Portable fuel tank ventilation

I am building a Sam Devlin "Dipper" This boat has a motor well with an enclosed area each side that is about 2' x 2' x 2'. This is a good size to put in a portable fuel tank and build a seat on top. My question is how much ventilation and what's the best way to ventilate this 8 cubic feet of enclose space with a portable fuel tank? Thanks.

 

Hi Kaladar, welcome aboard

I will refer you here to two sources essential for any backyard boatbuilder in Canada.

The first is the Construction Standards for Small Vessels - TP1332. This national standard applies to all boats under 15 tons / 12 passenger capacity except for commercial fishboats and a few specialized craft. You HAVE to meet or exceed its requirements (note that they are easy to meet with a bit of common sense).
http://www.tc.gc.ca/MarineSafety/tp/TP1332/menu.htm

The second is an American site that is still very applicable to Canadian builders. It's a great resource for hundreds of these common technical questions that come up during a build. Thanks to regular bd.net contributor "Ike" for the compilation:
http://newboatbuilders.com/

In your specific case, I presume you are talking about a purpose-built, properly certified plastic or aluminum portable tank of the type commonly used with small outboards. Refer to TP1332 section 6:

If you want to build the compartment with less than 0.34 square metres of vent area per cubic metre , you must install a ventilation system per TP1332 6.3.4.
Your 2'x2'x2' compartment would be 0.23 cubic metres, thus it needs 0.08 square metres of open, unobstructed vent area.
I would note also that if you are using portable tanks, the enclosure must be designed so they can be removed for filling.

 

15 square inches of open area for each cubic foot of volume for natural ventilation. 15 X 8 = 120 sq inches or 774.24 sq cm or just about the 0.08 sq meters from Matts post

 

It is worth noting that Canadian and American small craft standards are quite closely harmonized on most points
Where you will likely see a notable difference between the Canadian and American standards, Kaladar, is when it comes time to get your boat's capacity plate. Canucks make different assumptions than Yanks do regarding how much stuff can be safely carried by how much boat, and how much junk the average crew member will bring with him.

 

Thanks for the answers all.
I also recently found out that in Canada the Small Vessel Label program has been discontinued , see http://www.tc.gc.ca/BoatingSafety/news/discont-single-vessel-label-prgm.htm

You are still required to construct to TP1332 , but not required to obtain a Single Vessel Label or a Hull Identification Number.