# Gas smell under boat cover



## Mad-Eye Moody (May 27, 2008)

I have a boat cover this year for the first time and notice a relatively strong fuel smell under it when I take it off. It is professionally made with three round vents in top where the posts insert.

Is smelling fuel that is building up under the cover normal? The gas tank vent is in the center of the floor and I am guessing that is where it is coming from.


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## bocajemma (Dec 29, 2008)

Fuel smell buildup is never normal and always very dangerous. Confused about how your gas tank vent is in the center of the boat floor. We will need some more info.

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## freyedknot (Apr 10, 2004)

usually the gas tank vent is on the outside of the hull,close to the filling cap.


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## Mad-Eye Moody (May 27, 2008)

There is a black plastic perforated disk in the middle of the floor above the gas tank that I assume is the vent. The vent might be back by the fuel tank but even if it is it would still be under the cover.


I'm worried that one of Hesse days I am going to plug in the on board chargers and the whole thing is going to explode.


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## bocajemma (Dec 29, 2008)

Are we talking a permanent fuel tank below deck? A few years back while in storage we noticed a fuel odor when the boat was covered with plastic. Had a leaking gas tank. Couldn't smell it with the canvas covering the boat. I believe having a vent inside the boat is illegal for permanent mount tanks. Not only is it the vent but if you fill your tank you will occasionally get overflow. Either way you would get all kinds of fuel vapors which are heavier than air in your boat every time you fueled. 

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## FISNFOOL (May 12, 2009)

How old is the boat? Fuel lines may be failing, or you are covering up the outside vent when you put the cover on. Since you have an under deck tank, the vent is a through the hull fitting, with a hole about 3/4 inch round. It will be on the side of the boat, the fuel tank is on. It is connected to a vent fitting on the top of a permanent fuel tank.

I would lift the deck above the fuel tank and check all your fuel lines. And if it is an old pre-ethanol in the gas, then you should replace all your lines and filler hose with ethanol safe ones. It decays the old style fuel lines. The new style lines are a required safety for installed fuel tanks.

The vent hose loop in the diagram is to prevent water from getting into the fuel tank.


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## Mad-Eye Moody (May 27, 2008)

I called the manufacturer and they confirmed that the tank vent is part of the device that the gas cap is on. That device is at the front of the splash well and therefore under cover.

They also said that the poly tank that the gas is stored in is somewhat porous and that gas vapors will permeate throughout he tank given some weather conditions such as heat. Between the vent being under cover and the tank being porous the odor is somewhat natural.

I plan to pull the floor up anyways and check for leaks in the hoses and tanks. The floor appears relatively simple to remove. The boat is seven years old.

If there is not in fact a leak I might rig up a ventilation system to move air through the boat.


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## FISNFOOL (May 12, 2009)

I see you were covering the vent. This would build up fumes under the cover. As air expands in the tank, it is vented out through the gas cap vent your dealer said you have. Do not cover this vent.

You are wise to be checking the system out. Check for leaking fuel gauge sending unit gasket too. I have a poly Moeller 20 gallon fuel tank installed under my deck and do no ever get any fumes in the boat. If "porous" poly fuel tanks were venting fuel fumes under boat decks there would be more explosions.

You should have a bilge blower system on a boat with a below deck fuel tank. 

A poly fuel tank is not "porous" as you were told. If it is venting fumes under the deck, something is wrong. It is not a simple plastic tank. It is a special material.

Crosslink Polyethylene
Material with excellent chemical
resistant properties. Wall thicknesses are
designated by gallon capacity and are designed
to meet pertinent tests per ABYC H-24 standards.

http://www.moellermarine.com/sites/moellermarine/files/permanent-and-custom-tank-info_moellermarine.pdf

Your tank vent line would be on the smaller fitting of the gas cap unit.


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## bocajemma (Dec 29, 2008)

Interesting. Is the canvas somewhat tight to that area? I would also talk to your canvas maker. They should have considered the gas fill having the integral vent when they made the canvas. They may come up with a solution to get the gas fill/vent outside of your canvas. That is the best option. A vent system may work but if it stops when your not there you have a potential fire hazard if not explosion. Probably cut that area out of the canvas in a U shape and install a thick gasket or something.

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## 68rocks (Aug 2, 2013)

That vent you saw in the floor is most likely a drain for water to get off the deck and to your bilge.


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