of opposition. Near conjunction it is lost from view for about 120 days. Its two satellites can only be seen in a large telescope.

Jupiter, largest of the known planets, normally out-shines Mars, regularly reaching magnitude &#8211;2.0 or brighter at opposition. Oppositions occur at intervals of about 400 days, with the planet being visible for about 180 days be-fore and after opposition. The planet disappears for about 32 days at conjunction. Four satellites (of a total 16 currently known) are bright enough to be seen in binoculars. Their motions around Jupiter can be observed over the course of several hours.

Saturn, the outermost of the navigational planets, comes to opposition at intervals of about 380 days. It is visible for about 175 days before and after opposition, and disappears for about 25 days near conjunction. At opposition it becomes as bright as magnitude +0.8 to &#8211;0.2. Through good, high powered binoculars, Saturn appears as elongated because of its system of rings. A telescope is needed to examine the rings in any detail. Saturn is now known to have at least 18 satellites, none of which are visible to the unaided eye.
Uranus, Neptune and Pluto are too faint to be used for navigation; Uranus, at about magnitude 5.5, is faintly visible to the unaided eye.

1512. The Moon
The moon is the only satellite of direct navigational interest. It revolves around the earth once in about 27.3 days, as measured with respect to the stars. This is called the sidereal month. Because the moon rotates on its axis with the same period with which it revolves around the earth, the same side of the moon is always turned toward the earth. The cycle of phases depends on the moon&#8217;s revolution with respect to the sun. This synodic month is approximately 29.53 days, but can vary from this average by up to a quarter of a day during any given month.
When the moon is in conjunction with the sun (new moon), it rises and sets with the sun and is lost in the sun&#8217;s glare. The moon is always moving eastward at about 12.2 degrees &#61472;per day, so that sometime after conjunction (as little as 16 hours, or as long as two days), the thin lunar crescent can be observed after sunset, low in the west. For the next couple of weeks, the moon will wax, becoming more fully illuminated. From day to day, the moon will rise (and set) later, becoming increasingly visible in the evening sky, until (about 7 days after new moon) it reaches first quarter, when the moon rises about noon and sets about midnight. Over the next week the moon will rise later and later in the after-noon until full moon, when it rises about sunset and dominates the sky throughout the night. During the next couple of weeks the moon will wane, rising later and later at night. By last quarter (a week after full moon), the moon rises about midnight and sets at noon. As it approaches new moon, the moon becomes an increasingly thin crescent, and is seen only in the early morning sky. Sometime before conjunction (16 hours to 2 days before conjunction) the thin crescent will disappear in the glare of morning twilight. At full moon, the sun and moon are on opposite sides of the ecliptic. Therefore, in the winter the full moon rises early, crosses the celestial meridian high in the sky, and sets late; as the sun does in the summer. In the summer the full moon rises in the southeastern part of the sky (Northern Hemisphere), remains relatively low in the sky, and sets along the south-western horizon after a short time above the horizon. At the time of the autumnal equinox, the part of the ecliptic opposite the sun is most nearly parallel to the horizon.

Since the eastward motion of the moon is approximately along the ecliptic, the delay in the time of rising of the full moon from night to night is less than at other times of the year. The full moon nearest the autumnal equinox is called the harvest moon; the full moon a month later is called the hunter&#8217;s moon. See Figure 1512.










1513. Comets And Meteors
Although comets are noted as great spectacles of nature, very few are visible without a telescope. Those that become widely visible do so because they develop long, glowing tails. Comets are swarms of relatively small solid bodies held together by gravity. Around the nucleus, a gaseous head or coma and tail may form as the comet approaches the sun.

The tail is directed away from the sun, so that it follows the head while the comet is approaching the sun, and precedes the head while the comet is receding. The total mass of a comet is very small, and the tail is so thin that stars can easily be seen through it. 

In 1910, the earth passed through the tail of Halley&#8217;s comet without noticeable effect. Compared to the well-ordered orbits of the planets, comets are erratic and inconsistent. Some travel east to west and some west to east, in highly eccentric orbits inclined at any angle to the ecliptic. Periods of revolution range from about 3 years to thousands of years. Some comets may speed away from the solar system after gaining velocity as they pass by Jupiter or Saturn.

The short-period comets long ago lost the gasses needed to form a tail. Long period comets, such as Halley&#8217;s comet, are more likely to develop tails. The visibility of a comet depends very much on how close it approaches the earth. In 1910, Halley&#8217;s comet spread across the sky. Yet when it returned in 1986, the earth was not well situated to get a good view, and it was barely visible to the unaided eye. 










Meteors, popularly called shooting stars, are tiny, solid bodies too small to be seen until heated to incandescence by air friction while passing through the earth&#8217;s atmosphere. A particularly bright meteor is called a fireball.

One that explodes is called a bolide. A meteor that survives its trip through the atmosphere and lands as a solid particle is called a meteorite.
Vast numbers of meteors exist. It has been estimated that an average of about 1,000,000 bright enough to be seen enter the earth&#8217;s atmosphere each hour, and many times this number undoubtedly enter, but are too small to attract attention.

Meteor showers occur at certain times of the year when the earth passes through meteor swarms, the scattered remains of comets that have broken up. At these times the number of meteors observed is many times the usual number. A faint glow sometimes observed extending upward approximately along the ecliptic before sunrise and after sunset has been attributed to the reflection of sunlight from quantities of this material. This glow is called zodiacal light. A faint glow at that point of the ecliptic 180&#61616; degrees from the sun is called the gegenschein or counterglow.

1514. Stars
Stars are distant suns, in many ways resembling the body which provides the earth with most of its light and heat. Like the sun, stars are massive balls of gas that create their own energy through thermonuclear reactions. Although stars differ in size and temperature, these differences are apparent only through analysis by astronomers. Some differences in color are noticeable to the unaided eye. While most stars appear white, some (those of lower temperature) have a reddish hue. In Orion, blue Rigel and red Betelgeuse, located on opposite sides of the belt, constitute a noticeable contrast.
The stars are not distributed uniformly around the sky. Striking configurations, known as constellations, were noted by ancient peoples, who supplied them with names and myths. Today astronomers use constellations&#8212;88 in all&#8212;to identify areas of the sky.

Under ideal viewing conditions, the dimmest star that can be seen with the unaided eye is of the sixth magnitude. In the entire sky there are about 6,000 stars of this magnitude or brighter. Half of these are below the horizon at any time. Because of the greater absorption of light near the horizon, where the path of a ray travels for a greater distance through the atmosphere, not more than perhaps 2,500 stars are visible to the unaided eye at any time. However, the average navigator seldom uses more than perhaps 20 or 30 of the brighter stars.
Stars which exhibit a noticeable change of magnitude are called variable stars. A star which suddenly becomes several magnitudes brighter and then gradually fades is called a nova. A particularly bright nova is called a supernova.

Two stars which appear to be very close together are called a double star. If more than two stars are included in the group, it is called a multiple star. 
A group of a few dozen to several hundred stars moving through space together is called an open cluster. The Pleiades is an example of an open cluster. There are also spherically symmetric clusters of hundreds of thousands of stars known as globular clusters. The globular clusters are all too distant to be seen with the naked eye.

A cloudy patch of matter in the heavens is called a nebula. If it is within the galaxy of which the sun is a part, it is called a galactic nebula; if outside, it is called an extragalactic nebula.

Motion of a star through space can be classified by its vector components. That component in the line of sight is called radial motion, while that component across the line of sight, causing a star to change its apparent position relative to the background of more distant stars, is called proper motion.

1515.	Galaxies
A galaxy is a vast collection of clusters of stars and clouds of gas. The earth is located in the Milky Way galaxy, a slowly spinning disk more than 100,000 light years in diameter. All the bright stars in the sky are in the Milky Way. However, the most dense portions of the galaxy are seen as the great, broad band that glows in the summer nighttime sky. When we look toward the constellation Sagittarius, we are looking toward the center of the Milky Way, 30,000 light years away. Despite their size and luminance, almost all other galaxies are too far away to be seen with the unaided eye. An exception in the northern hemisphere is the Great Galaxy (sometimes called the Great Nebula) in Andromeda, which appears as a faint glow. In the southern hemisphere, the Large and Small Magellanic Clouds (named after Ferdinand Magellan) are the nearest known neighbors of the Milky Way. They are approximately 1,700,000 light years distant. The Magellanic Clouds can be seen as sizable glowing patches in the southern sky.










*To be cont.*


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## Fishers of Men

*Shoot, I got caught by the wind, drifted away and left chapter 14 behind, so here it is:
CHAPTER 14
ECDIS AND THE INTEGRATED BRIDGE
INTRODUCTION*
Operating Concept
Bridge watch officers have three main duties:
Navigation
&#8226;	Watch officers process navigation information from several different sources. They take fix positions from satellite and hyperbolic receivers. They measure bearing lines and radar ranges to suitable NAVAIDS. They then plot this information on a paper chart.
&#8226;	After plotting the information on a chart, watch officers evaluate the navigation picture. They determine if the ship&#8217;s present position is a safe one. They project the ship&#8217;s position ahead and plan for future contingencies. The evaluation step is the most important step in the navigation process. Properly executing this step is a function of the watch officer&#8217;s skill and how well the ship&#8217;s actual navigation situation is represented on the chart. 
That representation, in turn, is a function of both plotter and sensor accuracy.

Collision Avoidance
&#8226;	Watch officers evaluate the contact situation and calculate the closest points of approach (CPA&#8217;s) for various contacts.
&#8226;	Watch officers maneuver in accordance with the Rules of the Road to avoid close CPA&#8217;s and collisions.
Ship Management
&#8226;	Watch officers conduct evolutions that are part of an individual ship&#8217;s routine.
The integrated bridge is designed to reduce the time spent on navigation by eliminating manual data processing and providing the navigator with a display which aids him in quickly evaluating the navigation picture. Preliminary studies seem to indicate that time spent on navigation as a percentage of total watch officer duties drops significantly when using the integrated bridge. This does not necessarily lower the overall watch officer work-load, but it does increase the percentage of time he can devote to ship management and collision avoidance.

THE INTEGRATED BRIDGE
System Components
The term &#8220;integrated bridge&#8221; encompasses several possible combinations of equipment and software designed specifically for each individual vessel&#8217;s needs. Therefore, each integrated bridge system is different. This section introduces, in general terms, the major equipment likely to be found in an integrated bridge system.
&#8226;	Computer Processor and Network: This subsystem controls the processing of information from the ship&#8217;s navigation sensors and the flow of information between various system components. It takes inputs from the vessel&#8217;s navigation sensors. Electronic positioning information, contact information from radar, and gyro compass outputs, for ex-ample, can be integrated with the electronic chart to present the complete navigation and tactical picture to the conning officer. The system&#8217;s computer network processes the positioning information and controls the integrated bridge system&#8217;s display and control functions.
&#8226;	Chart Data Base: At the heart of any integrated bridge system lies an electronic chart. An electronic chart system meeting International Maritime Organization (IMO) specifications for complying with chart carrying requirements is an Electronic Chart Display and Information System (EC-DIS).
All other electronic charts are known as Electronic Chart Systems (ECS). Following sections discuss the differences between these two types of electronic charts.

An integrated bridge system may receive electronic chart data from the system manufacturer or from the appropriate government agency. The mariner can also digitize an existing paper chart if the system manufacturer provides a digitizer. Electronic charts can differentiate between and display different types of data far better than conventional charts. Paper charts are usually limited to four colors, and they display all their data continuously. An electronic chart can display several colors, and it can display only the data the user needs. If the electronic chart is part of an ECDIS, however, it must always display the minimum data required by IMO/IHO. The database for a typical civilian electronic chart contains layers consisting of hydrography, aids to navigation, obstructions, port facilities, shoreline, regulatory boundaries and certain topographic features. Other layers such as communication networks, power grids, detailed bathymetry, and radar reflectivity can also be made available. This allows the user to customize his chart according to his particular needs, something a paper chart cannot do.
System Display: This unit displays the ship&#8217;s position on an electronic chart and provides information on sensor status and ship&#8217;s control systems. It displays heading data and ship&#8217;s speed. It provides a station where the operator can input warning parameters such as minimum depth under the keel or maximum cross track error. It plots the ship&#8217;s position and its position in relation to a predetermined track.

There are two possible modes of display, relative and true. In the relative mode the ship remains fixed in the center of the screen and the chart moves past it. This requires a lot of computer power, as all the screen data must be updated and re-drawn at each fix. 

In true mode, the chart remains fixed and the ship moves across it. The operator always has the choice of the north-up display. On some equipment, the operator can select the course-up display as well. Each time the ship approaches the edge of the display, the screen will re-draw with the ship centered or at the opposite edge.

A separate monitor, or a window in the navigation monitor, can be used for display of alpha-numeric data such as course, speed, and cross-track error. It can also be used to display small scale charts of the area being navigated, or to look at other areas while the main display shows the ship&#8217;s current situation.

Planning Station: The navigator does his voyage planning at this station. He calculates great circle courses, planned tracks, and waypoints. The navigator digitizes his charts, if required, at this planning station.

Control System: Some integrated bridges provide a system that automatically adjusts course and speed to follow a planned track. If the system is equipped with this feature, the navigation process is reduced to monitoring system response and providing operator action when required by either a changing tactical situation or a system casualty.

Radar: Radar for navigation and collision avoidance is included in the integrated bridge. Since both the chart and the radar process their data digitally, data transfer between the two is possible. The &#8220;picture&#8221; from either one can be imposed on top of the picture of the other. This allows the navigator to see an integrated navigation and tactical display and to avoid both navigation hazards and interfering contacts.

ELECTRONIC CHART DISPLAY AND INFORMATION SYSTEM
The unqualified use of the electronic chart in the integrated bridge depends on the legal status of the electronic chart system in use. The IMO has defined the Electronic Chart Display and Information System as the integrated bridge system that complies with the up-to-date chart carrying requirements of international law. The Electronic Nautical Chart (ENC) is the ship&#8217;s electronic chart data base used in an ECDIS system. The ENC is a subset of the Electronic Chart Database (ECDB), the digital chart data-base maintained by the national hydrographic authority. ECDIS standards are still under development. This section will discuss some basic ECDIS design criteria.

Digital Chart Data Formats
One question in the development of ECDIS has been whether the nautical chart should be digitized in raster or vector format.

Raster chart data is a digitized &#8220;picture&#8221; of a chart. All data is in one layer and one format. The video display simply reproduces the picture from its digitized data file. With raster data, it is difficult to change individual elements of the chart since they are not separated in the data file. Raster data files tend to be large, since a data point must be entered for every picture element (pixel) on the chart. 

Vector chart data is organized into many separate files. It contains graphics programs to produce certain symbols, lines, area colors, and other chart elements. The programmer can change individual elements in the file and tag elements with additional data. Vector files are smaller and more versatile than raster files of the same area. The navigator can selectively display vector data, adjusting the display according to his needs. Current IMO/IHO standards for ECDIS recognize only the vector format as adequate. Whether a digital chart system uses a raster or vector data base, any change to that data base must come only from the hydrographic office (HO) that produced the ENC. Corrections from other sources affecting the data base should be applied only as an overlay to the official data base. This protects the integrity of the official data base.

Digital Chart Data Transfer
The IMO, in its performance standards for ECDIS, has mandated that individual national hydrographic offices will supply official ENC data for ECDIS use. A preliminary data transfer standard, known as DX 90, has been proposed within the IHO; IHO is debating the utility of this standard. Regardless of the transfer standard recommended, each national hydrographic office that produces a data base will decide what transfer standard it will use.
To ensure the reliability of the data, the ECDIS must not allow data from an unofficial source to erase, overwrite, or modify HO supplied data.

ECDIS Warnings And Alarms
Since the ECDIS is a &#8220;smart&#8221; system which combines several different functions into one computerized system, it is possible to program it to sound alarms or display warnings when certain parameters are met or exceeded. This helps the navigator to monitor close navigation hazards. IMO standards require that certain alarms be available on the ECDIS. Among these are:
1.	Deviating from a planned route.
2.	Chart on a different geodetic datum from the positioning system.
3.	Approach to waypoints and other critical points.
4.	Exceeding cross-track limits.
5.	Chart data displayed overscale (larger scale than originally digitized).
6.	Larger scale chart available.
7.	Failure of the positioning system.
8.	Vessel crossing safety contour.
9.	System malfunction or failure.
Alarms consist of audible and visible warnings. The navigator may determine some setpoints. For example, he may designate a safety depth contour or set a maximum allowed cross-track error. Operational details vary from one system to another, but all ECDIS will have the basic alarm capabilities noted. The navigator is responsible for becoming familiar with the system aboard his own ship and using it effectively.

ECDIS Units
The following units of measure will appear on the EC-DIS chart display:
Position: Latitude and Longitude will be shown in degrees, minutes, and decimal minutes, normally based on WGS-84 datum.

Depth: Depth will be indicated in meters and decimeters. Fathoms and feet may be used as an interim measure only:
when existing chart udata is held in those units only.
when there is an urgent need for an ENC of the applicable area, and time does not allow for an immediate conversion of the English units to their metric equivalents.

Height: Meters (preferred) or feet.
Distance: Nautical miles and decimal miles, or meters.
Speed: Knots and decimal knots.

ECDIS Priority Layers
ECDIS requires data layers to establish a priority of data displayed. The minimum number of information categories required and their relative priority from the highest to lowest priority, are listed below:
ECDIS Warnings and Messages.
Hydrographic Office Data.
Notice to Mariners Information.
Hydrographic Office Cautions.
Hydrographic Office Color-Fill Area Data.
Hydrographic Office On Demand Data.
Radar Information.
User&#8217;s Data.
Manufacturer&#8217;s Data.
User&#8217;s Color-Fill Area Data.
Manufacturer&#8217;s Color-Fill Area Data.

IMO standards for ECDIS will require that the operator be able to deselect the radar picture from the chart with minimum operator action for fast &#8220;uncluttering&#8221; of the chart presentation.

ECDIS Calculation Requirements
As a minimum, an ECDIS system must be able to per-form the following calculations:
Geographical coordinates to display coordinates, and display coordinates to geographical coordinates.

Transformation from local datum to WGS-84.
True distance and azimuth between two geographical positions.
Geographic position from a known position given distance and azimuth.
Projection calculations such as great circle and rhumb line courses and distances.

ELECTRONIC CHART SYSTEMS
ECS And ECDIS
Electronic Chart Systems (ECS) are those digital chart display systems that do not meet the IMO requirements for ECDIS. Until an ECDIS standard is approved and a particular ECS meets that standard, no ECS can be classified as an ECDIS. The practical consequence of this distinction is that an ECS cannot be used to replace a paper chart.

Legal requirements notwithstanding, several companies are producing very sophisticated integrated bridge systems based on electronic chart systems. These integrated bridges combine accurate electronic positioning sensors with electronic chart presentations to produce a video representation of a chart which displays and updates the ship&#8217;s charted position at frequent intervals. Electronic charts can also display tracklines, cross-track error, and other operational data. These systems have the potential to integrate radar systems and control systems to create a fully integrated bridge. The uncertainty surrounding the final ECDIS standard has not lessened the marine community&#8217;s demand to exploit the potential of this revolutionary technology. One consequence of this demand has been that some national hydrographic offices are producing official digital raster charts for use in electronic charting systems. In addition, a number of commercial companies have been licensed to digitize the paper charts of various national hydrographic offices. However, these are not the data bases envisioned by the IMO standard.

Remember that ECDIS is a system. The electronic chart data base is only a subset of this system. Therefore, even though electronic charts come from a national hydro-graphic office or from official charts, the integrated bridge system in which the chart is used may not meet the ECDIS system requirements.

System Description
DMA&#8217;s Vector Product Format (VPF) Digital Nautical Charts (DNC&#8217;s) are used in conjunction with the Navy&#8217;s version of the integrated bridge: the Navigation Sensor System Interface (NAVSSI). NAVSSI is being developed to fulfill three important functions:

Navigation Safety: NAVSSI distributes real time navigation data to the navigation team members to ensure navigation safety.

Weapons System Support: NAVSSI provides guidance initialization for use by weapons systems.

Battlegroup Planning: NAVSSI provides a worksation for battlegroup planning.
The navigation function of NAVSSI, therefore, is only one of several functions accomplished by the system. The navigational portion of NAVSSI is being designed to comply with the IMO/IHO ECDIS standards for content and function.

The heart of NAVSSI is the Real Time Subsystem (RTS). The RTS receives, processes and distributes navigational data to the navigation display, weapons systems, and other networked vessels. This ensures that all elements of a battle group have the same navigational picture. Inputs come from GPS, Loran, inertial navigation systems, gyro-compass, and speed log. The bridge display consists of a monitor and control panel, while the RTS is mounted below decks. ENC&#8217;s are contained in the Display and Control Subsystem (DCS) typically mounted in the chartroom with a monitor on the bridge. This is unlike many current commercial systems which have all hardware and software in a single unit on the bridge. A separate NAVSSI software package supports operator interface, waypoint capability, collision and grounding avoidance features, and other aspects of an ECDIS.

Figure 1410 illustrates a basic block diagram of the NAVSSI system. The RTS takes inputs from the inertial navigators (WSN-5&#8217;s), the GPS PPS (WRN-6), the gyro compass, the EM Log, and the SRN-25. The SRN-25 out-puts GPS SPS, Transit SATNAV, and Omega positions. 

The RTS distributes navigation information to the various tactical applications requiring navigation input, and it communicates via a fiber optic network with the DCS. The DCS exchanges information with the Navigator&#8217;s Workstation.










The Digital Nautical Chart
NAVSSI uses the Digital Nautical Chart (DNC) as its chart database. The DNC is in Vector Product Format and is based on the contents of the traditional paper harbor, approach, and coastal charts produced by DMA and NOS.

Horizontal datum is WGS 84 (NAD 83 in the U. S. is equivalent). There are three vertical datums. Topographic features are referenced to Mean Sea Level, and the shore line is referenced to Mean High Water. Hydrography is referenced to a low water level suitable for the region. All measurements are metric.
DNC data is layered together into 12 related feature classes:
Cultural Landmarks
Earth Cover
Inland Waterways
Relief
Landcover
Port Facilities
Aids to Navigation
Obstructions
Hydrography
Environment
Maritime Limiting Lines (channels, demarcation lines, anchorages, etc.)
Data Quality
Content is generally the same as on a paper chart. The data is stored in libraries; each library represents a different level of detail. The libraries are then stored on CD-ROM and organized as tiles according to the World Geodetic Reference System (GEOREF) tiling scheme.

Tile sizes are 15&#8217; X 15&#8217; for harbor charts, 30&#8217; X 30&#8217; for approach charts, and 3&#176; X 3&#176; for general charts. The data now contained on as many as 4000 conventional charts will eventually be contained on as few as 30 CD&#8217;s.

Correcting The Digital Nautical Chart
There are currently three proposed methods for correcting the DNC data base: Interactive Entry, Semi-Automatic Entry, and Fully Automatic Entry.
Interactive Entry: This method requires the interactive application of the textual Notice to Mariners. The operator determines the corrections from the Notice. Then, using a toolkit, he selects the symbol appropriate to the correction required, identifies the location of the symbol, and adds the appropriate textual information identifying the nature of the correction. This method of correction is labor intensive and subject to operator error. It also clutters the screen display because it can be applied only as an overlay to the ENC data. Semi-Automatic Entry: This method requires the operator to enter the correction data furnished in correct digital format by the originating hydrographic office into the system via electronic medium (a modem or floppy disc, for example). The ECDIS then processes these corrections automatically and displays an updated chart with the changed data indistinguishable from the remaining original data base.

Fully Automatic Entry: The fully automatic method of correction entry allows for a direct telecommunications link to receive the official digital update and input it into the ECDIS. This process is completely independent of any operator interface. Internal ECDIS processing is the same as that for semi-automatic updating of the data base.

CONCLUSION
The emergence of extremely accurate electronic positioning systems coupled with the technology to produce an electronic chart is effecting a revolution in navigation. When fully mature, this technology will replace the paper charts and plotting instruments used by navigators since the beginning of sea exploration. There are several hurdles to overcome in the process of full replacement of paper charts, some legal, some bureaucratic, and some technical. Until those hurdles are overcome, electronic charting will be in a transitional state, useful as a backup to traditional techniques, but insufficient to replace them. How this transition period will play out and the final form of the internationally recognized ECDIS system are subjects for the next edition of The American Practical Navigator.

*By the way, I forgot to mention that ALL charts are in the process of changing to the metric system. They are even out now.

End ch 14*


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## Fishers of Men

*Chapter 15 cont.
APPARENT MOTION*
1516.	Apparent Motion Due To Rotation Of The Earth
Apparent motion caused by the earth&#8217;s rotation is much greater than any other observed motion of celestial bodies. It is this motion that causes celestial bodies to appear to rise along the eastern half of the horizon, climb to maximum altitude as they cross the meridian, and set along the western horizon, at about the same point relative to due west as the rising point was to due east. This apparent motion along the daily path, or diurnal circle, of the body is approximately parallel to the plane of the equator. It would be exactly so if rotation of the earth were the only motion and the axis of rotation of the earth were stationary in space. The apparent effect due to rotation of the earth varies with the latitude of the observer. At the equator, where the equatorial plane is vertical (since the axis of rotation of the earth is parallel to the plane of the horizon), bodies appear to rise and set vertically. 

Every celestial body is above the horizon approximately half the time. The celestial sphere as seen by an observer at the equator is called the right sphere, shown in Figure 1516a.










For an observer at one of the poles, bodies having constant declination neither rise nor set (neglecting precession of the equinoxes and changes in refraction), but circle the sky, always at the same altitude, making one complete trip around the horizon each day. At the North Pole the motion is clockwise, and at the South Pole it is counterclockwise. Approximately half the stars are always above the horizon and the other half never are. The parallel sphere at the poles is illustrated in Figure 1516b.










Between these two extremes, the apparent motion is a combination of the two. On this oblique sphere, illustrated in Figure 1516c, circumpolar celestial bodies remain above the horizon during the entire 24 hours, circling the elevated celestial pole each day. The stars of Ursa Major (the Big Dipper) and Cassiopeia are circumpolar for many observers in the United States. An approximately equal part of the celestial sphere remains below the horizon during the entire day. Crux is not visible to most observers in the United States. Other bodies rise obliquely along the eastern horizon, climb to maximum altitude at the celestial meridian, and set along the western horizon. The length of time above the horizon and the altitude at meridian transit vary with both the latitude of the observer and the declination of the body. At the polar circles of the earth even the sun becomes circumpolar. This is the land of the midnight sun, where the sun does not set during part of the summer and does not rise during part of the winter.

The increased obliquity at higher latitudes explains why days and nights are always about the same longer in higher latitudes. Twilight is the period of length in the tropics, and the change of length of the day becomes greater as the latitude increases. It also explains why twilight lasts incomplete darkness following sunset and preceding sunrise.

Evening twilight starts at sunset, and morning twilight ends at sunrise. The darker limit of twilight occurs when the center of the sun is a stated number of degrees below the celestial horizon. Three kinds of twilight are defined: civil, nautical and astronomical.

The conditions at the darker limit are relative and vary considerably under different atmospheric conditions In Figure 1516d, the twilight band is shown, with the darker limits of the various kinds indicated. 










The nearly vertical celestial equator line is for an observer at latitude 20&#176;N. The nearly horizontal celestial equator line is for an observer at latitude 60&#176;N. The broken line in each case is the diurnal circle of the sun when its declination is 15&#176;N. 

The relative duration of any kind of twilight at the two latitudes is indicated by the portion of the diurnal circle between the horizon and the darker limit, although it is not directly proportional to the relative length of line shown since the projection is orthographic. The duration of twilight at the higher latitude is longer, proportionally, than shown. Note that complete darkness does not occur at latitude 60&#176;N when the declination of the sun is 15&#176;N.

1517.	Apparent Motion Due To Revolution Of The Earth
If it were possible to stop the rotation of the earth so that the celestial sphere would appear stationary, the effects of the revolution of the earth would become more noticeable. In one year the sun would appear to make one complete trip around the earth, from west to east. Hence, it would seem to move eastward a little less than 1&#176; per day. This motion can be observed by watching the changing position of the sun among the stars. But since both sun and stars generally are not visible at the same time, a better way is to observe the constellations at the same time each night. On any night a star rises nearly four minutes earlier than on the previous night. Thus, the celestial sphere appears to shift westward nearly 1&#176; each night, so that different constellations are associated with different seasons of the year. Apparent motions of planets and the moon are due to a combination of their motions and those of the earth. If the rotation of the earth were stopped, the combined apparent motion due to the revolutions of the earth and other bodies would be similar to that occurring if both rotation and revolution of the earth were stopped. Stars would appear nearly stationary in the sky but would undergo a small annual cycle of change due to aberration. The motion of the earth in its orbit is sufficiently fast to cause the light from stars to appear to shift slightly in the direction of the earth&#8217;s motion. This is similar to the effect one experiences when walking in vertically-falling rain that appears to come from ahead due to the observer&#8217;s own forward motion. The apparent direction of the light ray from the star is the vector difference of the motion of light and the motion of the earth, similar to that of apparent wind on a moving vessel. This effect is most apparent for a body perpendicular to the line of travel of the earth in its orbit, for which it reaches a maximum value of 20.5&#8221;. The effect of aberration can be noted by comparing the coordinates (declination and sidereal hour angle) of various stars through-out the year. 

A change is observed in some bodies as the year progresses, but at the end of the year the values have returned almost to what they were at the beginning. The reason they do not return exactly is due to proper motion and precession of the equinoxes. It is also due to nutation, an irregularity in the motion of the earth due to the disturbing effect of other celestial bodies, principally the moon. Polar motion is a slight wobbling of the earth about its axis of rotation and sometimes wandering of the poles. This motion, which does not exceed 40 feet from the mean position, produces slight variation of latitude and longitude of places on the earth.

1518.	Apparent Motion Due To Movement Of Other Celestial Bodies
Even if it were possible to stop both the rotation and revolution of the earth, celestial bodies would not appear stationary on the celestial sphere. The moon would make one revolution about the earth each sidereal month, rising in the west and setting in the east. The inferior planets would appear to move eastward and westward relative to the sun, staying within the zodiac. Superior planets would appear to make one revolution around the earth, from west to east, each sidereal period.

Since the sun (and the earth with it) and all other stars are in motion relative to each other, slow apparent motions would result in slight changes in the positions of the stars relative to each other. This space motion is, in fact, observed by telescope. The component of such motion across the line of sight, called proper motion, produces a change in the apparent position of the star. The maximum which has been observed is that of Barnard&#8217;s Star, which is moving at the rate of 10.3 seconds per year. This is a tenth-magnitude star, not visible to the unaided eye. Of the 57 stars listed on the daily
pages of the almanacs, Rigil Kentaurus has the greatest proper motion, about 3.7 seconds per year. 

Arcturus, with 2.3 seconds per year, has the greatest proper motion of the navigational stars in the Northern Hemisphere. In a few thousand years proper motion will be sufficient to materially alter some familiar configurations of stars, notably Ursa Major.

1519. The Ecliptic
The ecliptic is the path the sun appears to take among the stars due to the annual revolution of the earth in its orbit. It is considered a great circle of the celestial sphere, inclined at an angle of about 23&#176;26&#8217; to the celestial equator, but undergoing a continuous slight change. 

This angle is called the obliquity of the ecliptic. This inclination is due to the fact that the axis of rotation of the earth is not perpendicular to its orbit. It is this inclination which causes the sun to appear to move north and south during the year, giving the earth its seasons and changing lengths of periods of daylight.

Refer to Figure 1519a. The earth is at perihelion early in January and at aphelion 6 months later. On or about June 21, about 10 or 11 days before reaching aphelion, the northern part of the earth&#8217;s axis is tilted toward the sun. The north polar regions are having continuous sunlight; the Northern Hemisphere is having its summer with long, warm days and short nights; the Southern Hemisphere is having winter with short days and long, cold nights; and the south polar region is in continuous darkness. This is the summer solstice. 

Three months later, about September 23, the earth has moved a quarter of the way around the sun, but its axis of rotation still points in about the same direction in space. The sun shines equally on both hemispheres, and days and nights are the same length over the entire world. The sun is setting at the North Pole and rising at the South Pole. The Northern Hemisphere is having its autumn, and the Southern Hemisphere its spring. This is the autumnal equinox. In another three months, on or about December 22, the Southern Hemisphere is tilted toward the sun and conditions are the reverse of those six months earlier; the Northern Hemisphere is having its winter, and the Southern Hemisphere its summer. 

This is the winter solstice. Three months later, when both hemispheres again receive equal amounts of sunshine, the Northern Hemisphere is having spring and the Southern Hemisphere autumn, the reverse of conditions six months before. This is the vernal equinox. The word &#8220;equinox,&#8221; meaning &#8220;equal nights,&#8221; is applied because it occurs at the time when days and nights are of approximately equal length all over the earth. The word &#8220;solstice,&#8221; meaning &#8220;sun stands still,&#8221; is applied because the sun stops its apparent northward or southward motion and momentarily &#8220;stands still&#8221; before it starts in the opposite direction. This action, somewhat analogous to the &#8220;stand&#8221; of the tide, refers to the motion in a north-south direction only, and not to the daily apparent revolution around the earth. Note that it does not occur when the earth is at perihelion or aphelion. Refer to Figure 1519a. 










At the time of the vernal equinox, the sun is directly over the equator, crossing from the Southern Hemisphere to the Northern Hemisphere. It rises due east and sets due west, remaining above the horizon for approximately 12 hours. It is not exactly 12 hours because of refraction, semidiameter, and the height of the eye of the observer. These cause it to be above the horizon a little longer than below the horizon. Following the vernal equinox, the northerly declination increases, and the sun climbs higher in the sky each day (at the latitudes of the United States), until the summer solstice, when a declination of about 23&#176;26&#8217; north of the celestial equator is reached. The sun then gradually retreats southward until it is again over the equator at the autumnal equinox, at about 23&#176;26&#8217; south of the celestial equator at the winter solstice, and back over the celestial equator again at the next vernal equinox. 

The sun is nearest the earth during the northern hemisphere winter; it is not the distance between the earth and sun that is responsible for the difference in temperature during the different seasons. The reason is to be found in the altitude of the sun in the sky and the length of time it remains above the horizon. During the summer the rays are more nearly vertical, and hence more concentrated, as shown in Figure 1519b. 










Since the sun is above the horizon more than half the time, heat is being added by absorption during a longer period than it is being lost by radiation. This explains the lag of the seasons. Following the longest day, the earth continues to receive more heat than it dissipates, but at a decreasing proportion. Gradually the proportion decreases until a balance is reached, after which the earth cools, losing more heat than it gains. This is analogous to the day, when the highest temperatures normally occur several hours after the sun reaches maximum altitude at meridian transit. A similar lag occurs at other seasons of the year. Astronomically, the seasons begin at the equinoxes and solstices. Meteorologically, they differ from place to place.

Since the earth travels faster when nearest the sun, the northern hemisphere (astronomical) winter is shorter than its summer by about seven days.
Everywhere between the parallels of about 23 degrees 26&#8217;N and about 23 degrees 26&#8217;S the sun is directly overhead at some time during the year. Except at the extremes, this occurs twice: once as the sun appears to move northward, and the second time as it moves southward. This is the torrid zone. 

The northern limit is the Tropic of Cancer, and the southern limit&#8217;s the Tropic of Capricorn. These names come from the constellations which the sun entered at the solstices when the names were first applied more than 2,000 years ago. Today, the sun is in the next constellation toward the west because of precession of the equinoxes. The parallels about 23 degrees 26&#8217; from the poles, marking the approximate limits of the circumpolar sun, are called polar circles, the one in the Northern Hemisphere being the Arctic Circle and the one in the Southern Hemisphere the Antarctic Circle. The areas inside the polar circles are the north and south frigid zones. The regions between the frigid zones and the torrid zones are the north and south temperate zones. The expression &#8220;vernal equinox&#8221; and associated expressions are applied both to the times and points of occurrence of the various phenomena. 

Navigationally, the vernal equinox is sometimes called the first point of Aries because, when the name was given, the sun entered the constellation Aries, the ram, at this time.

This point is of interest to navigators because it is the origin for measuring sidereal hour angle. The expressions March equinox, June solstice, September equinox, and December solstice are occasionally applied as appropriate, because the more common names are associated with the seasons in the Northern Hemisphere and are six months out of step for the Southern Hemisphere.

The axis of the earth is undergoing a precessional motion similar to that of a top spinning with its axis tilted. In about 25,800 years the axis completes a cycle and returns to the position from which it started. Since the celestial equator is 90&#176; from the celestial poles, it too is moving. The result is a slow westward movement of the equinoxes and solstices, which has already carried them about 30&#176;, or one constellation, along the ecliptic from the positions they occupied when named more than 2,000 years ago. Since sidereal hour angle is measured from the vernal equinox, and declination from the celestial equator, the coordinates of celestial bodies would be changing even if the bodies themselves were stationary. 

This westward motion of the equinoxes along the ecliptic is called precession of the equinoxes. The total amount, called general precession, is about 50.27 seconds per year (in 1975). It may be considered divided into two components: precession in right ascension (about 46.10 seconds per year) measured along the celestial equator, and precession in declination (about 20.04&#8221; per year) measured perpendicular to the celestial equator. The annual change in the coordinates of any given star, due to precession alone, depends upon its position on the celestial sphere, since these coordinates are measured relative to the polar axis while the precessional motion is relative to the ecliptic axis.

Due to precession of the equinoxes, the celestial poles are slowly describing circles in the sky. The north celestial pole is moving closer to Polaris, which it will pass at a distance of approximately 28 minutes about the year 2102.

Following this, the polar distance will increase, and eventually other stars, in their turn, will become the Pole Star.
The precession of the earth&#8217;s axis is the result of gravitational forces exerted principally by the sun and moon on the earth&#8217;s equatorial bulge. The spinning earth responds to these forces in the manner of a gyroscope. Regression of the nodes introduces certain irregularities known as nutation in the precessional motion.

1520.	The Zodiac
The zodiac is a circular band of the sky extending 8&#176; on each side of the ecliptic. The navigational planets and the moon are within these limits. The zodiac is divided into 12 sections of 30&#176; each, each section being given the name and symbol (&#8220;sign&#8221 of a constellation. These are shown in Figure 1520. 










The names were assigned more than 2,000 years ago, when the sun entered Aries at the vernal equinox, Cancer at the summer solstice, Libra at the autumnal equinox, and Capricornus at the winter solstice. Because of precession, the zodiacal signs have shifted with respect to the constellations. Thus at the time of the vernal equinox, the sun is said to be at the &#8220;first point of Aries,&#8221; though it is in the constellation Pisces. The complete list of signs and names is given below.

Remember all that &#8220;time&#8221; discussion we did? Think you were confused then? Now you need it again! 

1521.	Time And The Calendar
Traditionally, astronomy has furnished the basis for measurement of time, a subject of primary importance to the navigator. 
The year is associated with the revolution of the earth in its orbit. 
The day is one rotation of the earth about its axis.
The duration of one rotation of the earth depends upon the external reference point used. One rotation relative to the sun is called a solar day. However, rotation relative to the apparent sun (the actual sun that appears in the sky) does not provide time of uniform rate because of variations in the rate of revolution and rotation of the earth. The error due to lack of uniform rate of revolution is removed by using a fictitious mean sun.

Thus, mean solar time is nearly equal to the average apparent solar time. Because the accumulated difference between these times, called the equation of time, is continually changing, the period of daylight is shifting slightly, in addition to its increase or decrease in length due to changing declination. Apparent and mean suns seldom cross the celestial meridian at the same time. The earliest sunset (in latitudes of the United States) occurs about two weeks before the winter solstice, and the latest sunrise occurs about two weeks after winter solstice. A similar but smaller apparent discrepancy occurs at the summer solstice.

Universal Time is a particular case of the measure known in general as mean solar time. Universal Time is the mean solar time on the Greenwich meridian, reckoned in days of 24 mean solar hours beginning with 0 hours at mid-night. Universal Time and sidereal time are rigorously related by a formula so that if one is known the other can be found. Universal Time is the standard in the application of astronomy to navigation.

If the vernal equinox is used as the reference, a sidereal day is obtained, and from it, sidereal time. This indicates the approximate positions of the stars, and for this reason it is the basis of star charts and star finders. Because of the revolution of the earth around the sun, a sidereal day is about 3 minutes 56 seconds shorter than a solar day, and there is one more sidereal than solar days in a year. One mean solar day equals 1.00273791 mean sidereal days.

Because of precession of the equinoxes, one rotation of the earth with respect to the stars is not quite the same as one rotation with respect to the vernal equinox. One mean solar day averages 1.0027378118868 rotations of the earth with respect to the stars.

In tide analysis, the moon is sometimes used as the reference, producing a lunar day averaging 24 hours 50 minutes (mean solar units) in length, and lunar time.

Since each kind of day is divided arbitrarily into 24 hours, each hour having 60 minutes of 60 seconds, the length of each of these units differs somewhat in the various kinds of time.
Time is also classified according to the terrestrial meridian used as a reference. Local time results if one&#8217;s own meridian is used, zone time if a nearby reference meridian is used over a spread of longitudes, and Greenwich or Universal Time if the Greenwich meridian is used.

The period from one vernal equinox to the next (the cycle of the seasons) is known as the tropical year. It is approximately 365 days, 5 hours, 48 minutes, 45 seconds, though the length has been slowly changing for many centuries. 

Our calendar, the Gregorian calendar, approximates the tropical year with a combination of common years of 365 days and leap years of 366 days. A leap year is any year divisible by four, unless it is a century year, which must be divisible by 400 to be a leap year. Thus, 1700, 1800, and 1900 were not leap years, but 2000 will be. A critical mistake was made by John Hamilton Moore in calling 1800 a leap year, causing an error in the tables in his book, The Practical Navigator. This error caused the loss of at least one ship and was later discovered by Nathaniel Bowditch while writing the first edition of The New American Practical Navigator.

See Chapter 18 for an in-depth discussion of time, And you can review our time section towards the beginning of this thread.

Just think, this all came about after a &#8220;just good read&#8221; post called: Moonglow the forgotten magic of our heavenly satellite&#8221; 

1522. Eclipses
If the orbit of the moon coincided with the plane of the ecliptic, the moon would pass in front of the sun at every new moon, causing a solar eclipse. At full moon, the moon would pass through the earth&#8217;s shadow, causing a lunar eclipse. 

Because of the moon&#8217;s orbit is inclined 5&#176;&#61472; with respect to the ecliptic, the moon usually passes above or below the sun at new moon and above or below the earth&#8217;s shadow at full moon. However, there are two points at which the plane of the moon&#8217;s orbit intersects the ecliptic. These are the nodes of the moon&#8217;s orbit. If the moon passes one of these points at the same time as the sun, a solar eclipse takes place. This is shown in Figure 1522. 










The sun and moon are of nearly the same apparent size to an observer on the earth. If the moon is at perigee, the moon&#8217;s apparent diameter is larger than that of the sun, and its shadow reaches the earth as a nearly round dot only a few miles in diameter. The dot moves rapidly across the earth, from west to east, as the moon continues in its orbit.
Within the dot, the sun is completely hidden from view, and a total eclipse of the sun occurs. 

For a considerable distance around the shadow, part of the surface of the sun is obscured, and a partial eclipse occurs. In the line of travel of the shadow a partial eclipse occurs as the round disk of the moon appears to move slowly across the surface of the sun, hiding an ever-increasing part of it, until the total eclipse occurs. Because of the uneven edge of the mountainous moon, the light is not cut off evenly. But several last illuminated portions appear through the valleys or passes between the mountain peaks. These are called Baily&#8217;s Beads. 

A total eclipse is a spectacular phenomenon. As the last light from the sun is cut off, the solar corona, or envelope of thin, illuminated gas around the sun becomes visible. Wisps of more dense gas may appear as solar prominences.

The only light reaching the observer is that diffused by the atmosphere surrounding the shadow. As the moon appears to continue on across the face of the sun, the sun finally emerges from the other side, first as Baily&#8217;s Beads, and then as an ever widening crescent until no part of its surface is obscured by the moon.

The duration of a total eclipse depends upon how nearly the moon crosses the center of the sun, the location of the shadow on the earth, the relative orbital speeds of the moon and earth, and (principally) the relative apparent diameters of the sun and moon. The maximum length that can occur is a little more than seven minutes.

If the moon is near apogee, its apparent diameter is less than that of the sun, and its shadow does not quite reach the earth. Over a small area of the earth directly in line with the moon and sun, the moon appears as a black disk almost covering the surface of the sun, but with a thin ring of the sun around its edge. This annular eclipse occurs a little more often than a total eclipse.

If the shadow of the moon passes close to the earth, but not directly in line with it, a partial eclipse may occur with-out a total or annular eclipse.
An eclipse of the moon (or lunar eclipse) occurs when the moon passes through the shadow of the earth, as shown in Figure 1522. Since the diameter of the earth is about 3-1/2 times that of the moon, the earth&#8217;s shadow at the distance of the moon is much larger than that of the moon. A total eclipse of the moon can last nearly 1-3/4 hours, and some part of the moon may be in the earth&#8217;s shadow for almost 4 hours. During a total solar eclipse no part of the sun is visible because the moon is in the line of sight. But during a lunar eclipse some light does reach the moon, diffracted by the atmosphere of the earth, and hence the eclipsed full moon is visible as a faint reddish disk. A lunar eclipse is visible over the entire hemisphere of the earth facing the moon. Anyone who can see the moon can see the eclipse. During any one year there may be as many as five eclipses of the sun, and always there are at least two. There may be as many as three eclipses of the moon, or none.

The total number of eclipses during a single year does not exceed seven, and can be as few as two. There are more solar than lunar eclipses, but the latter can be seen more often because of the restricted areas over which solar eclipses are visible. The sun, earth, and moon are nearly aligned on the line of nodes twice each eclipse year of 346.6 days. This is less than a calendar year because of regression of the nodes. In a little more than 18 years the line of nodes returns to approximately the same position with respect to the sun, earth, and moon. During an almost equal period, called the saros, a cycle of eclipses occurs. During the following saros the cycle is repeated with only minor differences.

COORDINATES
1523. Latitude And Longitude
Latitude and longitude are coordinates used to locate positions on the earth. This section discusses three different definitions of these coordinates.

Astronomic latitude is the angle (ABQ, Figure 1523) between a line in the direction of gravity (AB) at a station and the plane of the equator (QQ&#8217. 

Astronomic longitude is the angle between the plane of the celestial meridian at a station and the plane of the celestial meridian at Greenwich. 










These coordinates are customarily found by means of celestial observations. If the earth were perfectly homogeneous and round, these positions would be consistent and satisfactory. However, because of deflection of the vertical due to uneven distribution of the mass of the earth, lines of equal astronomic latitude and longitude are not circles, although the irregularities are small. In the United States the prime vertical component (affecting longitude) may be a little more than 18&#8221;, and the meridional component (affecting latitude) as much as 25&#8221;.

Geodetic latitude is the angle (ACQ, Figure 1523) between a normal to the spheroid (AC) at a station and the plane of the geodetic equator (QQ&#8217. Geodetic longitude is the angle between the plane defined by the normal to the spheroid and the axis of the earth and the plane of the geodetic meridian at Greenwich. These values are obtained when astronomical latitude and longitude are corrected for deflection of the vertical. These coordinates are used for charting and are frequently referred to as geographic latitude and geographic longitude, although these expressions are sometimes used to refer to astronomical latitude.

Geocentric latitude is the angle (ADQ, Figure 1523) at the center of the ellipsoid between the plane of its equator (QQ&#8217 and a straight line (AD) to a point on the surface of the earth. This differs from geodetic latitude because the earth is a spheroid rather than a sphere, and the meridians are ellipses. 

Since the parallels of latitude are considered to be circles, geodetic longitude is geocentric, and a separate expression is not used. The difference between geocentric and geodetic latitudes is a maximum of about 11.6&#8217; at latitude 45&#176;.

Because of the oblate shape of the ellipsoid, the length of a degree of geodetic latitude is not everywhere the same, increasing from about 59.7 nautical miles at the equator to about 60.3 nautical miles at the poles. The value of 60 nautical miles customarily used by the navigator is correct at about latitude 45&#176;.

*To be cont.*


----------



## Fishers of Men

*Chapter 15 cont.*
MEASUREMENTS ON THE CELESTIAL SPHERE
1524. Elements Of The Celestial Sphere
The celestial sphere (section 1501) is an imaginary sphere of infinite radius with the earth at its center (Figure 1524a). 










The north and south celestial poles of this sphere are located by extension of the earth&#8217;s axis. The celestial equator (sometimes called equinoctial) is formed by projecting the plane of the earth&#8217;s equator to the celestial sphere. A celestial meridian is formed by the intersection of the plane of a terrestrial meridian and the celestial sphere. It is the arc of a great circle through the poles of the celestial sphere. The point on the celestial sphere vertically overhead of an observer is the zenith, and the point on the opposite side of the sphere vertically below him is the nadir. The zenith and nadir are the extremities of a diameter of the celestial sphere through the observer and the common center of the earth and the celestial sphere. The arc of a celestial meridian between the poles is called the upper branch if it contains the zenith and the lower branch if it contains the nadir. The upper branch is frequently used in navigation, and references to a celestial meridian are understood to mean only its upper branch unless otherwise stated. 

Celestial meridians take the names of their terrestrial counterparts, such as 65&#176; west. An hour circle is a great circle through the celestial poles and a point or body on the celestial sphere. It is similar to a celestial meridian, but moves with the celestial sphere as it rotates about the earth, while a celestial meridian remains fixed with respect to the earth.

The location of a body on its hour circle is defined by the body&#8217;s angular distance from the celestial equator. This distance, called declination, is measured north or south of the celestial equator in degrees, from 0&#176; through 90&#176;, similar to latitude on the earth.

A circle parallel to the celestial equator is called a parallel of declination, since it connects all points of equal declination. It is similar to a parallel of latitude on the earth. The path of a celestial body during its daily apparent revolution around the earth is called its diurnal circle. It is not actually a circle if a body changes its declination. Since the declination of all navigational bodies is continually changing, the bodies are describing flat, spherical spirals as they circle the earth. However, since the change is relatively slow, a diurnal circle and a parallel of declination are usually considered identical.
A point on the celestial sphere may be identified at the intersection of its parallel of declination and its hour circle. The parallel of declination is identified by the declination.

Two basic methods of locating the hour circle are in use. First, the angular distance west of a reference hour circle through a point on the celestial sphere, called the vernal equinox or first point of Aries, is called sidereal hour angle (SHA) (Figure 1524b). This angle, measured eastward from the vernal equinox, is called right ascension and is usually expressed in time units.










The second method of locating the hour circle is to indicate its angular distance west of a celestial meridian (Figure 1524c). If the Greenwich celestial meridian is used as the reference, the angular distance is called Greenwich hour angle (GHA), and if the meridian of the observer, it is called local hour angle (LHA). It is sometimes more convenient to measure hour angle either eastward or west-ward, as longitude is measured on the earth, in which case it is called meridian angle (designated &#8220;t&#8221.

A point on the celestial sphere may also be located using altitude and azimuth coordinates based upon the horizon as the primary great circle instead of the celestial equator.










COORDINATE SYSTEMS
1525. The Celestial Equator System Of Coordinates
If the familiar graticule of latitude and longitude lines is expanded until it reaches the celestial sphere of infinite radius, it forms the basis of the celestial equator system of coordinates. On the celestial sphere latitude becomes declination, while longitude becomes sidereal hour angle, measured from the vernal equinox.

Declination is angular distance north or south of the celestial equator (d in Figure 1525a). It is measured along an hour circle, from 0&#176; at the celestial equator through 90&#176; at the celestial poles. It is labeled N or S to indicate the direction of measurement. 










All points having the same declination lie along a parallel of declination. Polar distance (p) is angular distance from a celestial pole, or the arc of an hour circle between the celestial pole and a point on the celestial sphere. It is measured along an hour circle and may vary from 0&#176; to 180&#176;, since either pole may be used as the origin of measurement. It is usually considered the complement of declination, though it may be either 90&#176; &#8211; d or 90&#176; + d, depending upon the pole used.

Local hour angle (LHA) is angular distance west of the local celestial meridian, or the arc of the celestial equator between the upper branch of the local celestial meridian and the hour circle through a point on the celestial sphere, measured westward from the local celestial meridian, through 360&#176;. It is also the similar arc of the parallel of declination and the angle at the celestial pole, similarly measured. If the Greenwich (0&#176 meridian is used as the reference, instead of the local meridian, the expression Greenwich hour angle (GHA) is applied. It is sometimes convenient to measure the arc or angle in either an easterly or westerly direction from the local meridian, through 180&#176;, when it is called meridian angle (t) and labeled E or W to indicate the direction of measurement.
All bodies or other points having the same hour angle lie along the same hour circle.

Because of the apparent daily rotation of the celestial sphere, hour angle continually increases, but meridian angle increases from 0&#176; at the celestial meridian to 180&#176;W,
which is also 180&#176;E, and then decreases to 0&#176; again. The rate of change for the mean sun is 15&#176; per hour. The rate of all other bodies except the moon is within 3&#8217; of this value.

The average rate of the moon is about 15.5&#176;.
As the celestial sphere rotates, each body crosses each branch of the celestial meridian approximately once a day. This crossing is called meridian transit (sometimes called culmination). It may be called upper transit to indicate crossing of the upper branch of the celestial meridian, and lower transit to indicate crossing of the lower branch.

