PART TWO: FUEL SYSTEMS
The Danger of Foam Burials
Many small production craft are built with aluminum fuel tanks installed buried in sprayed-in-place foam. This is per-
mitted with an exact reading of CFR Yacht, but it is poor construction. You can’t properly inspect such a tank for cor-
rosion or leaks, you can’t remove or replace the tank without major hull or deck surgery, and I’ve yet to hear of such
an installation that didn’t end up with at least some water accumulated between the foam and the tank surface—bad
news! Over time, leaks, fires, and explosions on such craft are virtually guaranteed.
This book makes it clear that burying aluminum tanks in foam is poor practice; however, since this practice is per-
mitted under the CFR, you will find aluminum tanks in many smaller production boats buried in foam in the bilge or in
some other compartment. If you are surveying or working on a boat with such an installation, you need to do your
best to inspect the tank for leaks. A pressure test may be the only option. You should also warn of potential corrosion
problems in any survey or condition reports.
Note that no tank of any ferrous material may be buried in foam under any circumstances. If you can, test the tank
with a magnet to determine if it is steel (though this will not identify stainless steel, which is no more acceptable than
any other ferrous metal in this application). If it is, the tank must be removed and replaced.
Aluminum, plastic, and fiberglass are nonferrous. For this reason, tanks of these materials can be accepted if buried
in foam (though, once again, not recommended). Note that fiberglass gasoline tanks are now suspect, as described in
the sidebar on page 87.
The CFR terms the foam: “cellular plastic used to encase fuel tanks.” Any such foam (cellular plastic) must not change
volume by more than 5 percent or dissolve after being immersed in gasoline, diesel, or a 5 percent solution of trisodium
phosphate in water, all for a 24-hour period. The foam cannot absorb more than 0.12 pound of water per square foot
of cut surface (0.58 kg/sq.m of cut surface).Foam-encapsulated fuel tanks (Courtesy ABYC)