Gasoline Fumes Under Deck

My front deck came out so well that I decided I would like to put one over the rear bench as well.

This deck will not be for standing on and fishing, more for aesthetics and I will add a couple hatch doors so the area behind the rear bench can be used as secure storage.

I'd also like to keep my gas tank under the deck and out of the way, but had some concerns about fumes building up in there. Is that a valid concern?

The rear bench seat (which the deck will go on top of) does not go all the way to the floor, there is 3-4" of space there. That will provide some ventilation. There will also be notches cut near the transom for fuel lines and wiring that will provide some ventilation as well.

Put in both a fwd & rear facing scupper (air funnel).

You can buy these pretty cheap.

If you don't have a spark source in the same compartment, the fire risk is low.

I'm not an expert and don't want to give you bad info. However, I agree that a vent would seem like a real good idea. I would think that a vent on top of your deck/hatch coupled with the space under the bench would provide for a good airflow. I think you are smart to have concerns about this, particularly if the space is going to be shared with a battery, elect connections, and/or bilge pump.

Thinking about this, I wondered if any portable tank with a vented cap is intended to be used as an under deck tank. Logically, I would think not, but then it looks like lots of bass boats have portable tanks in enclosed compartments. I assume those compartments are vented. I wonder if they are partitioned off (probably not). Hopefully some of the bass boat guys will weigh in.

The new EPA tanks vent a lot, just got two under deck and the 2 " scupper opposing vents were not adequate. So I put in a heavy expanded metal grate...no problem. Wanted 1" X 2 " angle frame, all the shop had was thick wall tube and very heavy mesh. Won't break this one. These are 6 gallon each. Also made a cut-out for the anchor line, the anchors sit between the tanks when under way. If I want dry storage, have two sizes of dry bags that fold tight and drop in behind the rear seat or on top of the fuel tanks. The batteries are in the full seat box extended deck. I don't want any electricity near the tanks!

Gas fumes are heavy so remember to vent the bottom. Batteries release light hydrogen and get vented on the top.

Have six "vents" via the rib drain channels on the bottom that are open, also lets spills out. When it got warm or when in tow, you would get overwhelmed six feet away from the boat by the fumes. These new tanks swell and then vent. I don't like them.

Since the grate went in last week, there is no build-up of fumes and the tanks/fuel stay cooler.