Permanent Gas Tank Compartment Venting

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blueflood
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Permanent Gas Tank Compartment Venting

Post by blueflood »

Hi all,

I was just wondering what kind of venting my permanent gas tank compartment needs ? The custom built 12 gal tank is vented up the the cabin roof via a standard Attwood gas tank vent and all properly wired and plumbed.

The compartment where the tank sits under sole is vented via two tubes (one on either side of the tank at bottom corners) and routed via tubes out to the side deck also with Attwood fuel vents fitted.

I was not and still am not convinced these two vents are adequate however. I think I would be more comfy with direct clam shell type vents on the hull side but maybe I am over worrying ? Do permanent tanks and fuel fill / supply hoses "leak" fumes even ? Or will the two fitted vents be enough to air out that compartment ?

Marc

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Re: Permanent Gas Tank Compartment Venting

Post by fallguy1000 »

blueflood wrote: Wed Dec 14, 2022 12:09 pm Hi all,

I was just wondering what kind of venting my permanent gas tank compartment needs ? The custom built 12 gal tank is vented up the the cabin roof via a standard Attwood gas tank vent and all properly wired and plumbed.

All fuel vents must vent overboard. This means below the gunwhale and outside. ABYC is clear on the matter. A fuel vent that comes up to a roof may leak vapors back down to a cockpit and would not be allowed. Another use of the fuel vent is to avoid overfilling. This is done by keeping the vent just below the fill. A third issue with roof venting is a swan neck is used to prevent watwr from entering the fuel system. A long line running upwards to a roof would not likely have the swan neck and also be subject to condensation as roof heats by day and cools at night more than a gunwhale line which is shorter. Not to mention the swan neck takes care of hose end condensation.


The compartment where the tank sits under sole is vented via two tubes (one on either side of the tank at bottom corners) and routed via tubes out to the side deck also with Attwood fuel vents fitted.

The ABYC is less clear on this requirement. What you have is good and exceeds the rules. I can look for citations for you, but don't see the need.

I was not and still am not convinced these two vents are adequate however. I think I would be more comfy with direct clam shell type vents on the hull side but maybe I am over worrying ? Do permanent tanks and fuel fill / supply hoses "leak" fumes even ? Or will the two fitted vents be enough to air out that compartment ?

Marc
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blueflood
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Re: Permanent Gas Tank Compartment Venting

Post by blueflood »

Hi Dan, thanks for this.

All fuel vents must vent overboard. This means below the gunwale and outside. ABYC is clear on the matter. A fuel vent that comes up to a roof may leak vapors back down to a cockpit and would not be allowed.

I never read anything about this during my build. Even the surveyor never picked this up and is a drag to change now but ABYC is clear. Surgery this spring. And I thought the other vents was my main issue :roll: :lol:

So vent situated below the gunwale and directly outside it is. (or keep using the portables and forget it all)

Marc

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Re: Permanent Gas Tank Compartment Venting

Post by Jaysen »

As has been stated a few times, ABYC is not enforced for non-commercial builds (and not always for commercial builds). Unless you have a very compelling reason, I’d wait until there evidence that you have a real problem.
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blueflood
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Re: Permanent Gas Tank Compartment Venting

Post by blueflood »

Hi Jaysen,

Yes I realize but the boat was constructed with (as much) to ABYC and it bugs me that this is incorrect. I'll look at the boat later as it is under a tarp and being - 10 deg out. Access to yank things out and redo is tight enough around the hose going up. .

I tend to over analyze things or worry too much about a perceived problem - that's my problem :lol:

Marc
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Re: Permanent Gas Tank Compartment Venting

Post by fallguy1000 »

I will try to copy paste ABYC, but venting as indicated is not what I would have done.
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fallguy1000
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Re: Permanent Gas Tank Compartment Venting

Post by fallguy1000 »

I was unable to find anything for public use from H-24 which is the relevant ABYC code.

Nothing you have done violates the premise of H-24, with the exception of fuel vapors and where they go...

I will warn you that any fuel tank ventilation is supposed to be 15" minimum from the compartment vents. This is to prevent backflow from a warming fuel tank to somehow enter the boat. So, the premise is all the same.

The swan neck; the proximity to the fill, the length of the vent line are all best practice measures and not governed. However, I would make darn sure water cannot enter my fuel vent, best practice or not..so if the thing exits a roof; I would wonder how it would not be subject to ingress..
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Re: Permanent Gas Tank Compartment Venting

Post by TomW1 »

Are we talking apples and oranges here. The fuel tank has a vent that must be vented out the side of the boat, so no fumes are introduced inside the hull. The compartment holding the gas tank no longer needs to be vented as the tanks must be built to be impermeable along with hoses and fittings per H-24 as fallguy found. Here are the fuel tank vent hardware available through the store here https://www.boatbuildercentral.com/prod ... rap-vents/ most will not allow water into the vent line. If you want to vent the compartment you need air entering at the bottom of the compartment and exiting at the top of the compartment. This provides a circular rotation of the air in the compartment. Put the vents at 180 degrees not opposite corners for best circulation.

I had an older 40G poly tank and could never smell fumes coming out of the vents.

Tom
Last edited by TomW1 on Wed Dec 14, 2022 5:47 pm, edited 2 times in total.
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fallguy1000
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Re: Permanent Gas Tank Compartment Venting

Post by fallguy1000 »

TomW1 wrote: Wed Dec 14, 2022 5:19 pm Are we talking apples and oranges here. The fuel tank has a vent that must be vented out the side of the boat, so no fumes are introduced inside the hull. The compartment holding the gas tank no longer needs to be vented as the tanks must be built to be impermeable along with hoses and fittings per H-24 as fallguy found. Here are the vent hardware available through the store here most will not allow water into the vent line. If you want to vent the compartment you need air entering at the bottom of the compartment and exiting at the top of the compartment. This provides a circular rotation of the air in the compartment. Put the vents at 180 degrees not opposite corners for best circulation.

I had an older 40G poly tank and could never smell fumes coming out of the vents.

Tom
Not apples and oranges.

He wants to vent the fuel tank COMPARTMENT and the tank itself. He is venting the tank itself through the cabin roof, not out the side with a swan neck exit.

The compartment vents must be 15" from the tank vent per abyc. I am telling him this based on the premise that he is moving the fuel tank vent so he doesn't violate the 15" rule.
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blueflood
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Re: Permanent Gas Tank Compartment Venting

Post by blueflood »

Hi Dan, Tom,

Correct, the gas tank is vented via a 5/8" hose going up thru the roof. Alum gas tank has an elbow welded on the top for the vent hose.

The gas tank compartment is vented via two hoses, one each side of the tank at the bottom corners and leading up to the deck next to the cabin. This should have been different i.e. one at bottom and one on top of the tank compartment to give that circular air rotation vs both at bottom.

All three hoses are fitted with an Attwood splash resistant fuel vent like this;
http://old.attwoodmarine.com/store/prod ... Straight01

I won't think about this any more and just use the boat as it is.

Marc

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