The time diagram shown in Figure 1525b illustrates the relationship between the various hour angles and meridian angle. The circle is the celestial equator as seen from above the South Pole, with the upper branch of the observer&#8217;s meridian (P s M) at the top. The radius P s G is the Greenwich meridian; P s is the hour circle of the vernal equinox. 










The sun&#8217;s hour circle is to the east of the observer&#8217;s meridian; the moon&#8217;s hour circle is to the west of the observer&#8217;s meridian Note that when LHA is less than 180&#176;, t is numerically the same and is labeled W, but that when LHA is greater than 180&#176;,t =360&#176; &#8211; LHA and is labeled E. In Figure 1525b arc GM is the longitude, which in this case is west. The relation-ships shown apply equally to other arrangements of radii, except for relative magnitudes of the quantities involved.

1526. The Horizons
The second set of celestial coordinates with which the navigator is directly concerned is based upon the horizon as the primary great circle. However, since several different horizons are defined, these should be thoroughly under-stood before proceeding with a consideration of the horizon system of coordinates.

The line where earth and sky appear to meet is called the visible or apparent horizon. On land this is usually an irregular line unless the terrain is level. At sea the visible horizon appears very regular and often very sharp. However, its position relative to the celestial sphere depends primarily upon (1) the refractive index of the air and (2) the height of the observer&#8217;s eye above the surface.

Figure 1526 shows a cross section of the earth and celestial sphere through the position of an observer at A above the surface of the earth. A straight line through A and the center of the earth O is the vertical of the observer and contains his zenith (Z) and nadir (Na). A plane perpendicular to the true vertical is a horizontal plane, and its intersection with the celestial sphere is a horizon.
It is the celestial horizon if the plane passes through the center of the earth, the geoidal horizon if it is tangent to the earth, and the sensible horizon if it passes through the eye of the observer at A. 

Since the radius of the earth is considered negligible with respect to that of the celestial sphere, these horizons become superimposed, and most measurements are referred only to the celestial horizon. This is sometimes called the rational horizon.

If the eye of the observer is at the surface of the earth, his visible horizon coincides with the plane of the geoidal horizon; but when elevated above the surface, as at A, his eye becomes the vertex of a cone which is tangent to the earth at the small circle BB, and which intersects the celestial sphere in B&#8217;B&#8217;, the geometrical horizon. This expression is sometimes applied to the celestial horizon. Because of refraction, the visible horizon C&#8217;C&#8217; appears above but is actually slightly below the geometrical horizon as shown in Figure 1526.










For any elevation above the surface, the celestial horizon is usually above the geometrical and visible horizons, the difference increasing as elevation increases. It is thus possible to observe a body which is above the visible horizon but below the celestial horizon. That is, the body&#8217;s altitude is negative and its zenith distance is greater than 90&#176;.

1527. The Horizon System Of Coordinates
This system is based upon the celestial horizon as the primary great circle and a series of secondary vertical circles which are great circles through the zenith and nadir of the observer and hence perpendicular to his horizon (Figure 1527a). Thus, the celestial horizon is similar to the equator, and the vertical circles are similar to meridians, but with one important difference. The celestial horizon and vertical circles are dependent upon the position of the observer and hence move with him as he changes position, while the primary and secondary great circles of both the geographical and celestial equator systems are independent of the observer. 










The horizon and celestial equator systems coincide for an observer at the geographical pole of the earth and are mutually perpendicular for an observer on the equator. At all other places the two are oblique.

The vertical circle through the north and south points of the horizon passes through the poles of the celestial equator system of coordinates. One of these poles (having the same name as the latitude) is above the horizon and is called the elevated pole. The other, called the depressed pole, is below the horizon. Since this vertical circle is a great circle through the celestial poles, and includes the zenith of the observer, it is also a celestial meridian. In the horizon sys-tem it is called the principal vertical circle. The vertical circle through the east and west points of the horizon, and hence perpendicular to the principal vertical circle, is called the prime vertical circle, or simply the prime vertical. 

As shown in Figure 1527b, altitude is angular distance above the horizon. It is measured along a vertical circle, from 0&#176; at the horizon through 90&#176; at the zenith. Altitude measured from the visible horizon may exceed 90&#176; because of the dip of the horizon, as shown in Figure 1526. Angular distance below the horizon, called negative altitude, is provided for by including certain negative altitudes in some tables for use in celestial navigation. All points having the same altitude lie along a parallel of altitude.










Zenith distance (z) is angular distance from the zenith, or the arc of a vertical circle between the zenith and a point on the celestial sphere. It is measured along a vertical circle from 0&#176; through 180&#176;. It is usually considered the complement of altitude. For a body above the celestial horizon it is equal to 90&#176;&#61472;&#8211; h and for a body below the celestial horizon it is equal to 90&#176;&#61472;&#8211; (&#8211; h) or 90&#176;&#61472;+ h.

The horizontal direction of a point on the celestial sphere, or the bearing of the geographical position, is called azimuth or azimuth angle depending upon the method of measurement. In both methods it is an arc of the horizon (or parallel of altitude), or an angle at the zenith. It is azimuth (Zn) if measured clockwise through 360&#176;, starting at the north point on the horizon, and azimuth angle (Z) if measured either clockwise or counterclockwise through 180&#176;, starting at the north point of the horizon in north latitude and the south point of the horizon in south latitude.

The ecliptic system is based upon the ecliptic as the primary great circle, analogous to the equator. The points 90&#176; &#61472;from the ecliptic are the north and south ecliptic poles. The series of great circles through these poles, analogous to meridians, are circles of latitude. The circles parallel to the plane of the ecliptic, analogous to parallels on the earth, are parallels of latitude or circles of longitude. Angular distance north or south of the ecliptic, analogous to latitude, is celestial latitude. Celestial longitude is measured eastward along the ecliptic through 360&#176;, starting at the vernal equinox.

This system of coordinates is of interest chiefly to astronomers.
1528.	Summary Of Coordinate Systems
The four systems of celestial coordinates are analogous to each other and to the terrestrial system, although each has distinctions such as differences in directions, units, and limits of measurement. Figure 1528 indicates the analogous term or terms under each system.



















*To be cont.*


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## Fishers of Men

*Chapter 15 cont.*
1529.	Diagram On The Plane Of The Celestial Meridian
From an imaginary point outside the celestial sphere and over the celestial equator, at such a distance that the view would be orthographic, the great circle appearing as the outer limit would be a celestial meridian. Other celestial meridians would appear as ellipses. The celestial equator would appear as a diameter 90&#61616;&#61472;from the poles, and parallels of declination as straight lines parallel to the equator. The view would be similar to an orthographic map of the earth. A number of useful relationships can be demonstrated by drawing a diagram on the plane of the celestial meridian showing this orthographic view. Arcs of circles can be substituted for the ellipses without destroying the basic relationships. Refer to Figure 1529a. In the lower diagram the circle represents the celestial meridian, QQ&#8217; the celestial equator, Pn and Ps the north and south celestial poles, respectively. If a star has a declination of 30&#61616;&#61472;N, an angle of 30&#61616;&#61472;can be measured from the celestial equator, as shown.










It could be measured either to the right or left, and would have been toward the south pole if the declination had been south. The parallel of declination is a line through this point and parallel to the celestial equator. The star is somewhere on this line (sound familiar? line of position?) (actually a circle viewed on edge). To locate the hour circle, draw the upper diagram so that Pn is directly above Pn of the lower figure (in line with the polar axis Pn-Ps), and the circle is of the same diameter as that of the lower figure. This is the plane view, looking down on the celestial sphere from the top. The circle is the celestial equator. Since the view is from above the north celestial pole, west is clockwise. The diameter QQ&#8217; is the celestial meridian shown as a circle in the lower diagram. If the right half is considered the upper branch, local hour angle is measured clockwise from this line to the hour circle, as shown. In this case the LHA is 80&#176;. The intersection of the hour circle and celestial equator, point A, can be projected down to the lower diagram (point A&#8217 by a straight line parallel to the polar axis. The elliptical hour circle can be represented approximately by an arc of a circle through A&#8217;, Pn, Ps. The center of this circle is somewhere along the celestial equator line QQ&#8217;, extended if necessary. It is usually found by trial and error. 

The intersection of the hour circle and parallel of declination locates the star. Since the upper diagram serves only to locate point A&#8217; in the lower diagram, the two can be combined. That is, the LHA arc can be drawn in the lower diagram, as shown, and point A projected upward to A&#8217;. In practice, the upper diagram is not drawn, being shown here for illustrative purposes. In this example the star is on that half of the sphere toward the observer, or the western part. If LHA had been greater than 180&#176;, the body would have been on the eastern or &#8220;back&#8221; side.

From the east or west point over the celestial horizon, the orthographic view of the horizon system of coordinates would be similar to that of the celestial equator system from a point over the celestial equator, since the celestial meridian is also the principal vertical circle. The horizon would appear as a diameter, parallels of altitude as straight lines parallel to the horizon, the zenith and nadir as poles 90&#176; from the horizon, and vertical circles as ellipses through the zenith and nadir, except for the principal vertical circle, which would appear as a circle, and the prime vertical, which would appear as a diameter perpendicular to the horizon. A celestial body can be located by altitude and azimuth in a manner similar to that used with the celestial equator system. If the altitude is 25&#176;, this angle is measured from the horizon toward the zenith and the parallel of altitude is drawn as a straight line parallel to the horizon, as shown at hh&#8217; in the lower diagram of Figure 1529b. 

The plane view from above the zenith is shown in the upper diagram. If north is taken at the left, as shown, azimuths are measured clockwise from this point. In the figure the azimuth is 290&#176; &#61472;and the azimuth angle is N70&#176; W. 










The vertical circle is located by measuring either arc. Point A thus located can be projected vertically downward to A&#8217; on the horizon of the lower diagram, and the vertical circle represented approximately by the arc of a circle through A&#8217; and the zenith and nadir. The center of this circle is on NS, extended if necessary. The body is at the intersection of the parallel of altitude and the vertical circle. Since the upper diagram serves only to locate A&#8217; on the lower diagram, the two can be combined, point A located on the lower diagram and projected upward to A&#8217;, as shown. Since the body of the example has an azimuth greater than 180&#176;, it is on the western or &#8220;front&#8221; side of the diagram. Since the celestial meridian appears the same in both the celestial equator and horizon systems, the two diagrams can be combined and, if properly oriented, a body can be located by one set of coordinates, and the coordinates of the other system can be determined by measurement. Refer to Figure 1529c, in which the black lines represent the celestial equator system, and the red lines the horizon system. By convention, the zenith is shown at the top and the north point of the horizon at the left. The west point on the horizon is at the center, and the east point directly behind it. In the figure the latitude is 37&#176; N. Therefore, the zenith is 37&#176; &#61472;north of the celestial equator. 










Since the zenith is established at the top of the diagram, the equator can be found by measuring an arc of 37&#176; &#61472;toward the south, along the celestial meridian. If the declination is 30&#176; N and the LHA is 80&#176;, the body can be located as shown by the black lines, and described above.

The altitude and azimuth can be determined by the reverse process to that described above. Draw a line hh&#8217; through the body and parallel to the horizon, NS. The altitude, 25&#176;, is found by measurement, as shown. Draw the arc of a circle through the body and the zenith and nadir. From A&#8217;, the intersection of this arc with the horizon, draw a vertical line intersecting the circle at A. The azimuth, N70&#176; W, is found by measurement, as shown. The prefix N is applied to agree with the latitude. The body is left (north) of ZNa, the prime vertical circle. The suffix W applies because the LHA, 80&#176;, shows that the body is west of the meridian. If altitude and azimuth are given, the body is located by means of the red lines. The parallel of declination is then drawn parallel to QQ&#8217;, the celestial equator, and the declination determined by measurement. Point L&#8217; is located by drawing the arc of a circle through Pn, the star, and Ps. From L&#8217; a line is drawn perpendicular to QQ&#8217;, locating L.

The meridian angle is then found by measurement. The declination is known to be north because the body is between the celestial equator and the north celestial pole. The meridian angle is west, to agree with the azimuth, and hence LHA is numerically the same.

Since QQ&#8217;and PnPs are perpendicular, and ZNa and NS are also perpendicular, arc NPn is equal to arc ZQ. That is, the altitude of the elevated pole is equal to the declination of the zenith, which is equal to the latitude. This relationship is the basis of the method of determining latitude by an observation of Polaris.

The diagram on the plane of the celestial meridian is useful in approximating a number of relationships. Consider Figure 1529d. The latitude of the observer (NPn or ZQ) is 45&#176;N. 










The declination of the sun (Q4) is 20&#176;N. Neglecting the change in declination for one day, note the following: At sunrise, position 1, the sun is on the horizon (NS), at the &#8220;back&#8221; of the diagram. Its altitude, h, is 0&#176;. Its azimuth angle, Z, is the arc NA, N63&#176;E. This is prefixed N to agree with the latitude and suffixed E to agree with the meridian angle of the sun at sunrise. Hence, Zn = 063&#176;. The amplitude, A, is the arc ZA, E27&#176;N. The meridian angle, t, is the arc QL, 110&#176;E. The suffix E is applied because the sun is east of the meridian at rising. The LHA is 360&#176; &#8211; 110&#176; = 250&#176;. As the sun moves upward along its parallel of declination, its altitude increases. It reaches position 2 at about 0600, when t = 90&#176;E. At position 3 it is on the prime vertical, ZNa. Its azimuth angle, Z, is N90&#176;E, and Zn = 090&#176;. The altitude is Nh&#8217; or Sh, 27&#176;.

Moving on up its parallel of declination, it arrives at position 4 on the celestial meridian about noon-when t and LHA are both 0&#176;, by definition. On the celestial meridian a body&#8217;s azimuth is 000&#176; or 180&#176;. In this case it is 180&#176; because the body is south of the zenith. The maximum altitude occurs at meridian transit. In this case the arc S4 represents the maximum altitude, 65&#176;. The zenith distance, z, is the arc Z4, 25&#176;. A body is not in the zenith at meridian transit unless its declination&#8217;s magnitude and name are the same as the latitude. Continuing on, the sun moves downward along the &#8220;front&#8221; or western side of the diagram. At position 3 it is again on the prime vertical. The altitude is the same as when previously on the prime vertical, and the azimuth angle is numerically the same, but now measured toward the west. The azimuth is 270&#176;. The sun reaches position 2 six hours after meridian transit and sets at position 1. At this point, the azimuth angle is numerically the same as at sunrise, but westerly, and Zn = 360&#176; &#8211; 63&#176; = 297&#176;. The amplitude is W27&#176;N. 

After sunset the sun continues on downward, along its parallel of declination, until it reaches position 5, on the lower branch of the celestial meridian, about midnight. Its negative altitude, arc N5, is now greatest, 25&#176;, and its azimuth is 000&#176;. At this point it starts back up along the &#8220;back&#8221; of the diagram, arriving at position 1 at the next sunrise, to start another cycle.

Half the cycle is from the crossing of the 90&#176; hour circle (the PnPs line, position 2) to the upper branch of the celestial meridian (position 4) and back to the PnPs line (position 2).
When the declination and latitude have the same name (both north or both south), more than half the parallel of declination (position 1 to 4 to 1) is above the horizon, and the body is above the horizon more than half the time, crossing the 90&#176; hour circle above the horizon. It rises and sets on the same side of the prime vertical as the elevated pole. If the declination is of the same name but numerically smaller than the latitude, the body crosses the prime vertical above the horizon. If the declination and latitude have the same name and are numerically equal, the body is in the zenith at upper transit.

If the declination is of the same name but numerically greater than the latitude, the body crosses the upper branch of the celestial meridian between the zenith and elevated pole and does not cross the prime vertical. If the declination is of the same name as the latitude and complementary to it (d + L = 90&#176, the body is on the horizon at lower transit and does not set. If the declination is of the same name as the latitude and numerically greater than the colatitude, the body is above the horizon during its entire daily cycle and has maximum and minimum altitudes. This is shown by the black dotted line in Figure 1529d.

If the declination is 0&#176; at any latitude, the body is above the horizon half the time, following the celestial equator QQ&#8217;, and rises and sets on the prime vertical. If the declination is of contrary name (one north and the other south), the body is above the horizon less than half the time and crosses the 90&#176; hour circle below the horizon. 

It rises and sets on the opposite side of the prime vertical from the elevated pole. If the declination is of contrary name and numerically smaller than the latitude, the body crosses the prime vertical below the horizon. This is the situation with the sun in winter follows when days are short. If the declination is of contrary name and numerically equal to the latitude, the body is in the nadir at lower transit. If the declination is of contrary name and complementary to the latitude, the body is on the horizon at upper transit. If the declination is of contrary name and numerically greater than the colatitude, the body does not rise.

All of these relationships, and those that follow, can be derived by means of a diagram on the plane of the celestial meridian. They are modified slightly by atmospheric refraction, height of eye, semidiameter, parallax, changes in declination, and apparent speed of the body along its diurnal circle.

It is customary to keep the same orientation in south latitude, as shown in Figure 1529e. In this illustration the latitude is 45&#176;S, and the declination of the body is 15&#176;N.
Since Ps is the elevated pole, it is shown above the southern horizon, with both SPs and ZQ equal to the latitude, 45&#176;.










The body rises at position 1, on the opposite side of the prime vertical from the elevated pole. It moves upward along its parallel of declination to position 2, on the upper branch of the celestial meridian, bearing north; and then it moves downward along the &#8220;front&#8221; of the diagram to position 1, where it sets. It remains above the horizon for less than half the time because declination and latitude are of contrary name. The azimuth at rising is arc NA, the amplitude ZA, and the azimuth angle SA. The altitude circle at meridian transit is shown at hh&#8217;.

A diagram on the plane of the celestial meridian can be used to demonstrate the effect of a change in latitude. As the latitude increases, the celestial equator becomes more nearly parallel to the horizon. The colatitude becomes smaller, increasing the number of circumpolar bodies and those which neither rise nor set. It also increases the difference in the length of the days between summer and winter. At the poles celestial bodies circle the sky, parallel to the horizon. At the equator the 90&#176; hour circle coincides with the horizon.

Bodies rise and set vertically; and are above the horizon half the time. At rising and setting the amplitude is equal to the declination. At meridian transit the altitude is equal to the codeclination. As the latitude changes name, the same-contrary name relationship with declination reverses.
This accounts for the fact that one hemisphere has winter while the other is having summer.
The error arising from showing the hour circles and vertical circles as arcs of circles instead of ellipses increases with increased declination or altitude. 

More accurate results can be obtained by measurement of azimuth on the parallel of altitude instead of the horizon, and of hour angle on the parallel of declination instead of the celestial equator. Refer to Figure 1529f. 



























The vertical circle shown is for a body having an azimuth angle of S60&#176;W. The arc of a circle is shown in black, and the ellipse in red. The black arc is obtained by measurement around the horizon, locating A&#8217; by means of A, as previously described. The intersection of this arc with the altitude circle at 60&#176; places the body at M. If a semicircle is drawn with the altitude circle as a diameter, and the azimuth angle measured around this, to B, a perpendicular to the hour circle locates the body at M&#8217;, on the ellipse. By this method the altitude circle, rather than the horizon, is, in effect, rotated through 90&#176; for the measurement. This refinement is seldom used because actual values are usually found mathematically, the diagram on the plane of the meridian being used primarily to indicate relationships.

With experience, one can visualize the diagram on the plane of the celestial meridian without making an actual drawing. Devices with two sets of spherical coordinates, on either the orthographic or stereographic projection, pivoted at the center, have been produced commercially to provide a mechanical diagram on the plane of the celestial meridian. However, since the diagram&#8217;s principal use is to illustrate certain relationships, such a device is not a necessary part of the navigator&#8217;s equipment.
Figure 1529g summarizes navigation coordinate systems.

To be cont.


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## ezbite

Fishers of Men said:


> EZ says, "I wish to have no Connection with any Ship that does not Sail fast for I intend to go in harm's way."



sounds like something id say.LOL. im still here van


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## Fishers of Men

*Ch 15 cont.*

1530. The Navigational Triangle
A triangle formed by arcs of great circles of a sphere is called a spherical triangle. A spherical triangle on the celestial sphere is called a celestial triangle. The spherical triangle of particular significance to navigators is called the navigational triangle, formed by arcs of a celestial meridian, an hour circle, and a vertical circle. Its vertices are the elevated pole, the zenith, and a point on the celestial sphere (usually a celestial body). The terrestrial counterpart is also called a navigational triangle, being formed by arcs of two meridians and the great circle connecting two places on the earth, one on each meridian. The vertices are the two places and a pole. In great-circle sailing these places are the point of departure and the destination. In celestial navigation they are the assumed position (AP) of the observer and the geographical position (GP) of the body (the place having the body in its zenith). The GP of the sun is sometimes called the subsolar point, that of the moon the sublunar point, that of a satellite (either natural or artificial) the subsatellite point, and that of a star its substellar or subastral point. When used to solve a celestial observation, either the celestial or terrestrial triangle may be called the astronomical triangle.

The navigational triangle is shown in Figure 1530a on a diagram on the plane of the celestial meridian.










The earth is at the center, O. The star is at M, dd&#8217; is its parallel of declination, and hh&#8217; is its altitude circle. In the figure, arc QZ of the celestial meridian is the latitude of the observer, and PnZ, one side of the triangle, is the colatitude. Arc AM of the vertical circle is the altitude of the body, and side ZM of the triangle is the zenith distance, or coaltitude. Arc LM of the hour circle is the declination of the body, and side PnM of the triangle is the polar distance, or codeclination.

The angle at the elevated pole, ZPnM, having the hour circle and the celestial meridian as sides, is the meridian angle, t. The angle at the zenith, PnZM, having the vertical circle and that arc of the celestial meridian, which includes the elevated pole, as sides, is the azimuth angle. The angle at the celestial body, ZMPn, having the hour circle and the vertical circle as sides, is the parallactic angle (X) (sometimes called the position angle), which is not generally used by the navigator.

A number of problems involving the navigational triangle are encountered by the navigator, either directly or indirectly. Of these, the most common are:
1.	Given latitude, declination, and meridian angle, to find altitude and azimuth angle. This is used in the reduction of a celestial observation to establish a line of position.
2.	Given latitude, altitude, and azimuth angle, to find declination and meridian angle. This is used to identify an unknown celestial body.
3.	Given meridian angle, declination, and altitude, to find azimuth angle. This may be used to find azimuth when the altitude is known.
4.	Given the latitude of two places on the earth and the difference of longitude between them, to find the initial great-circle course and the great-circle distance.
This involves the same parts of the triangle as in 1, above, but in the terrestrial triangle, and hence is defined differently.
Both celestial and terrestrial navigational triangles are shown in perspective in Figure 1530b.










IDENTIFICATION OF STARS AND PLANETS
1531. Introduction
A basic requirement of celestial navigation is the ability to identify the bodies observed. This is not difficult because relatively few stars and planets are commonly used for navigation, and various aids are available to assist in their identification. Some navigators may have access to a computer which can identify the celestial body observed given inputs of DR position and observed altitude. No problem is encountered in the identification of the sun and moon.

However, the planets can be mistaken for stars. A person working continually with the night sky recognizes a planet by its changing position among the relatively fixed stars. The planets are identified by noting their positions relative to each other, the sun, the moon, and the stars. They remain within the narrow limits of the zodiac, but are in almost constant motion relative to the stars. The magnitude and color may be helpful. The information needed is found in the Nautical Almanac. The &#8220;Planet Notes&#8221; near the front of that volume are particularly useful.
Sometimes the light from a planet seems steadier than that from a star. This is because fluctuation of the unsteady atmosphere causes scintillation or twinkling of a star, which has no measurable diameter with even the most powerful telescopes.
The navigational planets are less susceptible to the twinkling because of the broader apparent area giving light.
Planets can also be identified by planet diagram, star finder, sky diagram, or by computation.





































1532. Stars
The Nautical Almanac lists full navigational information on 19 first magnitude stars and 38 second magnitude stars, plus Polaris. Abbreviated information is listed for 115 more. Additional stars are listed in The Astronomical Almanac and in various star catalogs. About 6,000 stars of the sixth magnitude or brighter (on the entire celestial sphere) are visible to the unaided eye on a clear, dark night.

Stars are designated by one or more of the following naming systems:
&#8226; Common Name: Most names of stars, as now used, were given by the ancient Arabs and some by the Greeks or Romans. One of the stars of the Nautical Almanac, Nunki, was named by the Babylonians.
Only a relatively few stars have names. Several of the stars on the daily pages of the almanacs had no name prior to 1953.

&#8226; Bayer&#8217;s Name: Most bright stars, including those with names, have been given a designation consisting of a Greek letter followed by the possessive form of the name of the constellation, such as a Cygni (I can&#8217;t figure out how to put these Roman letters in here, oh well!) (Deneb, the brightest star in the constellation Cygnus, the swan). Roman letters are used when there are not enough Greek letters. Usually, the letters are assigned in order of brightness within the constellation; however, this is not always the case. For example, the letter designations of the stars in Ursa Major or the Big Dipper are assigned in order from the outer rim of the bowl to the end of the handle.
This system of star designation was suggested by John Bayer of Augsburg, Germany, in 1603. All of the 173 stars included in the list near the back of the Nautical Almanac are listed by Bayer&#8217;s name, and, when applicable, their common name.

&#8226; Flamsteed&#8217;s Number: This system assigns numbers to stars in each constellation, from west to east in the order in which they cross the celestial meridian. An example is 95 Leonis, the 95th star in the constellation Leo. This system was suggested by John
Flamsteed (1646-1719).

&#8226; Catalog Number: Stars are sometimes designated by the name of a star catalog and the number of the star as given in the catalog, such as A. G. Washington 632. In these catalogs, stars are listed in order from west to east, without regard to constellation, starting with the hour circle of the vernal equinox.
This system is used primarily for fainter stars having no other designation. Navigators seldom have occasion to use this system.

1533. Star Charts
It is useful to be able to identify stars by relative position.
A star chart (Figure 1533) is helpful in locating these relationships and others which may be useful. This method is limited to periods of relatively clear, dark skies with little or no overcast. Stars can also be identified by the Air Almanac sky diagrams, a star finder, Pub. No. 249, or by computation by hand or calculator.

Star charts are based upon the celestial equator system of coordinates, using declination and sidereal hour angle (or right ascension). The zenith of the observer is at the intersection of the parallel of declination equal to his latitude, and the hour circle coinciding with his celestial meridian. This hour circle has an SHA equal to 360&#176; &#8211; LHA (There is a symbol that goes here I can&#8217;t do) or RA = LHA . The horizon is everywhere 90&#176; from the zenith. A star globe is similar to a terrestrial sphere, but with stars (and often constellations) shown instead of geographical positions.

The Nautical Almanac includes instructions for using this device. On a star
globe the celestial sphere is shown as it would appear to an observer outside the sphere. Constellations appear reversed. Star charts may show a similar view, but more often they are based upon the view from inside the sphere, as seen from the earth. On these charts, north is at the top, as with maps, but east is to the left and west to the right. The directions seem correct when the chart is held overhead, with the top toward the north, so the relationship is similar to the sky.

The Nautical Almanac has four star charts. The two principal ones are on the polar azimuthal equidistant projection, one centered on each celestial pole. Each chart extends from its pole to declination 10&#176; (same name as pole). Below each polar chart is an auxiliary chart on the Mercator projection, from 30&#176;N to 30&#176;S. On any of these charts, the zenith can be located as indicated, to determine which stars are overhead. The horizon is 90&#176; from the zenith.
The charts can also be used to determine the location of a star relative to surrounding stars.

The Air Almanac contains a folded chart on the rectangular projection. This projection is suitable for indicating the coordinates of the stars, but excessive distortion occurs in regions of high declination. The celestial poles are represented by the top and bottom horizontal lines the same length as the celestial equator. To locate the horizon on this chart, first locate the zenith as indicated above, and then locate the four cardinal points.

The north and south points are 90&#176; from the zenith, along the celestial meridian. The distance to the elevated pole (having the same name as the latitude) is equal to the colatitude of the observer. The remainder of the 90&#176; (the latitude) is measured from the same pole, along the lower branch of the celestial meridian, 180&#176; from the upper branch containing the zenith. The east and west points are on the celestial equator at the hour circle 90&#176; east and west (or 90&#176; and 270&#176; in the same direction) from the celestial meridian. The horizon is a sine curve through the four cardinal points. Directions on this projection are distorted.

The star charts shown in Figure 1534 through Figure 1537, on the transverse Mercator projection, are designed to assist in learning Polaris and the stars listed on the daily pages of the Nautical Almanac. 










Each chart extends about 20&#176; beyond each celestial pole, and about 60&#176; (four hours) each side of the central hour circle (at the celestial equator).
Therefore, they do not coincide exactly with that half of the celestial sphere above the horizon at any one time or place.
The zenith, and hence the horizon, varies with the position of the observer on the earth. It also varies with the rotation of the earth (apparent rotation of the celestial sphere). The charts show all stars of fifth magnitude and brighter as they appear in the sky, but with some distortion toward the right and left edges.

The overprinted lines add certain information of use in locating the stars. Only Polaris and the 57 stars listed on the daily pages of the Nautical Almanac are named on the charts. The almanac star charts can be used to locate the additional stars given near the back of the Nautical Almanac and the Air Almanac. Dashed lines connect stars of some of the more prominent constellations. Solid lines indicate the celestial equator and useful relationships among stars in different constellations. The celestial poles are marked by crosses, and labeled. By means of the celestial equator and the poles, one can locate his zenith approximately along the mid hour circle, when this coincides with his celestial meridian, as shown in the table above. At any time earlier than those shown in the table the zenith is to the right of center, and at a later time it is to the left, approximately one-quarter of the distance from the center to the outer edge (at the celestial equator) for each hour that the time differs from that shown. The stars in the vicinity of the North Pole can be seen in proper perspective by inverting the chart, so that the
zenith of an observer in the Northern Hemisphere is up from the pole.

1534. Stars In The Vicinity Of Pegasus
In autumn the evening sky has few first magnitude stars. Most are near the southern horizon of an observer in the latitudes of the United States. A relatively large number of second and third magnitude stars seem conspicuous, perhaps because of the small number of brighter stars. High in the southern sky three third magnitude stars and one second magnitude star form a square with sides nearly 15&#176; of arc in length. This is Pegasus, the winged horse.

Only Markab at the southwestern corner and Alpheratz at the northeastern corner are listed on the daily pages of the Nautical Almanac. Alpheratz is part of the constellation Andromeda, the princess, extending in an arc toward the northeast and terminating at Mirfak in Perseus, legendary rescuer of Andromeda.

A line extending northward through the eastern side of the square of Pegasus passes through the leading (western) star of M-shaped (or W-shaped) Cassiopeia, the legendary mother of the princess Andromeda. The only star of this constellation listed on the daily pages of the Nautical Almanac is Schedar, the second star from the leading one as the configuration circles the pole in a counterclockwise direction. If the line through the eastern side of the square of Pegasus is continued on toward the north, it leads to second magnitude Polaris, the North Star (less than 1&#176; from the north celestial pole) and brightest star of Ursa Minor, the Little Dipper. Kochab, a second magnitude star at the other end of Ursa Minor, is also listed in the almanacs. At this season Ursa Major is low in the northern sky, below the celestial pole. A line extending from Kochab through Polaris leads to Mirfak, assisting in its identification when Pegasus and Andromeda are near or below the horizon.
Deneb, in Cygnus, the swan, and Vega are bright, first magnitude stars in the northwestern sky.

The line through the eastern side of the square of Pegasus approximates the hour circle of the vernal equinox, shown at Aries on the celestial equator to the south. The sun is at Aries on or about March 21, when it crosses the celestial equator from south to north. If the line through the eastern side of Pegasus is extended southward and curved slightly toward the east, it leads to second magnitude Diphda. A longer and straighter line southward through the western side of Pegasus leads to first magnitude Fomalhaut. A line extending northeasterly from Fomalhaut through Diphda leads to Menkar, a third magnitude star, but the brightest in its vicinity. Ankaa, Diphda, and Fomalhaut form an isosceles triangle, with the apex at Diphda. Ankaa is near or below the southern horizon of observers in latitudes of the United States. Four stars farther south than Ankaa may be visible when on the celestial meridian, just above the horizon of observers in latitudes of the extreme southern part of the United States. These are Acamar, Achernar, Al Na&#8217;ir, and Peacock. These stars, with each other and with Ankaa, Fomalhaut, and Diphda, form a series of triangles as shown in Figure 1534. Almanac stars near the bottom of Figure 1534 are discussed in succeeding articles. Two other almanac stars can be located by their positions relative to Pegasus. These are Hamal in the constellation Aries, the ram, east of Pegasus, and Enif, west of the southern part of the square, identified in Figure 1534.










The line leading to Hamal, if continued, leads to the Pleiades (the Seven Sisters), not used by navigators for celestial observations, but a prominent figure in the sky, heralding the approach of the many conspicuous stars of the winter evening sky.

1535.	Stars In The Vicinity Of Orion
As Pegasus leaves the meridian and moves into the western sky, Orion, the hunter, rises in the east. With the possible exception of Ursa Major, no other configuration of stars in the entire sky is as well known as Orion and its immediate surroundings. In no other region are there so many first magnitude stars.

The belt of Orion, nearly on the celestial equator, is visible in virtually any latitude, rising and setting almost on the prime vertical, and dividing its time equally above and below the horizon. Of the three second magnitude stars forming the belt, only Alnilam, the middle one, is listed on the daily pages of the Nautical Almanac.

Four conspicuous stars form a box around the belt. Rigel, a hot, blue star, is to the south. Betelgeuse, a cool, red star lies to the north. Bellatrix, bright for a second magnitude star but overshadowed by its first magnitude neighbors, is a few degrees west of Betelgeuse. Neither the second magnitude star forming the southeastern corner of the box, nor any star of the dagger, is listed on the daily pages of the Nautical Almanac.

A line extending eastward from the belt of Orion, and curving toward the south, leads to Sirius, the brightest star in the entire heavens, having a magnitude of &#8211;1.6. Only Mars and Jupiter at or near their greatest brilliance, the sun, moon, and Venus are brighter than Sirius. Sirius is part of the constellation Canis Major, the large hunting dog of Orion. Starting at Sirius a curved line extends northward through first magnitude Procyon, in Canis Minor, the small hunting dog; first magnitude Pollux and second magnitude Castor (not listed on the daily pages of the Nautical Almanac), the twins of Gemini; brilliant Capella in Auriga, the charioteer; and back down to first magnitude Aldebaran, the follower, which trails the Pleiades, the seven sisters. Aldebaran, brightest star in the head of Taurus, the bull, may also be found by a curved line extending northwestward from the belt of Orion. The V-shaped figure forming the outline of the head and horns of Taurus points toward third magnitude Menkar. At the summer solstice the sun is between Pollux and Aldebaran.

If the curved line from Orion&#8217;s belt southeastward to Sirius is continued, it leads to a conspicuous, small, nearly equilateral triangle of three bright second magnitude stars of nearly equal brilliancy. This is part of Canis Major. Only Adhara, the westernmost of the three stars, is listed on the daily pages of the Nautical Almanac. Continuing on with somewhat less curvature, the line leads to Canopus, second brightest star in the heavens and one of the two stars having a negative magnitude (&#8211;0.9). With Suhail and Miaplacidus, Canopus forms a large, equilateral triangle which partly encloses the group of stars often mistaken for Crux. The brightest star within this triangle is Avior, near its center. Canopus is also at one apex of a triangle formed with Adhara to the north and Suhail to the east, another triangle with Acamar to the west and Achernar to the southwest, and another with Achernar and Miaplacidus. Acamar, Achernar, and Ankaa form still another triangle toward the west.
Because of chart distortion, these triangles do not appear in the sky in exactly the relationship shown on the star chart. Other daily-page almanac stars near the bottom of Figure 1535 are discussed in succeeding articles.










In the winter evening sky, Ursa Major is east of Polaris, Ursa Minor is nearly below it, and Cassiopeia is west of it. Mirfak is northwest of Capella, nearly midway between it and Cassiopeia. Hamal is in the western sky. Regulus and Alphard are low in the eastern sky, heralding the approach of the configurations associated with the evening skies of spring.
*To be cont.*


----------



## Fishers of Men

*Ch 15 cont.*

1536.	Stars In The Vicinity Of Ursa Major
As if to enhance the splendor of the sky in the vicinity of Orion, the region toward the east, like that toward the west, has few bright stars, except in the vicinity of the south celestial pole. However, as Orion sets in the west, leaving Capella and Pollux in the northwestern sky, a number of good navigational stars move into favorable positions for observation.
Ursa Major, the great bear, appears prominently above the north celestial pole, directly opposite Cassiopeia, which appears as a &#8220;W&#8221; just above the northern horizon of most observers in latitudes of the United States. Of the seven stars forming Ursa Major, only Dubhe, Alioth, and Alkaid are listed on the daily pages of the Nautical Almanac.

The two second magnitude stars forming the outer part of the bowl of Ursa Major are often called the pointers because a line extending northward (down in spring evenings) through them points to Polaris. Ursa Minor, the Little Bear, contains Polaris at one end and Kochab at the other. Relative to its bowl, the handle of Ursa Minor curves in the opposite direction to that of Ursa Major.

A line extending southward through the pointers, and curving somewhat toward the west, leads to first magnitude Regulus, brightest star in Leo, the lion. The head, shoulders, and front legs of this constellation form a sickle, with Regulus at the end of the handle. Toward the east is second magnitude Denebola, the tail of the lion. On toward the southwest from Regulus is second magnitude Alphard, brightest star in Hydra, the sea serpent. A dark sky and considerable imagination are needed to trace the long, winding body of this figure.

A curved line extending the arc of the handle of Ursa Major leads to first magnitude Arcturus. With Alkaid and Alphecca, brightest star in Corona Borealis, the Northern Crown, Arcturus forms a large, inconspicuous triangle. If the arc through Arcturus is continued, it leads next to first magnitude Spica and then to Corvus, the crow. The brightest star in this constellation is Gienah, but three others are nearly as bright. At autumnal equinox, the sun is on the celestial equator, about midway between Regulus and Spica. A long, slightly curved line from Regulus, east-southeasterly through Spica, leads to Zubenelgenubi at the southwestern corner of an inconspicuous box-like figure called Libra, the scales.

Returning to Corvus, a line from Gienah, extending diagonally across the figure and then curving somewhat toward the east, leads to Menkent, just beyond Hydra. 

You wont see this from here.
Far to the south, below the horizon of most northern hemisphere observers, a group of bright stars is a prominent feature of the spring sky of the Southern Hemisphere. This is Crux, the Southern Cross. Crux is about 40&#176; south of Corvus. The &#8220;false cross&#8221; to the west is often mistaken for Crux. Acrux at the southern end of Crux and Gacrux at the northern end are listed on the daily pages of the Nautical Almanac. The triangles formed by Suhail, Miaplacidus, and Canopus, and by Suhail, Adhara, and Canopus, are west of Crux. Suhail is in line with the horizontal arm of Crux. A line from Canopus, through Miaplacidus, curved slightly toward the north, leads to Acrux. A line through the east-west arm of Crux, eastward and then curving toward the south, leads first to Hadar and then to Rigil Kentaurus, both very bright stars. Continuing on, the curved line leads to small Triangulum Australe, the Southern Triangle, the easternmost star of which is Atria.

1537. Stars In The Vicinity Of Cygnus
As the celestial sphere continues in its apparent westward rotation, the stars familiar to a spring evening observer sink low in the western sky. By midsummer, Ursa Major has moved to a position to the left of the north celestial pole, and the line from the pointers to Polaris is nearly horizontal. Ursa Minor, is standing on its handle, with Kochab above and to the left of the celestial pole. Cassiopeia is at the right of Polaris, opposite the handle of Ursa Major.

The only first magnitude star in the western sky is Arcturus, which forms a large, inconspicuous triangle with Alkaid, the end of the handle of Ursa Major, and Alphecca, the brightest star in Corona Borealis, the Northern Crown. The eastern sky is dominated by three very bright stars. The westernmost of these is Vega, the brightest star north of the celestial equator, and third brightest star in the heavens, with a magnitude of 0.1. With a declination of a little less than 39&#176;N, Vega passes through the zenith along a path across the central part of the United States, from Washington in the east to San Francisco on the Pacific coast. Vega forms a large but conspicuous triangle with its two bright neighbors, Deneb to the northeast and Altair to the southeast. The angle at Vega is nearly a right angle.

Deneb is at the end of the tail of Cygnus, the swan. This configuration is sometimes called the Northern Cross, with Deneb at the head. To modern youth it more nearly resembles a dive bomber, while it is still well toward the east, with Deneb at the nose of the fuselage. Altair has two fainter stars close by, on opposite sides. The line formed by Altair and its two fainter companions, if extended in a northwesterly direction, passes through Vega, and on to second magnitude Eltanin. The angular distance from Vega to Eltanin is about half that from Altair to Vega. 



















Vega and Altair, with second magnitude Rasalhague to the west, form a large equilateral triangle. This is less conspicuous than the Vega-Deneb-Altair triangle because the brilliance of Rasalhague is much less than that of the three first magnitude stars, and the triangle is overshadowed by the brighter one.

Far to the south of Rasalhague, and a little toward the west, is a striking configuration called Scorpius, the scorpion. The brightest star, forming the head, is red Antares. At the tail is Shaula.

Antares is at the southwestern corner of an approximate parallelogram formed by Antares, Sabik, Nunki, and Kaus Australis. With the exception of Antares, these stars are only slightly brighter than a number of others nearby, and so this parallelogram is not a striking figure. At winter solstice the sun is a short distance northwest of Nunki. Northwest of Scorpius is the box-like Libra, the scales, of which Zubenelgenubi marks the southwest corner. With Menkent and Rigil Kentaurus to the southwest, Antares forms a large but unimpressive triangle. For most observers in the latitudes of the United States, Antares is low in the southern sky, and the other two stars of the triangle are below the horizon. To an observer in the Southern Hemisphere Crux is to the right of the south celestial pole, which is not marked by a conspicuous star. A long, curved line, starting with the now-vertical arm of Crux and extending northward and then eastward, passes successively through Hadar, Rigil Kentaurus, Peacock, and Al Na&#8217;ir. Fomalhaut is low in the southeastern sky of the southern hemisphere observer, and Enif is low in the eastern sky at nearly any latitude. With the appearance of these stars it is not long before Pegasus will appear over the eastern horizon during the evening, and as the winged horse climbs evening by evening to a position higher in the sky, a new annual cycle approaches.

1538. Planet Diagram
The planet diagram in the Nautical Almanac shows, in graphical form for any date during the year, the LMT of meridian passage of the sun, for the five planets Mercury, Venus, Mars, Jupiter, and Saturn, and of each 30&#176; of SHA. The diagram provides a general picture of the availability of planets and stars for observation, and thus shows:
1.	Whether a planet or star is too close to the sun for observation.
2.	Whether a planet is a morning or evening star.
3.	Some indication of the planet&#8217;s position during twilight.
4.	The proximity of other planets.
5.	Whether a planet is visible from evening to morning twilight.
A band 45m wide is shaded on each side of the curve marking the LMT of meridian passage of the sun. Any planet and most stars lying within the shaded area are too close to the sun for observation.

When the meridian passage occurs at midnight, the body is in opposition to the sun and is visible all night; planets may be observable in both morning and evening twilights. As the time of meridian passage decreases, the body ceases to be observable in the morning, but its altitude above the eastern horizon during evening twilight gradually increases; this continues until the body is on the meridian at twilight. From then onwards the body is observable above the western horizon and its altitude at evening twilight gradually decreases; eventually the body comes too close to the sun for observation. When the body again becomes visible, it is seen as a morning star low in the east. Its altitude at twilight increases until meridian passage occurs at the time of morning twilight. Then, as the time of meridian passage decreases to 0h, the body is observable in the west in the morning twilight with a gradually decreasing altitude, until it once again reaches opposition.

Only about one-half the region of the sky along the ecliptic, as shown on the diagram, is above the horizon at one time. At sunrise (LMT about 6h) the sun and, hence, the region near the middle of the diagram, are rising in the east; the region at the bottom of the diagram is setting in the west. The region half way between is on the meridian. At sunset (LMT about 18h) the sun is setting in the west; the region at the top of the diagram is rising in the east. Marking the planet diagram of the Nautical Almanac so that east is at the top of the diagram and west is at the bottom can be useful to interpretation.

If the curve for a planet intersects the vertical line connecting the date graduations below the shaded area, the planet is a morning star; if the intersection is above the shaded area, the planet is an evening star. A similar planet location diagram in the Air Almanac represents the region of the sky along the ecliptic within which the sun, moon, and planets always move; it shows, for each date, the sun in the center and the relative positions of the moon, the five planets Mercury, Venus, Mars, Jupiter, Saturn and the four first magnitude stars Aldebaran, Antares, Spica, and Regulus, and also the position on the ecliptic which is north of Sirius (i.e. Sirius is 40&#176; south of this point). The first point of Aries is also shown for reference. The magnitudes of the planets are given at suitable intervals along the curves. The moon symbol shows the correct phase.Astraight line joining the date on the left-hand side with the same date of the right-hand side represents a complete circle around the sky, the two ends of the line representing the point 180&#176; from the sun; the intersections with the curves show the spacing of the bodies along the ecliptic on the date. The time scale indicates roughly the local mean time at which an object will be on the observer&#8217;s meridian.

At any time only about half the region on the diagram is above the horizon. At sunrise the sun (and hence the region near the middle of the diagram), is rising in the east and the region at the end marked &#8220;West&#8221; is setting in the west; the region half-way between these extremes is on the meridian, as will be indicated by the local time (about 6h). At the time of sunset (local time about 18h) the sun is setting in the west, and the region at the end marked &#8220;East&#8221; is rising in the east. The diagram should be used in conjunction with the Sky Diagrams.

1539. Star Finders
Various devices have been devised to help an observer find individual stars. The most widely used is the Star Finder and Identifier, formerly published by the U.S. Navy Hydrographic Office, and now published commercially. The current model, No. 2102D, as well as the previous 2102C model, patented by E. B. Collins, employs the same basic principle as that used in the Rude Star Finder patented by Captain G. T. Rude, USC&GS, and later sold to the Hydrographic Office. Successive models reflect various modifications to meet changing conditions and requirements.

The star base of No. 2102D consists of a thin, white, opaque, plastic disk about 8 &#189; inches in diameter, with a small peg in the center. On one side the north celestial pole is shown at the center, and on the opposite side the south celestial pole is at the center. All of the stars listed on the daily pages of the Nautical Almanac are shown on a polar azimuthal equidistant projection extending to the opposite pole. The south pole side is shown in Figure 1539a. Many copies of an older edition, No. 2102C, showing the stars listed in the almanacs prior to 1953, and having other minor differences, are still in use. These are not rendered obsolete by the newer edition, but should be corrected by means of the current almanac. The rim of each side is graduated to half a degree of LHA ( ) (or 360&#61616;&#61472;&#8211; SHA).










Ten transparent templates of the same diameter as the star base are provided. There is one template for each 10&#176; of latitude, labeled 5&#176;, 15&#176;, 25&#176;, etc., plus a 10th (printed in red) showing meridian angle and declination. The older edition (No. 2102C) did not have the red meridian angle declination template. Each template can be used on either side of the star base, being centered by placing a small center hole in the template over the center peg of the star base. Each latitude template has a family of altitude curves at 5&#176; intervals from the horizon (from altitude 10&#176; on the older No. 2102C) to 80&#176;. A second family of curves, also at 5&#176; intervals, indicates azimuth. The north-south azimuth line is the celestial meridian.

The star base, templates, and a set of instructions are kept in a circular leatherette container.
Since the sun, moon, and planets continually change apparent position relative to the &#8220;fixed&#8221; stars, they are not shown on the star base. However, their positions at any time, as well as the positions of additional stars, can be plotted. To do this, determine 360&#176; &#8211; SHA of the body. For the stars and planets, SHA is listed in the Nautical Almanac. For the sun and moon, 360&#176; &#8211; SHA is found by subtracting GHA of the body from GHA (Aries symbol) at the same time. Locate 360&#176; &#8211; SHA on the scale around the rim of the star base. A straight line from this point to the center represents the hour circle of the body.

From the celestial equator, shown as a circle midway between the center and the outer edge, measure the declination (from the almanac) of the body toward the center if the pole and declination have the same name (both N or both S), and away from the center if they are of contrary name. Use the scale along the north-south azimuth line of any template as a declination scale. 

The meridian angle-declination template (the latitude 5&#176; template of No. 2102C) has an open slot with declination graduations along one side, to assist in plotting positions, as shown in Figure 1539b. In the illustration, the celestial body being located has a 360&#176; &#8211; SHA of 285&#176;, and a declination of 14.5&#176;S. It is not practical to attempt to plot to greater precision than the nearest 0.1&#176;.










Positions of Venus, Mars, Jupiter, and Saturn, on June 1, 1975, are shown plotted on the star base in Figure 1539c. It is sometimes desirable to plot positions of the sun and moon to assist in planning. 










Plotted positions of stars need not be changed. Plotted positions of bodies of the solar system should be replotted from time to time, the more rapidly moving ones more often than others. The satisfactory interval for each body can be determined by experience. It is good practice to record the date of each plotted position of a body of the solar system, to serve later as an indication of the interval since it was plotted.

To orient the template properly for any given time, proceed as follows: enter the almanac with GMT, and determine GHA at this time. Apply the longitude to GHA , subtracting if west, or adding if east, to determine LHA . If LMT is substituted for GMT in entering the almanac, LHA can be taken directly from the almanac, to sufficient accuracy for orienting the star finder template. Select the template for the latitude nearest that of the observer, and center it over the star base, being careful that the correct sides (north or south to agree with the latitude) of both template and star base are used. Rotate the template relative to the star base, until the arrow on the celestial meridian (the north-south azimuth line) is over LHA on the star based graduations. The small cross at the origin of both families of curves now represents the zenith of the observer.

The approximate altitude and azimuth of the celestial bodies above the horizon can be visually interpolated from the star finder. Consider Polaris (not shown) as at the north celestial pole. For more accurate results, the template can be lifted clear of the center peg of the star base, and shifted along the celestial meridian until the latitude, on the altitude scale, is over the pole. This refinement is not needed for normal use of the device. It should not be used for a latitude differing more than 5&#176; from that for which the curves were drawn. If the altitude and azimuth of an identified body shown on the star base are known, the template can be oriented by rotating it until it is in correct position relative to that body.

1540.	Sight Reduction Tables for Air Navigation (Pub. No. 249)
Volume I of Pub. No. 249 can be used as a star finder for the stars tabulated at any given time. For these bodies the altitude and azimuth are tabulated for each 1&#176; of latitude and 1&#176; of LHA (2&#176; beyond latitude 69&#176. The principal limitation is the small number of stars listed.

1541.	Air Almanac Sky Diagram
Near the back of the Air Almanac are a number of sky diagrams. These are azimuthal equidistant projections of the celestial sphere on the plane of the horizon, at latitudes 75&#176;N, 50&#176;N, 25&#176;N, 0&#176;, 25&#176;S, and 50&#176;S, at intervals of 2 hours of local mean time each month. A number of the brighter stars, the visible planets, and several positions of the moon are shown at their correct altitude and azimuth. These are of limited value to marine navigators because of their small scale; the large increments of latitude, time, and date; and the limited number of bodies shown. However, in the absence of other methods, particularly a star finder, these diagrams can be useful. Allowance can be made for variations from the conditions for which each diagram is constructed. Instructions for use of the diagrams are included in the Air Almanac.

1542.	Identification By Computation
If the altitude and azimuth of the celestial body, and the approximate latitude of the observer, are known, the navigational triangle can be solved for meridian angle and declination. The meridian angle can be converted to LHA, and this to GHA. With this and GHA at the time of observation, the SHA of the body can be determined. With SHA and declination, one can identify the body by reference to an almanac. Any method of solving a spherical triangle, with two sides and the included angle being given, is suitable for this purpose. A large-scale, carefully-drawn diagram on the plane of the celestial meridian, using the refinement shown in Figure 1529f, should yield satisfactory results.
Although no formal star identification tables are included in Pub. No. 229, a simple approach to star identification is to scan the pages of the appropriate latitudes, and observe the combination of arguments which give the altitude and azimuth angle of the observation. Thus the declination and LHA Z are determined directly. The star&#8217;s SHA is found from SHA H = LHA H &#8211; LHA . From these quantities the star can be identified from the Nautical Almanac.

Another solution is available through an interchange of arguments using the nearest integral values. The procedure consists of entering Pub. No. 229 with the observer&#8217;s latitude (same name as declination), with the observed azimuth angle (converted from observed true azimuth as required) as LHA and the observed altitude as declination, and extracting from the tables the altitude and azimuth angle respondents. The extracted altitude becomes the body&#8217;s declination; the extracted azimuth angle (or its supplement) is the meridian angle of the body. Note that the tables are always entered with latitude of same name as declination. In north latitudes the tables can be entered with true azimuth as LHA. If the respondents are extracted from above the C-S Line on a right-hand page, the name of the latitude is actually contrary to the declination. Otherwise, the declination of the body has the same name as the latitude. If the azimuth angle respondent is extracted from above the C-S Line, the supplement of the tabular value is the meridian angle, t, of the body. If the body is east of the observer&#8217;s meridian, LHA = 360&#176; &#8211; t; if the body is west of the meridian, LHA = t.

*"Raging waves of the sea, foaming out their own shape; wandering stars, to whom is reserved the blackness of darkness forever." Jude 13

End chapter 15*


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## Fishers of Men

*A good time to throw this in:*

On 20 March, our sun crosses directly over Earth&#8217;s equator, passing from south to north. This event is known as the vernal equinox. Because the sun is above the equator, day and night are approximately equal.
The sun rises due east and sets due west only on the vernal and autumnal equinoxes. The ancients took advantage of this fact and built the Great Sphinx of Egypt facing due east so it would be illuminated by the rising sun on the equinoxes.

