The Trouble with Tanks
Even if you don’t have an aluminum boat, you probably have aluminum fuel tanks. While these can be perfectly safe, the U.S. Coast Guard noticed a recurring problem with leaking tanks. So it asked Underwriters Laboratory to see why. Not surprisingly, UL found that corrosion caused 92 percent of the failures. Most of it was caused by how the tanks were installed.
In general, aluminum tanks should be left bare. Paint can help. But if it’s not properly applied, it wears away, scratches or peels off, and moisture gets under the paint, concentrating and accelerating corrosion.
The most common fittings used in fuel systems are usually made from brass. Screw one of these directly into an aluminum tank and add some moisture, and you’ve got serious galvanic corrosion. Isolate these fittings from the tank by using 300-series stainless-steel washers or adapters.
The tank’s supports must not be moisture-absorbent, such as carpeting is. Suitable materials are stiff neoprene, Teflon or any high-density plastic. Water should drain from all tank surfaces when the boat is at rest; the bottom of the tank must be at least a quarter-inch above the hull to let air circulate and above the level normally reached by bilge water. The European standard says “no less than 25 mm [1 inch] above the top of the bilge pump inlet or the bilge pump automatic float switch.”
A fuel tank should be accessible for relatively easy inspection via a screwed-down, caulked hatch, but that is often not the case. Many builders install tanks so that a saw is needed for inspection or replacement. Too bad.