So this year I found my alumnium fuel tank leaking and am now in the middle of replaceing it. I have done some research on the fuel tanks and how to mount them, also how NOT to mount them. The one thing I found is NEVER use foam to mount an alumnium tank. The maker of my boat used foam. I was just thinking, Why has NTSB not done anything about this? I just had a recall on my 1999 ford truck for rusty fuel tank mounting straps. Not much I can think of that would be worse than a builge full of gas and the pump cut on. Any ideas on this or am I just way off base?
the US Coast Guard and this organization:
http://abyc.site-ym.com/?
regulate standards for the boating industry
Foaming in Fuel Tanks: (encasing the tank in plastic foam)
Sec. 183.552 Plastic encased fuel tanks: Installation.
(a) Each fuel tank encased in cellular plastic foam or in fiber reinforced plastic must have the connections, fittings, and labels accessible for inspection and maintenance.
(b) If a metallic fuel tank is encased in cellular plastic or in fiber reinforced plastic, water must not collect between the plastic and the surface of the tank or be held against the tank by capillary action.
(c) If the plastic is bonded to the surface of a metallic fuel tank, the adhesive strength of the metal to the plastic bond must exceed the cohesive strength of the plastic.
I believe that foaming a metal tank in place is a death sentence for the tank. Why? Because the foam traps moisture between the foam and the tank. It is that simple. Some builders like to foam tanks in place. It is simple, cushions the tank against impact, and they don't have to build a complicated mounting system for the tank. However, consider the consequences.
The US Coast Guard requires that if you foam a tank in place the strength of the bond of the foam to the tank must be stronger than the foam itself. In other words, a shearing force would break the foam before breaking the bond. In practice this is very difficult to achieve. What happens in reality is that after repeated slamming of the hull, and vibrations from the engine, the bond breaks. This creates a gap between the tank and the foam, and moisture gets trapped around and under the tank. Further, the requirements for tank installation are, no moisture can be trapped on the top of the tank, and the fuel fittings must be accessible. This means if you foam the tank you must leave an area clear of foam around the fittings, or not allow any foam above the top of the tank. Otherwise any moisture on top of the tank gets trapped there by the foam. In practice the above requirements are rarely achieved and the tank corrodes long before its normal life span.
Also consider aluminum tanks. Aluminum tanks are rarely painted because they have a natural aluminum oxide coating that is formed by exposing aluminum to air. This oxide protects them from corrosion. So aluminum tanks should always be mounted with space on all sides and the bottom. To paint aluminum or to bond foam to it, you must remove the aluminum oxide. You are removing the very thing that protects the tank from corrosion.
Plastic tanks on the other hand do not need coatings or paint. They need to be installed so that they will expand a little when first filled. Foam would not allow this expansion. Additionally foam will not adhere well to polyethylene plastic, so it is impractical to foam in a plastic tank.
bob