Similarly, the Stonehenge monoliths are aligned with the rising sun on these days. In Central America, the ancient Mayan Caracol Tower and the Temples of the Sun and Moon are aligned to coincide with the sun&#8217;s position on the equinoxes.

On the vernal equinox, the ancient Europeans celebrated the goddess of spring&#8217;s arrival. Ostara, also known as Eostre, is also a neopagan fertility god dess. Many historians believe that Eas ter gets its name from Eostre, who had a magical rabbit that could lay eggs. Decorated eggs, egg rolling and egg hunts originate from pagan fertility rites dedicated to her.

Eggs, which symbolize fertility and rebirth, were offered to the earth to ensure a productive harvest. The hare was regarded as the sacred animal of the lunar goddess because of its fertility. In 1971, the first Earth Day celebration was held on the vernal equinox.










15 Mar., Tonight, the moon is high in the west just below the Gemini Twins. Mars is a little more than 1 fist-width to the moon&#8217;s lower right, and Orion is slightly to the moon&#8217;s left, close to the horizon.

18 Mar., The moon passes within 1 degree of Regulus, the heart of Leo the Lion, as they move higher in the eastern sky this evening. Bright Saturn is to the moon&#8217;s lower left.

20 Mar., The vernal equinox occurs at 0548 UT as the sun, appearing to travel along the ecliptic, crosses the celestial equator into the northern celestial hemisphere.

27 Mar., Low in the south, the moon is in the middle of the constellation Scorpius just before sunrise. The red star Antares, the Scorpion&#8217;s heart, is less than 1 finger-width to the moon&#8217;s upper right.

8 Apr., Tonight is the perfect opportunity to admire the Pleiacies Cluster. About 1 &#189; to 2 hours after sunset, look for the thin waxing crescent moon low in the west. With the naked eye, you should be able to see a tight group of stars just below the moon. How many individual stars can you see? When you look with binoculars, you should be able to see all seven sisters. (use binoculars)

11. Apr., Look high in the west at dusk to see Mars one-half finger- width to the moon&#8217;s upper left. As evening passes, they slip toward the horizon and grow closer until they appear to touch just before midnight. (use binoculars)

14. Apr., The moon joins Regulus and Saturn high in the south this evening. Tonight, the moon is on the right; tomorrow, it will be on the left.

21 Apr., The Lyrid meteor shower is at its best tonight. Unfortunately, the bright moon will make viewing this sometimes strong shower difficult.

26 Apr., The moon is in the handle of the teapot constellation, Sagittarius, this morning. Jupiter is less than 1 fist-width to the moon&#8217;s left.

6 May, The thin waxing crescent moon is just above Mercury near the western horizon at sunset. This is one of the year&#8217;s best opportunities to see Mercury. (use binoculars)

9 May, Tonight, the moon lies between Mars to the upper left and the Gemini Twins to the right.

12 May, Saturn and Regulus are to the moon&#8217;s upper right this evening. Saturn is the brighter of the two.


----------



## Fishers of Men

*CHAPTER 16*
INSTRUMENTS FOR CELESTIAL NAVIGATION
THE MARINE SEXTANT
1600.	Description And Use
The marine sextant measures the angle between two points by bringing the direct ray from one point and a double-reflected ray from the other into coincidence. Its principal use is to measure the altitudes of celestial bodies above the visible sea horizon. It may also be used to measure vertical angles to find the range from an object of known height. Sometimes it is turned on its side and used for measuring the angular distance between two terrestrial objects.

A marine sextant can measure angles up to approximately 120&#176;. Originally, the term &#8220;sextant&#8221; was applied to the navigator&#8217;s double-reflecting, altitude-measuring instrument only if its arc was 60&#176; in length, or 1/6 of a circle, permitting measurement of angles from 0&#176; to 120&#176;. In modern usage the term is applied to all modern navigational altitude-measuring instruments regardless of angular range or principles of operation.

1601.	Optical Principles Of A Sextant
When a plane surface reflects a light ray, the angle of reflection equals the angle of incidence. The angle between the first and final directions of a ray of light that has undergone double reflection in the same plane is twice the angle the two reflecting surfaces make with each other (Figure 1601).










In Figure 1601, AB is a ray of light from a celestial body.

The index mirror of the sextant is at B, the horizon glass at C, and the eye of the observer at D. Construction lines EF and CF are perpendicular to the index mirror and horizon glass, respectively. Lines BG and CG are parallel to these mirrors.
Therefore, angles BFC and BGC are equal because their sides are mutually perpendicular. Angle BGC is the inclination of the two reflecting surfaces. The ray of light AB is reflected at mirror B, proceeds to mirror C, where it is again
reflected, and then continues on to the eye of the observer at D. Since the angle of reflection is equal to the angle of incidence,
ABE = EBC, and ABC = 2EBC.
BCF = FCD, and BCD = 2BCF.
Since an exterior angle of a triangle equals the sum of the two non adjacent interior angles, ABC = BDC+BCD, and EBC = BFC+BCF.
Transposing,
BDC = ABC-BCD, and BFC = EBC-BCF.

Substituting 2EBC for ABC, and 2BCF for BCD in the first of these equations,
BDC = 2EBC-2BCF, or BDC=2 (EBC-BCF).

Since BFC=EBC - BCF, and BFC = BGC, therefore BDC = 2BFC = 2BGC.

That is, BDC, the angle between the first and last directions of the ray of light, is equal to 2BGC, twice the angle of inclination of the reflecting surfaces. Angle BDC is the
altitude of the celestial body.

If the two mirrors are parallel, the incident ray from any observed body must be parallel to the observer&#8217;s line of sight through the horizon glass. In that case, the body&#8217;s altitude would be zero. The angle that these two reflecting surfaces make with each other is one-half the observed angle. The graduations on the arc reflect this half angle relationship between the angle observed and the mirrors&#8217; angle.

1602.	Micrometer Drum Sextant
Figure 1602 shows a modern marine sextant, called a micrometer drum sextant. In most marine sextants, brass or aluminum comprise the frame, A. Frames come in various designs; most are similar to this. Teeth mark the outer edge of the limb, B; each tooth marks one degree of altitude. The altitude graduations, C, along the limb, mark the arc. Some sextants have an arc marked in a strip of brass, silver, or platinum inlaid in the limb.










The index arm, D, is a movable bar of the same material as the frame. It pivots about the center of curvature of the limb. The tangent screw, E, is mounted perpendicularly on the end of the index arm, where it engages the teeth of the limb. Because the observer can move the index arm through the length of the arc by rotating the tangent screw, this is sometimes called an &#8220;endless tangent screw.&#8221; Contrast this with the limited-range device on older instruments. The release, F, is a spring-actuated clamp that keeps the tangent screw engaged with the limb&#8217;s teeth. The observer can disengage the tangent screw and move the index arm along the limb for rough adjustment. 

The end of the tangent screw mounts a micrometer drum, G, graduated in minutes of altitude. One complete turn of the drum moves the index arm one degree along the arc. Next to the micrometer drum and fixed on the index arm is a vernier, H, that reads in fractions of a minute. The vernier shown is graduated into ten parts, permitting readings to 1/10 of a minute of arc (0.1&#8217. Some sextants (generally of European manufacture) have verniers graduated into only five parts, permitting readings to 0.2&#8217;.

The index mirror, I, is a piece of silvered plate glass mounted on the index arm, perpendicular to the plane of the instrument, with the center of the reflecting surface directly over the pivot of the index arm. The horizon glass, J, is a piece of optical glass silvered on its half nearer the frame.
It is mounted on the frame, perpendicular to the plane of the sextant. The index mirror and horizon glass are mounted so that their surfaces are parallel when the micrometer drum is set at 0&#176;, if the instrument is in perfect adjustment. Shade glasses, K, of varying darkness are mounted on the sextant&#8217;s frame in front of the index mirror and horizon glass.
They can be moved into the line of sight as needed to reduce the intensity of light reaching the eye.

The telescope, L, screws into an adjustable collar in line with the horizon glass and parallel to the plane of the instrument. Most modern sextants are provided with only one telescope. When only one telescope is provided, it is of the &#8220;erect image type,&#8221; either as shown or with a wider &#8220;object glass&#8221; (far end of telescope), which generally is shorter in length and gives a greater field of view. The second telescope, if provided, may be the &#8220;inverting type.&#8221; The inverting telescope, having one lens less than the erect type,
absorbs less light, but at the expense of producing an inverted image. A small colored glass cap is sometimes provided, to be placed over the &#8220;eyepiece&#8221; (near end of telescope) to reduce glare. With this in place, shade glasses are generally not needed. A &#8220;peep sight,&#8221; or clear tube which serves to direct the line of sight of the observer when no telescope is used, may be fitted.

Sextants are designed to be held in the right hand.
Some have a small light on the index arm to assist in reading altitudes. The batteries for this light are fitted inside a recess in the handle, M. Not clearly shown in Figure 1602 are the tangent screw, E, and the three legs.

There are two basic designs commonly used for mounting and adjusting mirrors on marine sextants. On the U.S. Navy Mark 3 and certain other sextants, the mirror is mounted so that it can be moved against retaining or mounting springs within its frame. Only one perpendicular adjustment screw is required. On the U.S. Navy Mark 2 and other sextants the mirror is fixed within its frame. Two perpendicular adjustment screws are required. One screw must be loosened before the other screw bearing on the same surface is tightened.

1603.	Vernier Sextant
Most recent marine sextants are of the micrometer drum type, but at least two older-type sextants are still in use. These differ from the micrometer drum sextant principally in the manner in which the final reading is made. They are called vernier sextants.
The clamp screw vernier sextant is the older of the two. In place of the modern release clamp, a clamp screw is fitted on the underside of the index arm. To move the index arm, the clamp screw is loosened, releasing the arm. When the arm is placed at the approximate altitude of the body being observed, the clamp screw is tightened. Fixed to the clamp screw and engaged with the index arm is a long tangent screw. When this screw is turned, the index arm moves slowly, permitting accurate setting. Movement of the index arm by the tangent screw is limited to the length of the screw (several degrees of arc). Before an altitude is measured, this screw should be set to the approximate midpoint of its range. The final reading is made on a vernier set in the index arm below the arc. A small microscope or magnifying glass fitted to the index arm is used in making the final reading.

The endless tangent screw vernier sextant is identical to the micrometer drum sextant, except that it has no drum, and the fine reading is made by a vernier along the arc, as with theclamp screw vernier sextant. The release is the same as on the micrometer drum sextant, and teeth are cut into the underside of the limb which engage with the endless tangent screw.

1604.	Sextant Sun Sights
Hold the sextant vertically and direct the sight line at the horizon directly below the sun. After moving suitable shade glasses into the line of sight, move the index arm outward along the arc until the reflected image appears in the horizon glass near the direct view of the horizon. Rock the sextant slightly to the right and left to ensure it is perpendicular. As the observer rocks the sextant, the image of the sun appears to move in an arc, and the observer may have to turn slightly to prevent the image from moving off the horizon glass.

The sextant is vertical when the sun appears at the bottom
of the arc. This is the correct position for making the observation. The sun&#8217;s reflected image appears at the center of the horizon glass; one half appears on the silvered part, and the other half appears on the clear part. Move the index arm with the drum or vernier slowly until the sun appears to be resting exactly on the horizon, tangent to the lower limb. The novice observer needs practice to determine the exact point of tangency. Beginners often err by bringing the image down too far.
Some navigators get their most accurate observations by letting the body contact the horizon by its own motion, bringing it slightly below the horizon if rising, and above if setting. At the instant the horizon is tangent to the disk, the navigator notes the time. The sextant altitude is the uncorrected reading of the sextant.

1605.	Sextant Moon Sights
When observing the moon, follow the same procedure as for the sun. Because of the phases of the moon, the upper limb of the moon is observed more often than that of the sun. When the terminator (the line between light and dark areas) is nearly vertical, be careful in selecting the limb to shoot. Sights of the moon are best made during either daylight hours or that part of twilight in which the moon is least luminous. At night, false horizons may appear below the moon because the moon illuminates the water below it.

1606.	Sextant Star And Planet Sights
Use one of these three methods when making the initial altitude approximation on a star or planet:
Method 1. Set the index arm and micrometer drum on 0&#176; and direct the line of sight at the body to be observed.
Then, while keeping the reflected image of the body in the mirrored half of the horizon glass, swing the index arm out and rotate the frame of the sextant down. Keep the reflected image of the body in the mirror until the horizon appears in the clear part of the horizon glass. Then, make the observation.
When there is little contrast between brightness of the sky and the body, this procedure is difficult. If the body is &#8220;lost&#8221; while it is being brought down, it may not be recovered without starting over again.
Method 2. Direct the line of sight at the body while holding the sextant upside down. Slowly move the index arm out until the horizon appears in the horizon glass. Then invert the sextant and take the sight in the usual manner.
Method 3. Determine in advance the approximate altitude and azimuth of the body by a star finder such as No. 2102D. Set the sextant at the indicated altitude and face in the direction of the azimuth. The image of the body should appear in the horizon glass with a little searching.

When measuring the altitude of a star or planet, bring its center down to the horizon. Stars and planets have no discernible upper or lower limb; observe the center of the point of light. Because stars and planets have no discernible limb and because their visibility may be limited, the method of letting a star or planet intersect the horizon by its own motion is not recommended. As with the sun and moon, however, &#8220;rock the sextant&#8221; to establish perpendicularity.

1607.	Taking A Sight
Predict expected altitudes and azimuths for up to eight bodies when preparing to take celestial sights. Choose the stars and planets that give the best bearing spread. Try to select bodies with a predicted altitude between 30&#176; and 70&#176;.

Take sights of the brightest stars first in the evening; take sights of the brightest stars last in the morning.
Occasionally, fog, haze, or other ships in a formation may obscure the horizon directly below a body which the navigator wishes to observe. If the arc of the sextant is sufficiently long, a back sight might be obtained, using the opposite point of the horizon as the reference. For this the observer faces away from the body and observes the supplement of the altitude. If the sun or moon is observed in this manner, what appears in the horizon glass to be the lower limb is in fact the upper limb, and vice versa. 

In the case of the sun, it is usually preferable to observe what appears to be the upper limb. The arc that appears when rocking the sextant for a back sight is inverted; that is, the highest point indicates the position of perpendicularity.

If more than one telescope is furnished with the sextant, the erecting telescope is used to observe the sun. A wider field of view is present if the telescope is not used.
The collar into which the sextant telescope fits may be adjusted in or out, in relation to the frame. When moved in, more of the mirrored half of the horizon glass is visible to the navigator, and a star or planet is more easily observed when the sky is relatively bright. Near the darker limit of twilight, the telescope can be moved out, giving a broader view of the clear half of the glass, and making the less distinct horizon more easily discernible. If both eyes are kept open until the last moments of an observation, eye strain
will be lessened. Practice will permit observations to be made quickly, reducing inaccuracy due to eye fatigue.

When measuring an altitude, have an assistant note and record the time if possible, with a &#8220;stand-by&#8221; warning when the measurement is almost ready, and a &#8220;mark&#8221; at the moment a sight is made. If a flashlight is needed to see the comparing watch, the assistant should be careful not to interfere with the navigator&#8217;s night vision.
If an assistant is not available to time the observations, the observer holds the watch in the palm of his left hand, leaving his fingers free to manipulate the tangent screw of the sextant. After making the observation, he notes the time as quickly as possible. The delay between completing the altitude observation and noting the time should not be more than one or two seconds.

1608.	Reading The Sextant
Reading a micrometer drum sextant is done in three steps. 
The degrees are read by noting the position of the arrow on the index arm in relation to the arc. 
The minutes are read by noting the position of the zero on the vernier with
relation to the graduations on the micrometer drum. 
The fraction of a minute is read by noting which mark on the vernier most nearly coincides with one of the graduations on the micrometer drum. 
This is similar to reading the time with the hour, minute, and second hands of a watch. In both, the relationship of one part of the reading to the others should be kept in mind. Thus, if the hour hand of a watch were about on &#8220;4,&#8221; one would know that the time was about four o&#8217;clock. But if the minute hand were on &#8220;58,&#8221; one would know that the time was 0358 (or 1558), not 0458 (or 1658). Similarly, if the arc indicated a reading of about 40&#176;, and 58&#8217; on the micrometer drum were opposite zero on the vernier, one would know that the reading was 39&#176; 58&#8217;, not 40&#176;58&#8217;. Similarly, any doubt as to the correct minute can be removed by noting the fraction of a minute from the position of the vernier. In Figure 1608a the reading is 29&#176; 42.5&#8217;.










The arrow on the index mark is between 29&#176; and 30&#176;, the zero on the vernier is between 42&#8217; and 43&#8217;, and the 0.5&#8217; graduation on the vernier coincides with one of the graduations on the micrometer drum.

The principle of reading a vernier sextant is the same, but the reading is made in two steps. Figure 1608b shows a typical altitude setting. Each degree on the arc of this sextant is graduated into three parts, permitting an initial reading by the reference mark on the index arm to the nearest 20&#8217; of arc. In this illustration the reference mark lies between 29&#176;40&#8217; and 30&#176;00&#8217;, indicating a reading between these values. The reading for the fraction of 20&#8217; is made using the vernier, which is engraved on the index arm and has the small reference mark as its zero graduation. On this vernier, 40 graduations coincide with 39 graduations on the arc. Each graduation on the vernier is equivalent to 1/40 of one graduation of 20&#8217; on the arc, or 0.5&#8217;, or 30&#8221;










In the illustration, the vernier graduation representing 2 &#189;&#8217; (2&#8217;30&#8221 most nearly coincides with one of the graduations on the arc. Therefore, the reading is 29&#176;42&#8217;30&#8221;, or 29&#176;42.5&#8217;, as before.

When a vernier of this type is used, any doubt as to which mark on the vernier coincides with a graduation on the arc can usually be resolved by noting the position of the vernier mark on each side of the one that seems to be in coincidence.
Negative readings, such as a negative index correction, are made in the same manner as positive readings; the various figures are added algebraically. Thus, if the three parts of a micrometer drum reading are ( - )1&#176;, 56&#8217; and 0.3&#8217;, the
total reading is ( - )1&#176; + 56&#8217; + 0.3&#8217; = ( - )3.7&#8217;.

1609.	Developing Observational Skill
A well-constructed marine sextant is capable of measuring angles with an instrument error not exceeding 0.1&#8217;. Lines of position from altitudes of this accuracy would not be in error by more than about 200 yards. However, there are various sources of error, other than instrumental, in altitudes measured by sextant. One of the principal sources is the observer.

The first fix a student celestial navigator plots is likely to be disappointing. Most navigators require a great amount of practice to develop the skill necessary for good observations. But practice alone is not sufficient. Good technique should be developed early and refined throughout the navigator&#8217;s career. Many good pointers can be obtained from experienced navigators, but each develops his own technique, and a practice that proves successful for one observer may not help another. Also, an experienced navigator is not necessarily a good observer. Navigators have a natural tendency to judge the accuracy of their observations by the size of the figure formed when the lines of position are plotted. Although this is some indication, it is an imperfect one, because it does not indicate errors of individual observations, and may not reflect constant errors. Also, it is a compound of a number of errors, some of which are not subject to the navigator&#8217;s control.

Lines of position from celestial observations can be compared with good positions obtained by electronics or piloting.
Common sources of error are:
1.	The sextant may not be rocked properly.
2.	Tangency may not be judged accurately.
3.	A false horizon may have been used.
4.	Subnormal refraction (dip) might be present.
5.	The height of eye may be wrong.
6.	Time might be in error.
7.	The index correction may have been determined incorrectly.
8.	The sextant might be out of adjustment.
9.	An error may have been made in the computation.
Generally, it is possible to correct observation technique
errors, but occasionally a personal error will persist.
This error might vary as a function of the body observed, degree of fatigue of the observer, and other factors. For this reason, a personal error should be applied with caution.
To obtain greater accuracy, take a number of closely spaced observations. Plot the resulting altitudes versus time and fair a curve through the points. Unless the body is near the celestial meridian, this curve should be a straight line.
Use this graph to determine the altitude of the body at any time covered by the graph. It is best to use a point near the middle of the line. Using a calculator to reduce the sight will also yield greater accuracy because of the rounding errors inherent in the use of sight reduction tables.

A simpler method involves making observations at equal intervals. This procedure is based upon the assumption that, unless the body is on the celestial meridian, the change in altitude should be equal for equal intervals of time. Observations can be made at equal intervals of altitude or time. If time intervals are constant, the mid time and the average altitude are used as the observation. If altitude increments are constant, the average time and mid altitude are used.

If only a small number of observations is available, reduce and plot the resulting lines of position; then adjust them to a common time. The average position of the line might be used, but it is generally better practice to use the middle line. Reject any observation considered unreliable when determining the average.

1610.	Care Of The Sextant
A sextant is a rugged instrument. However, careless handling or neglect can cause it irreparable harm. If you drop it, take it to an instrument repair shop for testing and inspection. When not using the sextant, stow it in a sturdy and sufficiently padded case. Keep the sextant out of excessive heat and dampness. Do not expose it to excessive vibration. Do not leave it unattended when it is out of its case. Do not hold it by its limb, index arm, or telescope.

Lift it by its frame or handle. Do not lift it by its arc or index bar.
Next to careless handling, moisture is the sextant&#8217;s greatest enemy. Wipe the mirrors and the arc after each use. If the mirrors get dirty, clean them with lens paper and a small amount of alcohol. Clean the arc with ammonia; never use a polishing compound. When cleaning, do not apply excessive pressure to any part of the instrument.
Silica gel kept in the sextant case will help keep the instrument free from moisture and preserve the mirrors.
Occasionally heat the silica gel to remove the absorbed moisture.
Rinse the sextant with fresh water if sea water gets on it. Wipe the sextant gently with a soft cotton cloth and dry the optics with lens paper.

Glass optics do not transmit all the light received because glass surfaces reflect a small portion of light incident on their face. This loss of light reduces the brightness of the object viewed. Viewing an object through several glass optics affects the perceived brightness and makes the image indistinct. The reflection also causes glare which obscures the object being viewed. To reduce this effect to a minimum, the glass optics are treated with a thin, fragile, anti reflection coating. Therefore, apply only light pressure when polishing the coated optics. Blow loose dust off the lens before wiping them so grit does not scratch the lens.
Frequently oil and clean the tangent screw and the teeth on the side of the limb. Use the oil provided with the sextant or an all-purpose light machine oil. Occasionally set the index arm of an endless tangent screw at one extremity of the limb, oil it lightly, and then rotate the tangent screw over the length of the arc. This will clean the teeth and spread oil over them. When stowing a sextant for a long period, clean it thoroughly, polish and oil it, and protect its arc with a thin coat of petroleum jelly.
If the mirrors need re-silvering, take the sextant to an instrument shop.

1611.	Non Adjustable Sextant Errors
The non-adjustable sextant errors are prismatic error, graduation error, and centering error.
Prismatic error occurs when the faces of the shade glasses and mirrors are not parallel. Error due to lack of parallelism in the shade glasses may be called shade error.
The navigator can determine shade error in the shade glasses near the index mirror by comparing an angle measured when a shade glass is in the line of sight with the same angle measured when the glass is not in the line of sight. In this manner, determine and record the error for each shade glass. Before using a combination of shade glasses, determine their combined error. If certain observations require additional shading, use the colored telescope eyepiece cover.
This does not introduce an error because direct and reflected rays are traveling together when they reach the cover and are, therefore, affected equally by any lack of parallelism of its two sides.

Graduation errors occur in the arc, micrometer drum, and vernier of a sextant which is improperly cut or incorrectly calibrated. Normally, the navigator cannot determine whether the arc of a sextant is improperly cut, but the principle of the vernier makes it possible to determine the existence of graduation errors in the micrometer drum or vernier. This is a useful guide in detecting a poorly made instrument. The first and last markings on any vernier should align perfectly with one less graduation on the adjacent micrometer drum.

Centering error results if the index arm does not pivot at the exact center of the arc&#8217;s curvature. Calculate centering error by measuring known angles after removing all adjustable errors. Use horizontal angles accurately measured with a theodolite as references for this procedure.
Several readings by both theodolite and sextant should minimize errors. If a theodolite is not available, use calculated angles between the lines of sight to stars as the reference, comparing these calculated values with the values determined by the sextant. To minimize refraction errors, select stars at about the same altitude and avoid stars near the horizon.
The same shade glasses, if any, used for determining index error should be used for measuring centering error.
The manufacturer normally determines the magnitude of all three non-adjustable errors and reports them to the user as instrument error. The navigator should apply the correction for this error to each sextant reading.

1612.	Adjustable Sextant Error
The navigator should measure and remove the following adjustable sextant errors in the order listed:
1.	Perpendicularity Error: Adjust first for perpendicularity of the index mirror to the frame of the sextant. To test for perpendicularity, place the index arm at about 35&#176; on the arc and hold the sextant on its side with the index mirror up and toward the eye. Observe the direct and reflected views of the sextant arc, as illustrated in Figure 1612a. 










If the two views are not joined in a straight line, the index mirror is not perpendicular. If the reflected image is above the direct view, the mirror is inclined forward. If the reflected image is below the direct view, the mirror is inclined backward. Make the adjustment using two screws behind the index mirror.
2.	Side Error: An error resulting from the horizon glass
not being perpendicular is called side error. To test for side error, set the index arm at zero and direct the line of sight at a star. Then rotate the tangent screw back and forth so that the reflected image passes alternately above and below the direct view. If, in changing from one position to the other, the reflected image passes directly over the unreflected image, no side error exists. If it passes to one side, side error exists. Figure 1612b illustrates observations without side error (left) and with side error (right).










Whether the sextant reads zero when the true and reflected images are in coincidence is immaterial for this test. An alternative method is to observe a vertical line, such as one edge of the mast of another vessel (or the sextant can be held on its side and the horizon used). If the direct and reflected portions do not form a continuous line, the horizon glass is not perpendicular to the frame of the sextant. A third method involves holding the sextant vertically, as in observing the altitude of a celestial body.
Bring the reflected image of the horizon into coincidence with the direct view until it appears as a continuous line across the horizon glass. Then tilt the sextant right or left. If the horizon still appears continuous, the horizon glass is perpendicular to the frame, but if the reflected portion appears above or below the part seen directly, the glass is not perpendicular. Make the appropriate adjustment using two screws behind the horizon glass.
3.	Collimation Error: If the line of sight through the telescope is not parallel to the plane of the instrument, a collimation error will result. Altitudes measured will be greater than their actual values. To check for parallelism of the telescope, insert it in its collar and observe two stars 90&#176; or more apart. Bring the reflected image of one into coincidence with the direct view of the other near either the right or left edge of the field of view (the upper or lower edge if the sextant is horizontal). Then tilt the sextant so that the stars appear near the opposite edge. If they remain in coincidence, the telescope is parallel to the frame; if they separate, it is not. An alternative method involves placing the telescope in its collar and then laying the sextant on a flat table. Sight along the frame of the sextant and have an assistant place a mark on the opposite bulkhead, in line with the frame. Place another mark above the first, at a distance equal to the distance from the center of the telescope to the frame. This second line should be in the center of the field of view of the telescope if the telescope is parallel to the frame. Adjust the collar to correct for non-parallelism.
4.	Index Error: Index error is the error remaining after the navigator has removed perpendicularity error, side error, and collimation error. The index mirror and horizon glass not being parallel when the index arm is set exactly at zero is the major cause of index error. To test for parallelism of the mirrors, set the instrument at zero and direct the line of sight at the horizon. Adjust the sextant reading as necessary to cause both images of the horizon to come into line. The sextant&#8217;s reading when the horizon comes into line is the index error. If the index error is positive, subtract it from each sextant reading. If the index error is negative, add it to each sextant reading.

1613.	Selecting A Sextant
Carefully match the selected sextant to its required uses.
For occasional small craft or student use, a plastic sextant may be adequate. A plastic sextant may also be appropriate for an emergency navigation kit. Accurate offshore navigation requires a quality metal instrument. For ordinary use in measuring altitudes of celestial bodies, an arc of 90&#176; or slightly more is sufficient. If using a sextant for back sights or determining horizontal angles, purchase one with a longer arc. If necessary, have an experienced mariner examine the sextant and test it for non adjustable errors before purchase.

1614.	The Artificial Horizon
Measurement of altitude requires an exact horizontal reference.
At sea, the visible sea horizon normally provides this reference. If the horizon is not clearly visible, however, a different horizontal reference is required. Such a reference is commonly termed an artificial horizon. 

If it is attached to, or part of, the sextant, altitudes can be measured at sea, on land, or in the air, whenever celestial bodies are available for observations. Any horizontal reflecting surface will work. A pan of any liquid sheltered from the wind will serve. Foreign material on the surface of the liquid is likely to distort the image and introduce an error in the reading.
To use an external artificial horizon, stand or sit in such a position that the celestial body to be observed is reflected in the liquid, and is also visible in direct view. With the sextant, bring the double-reflected image into coincidence with the image appearing in the liquid. For a lower limb observation of the sun or the moon, bring the bottom of the double-reflected image into coincidence with the top of the image in the liquid. For an upper-limb observation, bring the opposite sides into coincidence. If one image covers the other, the observation is of the center of the body.
After the observation, apply the index correction and any other instrumental correction. Then take half the remaining angle and apply all other corrections except dip (height of eye) correction, since this is not applicable. If the center of the sun or moon is observed, omit the correction for semidiameter.

1615.	Artificial Horizon Sextants
Various types of artificial horizons have been used, including a bubble, gyroscope, and pendulum. Of these, the bubble has been most widely used. This type of instrument is fitted as a backup system to inertial and other positioning systems in a few aircraft, fulfilling the requirement for a self contained, non-emitting system. On land, a skilled observer using a 2-minute averaging bubble or pendulum sextant can measure altitudes to an accuracy of perhaps 2&#8217;, (2 miles).

This, of course, refers to the accuracy of measurement only, and does not include additional errors such as abnormal refraction, deflection of the vertical, computing and plotting errors, etc. In steady flight through smooth air the error of a 2-minute observation is increased to perhaps 5 to 10 miles. At sea, with virtually no roll or pitch, results should approach those on land. However, even a gentle roll causes large errors. Under these conditions observational errors of 10-16 miles are not unreasonable. With a moderate sea, errors of 30 miles or more are common. In a heavy sea, any useful observations are virtually impossible to obtain. Single altitude observations in a moderate sea can be in error by a matter of degrees.

When the horizon is obscured by ice or haze, polar navigators can sometimes obtain better results with an artificial horizon sextant than with a marine sextant. 

Some artificial Horizon sextants have provision for making observations with the natural horizon as a reference, but results are not generally as satisfactory as by marine sextant. Because of their more complicated optical systems, and the need for providing a horizontal reference, artificial-horizon sextants are generally much more costly to manufacture than marine
sextants.
Altitudes observed by artificial-horizon sextants are subject to the same errors as those observed by marine sextant, except that the dip (height of eye) correction does not apply. Also, when the center of the sun or moon is observed, no correction for semi-diameter is required.

CHRONOMETERS
1616.	The Marine Chronometer
The spring-driven marine chronometer is a precision timepiece. It is used aboard ship to provide accurate time for timing celestial observations. A chronometer differs from a spring-driven watch principally in that it contains a variable lever device to maintain even pressure on the mainspring, and a special balance designed to compensate for temperature variations.

A spring-driven chronometer is set approximately to Greenwich mean time (GMT) and is not reset until the instrument is overhauled and cleaned, usually at three-year intervals. The difference between GMT and chronometer time &#169; is carefully determined and applied as a correction to all chronometer readings. This difference, called chronometer error (CE), is fast (F) if chronometer time is later than GMT, and slow (S) if earlier. The amount by which chronometer error changes in 1 day is called chronometer rate. An erratic rate indicates a defective instrument requiring repair.

The principal maintenance requirement is regular winding at about the same time each day. At maximum intervals of about three years, a spring-driven chronometer should be sent to a chronometer repair shop for cleaning and overhaul.

1617.	Quartz Crystal Marine Chronometers
Quartz crystal marine chronometers have replaced spring-driven chronometers aboard many ships because of their greater accuracy. They are maintained on GMT directly from radio time signals. This eliminates chronometer error (CE) and watch error (WE) corrections. Should the second hand be in error by a readable amount, it can be reset electrically.
The basic element for time generation is a quartz crystal oscillator. The quartz crystal is temperature compensated and is hermetically sealed in an evacuated envelope.
A calibrated adjustment capability is provided to adjust for the aging of the crystal.
The chronometer is designed to operate for a minimum of 1 year on a single set of batteries. A good marine chronometer has a built-in push button battery test meter. The meter face is marked to indicate when the battery should be replaced. The chronometer continues to operate and keep the correct time for at least 5 minutes while the batteries are changed. The chronometer is designed to accommodate the gradual voltage drop during the life of the batteries while maintaining accuracy requirements.

1618.	Watches
A chronometer should not be removed from its case to time sights. Observations may be timed and ship&#8217;s clocks set with a comparing watch, which is set to chronometer time (GMT) and taken to the bridge wing for recording sight times. In practice, a wrist watch coordinated to the nearest second with the chronometer will be adequate.
A stop watch, either spring wound or digital, may also be used for celestial observations. In this case, the watch is started at a known GMT by chronometer, and the elapsed time of each sight added to this to obtain GMT of the sight.

&#8220;And they that be wise shall shine as the brightness of the firmament; and they that turn many to righteousness as the stars for ever and ever.&#8221; Dan 12:3

*End ch 16.
*


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## reel

Ahhh... Such memories.
...


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## Fishers of Men

*Chapter 17
AZIMUTHS AND AMPLITUDES*
INTRODUCTION
1700. Compass Checks
At sea, the mariner is constantly concerned about the accuracy of the gyro compass. There are several ways to check the accuracy of the gyro. He can, for example, compare it with an accurate electronic navigator such as an inertial navigaton system. Lacking a sophisticated electronic navigation suite, he can use the celestial techniques of comparing the measured and calculated azimuths and amplitudes of celestial bodies. The difference between the calculated value and the value determined by gyro measurement is gyro error. This chapter discusses these procedures. Theoretically, these procedures work with any celestial body. However, the sun and Polaris are used most often when measuring azimuths, and the sun when measuring amplitudes.
AZIMUTHS

1701. Compass Error By Azimuth Of The Sun
Mariners use Pub 229, Sight Reduction Tables for Marine Navigation to compute the sun&#8217;s azimuth. They compare the computed azimuth to the azimuth measured with the compass to determine compass error. In computing an azimuth, interpolate the tabular azimuth angle for the difference between the table arguments and the actual values of declination, latitude, and local hour angle. Do this triple interpolation of the azimuth angle as follows:
1. Enter the Sight Reduction Tables with the nearest integral values of declination, latitude, and local hour angle. For each of these arguments, extract a base azimuth angle.
2. Reenter the tables with the same latitude and LHA arguments but with the declination argument 1&#176; greater or less than the base declination argument, depending upon whether the actual declination is greater or less than the base argument. Record the difference between the respondent azimuth angle and the base azimuth angle and label it as the azimuth angle difference (Z Diff.).
3. Reenter the tables with the base declination and LHA arguments, but with the latitude argument 1&#176; greater or less than the base latitude argument, depending upon whether the actual (usually DR) latitude is greater or less than the base argument. Record the Z Diff. for the increment of latitude. 4. Reenter the tables with the base declination and latitude arguments, but with the LHA argument 1&#176; greater or less than the base LHA argument, depending upon whether the actual LHA is greater or less than the base argument. Record the Z Diff. for the increment of LHA.
5. Correct the base azimuth angle for each increment.
Example:
In DR latitude 33&#176; 24.0&#8217;N, the azimuth of the sun is 096.5&#176; pgc. At the time of the observation, the declination of the sun is 20&#176; 13.8&#8217;N; the local hour angle of the sun is 316&#176; 41.2&#8217;. Determine compass error.
Solution:
See Figure 1701 Enter the actual value of declination, DR latitude, and LHA. Round each argument to the nearest whole degree. In this case, round the declination and the latitude down to the nearest whole degree. Round the LHA up to the nearest whole degree. Enter the Sight Reduction Tables with these whole degree arguments and extract the base azimuth value for these rounded off arguments. Record the base azimuth value in the table.
As the first step in the triple interpolation process, increase the value of declination by 1&#176; to 21&#176; because the actual declination value was greater than the base declination. Enter the Sight Reduction Tables with the following arguments: 
(1) Declination = 21&#176;; 
(2) DR Latitude = 33&#176;;
(3) LHA = 317&#176;. Record the tabulated azimuth for these arguments.
As the second step in the triple interpolation process, increase the value of latitude by 1&#176; to 34&#176; because the actual DR latitude was greater than the base latitude. Enter the Sight Reduction Tables with the following arguments: 
(1) Declination = 20&#176;; 
(2) DR Latitude = 34&#176;; 
(3) LHA = 317&#176;.










Record the tabulated azimuth for these arguments. As the third and final step in the triple interpolation process, decrease the value of LHA to 316&#176; because the actual LHA value was smaller than the base LHA. Enter the Sight Reduction Tables with the following arguments: (1) Declination = 20&#176;; (2) DR Latitude = 33&#176;; (3) LHA = 316&#176;.
Record the tabulated azimuth for these arguments. Calculate the Z Difference by subtracting the base azimuth from the tabulated azimuth. Be careful to carry the correct sign.
Z Difference = Tab Z - Base Z
Next, determine the increment for each argument by taking the difference between the actual values of each argument and the base argument. Calculate the correction for each of the three argument interpolations by multiplying the increment by the Z difference and dividing the resulting product by 60. The sign of each correction is the same as the sign of the corresponding Z difference used to calculate it. In the above example, the total correction sums to -0.1&#8217;. Apply this value to the base azimuth of 97.8&#176; to obtain the true azimuth 97.7&#176;. Compare this to the compass reading of 096.5&#176; pgc. The compass error is 1.2&#176;E.

AZIMUTH OF POLARIS
1702.	Compass Error By Azimuth Of Polaris
The Polaris tables in the Nautical Almanac list the azimuth of Polaris for latitudes between the equator and 65&#176; N. Figure 2011 in Chapter 20 shows this table. Compare a compass bearing of Polaris to the tabular value of Polaris to determine compass error. The entering arguments for the table are LHA of Aries and observer latitude.
Example:
On March 17, 1994, at L 33&#176; 15.0&#8217; N and 045&#176; 00.0&#8217;W, at 02-00-00 GMT, Polaris bears 358.6&#176;T by compass. Calculate the compass error.
















Solution:
Enter the azimuth section of the Polaris table with the calculated LHA of Aries. In this case, go to the column for LHA Aries between 160&#176; and 169&#176;. Follow that column down and extract the value for the given latitude. Since the increment between tabulated values is so small, visual interpolation is sufficient. In this case, the azimuth for Polaris for the given LHA of Aries and the given latitude is 359.3&#176;.









AMPLITUDES
1703.	Amplitudes
A celestial body&#8217;s amplitude is the arc between the observed body on the horizon and the point where the observer&#8217;s horizon intersects the celestial equator. See Figure 1703.










Calculate an amplitude after observing a body on either the celestial or visual horizon. Compare a body&#8217;s measured amplitude with an amplitude extracted from the Amplitude
table. The difference between the two values represents compass error.
Give amplitudes the suffix N if the body from which it was determined has a northern declination and S if it has a southern declination. Give the amplitudes the prefix E if the body is rising and W if the body is setting.
The values in the Amplitude table assume that the body is on the celestial horizon. The sun is on the celestial horizon when its lower limb is about two-thirds of a diameter above the visible horizon. The moon is on the celestial horizon when its upper limb is on the visible horizon. Planets and stars are on the celestial horizon when they are approximately one sun diameter above the visible horizon.

When using a body on the visible, not celestial, horizon, correct the observed amplitude from Table 23 Apply this table&#8217;s correction to the observed amplitude and not to the amplitude extracted from the Amplitude table. For the sun, a planet, or a star, apply this correction to the observed amplitude in the direction away from the elevated pole. If using the moon, apply one-half of the Table 23 correction in the direction towards the elevated pole.

Navigators most often use the sun when determining amplitudes. The rule for applying the Table 23 corrections to a sun&#8217;s observed amplitude is summarized as follows. If the DR latitude is north and the sun is rising, or if the DR latitude is south and the sun is setting, add the Table 23 correction to the observed amplitude. Conversely, if the DR latitude is north and the sun is setting, or the DR latitude is south and the sun is rising, then subtract the Table 23 correction from the observed amplitude.
The following two sections demonstrate the procedure for obtaining the amplitude of the sun on both the celestial and visible horizons.

1704. Amplitude Of The Sun On The Celestial Horizon
Example:
The DR latitude of a ship is 51&#176; 24.6&#8217; N. The navigator observes the setting sun on the celestial horizon. Its declination is N 19&#176; 40.4&#8217;. Its observed amplitude is W 32.9&#176; N. (32.9&#176; &#8220;north of west,&#8221; or 302.9&#176.
Required:
Compass error.
Solution:
Interpolate in Table 22 for the sun&#8217;s calculated amplitude as follows. See Figure 1704. The actual values for latitude and declination are L = 51.4&#176; N and dec. = N 19.67&#176;. Find the tabulated values of latitude and declination closest to these actual values. In this case, these tabulated values are L = 51&#176; and dec. = 19.5&#176;. Record the amplitude corresponding to these base values, 32.0&#176;, as the base amplitude. Next, holding the base declination value constant at 19.5&#176;, increase the value of latitude to the next tabulated value: N 52&#176;. Note that this value of latitude was increased because the actual latitude value was greater than the base value of latitude. Record the tabulated amplitude for L = 52&#176; and dec. = 19.5&#176;: 32.8&#176;. Then, holding the base latitude value constant at 51&#176;, increase the declination value to the next tabulated value: 20&#176;. Record the tabulated amplitude for L = 51&#176; and dec. = 20&#176;: 32.9&#176;.
The latitude&#8217;s actual value (51.4&#176 is 0.4 of the way between the base value (51&#176 and the value used to determine the tabulated amplitude (52&#176. The declination&#8217;s actual value (19.67&#176 is 0.3 of the way between the base value (19.5&#176 and the value used to determine the tabulated amplitude (20.0&#176. To determine the total correction to base amplitude, multiply these increments (0.4 and 0.3) by the respective difference between the base and tabulated values (+0.8 and +0.9, respectively) and sum the products. The total correction is +0.6&#176;. Add the total correction (+0.6&#176 to the base amplitude (32.0&#176 to determine the final amplitude (32.6&#176.
Calculate the gyro error as follows:
Amplitude (observed) pgc = W 32.9&#176; N
Amplitude (from Table 22) = W 32.6&#176; N
Compass Error 0.3&#176;W

1705. Amplitude Of The Sun On The Visible Horizon
Example:
The same problem as section 1704, except that the sun is setting on the visible horizon.
Required:
Compass error.
Solution:
Interpolate in Table 23 to determine the correction for the sun on the visible horizon as follows. See Figure 1705.. Choose as base values of latitude and declination the tabular values of latitude and declination closest to the actual values. In this case, these tabulated values are L = 51&#176; N and dec. = 20&#176;. Record the correction corresponding to these base values, 1.1&#176;, as the base correction. Completing the interpolation procedure indicates that the base correction (1.1&#176 is the actual correction. Apply this correction in accordance with the rules discussed in section 1703. Since the vessel&#8217;s latitude was north and the sun was setting, subtract the correction from the observed amplitude. The observed amplitude was W 32.9 N. Subtracting the 1.1&#176; correction yields a corrected observed amplitude of W 31.8&#176; N. From section 1704, the tabular amplitude was W 32.6&#176; N.
Calculate the gyro error as follows:









1706. Amplitude By Calculation
As an alternative to using Table 22 and Table 23, use the following formulas to calculate amplitudes:



























End ch 17


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## Fishers of Men

*CHAPTER 18 No, we are not done with "time" yet!
TIME
TIME IN NAVIGATION*
1800. Solar Time
The earth&#8217;s rotation on its axis causes the sun and other celestial bodies to appear to move across the sky from east to west each day. If a person located on the earth&#8217;s equator measured the time interval between two successive transits overhead of a very distant star, he would be measuring the period of the earth&#8217;s rotation. If he then made a similar measurement of the sun, the resulting time would be about 4 minutes longer. This is due to the earth&#8217;s motion around the sun, which continuously changes the apparent place of the sun among the stars. Thus, during the course of a day the sun appears to move a little to the east among the stars so that the earth must rotate on its axis through more than 360&#176; in order to bring the sun overhead again. See Figure 1800.










If the sun is on the observer&#8217;s meridian when the earth is at point A in its orbit around the sun, it will not be on the observer&#8217;s meridian after the earth has rotated through 360&#176; because the earth will have moved along its orbit to point B. Before the sun is again on the observer&#8217;s meridian, the earth must turn still more on its axis. The sun will be on the observer&#8217;s meridian again when the earth has moved to point C in its orbit. Thus, during the course of a day the sun appears to move eastward with respect to the stars. The apparent positions of the stars are commonly reckoned with reference to an imaginary point called the vernal equinox, the intersection of the celestial equator and the ecliptic. The period of the earth&#8217;s rotation measured with respect to the vernal equinox is called a sidereal day. The period with respect to the sun is called an apparent solar day. When measuring time by the earth&#8217;s rotation, using the actual position of the sun results in apparent solar time. Use of the apparent sun as a time reference results in time of non-constant rate for at least three reasons. First, revolution of the earth in its orbit is not constant. Second, time is measured along the celestial equator and the path of the real sun is not along the celestial equator. Rather, its path is along the ecliptic, which is tilted at an angle of 23&#176; 27&#8217; with respect to the celestial equator. Third, rotation of the earth on its axis is not constant.
To obtain a constant rate of time, the apparent sun is replaced by a fictitious mean sun. This mean sun moves eastward along the celestial equator at a uniform speed equal to the average speed of the apparent sun along the ecliptic. This mean sun, therefore, provides a uniform measure of time which approximates the average apparent time. The speed of the mean sun along the celestial equator is 15&#176; per hour of mean solar time.

1801. Equation Of Time
Mean solar time, or mean time as it is commonly called, is sometimes ahead of and sometimes behind apparent solar time. This difference, which never exceeds about 16.4 minutes, is called the equation of time. The navigator most often deals with the equation of time when determining the time of upper meridian passage of the sun. The sun transits the observer&#8217;s upper meridian at local apparent noon. Were it not for the difference in rate between the mean and apparent sun, the sun would be on the observer&#8217;s meridian when the mean sun indicated 1200 local time. The apparent solar time of upper meridian passage, however, is offset from exactly 1200 mean solar time. This time difference, the equation of time at meridian transit, is listed on the right hand daily pages of the Nautical Almanac.
The sign of the equation of time is positive if the time of sun&#8217;s meridian passage is earlier than 1200 and negative if later than 1200. Therefore:
Apparent Time = Mean Time &#8211; (equation of time).
Example 1: Determine the time of the sun&#8217;s meridian passage (Local Apparent Noon) on June 16, 1994. Solution: See Figure 2007 in Chapter 20, the Nautical Almanac&#8217;s right hand daily page for June 16, 1994. The equation of time is listed in the bottom right hand corner of the page. There are two ways to solve the problem, depending on the accuracy required for the value of meridian passage. The time of the sun at meridian passage is given to the nearest minute in the &#8220;Mer. Pass.&#8221;column. For June 16, 1994, this value is 1201.

To determine the exact time of meridian passage, use the value given for the equation of time. This value is listed immediately to the left of the &#8220;Mer. Pass.&#8221; column on the daily pages. For June 16, 1994, the value is given as 00m37s. Use the &#8220;12h&#8221; column because the problem asked for meridian passage at LAN. The value of meridian passage from the &#8220;Mer. Pass.&#8221; column indicates that meridian passage occurs after 1200; therefore, add the 37 second correction to 1200 to obtain the exact time of meridian passage. The exact time of meridian passage for June 16, 1994, is 12h00m37s.

The equation of time&#8217;s maximum value approaches 16m22s in November.
If the Almanac lists the time of meridian passage as 1200, proceed as follows. Examine the equations of time listed in the Almanac to find the dividing line marking where the equation of time changes between positive and negative values. Examine the trend of the values near this dividing line to determine the correct sign for the equation of time.
Example 2: See Figure 1801. Determine the time of the upper meridian passage of the sun on April 16, 1995. 










Solution: From Figure 1801, upper meridian passage of the sun on April 16, 1995, is given as 1200. The dividing line between the values for upper and lower meridian passage on April 16th indicates that the sign of the equation of time changes between lower meridian passage and upper meridian passage on this date; the question, therefore, becomes: does it become positive or negative? Note that on April 18, 1995, upper meridian passage is given as 1159, indicating that on April 18, 1995, the equation of time is positive. All values for the equation of time on the same side of the dividing line as April 18th are positive. Therefore, the equation of time for upper meridian passage of the sun on April 16, 1995 is (+) 00m05s. Upper meridian passage, therefore, takes place at 11h59m55s.

To calculate latitude and longitude at LAN, the navigator seldom requires the time of meridian passage to accuracies greater than one minute. Therefore, use the time listed under the &#8220;Mer. Pass.&#8221; column to estimate LAN unless extraordinary accuracy is required.

1802. Fundamental Systems Of Time
The first fundamental system of time is Ephemeris Time (ET). Ephemeris Time is used by astronomers in calculating the fundamental ephemerides of the sun, moon, and planets. It is not used by navigators. The fundamental system of time of most interest to navigators is Universal Time (UT). UT is the mean solar time on the Greenwich meridian, reckoned in days of 24 mean solar hours beginning with 0h at midnight. Universal Time, in principle, is determined by the average rate of the apparent daily motion of the sun relative to the meridian of Greenwich; but in practice the numerical measure of Universal Time at any instant is computed from sidereal time. Universal Time is the standard in the application of astronomy to navigation. Observations of Universal Times are made by observing the times of transit of stars. The Universal Time determined directly from astronomical observations is denoted UT0. Since the earth&#8217;s rotation is non uniform, corrections must be applied to UT0 to obtain a more uniform time. This more uniform time is obtained by correcting for two known periodic motions.

One motion, the motion of the geographic poles, is the result of the axis of rotation continuously moving with respect to the earth&#8217;s crust. The corrections for this motion are quite small (&#177; 15 milliseconds for Washington, D.C.). On applying the correction to UT0, the result is UT1, which is the same as Greenwich mean time (GMT) used in celestial navigation.
The second known periodic motion is the variation in the earth&#8217;s speed of rotation due to winds, tides, and other phenomena. As a consequence, the earth suffers an annual variation in its speed of rotation, of about &#177; 30 milliseconds. When UT1 is corrected for the mean seasonal variations in the earth&#8217;s rate of rotation, the result is UT2. Although UT2 was at one time believed to be a uniform time system, it was later determined that there are variations in the earth&#8217;s rate of rotation, possibly caused by random accumulations of matter in the convection core of the earth. Such accumulations would change the earth&#8217;s moment of inertia and thus its rate of rotation. The third fundamental system of time, Atomic Time (AT), is based on transitions in the atom. The basic principle of the atomic clock is that electromagnetic waves of a particular frequency are emitted when an atomic transition occurs. The frequency of the cesium beam atomic clock is 9,192,631,770 cycles per second of Ephemeris Time.
The advent of atomic clocks having accuracies better than 1 part in 10 to the 13th power, led in 1961 to the coordination of time and frequency emissions of the U. S. Naval Observatory and the Royal Greenwich Observatory. The master oscillators controlling the signals were calibrated in terms of the cesium standard, and corrections determined at the U. S. Naval Observatory and the Royal Greenwich Observatory were made simultaneously at all transmitting stations. The result is Coordinated Universal Time (UTC).

1803. Time And Arc
One day represents one complete rotation of the earth. Each day is divided into 24 hours of 60 minutes; each minute has 60 seconds.
Time of day is an indication of the phase of rotation of the earth. That is, it indicates how much of a day has elapsed, or what part of a rotation has been completed. Thus, at zero hours the day begins. One hour later, the earth has turned through 1/24 of a day, or 1/24 of 360&#176;, or 360&#176; &#184; 24 = 15&#176; Smaller intervals can also be stated in angular units; since 1 hour or 60 minutes is equivalent to 15&#176;, 1 minute of time is equivalent to 15&#176; &#184; 60 = 0.25&#176; = 15&#8217;, and 1 second of time is equivalent to 15&#8217; &#184; 60 = 0.25&#8217; = 15&#8221;.


















Therefore any time interval can be expressed as an equivalent amount of rotation, and vice versa. Interconversion of these units can be made by the relationships indicated above.
To convert time to arc:
1.	Multiply the hours by 15 to obtain degrees of arc.
2.	Divide the minutes of time by four to obtain degrees.
3.	Multiply the remainder of step 2 by 15 to obtain minutes of arc.
4.	Divide the seconds of time by four to obtain minutes of arc
5.	Multiply the remainder by 15 to obtain seconds of arc.
6.	Add the resulting degrees, minutes, and seconds.
Example 1: Convert 14h21m39s to arc.
Solution:









To convert arc to time:
1.	Divide the degrees by 15 to obtain hours.
2.	Multiply the remainder from step 1 by four to obtain minutes of time.
3.	Divide the minutes of arc by 15 to obtain minutes of time.
4.	Multiply the remainder from step 3 by four to obtain seconds of time.
5.	Divide the seconds of arc by 15 to obtain seconds of time.
6.	Add the resulting hours, minutes, and seconds.
Example 2:
Convert 215&#176; 24&#8217; 45&#8221; to time units.

















