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Old 13-12-2019, 06:05   #1
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Ventilation suggestions for fuel tank area?

I need to install ventilation in the fuel tank area. The tanks (meeting all standards and from brand new) emit a dizzying odor. Fuel permeates through them and the tank manufacturer says it's normal. Well it's not normal to me. So I'm going to enclose them and ventilate.

What sort of deck/topsides vent is right for this situation? Prefer natural draft. Also not wanting to ruin the looks of the boat with some big vent.

I have easy access to the outboard topsides, inboard topsides (Catamaran) and the aft cockpit area. There is also a day bed over the tanks up at deck level.

Basically, they are under the daybed in a Gunboat 48 Catamaran. Down in the Port hull all the way down in the bilge. Here's a pic for clarity.

See the dark blue daybed? Mine is wider and continues over the Port hull. Down in the Port hull bilge are the stinky tanks.
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Old 13-12-2019, 06:30   #2
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Re: Ventilation suggestions for fuel tank area?

I'm not sure that you are going to get rid of the stink with passive ventilation only, but maybe you can include active ventilation with passive.

Start with the largest, up to about 5" diameter hose that you can run from the compartment to the top. Finish the top with a dorade box, such that you will not send water down to the compartment. Install in the hose a vent fan of the right diamenter, 4" fans being popular. You want the fan to suck air out of the compartment, not push it in. Then, be sure that the compartment is not so tight that air cannot get in, hence to be sucked out.

If the box is tight, you could try a somewhat more expensive but sophisticated route. Concentric stanless steel flexible hoses are sold for on-board heaters. Air comes down from the deck between the outer and the inner hoses, and the comes out through the inner hose. That's a closed system topped off with a stainless steel mushroom.
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Old 13-12-2019, 07:18   #3
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Re: Ventilation suggestions for fuel tank area?

Quote:
Originally Posted by Chotu View Post
I need to install ventilation in the fuel tank area. The tanks (meeting all standards and from brand new) emit a dizzying odor. Fuel permeates through them and the tank manufacturer says it's normal. Well it's not normal to me. So I'm going to enclose them and ventilate.

What sort of deck/topsides vent is right for this situation? Prefer natural draft. Also not wanting to ruin the looks of the boat with some big vent.

I have easy access to the outboard topsides, inboard topsides (Catamaran) and the aft cockpit area. There is also a day bed over the tanks up at deck level.

Basically, they are under the daybed in a Gunboat 48 Catamaran. Down in the Port hull all the way down in the bilge. Here's a pic for clarity.

See the dark blue daybed? Mine is wider and continues over the Port hull. Down in the Port hull bilge are the stinky tanks.
diesel or gasoline fumes?
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Old 13-12-2019, 07:23   #4
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Re: Ventilation suggestions for fuel tank area?

OMG. Please tell me this is not gasoline. Whole different issue.

More broadly stated, I resent a manufacturer installing a fuel tank the bleeds fumes and then shrugs and tells you to suck it up. A very basic standard should be that fuel tanks keep all the fuel inside. Any chance you can solve the problem by replacing the tank?
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Old 13-12-2019, 09:23   #5
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Re: Ventilation suggestions for fuel tank area?

are you sure there is no leftover spill residue..? or leaking at connections? or a split or pinhole in the tank..? assuming poly tanks here.

Fuel tanks manufactured for the purpose should not permeate odour. And especially not a dizzying amount. Something is wrong.
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Old 13-12-2019, 10:39   #6
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Re: Ventilation suggestions for fuel tank area?

Gasoline fumes but not enough to be an issue for anything other than indoor air quality.

Moller below deck 50 gallon gasoline tanks, proper ABYC installation and of course all new houses and everything. Brand new boat.

I've read on plenty of forums these tanks just do this.
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Old 13-12-2019, 10:42   #7
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Re: Ventilation suggestions for fuel tank area?

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are you sure there is no leftover spill residue..? or leaking at connections? or a split or pinhole in the tank..? assuming poly tanks here.

Fuel tanks manufactured for the purpose should not permeate odour. And especially not a dizzying amount. Something is wrong.
Everything is perfect. Except that tanks from the manufacturer do and are known to permeate. Ridiculous in my opinion, but it's the only ABYC compliant way to do it. No other tank type is permitted.
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Old 13-12-2019, 10:47   #8
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Re: Ventilation suggestions for fuel tank area?

I find that very strange. I have a Moeller tank for gasoline and there is no permeation odour.

Is there a technical difference between 'odour' and 'fumes'..? I can't see any amount of gasoline in the air being safe.
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Old 13-12-2019, 10:49   #9
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Re: Ventilation suggestions for fuel tank area?

IIRC there were new standards for permeation enacted in 2010?/2012..? if the tanks are earlier than this, they may be prone to more permeation than is now acceptable.
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Old 13-12-2019, 11:26   #10
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Re: Ventilation suggestions for fuel tank area?

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I find that very strange. I have a Moeller tank for gasoline and there is no permeation odour.

Is there a technical difference between 'odour' and 'fumes'..? I can't see any amount of gasoline in the air being safe.
Is it a below decks poly tank? Because their above deck tanks don't do it.

And yes. I'd say "odor" but it gets miserable when it's hot and there is zero ventilation.

And of course it takes very specific amounts of fuel in the air to cause a problem.
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Old 13-12-2019, 11:26   #11
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Re: Ventilation suggestions for fuel tank area?

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Originally Posted by sailortype View Post
IIRC there were new standards for permeation enacted in 2010?/2012..? if the tanks are earlier than this, they may be prone to more permeation than is now acceptable.
2015 tanks.
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Old 13-12-2019, 11:32   #12
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Re: Ventilation suggestions for fuel tank area?

My other ventilation thoughts?

Don't want to get too derailed on the cause. Need to isolate and ventilate.
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Old 13-12-2019, 11:46   #13
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Re: Ventilation suggestions for fuel tank area?

yes,,, sailboat tank.. below decks. Not a whiff of gas odour
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Old 13-12-2019, 12:01   #14
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Re: Ventilation suggestions for fuel tank area?

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yes,,, sailboat tank.. below decks. Not a whiff of gas odour
Wow. I guess itís just hit or miss. Certainly other people online have talked about the same problem Iím having. Count yourself lucky youíre not having the problem. I think a small amount of ventilation would take care of it, so maybe if you already have ventilation in the area the tank is and you are not noticing it?

Otherwise, count yourself lucky you didnít get the batch of tanks I have.
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Old 13-12-2019, 15:51   #15
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Re: Ventilation suggestions for fuel tank area?

I made mine out of fuel hoe running through a PVC re-openable conduit to a simple plastic automotive in-line fuel filter, thence to a flame-stop vermin-proof filter I made from a stainless length of tubing which was stuffed with stainless steel soap-less scouring pads located behind a perforated stainless steel disc. The hose vented in my case below the wing-deck, so any diesel fumes were blown well clear of the vessel hatches or opening port holes.

It is only to stop the pressure build-up of fuel vapour as the temperature rises and falls, and similar systems work with diesel or petrol.

Because fuel vapour is heavier than air, the breather needs to vent well clear of any open hatches
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