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Subject: TWL: Re: Aluminum Fuel Tanks
From: Ellis Simon (esimon@XXX.XXX)
Date: Thu Mar 29 2001 - 06:26:33 EST
The points regarding aluminum tank welds are well taken. But there is
another failure mode that IMHO is more common. Aluminum is susceptible to
corrosion. I lost two fuel tanks due to corrosion from the outside in.
The tanks were installed (in 1985) on a shelf with wooden battens holding
the base of the tanks in place. Some material, I suspect sawdust, found
its way between batten and tank. Some water soaked this material, and 10
years later, there was a dime sized penetration of the tank. When I got
the tanks out, gentle pressure with a screwdriver went right through the
aluminum oxide. While having new tanks fabricated (of aluminum), I saw
many junker tanks at the fabricator, all with the same outside-in corrosion
holes.
The Coast Guard recognized this hazard in the ten year interim, and issued
a directive that requires aluminum fuel tanks to be surrounded by
non-water-absorbing materials only. The trouble with this is that it does
not prevent someone from drilling a hole in wood above a tank and creating
the same problem.
I used the full Awlgrip process on the exterior of the new tanks. Then I
glued 2" x 2" x.125" rubber pads (in a checkerboard pattern) all over the
bottom of the tank and around the lower sides. The tanks were installed
with battens that are on spacers, so any errant water can drain out. Many
tank installations were done with just a couple of strips of neoprene to
hold the tank up off the shelf and away from battens, etc. Tanks flex when
filled with hundreds of pounds of fuel, and contact water absorbent
materials anyway.
If you have aluminum tanks, I urge you to assure that the spaces around the
tanks are scrupulously clean and dry. I was fortunate, I discovered the
problem while converting the boat from gasoline to diesel. Both engines
and the generator were out, so the tank replacement only added a couple of
manweeks and a thousand dollars to the project.
BTW, I found that my tanks were completely unsecured at the top, which
could have allowed a thousand pounds of fuel to slam back and forth in a
beam sea.
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