Solutions can also be made using arc to time conversion tables in the almanacs. In the Nautical Almanac, the table given near the back of the volume is in two parts, permitting separate entries with degrees, minutes, and quarter minutes of arc. This table is arranged in this manner because the navigator converts arc to time more often than the reverse.
Example 3: Convert 334&#176;18&#8217;22&#8221; to time units, using the Nautical Almanac arc to time conversion table.
Solution:
Convert the 22&#8221; to the nearest quarter minute of arc for solution to the nearest second of time. Interpolate if more precise results are required.
334&#176; 00.00m = 22h16m00s
000&#176; 18.25m = 00h01m13s
334&#176; 18&#8217; 22&#8221; = 22h17m13s

1804.	Time And Longitude
Suppose a celestial reference point were directly over a certain point on the earth. An hour later the earth would have turned through 15&#176;, and the celestial reference would be directly over a meridian 15&#176; farther west. Any difference of longitude between two points is a measure of the angle through which the earth must rotate to separate them. Therefore, places east of an observer have later time, and those west have earlier time, and the difference is exactly equal to the difference in longitude, expressed in time units. The difference in time between two places is equal to the difference of longitude between their meridians, expressed in time units instead of arc.

1805.	The Date Line
Since time is later toward the east and earlier toward the west of an observer, time at the lower branch of one&#8217;s meridian is 12 hours earlier or later depending upon the direction of reckoning. A traveler making a trip around the world gains or loses an entire day. To prevent the date from being in error, and to provide a starting place for each day, a date line is fixed by international agreement. This line coincides with the 180th meridian over most of its length. In crossing this line, the date is altered by one day. If a person is traveling eastward from east longitude to west longitude, time is becoming later, and when the date line is crossed the date becomes 1 day earlier. At any moment the date immediately to the west of the date line (east longitude) is 1 day later than the date immediately to the east of the line. When solving problems, convert local time to Greenwich time and then convert this to local time on the opposite side of the date line.

1806.	Zone Time
At sea, as well as ashore, watches and clocks are normally set to some form of zone time (ZT). At sea the nearest meridian exactly divisible by 15&#176; is usually used as the time meridian or zone meridian. Thus, within a time zone extending 7.5&#8217; on each side of the time meridian the time is the same, and time in consecutive zones differs by exactly one hour. The time is changed as convenient, usually at a whole hour, when crossing the boundary between zones. Each time zone is identified by the number of times the longitude of its zone meridian is divisible by 15&#176;, positive in west longitude and negative in east longitude. This number and its sign, called the zone description (ZD), is the number of whole hours that are added to or subtracted from the zone time to obtain Greenwich mean time (GMT). The mean sun is the celestial reference point for zone time.
See Figure 1806.










Converting ZT to GMT, a positive ZT is added and a negative one subtracted; converting GMT to ZT, a positive ZD is subtracted, and a negative one added.
Example: The GMT is 15h27m09s.
Required: (1) ZT at long. 156&#176;24.4&#8217; W.
(2) ZT at long. 039&#176;04.8&#8217; E.
Solutions:
(1)	GMT 15h27m09s 
ZD +10h (rev.)
ZT 05h27m09s
(2)	GMT 15h27m09s 
ZD &#8211;03 h (rev.) 
ZT 18h27m09s

1807.	Chronometer Time
Chronometer time &#169; is time indicated by a chronometer.
Since a chronometer is set approximately to GMT and not reset until it is overhauled and cleaned about every 3 years, there is nearly always a chronometer error (CE), either
fast (F) or slow (S). The change in chronometer error in 24 hours is called chronometer rate, or daily rate, and designated gaining or losing. With a consistent rate of 1s per day for three years, the chronometer error would be approximately 18m. Since chronometer error is subject to change, it should be determined from time to time, preferably daily at sea. Chronometer error is found by radio time signal, by comparison with another timepiece of known error, or byerror, or by applying chronometer rate to previous readings of the same instrument. It is recorded to the nearest whole or half second. Chronometer rate is recorded to the nearest 0.1 second.
Example: At GMT 1200 on May 12 the chronometer reads 12h04m21s. At GMT 1600 on May 18 it reads 4h04m25s. 
Required:
1. Chronometer error at 1200 GMT May 12.
2.	Chronometer error at 1600 GMT May 18.
3.	Chronometer rate.
4.	Chronometer error at GMT 0530, May 27.









Because GMT is on a 24-hour basis and chronometer time on a 12-hour basis, a 12-hour ambiguity exists. This is ignored in finding chronometer error. However, if chronometer error is applied to chronometer time to find GMT, a 12-hour error can result. This can be resolved by mentally applying the zone description to local time to obtain approximate GMT. A time diagram can be used for resolving doubt as to approximate GMT and Greenwich date. If the sun for the kind of time used (mean or apparent) is between the lower branches of two time meridians (as the standard meridian for local time, and the Greenwich meridian for GMT), the date at the place farther east is one day later than at the place farther west.

1808.	Watch Time
Watch time (WT) is usually an approximation of zone time, except that for timing celestial observations it is easiest to set a comparing watch to GMT. If the watch has a second-setting hand, the watch can be set exactly to ZT or GMT, and the time is so designated. If the watch is not set exactly to one of these times, the difference is known as watch error (WE), labeled fast (F) or slow (S) to indicate whether the watch is ahead of or behind the correct time. If a watch is to be set exactly to ZT or GMT, set it to some whole minute slightly ahead of the correct time and stopped. When the set time arrives, start the watch and check it for accuracy.

The GMT may be in error by 12h, but if the watch is graduated to 12 hours, this will not be reflected. If a watch with a 24-hour dial is used, the actual GMT should be determined. To determine watch error compare the reading of the watch with that of the chronometer at a selected moment. This may also be at some selected GMT. Unless a watch is graduated to 24 hours, its time is designated am before noon and pm after noon.
Even though a watch is set to zone time approximately, its error on GMT can be determined and used for timing observations. In this case the 12-hour ambiguity in GMT should be resolved, and a time diagram used to avoid error. This method requires additional work, and presents a greater probability of error, without compensating advantages. If a stopwatch is used for timing observations, it should be started at some convenient GMT, such as a whole 5m or 10m. The time of each observation is then the GMT plus the watch time. Digital stopwatches and wristwatches are ideal for this purpose, as they can be set from a convenient GMT and read immediately after the altitude is taken.

1809.	Local Mean Time
Local mean time (LMT), like zone time, uses the mean sun as the celestial reference point. It differs from zone time in that the local meridian is used as the terrestrial
reference, rather than a zone meridian. Thus, the local mean time at each meridian differs from every other meridian, the difference being equal to the difference of longitude expressed in time units. At each zone meridian, including 0&#176;, LMT and ZT are identical.

In navigation the principal use of LMT is in rising, setting, and twilight tables. The problem is usually one of converting the LMT taken from the table to ZT. At sea, the difference between the times is normally not more than 30m, and the conversion is made directly, without finding GMT as an intermediate step. This is done by applying a correction equal to the difference of longitude. If the observer is west of the time meridian, the correction is added, and if east of it, the correction is subtracted. If Greenwich time is desired, it is found from ZT.

Where there is an irregular zone boundary, the longitude may differ by more than 7.5&#176; (30m) from the time meridian. If LMT is to be corrected to daylight saving time, the difference in longitude between the local and time meridian can be used, or the ZT can first be found and then increased by one hour.
Conversion of ZT (including GMT) to LMT is the same as conversion in the opposite direction, except that the sign of difference of longitude is reversed. This problem is not normally encountered in navigation.

1810.	Sidereal Time
Sidereal time uses the first point of Aries (vernal equinox) as the celestial reference point. Since the earth revolves around the sun, and since the direction of the earth&#8217;s rotation and revolution are the same, it completes a rotation with respect to the stars in less time (about 3m56.6s of mean solar units) than with respect to the sun, and during one revolution about the sun (1 year) it makes one complete rotation more with respect to the stars than with the sun. This accounts for the daily shift of the stars nearly 1&#176; westward each night. Hence, sidereal days are shorter than solar days, and its hours, minutes, and seconds are correspondingly shorter. Because of nutation, sidereal time is not quite constant in rate. Time based upon the average rate is called mean sidereal time, when it is to be distinguished from the slightly irregular sidereal time. The ratio of mean solar time units to mean sidereal time units is 1:1.00273791.

A navigator very seldom uses sidereal time. Astronomers use it to regulate mean time because its celestial reference point remains almost fixed in relation to the stars.

1811.	Time And Hour Angle
Both time and hour angle are a measure of the phase of rotation of the earth, since both indicate the angular distance of a celestial reference point west of a terrestrial reference meridian. Hour angle, however, applies to any point on the celestial sphere. Time might be used in this respect, but only the apparent sun, mean sun, the first point of Aries, and occasionally the moon, are commonly used. Hour angles are usually expressed in arc units, and are measured from the upper branch of the celestial meridian. Time is customarily expressed in time units. Sidereal time is measured from the upper branch of the celestial meridian, like hour angle, but solar time is measured from the lower branch. Thus, LMT = LHA mean sun plus or minus 180&#176;, LAT = LHA apparent sun plus or minus 180&#176;, and LST = LHA Aries. As with time, local hour angle (LHA) at two places differs by their difference in longitude, and LHA at longitude 0&#176; is called Greenwich hour angle (GHA). In addition, it is often convenient to express hour angle in terms of the shorter arc between the local meridian and the body. This is similar to measurement of longitude from the Greenwich meridian. Local hour angle measured in this way is called meridian angle (t), which is labeled east or west, like longitude, to indicate the direction of measurement. A westerly meridian angle is numerically equal to LHA, while an easterly meridian angle is equal to 360&#176; &#8211; LHA. LHA = t (W), and LHA = 360&#176; &#8211; t (E). Meridian angle is used in the solution of the navigational triangle.
Example: Find LHA and t of the sun at GMT 3h24m16s on June 1, 1975, for long. 118&#176;48.2&#8217; W.
Solution:









*To be cont.*


----------



## Fishers of Men

*Ch 18 cont.*
RADIO DISSEMINATION OF TIME SIGNALS
1812.	Dissemination Systems
Of the many systems for time and frequency dissemination, the majority employ some type of radio transmission, either in dedicated time and frequency emissions or established systems such as radionavigation systems. The most accurate means of time and frequency dissemination today is by the mutual exchange of time signals through communication (commonly called Two-Way) and by the mutual observation of navigation satellites (commonly called Common View).

Radio time signals can be used either to perform a clock&#8217;s function or to set clocks. When using a radio wave instead of a clock, however, new considerations evolve. One is the delay time of approximately 3 microseconds per kilometer it takes the radio wave to propagate and arrive at the reception point. Thus, a user 1,000 kilometers from a transmitter receives the time signal about 3 milliseconds later than the on-time transmitter signal. If time is needed to better than 3 milliseconds, a correction must be made for the time it takes the signal to pass through the receiver. In most cases standard time and frequency emissions as received are more than adequate for ordinary needs. However, many systems exist for the more exacting scientific requirements.

1813.	Characteristic Elements Of Dissemination Systems
A number of common elements characterize most time and frequency dissemination systems. Among the more important elements are accuracy, ambiguity, repeatability, coverage, availability of time signal, reliability, ease of use, cost to the user, and the number of users served. No single system incorporates all desired characteristics. The relative importance of these characteristics will vary from one user to the next, and the solution for one user may not be satisfactory to another. These common elements are discussed in the following examination of a hypothetical radio signal.










Consider a very simple system consisting of an unmodulated 10-kHz signal as shown in Figure 1813. This signal, leaving the transmitter at 0000 UTC, will reach the receiver at a later time equivalent to the propagation delay. The user must know this delay because the accuracy of his knowledge of time can be no better than the degree to which the delay is known. Since all cycles of the signal are identical, the signal is ambiguous and the user must somehow decide which cycle is the &#8220;on time&#8221; cycle. This means, in the case of the hypothetical 10-kHz signal, that the user must know the time to &#177; 50 microseconds (half the period of the signal). Further, the user may desire to use this system, say once a day, for an extended period of time to check his clock or frequency standard. However, if the delay varies from one day to the next without the user knowing, accuracy will be limited by the lack of repeatability. Many users are interested in making time coordinated measurements over large geographic areas. They would like all measurements to be referenced to one time system to eliminate corrections for different time systems used at scattered or remote locations. This is a very important practical consideration when measurements are undertaken in the field. In addition, a one-reference system, such as a single time broadcast, increases confidence that all measurements can be related to each other in some known way. Thus, the coverage of a system is an important concept. Another important characteristic of a timing system is the percent of time available. The man on the street who has to keep an appointment needs to know the time perhaps to a minute or so. Although requiring only coarse time information, he wants it on demand, so he carries a wristwatch that gives the time 24 hours a day. On the other hand, a user who needs time to a few microseconds employs a very good clock which only needs an occasional update, perhaps only once or twice a day. An additional characteristic of time and frequency dissemination is reliability, i.e., the likelihood that a time signal will be available when scheduled. Propagation fadeout can sometimes prevent reception of HF signals.

1814.	Radio Propagation Factors
Radio has been used to transmit standard time and frequency signals since the early 1900&#8217;s. As opposed to the physical transfer of time via portable clocks, the transfer of information by radio entails propagation of electromagnetic energy through some propagation medium from a transmitter to a distant receiver.

In a typical standard frequency and time broadcast, the signals are directly related to some master clock and are transmitted with little or no degradation in accuracy. In a vacuum and with a noise free background, the signals should be received at a distant point essentially as transmitted, except for a constant path delay with the radio wave propagating near the speed of light (299,773 kilometers per second). The propagation media, including the earth, atmosphere, and ionosphere, as well as physical and electrical characteristics of transmitters and receivers, influence the stability and accuracy of received radio signals, dependent upon the frequency of the transmission and length of signal path. Propagation delays are affected in varying degrees by extraneous radiations in the propagation media, solar disturbances, diurnal effects, and weather conditions, among others.

Radio dissemination systems can be classified in a number of different ways. One way is to divide those carrier frequencies low enough to be reflected by the ionosphere (below 30 MHz) from those sufficiently high to penetrate the ionosphere (above 30 MHz). The former can be observed at great distances from the transmitter but suffer from ionospheric propagation anomalies that limit accuracy; the latter are restricted to line-of-sight applications but show little or no signal deterioration caused by propagation anomalies. The most accurate systems tend to be those which use the higher, line-of-sight frequencies, while broadcasts of the lower carrier frequencies show the greatest number of users.

1815.	Standard Time Broadcasts
The World Administrative Radio Council (WARC) has allocated certain frequencies in five bands for standard frequency and time signal emission. For such dedicated standard frequency transmissions, the International Radio Consultative Committee (CCIR) recommends that carrier frequencies be maintained so that the average daily fractional frequency deviations from the internationally designated standard for measurement of time interval should not exceed 1 X 10-10. The U. S. Naval Observatory Time Service Announcement Series 1, No. 2, gives characteristics of standard time signals assigned to allocated bands, as reported by the CCIR.

1816. Time Signals
The usual method of determining chronometer error and daily rate is by radio time signals, popularly called time ticks. Most maritime nations broadcast time signals several times daily from one or more stations, and a vessel equipped with radio receiving equipment normally has no difficulty in obtaining a time tick anywhere in the world. Normally, the time transmitted is maintained virtually uniform with respect to atomic clocks. The Coordinated Universal Time (UTC) as received by a vessel may differ from (GMT) by as much as 0.9 second. The majority of radio time signals are transmitted automatically, being controlled by the standard clock of an astronomical observatory or a national measurement standards laboratory. Absolute reliance may be had in these signals because they are required to be accurate to at least 0.001s as transmitted.

Other radio stations, however, have no automatic transmission system installed, and the signals are given by hand. In this instance the operator is guided by the standard clock at the station. The clock is checked by astronomical observations or radio time signals and is normally correct to 0.25 second.

At sea, a spring-driven chronometer should be checked daily by radio time signal, and in port daily checks should be maintained, or begun at least three days prior to departure, if conditions permit. Error and rate are entered in the chronometer record book (or record sheet) each time they are determined.
The various time signal systems used throughout the world are discussed in Pub. No. 117, Radio Navigational Aids, and volume 5 of Admiralty List of Radio Signals.

Only the United States signals are discussed here. The National Institute of Standards and Technology (NIST) broadcasts continuous time and frequency reference signals from WWV, WWVH, WWVB, and the GOES satellite system. Because of their wide coverage and relative simplicity, the HF services from WWV and WWVH are used extensively for navigation.

Station WWV broadcasts from Fort Collins, Colorado at the internationally allocated frequencies of 2.5, 5.0, 10.0, 15.0, and 20.0 MHz; station WWVH transmits from Kauai, Hawaii on the same frequencies with the exception of 20.0 MHz. The broadcast signals include standard time and frequencies, and various voice announcements. Details of these broadcasts are given in NIST Special Publication 432, NIST Frequency and Time Dissemination Services. Both HF emissions are directly controlled by cesium beam frequency standards with periodic reference to the NIST atomic frequency and time standards.



















The time ticks in the WWV and WWVH emissions are shown in Figure 1816a and Figure 1816b. The 1-second UTC markers are transmitted continuously by WWV and WWVH, except for omission of the 29th and 59th marker each minute. With the exception of the beginning tone at each minute (800 milliseconds) all 1-second markers are of 5 milliseconds duration. Each pulse is preceded by 10 milliseconds of silence and followed by 25 milliseconds of silence. Time voice announcements are given also at 1-minute intervals. All time announcements are UTC.
Pub. No. 117, Radio Navigational Aids, should be referred to for further information on time signals.

1817. Leap-Second Adjustments
By international agreement, UTC is maintained within about 0.9 seconds of the celestial navigator&#8217;s time scale, UT1. The introduction of leap seconds allows a good clock to keep approximate step with the sun. Because of the variations in the rate of rotation of the earth, however, the occurrences of the leap seconds are not predictable in detail. The Central Bureau of the International Earth Rotation Service (IERS) decides upon and announces the introduction of a leap second. The IERS announces the new leap second at least several weeks in advance. A positive or negative leap second is introduced the last second of a UTC month, but first preference is given to the end of December and June, and second preference is given to the end of March and September. A positive leap second begins at 23h59m60s and ends at 00h00m00s of the first day of the following month. In the case of a negative leap second, 23h59m58s is followed one second later by 00h00m00s of the first day of the following month.

The dating of events in the vicinity of a leap second is effected in the manner indicated in Figure 1817a and Figure 1817b.
Whenever leap second adjustments are to be made to UTC, mariners are advised by messages from the Defense Mapping Agency Hydrographic/Topographic Center.



















*End Chapter 18*


----------



## Fishers of Men

*CHAPTER 19*
THE ALMANACS
PURPOSE OF ALMANACS
1900.	Introduction
Celestial navigation requires accurate predictions of the geographic positions of the celestial bodies observed. These predictions are available from three almanacs published annually by the United States Naval Observatory and H. M. Nautical Almanac Office, Royal Greenwich Observatory. The Astronomical Almanac precisely tabulates celestial data for the exacting requirements found in several scientific fields. Its precision is far greater than that required by celestial navigation. Even if the Astronomical Almanac is used for celestial navigation, it will not necessarily result in more accurate fixes due to the limitations of other aspects of the celestial navigation process.

The Nautical Almanac contains the astronomical information specifically needed by marine navigators. Information is tabulated to the nearest 0.1&#8217; of arc and 1 second of time. GHA and declination are available for the sun, moon, planets, and 173 stars, as well as corrections necessary to reduce the observed values to true.

The Air Almanac is intended primarily for air navigators. In general, the information is similar to the Nautical Almanac, but is given to a precision of 1&#8217; of arc and 1 second of time, at intervals of 10 minutes (values for the sun and Aries are given to a precision of 0.1&#8217. This publication is suitable for ordinary navigation at sea, but may lack the precision of the Nautical Almanac, and provides GHA and declination for only the 57 commonly used navigation stars. 

The Floppy Almanac is a computer software program produced by the U.S. Naval Observatory which not only contains ephemeris data, but also computes rising, setting, and twilight problems; does sight planning given course and speed (this function includes a computer-generated star finder centered on the observer&#8217;s zenith); computes great circle and rumb line routes; computes compass error from celestial observations; and does complete sight reduction solutions including computer plotting and weighted analysis of the LOP&#8217;s. The Floppy Almanac is in DOS format.

FORMAT OF THE NAUTICAL AND AIR ALMANACS

1901.	Nautical Almanac
The major portion of the Nautical Almanac is devoted to hourly tabulations of Greenwich Hour Angle (GHA) and declination, to the nearest 0.1&#8217; of arc. On each set of facing pages, information is listed for three consecutive days. On the left-hand page, successive columns list GHA of Aries( ), and both GHA and declination of Venus, Mars, Jupiter, and Saturn, followed by the Sidereal Hour Angle (SHA) and declination of 57 stars. The GHA and declination of the sun and moon, and the horizontal parallax of the moon, are listed on the right-hand page. Where applicable, the quantities v and d are given to assist in interpolation. The quantity v is the difference between the actual change of GHA in 1 hour and a constant value used in the interpolation tables, while d is the change in declination in 1 hour. Both v and d are listed to the nearest 0.1&#8217;. To the right of the moon data is listed the Local Mean Time (LMT) of sunrise, sunset, and beginning and ending of nautical and civil twilight for latitudes from 72&#176;N to 60&#176;S. The LMT of moonrise and moonset at the same latitudes is listed for each of the three days for which other information is given, and for the following day. 

Magnitude of each planet at UT 1200 of the middle day is listed at the top of the column. The UT of transit across the celestial meridian of Greenwich is listed as &#8220;Mer. Pass.&#8221;. The value for the first point of Aries for the middle of the three days is listed to the nearest 0.1&#8217; at the bottom of the Aries column. The time of transit of the planets for the middle day is given to the nearest whole minute, with SHA (at UT 0000 of the middle day) to the nearest 0.1&#8217;, below the list of stars. For the sun and moon, the time of transit to the nearest whole minute is given for each day. For the moon, both upper and lower transits are given. This information is tabulated below the rising, setting, and twilight information. Also listed, are the equation of time for 0h and 12h, and the age and phase of the moon. Equation of time is listed, without sign, to the nearest whole second. Age is given to the nearest whole day. Phase is given by symbol.

The main tabulation is preceded by a list of religious and civil holidays, phases of the Moon, a calendar, information on eclipses occurring during the year, and notes and a diagram giving information on the planets. 

The main tabulation is followed by explanations and examples. Next are four pages of standard times (zone descriptions). 

Star charts are next, followed by a list of 173 stars in order of increasing SHA. This list includes the stars given on the daily pages. It gives the SHA and declination each month, and the magnitude. Stars are listed by Bayer&#8217;s name and also by popular name where applicable. Following the star list are the Polaris tables. These tables give the azimuth and the corrections to be applied to the observed altitude to find the latitude.

Following the Polaris table is a section that gives formulas and examples for the entry of almanac data, the calculations that reduce a sight, and a method of solution for position, all for use with a calculator or microcomputer. This is followed by concise sight reduction tables, with instructions and examples, for use when a calculator or traditional sight reduction tables are not available. Tabular precision of the concise tables is one minute of arc. Next is a table for converting arc to time units. This is followed by a 30-page table called &#8220;Increments and Corrections,&#8221; used for interpolation of GHA and declination. This table is printed on tinted paper, for quick location. Then come tables for interpolating for times of rise, set, and twilight; followed by two indices of the 57 stars listed on the daily pages, one index in alphabetical order, and the other in order of decreasing SHA.

Sextant altitude corrections are given at the front and back of the almanac. Tables for the sun, stars, and planets, and a dip table, are given on the inside front cover and facing page, with an additional correction for nonstandard temperature and atmospheric pressure on the following page. Tables for the moon, and an abbreviated dip table, are given on the inside back cover and facing page. Corrections for the sun, stars, and planets for altitudes greater than 10&#176;, and the dip table, are repeated on one side of a loose bookmark. The star indices are repeated on the other side.

1902.	Air Almanac
As in the Nautical Almanac, the major portion of the Air Almanac is devoted to a tabulation of GHA and declination. However, in the Air Almanac values are listed at intervals of 10 minutes, to a precision of 0.1&#8217; for the sun and Aries, and to a precision of 1&#8217; for the moon and the planets. Values are given for the sun, first point of Aries (GHA only), the three navigational planets most favorably located for observation, and the moon. The magnitude of each planet listed is given at the top of its column, and the phase of the moon is given at the top of its column. Values for the first 12 hours of the day are given on the right-hand page, and those for the second half of the day on the back. In addition, each page has a table of the moon&#8217;s parallax in altitude, and below this the semidiameter of the sun, and both the semidiameter and age of the moon. Each daily page includes the LMT of moonrise and moonset; and a difference column to find the time of moonrise and moonset at any longitude. Critical tables for interpolation for GHA are given on the inside front cover, which also has an alphabetical listing of the stars, with the number, magnitude, SHA, and declination of each. The same interpolation table and star list are printed on a flap which follows the daily pages. This flap also contains a star chart, a star index in order of decreasing SHA, and a table for interpolation of the LMT of moonrise and moonset for longitude.

Following the flap are instructions for the use of the almanac; a list of symbols and abbreviations in English, French, and Spanish; a list of time differences between Greenwich and other places; sky diagrams; a planet location diagram; star recognition diagrams for periscopic sextants; sunrise, sunset, and civil twilight tables; rising, setting, and depression graphs; semiduration graphs of sunlight, twilight, and moonlight in high latitudes; percentage of the moon illuminated at 6 and 18 hours UT daily; a list of 173 stars by number and Bayer&#8217;s name (also popular name where there is one), giving the SHA and declination each month (to a precision of 0.1&#8217, and the magnitude; tables for interpolation of GHA sun and GHA hours; a table for converting arc to time; a single Polaris correction table; an aircraft standard dome refraction table; a refraction correction table; a Coriolis correction table; and on the inside back cover, a correction table for dip of the horizon.

USING THE ALMANACS
1903.	Entering Arguments
The time used as an entering argument in the almanacs is 12h + GHA of the mean sun and is denoted by UT. This scale may differ from the broadcast time signals by an amount which, if ignored, will introduce an error of up to 0.2&#8217; in longitude determined from astronomical observations.
The difference arises because the time argument depends on the variable rate of rotation of the earth while the broadcast time signals are now based on atomic time. Step adjustments of exactly one second are made to the time signals as required (primarily at 24h on December 31 and June 30) so that the difference between the time signals and UT, as used in the almanacs, may not exceed 0.9s.










If observations to a precision of better than 1s are required, corrections must be obtained from coding in the signal, or from other sources. The correction may be applied to each of the times of observation. Alternatively, the longitude, when determined from observations, may be corrected by the corresponding amount shown in Table 1903.
The main contents of the almanacs consist of data from which the GHA and the declination of all the bodies used for navigation can be obtained for any instant of UT. The LHA can then be obtained the formula with:
LHA = GHA + east longitude.
LHA = GHA - west longitude.

For the sun, moon, and the four navigational planets, the GHA and declination are tabulated directly in the Nautical Almanac for each hour of GMT throughout the year; in the Air Almanac, the values are tabulated for each whole 10 m of GMT. For the stars, the SHA is given, and the GHA is obtained from:
GHA Star = GHA hours + SHA Star.
The SHA and declination of the stars change slowly and may be regarded as constant over periods of several days or even months if lesser accuracy is required. The SHA and declination of stars tabulated in the Air Almanac may be considered constant to a precision of 1.5&#8217; to 2&#8217; for the period covered by each of the volumes providing the data for a whole year, with most data being closer to the smaller value. GHA , or the GHA of the first point of Aries (the vernal equinox), is tabulated for each hour in the Nautical Almanac and for each whole 10m in the Air Almanac. Permanent tables list the appropriate increments to the tabulated values of GHA and declination for the minutes and seconds of time.

In the Nautical Almanac, the permanent table for increments also includes corrections for v, the difference between the actual change of GHA in one hour and a constant value used in the interpolation tables; and d, the change in declination in one hour.
In the Nautical Almanac, v is always positive unless a negative sign (-) is shown. This occurs only in the case of Venus. For the sun, the tabulated values of GHA have been adjusted to reduce to a minimum the error caused by treating v as negligible; there is no v tabulated for the sun. No sign is given for tabulated values of d, which is positive if declination is increasing, and negative if decreasing. The sign of a v or d value is also given to the related correction. 

In the Air Almanac, the tabular values of the GHA of the moon are adjusted so that use of an interpolation table based on a fixed rate of change gives rise to negligible error; no such adjustment is necessary for the sun and planets. The tabulated declination values, except for the sun, are those for the middle of the interval between the time indicated and the next following time for which a value is given, making interpolation unnecessary. Thus, it is always important to take out the GHA and declination for the time immediately before the time of observation.

In the Air Almanac, GHA and the GHA and declination of the sun are tabulated to a precision of 0.1&#8217;. If these values are extracted with the tabular precision, the &#8220;Interpolation of GHA&#8221; table on the inside front cover (and flap) should not be used; use the &#8220;Interpolation of GHA Sun&#8221; and &#8220;Interpolation of GHA Aries&#8217; tables, as appropriate. These tables are found immediately preceding the Polaris Table.

1904.	Finding GHA And Declination Of The Sun
Nautical Almanac: Enter the daily page table with the whole hour before the given GMT, unless the exact time is a whole hour, and take out the tabulated GHA and declination. Also record the d value given at the bottom of the declination column. Next, enter the increments and corrections table for the number of minutes of GMT. If there are seconds, use the next earlier whole minute. On the line corresponding to the seconds of GMT, extract the value from the Sun-Planets column. Add this to the value of GHA from the daily page. This is GHA of the sun. Next, enter the correction table for the same minute with the d value and take out the correction. Give this the sign of the d value and apply it to the declination from the daily page. This is the declination. 

The correction table for GHA of the Sun is based upon a rate of change of 15&#176; per hour, the average rate during a year. At most times the rate differs slightly. The slight error is minimized by adjustment of the tabular values. The d value is the amount that the declination changes between 1200 and 1300 on the middle day of the three shown. 

Air Almanac: Enter the daily page with the whole 10m preceding the given GMT, unless the time is itself a whole 10m, and extract the GHA. The declination is extracted without interpolation from the same line as the tabulated GHA or, in the case of planets, the top line of the block of six. If the values extracted are rounded to the nearest minute, next enter the &#8220;Interpolation of GHA&#8221; table on the inside front cover (and flap), using the &#8220;Sun, etc.&#8221; entry column, and take out the value for the remaining minutes and seconds of GMT. If the entry time is an exact tabulated value, use the correction listed half a line above the entry time. Add this correction to the GHA taken from the daily page. This is GHA. No adjustment of declination is needed. If the values are extracted with a precision of 0.1&#8217;, the table for interpolating the GHA of the sun to a precision of 0.1&#8217; must be used. Again no adjustment of declination is needed.

1905.	Finding GHA And Declination Of The Moon
Nautical Almanac: Enter the daily page table with the whole hour before the given GMT, unless this time is itself a whole hour, and extract the tabulated GHA and declination. Record the corresponding v and d values tabulated on the same line, and determine the sign of the d value. The v value of the moon is always positive (+) and is not marked in the almanac. Next, enter the increments and corrections table for the minutes of GMT, and on the line for the seconds of GMT, take the GHA correction from the moon column. Then, enter the correction table for the same minute with the v value, and extract the correction. Add both of these corrections to the GHA from the daily page. This is GHA of the moon. Then, enter the same correction table with the d value and extract the correction. Give this correction the sign of the d value and apply it to the declination from the daily page. This is declination.

The correction table for GHA of the moon is based upon the minimum rate at which the moon&#8217;s GHA increases, 14&#176;19.0&#8217; per hour. The v correction adjusts for the actual rate. The v value is the difference between the minimum rate and the actual rate during the hour following the tabulated time. The d value is the amount that the declination changes during the hour following the tabulated time.

Air Almanac: Enter the daily page with the whole 10m next preceding the given GMT, unless this time is a whole 10m, and extract the tabulated GHA and the declination without interpolation. Next, enter the &#8220;Interpolation of GHA&#8221; table on the inside front cover, using the &#8220;moon&#8221; entry column, and extract the value for the remaining minutes and seconds of GMT. If the entry time is an exact tabulated value, use the correction given half a line above the entry time. Add this correction to the GHA taken from the daily page to find the GHA at the given time. No adjustment of declination is needed.
The declination given in the table is correct for the time 5 minutes later than tabulated, so that it can be used for the 10-minute interval without interpolation, to an accuracy to meet most requirements. Declination changes much more slowly than GHA. If greater accuracy is needed, it can be obtained by interpolation, remembering to allow for the 5 minutes.

1906.	Finding GHA And Declination Of A Planet
Nautical Almanac: Enter the daily page table with the whole hour before the given GMT, unless the time is a whole hour, and extract the tabulated GHA and declination. Record the v value given at the bottom of each of these columns. Next, enter the increments and corrections table for the minutes of GMT, and on the line for the seconds of GMT, take the GHA correction from the sun-planets column. Next, enter the correction table with the v value and extract the correction, giving it the sign of the v value. Add the first correction to the GHA from the daily page, and apply the second correction in accordance with its sign. This is GHA. Then enter the correction table for the same minute with the d value, and extract the correction. Give this correction the sign of the d value, and apply it to the declination from the daily page to find the declination at the given time.

The correction table for GHA of planets is based upon the mean rate of the sun, 15&#176; per hour. The v value is the difference between 15&#176; and the change of GHA of the planet between 1200 and 1300 on the middle day of the three shown. The d value is the amount the declination changes between 1200 and 1300 on the middle day. Venus is the only body listed which ever has a negative v value. 

Air Almanac: Enter the daily page with the whole 10m before the given GMT, unless this time is a whole 10m, and extract the tabulated GHA and declination, without interpolation. The tabulated declination is correct for the time 30m later than tabulated, so interpolation during the hour following tabulation is not needed for most purposes. Next, enter the &#8220;Interpolation of GHA&#8221; table on the inside front cover, using the &#8220;sun, etc.&#8221; column, and take out the value for the remaining minutes and seconds of GMT. If the entry time is an exact tabulated value, use the correction half a line above the entry time. Add this correction to the GHA from the daily page to find the GHA at the given time. No adjustment of declination is needed.

1907.	Finding GHA And Declination Of A Star
If the GHA and declination of each navigational star were tabulated separately, the almanacs would be several times their present size. But since the sidereal hour angle and the declination are nearly constant over several days (to the nearest 0.1&#8217 or months (to the nearest 1&#8217, separate tabulations are not needed. Instead, the GHA of the first point of Aries, from which SHA is measured, is tabulated on the daily pages, and a single listing of SHA and declination is given for each double page of the Nautical Almanac, and for an entire volume of the Air Almanac. Finding the GHA is similar to finding the GHA of the sun, moon, and planets.

Nautical Almanac: Enter the daily page table with the whole hour before the given GMT, unless this time is a whole hour, and extract the tabulated GHA of Aries. Also record the tabulated SHA and declination of the star from the listing on the left-hand daily page. Next, enter the increments and corrections table for the minutes of GMT, and, on the line for the seconds of GMT, extract the GHA correction from the Aries column. Add this correction and the SHA of the star to the GHA hours on the daily page to find the GHA of the star at the given time. No adjustment of declination is needed. 

The SHA and declination of 173 stars, including Polaris and the 57 listed on the daily pages, are given for the middle of each month. For a star not listed on the daily pages, this is the only almanac source of this information. Interpolation in this table is not necessary for ordinary purposes of navigation, but is sometimes needed for precise results. 

Air Almanac: Enter the daily page with the whole 10m before the given GMT, unless this is a whole 10m, and extract the tabulated GHA hours . Next, enter the &#8220;Interpolation of GHA&#8221; table on the inside front cover, using the &#8220;Sun, etc.&#8221; entry column, and extract the value for the remaining minutes and seconds of GMT. If the entry time is an exact tabulated value, use the correction given half a line above the entry time. From the tabulation at the left side of the same page, extract the SHA and declination of the star. Add the GHA from the daily page and the two values taken from the inside front cover to find the GHA at the given time. No adjustment of declination is needed.

RISING, SETTING, AND TWILIGHT
1908.	Rising, Setting, And Twilight
In both Air and Nautical Almanacs, the times of sunrise, sunset, moonrise, moonset, and twilight information, at various latitudes between 72&#176;N and 60&#176;S, is listed to the nearest whole minute. By definition, rising or setting occurs when the upper limb of the body is on the visible horizon, assuming standard refraction for zero height of eye. Because of variations in refraction and height of eye, computation to a greater precision than 1 minute of time is not justified. In high latitudes, some of the phenomena do not occur during certain periods. Symbols are used in the almanacs to indicate:
1.	Sun or moon does not set, but remains continuously above the horizon, indicated by an open rectangle.
2.	Sun or moon does not rise, but remains continuously below the horizon, indicated by a solid rectangle.
3.	Twilight lasts all night, indicated by 4 slashes (////).

The Nautical Almanac makes no provision for finding the times of rising, setting, or twilight in polar regions. The Air Almanac has graphs for this purpose.

In the Nautical Almanac, sunrise, sunset, and twilight tables are given only once for the middle of the three days on each page opening. For navigational purposes this information can be used for all three days. Both almanacs have moonrise and moonset tables for each day. 

The tabulations are in LMT. On the zone meridian, this is the zone time (ZT). For every 15&#8217; of longitude the observer&#8217;s position differs from the zone meridian, the zone time of the phenomena differs by 1m, being later if the observer is west of the zone meridian, and earlier if east of the zone meridian. The LMT of the phenomena varies with latitude of the observer, declination of the body, and hour angle of the body relative to the mean sun.

The UT of the phenomenon is found from LMT by the formula:
UT = LMT + W Longitude
UT = LMT - E Longitude.
To use this formula, convert the longitude to time using the table on page i or by computation, and add or subtract as indicated. Apply the zone description (ZD) to find the zone time of the phenomena.
Sunrise and sunset are also tabulated in the tide tables (from 76&#176;N to 60&#176;S).

1909.	Finding Times Of Sunrise And Sunset
To find the time of sunrise or sunset in the Nautical Almanac, enter the table on the daily page, and extract the LMT for the latitude next smaller than your own (unless it is exactly the same). Apply a correction from Table I on almanac page xxxii to interpolate for altitude, determining the sign by inspection. Then convert LMT to ZT using the difference of longitude between the local and zone meridians.

For the Air Almanac, the procedure is the same as for the Nautical Almanac, except that the LMT is taken from the tables of sunrise and sunset instead of from the daily page, and the latitude correction is by linear interpolation. 

The tabulated times are for the Greenwich meridian. Except in high latitudes near the time of the equinoxes, the time of sunrise and sunset varies so little from day to day that no interpolation is needed for longitude. In high latitudes interpolation is not always possible. Between two tabulated entries, the sun may in fact cease to set. In this case, the time of rising and setting is greatly influenced by small variations in refraction and changes in height of eye.

1910.	Twilight
Morning twilight ends at sunrise, and evening twilight begins at sunset. The time of the darker limit can be found from the almanacs. The time of the darker limits of both civil and nautical twilights (center of the sun 6&#176; and 12&#176;, respectively, below the celestial horizon) is given in the Nautical Almanac. The Air Almanac provides tabulations of civil twilight from 60&#176;S to 72&#176;N. The brightness of the sky at any given depression of the sun below the horizon may vary considerably from day to day, depending upon the amount of cloudiness, haze, and other atmospheric conditions. In general, the most effective period for observing stars and planets occurs when the center of the sun is between about 3&#176; and 9&#176; below the celestial horizon. Hence, the darker limit of civil twilight occurs at about the midpoint of this period. 

At the darker limit of nautical twilight, the horizon is generally too dark for good observations. At the darker limit of astronomical twilight (center of the sun 18&#176; below the celestial horizon), full night has set in. The time of this twilight is given in the Astronomical Almanac. Its approximate value can be determined by extrapolation in the Nautical Almanac, noting that the duration of the different kinds of twilight is not proportional to the number of degrees of depression at the darker limit. More precise determination of the time at which the center of the sun is any given number of degrees below the celestial horizon can be determined by a large-scale diagram on the plane of the celestial meridian, or by computation. Duration of twilight in latitudes higher than 65&#176;N is given in a graph in the Air Almanac.

In both Nautical and Air Almanacs, the method of finding the darker limit of twilight is the same as that for sunrise and sunset.
Sometimes in high latitudes the sun does not rise but twilight occurs. This is indicated in the Air Almanac by a solid black rectangle symbol in the sunrise and sunset column. To find the time of beginning of morning twilight, subtract half the duration of twilight as obtained from the duration of twilight graph from the time of meridian transit of the sun; and for the time of ending of evening twilight, add it to the time of meridian transit. The LMT of meridian transit never differs by more than 16.4m (approximately) from 1200. The actual time on any date can be determined from the almanac.

1911.	Moonrise And Moonset
Finding the time of moonrise and moonset is similar to finding the time of sunrise and sunset, with one important difference. Because of the moon&#8217;s rapid change of declination, and its fast eastward motion relative to the sun, the time of moonrise and moonset varies considerably from day to day. These changes of position on the celestial sphere are continuous, as moonrise and moonset occur successively at various longitudes around the earth. Therefore, the change in time is distributed over all longitudes. For precise results, it would be necessary to compute the time of the phenomena at any given place by lengthy complex calculation. For ordinary purposes of navigation, however, it is sufficiently accurate to interpolate between consecutive moonrises or moonsets at the Greenwich meridian. Since apparent motion of the moon is westward, relative to an observer on the earth, interpolation in west longitude is between the phenomenon on the given date and the following one. In east longitude it is between the phenomenon on the given date and the preceding one.

To find the time of moonrise or moonset in the Nautical Almanac, enter the daily-page table with latitude, and extract the LMT for the tabulated latitude next smaller than the observer&#8217;s latitude (unless this is an exact tabulated value). Apply a correction from table I of almanac page xxxii to interpolate for latitude, determining the sign of the correction by inspection. Repeat this procedure for the day following the given date, if in west longitude; or for the day preceding, if in east longitude. Using the difference between these two times, and the longitude, enter table II of the almanac on the same page and take out the correction. Apply this correction to the LMT of moonrise or moonset at the Greenwich meridian on the given date to find the LMT at the position of the observer. The sign to be given the correction is such as to make the corrected time fall between the times for the two dates between which interpolation is being made. This is nearly always positive (+) in west longitude and negative (-) in east longitude. Convert the corrected LMT to ZT. 

To find the time of moonrise or moonset by the Air Almanac for the given date, determine LMT for the observer&#8217;s latitude at the Greenwich meridian in the same manner as with the Nautical Almanac, except that linear interpolation is made directly from the main tables, since no interpolation table is provided. Extract, also, the value from the &#8220;Diff.&#8221; column to the right of the moonrise and moonset column, interpolating if necessary. This &#8220;Diff.&#8221; is one-fourth of one half of the daily difference. The error introduced by this approximation is generally not more than a few minutes, although it increases with latitude. Using this difference, and the longitude, enter the &#8220;Interpolation of Moonrise, Moonset&#8221; table on flap F4 of the Air Almanac and extract the correction.

The Air Almanac recommends taking the correction from this table without interpolation. The results thus obtained are sufficiently accurate for ordinary purposes of navigation. If greater accuracy is desired, the correction can be taken by interpolation. However, since the &#8220;Diff.&#8221; itself is an approximation, the Nautical Almanac or computation should be used if accuracy is a consideration. Apply the correction to the LMT of moonrise or moonset at the Greenwich meridian on the given date to find the LMT at the position of the observer. The correction is positive (+) for west longitude, and negative (-) for east longitude, unless the &#8220;Diff.&#8221; on the daily page is preceded by the negative sign (-), when the correction is negative (-) for west longitude, and positive (+) for east longitude. If the time is near midnight, record the date at each step, as in the Nautical Almanac solution.

As with the sun, there are times in high latitudes when interpolation is inaccurate or impossible. At such periods, the times of the phenomena themselves are uncertain, but an approximate answer can be obtained by the moonlight graph in the Air Almanac, or by computation. With the moon, this condition occurs when the moon rises or sets at one latitude, but not at the next higher tabulated latitude, as with the sun. It also occurs when the moon rises or sets on one day, but not on the preceding or following day. This latter condition is indicated in the Air Almanac by the symbol * in the &#8220;Diff.&#8221; column. Because of the eastward revolution of the moon around the earth, there is one day each synodical month (29 &#189; days) when the moon does not rise, and one day when it does not set. These occur near last quarter and first quarter, respectively.
Since this day is not the same at all latitudes or at all longitudes, the time of moonrise or moonset found from the almanac may occasionally be the preceding or succeeding
one to that desired. When interpolating near midnight, caution will prevent an error.

The effect of the revolution of the moon around the earth is to cause the moon to rise or set later from day to day. The daily retardation due to this effect does not differ greatly from 50m. However, the change in declination of the moon may increase or decrease this effect. This effect increases with latitude, and in extreme conditions it may be greater than the effect due to revolution of the moon. Hence, the interval between successive moonrises or moonsets is more erratic in high latitudes than in low latitudes. When the two effects act in the same direction, daily differences can be quite large. When they act in opposite directions, they are small, and when the effect due to change in declination is larger than that due to revolution, the moon sets earlier on succeeding days. This condition is reflected in the Air Almanac by a negative &#8220;Diff.&#8221; If this happens near the last quarter or first quarter, two moonrises or moonsets might occur on the same day, one a few minutes after the day begins, and the other a few minutes before it ends, as on June 19, where two times are listed in the same space.

Interpolation for longitude is always made between consecutive moonrises or moonsets, regardless of the days on which they fall.

Beyond the northern limits of the almanacs the values can be obtained from a series of graphs given near the back of the Air Almanac. For high latitudes, graphs are used instead of tables because graphs give a clearer picture of conditions, which may change radically with relatively little change in position or date. Under these conditions interpolation to practical precision is simpler by graph than by table. In those parts of the graph which are difficult to read, the times of the phenomena&#8217;s occurrence are uncertain, being altered considerably by a relatively small change in refraction or height of eye.

On all of these graphs, any given latitude is represented by a horizontal line and any given date by a vertical line. At the intersection of these two lines the duration is read from the curves, interpolating by eye between curves. 

The &#8220;Semiduration of Sunlight&#8221; graph gives the number of hours between sunrise and meridian transit or between meridian transit and sunset. The dot scale near the top of the graph indicates the LMT of meridian transit, the time represented by the minute dot nearest the vertical dateline being used. If the intersection occurs in the area marked &#8220;sun above horizon,&#8221; the sun does not set; and if in the area marked &#8220;sun below horizon,&#8221; the sun does not rise. The &#8220;Duration of Twilight&#8221; graph gives the number of hours between the beginning of morning civil twilight (center of sun 6&#176; below the horizon) and sunrise, or between sunset and the end of evening civil twilight. If the sun does not rise, but twilight occurs, the time taken from the graph is half the total length of the single twilight period, or the number of hours from beginning of morning twilight to LAN, or from LAN to end of evening twilight. If the intersection occurs in the area marked &#8220;continuous twilight or sunlight,&#8221; the center of the sun does not move more than 6&#176; below the horizon, and if in the area marked &#8220;no twilight nor sunlight,&#8221; the sun remains more than 6&#176; below the horizon throughout the entire day.

The &#8220;Semiduration of Moonlight&#8221; graph gives the number of hours between moonrise and meridian transit or between meridian transit and moonset. The dot scale near the top of the graph indicates the LMT of meridian transit, each dot representing one hour. The phase symbols indicate the date on which the principal moon phases occur, the open circle indicating full moon and the dark circle indicating new moon. If the intersection of the vertical dateline and the horizontal latitude line falls in the &#8220;moon above horizon&#8221; or &#8220;moon below horizon&#8221; area, the moon remains above or below the horizon, respectively, for the entire 24 hours of the day.

If approximations of the times of moonrise and moonset are sufficient, the semiduration of moonlight is taken for the time of meridian passage and can be used without adjustment. When as estimated time of rise falls on the preceding day, that phenomenon may be recalculated using the meridian passage and semiduration for the day following. When an estimated time of set falls on the following day, that phenomenon may be recalculated using meridian passage and semiduration for the preceding day. For more accurate results (seldom justified), the times on the required date and the adjacent date (the following date in W longitude and the preceding date in E longitude) should be determined, and an interpolation made for longitude, as in any latitude, since the intervals given are for the Greenwich meridian.

Sunlight, twilight, and moonlight graphs are not given for south latitudes. Beyond latitude 65&#176;S, the northern hemisphere graphs can be used for determining the semiduration or duration, by using the vertical dateline for a day when the declination has the same numerical value but opposite sign. The time of meridian transit and the phase of the moon are determined as explained above, using the correct date. Between latitudes 60&#176;S and 65&#176;S, the solution is made by interpolation between the tables and the graphs.

Other methods of solution of these phenomena are available. The Tide Tables tabulate sunrise and sunset from latitude 76&#176;N to 60&#176;S. Semiduration or duration can be determined graphically using a diagram on the plane of the celestial meridian, or by computation. When computation is used, solution is made for the meridian angle at which the required negative altitude occurs. The meridian angle expressed in time units is the semiduration in the case of sunrise, sunset, moonrise, and moonset; and the semiduration
of the combined sunlight and twilight, or the time from meridian transit at which morning twilight begins or evening twilight ends. For sunrise and sunset the altitude used is (-)50&#8217;. Allowance for height of eye can be made by algebraically subtracting (numerically adding) the dip correction from this altitude. The altitude used for twilight is (-)6&#176;, (-)12&#176;, or (-)18&#176; for civil, nautical, or astronomical twilight, respectively. The altitude used for moonrise and moonset is -34&#8217; - SD + HP, where SD is semidiameter and HP is horizontal parallax, from the daily pages of the Nautical Almanac.

1912.	Rising, Setting, And Twilight On A Moving Craft
Instructions to this point relate to a fixed position on the earth. Aboard a moving craft the problem is complicated somewhat by the fact that time of occurrence depends upon position of the craft, which itself depends on the time. At ship speeds, it is generally sufficiently accurate to make an approximate mental solution and use the position of the vessel at this time to make a more accurate solution. If greater accuracy is required, the position at the time indicated in the second solution can be used for a third solution. If desired, this process can be repeated until the same answer is obtained from two consecutive solutions. However, it is generally sufficient to alter the first solution by 1m for each 15&#8217; of longitude that the position of the craft differs from that used in the solution, adding if west of the estimated position, and subtracting if east of it. In applying this rule, use both longitudes to the nearest 15&#8217;. The first solution is the first estimate; the second solution is the second estimate.

*End chapter 19
*


----------



## Fishers of Men

*CHAPTER 20*
SIGHT REDUCTION
BASIC PRINCIPLES
2000. Introduction
Reducing a celestial sight to obtain a line of position consists of six steps:
1.	Correcting sextant altitude (hs) to obtain observed altitude (ho).
2.	Determining the body&#8217;s GHA and declination.
3.	Selecting an assumed position and finding that position&#8217;s local hour angle.
4.	Computing altitude and azimuth for the assumed position.
5.	Comparing computed and observed altitudes.
6.	Plotting the line of position.
This chapter concentrates on using the Nautical Almanac
and Pub. No. 229, Sight Reduction Tables for Marine Navigation.

The introduction to each volume of the Sight Reduction Tables contains information: (1) discussing use of the publication in a variety of special celestial navigation techniques;
(2) discussing interpolation, explaining the double second difference interpolation required in some sight reductions, and providing tables to facilitate the interpolation process; and (3) discussing the publication&#8217;s use in solving problems of great circle sailings. Prior to using the Sight Reduction Tables, carefully read this introductory material. Celestial navigation involves determining a circular line of position based on an observer&#8217;s distance from a celestial body&#8217;s geographic position (GP). Should the observer determine both a body&#8217;s GP and his distance from the GP, he would have enough information to plot a line of position; he would be somewhere on a circle whose center was the GP and whose radius equaled his distance from that GP. That circle, from all points on which a body&#8217;s measured altitude would be equal, is a circle of equal altitude.

There is a direct proportionality between a body&#8217;s altitude as measured by an observer and the distance of its GP from that observer; the lower the altitude, the farther away the GP. Therefore, when an observer measures a body&#8217;s altitude he obtains an indirect measure of the distance between himself and the body&#8217;s GP. Sight reduction is the process of converting that indirect measurement into a line of position. Sight reduction reduces the problem scale to manageable size. Depending on a body&#8217;s altitude, its GP could be thousands of miles from the observer&#8217;s position. The size of a chart required to plot this large distance would be impractical. To eliminate this problem, the navigator does not plot this line of position directly. Indeed, he does not plot the GP at all. Rather, he chooses an assumed position (AP) near, but usually not coincident with, his DR position. The navigator chooses the AP&#8217;s latitude and longitude to correspond to the entering arguments of LHA and latitude used in the Sight Reduction Tables. From the Sight Reduction Tables, the navigator computes what the body&#8217;s altitude would have been had it been measured from the AP. This yields the computed altitude (hc). He then compares this computed value with the observed altitude (ho) obtained at his actual position. The difference between the computed and observed altitudes is directly proportional to the distance between the circles of equal altitude for the assumed position and the actual position. 

The Sight Reduction Tables also give the direction from the GP to the AP. Having selected the assumed position, calculated the distance between the circles of equal altitude for that AP and his actual position, and determined the direction from the assumed position to the body&#8217;s GP, the navigator has enough information to plot a line of position (LOP). To plot an LOP, plot the assumed position on either a chart or a plotting sheet. From the Sight Reduction Tables, determine: 1) the altitude of the body for a sight taken at the AP and 2) the direction from the AP to the GP. Then, determine the difference between the body&#8217;s calculated altitude at this AP and the body&#8217;s measured altitude. This difference represents the difference in radii between the equal altitude circle passing through the AP and the equal altitude circle passing through the actual position. Plot this difference from the AP either towards or away from the GP along the axis between the AP and the GP. Finally, draw the circle of equal altitude representing the circle with the body&#8217;s GP at the center and with a radius equal to the distance between the GP and the navigator&#8217;s actual position.

