Ventilation suggestions for fuel tank area?

[Chotu]

Originally Posted by Mike Banks

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

Thanks for that input. I was thinking about going below the bridge deck also. Just so it looks nicer. Maybe put one of those clam shells that goes facing a stern to allow some of the air passing through to suck out the fumes. I don’t like opening up anything forward of the water tight bulkhead, but I’m not seeing any other way to do this.

[David B]

Originally Posted by Chotu

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.

For what it's worth, this does not sound at all correct. Our fuel tank is plastic, and directly under the starboard berth - sleeping in there, you are effectively lying right on top of the fuel tank. There is absolutely no odour at all, even when you lift the board that separates the mattress from the tank. There must be an issue there somewhere to cause any odour, let alone the level you are describing.

[Chotu]

Originally Posted by David B

For what it's worth, this does not sound at all correct. Our fuel tank is plastic, and directly under the starboard berth - sleeping in there, you are effectively lying right on top of the fuel tank. There is absolutely no odour at all, even when you lift the board that separates the mattress from the tank. There must be an issue there somewhere to cause any odour, let alone the level you are describing.

I’m not aware that a Beneteau Oceanis comes with Moller below decks gasoline tanks. Does it?

Don’t you have whatever french tanks they use?

Don’t you have Diesel? That doesn’t permeate.

[David B]

Originally Posted by Chotu

I’m not aware that a Beneteau Oceanis comes with Moller below decks gasoline tanks. Does it?

Don’t you have whatever french tanks they use?

Don’t you have Diesel? That doesn’t permeate.

Petrol or diesel, it does permeate, and with petrol, explosive fumes are all the more concern. If you want a petrol comparison, the Bayliner my brother-in-law has at our holiday home also does not have fumes (I put my head in that area regularly in service and inspection work for him), and again, that is a plastic tank.

It just does not sound right to me.

[Chotu]

Originally Posted by David B

Petrol or diesel, it does permeate, and with petrol, explosive fumes are all the more concern. If you want a petrol comparison, the Bayliner my brother-in-law has at our holiday home also does not have fumes (I put my head in that area regularly in service and inspection work for him), and again, that is a plastic tank.

It just does not sound right to me.

Diesel has larger molecules and just doesn’t create the vapor pressure the gasoline does. Does your brother in law’s Bayliner have a Moller poly tank from 2014 or so?

Of course something is wrong. These tanks are junk. So I have to fix that situation.

[David B]

Originally Posted by Chotu

Diesel has larger molecules and just doesn’t create the vapor pressure the gasoline does. Does your brother in law’s Bayliner have a Moller poly tank from 2014 or so?

Of course something is wrong. These tanks are junk. So I have to fix that situation.

2014 would be about the vintage. Next time we are down there, I will check the brand. All I can tell you now is that it's translucent, rather than the black tank we have on the Beneteau.

[clockwork orange]

You are not alone. I installed two Moller below deck gasoline tanks in my Gemini cat in about 2012 and they also permeate. Fortunately they are not in the accommodation but are in the lazzarettes and it is quite mild but it is there.

[Chotu]

For those that think poly below decks tanks don't permeate fuel odors, I've recently stumbled upon the regulations to ventilate places they are enclosed.

https://www.uscgboating.org/regulati...ENTILATION.pdf

I've had this handbook for the whole build. Must have missed this part or assumed tanks would be impermeable.