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Another Aluminum Fuel Tank Story

Inspector

New member
OK, way back in 2011 I melted some pistons in the 502s in my 1997 283 and pulled the engines (not the point of this post). While draining the fuel from the tank I noticed a fuel smell inside the boat and ended up cutting the floor and removing the tank. There were randomly located pitted areas in the tank of which one of them was all the way through (the source of the fuel leak).

Well 9 years later I am getting back to this project. The plan is to grind out and weld in the pitted areas and reinstall the same tank (with larger fuel pickup lines and bungs for fuel returns).

My questions are about the best method for installing the tank. I have been reading through posts on this site and others looking for information on installing an aluminum fuel tank and on most sites there is an ongoing battle as to weather or not expanding foam should be used around the tank, especially in a performance boat capable of higher speeds.

The 97 had foam surrounding the tank on the sides and bottom except for the rear bottom of the tank. The hull structure (stringers and bulkheads) surrounding the tank is sealed with no drain at the rear (I believe this is in case of a tank leak, the fuel won't get into the engine compartment). The cockpit floor above the tank has an opening under the rear seat which was always open (no cover and no lip around the edge to guide water away from draining into the tank compartment). So to me it looks like Checkmate sold the boat with an easy access for water to get into the tank area and no way for it to get out... Hmmm...

My concerns about not foaming the tank in are about tank support. Lateral support could easily be solved with plastic inserts on each side. But vertical support of the tank concerns me. Does the bottom wall of the aluminum tank flex during harsh impacts and the weight of the fuel? (Pretty sue it will if unsupported) If you install plastic strips between the bottom of the tank and the hull these will only support the tank locally and not spread the load as complete coverage foam would give (although I am not sure the foam doesn't compress with time and give no support).

Foam in place or plastic strips?

If plastic is best, should it contact the tank and hull when the tabs on the sides of the tank are screwed to the stringers or should there be a minimal gap or even another material between the plastic and hull (RTV, 5200, high density closed cell foam)? Also what is the correct width and placing of plastic strips on a 130 gallon tank?

Thanks.
 

Jimway

Well-known member
Here is a thread that could also go up in smoke. Never repair a leaking fuel tank. Replace it or have one made. Study coast guard regs and boat building regs concerning inboard gasoline tanks, what they can be made of and how to install. Aluminum has some peculiar characteristics that must be taken into account. Foaming one in will get you right back to a leak eventually. Fittings and such can be safely repaired to a point. Depending on type of tank where it goes as far as bow or stern or port or starboard, maybe you can build a cradle for it that would support the sides and bottom.
 
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