One final consideration simplifies the plotting of the equal altitude circle. Recall that the GP is usually thousands of miles away from the navigator&#8217;s position. The equal altitude circle&#8217;s radius, therefore, can be extremely large. Since this radius is so large, the navigator can approximate the section close to his position with a straight line drawn perpendicular to the line connecting the AP and the GP. This straight line approximation is good only for sights of relatively low altitudes. The higher the altitude, the shorter the distance between the GP and the actual position, and the smaller the circle of equal altitude. The shorter this distance, the greater the inaccuracy introduced by this approximation.

2001.	Selection Of The Assumed Position (AP)
Use the following arguments when entering the Sight Reduction Tables to compute altitude (hc) and azimuth:
1.	Latitude (L).
2.	Declination (d or Dec.).
3.	Local hour angle (LHA).
Latitude and LHA are functions of the assumed position.
Select an AP longitude resulting in a whole degree of LHA and an AP latitude equal to that whole degree of latitude closest to the DR position. Selecting the AP in this manner eliminates interpolation for LHA and latitude in the Sight Reduction Tables.

Reducing the sight using a computer or calculator simplifies this AP selection process. Simply choose any convenient position such as the vessel&#8217;s DR position as the assumed position. Enter the information required by the specific celestial program in use. Using a calculator reduces the math and interpolation errors inherent in using the Sight Reduction tables. Enter the required calculator data carefully.

2002.	Comparison Of Computed And Observed
Altitudes
The difference between the computed altitude (hc) and the observed altitude (ho) is the altitude intercept (a).
The altitude intercept is the difference in the length of the radii of the circles of equal altitude passing through the AP and the observers actual position. The position having the greater altitude is on the circle of smaller radius and is closer to the observed body&#8217;s GP. 

In Figure 2003, the AP is shown on the inner circle. Therefore, hc is greater than ho. Express the altitude intercept in nautical miles and label it T or A to indicate whether the line of position is toward or away from the GP, as measured from the AP.
A useful aid in remembering the relation between ho, hc, and the altitude intercept is: Ho Mo To for Ho More Toward.

Another is C-G-A: Computed Greater Away, remembered as Coast Guard Academy. In other words, if ho is greater than hc, the line of position intersects a point measured from the AP towards the GP a distance equal to the altitude intercept. Draw the LOP through this intersection point perpendicular to the axis between the AP and GP.

2003. Plotting The Line Of Position
Plot the line of position as shown in Figure 2003. Plot the AP first; then plot the azimuth line from the AP toward or away from the GP. Then, measure the altitude intercept along this line. At the point on the azimuth line equal to the intercept distance, draw a line perpendicular to the azimuth line. This perpendicular represents that section of the circle of equal altitude passing through the navigator&#8217;s actual position. This is the line of position.










A navigator often takes sights of more than one celestial body when determining a celestial fix. After plotting the lines of position from these several sights, advance the resulting LOP&#8217;s along the track to the time of the last sight and label the resulting fix with the time of this last sight.

2004. Recommended Sight Reduction Procedure
Just as it is important to understand the theory of sight reduction, it is also important to develop a working procedure to reduce celestial sights accurately. Sight reduction involves several consecutive steps, the accuracy of each completely dependent on the accuracy of the steps that went before. Sight reduction tables have, for the most part, reduced the mathematics involved to simple addition and subtraction. However, careless errors will render even the most skillfully measured sights inaccurate. The navigator must work methodically to reduce these careless errors. 

Naval navigators will most likely use OPNAV 3530, U.S. Navy Navigation Workbook, which contains pre-formatted pages with &#8220;strip forms&#8221; to guide the navigator through sight reduction. A variety of commercially-produced forms are also available. Pick a form and learn its method thoroughly. With familiarity will come increasing understanding. 

Figure 2004 represents a functional and complete worksheet designed to ensure a methodical approach to any sight reduction problem. The recommended procedure discussed below is not the only one available; however, the navigator who uses it can be assured that he has considered every correction required to obtain an accurate fix. SECTION ONE consists of two parts: (1) Correcting sextant altitude to obtain apparent altitude; and (2) Correcting the apparent altitude to obtain the observed altitude. Body: Enter the name of the body whose altitude you have measured. If using the sun or the moon, indicate which limb was measured.
Index Correction: This is determined by the characteristics of the individual sextant used. 

Chapter 16 discusses determining its magnitude and algebraic sign. 

Dip: The dip correction is a function of the height of eye of the observer. It is always negative; its magnitude is determined from the Dip Table on the inside front covert of the Nautical Almanac.
Sum: Enter the algebraic sum of the dip correction and the index correction.
Sextant Altitude: Enter the altitude of the body measured
by the sextant.
Apparent Altitude: Apply the sum correction determined above to the measured altitude and enter the result as the apparent altitude.
Altitude Correction: Every observation requires an altitude correction. This correction is a function of the apparent altitude of the body. The Almanac contains tables for determining these corrections. For the sun, planets, and stars, these tables are located on the inside front cover and facing page. For the moon, these tables are located on the back inside cover and preceding page.

Mars or Venus Additional Correction: 
As the name implies, this correction is applied to sights of Mars and Venus. The correction is a function of the planet measured, the time of year, and the apparent altitude. The inside front cover of the Almanac lists these corrections.
Additional Correction: Enter this additional correction from Table A 4 located at the front of the Almanac when obtaining a sight under non-standard atmospheric temperature and pressure conditions. This correction is a function of atmospheric pressure, temperature, and apparent altitude.

Horizontal Parallax Correction: 
This correction is unique to reducing moon sights. Obtain the H.P. correction value from the daily pages of the Almanac. Enter the H.P correction table at the back of the Almanac with this value. The H.P correction is a function of the limb of the moon used (upper or lower), the apparent altitude, and the H.P. correction factor. The H.P. correction is always added to the apparent altitude. Moon Upper Limb Correction: Enter -30&#8217; for this correction if the sight was of the upper limb of the moon. Correction to Apparent Altitude: Sum the altitude correction, the Mars or Venus additional correction, the additional correction, the horizontal parallax correction, and the moon&#8217;s upper limb correction. Be careful to determine and carry the algebraic sign of the corrections and their sum correctly. Enter this sum as the correction to the apparent altitude. Observed Altitude: Apply the Correction to Apparent Altitude algebraically to the apparent altitude. The result is the observed altitude.

SECTION TWO determines the Greenwich Mean Time (GMT) and GMT date of the sight.
Date:	Enter the local time zone date of the sight.
DR Latitude: Enter the dead reckoning latitude of the vessel.
DR Longitude: 
Enter the dead reckoning longitude of the vessel.
Observation Time: Enter the local time of the sight as recorded on the ship&#8217;s chronometer or other timepiece. Watch Error: Enter a correction for any known watch error.
Zone Time: Correct the observation time with watch error to determine zone time.
Zone Description: Enter the zone description of the time zone indicated by the DR longitude. If the longitude is west of the Greenwich Meridian, the zone description is positive. Conversely, if the longitude is east of the Greenwich Meridian, the zone description is negative. The zone description represents the correction necessary to convert local time to Greenwich Mean Time.
Greenwich Mean Time: Add to the zone description the zone time to determine Greenwich Mean Time.
Date:	Carefully evaluate the time correction applied above and determine if the correction has changed the date.
Enter the GMT date. 
SECTION THREE determines two of the three arguments required to enter the Sight Reduction Tables:
Local Hour Angle (LHA) and Declination. This section employs the principle that a celestial body&#8217;s LHA is the algebraic sum of its Greenwich Hour Angle (GHA) and the observer&#8217;s longitude. Therefore, the basic method employed in this section is: 
(1) Determine the body&#8217;s GHA;
(2) Determine an assumed longitude;
(3) Algebraically combine the two quantities, remembering to subtract a western assumed longitude from GHA and to add an eastern longitude to GHA; and 
(4) Extract the declination of the body from the appropriate Almanac table, correcting the tabular value if required.










(1)	Tabulated GHA and 
(2) v Correction Factor:
(1)	For the sun, the moon, or a planet, extract the value for the whole hour of GHA corresponding to the sight. For example, if the sight was obtained at 13-50-45 GMT, extract the GHA value for 1300. For a star sight reduction, extract the value of the GHA of Aries (GHA ), again using the value corresponding to the whole hour of the time of the sight.
(2)	For a planet or moon sight reduction, enter the v correction value. This quantity is not applicable to a sun or star sight. The v correction for a planet sight is found at the bottom of the column for each particular planet. The v correction factor for the moon is located directly beside the tabulated hourly GHA values. The v correction factor for the moon is always positive. If a planet&#8217;s v correction factor is listed without sign, it is positive. If listed with a negative sign, the planet&#8217;s v correction factor is negative. This v correction factor is not the magnitude of the v correction; it is used later to enter the Increments and Correction table to determine the magnitude of the correction.

GHA Increment: The GHA increment serves as an interpolation factor, correcting for the time that the sight differed from the whole hour. For example, in the sight at 13-50-45 discussed above, this increment correction accounts for the 50 minutes and 45 seconds after the whole hour at which the sight was taken. Obtain this correction value from the Increments and Corrections tables in the Almanac. The entering arguments for these tables are the minutes and seconds after the hour at which the sight was taken and the body sighted. Extract the proper correction from the applicable table and enter the correction here.

Sidereal Hour Angle or v Correction: If reducing a star sight, enter the star&#8217;s Sidereal Hour Angle (SHA). The SHA is found in the star column of the daily pages of the Almanac. The SHA combined with the GHA of Aries results in the star&#8217;s GHA. The SHA entry is applicable only to a star. If reducing a planet or moon sight, obtain the v correction from the Increments and Corrections Table. The correction is a function of only the v correction factor; its magnitude is the same for both the moon and the planets. GHA: A star&#8217;s GHA equals the sum of the Tabulated GHA of Aries, the GHA Increment, and the star&#8217;s SHA. The sun&#8217;s GHA equals the sum of the Tabulated GHA and the GHA Increment. The GHA of the moon or a planet equals the sum of the Tabulated GHA, the GHA Increment, and the v correction.

+ or &#8211; 360&#176; (if needed): Since the LHA will be determined from subtracting or adding the assumed longitude to the GHA, adjust the GHA by 360&#176; if needed to facilitate the addition or subtraction.

Assumed Longitude: If the vessel is west of the prime meridian, the assumed longitude will be subtracted from the GHA to determine LHA. If the vessel is east of the prime meridian, the assumed longitude will be added to the GHA to determine the LHA. Select the assumed longitude to meet the following two criteria: (1) When added or subtracted (as applicable) to the GHA determined above, a whole degree of LHA will result; and (2) It is the longitude closest to that DR longitude that meets criterion (1) above.
Local Hour Angle (LHA): Combine the body&#8217;s GHA with the assumed longitude as discussed above to determine the body&#8217;s LHA.

Tabulated Declination and d Correction factor:	
(1)	Obtain the tabulated declination for the sun, the moon, the stars, or the planets from the daily pages of the Almanac. The declination values for the stars are given for the entire three day period covered by the daily page of the Almanac. The values for the sun, moon, and planets are listed in hourly increments. For these bodies, enter the declination value for the whole hour of the sight. For example, if the sight is at 12-58-40, enter the tabulated declination for 1200. 
(2) There is no d correction factor for a star sight. There are d correction factors for sun, moon, and planet sights. Similar to the v correction factor discussed above, the d correction factor does not equal the magnitude of the d correction; it provides the argument to enter the Increments and Corrections tables in the Almanac. The sign of the d correction factor, which determines the sign of the d correction, is determined by the trend of declination values, not the trend of d values. The d correction factor is simply an interpolation factor; therefore, to determine its sign, look at the declination values for the hours that frame the time of the sight. For example, suppose the sight was taken on a certain date at 12-30-00. Compare the declination value for 1200 and 1300 and determine if the declination has increased or decreased. If it has increased, the d correction factor is positive. If it has decreased, the d correction factor is negative. 
d correction:
Enter the Increments and Corrections table with the d correction factor discussed above. Extract the proper correction, being careful to retain the proper sign. 
True Declination: 
Combine the tabulated declination and the d correction to obtain the true declination.

Assumed Latitude: Choose as the assumed latitude that whole value of latitude closest to the vessel&#8217;s DR latitude.

If the assumed latitude and declination are both north or both south, label the assumed latitude same. If one is north and the other is south, label the assumed latitude contrary.

SECTION FOUR uses the arguments of assumed latitude, LHA, and declination determined in Section Three to enter the Sight Reduction Tables to determine azimuth and computed altitude. Then, Section Four compares computed and observed altitudes to calculate the altitude intercept. The navigator then has enough information to plot the line of position.

(1)	Declination Increment and 
(2) d Interpolation Factor:
Note that two of the three arguments used to enter the Sight Reduction Tables, LHA and latitude, are whole degree values. Section Three does not determine the third argument, declination, as a whole degree. Therefore, the navigator must interpolate in the Sight Reduction Tables for declination, given whole degrees of LHA and latitude. The first steps of Section Four involve this interpolation for declination. Since declination values are tabulated every whole degree in the Sight Reduction Tables, the declination increment is the minutes and tenths of the true declination.

For example, if the true declination is 13&#176; 15.6&#8217;, then the declination increment is 15.6&#8217;. (2) The Sight Reduction Tables also list a d Interpolation Factor. This is the magnitude of the difference between the two successive tabulated values for declination that frame the true declination. Therefore, for the hypothetical declination listed above, the tabulated d interpolation factor listed in the table would be the difference between declination values given for 13&#176; and 14&#176;. If the declination increases between these two values, d is positive. If the declination decreases between these two values, d is negative.

Computed Altitude (Tabulated): Enter the Sight Reduction
Tables with the following arguments: 
(1) LHA from Section Three; 
(2) assumed latitude from Section Three; 
(3) the whole degree value of the true declination. For example, if the true declination were 13&#176; 15.6&#8217;, then enter the Sight Reduction Tables with 13&#176; as the value for declination. Record the tabulated computed altitude.

Double Second Difference Correction: 
Use this correction when linear interpolation of declination for computed altitude is not sufficiently accurate due to the non linear change in the computed altitude as a function of declination. The need for double second difference interpolation is indicated by the d interpolation factor appearing in italic type followed by a small dot. When this procedure must be employed, refer to detailed instructions in the Sight Reduction Tables introduction.

Total Correction: The total correction is the sum of the double second difference (if required) and the interpolation corrections. Calculate the interpolation correction by dividing the declination increment by 60&#8217; and multiply the resulting quotient by the d interpolation factor.

Computed Altitude (hc):
Apply the total correction, being careful to carry the correct sign, to the tabulated computed altitude. This yields the computed altitude. Observed Altitude (ho): Enter the observed altitude from Section One.

Altitude Intercept:
Compare hc and ho. Subtract the smaller from the larger. The resulting difference is the magnitude of the altitude intercept. If ho is greater than hc, then label the altitude intercept toward. If hc is greater than ho, then label the altitude intercept away.

Azimuth Angle: Obtain the azimuth angle (Z) from the Sight Reduction Tables, using the same arguments which determined tabulated computed altitude. Visual interpolation is sufficiently accurate.

True Azimuth: Calculate the true azimuth (Zn) from the azimuth angle (Z) as follows:
a)	If in northern latitudes:
LHA > 180&#176;, then Zn = Z
LHA < 180&#176;, then Zn = 360&#176;&#8211;Z

b)	If in southern latitudes:
LHA > 180&#176;, then Zn = 180&#176; &#8211; Z
LHA < 180&#176;, then Zn = 180&#176;+Z

SIGHT REDUCTION
The section above discussed the basic theory of sight reduction and proposed a method to be followed when reducing sights. This section puts that method into practice in reducing sights of a star, the sun, the moon, and planets.

*to be con*t.


----------



## Fishers of Men

*ch 20 cont.
I think this stuff has the computer confused, I have to edit upper and lower #'s and the degree symbol only works sometimes when pasted here it makes a ? mark. So, try to decipher it! 
2005. Reducing Star Sights To A Fix*
On May 16, 1995, at the times indicated, the navigator takes and records the following sights:
Height of eye is 48 feet and index correction (IC) is +2.1&#8217;. The DR latitude for both sights is 39&#176; N. The DR longitude for the Spica sight is 157&#176; 10&#8217;W. The DR longitude for the Kochab sight is 157&#176; 08.0&#8217;W. Determine the intercept and azimuth for both sights. See Figure 2005. 










First, convert the sextant altitudes to observed altitudes.
Reduce the Spica sight first:
Star Sextant Altitude Zone Time
Kochab 47&#176; 19.1&#8217; 20-07-43
Spica 32&#176; 34.8&#8217; 20-11-26
Body Spica
Index Correction +2.1&#8217;
Dip (height 48 ft) -6.7&#8217;
Sum -4.6&#8217;
Sextant Altitude (hs) 32 degrees &#61472;34.8&#8217;
Apparent Altitude (ha) 32 degrees &#61472;30.2&#8217;
Altitude Correction -1.5&#8217;
Additional Correction 0
Horizontal Parallax 0
Correction to ha -1.5'
Observed Altitude (ho) 32&#176; 28.7

Determine the sum of the index correction and the dip correction. Go to the inside front cover of the Nautical Almanac to the table entitled DIP. This table lists dip corrections as a function of height of eye measured in either feet or meters. In the above problem, the observer&#8217;s height of eye is 48 feet. The heights of eye are tabulated in intervals, with the correction corresponding to each interval listed between the interval&#8217;s endpoints. In this case, 48 feet lies between the tabulated 46.9 to 48.4 feet interval; the corresponding correction for this interval is -6.7&#8217;. Add the IC and the dip correction, being careful to carry the correct sign. The sum of the corrections here is -4.6&#8217;. Apply this correction to the sextant altitude to obtain the apparent altitude (ha). 

Next, apply the altitude correction. Find the altitude correction table on the inside front cover of the Nautical Almanac next to the dip table. The altitude correction varies as a function of both the type of body sighted (sun, star, or planet) and the body&#8217;s apparent altitude. For the problem above, enter the star altitude correction table. Again, the correction is given within an altitude interval; ha in this case was 32&#176; 30.2&#8217;. This value lies between the tabulated endpoints 32&#176; 00.0&#8217; and 33&#176; 45.0&#8217;. The correction corresponding to this interval is -1.5&#8217;. Applying this correction to ha yields an observed altitude of 32&#176; 28.7&#8217;.

Having calculated the observed altitude, determine the time and date of the sight in Greenwich Mean Time:
Date 16 May 1995
DR Latitude 39 degrees &#61472;N
DR Longitude 157 degrees &#61472;10' W
Observation Time 20-11-26
Watch Error 0
Zone Time 20-11-26
Zone Description +10
GMT 06-11-26
GMT Date 17 May 1995
Record the observation time and then apply any watch error to determine zone time. Then, use the DR longitude at the time of the sight to determine time zone description. In this case, the DR longitude indicates a zone description of +10 hours. Add the zone description to the zone time to obtain GMT. It is important to carry the correct date when applying this correction. In this case, the +10 correction made it 06-11-26 GMT on May 17, when the date in the local time zone was May 16.

After calculating both the observed altitude and the GMT time, enter the daily pages of the Nautical Almanac to calculate the star&#8217;s Greenwich Hour Angle (GHA) and declination. 
Tab GHA ( ) 324 degrees &#61472;28.4'
GHA Increment 2 degrees 52.0'
SHA 158 degrees &#61472;45.3'
GHA 486 degrees &#61472;05.7'
+/- 360 degrees &#61472;not required
Assumed Longitude 157 degrees &#61472;05.7'
LHA 329 degrees
Tabulated Dec/d S 11 degrees &#61472;08.4'/n.a.
d Correction &#8212;
True Declination S 11 degrees 08.4'
Assumed Latitude N 39 degrees &#61472;contrary

First, record the GHA of Aries from the May 17, 1995 daily page: 324&#176; 28.4&#8217;.

Next, determine the incremental addition for the minutes and seconds after 0600 from the Increments and Corrections table in the back of the Nautical Almanac. The increment for 11 minutes and 26 seconds is 2&#176; 52&#8217;.

Then, calculate the GHA of the star. Remember:
GHA (star) = GHA ( ) + SHA (star)
The Nautical Almanac lists the SHA of selected stars on each daily page. The SHA of Spica on May 17, 1995:158&#176; 45.3&#8217;.

The Sight Reduction Tables&#8217; entering arguments are whole degrees of LHA and assumed latitude. Remember that LHA = GHA - west longitude or GHA + east longitude. Since in this example the vessel is in west longitude, subtract its assumed longitude from the GHA of the body to obtain the LHA. Assume a longitude meeting the criteria listed in section 2004.

From those criteria, the assumed longitude must end in 05.7 minutes so that, when subtracted from the calculated GHA, a whole degree of LHA will result. Since the DR longitude was 157&#176; 10.0&#8217;, then the assumed longitude ending in 05.7&#8217; closest to the DR longitude is 157&#176; 05.7&#8217;. Subtracting this assumed longitude from the calculated GHA of the star yields an LHA of 329&#176;.

The next value of concern is the star&#8217;s true declination. This value is found on the May 17th daily page next to the star&#8217;s SHA. Spica&#8217;s declination is S 11&#176; 08.4&#8217;. There is no d correction for a star sight, so the star&#8217;s true declination equals its tabulated declination. The assumed latitude is determined from the whole degree of latitude closest to the DR latitude at the time of the sight. In this case, the assumed latitude is N 39&#176;. It is marked &#8220;contrary&#8221; because the DR latitude is north while the star&#8217;s declination is south. 

The following information is known: (1) the assumed position&#8217;s LHA (329&#176 and assumed latitude (39&#176;N contrary name); and (2) the body&#8217;s declination (S11&#176; 08.4&#8217.

Find the page in the Sight Reduction Table corresponding to an LHA of 329&#176; and an assumed latitude of N 39&#176;, with latitude contrary to declination. Enter this table with the body&#8217;s whole degree of declination. In this case, the body&#8217;s whole degree of declination is 11&#176;. This declination corresponds to a tabulated altitude of 32&#176; 15.9&#8217;. This value is for a declination of 11&#176;; the true declination is 11&#176; 08.4&#8217;. Therefore, interpolate to determine the correction to add to the tabulated altitude to obtain the computed altitude. 
The difference between the tabulated altitudes for 11&#176; and 12&#176; is given in the Sight Reduction Tables as the value d; in this case, d = -53.0. Express as a ratio the declination increment (in this case, 8.4&#8217 and the total interval between the tabulated declination values (in this case, 60&#8217 to obtain the percentage of the distance between the tabulated declination values represented by the declination increment.
Next, multiply that percentage by the increment between the two values for computed altitude. In this case:
8.4
60 degrees &#61480;&#8211;53.0&#61481;= &#8211;7.
Subtract 7.4&#8217; from the tabulated altitude to obtain the final computed altitude: Hc = 32&#176; 08.5&#8217;.
Dec Inc / + or - d 8.4' / -53.0
hc (tabulated) 32 degrees &#61472;15.9'
Correction (+ or -) -7.4'
hc (computed) 32 degrees 08.5'
It will be valuable here to review exactly what ho and hc represent. Recall the methodology of the altitude-intercept method. The navigator first measures and corrects an altitude for a celestial body. This corrected altitude, ho, corresponds to a circle of equal altitude passing through the navigator&#8217;s actual position whose center is the geographic position (GP) of the body. The navigator then determines an assumed position (AP) near, but not coincident with, his actual position; he then calculates an altitude for an observer at that assumed position (AP).The circle of equal altitude passing through this assumed position is concentric with the circle of equal altitude passing through the navigator&#8217;s actual position. The difference between the body&#8217;s altitude at the assumed position (hc) and the body&#8217;s observed altitude (ho) is equal to the differences in radii length of the two corresponding circles of equal altitude. In the above problem, therefore, the navigator knows that the equal altitude circle passing through his actual position is: 
ho = 32 degrees 28.7 degrees
&#8211;hc
32 degrees 08.5 degrees
20.2 NM
away from the equal altitude circle passing through his assumed position. Since ho is greater than hc, the navigator knows that the radius of the equal altitude circle passing through his actual position is less than the radius of the equal altitude circle passing through the assumed position. 

The only remaining question is: in what direction from the assumed and actual position is the body&#8217;s geographic position. The Sight Reduction Tables also provide this final piece of information. This is the value for Z tabulated with the hc and d values discussed above. In this case, enter the Sight Reduction Tables as before, with LHA, assumed latitude, and declination. Visual interpolation is sufficient.

Extract the value Z = 143.3&#176;. The relation between Z and Zn, the true azimuth, is as follows:
In northern latitudes:
LHA 180 degrees &#61472;then Zn degrees= Z
LHA degrees 180 degrees &#61484;&#61472;then Zn = 360 &#61472;degrees&#8211; Z
In southern latitudes:
LHA degrees &#61472;180 degrees &#61484;&#61472;then Zn = 180 degrees&#61472;&#8211; Z
LHA degrees &#61472;180 degrees then Zn = 180 degrees &#61472;+ Z
In this case, LHA > 180&#176; and the vessel is in northern latitude. Therefore, Zn = Z = 143.3&#176;T. The navigator now has enough information to plot a line of position.
The values for the reduction of the Kochab sight follow:
Body Kochab
Index Correction +2.1&#8217;
Dip Correction -6.7&#8217;
Sum -4.6&#8217;
hs 47&#176; 19.1&#8217;
ha 47&#176; 14.5&#8217;
Altitude Correction -.9&#8217;
Additional Correction not applicable
Horizontal Parallax not applicable
Correction to ha -9&#8217;
ho 47&#176; 13.6&#8217;
Date 16 May 1995
DR latitude 39&#176;N
DR longitude 157&#176; 08.0&#8217; W
Observation Time 20-07-43
Watch Error 0
Zone Time 20-07-43
Zone Description +10
GMT 06-07-43
GMT Date 17 May 1995
Tab GHA 324&#176; 28.4&#8217;
GHA Increment 1&#176; 56.1&#8217;
SHA 137&#176; 18.5&#8217;
GHA 463&#176; 43.0&#8217;
+/- 360 degrees &#61472;not applicable
Assumed Longitude 156 degrees &#61472;43.0&#8217;
LHA 307 degrees
Tab Dec / d N74 degrees 10.6&#8217; / n.a.
d Correction not applicable
True Declination N74 degrees &#61472;10.6&#8217;
Assumed Latitude 39 degrees N (same)
Dec Inc / + or - d 10.6&#8217; / -24.8
hc 47 degrees &#61472;12.6&#8217;
Total Correction -4.2&#8217;










hc (computed) 47 degrees &#61472;08.2&#8217;
ho 47 degrees &#61472;13.6&#8217;
a (intercept) 5.4 towards
Z 018.9 degrees
Zn 018.9 degrees

2006. Reducing A Sun Sight
The example below points out the similarities between reducing a sun sight and reducing a star sight. It also demonstrates the additional corrections required for low altitude (<10 degrees) sights and sights taken during non-standard temperature and pressure conditions.

On June 16, 1994, at 05-15-23 local time, at DR position L 30 degrees N degrees &#61472;45 degrees W, a navigator takes a sight of the sun&#8217;s upper limb. The navigator has a height of eye of 18 feet, the temperature is 88 degrees &#61472;F, and the atmospheric pressure is 982 mb. The sextant altitude is 3 degrees &#61472;20.2&#8217;. There is no index error. Determine the observed altitude. See Figure 2007.

Body Sun UL
Index Correction 0
Dip Correction (18 ft) -4.1'
Sum -4.1'
hs 3 degrees &#61472;20.2'
ha 3 degrees &#61472;16.1'
Altitude Correction -29.4'
Additional Correction +1.4'
Horizontal Parallax 0
Correction to ha -28.0'
ho 2 degrees &#61472;48.1'

Apply the index and dip corrections to hs to obtain ha. Because ha is less than 10 degrees, use the special altitude correction table for sights between 0 degrees &#61472;and 10 degrees &#61472;located on the right inside front page of the Nautical Almanac.

Enter the table with the apparent altitude, the limb of the sun used for the sight, and the period of the year. Interpolation for the apparent altitude is not required. In this case, the table yields a correction of -29.4&#8217;. The correction&#8217;s algebraic sign is found at the head of each group of entries and at every change of sign.

The additional correction is required because of the nonstandard temperature and atmospheric pressure under which the sight was taken. The correction for these non-standard conditions is found in the Additional Corrections table located on page A4 in the front of the Nautical Almanac. 

First, enter the Additional Corrections table with the temperature and pressure to determine the correct zone letter: in this case, zone L. Then, locate the correction in the L column corresponding to the apparent altitude of 3&#61616;&#61472;16.1&#8217;. Interpolate between the table arguments of 3 degrees 00.0&#8217; and 3 degrees &#61472;30.0&#8217; to determine the additional correction: +1.4&#8217;. The total correction to the apparent altitude is the sum of the altitude and additional corrections: -28.0&#8217;. This results in an ho of 2 degrees &#61472;48.1&#8217;. Next, determine the sun&#8217;s GHA and declination. Again, this process is similar to the star sights reduced above. Notice, however, that SHA, a quantity unique to star sight reduction, is not used in sun sight reduction.

Date June 16, 1994
DR Latitude N30 degrees &#61472;00.0'
DR Longitude W045 degrees &#61472;00.0'
Observation Time 05-15-23
Watch Error 0
Zone Time 05-15-23
Zone Description +03
GMT 08-15-23
Date GMT June 16, 1994
Tab GHA / v 299 &#61472;degrees 51.3' / n.a.
GHA Increment 3 degrees &#61472;50.8'
SHA or v correction not applicable
GHA 303 degrees 42.1'
Assumed Longitude 44 degrees &#61472;42.1' W
LHA 259 degrees
Tab Declination / d N23 degrees &#61472;20.5' / +0.1'
d Correction 0.0
True Declination N23 degrees &#61472;20.5'
Assumed Latitude N30 degrees &#61472;(same)

Determining the sun&#8217;s GHA is less complicated than determining a star&#8217;s GHA. The Nautical Almanac&#8217;s daily pages list the sun&#8217;s GHA in hourly increments. In this case, the sun&#8217;s GHA at 0800 GMT on June 16, 1994 is 299 degrees &#61472;51.3&#8217;. The v correction is not applicable for a sun sight; therefore, applying the increment correction yields the sun&#8217;s GHA. In this case, the GHA is 303 degrees &#61472;42.1&#8217;.

Determining the sun&#8217;s LHA is similar to determining a star&#8217;s LHA. In determining the sun&#8217;s declination, however, an additional correction not encountered in the star sight, the d correction, must be considered. The bottom of the sun column on the daily pages of the Nautical Almanac lists the d value. This is an interpolation factor for the sun&#8217;s declination. The sign of the d factor is not given; it must be determined by noting from the Almanac if the sun&#8217;s declination is increasing or decreasing throughout the day. If it is increasing, the factor is positive; if it is decreasing, the factor is negative. In the above problem, the sun&#8217;s declination is increasing throughout the day. Therefore, the d factor is +0.1.

Having obtained the d factor, enter the 15 minute increment and correction table. Under the column labeled &#8220;v or d corr,&#8221; find the value for d in the left hand column. The corresponding number in the right hand column is the correction; apply it to the tabulated declination. In this case, the correction corresponding to a d value of +0.1 is 0.0&#8217;. The final step will be to determine hc and Zn. Enter the Sight Reduction Tables with an LHA of 259 degrees, a declination of N23 degrees &#61472;20.5&#8217;, and an assumed latitude of 30 degrees N.
Declination Increment / + or - d 20.5' / +31.5
Tabulated Altitude 2&#61616;&#61472;28.8'










Correction (+ or -) +10.8'
Computed Altitude (hc) 2 degrees&#61472; 39.6'
Observed Altitude (ho) 2 degrees &#61472;48.1'
Intercept 8.5 NM (towards)
Z 064.7 degrees
Zn 064.7 degrees

2007. Reducing A Moon Sight
The moon is easy to identify and is often visible during the day. However, the moon&#8217;s proximity to the earth requires applying additional corrections to ha to obtain ho. This section will cover moon sight reduction.

At 10-00-00 GMT, June 16, 1994, the navigator obtains a sight of the moon&#8217;s upper limb. Hs is 26 degrees &#61472;06.7'. Height of eye is 18 feet; there is no index error. Determine ho, the moon&#8217;s GHA, and the moon&#8217;s declination. See Figure 2007.










Body Moon (UL)
Index Correction 0.0'
Dip (18 feet) -4.1'
Sum -4.1'
Sextant Altitude (hs) 26 degrees 06.7'
Apparent Altitude (ha) 26 degrees 02.6'
Altitude Correction +60.5'
Additional Correction 0.0'
Horizontal Parallax (58.4) +4.0'
Moon Upper Limb Correction -30.0'
Correction to ha +34.5'
Observed Altitude (ho) 26 degrees &#61472;37.1

This procedure demonstrates the extra corrections required for obtaining ho for a moon sight. Apply the index and dip corrections and in the same manner as for star and sun sights. The altitude correction comes from tables located on the inside back covers of the Nautical Almanac.

In this case, the apparent altitude was 26 degrees 02.6'. Enter the
altitude correction table for the moon with the above apparent
altitude. Interpolation is not required. The correction is
+60.5'. The additional correction in this case is not applicable
because the sight was taken under standard temperature and
pressure conditions.

The horizontal parallax correction is unique to moon sights. The table for determining this HP correction is on the back inside cover of the Nautical Almanac. First, go to the daily page for June 16 at 10-00-00 GMT. In the column for the moon, find the HP correction factor corresponding to 10-00-00. Its value is 58.4. Take this value to the HP correction table on the inside back cover of the Almanac. Notice that the HP correction columns line up vertically with the moon altitude correction table columns. Find the HP correction column directly under the altitude correction table heading corresponding to the apparent altitude. Enter that column with the HP correction factor from the daily pages. The column has two sets of figures listed under &#8220;U&#8221; and &#8220;L&#8221; for upper and lower limb, respectively. In this case, trace down the &#8220;U&#8221; column until it intersects with the HP correction factor of 58.4. Interpolating between 58.2 and 58.5 yields a value of +4.0' for the horizontal parallax correction.

The final correction is a constant -30.0' correction to ha applied only to sights of the moon&#8217;s upper limb. This correction is always negative; apply it only to sights of the moon&#8217;s upper limb, not its lower limb. The total correction to ha is the sum of all the corrections; in this case, this total correction is +34.5 minutes.

To obtain the moon&#8217;s GHA, enter the daily pages in the moon column and extract the applicable data just as for a star or sun sight. Determining the moon&#8217;s GHA requires an additional correction, the v correction.
GHA moon and v 245 degrees &#61472;45.1' and +11.3
GHA Increment 0 degrees &#61472;00.0'
v Correction +0.1'
GHA 245 degrees &#61472;45.2'

First, record the GHA of the moon for 10-00-00 on June 16, 1994, from the daily pages of the Nautical Almanac.

Record also the v correction factor; in this case, it is +11.3. The v correction factor for the moon is always positive.
The increment correction is, in this case, zero because the sight was recorded on the even hour. To obtain the v correction, go to the tables of increments and corrections. In the 0 minute table in the v or d correction columns, find the correction that corresponds to a v = 11.3. The table yields a correction of +0.1'. Adding this correction to the tabulated GHA gives the final GHA as 245 degrees &#61472;45.2'.

Finding the moon&#8217;s declination is similar to finding the declination for the sun or stars. Go to the daily pages for June 16, 1994; extract the moon&#8217;s declination and d factor.
Tabulated Declination / d S 00 degrees &#61472;13.7' / +12.1
d Correction +0.1'
True Declination S 00 degrees &#61472;13.8

The tabulated declination and the d factor come from the Nautical Almanac&#8217;s daily pages. Record the declination and d correction and go to the increment and correction pages to extract the proper correction for the given d factor.

In this case, go to the correction page for 0 minutes. The correction corresponding to a d factor of +12.1 is +0.1. It is important to extract the correction with the correct algebraic sign. The d correction may be positive or negative depending on whether the moon&#8217;s declination is increasing or decreasing in the interval covered by the d factor. In this case, the moon&#8217;s declination at 10-00-00 GMT on 16 June was S 00 degrees &#61472;13.7&#8217;; at 11-00-00 on the same date the moon&#8217;s declination was S 00 degrees &#61472;25.8&#8217;. Therefore, since the declination was increasing over this period, the d correction is positive.
Do not determine the sign of this correction by noting the trend in the d factor. In other words, had the d factor for 11-00-00 been a value less than 12.1, that would not indicate that the d correction should be negative. 

Remember that the d factor is analogous to an interpolation factor; it provides a correction to declination. Therefore, the trend in declination values, not the trend in d values, controls the sign of the d correction. Combine the tabulated declination and the d correction factor to determine the true declination. In this case, the moon&#8217;s true declination is S 00&#61616;&#61472;13.8&#8217; Having obtained the moon&#8217;s GHA and declination, calculate LHA and determine the assumed latitude. Enter the Sight Reduction Table with the LHA, assumed latitude, and calculated declination. Calculate the intercept and azimuth in the same manner used for star and sun sights.










*to be cont.*


----------



## Fishers of Men

*chapter 20 cont.*

2008. Reducing A Planet Sight
There are four navigational planets: Venus, Mars, Jupiter, and Saturn. Reducing a planet sight is similar to reducing a sun or star sight, but there are a few important differences. This section will cover the procedure for determining ho, the GHA and the declination for a planet sight. On July 27, 1995, at 09-45-20 GMT, you take a sight of Mars. Hs is 33&#176; 20.5&#8217;. The height of eye is 25 feet, and the index correction is +0.2&#8217;. Determine ho, GHA, and declination. See Figure 2008.










Body Mars
Index Correction +0.2'
Dip Correction (25 feet) -4.9'
Sum -4.7'
hs 33 degrees&#61472;&#61472; 20.5'
ha 33 degrees&#61472; 15.8'
Altitude Correction -1.5'
Additional Correction Not applicable
Horizontal Parallax Not applicable
Additional Correction for Mars +0.1'
Correction to ha -1.4'
ho 33 degrees&#61472;14.4'

The table above demonstrates the similarity between reducing planet sights and reducing sights of the sun and stars. Calculate and apply the index and dip corrections exactly as for any other sight. Take the resulting apparent altitude and enter the altitude correction table for the stars and planets on the inside front cover of the Nautical Almanac.

In this case, the altitude correction for 33&#176; 15.8&#8217; results in a correction of -1.5&#8217;. The additional correction is not applicable because the sight was taken at standard temperature and pressure; the horizontal parallax correction is not applicable to a planet sight. All that remains is the correction specific to Mars or Venus. The altitude correction table in the Nautical Almanac also contains this correction. Its magnitude is a function of the body sighted (Mars or Venus), the time of year, and the body&#8217;s apparent altitude. Entering this table with the data for this problem yields a correction of +0.1&#8217;. Applying these corrections to ha results in an ho of 33&#176; 14.4&#8217;.
Tabulated GHA / v 256 degrees&#61472; 10.6' / 1.1
GHA Increment 11 degrees&#61472; 20.0'
v correction +0.8'
GHA 267 degrees&#61472; 31.4'

The only difference between determining the sun&#8217;s GHA and a planet&#8217;s GHA lies in applying the v correction. Calculate this correction from the v or d correction section of the Increments and Correction table in the Nautical Almanac. Find the v factor at the bottom of the planets&#8217; GHA columns on the daily pages of the Nautical Almanac. 

For Mars on July 27, 1995, the v factor is 1.1. If no algebraic sign precedes the v factor, add the resulting correction to the tabulated GHA. Subtract the resulting correction only when a negative sign precedes the v factor. Entering the v or d correction table corresponding to 45 minutes yields a correction of 0.8&#8217;. Remember, because no sign preceded the v factor on the daily pages, add this correction to the tabulated GHA. The final GHA is 267&#176;31.4&#8217;.

Read the tabulated declination directly from the daily pages of the Nautical Almanac. The d correction factor is listed at the bottom of the planet column; in this case, the factor is 0.6. Note the trend in the declination values for the planet; if they are increasing during the day, the correction factor is positive. If the planet&#8217;s declination is decreasing during the day, the correction factor is negative. Next, enter the v or d correction table corresponding to 45 minutes and extract the correction for a d factor of 0.6. The correction in this case is +0.5&#8217;.
From this point, reducing a planet sight is exactly the same as reducing a sun sight.

MERIDIAN PASSAGE
This section covers determining both latitude and longitude at the meridian passage of the sun, or Local Apparent Noon (LAN). Determining a vessel&#8217;s latitude at LAN requires calculating the sun&#8217;s zenith distance and declination and combining them according to the rules discussed below. Latitude at LAN is a special case of the navigational triangle where the sun is on the observer&#8217;s meridian and the triangle becomes a straight north/south line. No &#8220;solution&#8221; is necessary, except to combine the sun&#8217;s zenith distance and its declination according to the rules discussed below. Longitude at LAN is a function of the time elapsed since the sun passed the Greenwich meridian. The navigator must determine the time of LAN and calculate the GHA of the sun at that time. The following examples demonstrates these processes.

2009. Latitude At Meridian Passage
At 1056 ZT, May 16, 1995, a vessel&#8217;s DR position is L 40&#176; 04.3&#8217;N and l 157&#176; 18.5&#8217; W. The ship is on course 200&#176;T at a speed of ten knots. (1) Calculate the first and second estimates of Local Apparent Noon. (2) The navigator actually observes LAN at 12-23-30 zone time. The sextant altitude at LAN is 69&#176; 16.0&#8217;. The index correction is +2.1&#8217; and the height of eye is 45 feet. Determine the vessel&#8217;s latitude. 
Date 16 May 1995
DR Latitude (1156 ZT) 39 degrees&#61472; &#61472;55.0' N
DR Longitude (1156 ZT) 157 degrees&#61472; &#61472;23.0' W
Central Meridian 150 degrees&#61472; &#61472;W
d Longitude (arc) 7 degrees&#61472; 23' W
d Longitude (time) +29 min. 32 sec
Meridian Passage (LMT) 1156
ZT (first estimate) 12-25-32
DR Longitude (12-25-32) 157 degrees&#61472; &#61472;25.2'
d Longitude (arc) 7 degrees&#61472; 25.2'
d Longitude (time) +29 min. 41 sec
Meridian Passage 1156
ZT (second estimate) 12-25-41
ZT (actual transit) 12-23-30 local
Zone Description +10
GMT 22-23-30
Date (GMT) 16 May 1995
Tabulated Declination / d N 19 degrees&#61472; &#61472;09.0' / +0.6
d correction +0.2'
True Declination N 19 degrees&#61472; &#61472;09.2'
Index Correction +2.1'
Dip (48 ft) -6.7'
Sum -4.6'
hs (at LAN) 69 degrees&#61472; &#61472;16.0'
ha 69 degrees&#61472; &#61472;11.4'
Altitude Correction +15.6'
89 degrees&#61472; &#61472;60' 89 degrees&#61472; 60.0'
ho 69 degrees&#61472; &#61472;27.0'
Zenith Distance N 20 degrees&#61472; &#61472;33.0'
True Declination N 19 degrees&#61472; &#61472;09.2'
Latitude 39 degrees&#61472; &#61472;42.2'

First, determine the time of meridian passage from the daily pages of the Nautical Almanac. In this case, the meridian passage for May 16, 1995, is 1156. That is, the sun crosses the central meridian of the time zone at 1156 ZT and the observer&#8217;s local meridian at 1156 local time. Next, determine the vessel&#8217;s DR longitude for the time of meridian passage. In this case, the vessel&#8217;s 1156 DR longitude is 157&#176; 23.0&#8217; W. Determine the time zone in which this DR longitude falls and record the longitude of that time zone&#8217;s central meridian. In this case, the central meridian is 150&#176; W. Enter the Conversion of Arc to Time table in the Nautical Almanac with the difference between the DR longitude and the central meridian longitude. The conversion for 7&#176; of arc is 28m of time, and the conversion for 23&#8217; of arc is 1m32s of time. Sum these two times. If the DR position is west of the central meridian (as it is in this case), add this time to the time of tabulated meridian passage. If the longitude difference is to the east of the central meridian, subtract this time from the tabulated meridian passage. In this case, the DR position is west of the central meridian. Therefore, add 29 minutes and 32 seconds to 1156, the tabulated time of meridian passage. The estimated time of LAN is 12-25-32 ZT. 

This first estimate for LAN does not take into account the vessel&#8217;s movement. To calculate the second estimate of LAN, first determine the DR longitude for the time of first estimate of LAN (12-25-32 ZT). 

In this case, that longitude would be 157&#176; 25.2&#8217; W. Then, calculate the difference between the longitude of the 12-25-32 DR position and the central meridian longitude. This would be 7&#176; 25.2&#8217;. Again, enter the arc to time conversion table and calculate the time difference corresponding to this longitude difference. The correction for 7&#176; of arc is 28&#8217; of time, and the correction for 25.2&#8217; of arc is 1&#8217;41&#8221; of time. Finally, apply this time correction to the original tabulated time of meridian passage (1156 ZT). The resulting time, 12-25-41 ZT, is the second estimate of LAN.

Solving for latitude requires that the navigator calculate two quantities: the sun&#8217;s declination and the sun&#8217;s zenith distance. First, calculate the sun&#8217;s true declination at LAN. The problem states that LAN is 12-28-30. (Determining the exact time of LAN is covered in section 2010.) Enter the time of observed LAN and add the correct zone description to determine GMT. Determine the sun&#8217;s declination in the same manner as in the sight reduction problem in section 2006. In this case, the tabulated declination was N 19&#176; 19.1&#8217;, and the d correction +0.2&#8217;. The true declination, therefore, is N 19&#176; 19.3&#8217;. Next, calculate zenith distance. Recall from Navigational Astronomy that zenith distance is simply 90&#176; - observed altitude. Therefore, correct hs to obtain ha; then correct ha to obtain ho.

Then, subtract ho from 90&#176; to determine the zenith distance. Name the zenith distance North or South depending on the relative position of the observer and the sun&#8217;s declination. If the observer is to the north of the sun&#8217;s declination, name the zenith distance north. Conversely, if the observer is to the south of the sun&#8217;s declination, name the zenith distance south. In this case, the DR latitude is N 39&#176; 55.0&#8217; and the sun&#8217;s declination is N 19&#176; 19.3&#8217;.

The observer is to the north of the sun&#8217;s declination; therefore, name the zenith distance north. Next, compare the names of the zenith distance and the declination. If their names are the same (i.e., both are north or both are south), add the two values together to obtain the latitude. This was the case in this problem. Both the sun&#8217;s declination and zenith distance were north; therefore, the observer&#8217;s latitude is the sum of the two. 

If the name of the body&#8217;s zenith distance is contrary to the name of the sun&#8217;s declination, then subtract the smaller of the two quantities from the larger, carrying for the name of the difference the name of the larger of the two quantities. The result is the observer&#8217;s latitude. The following examples illustrate this process.
Zenith Distance N 25 degrees&#61472; &#61472;Zenith Distance S 50 degrees&#61472;
True Declination S 15 degrees&#61472; &#61472;True Declination N10 degrees&#61472;
Latitude N 10 degrees&#61472; &#61472;Latitude S 40 degrees&#61472;

2010 Longitude At Meridian Passage
Determining a vessel&#8217;s longitude at LAN is straightforward. In the western hemisphere, the sun&#8217;s GHA at LAN equals the vessel&#8217;s longitude. In the eastern hemisphere, subtract the sun&#8217;s GHA from 360&#176; to determine longitude. The difficult part lies in determining the precise moment of meridian passage.

Determining the time of meridian passage presents a problem because the sun appears to hang for a finite time at its local maximum altitude. Therefore, noting the time of maximum sextant altitude is not sufficient for determining the precise time of LAN. Two methods are available to obtain LAN with a precision sufficient for determining longitude: 
(1) the graphical method and 
(2) the calculation method. The graphical method is discussed first below. See Figure 2010. 










Approximately 30 minutes before the estimated time of LAN, measure and record sextant altitudes and their corresponding times. Continue taking sights for about 30 minutes after the sun has descended from the maximum recorded altitude. Increase the sighting frequency near the predicted meridian passage. One sight every 20-30 seconds should yield good results near meridian passage; less frequent sights are required before and after. 

Plot the resulting data on a graph of sextant altitude versus time. Fair a curve through the plotted data. Next, draw a series of horizontal lines across the curve formed by the data points. These lines will intersect the faired curve at two different points. The x coordinates of the points where these lines intersect the faired curve represent the two different times when the sun&#8217;s altitude was equal (one time when the sun was ascending; the other time when the sun was descending). Draw three such lines, and ensure the lines have sufficient vertical separation. For each line, average the two times where it intersects the faired curve. Finally, average the three resulting times to obtain a final value for the time of LAN. From the Nautical Almanac, determine the sun&#8217;s GHA at that time; this is your longitude in the western hemisphere. In the eastern hemisphere, subtract the sun&#8217;s GHA from 360&#176; to determine longitude. 

The second method of determining LAN is similar to the first. Estimate the time of LAN as discussed above, Measure and record the sun&#8217;s altitude as the sun approaches its maximum altitude. As the sun begins to descend, set the sextant to correspond to the altitude recorded just before the sun&#8217;s reaching its maximum altitude. Note the time when the sun is again at that altitude. Average the two times. Repeat this procedure with two other altitudes recorded before LAN, each time presetting the sextant to those altitudes and recording the corresponding times that the sun, now on its descent, passes through those altitudes. Average these corresponding times. Take a final average among the three averaged times; the result will be the time of meridian passage. Determine the vessel&#8217;s longitude by determining the sun&#8217;s GHA at the exact time of LAN.

2011. Latitude By Polaris
Since Polaris is always within about 1&#176; of the North Pole, the altitude of Polaris, with a few minor corrections, equals the latitude of the observer. This relationship makes Polaris an extremely important navigational star in the northern hemisphere.

The corrections are necessary because Polaris orbits in a small circle around the pole. When Polaris is at the exact same altitude as the pole, the correction is zero. At two points in its orbit it is in a direct line with the observer and the pole, either nearer than or beyond the pole. At these points the corrections are maximum. The following example illustrates converting a Polaris sight to latitude.

Latitude = ho &#8211; 1&#61616;+A0+A1+A2

At 23-18-56 GMT, on April 21, 1994, at DR &#955;=37&#176; 14.0&#8217; W, L = 50&#176; 23.8&#8217; N, the observed altitude of Polaris (ho) is 49&#176; 31.6&#8217;. Find the vessel&#8217;s latitude.

To solve this problem, use the equation:
where ho is the sextant altitude (hs) corrected as in any other star sight; 1&#176; is a constant; and A0, A1, and A2 are correction factors from the Polaris tables found in the Nautical Almanac. These three correction factors are always positive. One needs the following information to enter the tables: LHA of Aries, DR latitude, and the month of the year.

Therefore:
Tabulated GHA (2300 hrs.) 194 degrees&#61472; &#61472;32.7'
Increment (18-56) 4 degrees&#61472; &#61472;44.8'
GHA 199 degrees&#61472; 17.5'
DR Longitude (-W +E) 37 degrees&#61472; &#61472;14.0
LHA 162 degrees&#61472; &#61472;03.5'
A0 (162 degrees&#61472; &#61472;03.5') +1 degrees&#61472; &#61472;25.4'
A1 (L = 50 degrees&#61472; N) +0.6'
A2 (April) +0.9'
Sum 1 degrees&#61472; &#61472;26.9'
Constant -1 degrees&#61472; &#61472;00.0'
Observed Altitude 49 degrees&#61472; &#61472;31.6'
Total Correction +26.9'
Latitude N 49 degrees&#61472; &#61472;58.5

Enter the Polaris table with the calculated LHA of Aries (162&#176; 03.5&#8217. See Figure 2011.










The first correction, A0, is a function solely of the LHA of Aries. Enter the table column indicating the proper range of LHA of Aries; in this case, enter the 160&#176;-169&#176; column. The numbers on the left hand side of the A0 correction table represent the whole degrees of LHA ; interpolate to determine the proper A0 correction. In this case, LHA was 162&#176; 03.5&#8217;. The A0 correction for LHA = 162&#176; is 1&#176; 25.4&#8217; and the A0 correction for LHA = 163&#176; is 1&#176; 26.1&#8217;. The A0 correction for 162&#176; 03.5&#8217; is 1&#176; 25.4&#8217;. 

To calculate the A1 correction, enter the A1 correction table with the DR latitude, being careful to stay in the 160&#176;-169&#176; LHA column. There is no need to interpolate here; simply choose the latitude that is closest to the vessel&#8217;s DR latitude. In this case, L is 50&#176;N. The A1 correction corresponding to an LHA range of 160&#176;-169&#176; and a latitude of 50&#176;N is + 0.6&#8217;.

Finally, to calculate the A2 correction factor, stay in the 160&#176;-169&#176; LHA column and enter the A2 correction table. Follow the column down to the month of the year; in this case, it is April. The correction for April is + 0.9&#8217;. Sum the corrections, remembering that all three are always positive. Subtract 1&#176; from the sum to determine the total correction; then apply the resulting value to the observed altitude of Polaris. This is the vessel&#8217;s latitude.

*End chapter 20
*


----------



## Fishers of Men

*CHAPTER 21*
NAVIGATIONAL MATHEMATICS
GEOMETRY

I am tired of fighting the symbols to go in here, so a question mark after a number= degrees.

2100.	Definition
Geometry deals with the properties, relations, and measurement of lines, surfaces, solids, and angles. Plane geometry deals with plane figures, and solid geometry deals with three&#8211;dimensional figures.

A point, considered mathematically, is a place having position but no extent. It has no length, breadth, or thickness. A point in motion produces a line, which has length, but neither breadth nor thickness. A straight or right line is the shortest distance between two points in space. A line in motion in any direction except along itself produces a surface, which has length and breadth, but not thickness. A plane surface or plane is a surface without curvature. A straight line connecting any two of its points lies wholly within the plane. A plane surface in motion in any direction except within its plane produces a solid, which has length, breadth, and thickness. Parallel lines or surfaces are those which are everywhere equidistant. Perpendicular lines or surfaces are those which meet at right or 90&#176; angles. A perpendicular may be called a normal, particularly when it is perpendicular to the tangent to a curved line or surface at the point of tangency. All points equidistant from the ends of a straight line are on the perpendicular bisector of that line. The shortest distance from a point to a line is the length of the perpendicular between them.

2101.	Angles
An angle is formed by two straight lines which meet at a point. It is measured by the arc of a circle intercepted between the two lines forming the angle, the center of the circle being at the point of intersection. In Figure 2101, the angle formed by lines AB and BC, may be designated &#8220;angle B,&#8221; &#8220;angle ABC,&#8221; or &#8220;angle CBA&#8221;; or by Greek letter as &#8220;angle a.&#8221; The three letter designation is preferred if there is more than one angle at the point. When three letters are used, the middle one should always be that at the vertex of the angle. An acute angle is one less than a right angle (90&#176.

A right angle is one whose sides are perpendicular (90&#176. An obtuse angle is one greater than a right angle (90&#176 but less than 180&#176;.

A straight angle is one whose sides form a continuous straight line (180&#176.

A reflex angle is one greater than a straight angle (180&#176 but less than a circle (360&#176. Any two lines meeting at a point form two angles, one less than a straight angle of 180&#176; (unless exactly a straight angle) and the other greater than a straight angle.

An oblique angle is any angle not a multiple of 90&#176;. 

Two angles whose sum is a right angle (90&#176 are complementary angles, and either is the complement of the other.

Two angles whose sum is a straight angle (180&#176 are supplementary angles, and either is the supplement of the other.

Two angles whose sum is a circle (360&#176 are explementary angles, and either is the explement of the other. The two angles formed when any two lines terminate at a common point are explementary.

If the sides of one angle are perpendicular to those of another, the two angles are either equal or supplementary. Also, if the sides of one angle are parallel to those of another, the two angles are either equal or supplementary. 

When two straight lines intersect, forming four angles, the two opposite angles, called vertical angles, are equal. Angles which have the same vertex and lie on opposite sides of a common side are adjacent angles. Adjacent angles formed by intersecting lines are supplementary, since each pair of adjacent angles forms a straight angle. A transversal is a line that intersects two or more other lines.

If two or more parallel lines are cut by a transversal, groups of adjacent and vertical angles are formed, A dihedral angle is the angle between two intersecting planes.










2102. Triangles
A plane triangle is a closed figure formed by three straight lines, called sides, which meet at three points called vertices. The vertices are labeled with capital letters and the sides with lowercase letters, as shown in Figure 2102a. An equilateral triangle is one with its three sides equal in length. It must also be equiangular, with its three angles equal.

An isosceles triangle is one with two equal sides, called legs. The angles opposite the legs are equal. A line which bisects (divides into two equal parts) the unequal angle of an isosceles triangle is the perpendicular bisector of the opposite side, and divides the triangle into two equal right triangles.

A scalene triangle is one with no two sides equal. In such a triangle, no two angles are equal. An acute triangle is one with three acute angles. A right triangle is one having a right angle. The side opposite the right angle is called the hypotenuse. The other two sides may be called legs. A plane triangle can have only one right angle.

An obtuse triangle is one with an obtuse angle. A plane triangle can have only one obtuse angle. An oblique triangle is one which does not contain a right angle.










The altitude of a triangle is a line or the distance from any vertex perpendicular to the opposite side. A median of a triangle is a line from any vertex to the center of the opposite side. The three medians of a triangle meet at a point called the centroid of the triangle. This point divides each median into two parts, that part between the centroid and the vertex being twice as long as the other part. 

Lines bisecting the three angles of a triangle meet at a point which is equidistant from the three sides, which is the center of the inscribed circle, as shown in Figure 2102b. This point is of particular interest to navigators because it is the point theoretically taken as the fix when three lines of position of equal weight and having only random errors do not meet at a common point. In practical navigation, the point is found visually, not by construction, and other factors often influence the chosen fix position. 

The perpendicular bisectors of the three sides of a triangle meet at a point which is equidistant from the three vertices, which is the center of the circumscribed circle, the circle through the three vertices and the smallest circle which can be drawn enclosing the triangle. The center of a circumscribed circle is within an acute triangle, on the hypotenuse of a right triangle, and outside an obtuse triangle. 

A line connecting the mid&#8211;points of two sides of a triangle is always parallel to the third side and half as long. Also, a line parallel to one side of a triangle and intersecting the other two sides divides these sides proportionally. This principle can be used to divide a line into any number of equal or proportional parts.

The sum of the angles of a plane triangle is always 180&#176;. Therefore, the sum of the acute angles of a right triangle is 90&#176;, and the angles are complementary. If one side of a triangle is extended, the exterior angle thus formed is supplementary to the adjacent interior angle and is therefore equal to the sum of the two non adjacent angles. If two angles of one triangle are equal to two angles of another triangle, the third angles are also equal, and the triangles are similar. If the area of one triangle is equal to the area of another, the triangles are equal. Triangles having equal bases and altitudes also have equal areas. Two figures are congruent if one can be placed over the other to make an exact fit. Congruent figures are both similar and equal. If any side of one triangle is equal to any side of a similar triangle, the triangles are congruent. For example, if two right triangles have equal sides, they are congruent; if two right triangles have two corresponding sides equal, they are congruent. Triangles are congruent only if the sides and angles are equal.

The sum of two sides of a plane triangle is always greater than the third side; their difference is always less than the third side.
The area of a triangle is equal to &#189; of the area of the polygon formed from its base and height. This can be stated algebraically as:










The square of the hypotenuse of a right triangle is equal to the sum of the squares of the other two sides, or a2 + b2 = c2. (these are to the 2nd power)
Therefore the length of the hypotenuse of plane right triangle can be found by the formula :










2103.	Circles
A circle is a plane, closed curve, all points of which are equidistant from a point within, called the center. 

The distance around a circle is called the circumference. 

Technically the length of this line is the perimeter, although the term &#8220;circumference&#8221; is often used. An arc is part of a circumference. A major arc is more than a semicircle (180&#61616, a minor are is less than a semicircle (180&#61616. A semi&#8211;circle is half a circle (180&#61616, a quadrant is a quarter of a circle (90&#61616, a quintant is a fifth of a circle (72&#61616, a sextant is a sixth of a circle (60&#61616, an octant is an eighth of a circle (45&#61616. Some of these names have been applied to instruments used by navigators for measuring altitudes of celestial bodies because of the part of a circle used for the length of the arc of the instrument.

Concentric circles have a common center. A radius (plural radii) or semidiameter is a straight line connecting the center of a circle with any point on its circumference. A diameter of a circle is a straight line passing through its center and terminating at opposite sides of the circumference. It divides a circle into two equal parts. The ratio of the length of the circumference of any circle to the length of its diameter is 3.14159+, or &#61472;(the Greek letter pi), a relationship that has many useful applications.

A sector is that part of a circle bounded by two radii and an arc. The angle formed by two radii is called a central angle. Any pair of radii divides a circle into sectors, one less than a semicircle (180&#61616 and the other greater than a semicircle (unless the two radii form a diameter). A chord is a straight line connecting any two points on the circumference of a circle. Chords equidistant from the center of a circle are equal in length.

A segment is the part of a circle bounded by a chord and the intercepted arc. A chord divides a circle into two segments, one less than a semicircle (180&#61616, and the other greater than a semicircle (unless the chord is a diameter). A diameter perpendicular to a chord bisects it, its arc, and its segments. Either pair of vertical angles formed by intersecting chords has a combined number of degrees equal to the sum of the number of degrees in the two arcs intercepted by the two angles.

An inscribed angle is one whose vertex is on the circumference of a circle and whose sides are chords. It has half as many degrees as the arc it intercepts. Hence, an angle inscribed in a semicircle is a right angle if its sides terminate at the ends of the diameter forming the semicircle. A secant of a circle is a line intersecting the circle, or a chord extended beyond the circumference. 

A tangent to a circle is a straight line, in the plane of the circle, which has only one point in common with the circumference. A tangent is perpendicular to the radius at the point of tangency. Two tangents from a common point to opposite sides of a circle are equal in length, and a line from the point to the center of the circle bisects the angle formed by the two tangents. An angle formed outside a circle by the intersection of two tangents, a tangent and a secant, or two secants has half as many degrees as the difference between the two intercepted arcs. An angle formed by a tangent and a chord, with the apex at the point of tangency, has half as many degrees as the arc it intercepts. A common tangent is one tangent to more than one circle. Two circles are tangent to each other if they touch at one point only. If of different sizes, the smaller circle may be either inside or outside the larger one.

Parallel lines intersecting a circle intercept equal arcs. If A = area; r = radius; d = diameter; C = circumference; s = linear length of an arc; a = angular length of an arc, or the angle it subtends at the center of a circle, in degrees; b = angular length of an arc, or the angle it subtends at the center of a circle, in radians:










2104.	Spheres
A sphere is a solid bounded by a surface every point of which is equidistant from a point within called the center. It may also be formed by rotating a circle about any diameter. A radius or semidiameter of a sphere is a straight line connecting its center with any point on its surface. A diameter of a sphere is a straight line through its center and terminated at both ends by the surface of the sphere.

The intersection of a plane and the surface of a sphere is a circle, a great circle if the plane passes through the center of the sphere, and a small circle if it does not. The shorter arc of the great circle between two points on the surface of a sphere is the shortest distance, on the surface of the sphere, between the points. Every great circle of a sphere bisects every
other great circle of that sphere. The poles of a circle on a sphere are the extremities of the sphere&#8217;s diameter which is perpendicular to the plane of the circle. All points on the circumference of the circle are equidistant from either of its poles. In the ease of a great circle, both poles are 90&#176; from any point on the circumference of the circle. Any great circle may be considered a primary, particularly when it serves as the origin of measurement of a coordinate. 

The great circles through its poles are called secondary. Secondaries are perpendicular to their primary.

A spherical triangle is the figure formed on the surface of a sphere by the intersection of three great circles. The lengths of the sides of a spherical triangle are measured in degrees, minutes, and seconds, as the angular lengths of the arcs forming them. The sum of the three sides is always less than 360&#61616;. The sum of the three angles is always more than 180&#61616;&#61472; and less than 540&#61616;.
A lune is the part of the surface of a sphere bounded by halves of two great circles.

2105.	Coordinates
Coordinates are magnitudes used to define a position. Many different types of coordinates are used. Important navigational ones are described below.
If a position is known to be on a given line, only one magnitude (coordinate) is needed to identify the position if an origin is stated or understood.
If a position is known to be on a given surface, two magnitudes (coordinates) are needed to define the position. If nothing is known regarding a position other than that it exists in space, three magnitudes (coordinates) are needed to define its position.

Each coordinate requires an origin, either stated or implied. If a position is known to be on a given plane, it might be defined by means of its distance from each of two intersecting lines, called axes. These are called rectangular coordinates. In Figure 2105, OY is called the ordinate, and OX is called the abscissa. Point O is the origin, and lines OX and OY the axes (called the X and Y axes, respectively). Point A is at position x,y. If the axes are not perpendicular but the lines x and y are drawn parallel to the axes, oblique coordinates result. Either type are called Cartesian coordinates. A three&#8211;dimensional system of Cartesian coordinates, with X Y, and Z axes, is called space coordinates.

Another system of plane coordinates in common usage consists of the direction and distance from the origin (called the pole). A line extending in the direction indicated is called a radius vector. Direction and distance from a fixed point constitute polar coordinates, sometimes called the rho&#8211;theta (the Greek (p), to indicate distance, and the Greek (0 with a line thru it), to indicate direction) system. An example of its use is the radar scope.

Spherical coordinates are used to define a position on the surface of a sphere or spheroid by indicating angular distance from a primary great circle and a reference secondary great circle. Examples used in navigation are latitude and longitude, altitude and azimuth, and declination and hour angle.










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## Fishers of Men

*ch 21 cont.*
I'll be glad to get done with this chapter, I have to make too much into photos! Remember if you see a ? it is supposed to be a 0 for degrees.
TRIGONOMETRY
2106.	Definitions
Trigonometry deals with the relations among the angles and sides of triangles. Plane trigonometry deals with plane triangles, those on a plane surface. Spherical trigonometry deals with spherical triangles, which are drawn on the surface of a sphere. In navigation, the common methods of celestial sight reduction use spherical triangles on the surface of the earth. For most navigational purposes, the earth is assumed to be a sphere, though it is somewhat flattened.

2107.	Angular Measure
A circle may be divided into 360 degrees (&#61616, which is the angular length of its circumference. Each degree may be divided into 60 minutes (&#8216, and each minute into 60 seconds (&#8220. The angular length of an arc is usually expressed
in these units. By this system a right angle or quadrant has 90&#61616;&#61472; and a straight angle or semicircle 180&#61616;. In marine navigation, altitudes, latitudes, and longitudes are usually expressed in degrees, minutes, and tenths (27&#176;14.4&#8217. Azimuths are usually expressed in degrees and tenths (164.7&#176.The system of degrees, minutes, and seconds indicated above is the sexagesimal system. In the centesimal system used chiefly in France, the circle is divided into 400 centesimal degrees (sometimes called grades) each of which is divided into 100 centesimal minutes of 100 centesimal seconds each.

A radian is the angle subtended at the center of a circle by an arc having a linear length equal to the radius of the circle. A circle (360&#176 = &#960;/2 radians, a semicircle (180&#176 = p radians, a right angle (90&#176 = p/2 radians. The length of the arc of a circle is equal to the radius multiplied by the angle subtended in radians.

2108. Trigonometric Functions
Trigonometric functions are the various proportions or ratios of the sides of a plane right triangle, defined in relation to one of the acute angles. In Figure 2108a, let q be any acute angle. From any point R on line OA, draw a line
perpendicular to OB at F. From any other point R&#8217; on OA, draw a line perpendicular to OB at F&#8217;. Then triangles OFR and OF&#8217;R&#8217; are similar right triangles because all their corresponding angles are equal. Since in any pair of similar triangles the ratio of any two sides of one triangle is equal to the ratio of the corresponding two sides of the other triangle,










No matter where the point R is located on OA, the ratio between the lengths of any two sides in the triangle OFR has a constant value. Hence, for any value of the acute angle &#61553;, there is a fixed set of values for the ratios of the various sides of the triangle. These ratios are defined as follows:










Of these six principal functions, the second three are the reciprocals reciprocals of the first three; therefore



















In Figure 2108b, A, B, and C are the angles of a plane right triangle, with the right angle at C. The sides are labeled a, b, c, opposite angles A, B, and C respectively. The six principal trigonometric functions of angle B are:



















Since A and B are complementary, these relations show that the sine of an angle is the cosine of its complement, the tangent of an angle is the cotangent of its complement, and the secant of an angle is the cosecant of its complement. Thus, the co-function of an angle is the function of its complement.
sin&#61480;90&#61616;&#61472;&#8211; A&#61481;&#61472;= cosA
cos &#61480;90&#61616;&#61472;&#8211; A&#61481;&#61472;= sinA
tan&#61480;90&#61616;&#61472;&#8211; A&#61481;&#61472;= cotA
csc &#61480;90&#61616;&#61472;&#8211; A&#61481;&#61472;= secA
sec&#61480;90&#61616;&#61472;&#8211; A&#61481;&#61472;= cscA
cot &#61480;90&#61616;&#61472;&#8211; A&#61481;&#61472;= tanA

The numerical value of a trigonometric function is sometimes called the natural function to distinguish it from the logarithm of the function, called the logarithmic function. Numerical values of the six principal functions are given at 1&#8217; intervals in the table of natural trigonometric functions. Logarithms are given at the same intervals in another table.

Since the relationships of 30&#61616;, 60&#61616;, and 45&#61616; &#61472;right triangles are as shown in Figure 2108c, certain values of the basic functions can be stated exactly, as shown in Table 2108.

















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## Fishers of Men

*21 cont*
remember a ? mark is supposed to be a "o" for degrees.
2109. Functions In Various Quadrants
To make the definitions of the trigonometric functions more general to include those angles greater than 90&#176;, the functions are defined in terms of the rectangular Cartesian coordinates of point R of Figure 2108a, due regard being given to the sign of the function. In Figure 2109a, OR is assumed to be a unit radius. By convention the sign of OR is always positive. This radius is imagined to rotate in a counterclockwise direction through 360&#61616;&#61472;from the horizontal position at 0&#61616;, the positive direction along the X axis. Ninety degrees (90&#61616 is the positive direction along the Y axis. The angle between the original position of the radius and its position at any time increases from 0&#61616;&#61472;to 90&#61616;&#61472;in the first quadrant (I), 90&#61616;&#61472;to 180&#61616;&#61472;in the second quadrant (II), 180&#61616;&#61472;to 270&#61616;&#61472;in the third quadrant (III), and 270&#61616;&#61472;to 360&#61616;&#61472;in the fourth quadrant (IV).

The numerical value of the sine of an angle is equal to the projection of the unit radius on the Y&#8211;axis. According to the definition given in article 2108, the sine of angle in 



































The cosecant, secant, and cotangent functions of angles in the various quadrants are similarly determined.



















The numerical values vary by quadrant as shown above:









2110. Trigonometric Identities
A trigonometric identity is an equality involving trigonometric functions of &#61553;&#61472;which is true for all values of &#61553;, except those values for which one of the functions is not defined or for which a denominator in the equality is equal to zero. The fundamental identities are those identities from which other identities can be derived.


























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## Fishers of Men

*ch 21 cont*
2111. Inverse Trigonometric Functions
An angle having a given trigonometric function may be indicated in any of several ways. Thus, sin y = x, y = arc sin x, and y = sin&#8211;1 x have the same meaning. The superior &#8220;&#8211;1&#8221; is not an exponent in this case. In each case, y is &#8220;the angle whose sine is x.&#8221; In this case, y is the inverse sine of x. Similar relationships hold for all trigonometric functions.

SOLUTION OF TRIANGLES
A triangle is composed of six parts: three angles and three sides. The angles may be designated A, B, and C; and the sides opposite these angles as a, b, and c, respectively. In general, when any three parts are known, the other three parts can be found, unless the known parts are the three angles.

2112. Right Plane Triangles
In a right plane triangle it is only necessary to substitute numerical values in the appropriate formulas representing the basic trigonometric functions and solve. Thus, if a and b are known,









2113. Oblique Plane Triangles
When solving an oblique plane triangle, it is often desirable to draw a rough sketch of the triangle approximately to scale, as shown in Figure 2113. The following laws are helpful in solving such triangles:








The unknown parts of oblique plane triangles can be computed by the formulas in Table 2113, among others. By reassignment of letters to sides and angles, these formulas can be used to solve for all unknown parts of oblique plane triangles.
















SPHERICAL TRIGONOMETRY

2114. Napier&#8217;s Rules
Right spherical triangles can be solved with the aid of Napier&#8217;s Rules of Circular Parts. If the right angle is omitted, the triangle has five parts: two angles and three sides, as shown in Figure 2114a. Since the right angle is already known, the triangle can be solved if any two other parts are known. If the two sides forming the right angle, and the complements of the other three parts are used, these elements (called &#8220;parts&#8221; in the rules) can be arranged in five sectors of a circle in the same order in which they occur in the triangle, as shown in Figure 2114b. Considering any part as the middle part, the two parts nearest it in the diagram are considered the adjacent parts, and the two farthest from it the opposite parts.








Napier&#8217;s Rules state: The sine of a middle part equals the product of (1) the tangents of the adjacent parts or (2) the cosines of the opposite parts.
In the use of these rules, the co&#8211;function of a complement can be given as the function of the element. Thus, the cosine of co&#8211;A is the same as the sine of A. From these rules the following formulas can be derived:
sin a=tan b cot B=sin c sin A
sin b=tan a cot A=sin c sin B
cos c=cot A cot B=cos a cos b
cos A=tan b cot c=cos a sin B
cos B=tan a cot c=cos b sinA

The following rules apply:
1.	An oblique angle and the side opposite are in the same quadrant.
2.	Side c (the hypotenuse) is less then 90&#61616;&#61472;when a and b are in the same quadrant, and more than 90&#61616;&#61472;when a and b are in different quadrants.
If the known parts are an angle and its opposite side, two solutions are possible.
A quadrantal spherical triangle is one having one side of 90&#61616;. A biquadrantal spherical triangle has two sides of 90&#61616;. A triquadrantal spherical triangle has three sides of 90&#61616;. A biquadrantal spherical triangle is isosceles and has two right angles opposite the 90&#61616;&#61472;sides. A triquadrantal spherical triangle is equilateral, has three right angles, and bounds an octant (one&#8211;eighth) of the surface of the sphere. A quadrantal spherical triangle can be solved by Napier&#8217;s rules provided any two elements in addition to the 90&#61616;&#61472;side are known. The 90&#61616;&#61472;side is omitted and the other parts are arranged in order in a five&#8211;sectored circle, using the complements of the three parts farthest from the 90&#61616;&#61472;side. In the case of a quadrantal triangle, rule 1 above is used, and rule 2 restated: angle C (the angle opposite the side of 90&#61616 is more than 90&#61616;&#61472;when A and B are in the same quadrant, and less than 90&#61616;&#61472;when A and B are in different quadrants. If the rule requires an angle of more than 90&#61616;&#61472;and the solution produces an angle of less than 90&#61616;, subtract the solved angle from 180&#61616;.

2115. Oblique Spherical Triangles
An oblique spherical triangle can be solved by dropping a perpendicular from one of the apexes to the opposite side, subtended if necessary, to form two right spherical triangles.
It can also be solved by the following formulas in Table 2115, reassigning the letters as necessary.









*conclusion of 21 thankfully!*


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## Fishers of Men

I am omitting two chapters, if you want them, e-mail me and I will send you the files. It's just too difficult to post mathematics on here:
CHAPTER 22 NAVIGATIONAL CALCULATIONS
CHAPTER 23 NAVIGATIONAL ERRORS

*On we go to ch 24*
THE SAILINGS we touched on this in the beginning, remember?

INTRODUCTION
2400.	Introduction (remember the "?" is supposed to be a "o" for degrees.)
Dead reckoning involves the determination of one&#8217;s present or future position by projecting the ship&#8217;s course and distance run from a known position. A closely related problem is that of finding the course and distance from one known point to another known point. For short distances, these problems are easily solved directly on charts, but for long distances, a purely mathematical solution is often a better method. Collectively, these methods are called The Sailings.

Navigational computer programs and calculators commonly contain algorithms for computing all of the problems of the sailings. For those situations when a calculator is not available, this chapter also discusses sailing solutions by Table 4, the Traverse Tables.

2401.	Rhumb Lines And Great Circles
The principal advantage of a rhumb line is that it maintains constant true direction. A ship following the rhumb line between two places does not change true course. A rhumb line makes the same angle with all meridians it crosses and appears as a straight line on a Mercator chart. For any other case, the difference between the rhumb line and the great circle connecting two points increases (1) as the latitude increases, (2) as the difference of latitude between the two points decreases, and (3) as the difference of longitude increases.

A great circle is the intersection of the surface of a sphere and a plane passing through the center of the sphere. It is the largest circle that can be drawn on the surface of the sphere, and is the shortest distance along the surface between any two points. Any two points are connected by only one great circle unless the points are antipodal (180&#61616;&#61472;apart on the earth), and then an infinite number of great circles passes through them. Every great circle bisects every other great circle. Thus, except for the equator, every great circle lies exactly half in the Northern Hemisphere and half in the Southern Hemisphere. Any two points 180&#61616;&#61472;apart on a great circle have the same latitude numerically, but contrary names, and are 180&#61616;&#61472;apart in longitude. The point of greatest latitude is called the vertex. For each great circle, there is a vertex in each hemisphere, 180&#61616;&#61472;apart in longitude. At these points the great circle is tangent to a parallel of latitude, and its direction is due east-west. On each side of these vertices the direction changes progressively until the intersection with the equator is reached, 90&#61616;&#61472;in longitude away, where the great circle crosses the equator at an angle equal to the latitude of the vertex.

On a Mercator chart a great circle appears as a sine curve extending equal distances each side of the equator. The rhumb line connecting any two points of the great circle on the same side of the equator is a chord of the curve. Along any intersecting meridian the great circle crosses at a higher latitude than the rhumb line. If the two points are on opposite sides of the equator, the direction of curvature of the great circle relative to the rhumb line changes at the equator. The rhumb line and great circle may intersect each other, and if the points are equal distances on each side of the equator, the intersection takes place at the equator. Great circle sailing takes advantage of the shorter distance along the great circle between two points, rather than the longer rhumb line. The arc of the great circle between the points is called the great circle track. If it could be followed exactly, the destination would be dead ahead throughout the voyage (assuming course and heading were the same). The rhumb line appears the more direct route on a Mercator chart because of chart distortion. The great circle crosses meridians at higher latitudes, where the distance between them is less. This is why the great circle route is shorter than the rhumb line.

The decision as to whether or not to use great-circle sailing depends upon the conditions. The saving in distance should be worth the additional effort, and of course the great circle route cannot cross land, nor should it carry the vessel into dangerous waters. Composite sailing (see section 2402 and section 2411) may save time and distance over the rhumb line track without leading the vessel into danger. Since great circles other than a meridian or the equator are curved lines whose true direction changes continually, the navigator does not attempt to follow it exactly. Rather, he selects a number of points along the great circle, constructs rhumb lines between the points, and follows these rhumb lines from point to point.

2402.	Kinds Of Sailings
There are seven types of sailings:
1.	Plane sailing solves problems involving a single course and distance, difference of latitude, and departure, in which the earth is regarded as a plane surface. This method, therefore, provides solution for latitude of the point of arrival, but not for longitude. To calculate the longitude, the spherical sailings are necessary. Do not use this method for distances of more than a few hundred miles.
2.	Traverse sailing combines the plane sailing solutions when there are two or more courses and
determines the equivalent course and distance made good by a vessel steaming along a series of rhumb lines.
3.	Parallel sailing is the interconversion of departure and difference of longitude when a vessel is proceeding due east or due west.
4.	Middle- (or mid-) latitude sailing uses the mean latitude for converting departure to difference of longitude when the course is not due east or due west.
5.	Mercator sailing provides a mathematical solution of the plot as made on a Mercator chart. It is similar to plane sailing, but uses meridional difference and difference of longitude in place of difference of latitude and departure.
6.	Great circle sailing involves the solution of courses, distances, and points along a great circle between two points.
7.	Composite sailing is a modification of great-circle sailing to limit the maximum latitude, generally to avoid ice or severe weather near the poles.

2403.	Terms And Definitions
In solutions of the sailings, the following quantities are used:
1.	Latitude (L). The latitude of the point of departure is designated Ll; that of the destination, L2; middle (mid) or mean latitude, Lm; latitude of the vertex of a great circle, Lv; and latitude of any point on a great circle, Lx.
2.	Mean latitude (Lm). Half the arithmetical sum of the latitudes of two places on the same side of the equator.
3.	Middle or mid latitude (Lm). The latitude at which the arc length of the parallel separating the meridians passing through two specific points is exactly equal to the departure in proceeding from one point to the other. The mean latitude is used when there is no practicable means of determining the middle latitude.
4.	Difference of latitude (l or DLat.).
5.	Meridional parts (M). The meridional parts of the point of departure are designated Ml, and of the point of arrival or the destination, M2.
6.	Meridional difference (m).
7.	Longitude (&#61548. The longitude of the point of departure is designated &#61548;1; that of the point of arrival or the destination, &#61548;2; of the vertex of a great circle, lv; and of any point on a great circle, &#61548;x
8.	Difference of longitude (DLo).
9.	Departure (p or Dep.).
10.	Course or course angle (Cn or C).
11.	Distance (D or Dist.).

GREAT CIRCLE SAILING
2404.	Great Circle Sailing By Chart
Navigators can most easily solve great-circle sailing problems graphically. DMAHTC publishes several gnomonic projections covering the principal navigable waters of the world. On these great circle charts, any straight line is a great circle. The chart, however, is not conformal; therefore, the navigator cannot directly measure directions and distances as on a Mercator chart.

The usual method of using a gnomonic chart is to plot the route and pick points along the track every 5&#61616;&#61472;of longitude using the latitude and longitude scales in the immediate vicinity of each point. These points are then transferred to a Mercator chart and connected by rhumb lines. The course and distance for each leg is measured on the Mercator chart. See Chapter 25 for a discussion of this process.

2405.	Great Circle Sailing By Sight Reduction Tables
Any method of solving a celestial spherical triangle can be used for solving great circle sailing problems. The point of departure replaces the assumed position of the observer, the destination replaces the geographical position of the body, difference of longitude replaces meridian angle or local hour angle, initial course angle replaces azimuth angle, and great circle distance replaces zenith distance (90&#61616;&#61472;- altitude). See Figure 2405. Therefore, any table of azimuths (if the entering values are meridian angle, declination, and latitude) can be used for determining initial great-circle course. Tables which solve for altitude, such as Pub. No. 229, can be used for determining great circle distance. The required distance is 90&#61616;&#61472;- altitude. In inspection tables such as Pub. No. 229, the given combination of L1, L2, and DLo may not be tabulated. In this case reverse the name of L2 and use 180&#61616;&#61472;- DLo for entering the table. The required course angle is then 180&#61616;&#61472;minus the tabulated azimuth, and distance is 90&#61616;&#61472;plus the altitude. If neither combination can be found, solution cannot be made by that method. By interchanging L1 and L2, one can find the supplement of the final course angle.








Solution by table often provides a rapid approximate check, but accurate results usually require triple interpolation. Except for Pub. No. 229, inspection tables do not provide a solution for points along the great circle. Pub. No. 229 provides solutions for these points only if interpolation is not required.

2406. Great Circle Sailing By Pub. No. 229
By entering Pub. No. 229 with the latitude of the point of departure as latitude, latitude of destination as declination, and difference of longitude as LHA, the tabular altitude and azimuth angle may be extracted and converted to great-circle distance and course. As in sight reduction, the tables are entered according to whether the name of the latitude of the point of departure is the same as or contrary to the name of the latitude of the destination (declination). If the values correspond to those of a celestial body above the celestial horizon, 90&#61616;&#61472;minus the arc of the tabular altitude becomes the distance; the tabular azimuth angle becomes the initial great-circle course angle. If the respondents correspond to those of a celestial body below the celestial horizon, the arc of the tabular altitude plus 90&#61616;&#61472;becomes the distance; the supplement of the tabular azimuth angle becomes the initial great-circle course angle. When the Contrary/Same (CS) Line is crossed in either direction, the altitude becomes negative; the body lies below the celestial horizon. For example: If the tables are entered with the LHA (DLo) at the bottom of a right-hand page and declination (L2) such that the respondents lie above the CS Line, the CS Line has been crossed. Then the distance is 90&#61616;&#61472;plus the tabular altitude; the initial course angle is the supplement of the tabular azimuth angle. Similarly, if the tables are entered with the LHA (DLo) at the top of a right-hand page and the respondents are found below the CS Line, the distance is 90&#61616;&#61472;plus the tabular altitude; the initial course angle is the supplement of the tabular azimuth angle. If the tables are entered with the LHA (DLo) at the bottom of a right-hand page and the name of L2 is contrary to L1, the respondents are found in the column for L1 on the facing page. In this case, the CS Line has been crossed; the distance is 90&#61616;&#61472;plus the tabular altitude; the initial course angle is the supplement of the tabular azimuth angle.

The tabular azimuth angle, or its supplement, is prefixed N or S for the latitude of the point of departure and suffixed E or W depending upon the destination being east or west of the point of departure.
If all entering arguments are integral degrees, the distance and course angle are obtained directly from the tables without interpolation. If the latitude of the destination is nonintegral, interpolation for the additional minutes of latitude is done as in correcting altitude for any declination increment; if the latitude of departure or difference of longitude is nonintegral, the additional interpolation is done graphically.

Since the latitude of destination becomes the declination entry, and all declinations appear on every page, the great circle solution can always be extracted from the volume which covers the latitude of the point of departure.
Example 1: Using Pub. No. 229 find the distance and initial great circle course from lat. 32&#61616;S, long.
116&#61616;E to lat. 30&#61616;S, long. 31&#61616;E.
Solution: Refer to Figure 2405. The point of departure (lat. 32&#61616;S, long. 116&#61616;E) replaces the AP of the observer; the destination (lat. 30&#61616;S, long. 31&#61616;E) replaces the GP of the celestial body; the difference of longitude (DLo 85&#61616 replaces local hour angle (LHA) of the body.
Enter Pub. 229, Volume 3 with lat. 32&#61616;&#61472;(Same Name), LHA 85&#61616;, and declination 30&#61616;. The respondents correspond to a celestial body above the celestial horizon. Therefore, 90&#61616;&#61472;minus the tabular altitude (90&#61616;&#61472;- 19&#61616;12.4&#8217; = 70&#61616;47.6&#8217 becomes the distance; the tabular azimuth angle (S66.0&#61616;W) becomes the initial great circle course angle, prefixed S for the latitude of the point of departure and suffixed W due to the destination being west of the point of departure.
Answer:
D = 4248 nautical miles
C = S66.0&#61616;W = 246.0&#61616;.
Example 2: Using Pub. No. 229 find the distance and initial great circle course from lat. 38&#61616;N, long. 122&#61616;W to lat. 24&#61616;S, long. 151&#61616;E.
Solution: Refer to Figure 2405. The point of departure (lat. 38&#61616;N, long. 122&#61616;W) replaces the AP of the observer;
the destination (lat. 24&#61616;S, long. 151&#61616;E) replaces the GP of the celestial body; the difference of longitude (DLo 87&#61616 replaces local hour angle (LHA) of the body Enter Pub. No. 229 Volume 3 with lat. 38&#61616;&#61472;(Contrary Name), LHA 87&#61616;, and declination 24&#61616;. The respondents correspond to those of a celestial body below the celestial horizon. Therefore, the tabular altitude plus 90&#61616;&#61472;(12&#61616;17.0&#8217; + 90&#61616;&#61472;= 102&#61616;17.0&#8217 becomes the distance; the supplement of tabular
azimuth angle (180&#61616;&#61472;- 69.0&#61616;&#61472;= 111.0&#61616 becomes the initial great circle course angle, prefixed N for the latitude of the point of departure and suffixed W since the destination is west of the point of departure.

Note that the data is extracted from across the CS Line from the entering argument (LHA 87&#61616, indicating that the corresponding celestial body would be below the celestial horizon.
Answer:
D = 6137 nautical miles
C = N111.0&#61616;W = 249&#61616;.

2407. Great Circle Sailing By Computation
In Figure 2407, 1 is the point of departure, 2 the destination, P the pole nearer 1, l-X-V-2 the great circle through 1 and 2, V the vertex, and X any point on the great circle. The arcs P1, PX, PV, and P2 are the colatitudes of points 1, X, V, and 2, respectively. If 1 and 2 are on opposite sides of the equator, P2 is 90&#61616;+ L2. The length of arc 1-2 is the greatcircle distance between 1 and 2. Arcs 1-2, P1, and P2 form a spherical triangle. The angle at 1 is the initial great-circle course from 1 to 2, that at 2 the supplement of the final great-circle course (or the initial course from 2 to 1), and that at P the DLo between 1 and 2.








Great circle sailing by computation usually involves solving for the initial great circle course; the distance; latitude and longitude, and sometimes the distance, of the vertex; and the latitude and longitude of various points (X) on the great circle. The computation for initial course and the distance involves solution of an oblique spherical triangle, and any method of solving such a triangle can be used. If 2 is
the geographical position (GP) of a celestial body (the point
at which the body is in the zenith), this triangle is solved in
celestial navigation, except that 90&#176; - D (the altitude) is desired
instead of D. The solution for the vertex and any point
X usually involves the solution of right spherical triangles

*to be cont.*


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## Fishers of Men

*ch 24 cont*
2408. Points Along The Great Circle
If the latitude of the point of departure and the initial great-circle course angle are integral degrees, points along the great circle are found by entering the tables with the latitude of departure as the latitude argument (always Same Name), the initial great circle course angle as the LHA argument,
and 90&#176; minus distance to a point on the great circle as the declination argument. The latitude of the point on the great circle and the difference of longitude between that point and the point of departure are the tabular altitude and azimuth angle, respectively. If, however, the respondents
are extracted from across the CS Line, the tabular altitude corresponds to a latitude on the side of the equator opposite from that of the point of departure; the tabular azimuth angle is the supplement of the difference of longitude.
Example 1: Find a number of points along the great circle from latitude 38&#176;N, longitude 125&#176;W when the initial great circle course angle is N111&#176;W.
Solution: Entering the tables with latitude 38&#176; (Same Name), LHA 111&#176;, and with successive declinations of 85&#176;, 80&#176;, 75&#176;, etc., the latitudes and
differences in longitude from 125&#176;W are found as tabular altitudes and azimuth angles respectively:

Answer:
D (NM) 300 600 900 3600
D (arc) 5&#176; 10&#176; 15&#176; 60&#176;
dec 85&#176; 80&#176; 75&#176; 30&#176;
Lat. 36.1&#176; N 33.9&#176; N 31.4&#176; N 3.6&#176; N
Dep. 125&#176; W 125&#176; W 125&#176; W 125&#176; W
DLo 5.8&#176; 11.3&#176; 16.5&#176; 54.1&#176;
Long 130.8&#176;W 136.3&#176;W 141.5&#176;W 179.1&#176;W


Example 2: Find a number of points along the great circle track from latitude 38&#176;N, long. 125&#176;W when the initial great circle course angle is N 69&#176; W.
Solution: Enter the tables with latitude 38&#176; (Same Name), LHA 69&#176;, and with successive declinations as shown. Find the latitudes and differences of
longitude from 125&#176;W as tabular altitudes and azimuth angles, respectively:
Answer:
D (NM.) 300 600 900 6600
D (arc) 5&#176; 10&#176; 15&#176; 110&#176;
dec 85&#176; 80&#176; 75&#176; 20&#176;
Lat. 39.6&#176; N 40.9&#176; N 41.9&#176; N 3.1&#176; N
Dep. 125&#176; W 125&#176; W 125&#176; W 125&#176; W
DLo 6.1&#176; 12.4&#176; 18.9&#176; 118.5&#176;
Long 131.1&#176;W 137.4&#176;W 143.9&#176;W 116.5&#176;E

2409. Finding The Vertex
Using Pub. No. 229 to find the approximate position of the vertex of a great circle track provides a rapid check on the solution by computation. This approximate solution is also useful for voyage planning purposes.

Using the procedures for finding points along the great circle, inspect the column of data for the latitude of the point of departure and find the maximum value of tabular altitude. This maximum tabular altitude and the tabular azimuth angle correspond to the latitude of the vertex and the
difference of longitude of the vertex and the point of departure.

Example 1: Find the vertex of the great circle track from lat. 38&#176;N, long. 125&#176;W when the initial great circle course angle is N69&#176;W.

Solution: Enter Pub. No. 229 with lat. 38&#176; (Same
Name), LHA 69&#176;, and inspect the column for lat. 38&#176; to find the maximum tabular altitude. The maximum altitude is 42&#176;38.1&#8217; at a distance of 1500
nautical miles (90&#176; - 65&#176; = 25&#176 from the point of departure. The corresponding tabular azimuth angle is 32.4&#176;. Therefore, the difference of longitude of vertex and point of departure is 32.4&#176;.
Answer:

Latitude of vertex = 42&#176;38.1&#8217;N.
Longitude of vertex = 125&#176; + 32.4&#176; = 157.4&#176;W.

2410. Altering A Great Circle Track To Avoid Obstructions

Land, ice, or severe weather may prevent the use of great circle sailing for some or all of one&#8217;s route. One of the principal advantages of solution by great circle chart is that the presence of any hazards is immediately apparent. The pilot charts are particularly useful in this regard. Often a relatively short run by rhumb line is sufficient to reach a point from which the great circle track can be followed. Where a choice is possible, the rhumb line selected should conform as nearly as practicable to the direct great circle.

If the great circle route crosses a navigation hazard, change the track. It may be satisfactory to follow a great circle to the vicinity of the hazard, one or more rhumb lines along the edge of the hazard, and another great circle to the destination. Another possible solution is the use of composite sailing; still another is the use of two great circles, one from the point of departure to a point near the maximum latitude of unobstructed water and the second from this point to the destination.

2411. Composite Sailing
When the great circle would carry a vessel to a higher latitude than desired, a modification of great circle sailing called composite sailing may be used to good advantage.

The composite track consists of a great circle from the point of departure and tangent to the limiting parallel, a course line along the parallel, and a great circle tangent to the limiting parallel and through the destination.

Solution of composite sailing problems is most easily made with a great circle chart. For this solution, draw lines from the point of departure and the destination, tangent to the limiting parallel. Then measure the coordinates of various selected points along the composite track and transfer them to a Mercator chart, as in great circle sailing. Composite sailing problems can also be solved by computation, using the equation:
cos DLovx = tan Lx cotLv
The point of departure and the destination are used successively as point X. Solve the two great circles at each end of the limiting parallel, and use parallel sailing along the limiting parallel. Since both great circles have vertices at the same parallel, computation for C, D, and DLovx can be made by considering them parts of the same great circle with L1, L2, and Lv as given and DLo = DLov1 + DLov2.

The total distance is the sum of the great circle and parallel
distances.

TRAVERSE TABLES
2412. Using Traverse Tables
Traverse tables can be used in the solution of any of the sailings except great circle and composite. They consist of the tabulation of the solutions of plane right triangles.
Because the solutions are for integral values of the course angle and the distance, interpolation for intermediate values may be required. Through appropriate interchanges of the headings of the columns, solutions for other than plane sailing can be made. For the solution of the plane right triangle,
any value N in the distance (Dist.) column is the hypotenuse; the value opposite in the difference of latitude (D. Lat.) column is the product of N and the cosine of the acute angle; and the other number opposite in the departure (Dep.) column is the product of N and the sine of the acute
angle. Or, the number in the D. Lat. column is the value of the side adjacent, and the number in the Dep. column is the value of the side opposite the acute angle. Hence, if the acute angle is the course angle, the side adjacent in the D. Lat. column is meridional difference m; the side opposite in the Dep. column is DLo. If the acute angle is the midlatitude of the formula p = DLo cos Lm, then DLo is any value N in the Dist. column, and the departure is the value N X cos Lm in the D. Lat. column.

The examples below clarify the use of the traverse tables for plane, traverse, parallel, mid latitude, and Mercator sailings.

2413. Plane Sailing
In plane sailing the figure formed by the meridian through the point of departure, the parallel through the point of arrival, and the course line is considered a plane right triangle.

This is illustrated in Figure 2413a. P1 and P2 are the
points of departure and arrival, respectively. The course angle and the three sides are as labeled. From this triangle:








































































38&#176; and 39&#176; must be interpolated for the minutes of latitude.
Corresponding to Dep. 215.5 miles in the former is DLo 273.5&#8217;, and in the latter DLo 277.3&#8217;. Interpolating for minutes of latitude, the DLo is 274.4&#8217;W.
Answer:
DLo = 4&#176; 34.4&#8217;

*to be cont.*


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## Fishers of Men

*24 cont.*
remember the "?" marks are degrees.
2416. Middle-Latitude Sailing
Middle-latitude sailing combines plane sailing and parallel sailing. Plane sailing is used to find difference of latitude and departure when course and distance are known, or vice versa. Parallel sailing is used to interconvert departure and difference of longitude. The mean latitude (Lm) is normally used for want of a practicable means of determining the middle latitude, the latitude at which the arc length of the parallel separating the meridians passing through two specific points is exactly equal to the departure in proceeding from one point to the other. The formulas for these transformations are:
DLo=p sec Lm p= DLo cos Lm.

The mean latitude (Lm) is half the arithmetical sum of the latitudes of two places on the same side of the equator.

It is labeled N or S to indicate its position north or south of the equator. If a course line crosses the equator, solve each course line segment separately.
Example 1: A vessel steams 1,253 miles on course 070&#61616;&#61472;from lat. 15&#61616;17.0&#8217; N, long. 151&#61616;37.0&#8217; E.

Required: Latitude and longitude of the point of arrival by (1) computation and (2) traverse table.










Refer to Figure 2416a. Enter the traverse table with course 070&#61616;&#61472;and distance 1,253 miles. Because a number as high as 1,253 is not tabulated in the Dist. column, obtain the values for D. Lat. and Dep. for a distance of 125.3 miles and multiply them by 10. Interpolating between the tabular distance arguments yields D. Lat. = 429&#8217; and Dep. = 1,178 miles. Converting the D. Lat. value to degrees of latitude yields 7&#61616;&#61472;09.0&#8217;. The point of arrival&#8217;s latitude, therefore, is 22&#61616;&#61472;26&#8217; N. This results in a mean latitude of 18&#61616;&#61472;51.5&#8217; N.

Re-enter the table with the mean latitude as course angle and substitute DLo as the heading of the Dist. column and Dep. as the heading of the D. Lat. column. Since the table is computed for integral degrees of course angle (or latitude), the tabulations in the pages for 18&#61616;&#61472;and 19&#61616;&#61472;must be interpolated for the minutes of Lm. In the 18&#61616;&#61472;table, interpolate for DLo between the departure values of 117.0 miles and 117.9 miles. This results in a DLo value of 123.9. In the 19&#61616;&#61472;table, interpolate for DLo between the departure values of 117.2 and 118.2. This yields a DLo value of 124.6. Having obtained the DLo values corresponding to mean latitudes of 18&#61616;&#61472;and 19&#61616;, interpolate for the actual value of the mean latitude: 18&#61616;&#61472;51.5&#8217; N. This yields the value of DLo: 124.5. Multiply this final value by ten to obtain DLo = 1245 minutes = 20&#61616;&#61472;45&#8217; E.
Add the changes in latitude and longitude to the original position&#8217;s latitude and longitude to obtain the final position.










D = 1008.2 miles










Answer:
C = 240.4&#61616;
D = 1008.2 miles
The labels (N, S, E, W) of l, p, and C are determined by noting the direction of motion or the relative positions of the two places.
(2) Solution by traverse tables:
Refer to Figure 2416b. Enter the traverse table with the mean latitude as course angle and substitute DLo as the heading of the Dist. column and Dep. as the heading of the D. Lat. column. Since the table is computed for integral values of course angle (or latitude), it is usually necessary to extract the value of departure for values just less and just greater than the Lm and then interpolate for the minutes of Lm. In this case where Lm is almost 13&#61616;, enter the table with Lm 13&#61616;&#61472;and DLo 898.3&#8217; to find Dep. 875 miles. The departure is found for DLo 89.9&#8217;, and then multiplied by 10.

Re-enter the table to find the numbers 875 and 498 beside each other in the columns labeled Dep. and D. Lat., respectively. Because these high numbers are not tabulated, divide them by 10, and find 87.5 and 49.8. This occurs most nearly on the page for course angle 60&#61616;&#61472;(fig. 2414c). Interpolating for intermediate values, the corresponding number in the Dist. column is about 100.5. Multiplying this by 10, the distance is about 1005 miles.
Answer:
C = 240&#61616;
D = 1005 miles.










The labels (N, S, E, W) of l, p, DLo, and C are determined by noting the direction of motion or the relative positions of the two places.




























(2) Solution by traverse table:
Refer to Figure 2417b. Substitute m as the heading of the D. Lat. column and DLo as the heading of the Dep. column. Inspect the table for the numbers 343.7 and 553.3 in the columns relabeled m and DLo, respectively.
Because a number as high as 343.7 is not tabulated in the m column, it is necessary to divide m and DLo by 10. Then inspect to find 34.4 and 55.3 abreast in the m and DLo columns, respectively. This occurs most nearly on the page for course angle 58&#61616;&#61472;or course 302&#61616;.
Re-enter the table with course 302&#61616;&#61472;to find Dist. for D. Lat. 284.0&#8217;. This distance is 536 miles.
Answer:
C = 302&#61616;
D = 536 miles
Example 2: A ship at lat. 75&#61616;31.7&#8217; N, long. 79&#61616;08.7&#8217;W, in Baffin Bay, steams 263.5 miles on course 155&#61616;.
Required: Latitude and longitude of point of arrival by
(1)	computation and (2) traverse table.

*Answer next post*


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## Fishers of Men

*Conclusion of ch 24*

Solution:
(1)	Solution by computation:
l = D cos C; and DLo = m tan C










The labels (N, S, E, W) of l, DLo, and C are determined by noting the direction of motion or the relative positions of the two places.
Answer:


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## Fishers of Men

*CHAPTER 25*
THE NAVIGATION PROCESS
INTRODUCTION
2500. Fundamentals
This chapter emphasizes the operational aspects of navigating in the open ocean. It is in this operational process that an individual navigator&#8217;s experience and judgment become most crucial. Compounding this subject&#8217;s difficulty is the fact that there are no set rules regarding the optimum employment of navigational systems and techniques. The navigation system&#8217;s optimum use varies as a function of the type of vessel, the quality of the navigation equipment on board, and the experience and skill of the particular navigator.

For the watch officer, ensuring ship safety always takes priority over completing operational commitments and carrying out the ship&#8217;s routine. This chapter discusses several basic safety considerations designed to minimize the probability of human error leading to a marine accident. 

VOYAGE PLANNING
Voyage planning determines the safest and most efficient track for the ship to follow to ensure that the vessel completes its operational commitments. Constructing a planned track for a voyage is fundamentally important for ship&#8217;s safety. The commanding officer and the navigator must carefully review and approve the track followed by the conning officer. Several ships&#8217; groundings have occurred because of unauthorized deviations from an approved track.

2501. Constructing A Voyage Plan Track
Construct the track using a navigation computer, a great circle (gnomonic) chart, or the sailings. This chapter will discuss only the navigation computer and the great circle chart. Chapter 24 covers the sailings. Use a navigation computer if one is available because the computer eliminates the plotting errors inherent in transferring the track from gnomonic to a Mercator projection.

When using a navigation computer, the navigator simply inputs the two endpoints of his planned voyage. The computer computes waypoints marking the great circle track between the two endpoints. The computer determines each track leg&#8217;s distance and, given a speed of advance, calculates the times the vessel can expect to pass each waypoint. Construct the track on the Mercator chart by plotting the computer-generated waypoints and the tracks between them.

After adjusting the track as necessary to pass well clear of any hazard, choose a speed of advance (SOA) that ensures the
ship will arrive on time at any required point. Given an SOA, mark the track with the ship&#8217;s planned hourly positions. These planned positions are points of intended movement (PIM&#8217;s).

The SOA chosen for each track leg is the PIM speed. If a navigation computer is not available, use a gnomonic chart to plot a great circle route between points and to determine the position of resulting track points. Transfer these points to a Mercator chart as a succession of waypoints connected by rhumb lines. Figure 2501 illustrates this method. This figure shows a great circle route plotted as a straight line on a gnomonic chart and as a series of points when transferred to a Mercator chart. The arrows represent corresponding points on the two charts. An operation order often assigns a naval vessel to an operating area. In that case, plan a track from the departure to the edge of the operating area to ensure that the vessel arrives at the operating area on time. Following a planned track inside the assigned area may be impossible because of the dynamic nature of a planned exercise. In that case, carefully examine the entire operating area for navigation hazards. If simply transiting through the area, the ship should still follow a planned and approved track.

2502. Following A Voyage Plan
Complete the planning discussed in section 2501 prior to leaving port. Once the ship is transiting, frequently compare the ship&#8217;s actual position to the planned position and adjust the ship&#8217;s course and speed to compensate for any deviations. Order courses and speeds to keep the vessel on track without significant deviation.

Often a vessel will have its operational commitments changed after it gets underway. If this happens, begin the voyage planning process anew. Ensure the ship&#8217;s navigator and captain approve the new track corresponding to the new mission. The conning officer must understand that, unless transiting in an operating area as discussed above, he should never transit on a chart that does not have an approved track for him to follow.










VOYAGE PREPARATION
2503. Equipment Inventory
Prior to getting the ship underway, inventory all navigation equipment, charts, and publications. The navigator should develop a checklist of navigation equipment specific to his vessel and check that all required equipment is onboard.

The navigator should have all applicable Sailing
Directions, pilot charts, and navigation charts covering his planned route. He should also have all charts and sailing direction covering ports at which his vessel may call. He should have all the equipment and publications required to support celestial navigation. Finally, he must have all technical documentation required to support the operation of his electronic navigation suite.
Complete this chart, publication, and equipment inventory well before the underway date and obtain all missing items before sailing.

2504. Chart Preparation
Just as the navigator must prepare charts for piloting, he must also prepare his charts for an open ocean transit. The following is a list of the minimum chart preparation required for an open ocean or coastal transit. Complete this preparation well before using the chart to maintain the plot. Correcting The Chart: Correct all applicable charts through the latest Notice to Mariners, Local Notice to Mariners, and Broadcast Notice to Mariners. Ensure the chart to be used is the correct edition.

Plotting Approved Track: Section 2501 above discusses constructing the track. Mark the track course above the track line with a &#8220;C&#8221; followed by the course. Similarly, mark each track leg&#8217;s distance under the course line with a &#8220;D&#8221; followed by the distance in nautical miles. Mark the PIM&#8217;s at hourly intervals, and mark the time corresponding to each PIM.

Calculating Minimum Expected, Danger, And Warning Soundings: 
Chapter 8 discusses calculating minimum expected, danger and warning soundings. Determining these soundings is particularly important for ships passing a shoal close aboard. Set these soundings to warn the conning officer that he is passing too close to the shoal. Mark the minimum expected sounding, the warning sounding, and the danger sounding clearly on the chart and indicate the section of the track for which they are applicable.

Marking Allowed Operating Areas: 
This chart preparation step is applicable to military vessels. Often an operation order assigns a naval vessel to an operating area for a specific period of time. There may be operational restrictions placed on the ship while within this area. For example, a surface ship assigned to an operating area may be ordered not to exceed a certain speed for the duration of an exercise. When assigned an operating area, clearly mark that area on the chart. Label it with the time the vessel must remain in the area and what, if any, operational restrictions it must follow. The conning officer and the captain should be able to glean the entire navigation situation from the chart alone without reference to the directive from which the chart was constructed. Therefore, put all operationally important information directly on the chart.

Marking Chart Shift Points: If the transit will require the ship to operate on more than one chart, mark the chart points where the navigator must shift to the next chart.

Examining 50nm On Either Side Of Track: 
Highlight any shoal water or other navigation hazard within 50nm of the planned track. This will alert the conning officer as he approaches a possible danger.

NAVIGATION ROUTINE AT SEA
2505. Frequency Of Position Determination
The table below lists recommended fix intervals as a function of navigation phase:










Shorten the suggested fix interval if required to ensure the vessel remains at least two fix intervals from the nearest danger. However, do not exceed the times recommended above. Choose a fix interval that provides a sufficient safety margin from all charted hazards.

Use all available fix information. With the advent of accurate satellite navigation systems, it is especially tempting to disregard this maxim. However, the experienced navigator never feels comfortable relying solely on one particular system. Supplement the satellite position with positions from Loran, celestial sights, radar lines of position, and visual observations. Evaluate the accuracy of the various fix methods against the satellite position; when the satellite receiver fails, the knowledge, for example, that Loran fixes consistently plotted 1 nm to the west of GPS can be helpful.
Use an inertial navigator if one is available. The inertial navigator may produce estimated positions more accurate than fix positions. Inertial navigators are completely independent of any external fix input. Therefore, they are invaluable for maintaining an accurate ship&#8217;s position during periods when external fix sources are unavailable. Always check a position determined by a fix, inertial navigator, or DR by comparing the charted sounding at the position with the fathometer reading. If the soundings do not correlate, investigate the discrepancy.

Chapter 7 covers the importance of maintaining a proper DR. It bears repeating here. Determine the difference between the fix and the DR positions at every fix and use this information to calculate an EP from every DR. Constant application of set and drift to the DR is crucial if the vessel must pass a known navigation hazard close aboard.

2506. Fathometer Operations
Use Figure 2506 to develop a standard procedure for operating the fathometer.










2507. The Modified Piloting Party
If operating out of piloting waters but near a navigation hazard, station a modified piloting party. As the name implies, this team does not consist of the entire piloting party. It could consist of only the navigator or assistant navigator, a plotter, and a recorder. Its purpose is to increase supervision of the navigation plot in areas that could pose a hazard to the vessel.

The navigator and captain should develop a standing order covering the stationing of a modified piloting party. A good rule is to station the modified piloting party when operating within 10 nm of a known hazard.

2508. Compass Checks
Determine gyro compass error at least daily as part of the at-sea routine. Check the gyro compass reading against the inertial navigator if the vessel has an inertial navigator. If the vessel does not have an inertial navigator, check gyro error using the celestial techniques discussed in Chapter 17. Report any error greater than 1&#176; to the navigator and commanding officer.
Check the gyro repeaters and the magnetic compass against the gyro compass hourly and after each course change. When comparing the magnetic and gyro compasses, account for changes in variation and deviation. Report any repeater error greater than 1&#176; to the commanding officer.

2509. Commanding Officer&#8217;s Night Orders And Standing Orders
The Night Order book is the vehicle by which the captain informs the officer of the deck of the captain&#8217;s orders for operating the ship. The Night Order book, despite its name, can contain orders for the entire 24 hour period after which the CO issues it.

The navigator may write the Night Orders pertaining to navigation. Such orders include assigned operating areas, maximum speeds allowed, required positions with respect to PIM, and, regarding submarines, the maximum depth at which the ship can operate. Each department head should include in the Night Order book the evolutions he wants to accomplish during the night that would normally require the captain&#8217;s permission. The captain can add further orders and directions as required. When the captain signs the Night Order book, it becomes an official order to the Officer of the Deck. The Officer of the Deck must not follow the Night Orders blindly. Circumstances under which the captain signed the Orders may have changed, rendering some evolutions ordered impractical to complete. The Officer of the Deck, when exercising his judgment on completing ordered evolutions, must always inform the captain of any deviation from the Night Orders as soon as such a deviation occurs. The Commanding Officer&#8217;s Night Orders are in effect only for the 24 hours after they are written; his Standing Orders are continuously in force. The captain sets the ship&#8217;s navigation policy in these orders. He sets required fix intervals, intervals for fathometer operations, minimum CPA&#8217;s, and other general navigation and collision avoidance requirements. The Officer of the Deck must follow the Commanding Officer&#8217;s Standing Orders at all times. Report any deviation from these orders immediately to the Commanding Officer.

2510. Position Reports
If the captain requires position reports, deliver them at 0800, 1200, and 2000 each day. Prepare these reports approximately 30 minutes ahead of the time when they are due. Use the DR positions for the time of the report. For example, prepare the 2000 position report at 1930 using the ship&#8217;s 2000 DR position. Often the captain will require additional information with these position reports. Some captains, for example, may want status reports on the engine room. Tailor each position report to contain the information the captain wants.

2511. Watch Relief Procedures
When a watch officer relieves as Officer of the Deck (OOD), he assumes the responsibility for the safe navigation of the ship. He becomes the Commanding Officer&#8217;s direct representative in ensuring ship safety. As such, he must prepare himself fully prior to assuming the watch. The following list contains those items that, as a minimum, the relieving OOD must check prior to assuming the watch.
&#8226;	Conduct a Pre Watch Tour: The relieving OOD should tour the ship prior to his watch. He should familiarize himself with any maintenance in progress.
He should check for general cleanliness and stowage. He should order any loose gear that could pose a safety hazard in rough seas secured.
&#8226;	Check the Position Log and Chart: Check the type and accuracy of the ship&#8217;s last fix. Verify that the navigation watch has plotted the last fix properly. Ensure there is a properly constructed DR plot on the chart. Examine the DR for any potential navigation hazards. Check ship&#8217;s position with respect to the PIM. Ensure that the ship is in the correct operating area, if applicable. Check to ensure that the navigation watch has properly applied fix expansion in accordance with the navigator&#8217;s instructions.
&#8226;	Check the Fathometer Log: Ensure that previous watches have taken soundings at required intervals and that the navigation watch took a sounding at the last fix. Verify that the present sounding matches the charted sounding at the vessel&#8217;s charted position.
&#8226;	Check the Compass Record Log: Verify that the navigation watch has conducted compass checks at the proper interval. Verify that gyro error is less than 1&#176; and that all repeaters agree within 1&#176; with the master gyro.
&#8226;	Read the Commanding Officer Night Orders:
Check the Night Order Book for the captain&#8217;s directions for the duration of the watch.
&#8226;	Check Planned Operations: For any planned operations, verify that the ship has met all operational prerequisites, that the ship is in the correct operating area, and that all watchstanders have reviewed the operation order. If the operation is a complicated one, consider holding an operations brief with applicable watchstanders prior to assuming the watch.
&#8226;	Check the Broadcast Schedule: Read any message traffic that could have a bearing on the upcoming watch. If the ship is on a broadcast schedule, find out when the radio operator received the last broadcast (military vessels only). Determine if the radio operator has any messages to transmit during the watch.
&#8226;	Ascertain the Contact Situation: Check the radar and sonar contact picture, if so equipped. Determine which contact has the closest CPA and what maneuvers, if any, will be required to open CPA. Find out from the offgoing OOD if there have been any bridge-to-bridge communications with any vessels in the area. Check that no CPA will be less than the minimum set by the Commanding Officer&#8217;s Standing Orders.
&#8226;	Review Watchstander Logs: Review the log readings for all watchstanders. Note any out of specification readings or any trends in log readings indicating that a parameter will soon go out of specification.
After conducting the above listed checks, the relieving OOD should report to the on watch OOD that he is ready to relieve the watch. The on watch OOD then should brief the relieving OOD on the following:
&#8226;	Vessel&#8217;s present course and speed.
&#8226;	Vessel&#8217;s present depth (submarines only).
&#8226;	Any evolutions planned or in progress.
&#8226;	The status of the engineering plant.
&#8226;	The status of repair on any out of commission equipment that effects the ship&#8217;s operational capability.
&#8226;	Any orders from the Commanding Officer not expressly given in the Night Orders.
&#8226;	Status of cargo (merchant vessels only).
&#8226;	Any hazardous maintenance planned or in progress.
&#8226;	Any routine maintenance planned or in progress.
&#8226;	Any planned ship&#8217;s drills.
If the relieving OOD has no questions following this brief, then he should relieve the watch. Upon relieving the watch, he should announce to both the helmsman and the quartermaster that he has the deck and the conn. The quartermaster should log the change of watch in the ship&#8217;s deck log.
Watch officers should not relieve the watch in the middle of an evolution or when casualty procedures are being carried out. Relieve the watch only during a steady state operational and tactical situation. This ensures that there is watchstander continuity when carrying out a specific evolution or combating a casualty.

THE DAY&#8217;S WORK IN CELESTIAL NAVIGATION
The advent of accurate electronic and satellite navigation systems has relegated celestial navigation to use solely as a backup navigation method. Seldom if ever will a ship undertake an ocean transit relying only on celestial navigation. Therefore, the navigator need not follow the entire routine listed below if celestial navigation is not his primary navigation source. Use only the steps of the celestial day&#8217;s work that are necessary to provide a meaningful check on the primary fix source&#8217;s accuracy. Should the electronic navigation system fail, however, and should celestial navigation become the primary means of navigation, this section provides a comprehensive procedure to follow.

2512. Celestial Navigation Routine
Complete a typical day&#8217;s work in open celestial navigation as follows:
1. Plot the dead reckoning position.
2. Reduce celestial observations for a fix during morning twilight.
3. Wind the chronometer and determine chronometer error.
4. Reduce a sun sight for a morning sun line.
5. Calculate an azimuth of the sun for a compass check. The navigator normally obtains an azimuth at about the same time as he takes a morning sun observation. He may also check the compass with an amplitude observation at sunrise.
6. Observe the sun at local apparent noon. Cross the resulting LOP with an advanced morning sun line or with a longitude determined at LAN for a fix or running fix.
7. Reduce a sun sight during the afternoon. This is primarily for use with an advanced noon sun line, or with a moon or Venus line, if the skies are overcast during evening twilight.
8. Calculate an azimuth of the sun for a compass check at about the same time as the afternoon sun observation. The navigator may replace this azimuth with an amplitude observation at sunset.
9. Reduce celestial observations for a fix during evening twilight.
Chapter 7, Chapter 17, and Chapter 20 contain detailed explanations of the procedures required to carry out this routine.










SPECIAL CONSIDERATIONS FOR SMALL CRAFT
2513. Navigation Of Small Craft
In principle, the navigation of small craft is the same as that of larger vessels. However, because of a small craft&#8217;s shallower draft, greater maneuverability, and possible limitations of equipment and expertise, there are important differences. Small craft often spend most of their time within sight of land, and their navigation is largely a matter of piloting. They generally are close enough inshore to reach safety in case of storm or fog. Since most of them are primarily pleasure craft, there is a tendency for their navigation to be a less professional process than in commercial or military craft.
Regardless of the nature of the craft, it should carry the minimum safety equipment required by the U.S. Coast Guard. In addition to this Coast Guard mandated safety equipment, a small craft should also carry a compass, charts, plotting devices, speed log, tide tables, Coast Pilot or Sailing Directions, and binoculars.

All craft venturing offshore should carry a properly registered EPIRB and VHF radio. Loran C, Omega, and GPS receivers are available; boats that transit out of sight of land should have at least one of these.

If the craft is to proceed out of sight of land for more than short intervals, celestial navigation equipment should be aboard. This equipment should include a sextant, an accurate timepiece, a means of receiving time signals, an almanac, and sight reduction tables. Celestial navigation calculators or computer programs are also useful. A small craft navigator of limited experience may underestimate the importance of professional navigation.
However, his vessel&#8217;s safety depends on his skill. He must plan his track and know his position at all times. Small craft navigation also requires a complete, accurate, and neat plot. Where this is impractical because of heavy weather or limited plotting space, use a careful log and dead reckoning plot. 

CONCLUSION
2514. The Importance Of The Navigation Process
Navigating a vessel is a dynamic process. Schedules change; missions change. Planning a voyage is a process that begins well before the ship gets underway. Executing that plan does not end until the ship ties up at the pier at its final destination. Develop a navigation process encompassing the principles discussed in this chapter. Carefully planning a route, preparing required charts, and closely monitoring the ship&#8217;s position enroute are fundamental concepts of safe navigation. A mariner should never feel comfortable unless he is following an approved track plotted on a corrected chart on which he has frequently updated his position. Developing and implementing such a routine is only half of the battle. Watchstanders must follow approved procedures.

U.S. Navy grounding reports and U.S. Coast
Guard accident reports attest to the danger courted when a vessel disregards basic navigation safety.


----------



## Fishers of Men

*CHAPTER 26*
EMERGENCY NAVIGATION
INTRODUCTION
2600. Planning For Emergency Navigation
With a complete set of emergency equipment, emergency navigation differs little from traditional shipboard navigation routine. Increasing reliance on complex electronic systems has changed the perspective of emergency navigation. Today it is more likely that a navigator will suffer failure of electronic devices and be left with little more than a sextant with which to navigate than that he will be forced to navigate a lifeboat. In the event of failure or destruction of electronic systems, navigational equipment and methods may need to be improvised. The officer who regularly navigates by blindly &#8220;filling in the blanks&#8221; or reading the coordinates from &#8220;black boxes&#8221; will not be prepared to use basic principles to improvise solutions in an emergency.

For offshore voyaging, the professional navigator must become thoroughly familiar with the theory of celestial navigation. He should be able to identify the most useful stars and know how to solve his sights by any widely used method. He should be able to construct a plotting sheet with a protractor and improvise a sextant. For the navigator prepared with such knowledge the situation is never hopeless. Some method of navigation is always available. This was recently proven by a sailor who circumnavigated the earth using no instruments of any kind, not even a compass. Basic knowledge can suffice.
The modern ship&#8217;s regular navigation gear consists of many complex electronic systems. Though they may posses a limited backup power supply, most depend on an uninterrupted supply of electrical power. The failure of that power due to hostile action, fire, or breakdown can instantly render the unprepared navigator helpless. This discussion is intended to provide the navigator with the information needed to navigate a vessel in the absence of the regular suite of navigation gear. Training and preparation for a navigation emergency are essential. This should consist of regular practice in the techniques discussed herein while the regular navigation routine is in effect, so that confidence in emergency procedures is established.

BASIC TECHNIQUES OF EMERGENCY NAVIGATION
2601. Emergency Navigation Kit
The navigator should assemble a kit containing equipment for emergency navigation. Even with no expectation of danger, it is good practice to have such a kit permanently located in the chart room or on the bridge so that it can be quickly broken out if needed. It can be used on the bridge in the event of destruction or failure of regular navigation systems, or taken to a lifeboat if the &#8220;abandon ship&#8221; call is made.

If practical, full navigational equipment should be provided in the emergency kit. As many as possible of the items in the following list should be included.
1. A notebook or journal suitable for use as a deck log and for performing computations.
2. Charts and plotting sheets. A pilot chart is excellent for emergency use. It can be used for plotting and as a source of information on compass variation, shipping lanes, currents, winds, and weather. Charts for both summer and winter seasons should be included. Plotting sheets are useful but not essential if charts are available.

Universal plotting sheets may be preferred, particularly if the latitude coverage is large. Include maneuvering boards and graph paper.
3. Plotting equipment. Pencils, erasers, a straightedge, protractor or plotter, dividers and compasses, and a knife or pencil sharpener should be included. A ruler is also useful.
4. Timepiece. A good watch is needed if longitude is to be determined astronomically. It should be waterproof or kept in a waterproof container which permits reading and winding of the watch if necessary without exposing it to the elements. The optimum timepiece is a quartz crystal chronometer, but any high-quality digital wristwatch will suffice if it is synchronized with the ship&#8217;s chronometer. A portable radio capable of receiving time signals, together with a good wristwatch, will also suffice.
5. Sextant. A marine sextant should be included. If this is impractical, an inexpensive plastic sextant will suffice. Several types are available commercially. The emergency sextant should be used periodically in actual daily navigation so its limitations and capabilities are fully understood. Plastic sextants have been used safely on extensive ocean voyages. Do not hesitate to use them in an emergency.
6. Almanac. A current Nautical Almanac contains ephemeral data and concise sight reduction tables. Another year&#8217;s almanac can be used for stars and the sun without serious error by emergency standards.
Some form of long-term almanac might be copied or pasted in the notebook.

7. Tables. Some form of table will be needed for reducing celestial observations. The Nautical Almanac produced by the U. S. Naval Observatory contains detailed procedures for calculator sight reduction and a compact sight reduction table.
8. Compass. Each lifeboat must carry a magnetic compass. For shipboard use, make a deviation table for each compass with magnetic material in its normal place. The accuracy of each table should be checked periodically.
9. Flashlight. A flashlight is required in each lifeboat. Check the batteries periodically and include extra batteries and bulbs in the kit.
10.	Portable radio. A transmitting-receiving set approved by the Federal Communications
Commission for emergency use can establish communications with rescue authorities. A small portable radio may be used as a radio direction finder or for receiving time signals.
11. An Emergency Position Indicating Radiobeacon (EPIRB) is essential. When activated, this device emits a signal which will be picked up by the COSPAS/SARSAT satellite system and automatically relayed to a ground station. It is then routed directly to rescue authorities. The location of the distress can be determined very accurately. Depending on the type of EPIRB, the signal may even identify the individual vessel in distress, thus allowing rescuers to determine how many people are in danger, the type of emergency gear they may have, and other facts to aid in the rescue. Because of this system, the navigator must question the wisdom of navigating away from the scene of the distress. It may well be easier for rescue forces to find him if he remains in one place. See Chapter 28, The Global Maritime Distress and Safety System (GMDSS).

2602. Most Probable Position
In the event of failure of primary electronic navigation systems, the navigator may need to establish the most probable position (MPP) of the vessel. Usually there is usually little doubt as to the position. The most recent fix updated with a DR position will be adequate. But when conflicting information or information of questionable reliability is received, the navigator must determine an MPP. When complete positional information is lacking, or when the available information is questionable, the most probable position might be determined from the intersection of a single line of position and a DR, from a line of soundings, from lines of position which are somewhat inconsistent, or from a dead reckoning position with a correction for current or wind. Continue a dead reckoning plot from one fix to another because the DR plot often provides the best estimate of the MPP.

A series of estimated positions may not be consistent because of the continual revision of the estimate as additional information is received. However, it is good practice to plot all MPP&#8217;s, and sometimes to maintain a separate EP plot based upon the best estimate of track and speed made good over the ground. This could indicate whether the present course is a safe one. See Chapter 23.

2603. Plotting Sheets
If plotting sheets are not available, a Mercator plotting sheet can be constructed through either of two alternative methods based upon a graphical solution of the secant of the latitude, which approximates the expansion of latitude.
First method (Figure 2603a):










Step one. Draw a series of equally spaced vertical lines at any spacing desired. These are the meridians; label them at any desired interval, such as 1&#8217;, 2&#8217;, 5&#8217;, 10&#8217;, 30&#8217;, 1&#176;, etc.
Step two. Draw and label a horizontal line through the center of the sheet to represent the parallel of the mid-latitude of the area.
Step three. Through any convenient point, such as the intersection of the central meridian and the parallel of the mid-latitude, draw a line making an angle with the horizontal equal to the mid-latitude.

In Figure 2603a this angle is 35&#176;.
Step four. Draw in and label additional parallels.
The length of the oblique line between meridians is the perpendicular distance between parallels, as shown by the broken arc. The number of minutes of arc between parallels is the same as that between the meridians.
Step five. Graduate the oblique line into convenient units. If 1&#8217; is selected, this scale serves as both a latitude and mile scale. It can also be used as a longitude scale by measuring horizontally from a meridian instead of obliquely along the line.

The meridians may be shown at the desired interval and the mid-parallel may be printed and graduated in units of longitude. In using the sheet it is necessary only to label the meridians and draw the oblique line. From it determine the interval used to draw in and label additional parallels. If the central meridian is graduated, the oblique line need not be. Second method (Figure 2603b).










Step one. At the center of the sheet draw a circle with a radius equal to 1&#176; (or any other convenient unit) of latitude at the desired scale. If a sheet with a compass rose is available, as in Figure 2603b, the compass rose can be used as the circle and will prove useful for measuring directions. It need not limit the scale of the chart, as an additional concentric circle can be drawn, and desired graduations extended to it.

Step two. Draw horizontal lines through the center of the circle and tangent at the top and bottom. These are parallels of latitude; label them accordingly, at the selected interval (as every 1&#176;, 30&#8217;, etc.).
Step three. From the center of the circle draw a line making an angle with the horizontal equal to the mid-latitude. In Figure
2603b this angle is 40&#176;.
Step four. Draw in and label the meridians. The first is a vertical line through the center of the circle. The second is a vertical line through the intersection of the oblique line and the circle. Additional meridians are drawn the same distance apart as the first two.
Step five. Graduate the oblique line into convenient units. If 1&#8217; is selected, this scale serves as a latitude and mile scale. It can
also be used as a longitude scale by measuring horizontally from a meridian, instead of obliquely along the line.

In the second method, the parallels may be shown at the desired interval, and the central meridian may be printed and graduated in units of latitude. In using the sheet it is necessary only to label the parallels, draw the oblique line, and from it determine the interval and draw in and label additional meridians. If the central meridian is graduated, as shown in Figure 2603b, the oblique line need not be. The same result is produced by either method. The first method, starting with the selection of the longitude scale, is particularly useful when the longitude limits of the plotting sheet determine the scale. When the latitude coverage is more important, the second method may be preferable. In either method a central compass rose might be printed. Figure 2603a. Small area plotting sheet with selected longitude scale.
Both methods use a constant relationship of latitude to longitude over the entire sheet and both fail to allow for the ellipticity of the earth. For practical navigation these are not important considerations.

2604. Dead Reckoning
Of the various types of navigation, dead reckoning alone is always available in some form. In an emergency it is of more than average importance. With electronic systems out of service, keep a close check on speed, direction, and distance made good. Carefully evaluate the effects of wind and current. Long voyages with accurate landfalls have been successfully completed by this method alone. This is not meant to minimize the importance of other methods of determining position. However, dead reckoning positions may be more accurate than those determined by other methods. If the means of determining direction and distance (the elements of dead reckoning) are accurate, it may be best to adjust the dead reckoning only after a confirmed fix. Plotting can be done directly on a pilot chart or plotting sheet. If this proves too difficult, or if an independent check is desired, some form of mathematical reckoning may be useful. Table 2604, a simplified traverse table, can be used for this purpose. This is a critical-type table, various factors being given for limiting values of certain angles. To find the difference or change of latitude in minutes, enter the table with course angle, reckoned from north or south toward the east or west. Multiply the distance run, in miles, by the factor. To find the departure in miles, enter the table with the complement of the course angle. Multiply the distance run in miles by the factor. To convert departure to difference of longitude in minutes, enter the table with mid-latitude and divide the departure by the factor.








Example: A vessel travels 26 miles on course 205&#176;, from Lat. 41&#176;44&#8217;N, Long. 56&#176;21&#8217;W.
Required: Latitude and longitude of the point of arrival.
Solution: The course angle is 205&#176; - 180&#176; = S25&#176;W, and the complement is 90&#176; - 25&#176; = 65&#176;. The factors corresponding
to these angles are 0.9 and 0.4, respectively. The difference of latitude is 26 &#180; 0.9 = 23&#8217; (to the nearest minute) and the departure is 26 &#180; 0.4 = 10 mi. Since the course is in the southwestern quadrant, in the Northern Hemisphere, the latitude of the point of arrival is 41&#176;44&#8217; N -23&#8217; = 41&#176;21&#8217;N. The factor corresponding to the mid-latitude 41&#176;32&#8217;N is 0.7. The difference of longitude is 10 &#184; 0.7 = 14&#8217;. The longitude of the point of arrival is 56&#176;21&#8217;W + 14 = 56&#176;35&#8217;W.
Answer: Lat. 41&#176;21&#8217;N, Long. 56&#176;35&#8217;W.

2605. Deck Log
At the beginning of a navigation emergency a navigation log should be started. The date and time of the casualty should be the first entry, followed by navigational information such as ship&#8217;s position, status of all navigation systems, the decisions made, and the reasons for them.

The best determination of the position of the casualty should be recorded, followed by a full account of courses, distances, positions, winds, currents, and leeway. No important navigational information should be left to memory if it can be recorded.

2606. Direction
Direction is one of the elements of dead reckoning. A deviation table for each compass, including lifeboat compasses, should already have been determined. In the event of destruction or failure of the gyrocompass and bridge magnetic compass, lifeboat compasses can be used. If an almanac, accurate Greenwich time, and the necessary tables are available, the azimuth of any celestial body can be computed and this value compared with an azimuth measured by the compass. If it is difficult to observe the compass azimuth, select a body dead ahead and note the compass heading. The difference between the computed and observed azimuths is compass error on that heading. This is of more immediate value than deviation, but if the latter is desired, it can be determined by applying variation to the compass error. Several unique astronomical situations occur, permitting determination of azimuth without computation:
Polaris: Polaris is always within 2&#176; of true north for observers between the equator and latitude 60&#176;N. When this star is directly above or below the celestial pole, its azimuth is exactly north at any latitude. This occurs approximately when the trailing star of either Cassiopeia or the Big Dipper (Alkaid) is directly above or directly below Polaris (Figure 2611). When a line through the trailing stars and Polaris is horizontal, the maximum correction should be applied. Below latitude 50&#176; this can be considered 1&#176;; and between 50&#176; and 65&#176;, 2&#176;. If Cassiopeia is to the right of Polaris, the azimuth is 001&#176; (or 002&#176, and if to the left, 359&#176; (or 358&#176. The south celestial pole is located approximately at the intersection of a line through the longer axis of the Southern Cross with a line from the northernmost star of Triangulum Australe perpendicular to the line joining the other two stars of the triangle. No conspicuous star marks this spot (See star charts in Chapter 15).
Meridian transit: Any celestial body bears due north or south at meridian transit, either upper or lower. This is the moment of maximum (or minimum) altitude of the body. However, since the altitude at this time is nearly constant during a considerable change of azimuth, the instant of meridian transit may be difficult to determine. If time and an almanac are available, and the longitude is known, the time of transit can be computed. It can also be graphed as a curve on graph paper and the time of meridian transit determined with sufficient accuracy for emergency purposes. Body on prime vertical: If any method is available for determining when a body is on the prime vertical (due east or west), the compass azimuth at this time can be observed. Table 20, Meridian Angle and Altitude of a Body on the Prime Vertical Circle provides this information. Any body on the celestial equator (declination 0&#176 is on the prime vertical at the time of rising or setting. For the sun this occurs at the time of the equinoxes. The star Mintaka (d Orionis), the leading star of Orion&#8217;s belt, has a declination of approximately 0.3&#176;S and can be considered on the celestial equator. For an observer near the equator, such a body is always nearly east or west. Because of refraction and dip, the azimuth should be noted when the center of the sun or a star is a little more than one sun diameter (half a degree) above the horizon. The moon should be observed when its upper limb is on the horizon.

Body at rising or setting: Except for the moon, the azimuth angle of a body is almost the same at rising as at setting, except that the former is toward the east and the latter toward the west. If the azimuth is measured both at rising and setting, true south (or north) is midway between the two observed values, and the difference between this value and 180&#176; (or 000&#176 is the compass error. Thus, if the compass azimuth of a body is 073&#176; at rising, and 277&#176; at setting, true south (180&#176 is







compass error is 5&#176;E. This method may be in error if the vessel is moving rapidly in a north or south direction. If the declination and latitude are known, the true azimuth of any body at rising or setting can be determined by means of a diagram on the plane of the celestial meridian or by computation. For this purpose, the body (except the moon) should be considered as rising or setting when its center is a little more than one sun diameter (half a degree) above the horizon, because of refraction and dip.

Finding direction by the relationship of the sun to the hands of a watch is sometimes advocated, but the limitations of this method prevent its practical use at sea.

A simple technique can be used for determining deviation.
An object that will float but not drift rapidly before the wind is thrown overboard. The vessel is then steered steadily in the opposite direction to that desired. At a distance of perhaps half a mile, or more if the floating object is still clearly in view, the vessel is turned around in the smallest practical radius, and headed back toward the floating object. The
magnetic course is midway between the course toward the object and the reciprocal of the course away from the object. Thus, if the boat is on compass course 151&#176; while heading away from the object, and 337&#176; while returning, the magnetic course is midway between 337&#176; and 151&#176; + 180&#176;







Since 334&#176; magnetic is the same as 337&#176; by compass, the deviation on this heading is 3&#176;W.

If a compass is not available, any celestial body can be used to steer by, if its diurnal apparent motion is considered. A reasonably straight course can be steered by noting the direction of the wind, the movement of the clouds, the direction of the waves, or by watching the wake of the vessel. The angle between the centerline and the wake is an indication of the amount of leeway.

A body having a declination the same as the latitude of the destination is directly over the destination once each day, when its hour angle equals the longitude, measured westward through 360&#176;. At this time it should be dead ahead if the vessel is following the great circle leading directly to the destination. The Nautical Almanac can be inspected to find a body with a suitable declination.

2607. Almanacs
Almanac information, particularly declination and Greenwich hour angle of bodies, is important to celestial navigation. If the current Nautical Almanac is available, there is no problem. If the only copy available is for a previous year, it can be used for the sun, Aries, and stars without serious error, by emergency standards. However, for greater accuracy, proceed as follows:
For declination of the sun, enter the almanac with a time that is earlier than the correct time by 5h 49m times the number of years between the date of the almanac and the correct date, adding 24 hours for each February 29 that occurs between the dates. If the date is February 29, use March 1 and reduce by one the number of 24 hour periods added. For GHA of the sun or Aries, determine the value for the correct time, adjusting the minutes and tenths of arc to agree with that at the time for which the declination is determined. Since the adjustment never exceeds half a degree, care should be used when the value is near a whole degree, to prevent the value from being in error by 1&#176;. If no almanac is available, a rough approximation of the declination of the sun can be obtained as follows: Count the days from the given date to the nearer solstice (June 21 or December 22). Divide this by the number of days from that solstice to the equinox (March 21 or September 23), using the equinox that will result in the given date being between it and the solstice. Multiply the result by 90&#176;. Enter Table 2604 with the angle so found and extract the factor. Multiply this by 23.45&#176; to find the declination.
Example 1: The date is August 24.
Required: The approximate declination of the sun. Solution: The number of days from the given date to the nearer solstice (June 21) is 64. There are 94 days between June 21 and September 23. Dividing and multiplying by 90&#176;,







The factor from Table 2604 is 0.5. The declination is 23.45&#176; &#180; 0.5 = 11.7&#176;. We know it is north because of the date. Answer: Dec. 11.7&#176;N.
The accuracy of this solution can be improved by considering the factor of Table 2604 as the value for the midangle between the two limiting ones (except that 1.00 is correct for 0&#176; and 0.00 is correct for 90&#176, and interpolating to one additional decimal. In this instance the interpolation would be between 0.50 at 59.5 and 0.40 at 66&#176;. The interpolated value is 0.47, giving a declination of 11.0&#176;N. Still greater accuracy can be obtained by using a table of natural cosines instead of Table 2604. By natural cosine the value is 11.3&#176;N.

If the latitude is known, the declination of any body can be determined by observing a meridian altitude. It is usually best to make a number of observations shortly before and after transit, plot the values on graph paper, letting the ordinate (vertical scale) represent altitude, and the abscissa (horizontal scale) the time. The altitude is found by fairing a curve or drawing an arc of a circle through the points, and taking the highest value. A meridian altitude problem is then solved in reverse.
Example 2: The latitude of a vessel is 40&#176;16&#8217;S. The sun is observed on the meridian, bearing north. The observed altitude is 36&#176;29&#8217;.
Required: Declination of the sun.
Solution: The zenith distance is 90&#176; - 36&#176;29&#8217; = 53&#176;31&#8217;. The sun is 53&#176;31&#8217; north of the observer, or 13&#176;15&#8217; north of the equator. Hence, the declination is 13&#176;15&#8217; N.
Answer: Dec. 13&#176;15&#8217; N.
The GHA of Aries can be determined approximately by considering it equal to GMT (in angular units) on September 23.

To find GHA Aries on any other date, add 1&#176; for each day following September 23. The value is approximately 90&#176; on December 22, 180&#176; on March 21, and 270&#176; on June 21. The values so found can be in error by as much as several degrees, and so should not be used if better information is available. An approximate check is provided by the great circle through Polaris, Caph (the leading star of Cassiopeia), and the eastern side of the square of Pegasus. When this great circle coincides with the meridian, LHA hour angle is approximately 0&#176;. The hour angle of a body is equal to its SHA plus the hour angle of Aries.

If an error of up to 4&#176;, or a little more, is acceptable, the GHA of the sun can be considered equal to GMT &#177; 180&#176; (12h). For more accurate results, one can make a table of the equation of time from the Nautical Almanac perhaps at five- or ten-day intervals, and include this in the emergency navigation kit. The equation of time is applied according to its sign to GMT &#177; 180&#176; to find GHA.

2608. Altitude Measurement
With a sextant, altitudes are measured in the usual manner. If in a small boat or lifeboat, it is a good idea to make a number of observations and average both the altitudes and times, or plot on graph paper the altitudes versus time. The rougher the sea, the more important is this process, which tends to average out errors caused by heavy weather observations.

The improvisations which may be made in the absence of a sextant are so varied that in virtually any circumstances a little ingenuity will produce a device to measure altitude. The results obtained with any improvised method will be approximate at best, but if a number of observations are averaged, the accuracy can be improved. A measurement, however approximate, is better than an estimate. Two general types of improvisation are available:
1. Circle. Any circular degree scale, such as a maneuvering board, compass rose, protractor, or plotter can be used to measure altitude or zenith distance directly. This is the principle of the ancient astrolabe. A maneuvering board or compass rose can be mounted on a flat board. A protractor or plotter may be used directly. There are a number of variations of the technique of using such a device. Some of them are:
A peg or nail is placed at the center of the circle. A weight is hung from the 90&#176; graduation, and a string for holding the device is attached at the 270&#176; graduation. When it is held with the weight acting as a plumb bob, the 0&#176; - 180&#176; line is horizontal. In this position the board is turned in azimuth until it is in line with the sun. The intersection of the shadow of the center peg with the arc of the circle indicates the altitude of the center of the sun.
The weight and loop can be omitted and pegs placed at the 0&#176; and 180&#176; points of the circle. While one observer sights along the line of pegs to the horizon, an assistant notes the altitude.

The weight can be attached to the center pin, and the three pins (0&#176;, center, 180&#176 aligned with the celestial body. The reading is made at the point where the string holding the weight crosses the scale. The reading thus obtained is the zenith distance unless the graduations are labeled to indicate altitude. This method, illustrated in Figure 2608b, is used for bodies other than the sun.
Whatever the technique, reverse the device for half the readings of a series, to minimize errors of construction.

Generally, the circle method produces more accurate results than the right triangle method, described below.










2. Right triangle. A cross-staff can be used to establish one or more right triangles, which can be solved by measurement of the angle representing the altitude, either directly or by reconstructing the triangle. Another way of determining the altitude is to measure two of the sides of the triangle and divide one by the other to determine one of the trigonometric functions. This procedure, of course, requires a source of information on the values of trigonometric functions corresponding to various angles. If the cosine is found, Table 2604 can be used. The tabulated factors can be considered correct to one additional decimal for the value midway between the limited values (except that 1.00 is the correct value for 0&#176; and 0.00 is the correct value for 90&#176 without serious error by emergency standards. Interpolation can then be made between such values.

By either protractor or table, most devices can be graduated in advance so that angles can be read directly. There are many variations of the right triangle method. Some of these are described below.

Two straight pieces of wood can be attached to each other in such a way that the shorter one can be moved along the longer, the two always being perpendicular to each other. The shorter piece is attached at its center. One end of the longer arm is held to the eye. The shorter arm is moved until its top edge is in line with the celestial body, and its bottom edge is in line with the horizon. Thus, two right triangles are formed, each representing half the altitude. For low altitudes, only one of the triangles is used, the long arm being held in line with the horizon. The length of half the short arm, divided by the length of that part of the long arm between the eye and the intersection with the short arm, is the tangent of half the altitude (the whole altitude if only one right triangle is used). The cosine can be found by dividing that part of the long arm between the eye and the intersection with the short arm by the slant distance from the eye to one end of the short arm. Graduations consist of a series of marks along the long arm indicating settings for various angles. The device should be inverted for alternate readings of a series.
A rule or any stick can be held at arm&#8217;s length. The top of the rule is placed in line with the celestial body being observed, and the top of the thumb is placed in line with the horizon. 










The rule is held vertically. The length of rule above the thumb, divided by the distance from the eye to the top of the thumb, is the tangent of the angle observed. The cosine can be found by dividing the distance from the eye to the top of the thumb by the distance from the eye to the top of the rule. If the rule is tilted toward the eye until the minimum of rule is used, the distance from the eye to the middle of the rule is substituted for the distance from the eye to the top of the thumb, half the length of the rule above the thumb is used, and the angle found is multiplied by 2. Graduations consist of marks on the rule or stick indicating various altitudes. For the average observer each inch of rule will subtend an angle of about 2.3&#176;, assuming an eye-to-ruler distance of 25 inches. This relationship is good to a maximum altitude of about 20&#176;. The accuracy of this relationship can be checked by comparing the measurement against known angles in the sky. Angular distances between stars can be computed by sight reduction methods, including Pub. No. 229, by using the declination of one star as the latitude of the assumed position, and the difference between the hour angles (or SHA&#8217;s) of the two bodies as the local hour angle. The angular distance is the complement of the computed altitude. The angular distances between some well-known star pairs are: end stars of Orion&#8217;s belt, 2.7&#176;; pointers of the Big Dipper, 5.4&#176;, Rigel to Orion&#8217;s belt, 9.0&#176;; eastern side of the great square of Pegasus, 14.0&#176;; Dubhe (the pointer nearer Polaris) and Mizar (the second star in the Big Dipper, counting from the end of the handle), 19.3&#176;.

The angle between the lines of sight from each eye is, at arm&#8217;s length, about 6&#176;. By holding a pencil or finger horizontally, and placing the head on its side, one can estimate an angle of about 6&#176; by closing first one eye and then the other, and noting how much the pencil or finger appears to move in the sky. The length of the shadow of a peg or nail mounted perpendicular to a horizontal board can be used as one side of an altitude triangle. The other sides are the height of the peg and the slant distance from the top of the peg to the end of the shadow. The height of the peg, divided by the length of the shadow, is the tangent of the altitude of the center of the sun. The length of the shadow, divided by the slant distance, is the cosine. Graduations consist of a series of concentric circles indicating various altitudes, the peg being at the common center. The device is kept horizontal by floating it in a bucket of water. Half the readings of a series are taken with the board turned 180&#176; in azimuth. Two pegs or nails can be mounted perpendicular to a board, with a weight hung from the one farther from the eye. The board is held vertically and the two pegs aligned with the body being observed. A finger is then placed over the string holding the weight, to keep it in position as the board is turned on its side. A perpendicular line is dropped from the peg nearer the eye, to the string. The body&#8217;s altitude is the acute angle nearer the eye. For alternate readings of a series, the board should be inverted. Graduations consist of a series of marks indicating the position of the string at various altitudes. As the altitude decreases, the triangle becomes smaller.

At the celestial horizon it becomes a straight line. No instrument is needed to measure the altitude when either the upper or lower limb is tangent to the horizon, as the sextant altitude is then 0&#176;.

2609. Sextant Altitude Corrections
If altitudes are measured by a marine sextant, the usual sextant altitude corrections apply. If the center of the sun or moon is observed, either by sighting at the center or by shadow, the lower-limb corrections should be applied, as usual, and an additional correction of minus 16&#8217; applied. If the upper limb is observed, use minus 32&#8217;. If a weight is used as a plumb bob, or if the length of a shadow is measured, omit the dip (height of eye) correction.
If an almanac is not available for corrections, each source of error can be corrected separately, as follows:
If a sextant is used, the index correction should be determined and applied to all observations, or the sextant adjusted to eliminate index error.

Refraction is given to the nearest minute of arc in Table 2609. The value for a horizon observation is 34&#8217;. If the nearest 0.1&#176; is sufficiently accurate, as with an improvised method of observing altitude, a correction of 0.1&#176; should be applied for altitudes between 5&#176; and 18&#176;, and no correction applied for greater altitudes. Refraction applies to all observations, and is always minus.
Dip, in minutes of arc, is approximately equal to the square root of the height of eye, in feet. The dip correction applies to all observations in which the horizon is used as the horizontal reference. It is always a minus. If 0.1&#176; accuracy is acceptable, no dip correction is needed for small boat heights of eye. The semidiameter of the sun and moon is approximately 16&#8217; of arc. The correction does not apply to other bodies or to observations of the center of the sun and moon, by whatever method, including shadow. The correction is positive if the lower limb is observed, and negative if the upper limb is observed.

For emergency accuracy, parallax is applied to observations of the moon only. An approximate value, in minutes of arc, can be found by multiplying 57&#8217; by the factor from Table 2604, entering that table with altitude. For more accurate results, the factors can be considered correct to one additional decimal for the altitude midway between the limiting values (except that 1.00 is correct for 0&#176; and 0.00 is correct for 90&#176, and the values for other altitudes can be found by interpolation. This correction is always positive. For observations of celestial bodies on the horizon, the total correction for zero height of eye is:
Sun: Lower limb: (&#821118&#8217;, upper limb: (&#821150&#8217;.
Moon: Lower limb: (+)39&#8217;, upper limb: (+)7&#8217;.
Planet/star: (&#821134&#8217;.
Dip should be added algebraically to these values. Since the &#8220;sextant&#8221; altitude is zero, the &#8220;observed&#8221; altitude is equal to the total correction.

2610. Sight Reduction
Sight reduction tables should be used, if available. If not, use the compact sight reduction tables found in the Nautical Almanac. If trigonometric tables and the necessary formulas are available, they will serve the purpose. Speed in solution is seldom a factor in a lifeboat, but might be important aboard ship, particularly in hostile areas. If tables but no formulas are available, determine the mathematical knowledge possessed by the crew. Someone may be able to provide the missing information. If the formulas are available, but no tables, approximate natural values of the various trigonometric functions can be obtained graphically. Graphical solution of the navigational triangle can be made by the orthographic method explained in the chapter on Navigational Astronomy. A maneuvering board might prove helpful in the graphical solution for either trigonometric functions or altitude and azimuth. Very careful work will be needed for useful results by either method. Unless full navigational equipment is available, better results might be obtained by making separate determinations of latitude and longitude.

2611. Latitude Determination
Several methods are available for determining latitude; none requires accurate time.
Latitude can be determined using a meridian altitude of any body, if its declination is known. If accurate time, knowledge of the longitude, and an almanac are available, the observation can be made at the correct moment, as determined in advance. However, if any of these is lacking, or if an accurate altitude-measuring instrument is unavailable, a better procedure is to make a number of altitude observations before and after meridian transit. Then plot altitude versus time on graph paper, and the highest (or lowest, for lower transit) altitude is scaled from a curve faired through the plotted points. At small boat speeds, this procedure is not likely to introduce a significant error. The time used for plotting the observations need not be accurate, as elapsed time between observations is all that is needed, and this is not of critical accuracy. Any altitudes that are not consistent with others of the series should be discarded.










Latitude by Polaris is explained in Chapter 20, Sight Reduction. In an emergency, only the first correction is of practical significance. If suitable tables are not available, this correction can be estimated. The trailing star of Cassiopeia (&#206; Cassiopeiae) and Polaris have almost exactly the same SHA. The trailing star of the Big Dipper (Alkaid) is nearly opposite Polaris and &#206; Cassiopeiae. These three stars, &#206; Cassiopeiae, Polaris, and Alkaid, form a line through the pole (approximately). When this line is horizontal, there is no correction. When it is vertical, the maximum correction of 56&#8217; applies. It should be added to the observed altitude if Alkaid is at the top, and subtracted if &#206; Cassiopeiae is at the top. For any other position, estimate the angle this line makes with the vertical, and multiply the maximum correction (56&#8217 by the factor from Table 2604, adding if Alkaid is higher than &#206; Cassiopeiae, and subtracting if it is lower. For more accurate results, the factor from Table 2604 can be considered accurate to one additional decimal for the mid-value between those tabulated (except that 1.00 is correct for 0&#176; and 0.00 for 90&#176. Other values can be found by interpolation.
The length of the day varies with latitude. Hence, latitude can be determined if the elapsed time between sunrise and sunset can be accurately observed. Correct the observed length of day by adding 1 minute for each 15&#8217; of longitude traveled toward the east and subtracting 1 minute for each 15&#8217; of longitude traveled toward the west. The latitude determined by length of day is the value for the time of meridian transit. Since meridian transit occurs approximately midway between sunrise and sunset, half the interval may be observed and doubled. If a sunrise and sunset table is not available, the length of daylight can be determined graphically using a diagram on the plane of the celestial meridian, as explained in Chapter 15. A maneuvering board is useful for this purpose. This method cannot be used near the time of the equinoxes and is of little value near the equator. The moon can be used if moonrise and moonset tables are available. However, with the moon, the half-interval method is of insufficient accuracy, and allowance should be made for the longitude correction.

The declination of a body in zenith is equal to the latitude of the observer. If no means are available to measure altitude, the position of the zenith can be determined by holding a weighted string overhead.










2612. Longitude Determination
Unlike latitude, determining longitude requires accurate Greenwich time. All such methods consist of noting the Greenwich time at which a phenomenon occurs locally. In addition, a table indicating the time of occurrence of the same phenomenon at Greenwich, or equivalent information, is needed. Three methods may be used to determine longitude. When a body is on the local celestial meridian, its GHA is the same as the longitude of the observer if in west longitude, or 360 - l in east longitude. Thus, if the GMT of local time of transit is determined and a table of Greenwich hour angles (or time of transit of the Greenwich meridian) is available, longitude can be computed. If only the equation of time is available, the method can be used with the sun. This is the reverse of the problem of finding the time of transit of a body. The time of transit is not always apparent. If a curve is made of altitude versus time, as suggested previously, the time corresponding to the highest altitude is used in the determination of longitude. Under some conditions, it may be preferable to observe an altitude before meridian transit, and then again after meridian transit, when the body has returned to the same altitude as at the first observation. Meridian transit occurs midway between these two times. A body in the zenith is on the celestial meridian. If accurate azimuth measurement is available, note the time when the azimuth is 000&#176; or 180&#176;.
The difference between the observed GMT of sunrise or sunset and the LMT tabulated in the almanac is the longitude in time units, which can then be converted to angular measure. If the Nautical Almanac is used, this information is tabulated for each third day only. Greater accuracy can be obtained if interpolation is used for determining intermediate values. Moonrise or moonset can be used if the tabulated LMT is corrected for longitude. Planets and stars can be used if the time of rising or setting can be determined. This can be computed, or approximated using a diagram on the plane of the celestial meridian (See Chapter 15, Navigational Astronomy).
Either of these methods can be used in reverse to set a watch that has run down or to check the accuracy of a watch if the longitude is known. In the case of a meridian transit, the time need not be determined at the instant of transit. The watch is started, and the altitude is then measured several times before and after transit, or at equal altitudes before and after. The times of these observations are noted, and from them the time of meridian transit is determined. The difference between this time and the correct time of transit can then be used as a correction to reset the watch.


----------



## Fishers of Men

*CHAPTER 27*
NAVIGATION REGULATIONS
SHIP ROUTING
*You need to know these things if you are boating where large ships frequent.*
2700.	Purpose And Types Of Routing Systems
Navigation, once truly independent throughout the world, is an increasingly regulated activity. The consequences of collision or grounding for a large, modern ship carrying tremendous quantities of high-value, perhaps dangerous cargo, are so severe that authorities have instituted many types of regulations and control systems to minimize the chances of loss. These range from informal and voluntary systems to closely controlled systems requiring compliance with numerous regulations. The regulations may concern navigation, communications, equipment, procedures, personnel, and many other aspects of ship management. This chapter will be concerned primarily with navigation regulations and procedures.

There are several specific types of regulation systems. For commonly used open ocean routes where risk of collision is present, the use of recommended routes separates ships going in opposite directions. In areas where ships converge at headlands, straits, and major harbors, traffic separation schemes (TSS) have been instituted to separate vessels and control crossing and meeting situations. Environmentally sensitive areas may be protected by areas to be avoided which prevent vessels of a certain size or carrying certain cargoes from navigating within specified boundaries. In confined waterways such as canals, lock systems, and rivers leading to major ports, local navigation regulations control ship movement.

2701.	Definitions
The following terms relate to ship&#8217;s routing:
Routing System: Any system of routes or routing measures designed to minimize the possibility of collisions between ships, including TSS&#8217;s, twoway routes, recommended tracks, areas to be avoided, inshore traffic zones, precautionary areas, and deep-water routes.

Traffic Separation Scheme: A routing measure which separates opposing traffic flow with traffic lanes. Separation Zone or Line: A zone or line which separates opposing traffic, separates traffic from adjacent areas, or separates different classes of ships from one another.

Traffic Lane: An area within which one-way traffic is established.
Roundabout: A circular traffic lane used at junctions of several routes, within which traffic moves counterclockwise around a separation point or zone.
Inshore Traffic Zone: The area between a traffic separation scheme and the adjacent coast, usually designated for coastal traffic.
Two-way Route: A two-way track for guidance of ships through hazardous areas.

Recommended Route: A route established for convenience of ship navigation, often marked with centerline buoys.

Recommended Track: A route, generally found to be free of dangers, which ships are advised to follow to avoid possible hazards nearby.
Deep-Water Route: A route surveyed and chosen for the passage of deep-draft vessels through shoal areas.

Precautionary Area: A defined area within which ships must use particular caution and should follow the recommended direction of traffic flow.
Area To Be Avoided: An area within which navigation by certain classes of ships is prevented because of particular navigational dangers or environmentally sensitive natural features.
Established Direction of Traffic Flow: The direction in which traffic within a lane must travel.
Recommended Direction of Traffic Flow: The direction in which traffic is recommended to travel.

There are various methods by which ships may be separated using Traffic Separation Schemes. The simplest 390 NAVIGATION REGULATIONS scheme might consist of just one method; more complex schemes will use several different methods together in a coordinated pattern to route ships to and from several areas at once. Schemes may be just a few miles in extent, or cover relatively large sea areas.

2702.	Recommended Routes And Tracks
Recommended routes across the North Atlantic have been followed since 1898, when the risk of collision between increasing numbers of ships became too great, particularly at junction points. The International Convention for the Safety of Life at Sea (SOLAS) codifies the use of certain routes. These routes vary with the seasons, with winter and summer tracks chosen so as to avoid icebergprone areas. These routes are often shown on charts, particularly small scale ones, and are generally used to calculate distances between ports in tables.

Recommended routes consists of single tracks, either one-way or two-way. Two-way routes show the best water through confined areas such as inland routes among islands and reefs. Ships following these routes can expect to meet other vessels head-on and engage in normal passings. Oneway routes are generally found in areas where many ships are on similar or opposing courses. They and are intended to separate opposing traffic so that most maneuvers are overtaking situations instead of the more dangerous meeting situation.

2703.	Charting Recommended Routes
Recommended routes and recommended tracks are generally indicated on charts by black lines, with arrowheads indicating the desired direction of traffic. Not all recommended routes are charted. DMA charts generally depict recommended routes only on modified facsimiles made directly from foreign charts. In all cases, recommended routes are discussed in detail in the Sailing Directions.

TRAFFIC SEPARATION SCHEMES *(On your charts)*
2704.	Traffic Separation Schemes (TSS)
In 1961, representatives from England, France, and Germany met to discuss ways to separate traffic in the congested Straits of Dover and subsequently in other congested
areas. Their proposals were submitted to the International Maritime Organization (IMO) and were adopted in general form. IMO expanded on the proposals and has since instituted a system of Traffic Separation Schemes (TSS) throughout the world.

The IMO is the only international body responsible for establishing and recommending measures for ship&#8217;s routing in international waters. It does not attempt to regulate traffic within the territorial waters of any nation.

In deciding whether or not to adopt a TSS, IMO considers the aids to navigation system in the area, the state of hydrographic surveys in the area, the scheme&#8217;s adherence to accepted standards of routing, and the International Rules of the Road. The selection and development of TSS&#8217;s are the responsibility of individual governments, who may seek IMO adoption of their plans, especially if the system extends into international waters.
Governments may develop and implement TSS&#8217;s not adopted by the IMO, but in general only IMO-adopted schemes are charted. Rule 10 of the International Regulations for Preventing Collisions at Sea (Rules of the Road) addresses the subject of TSS&#8217;s. This rule specifies the actions to be taken by various classes of vessels in and near traffic schemes.

Traffic separation schemes adopted by the IMO are listed in Ship&#8217;s Routing, a publication of the IMO, 4 Albert Embankment, London SE1 7SR, United Kingdom. Because of differences in datums, chartlets in this publication which depict the various schemes must not be used either for navigation or to chart the schemes on navigational charts. The Notice to Mariners should be consulted for charting details.

2705.	Methods Of Traffic Separation
A number of different methods of separating traffic have been developed, using various zones, lines, and defined areas. One or more methods may be employed in a given traffic scheme to direct and control converging or passing traffic. These are discussed below. Refer to definitions in section 2701.

Method 1. Separation of opposing streams of traffic by separation zones or lines. In this method, typically a central separation zone is established within which ships are not to navigate. The central zone is bordered by traffic lanes with established directions of traffic flow. The lanes are bounded on the outside by limiting lines.

Method 2. Separation of opposing streams of traffic by natural features or defined objects. In this method islands, rocks, or other features may be used to separate traffic. The feature itself becomes the separation zone.

Method 3. The separation of through traffic from local traffic by provision of inshore traffic zones. Outside of traffic schemes, ships may generally navigate in any direction. Inshore traffic zones provide an area within which local traffic may travel at will without interference with through traffic in the lanes. Inshore zones are separated from traffic lanes by separation zones or lines.

Method 4. Division of traffic from several different direction into sectors. This approach is used at points of convergence such as pilot stations and major entrances. 
Method 5. Routing traffic through junctions of two or more major shipping routes. The exact design of the scheme in this method varies with conditions. It may be a circular or rectangular precautionary area, a roundabout, or a junction of two routes with crossing routes and directions of flow well-defined.

2706.	Representing TSS&#8217;s On Charts
See Figure 2706. Depiction of TSS&#8217;s on charts uses magenta (purple) as the primary color. Zones are shown by purple tint, limits are shown by T-dashes such as are used in other maritime limits, and lines are dashed. Arrows are openlined or dashed-lined depending on use. Special provisions applying to a scheme may be mentioned in notes on the chart. Deep water routes will be marked with the designation &#8220;DW&#8221; in bold purple letters, and the least depth may be indicated. Figure 2706. Traffic separation scheme symbology. On charts the symbols are usually in magenta.

2707.	Use Of Traffic Separation Schemes
A TSS is not officially approved for use until adopted by the IMO. Once adopted, it is implemented as of a certain time and date, as announced in the Notice to Mariners and perhaps through other means. The Notice to Mariners will also describe the scheme&#8217;s general location and purpose and give specific directions in the chart correction section on plotting the various zones and lines which define it. These corrections usually apply to several charts. Because the charts may range in scale from quite small to very large, the corrections for each should be followed closely. The positions for the various features may be slightly different from chart to chart due to differences in rounding off positions or chart datum. A TSS may be amended for periods of time ranging from a few hours to several years. Underwater construction works, surveying, dredging, and other transitory activities will be noted by radio broadcast, Local Notice To Mariners, or other means. Longer duration activities such as placement of oil drilling rigs, platforms, or pipelines may require a charted change to the scheme, which may become a permanent feature. These will be Notice to Mariners items. Use of TSS&#8217;s by all ships is recommended. They are intended for use in all weather, day and night. Adequate aids to navigation are a part of all TSS&#8217;s. There is no special right of one ship over another in TSS&#8217;s because the Rules of the Road apply in all cases. Deep-water routes should be avoided by ships which do not need them to keep them clear for deep-draft vessels. Ships need not keep strictly to the courses indicated by the arrows, but are free to navigate as necessary within their lanes to avoid other traffic. The signal &#8220;YG&#8221; is provided in the International Code of Signals to indicate to another ship: &#8220;You appear not to be complying with the traffic separation scheme.&#8221;
TSS&#8217;s are discussed in detail in the Sailing Directions for the areas where they are found.

2708.	Areas To Be Avoided
Areas to be avoided are adopted by the IMO and are usually established to prevent possible grounding of tankers and other ships carrying hazardous cargo in environmentally sensitive areas. They may also be established to keep particular classes of ships away from areas where navigation is particularly hazardous.
They are depicted on charts by dashed lines or T-dashed lines, either point to point straight lines or as a circle centered on a feature in question such as a rock or island. The smallest may cover less than a mile in extent; the largest may cover hundreds of square miles of coral reefs or dangerous shoals. Notes on the appropriate charts and in Sailing Directions tell which classes of ships are excluded from the area.

2709.	Special Rules
Certain special rules adopted by IMO apply in constricted areas such as the Straits of Malacca and Singapore, the English Channel and Dover Strait, and in the Gulf of Suez. These regulations are summarized in the appropriate Sailing Directions (Planning Guides). For a complete summary of worldwide ships&#8217; routing measures, the IMO publication Ship&#8217;s Routing should be obtained. See paragraph 2704.

VESSEL TRAFFIC SERVICES (VTS)
2710.	Development And Purpose
The purpose of Vessel Traffic Services (VTS) is to provide active monitoring and navigational advice for vessels in particularly confined and busy waterways. There are two main types of VTS, surveilled and non-surveilled. Surveilled systems consist of one or more land-based radar sites which output their signals to a central location where operators monitor and to a certain extent control traffic flows. Non-surveilled systems consist of one or more calling-in points at which ships are required to report their identity, course, speed, and other data to the monitoring authority. Vessel Traffic Services in the U.S. are implemented under the authority of the Ports and Waterways Safety Act of 1972 (Public Law 92-340 as amended) and the St. Lawrence Seaway Act (Public Law 358). They encompass a wide range of techniques and capabilities aimed at preventing vessel collisions, rammings, and groundings in the harbor/harbor approach and inland waterway phase of navigation. They are also designed to expedite ship movements, increase transportation system capacity, and improve all-weather operating capability.

A VHF-FM communications network forms the basis of most major services. Transiting vessels make position reports to an operations center by radiotelephone and are in turn provided with accurate, complete, and timely navigational safety information. The addition of a network of radars for surveillance and computer-assisted tracking and tagging, similar to that used in air traffic control, allows the VTS to play a more significant role in marine traffic management, thereby decreasing vessel congestion, critical encounter situations, and the probability of a marine casualty resulting in environmental damage. Surveilled VTS&#8217;s are found in many large ports and harbors where congestion is a safety and operational hazard. Less sophisticated services have been established in other areas in response to hazardous navigational conditions according to the needs and resources of the authorities.

2711.	Brief History Of VTS
Since the early 1960&#8217;s the U.S. Coast Guard has been investigating various concepts by which navigational safety can be improved in the harbor and harbor approach areas. Equipment installations in various ports for this investigation have included shore-based radar; low light level, closed-circuit television (LLL-CCTV); VHF-FM communications;
broadcast television; and computer driven
electronic situation displays.

In 1962 an experimental installation called Ratan (Radar and Television Aid to Navigation) was completed in New York Harbor. In this system a radar at Sandy Hook, New Jersey, scanned the approaches to the harbor. The radar video, formatted by a scan conversion storage tube, was broadcast by a television band UHF transmitter. This enabled mariners to observe on commercial television sets the presentation on the radarscope at Sandy Hook. The mariner could identify his vessel on the television screen by executing a turn and by observing the motions of the targets. The high persistency created by the scan converter provided target &#8220;tails&#8221; which aided in observing target movement. This Ratan experiment was discontinued primarily because of allocation of the commercial television frequency spectrum for other purposes.

In January 1970 the Coast Guard established a harbor radar facility in San Francisco to gather data on vessel traffic patterns. The information was used to determine parameters for new equipment procurements. The initial installation consisted of standard marine X-band (3-centimeter) search radars located on Point Bonita and Yerba Buena Island in San Francisco Bay. Radar video was relayed from these two radar sites to a manned center colocated with the San Francisco Marine Exchange. When the parameter definition work was completed, VHF-FM communications equipment was added to enable communications throughout the harbor area. This experimental system, previously called Harbor Advisory Radar (HAR) was designated in August 1972 as an operational Vessel Traffic System (VTS); a continuous radar watch with advisory radio broadcasts to traffic in the harbor was provided. This change from HAR to VTS coincided with the effective date of the Ports and Waterways Safety Act of 1972, authorizing the U.S. Coast Guard to install and operate such systems in United States waters to increase vessel safety and there by protect the environment. In late 1972 improved developmental radar systems were installed side by side with the operational system, operated by a new research evaluation center at Yerba Buena Island. Redundant operator-switchable transceivers provided 50 kW peak power and incorporated receivers with large dynamic ranges of automatic gain control giving considerable protection against receiver saturation by interfering signals and interference by rain and sea clutter. Parabolic antennas with apertures of 27 feet (8.2 meters) and beam widths of 0.3 degrees improved the radar system accuracy. Variable pulse lengths (50 and 200 nanoseconds), three pulse repetition rates (1000, 2500, and 4000 pps), two receiver bandwidths (22 MHz and 2 MHz), and three antenna polarizations (horizontal, vertical, and circular) were provided to evaluate the optimum parameters for future procurements. After a period of extensive engineering evaluation, the radar system was accepted in May 1973 as an operational replacement for the equipment installed earlier at the HAR. In 1980 an analysis indicated that a modified version of the Coast Guard standard shipboard radar would meet all the VTS standard operating requirements. Additionally, it was more cost effective to procure and maintain than the specially designed, non-standard radar. After a period of evaluation at VTS San Francisco and with certain technical modifications, the standard radar was accepted for VTS use. The radar includes a tracking system which enhances the radar capability by allowing the VTS to track up to 20 targets automatically. The PPI can operate in an environment that is half as bright as a normal room with an option for a TV type display that can operate under any lighting conditions. These new radars are also required to provide data to a computer system, have 60 navigational line capability, and display ranges in yards or nautical miles.

The new radar was installed in VTS Prince William Sound in August 1984. VTS Houston-Galveston&#8217;s radar was replaced in January 1985. VTS San Francisco radars were replaced in May 1985. VTS New York reopened in late 1990 and will continue to add coverage areas until the project is completed in 1995.

2712.	Operational Systems
VTS New York became operational in December 1990. It had been open previously but was closed in 1988 due to a change in funding priorities.
This VTS has the responsibility of coordinating vessel traffic movements in the busy ports of New York and New Jersey. The VTS New York area includes the entrance to the harbor via Ambrose and Sandy Hook Channels, through the Verrazano Narrows Bridge to the Brooklyn Bridge in the East River, to the Holland Tunnel in the Hudson River, and the Kill Van Kull including Newark Bay. Future plans call for the VTS area to be expanded to include the East River to Throgs Neck, all of Arthur Kill, and Raritan Bay. VTS New York is presently undergoing an upgrade which includes the installation of state-of-the-art equipment in a new operations center. The current operation uses surveillance data provided by 4 radar sites and 3 closed circuit TV sites. VTS communications are on VHF/FM channels 12 and 14.

VTS San Francisco was commissioned in August of 1972. When the original radar system became operational in May 1973, the control center for VTS San Francisco was shifted to the Yerba Buena Island. This center was designated a Vessel Traffic Center (VTC).

As of early 1985, the major components of the system include a Vessel Traffic Center at Yerba Buena Island, two high resolution radars, a VHF-FM communications network, a traffic separation scheme, and a vessel movement reporting system (VMRS). Channels 12 and 14 are the working frequencies. In 1985, all existing radar equipment was replaced with the standard Coast Guard radar. VTS San Francisco also operates an Offshore Vessel Movement Reporting System (OVMRS). The OVMRS is completely voluntary and operates using a broadcast system with information provided by participants.

VTS Puget Sound became operational in September 1972 as the second Vessel Traffic Service. It collected vessel movement report data and provided traffic advisories by means of a VHF-FM communications network. In this early service a VMRS was operated in conjunction with a Traffic Separation Scheme (TSS), without radar surveillance. Operational experience gained from this service and VTS San Francisco soon proved the expected need for radar surveillance in those services with complex traffic flow.

In 1973 radar coverage in critical areas of Puget Sound was provided. Efforts to develop a production generation of radar equipment for future port development were initiated. To satisfy the need for immediate radar coverage, redundant military grade Coast Guard shipboard radar transceivers were installed at four Coast Guard light stations along the Admiralty Inlet part of Puget Sound. Combination microwave radio link and radar antenna towers were installed at each site. Radar video and azimuth data, in a format similar to that used with VTS San Francisco, were relayed by broad band video links to the VTC in Seattle. At that Center, standard Navy shipboard repeaters were used for operator display. Although the resolution parameters and display accuracy of the equipment were less than those of the VTS San Francisco equipment, the use of a shorter range scale (8 nautical miles) and overlapping coverage resulted in very satisfactory operation. In December 1980 additional radar surveillance was added in the Strait of Juan De Fuca and Rosario Strait, as well as increased surveillance of the Seattle area, making a total of 10 remote radar sites.

The communications equipment was upgraded in July 1991 to be capable of a two frequency, four sector system. Channels 5A and 14 are the frequencies for VTS Puget Sound. A total of 13 Communication sites are in operation (3 extended area sites, 10 low level sites). The 3 extended area sites allow the VTS the ability to communicate in a large area when needed. The low level sites can be used in conjunction with one another without interference, and have greatly reduced congestion on the frequency. VTS Puget Sound now covers the Strait of Juan de Fuca, Rosario Strait, Admiralty Inlet, and Puget Sound south as far as Olympia. The major components of the system include the Vessel Traffic Center at Pier 36 in Seattle; a VHF-FM communications network; a traffic separation scheme; radar surveillance of about 80&#37; of the VTS area, and a Vessel Movement Reporting System. Regulations are in effect which require certain classes of vessels to participate in the system and make movement reports at specified points. The traffic separation scheme in the Strait of Juan de Fuca was extended as far west as Cape Flattery in March 1975 in cooperation with Canada and was formally adopted by the International Maritime Organization in 1982.

Under an agreement between the United States and Canada, regulations for the Strait of Juan de Fuca took effect in 1984. The Cooperative Vessel Traffic Management System (CVTMS) divides responsibility among the two Canadian VTS&#8217;s and VTS Puget Sound.
VTS Houston-Galveston became operational in February 1975 as the third Vessel Traffic Service. The operating area is the Houston Ship Channel from the sea buoy to the Turning Basin (a distance of 53 miles) and the side channels to Galveston, Texas City, Bayport, and the Intracoastal Waterway. The area contains approximately 70 miles of restricted waterways. The greater part of the Houston Ship Channel is 400 feet wide with depths of 36-40 feet. Several bends in the channel are in excess of 90 degrees. The major components of the system include the VTC at Galena Park, Houston; a VHF-FM communications network; low light level, closed circuit television (LLL-CCTV) surveillance covering approximately 3 miles south of Morgan&#8217;s Point west through the ship channel to City Dock #27 in Houston; a Vessel Movement Reporting System; and a radar surveillance system covering lower Galveston Bay approaches, Bolivar Roads, and Lower Galveston Bay. A second radar was installed in 1994. This radar will provide surveillance coverage between the Texas City channel and Morgan&#8217;s Point.
VTS Prince William Sound is required by The Trans-Alaska Pipeline Authorization Act (Public Law 93-153), pursuant to authority contained in Title 1 of the Ports and Waterways Safety Act of 1972 (86 Stat. 424, Public Law 92-340). The southern terminus of the pipeline is on the south shoreline of Port Valdez, at the Alyeska Pipeline Service Company tanker terminal. Port Valdez is at the north end of Prince William Sound, and Cape Hinchinbrook is at the south entrance. Geographically, the area is comprised of deep open waterways surrounded by mountainous terrain. The only constrictions to navigation are at Cape Hinchinbrook, the primary entrance to Prince William Sound, and at Valdez Narrows, the entrance to Port Valdez.

The vessel traffic center is located in Valdez. The system is composed of two radars, two major microwave data relay systems, and a VMRS which covers Port Valdez, Prince William Sound, and Gulf of Alaska. There is also a vessel traffic separation scheme from Cape Hinchinbrook to Valdez Arm. The Coast Guard is installing a dependent surveillance system to improve its ability to track tankers transiting Prince William Sound. To extend radar coverage the length of the traffic lanes in Prince William Sound would require several radars at remote, difficult-to-access sites and an extensive data relay network. As an alternative to radar, the Coast Guard is installing a dependent surveillance system that will require vessels to carry position and identification reporting equipment. The ability to supplement radar with dependent surveillance will bridge the gap in areas where conditions dictate some form of surveillance and where radar coverage is impractical. Once the dependent surveillance information is returned to the vessel traffic center, it will be integrated with radar data and presented to the watchstander on an electronic chart display.

REGULATED WATERWAYS
2713.	Purpose And Authorities
In confined waterways not considered international waters, local authorities may establish certain regulations for the safe passage of ships and operate waterway systems consisting of locks, canals, channels, and ports. This occurs generally in very busy or very highly developed waterways which form the major constrictions on international shipping routes. The Panama Canal, St. Lawrence Seaway, and the Suez Canal represent systems of this type. Nearly all ports and harbors have a body of regulations concerning the operation of vessels within the port limits, particularly if locks and other structures are part of the system. The regulations covering navigation through these areas are typically part of a much larger body of regulations relating to assessment and payment of tariffs and tolls, vessel condition and equipment, personnel, communications equipment, and many other factors. In general the larger the investment in the system, the larger will be the body of regulations which control it. Where the waterway separates two countries, a joint authority may be established to administer the regulations, collect tolls, and operate the system, as in the St. Lawrence Seaway.

Copies of the regulations are usually required to be aboard each vessel in transit. These regulations are available from the authority in charge or an authorized agent. Summaries of the regulations are contained in the appropriate volumes of the Sailing Directions (Enroute).


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## Fishers of Men

*CHAPTER 28*
GLOBAL MARITIME DISTRESS AND SAFETY SYSTEM
DEVELOPMENT

*Since the time of this publication, DSC has been made available to the public.*

2800. Introduction
The Global Maritime Distress and Safety System
(GMDSS) represents a significant improvement in marine safety over the previous system of short range and high seas radio transmissions. Its many parts include satellite as well as advanced terrestrial communications systems. Operational service of the GMDSS began on 1 February 1992, with full implementation scheduled by 1 February 1999.

2801. Background
The GMDSS was adopted by amendments in 1988 by the Conference of Contracting Governments to the International Convention for the Safety of Life at Sea (SOLAS), 1974. This was the culmination of more than a decade of work by the International Maritime Organization (IMO) in conjunction with the International Telecommunications Union (ITU), International Hydrographic Organization (IHO), World Meteorological Organization (WMO), International Maritime Satellite Organization (INMARSAT), and others.

The GMDSS offers the greatest advancement in maritime safety since the enactment of regulations following the Titanic disaster in 1912. It is an automated ship-to-ship, shore-to-ship and ship-to-shore system covering distress alerting and relay, the provision of maritime safety information (MSI) and basic communication links. Satellite and advanced terrestrial systems are incorporated into a modern communications network to promote and improve safety of life and property at sea throughout the world. The equipment required on board ships will depend not on their tonnage, but rather on the sea area in which the vessel operates. This is fundamentally different from the previous system, which based requirements on vessel size alone. The greatest benefit of the GMDSS is that it vastly reduces the chances of ships sinking without a trace and enables search and rescue (SAR) operations to be launched without delay.

SHIP REQUIREMENTS
2802. Ship Carriage Requirements
By the terms of the SOLAS Convention, the GMDSS provisions apply to cargo ships of 300 gross tons and over and ships carrying more than 12 passengers on international voyages. Unlike previous shipboard carriage regulations that specified equipment according to size of vessel, the GMDSS carriage requirements stipulate equipment according to the area the vessel operates in. These sea areas are designated as follows:
Sea Area A1 An area within the radiotelephone coverage of at least one VHF coast station in which continuous Digital Selective Calling (DSC - a radio receiver that performs distress alerting and safety calling on HF, MF and VHF frequencies) is available, as may be defined by a Contracting Government to the 1974 SOLAS Convention. This area extends from the coast to about 20 miles offshore.
Sea Area A2 An area, excluding sea area A1, within the radiotelephone coverage
of at least one MF coast station in which continuous DSC alerting is available, as may be defined by a Contracting Government. 

The general area is from the A1 limit out to about 100 miles offshore.
Sea Area A3 An area, excluding sea areas A1 and A2, within the coverage of an INMARSAT geostationary satellite in which continuous alerting is available.

This area is from about 70&#176;N to 70&#176;S.
Sea Area A4 All areas outside of sea areas A1, A2 and A3. This area includes the polar regions, where geostationary satellite coverage is not available.
Ships at sea must be capable of the following functional GMDSS requirements:
1. Ship-to-shore distress alerting.
2. Shore-to-ship distress alerting.
3. Ship-to-ship distress alerting.
4. SAR coordination.
5. On-scene communications.
6. Transmission and receipt of emergency locating signals.
7. Transmission and receipt of MSI.
8. General radio communications.
9. Bridge-to-bridge communications.

To meet the requirements of the functional areas above the following is a list of the minimum communications equipment needed for all ships:
1. VHF radio capable of transmitting and receiving DSC on channel 70 and radio telephony on channels 6, 13 and 16.
2. Radio receiver capable of maintaining a continuous DSC watch on channel 70 VHF.
3. Search and rescue transponders (SART), a minimum of two, operating in the 9 GHz band.
4. Receiver capable of receiving NAVTEX broadcasts anywhere NAVTEX service is available.
5. Receiver capable of receiving SafetyNET anywhere NAVTEX is not available.
6. Satellite emergency position indicating radiobeacon (EPIRB), manually activated or float-free selfactivated. 7. Two-way handheld VHF radios (two sets minimum on 300-500 gross tons cargo vessels and three sets minimum on cargo vessels of 500 gross tons and upward and on all passenger ships).
8. Until 1 Feb. 1999, a 2182 kHz watch receiver. Additionally, each sea area has its own requirements under GMDSS which are as follows:
Sea Area A1
1. General VHF radio telephone capability. 2. Free-floating EPIRB transmitting DSC on channel 70 VHF, or satellite EPIRB.
3. Capability of initiating a distress alert from a navigational position using DSC on either VHF, HF or MF; manually activated EPIRB; or Ship Earth Station (SES).
Sea Areas A1 and A2
1. Radio telephone MF 2182 kHz and DSC on 2187.5 kHz.
2. Equipment capable of maintaining a continuous DSC watch on 2187.5 kHz.
3. General working radio communications in the MF band 1605-4000 kHz, or INMARSAT SES. 4. Capability of initiating a distress alert by HF (using DSC), manual activation of an EPIRB, or INMARSAT SES.
Sea Areas A1, A2 and A3
1. Radio telephone MF 2182 kHz and DSC 2187.5 kHz. 2. Equipment capable of maintaining a continuous DSC watch on 2187.5 kHz.
3. INMARSAT A, B or C (class 2) SES Enhanced Group Call (EGC), or HF as required for sea area A4. 4. Capability of initiating a distress alert by two of the following: a. INMARSAT A, B or C (class 2) SES. b. Manually activated satellite EPIRB. c. HF/DSC radio communication.
Sea Area A4
1. HF/MF receiving and transmitting equipment for band 1605-27500 kHz using DSC, radiotelephone and direct printing.
2. Equipment capable of selecting any safety and distress DSC frequency for band 4000-27500 kHz, maintaining DSC watch on 2187.5, 8414.5 kHz and at least one additional safety and distress DSC frequency in the band.
3. Ability to initiate a distress alert from a navigational position via the Polar Orbiting System on 406 MHz (manual activation of 406 MHz satellite EPIRB).

COMMUNICATIONS
2803.	The INMARSAT System
The International Maritime Satellite Organization
(INMARSAT), a key player within GMDSS, is an international consortium comprising over 75 international partners who provide maritime safety communications for ships at sea. In accordance with its convention, INMARSAT provides the space segment necessary for improving distress communications, efficiency and management of ships, as well as maritime correspondence services.
The basic components of the INMARSAT system include the INMARSAT space segment, Land Earth Stations (LES), also referred to as Coast Earth Stations (CES), and mobile Ship Earth Stations (SES).

The INMARSAT space segment consists of 11 geostationary satellites. Four operational INMARSAT satellites provide primary coverage, four additional satellites (including satellites leased from the European Space Agency (ESA) and the International Telecommunications Satellite Organization (INTELSAT)) serve as spares and three remaining satellites (leased from COMSAT Corporation, the U.S. signatory to INMARSAT) serve as back-ups. The polar regions are not visible to the operational satellites and coverage is available from 70&#176;N to 70&#176;S. Satellite coverage (Figure 2803) is divided into four regions, which are:
1.	Atlantic Ocean - East (AOR-E)
2.	Atlantic Ocean - West (AOR-W)
3.	Pacific Ocean (POR)
4.	Indian Ocean (IOR)










The LES&#8217;s provide the link between the Space Segment and the land-based National/International fixed communications networks. These communications networks are funded and operated by the authorized communications authorities of a participating nation. This network links registered information providers to the LES. The data then travels from the LES to the INMARSAT Network Coordination Station (NCS) and then down to the SES&#8217;s on ships at sea. The SES&#8217;s provide two-way communications between ship and shore. INMARSAT A, the original INMARSAT system, operates at a transfer rate of up to 9600 bits per second and is telephone, telex and facsimile (fax) capable. It is being replaced by a similarly sized INMARSAT B system that uses digital technology to give better quality fax and higher data transmission rates.
INMARSAT C provides a store and forward data messaging capability (but no voice) at 600 bits per second and was designed specifically to meet the GMDSS requirements for receiving MSI data on board ship. These units are small, lightweight and use an omni-directional antenna.

2804.	SafetyNET
SafetyNET is a service of INMARSAT C&#8217;s Enhanced Group Call (EGC) system. The EGC system (Figure 2804) is a method used to specifically address particular regions or ships. Its unique addressing capabilities allow messages to be sent to all vessels in both fixed geographical areas or to predetermined groups of ships. SafetyNET is the service designated by the IMO through which ships receive maritime safety information. The other service under the EGC system, called FleetNET, is used by commercial companies to directly (and privately) communicate to their individual fleets.










SafetyNET is an international direct-printing satellitebased service for the promulgation of navigational and meteorological warnings, and distress alerts, forecasts, and other safety messages. It fulfills an integral role in GMDSS as developed by the IMO. The ability to receive SafetyNET service information is necessary for all ships that sail beyond coverage of NAVTEX (approximately 200 miles from shore) and is recommended to all administrations having the responsibility for marine affairs and mariners who require effective MSI service in waters not served by NAVTEX. SafetyNET can direct a message to a given geographic area based on EGC addressing. The area may be fixed, as in the case of a NAVAREA or weather forecast area, or it may be uniquely defined by the originator. This is particularly useful for messages such as local storm warnings or a shipto-shore distress alert for which it would be inappropriate to alert ships in an entire ocean region.

SafetyNET messages can be originated by a Registered Information Provider anywhere in the world and broadcast to the appropriate ocean area through an INMARSAT-C LES. Messages are broadcast according to their priority (i.e., Distress, Urgent, Safety, and Routine). Virtually all navigable waters of the world are covered by the operational satellites in the INMARSAT system. Each satellite broadcasts EGC traffic on a designated channel.

Any ship sailing within the coverage area of an INMARSAT satellite will be able to receive all the Safety-NET messages broadcast over this channel. The EGC channel is optimized to enable the signal to be monitored by SES&#8217;s dedicated to the reception of EGC messages. This capability can be built into other standard SES&#8217;s. It is a feature of satellite communications that reception is not generally affected by the position of the ship within the ocean region, atmospheric conditions, or time of day.

Messages can be transmitted either to geographic areas (area calls) or to groups of ships (group calls):
1.	Area calls can be to a fixed geographic area such as one of the 16 NAVAREA&#8217;s or to a temporary geographic area selected by the originator. Area calls will be received automatically by any ship whose receiver has been set to one or more fixed areas or recognizes an area by geographic position.
2.	Group calls will be received automatically by any ship whose receiver acknowledges the unique group identity associated with a particular message. Reliable delivery of messages is ensured by forward error correction techniques. Experience has demonstrated that the transmission link is generally error-free and low error reception is achieved under normal circumstances. Given the vast ocean coverage by satellite, some form of discrimination and selectivity in printing the various messages is required. Area calls will be received by all ships within the ocean region coverage of the satellite; however, they will be printed only by those receivers that recognize the fixed area or the geographic position in the message. The message format includes a preamble that enables the microprocessor in a ship&#8217;s receiver to decide to print those MSI messages that relate to the present position, intended route or a fixed area programmed by the operator. This preamble also allows suppression of certain types of MSI that are not relevant to a particular ship. As each message will also have a unique identity, the reprinting of messages already received correctly is automatically suppressed.

MSI is promulgated by various information providers around the world. Messages for transmission through the SafetyNET service will, in many cases, be the result of coordination between authorities. Information providers will be authorized to broadcast via SafetyNET by IMO. Authorized information providers are:
1.	National hydrographic offices for navigational warnings.
2.	National weather services for meteorological warnings and forecasts.
3.	Rescue Coordination Centers for ship-to-shore distress alerts and other urgent information.
4.	In the U.S., the International Ice Patrol for North Atlantic ice hazards.
Each information provider prepares their SafetyNET messages with certain characteristics recognized by the EGC service. These characteristics, known as &#8220;C&#8221; codes are combined into a generalized message header format as follows:
C1: C2: C3: C4: C5. Each &#8220;C&#8221; code controls a different broadcast criterion and is assigned a numerical value according to available options. A sixth &#8220;C&#8221; code, &#8220;C0&#8221; may be used to indicate the ocean region (i.e., AOR-E, AOR-W, POR, IOR) when sending a message to an LES which operates in more than one ocean region. Because errors in the header format of a message may prevent its being released, MSI providers must install an INMARSAT SafetyNET receiver to monitor the broadcasts it originates. This also ensures quality control.

The &#8220;C&#8221; codes are transparent to the mariner but are used by information providers to identify various transmitting parameters. C1 designates the message priority from distress to urgent, safety, and routine. MSI messages will always be at least at the safety level. C2 is the service code or type of message (for example, long range NAVAREA warning or coastal NAVTEX warning). It also tells the receiver the length of the address (the C3 code) it will need to decode. C3 is the address code. It can be the two digit code for the NAVAREA number for instance, or a 10 digit number to indicate a circular area for a meteorological warning. C4 is the repetition code which instructs the LES in how long and when to send the message to the NCS for actual broadcast. A six minute echo (repeat) may also be used to ensure that an urgent (unscheduled) message has been received by all ships affected. C5 is a constant and represents a presentation code, International Alphabet number 5, &#8220;00&#8221;. Broadcasts of MSI in the international SafetyNET service are in English.

2805.	NAVTEX
NAVTEX is a maritime radio warning system consisting of a series of coast stations transmitting radio teletype (standard narrow-band direct printing, also sometimes called Sitor) safety messages on the internationally standard medium frequency of 518 kHz. It is a GMDSS requirement for the reception of MSI in coastal and local waters. Coast stations transmit during previously arranged time slots to minimize mutual interference. Routine messages are normally broadcast four times daily. Urgent messages are broadcast upon receipt, provided that an adjacent station is not transmitting. Since the broadcast uses the medium frequency band, a typical station service radius ranges from 100 to 500 NM day and night (although a 200 mile rule of thumb is applied in the U.S.). Interference from or receipt of stations farther away occasionally occurs at night. Each NAVTEX message broadcast contains a fourcharacter header describing: identification of station (first character); message content or type (second character); and message serial number (third and fourth characters). This header allows the microprocessor in the shipboard receiver to screen messages from only those stations relevant to the user, messages of subject categories needed by the user and messages not previously received by the user. Messages so screened are printed as they are received, to be read by the mariner when convenient. All other messages are suppressed. Suppression of unwanted messages is becoming more and more a necessity to the mariner as the number of messages, including rebroadcast messages, increases yearly. With NAVTEX, a mariner will not find it necessary to listen to, or sift through, a large number of non-relevant data to obtain the information necessary for safe navigation. The NAVTEX receiver is a small unit with an internal printer, which takes a minimum of room on the bridge. Its antenna is also of modest size, needing only a receive capability.

2806.	Maritime Safety Information (MSI)
Major categories of MSI for both NAVTEX and Safety-NET are:
1.	Navigational warnings
2.	Meteorological warnings
3.	Ice reports
4.	Search and rescue information
5.	Meteorological forecasts
6.	Pilot service messages (not in the U.S.)
7.	Electronic navigation system messages (i.e., OMEGA, LORAN, DECCA, GPS, DGPS, SATNAV, etc.)
Broadcasts of MSI in NAVTEX international service are in English, but may be in languages other than English, to meet requirements of the host government.

2807.	Digital Selective Calling (DSC)
Digital Selective Calling (DSC) is a method of auto402 GLOBAL MARITIME DISTRESS AND SAFETY SYSTEM matically placing a call directly from one radio to another. This is accomplished by addressing the call so it will be received automatically by the other radio. It permits a radio to be used like a telephone. Since the DSC system will sound an alarm (much like a ringing telephone) when it senses an incoming call, there is no need for dedicated, aural watchstanding. DSC techniques can be used with VHF, HF and MF radio communications. DSC&#8217;s principal uses are in distress alerting and safety calling. Numerous frequencies have been assigned. They are 2187.5 kHz in the MF band;
4207.5 kHz, 6312 kHz, 8414.5 kHz, 12577 kHz and 16804.5 kHz in the HF band; and 156.525 MHz (channel 70) in the VHF band.

2808. Emergency Position-Indicating Radio Beacons
Emergency Position-Indicating Radio Beacons (EPIRBs) are designed to transmit a satellite alert in the event of sudden accident either automatically or manually. The automatic models are designed and mounted so that they will float free of a sinking vessel and be activated by sea- water. The manual ones are controlled by a switch. Under GMDSS, satellite EPIRBs will operate either on 1.6 GHz (the INMARSAT E, L Band) or the 406 MHz frequency used by the COSPAS-SARSAT system.
GMDSS requires 1 satellite EPIRB along with 2 search and rescue transponders (SART&#8217;s). These SART&#8217;s generate a series of response signals when interrogated by any ordinary 9 GHz radar set. The signals produce a line of 20 blips on the radar screen of the rescue ship or aircraft.

Under GMDSS, the COSPAS-SARSAT and INMARSAT communication systems are the two basic media through which the EPIRB signal is relayed to ground and sea stations. COSPAS-SARSAT is a joint international satellite-aided SAR system operated by multi-national organizations in Canada, France, the U.S. and the Russian Federation. It uses low polar orbiting satellites which receive and relay distress signals from EPIRBs and determine their position. INMARSAT, with over 75 member nations, operates a global satellite EPIRB system (excluding the poles). Further details of the COSPAS-SARSAT system are found in Chapter 29, Position Reporting Systems.


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## Fishers of Men

CHAPTER 29
POSITION REPORTING SYSTEMS
INTRODUCTION
2900. Purpose
The purpose of position reporting systems is to monitor vessel positions and inform authorities and other vessels of an emergency or distress at sea so that a response can be coordinated among those best able to help. It is important that distress information be immediately available to Search and Rescue (SAR) coordinators so that assistance can be obtained with the least delay. Establishing communications is sometimes difficult even when automatic alarms are used, and determination of SAR capabilities and intentions of vessels is time-consuming, unless the essential information has been made readily available beforehand by their participation in a position reporting system.

The Convention on Safety of Life at Sea (SOLAS) obligates the master of any vessel who becomes aware of a distress incident to proceed to the emergency and assist until other aid is at hand or until released by the distressed vessel. Other international treaties and conventions impose the same requirement. Position reporting systems permit determination of the most appropriate early assistance, provide the means for a timely resolution of distress cases, and enable vessels responding to distress calls to continue their passage with a minimum amount of delay.

Other resolutions recommend that governments encourage participation in position reporting schemes by ensuring that no costs are incurred by the vessel for participation. There are currently many position reporting systems in operation throughout the world. The particulars of each system are given in publications of the International Maritime Organization (IMO). Masters of vessels making offshore passages are requested by the U.S. Coast Guard to always participate in the AMVER System and to participate in the other systems when in the areas covered by them.

AMVER
2901. The Automated Mutual-Assistance Vessel Rescue System (AMVER)
AMVER, operated by the United States Coast Guard, is an international maritime mutual assistance program which assists search and rescue efforts in many offshore areas of the world. Merchant ships of all nations making offshore passages are encouraged to send movement (sailing) reports and periodic position reports voluntarily to the AMVER Center in New York via selected radio stations. Information from these reports is entered into a computer which maintains dead reckoning positions for the vessels.
Information concerning the predicted location and SAR characteristics of each vessel is available upon request to recognized SAR agencies of any nation or to vessels needing assistance. Predicted locations are disclosed only for reasons related to marine safety.

Messages sent within the AMVER System are at no cost to the ship or owner. Benefits to shipping include: (1) improved chances of aid in emergencies, (2) reduced number of calls for assistance to vessels not favorably located, and (3) reduced time lost for vessels responding to calls for assistance. An AMVER participant is under no greater obligation to render assistance during an emergency than a non-participating vessel. All AMVER messages are addressed to Coast Guard, New York, regardless of the station to which the message is delivered, except those sent to Canadian stations which should be addressed to AMVER Halifax or AMVER Vancouver. This avoids incurring charges to the vessel.

In addition to the information calculated from sailing plans and position reports, the AMVER Center stores data on the characteristics of vessels. This includes the following: vessel name; international call sign; nation of registry; owner or operator; type of rig; type of propulsion; gross tonnage; length; normal cruising speed; radio schedule; radio facilities; radio telephone installed; surface search radar installed; doctor normally carried. Vessels can assist the AMVER Center in keeping this data accurate by sending a complete report by message, letter, or by completing a SAR Information Questionnaire available from AMVER, and sending corrections as the characteristics change. Corrections may be included in regular AMVER reports as remarks.

For AMVER participants bound for U.S. ports there is an additional benefit. AMVER messages which include the necessary information are considered to meet the requirements of 33 CFR 161 (Notice of arrival).

2902. AMVER System Communications Network
An extensive radio network supports the AMVER system. Propagation conditions, location of vessel, and message density will normally determine which station should be contacted to establish communications. To ensure that no charge is applied, all AMVER messages should be passed through specified radio stations. Those which currently accept AMVER messages and apply to coastal station, ship station, or landline charge are listed in each issue of the AMVER Bulletin, together with respective call sign, location, frequency bands, and hours of guard. Although AMVER messages may be sent through other stations, the Coast Guard cannot reimburse the sender for any charges.

2903. The AMVER Bulletin
The AMVER Bulletin, published quarterly by the U.S. Coast Guard, provides information on the operation of the AMVER System of general interest to the mariner. It also provides up-to-date information on the AMVER communications network and Radio Wave Propagation Charts which indicate recommended frequencies for contacting U.S. coast radio stations participating in the AMVER System, according to the time of day and the season of the year.

2904.	AMVER Participation
Instructions guiding participation in the AMVER System are available in the following languages: Chinese, Danish, Dutch, English, French, German, Greek, Italian, Japanese, Korean, Norwegian, Polish, Portuguese, Russian, Spanish and Swedish. The AMVER Users Manual is available from: Commander, Atlantic Area, U.S. Coast Guard, Governors Island, NY, 10004; Commander Pacific Area, U.S. Coast Guard, Government Island, Alameda, CA 94501; and at U.S. Coast Guard District Offices, Marine Safety Offices, Marine Inspection Offices and Captain of the Port Offices in major U.S. ports. Requests for instructions should state the language desired if other than English. Search and Rescue operation procedures are contained in the Merchant Ship Search and Rescue Manual (MERSAR) published by the International Maritime Organization (IMO). U.S. flag vessels may obtain a copy of MERSAR from local Coast Guard Marine Safety Offices and Marine Inspection Offices or by writing to U.S. Coast Guard (G-OSR), Washington, DC 20593. Other flag vessels may purchase MERSAR directly from IMO.

In connection with a vessel&#8217;s first AMVER-plotted voyage, the master is requested to complete a questionnaire providing the radio watch schedule, available medical and communications facilities, and other useful characteristics. Stored in the AMVER computer, this information can be electronically processed in an emergency, while a position is calculated.

Any vessel of any nation departing on an offshore passage of 24 hours duration or greater is encouraged to become a participant in the AMVER System by sending appropriate AMVER messages in one of several formats. 

The messages may be transmitted at any convenient time as long as the information is accurate.

There are five types of AMVER Reports.
1.	Sailing Plan.
2.	Departure Report.
3.	Arrival Report.
4.	Position Report.
5.	Deviation Reports.
AMVER permits sailing plan and departure information to be combined into a single report. It also accepts sailing plan information separately.

Only the above five types of AMVER messages require specific formats. (See DMAHTC Pub. 117, Radio Navigational Aids). Other messages relating to a vessel&#8217;s AMVER participation or data, such as facts on her SAR capabilities, may also be sent via the AMVER communications network. Additional information concerning the AMVER System may be obtained by writing to: Commandant, U.S. Coast Guard, Washington, DC 20590, or by writing or visiting Commander, Atlantic Area, U.S. Coast Guard, Governors Island, New York, NY 10004. The AMVER System in the Pacific is coordinated by Commander, Pacific Area, U.S. Coast Guard, Government Island, Alameda, CA 94501. Other countries such as Canada are a formal part of the AMVER System and provide radio stations for relay of AMVER reports, as well as coordinating rescue efforts in certain regions. Applicable instructions have been promulgated by official publications of the participating countries.

2905.	AMVER Reporting Required
The U.S. Maritime Administration regulations state that certain U.S. flag vessels and foreign flag &#8220;War Risk&#8221; vessels must report and regularly update their voyages to the AMVER Center. This reporting is required of the following:
(a)	U.S. flag vessels of 1,000 tons or greater,
operating in foreign commerce; (b) foreign flag vessels of 1,000 gross tons or greater, for which an Interim War Risk Insurance Binder has been issued under the provisions of Title XII, Merchant Marine Act, 1936.

2906.	AMVER Plot Information
The information stored in the computer can be used to provide several types of display according to the needs of controllers at Rescue Coordination Centers. The surface picture (SURPIC) can be displayed as a Radius SURPIC (Figure 2906a). When requesting a Radius SURPIC, the controller specifies the date and time, a latitude and longitude to mark the center (P), the radius (in nautical miles) that the SURPIC should cover &#174;, and whether the names of all ships are desired (or only those with doctors, or perhaps those heading either east or west).










A Radius SURPIC may be requested for any radius from 1 to 999 miles. A sample request is as follows:

&#8220;REQUEST 062100Z RADIUS SURPIC OF DOCTORSHIPS WITHIN 800 MILES OF 43.6N 030.2W FOR MEDICAL EVALUATION M/V SEVEN SEAS.&#8221;

The Area SURPIC is obtained by specifying the date, time, and two latitudes and two longitudes. The controller can limit the ships to be listed as with the Radius SURPIC. There is no maximum or minimum size limitation on an Area SURPIC.

A sample Area SURPIC request is as follows:
&#8220;REQUEST 151300Z AREA SURPIC OF WESTBOUND SHIPS FROM 43N TO 31N LATITUDE AND FROM 130W TO 150W LONGITUDE FOR SHIP DISTRESS M/V EVENING SUN LOCATION 37N, 140W.&#8221; 

The Trackline SURPIC is obtained by specifying the date and time, two points (P1 and P2), whether the trackline should be rhumb line or great circle, what the half-width (D) coverage should be (in nautical miles), and whether all ships are desired (or only doctor ships, or just those east or westbound). The half-width (D) specified should not exceed 100 miles. When received, the SURPIC will list ships in order from P1 to P2. There is no maximum or minimum distance between P1 and P2.

A sample Trackline SURPIC request is as follows:
&#8220;REQUEST 310100Z GREAT CIRCLE TRACKLINE SURPIC OF ALL SHIPS WITHIN 50 MILES OF A LINE FROM 20.1N 150.2W TO 21.5N 158.0W FOR AIRCRAFT PRECAUTION.&#8221;

A Location Vessel is used to determine the location of a specific ship. It permits a controller to determine the DR position of an AMVER participant wherever located.
A sample Location Vessel request is as follows:
&#8220;REQUEST PRESENT POSITION, COURSE, AND
SPEED OF M/V POLARIS&#8221;
A Radius SURPIC as it would be received by a rescue center, listing all ships within a 200-mile radius of 26.2N, 179.9W, is shown in Figure 2906b.











2907. Uses Of AMVER Plot Information
An example of the use of a Radius SURPIC is depicted in Figure 2907. In this situation rescue authorities believe that a ship in distress, or her survivors, will be found in the rectangular area. The Rescue Coordination Center requests a listing of all eastbound ships within 100 miles of a carefully chosen position. Once this list is received by the Rescue Coordination Center a few moments later, messages can be prepared for satellite transmission to each vessel, or arrangements made to contact them by radio.

Each ship contacted may be asked to sail a rhumb line between two specified points, one at the beginning of the search area and one at the end. By carefully assigning ships to areas of needed coverage, very little time need be lost from the sailing schedule of each cooperating ship. Those ships joining the search would report their positions every few hours to the Rescue Coordination Center, together with weather data and any significant sightings. In order to achieve saturation coverage, a westbound SURPIC at the eastern extremity of the search area would also be used. The Trackline SURPIC is most commonly used as a precautionary measure for aircraft. Rarely, if ever, is a major airliner forced to ditch at sea anymore. But occasions sometimes arise where a plane loses of one or more of its engines. A Trackline SURPIC, provided from the point of difficulty to the destination, provides the pilot with the added assurance of knowing the positions of vessels beneath him and that they have been alerted. SURPIC&#8217;s have been used successfully to save the lives of pilots of small aircraft.










EMERGENCY POSITION INDICATING RADIOBEACONS (EPIRB&#8217;S)
2908. Description And Capabilities
Emergency Position Indicating Radiobeacons (EPIRB&#8217;s), devices which cost from $200 to over $1500, are designed to save lives by automatically alerting rescue authorities and indicating the distress location. EPIRB types are described below:
121.5/243 MHz EPIRB&#8217;s (Class A, B, S): These are the most common and least expensive type of EPIRB, designed to be detected by overflying commercial or military aircraft. Satellites were designed to detect these EPIRB&#8217;s but are limited for the following reasons:
1. Satellite detection range is limited for these EPIRB&#8217;s (satellites must be within line of sight of both the EPIRB and a ground terminal for detection to occur). 2. EPIRB design and frequency congestion cause them to be subject to a high false alert/false alarm rate (over 99&#37; consequently, confirmation is required before SAR forces can be deployed;
3. EPIRB&#8217;s manufactured before October 1988 may have design or construction problems (e.g. some models will leak and cease operating when immersed in water) or may not be detectable by satellite.


















Class C EPIRB&#8217;s: These are manually activated devices intended for pleasure craft which do not venture far offshore, and for vessels on the Great Lakes. They transmit a short burst on VHF-FM 156.8 MHz (Ch. 16) and a longer homing signal on 156.75 MHz (Ch. 15). Their usefulness depends upon a coast station or another vessel guarding channel 16 and recognizing the brief, recurring tone as an EPIRB. Class C EPIRB&#8217;s are not recognized outside of the United States. Class C EPIRB&#8217;s cannot be manufactured or sold in the United States after February 1995. Class C EPIRB&#8217;s installed on board vessel&#8217;s prior to February 1995 may be utilized until 1 February 1999 and not thereafter.

406 MHz EPIRB&#8217;s (Category I, II): The 406 MHz
EPIRB was designed to operate with satellites. Its signal allows a satellite local user terminal to locate the EPIRB (much more accurately than 121.5/243 MHz devices) and identify the vessel (the signal is encoded with the vessel&#8217;s identity) anywhere in the world. There is no range limitation. These devices also include a 121.5 MHz homing signal, allowing aircraft and rescue vessels to quickly find the vessel in distress. These are the only type of EPIRB which must be tested by Coast Guard-approved independent laboratories before they can be sold for use within the United States.

An automatically activated, float-free version of this EPIRB has been required on SOLAS vessels (cargo ships over 300 tons and passenger ships on international voyages)
since 1 August 1993. The Coast Guard requires U.S. commercial fishing vessels to carry this device (unless they carry a Class A EPIRB), and will require the same for other U.S. commercial uninspected vessels which travel more than 3 miles offshore.

Mariners should be aware of the differences between capabilities of 121.5/243 MHz and 121.5/406 MHz EPIRB&#8217;s, as they have implications for alerting and locating of distress sites, as well as response by SAR forces. The advantages of 121.5/406 MHz devices are substantial, and are further enhanced by EPIRB-transmitted registration data on the carrying vessel. Owners of 121.5/406 MHz EPIRB&#8217;s furnish registration information about their vessel, survival gear, and emergency points of contact ashore, all of which greatly enhance the response. The database for U.S. vessels is maintained by the National Oceanographic and Atmospheric Administration, and is accessed worldwide by SAR authorities to facilitate SAR response.

2909.	Testing EPIRB&#8217;s
EPIRB owners should periodically check for water tightness, battery expiration date, and signal presence. FCC rules allow Class A, B, and S EPIRB&#8217;s to be turned on briefly (for three audio sweeps, or 1 second only) during the first 5 minutes of any hour. Signal presence can be detected by an FM radio tuned to 99.5 MHz, or an AM radio tuned to any vacant frequency and located close to an EPIRB. FCC rules allow Class C EPIRB&#8217;s to be tested within the first 5 minutes of any hour, for not more than 10 seconds. Class C EPIRB&#8217;s can be detected by a marine radio tuned to channel 15 or 16. All 121.5/406 MHz EPIRB&#8217;s have a self-test function that should be used in accordance with manufacturers&#8217; instructions at least monthly.

2910.	The COSPAS/SARSAT System
COSPAS is a Russian acronym for &#8220;Space System for Search of Distressed Vessels&#8221;; SARSAT signifies &#8220;Search And Rescue Satellite-Aided Tracking.&#8221; COSPAS-SARSAT is an international satellite-based search and rescue system established by the U.S., Russia, Canada, and France to locate emergency radiobeacons transmitting on the frequencies 121.5, 243, and 406 MHz. Since its inception, the COSPAS-SARSAT system (SARSAT satellite only) has contributed to saving over 3000 lives.
The USCG receives data from MRCC stations and SAR Points of Contact (SPOC). See Figure 2910.










2911. Operation Of The COSPAS/SARSAT System
If an EPIRB is activated, COSPAS/SARSAT picks up the signal, locates the source and passes the information to a land station. From there, the information is relayed, either via coast radio or satellite, to Rescue Coordination Centers, rescue vessels and nearby ships. This constitutes a one-way only communications system, from the EPIRB via the satellite to the rescuers. It employs low altitude, near polar orbiting satellites and by exploiting the Doppler principle, locates the transmitting EPIRB within about two miles. Due to the low polar orbit, there may by a delay in receiving the distress message unless the footprint of the satellite is simultaneously in view with a monitoring station. However, unlike SafetyNET, worldwide coverage is provided.

As a satellite approaches a transmitting EPIRB, the frequency of the signals it receives is higher than that being transmitted; when the satellite has passed the EPIRB, the
received frequency is lower. This creates a notable Doppler shift. Calculations which take into account the earth&#8217;s rotation and other factors then determine the location of the EPIRB.

The 406 MHz EPIRB&#8217;s incorporate an identification code. Once the satellite receives the beacon&#8217;s signals, the Doppler shift is measured and the beacon&#8217;s digital data is recovered from the signal. The information is time-lagged, formatted as digital data and transferred to the repeater downlink for real time transmission to any local user terminal. The digital data coded into each 406 MHz EPIRB&#8217;s memory provides distress information to SAR authorities for more rapid and efficient rescue. The data includes a maritime identification digit (MID, a 3 digit number identifying the administrative country) and either a ship station identifier (SSI, a 6 digit number assigned to specific ships), a ship radio call sign or a serial number to identify the ship in distress.
With the INMARSAT E satellite EPIRB&#8217;s, coverage does not extend to very high latitudes, but within the coverage area the satellite connection is instantaneous. However, to establish the EPIRB&#8217;s position, an interface with a GPS receiver or other sensor is needed.

2912. Alarm, Warning, And Alerting Signals
For MF (i.e. 2182 kHz), the EPIRB signal consists of either (1) a keyed emission modulated by a tone of 1280 Hz to 1320 Hz with alternating periods of emission and silence of 1 to 1.2 seconds each; or (2) the radiotelephone alarm signal followed by Morse code B (&#8212; &#8226; &#8226; &#8226 and/or the call sign of the transmitting ship, sent by keying a carrier modulated by a tone of 1300 Hz or 2200 Hz. For VHF (i.e. 121.5 MHz and 243 MHz), the signal characteristics are in accordance with the specifications of Appendix 37A of the ITU Radio Regulations. For 156.525 MHz and UHF (i.e. 406 MHz to 406.1 MHz and 1645.5 MHz to 1646.5 MHz), the signal characteristics are in accordance with CCIR recommendations.

The purpose of these signals is to help determine the position of survivors for SAR operations. They indicate that one or more persons are in distress, may no longer be aboard a ship or aircraft, and may not have a receiver available.

Any vessel or aircraft receiving an EPIRB signal while no distress or urgent traffic is being passed shall initiate a distress message on the assumption that the EPIRB sending station is unable to transmit a distress message. The keying cycles for MF EPIRB&#8217;s may be interrupted for speech transmission.


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## Fishers of Men

Part 2 of this thread:

http://www.ohiogamefishing.com/community/showthread.php?t=90959&highlight=moonglow


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