My apologies for not posting in a few weeks. Travel brought me to some places where internet access was quite limited or non-existent. That is both a frustration and a comfort in this day and age. Frustration when you have work to do but a nice quaint touch when you feel like you want to be left alone for a while. Anyhow I’m back at the boatyard and yesterday I had a chance to shoot a couple of photos of a job the gang here is working on, a leaking gasoline fuel tank replacement. What’s interesting to me about this job is that the tank was actually installed the last time (1988 boat, second fuel tank replacement) in complete accordance with ABYC Standard H-24 and it still failed prematurely. Let’s talk about why because whether you own a power boat or a sailboat, this little nuance could affect you and be the cause of a really dangerous situation at worst and at the least be the cause of a really expensive repair.
The aluminum fuel tank is dated according to the USCG required label shown above as being manufactured in March of 2002. Now that doesn’t necessarily mean it was replaced in 2002, but it does tell us the tank is over ten years old. Now, most of us in the field will tell you that the average life expectancy of an aluminum fuel tank is in the 15-20 year range on average. So for sure this one failed prematurely. Directly to the left of the yellow tape in the photo above you can see a small brown spot. It’s the pinhole where the leak occurred. The rest of the corrosion on the bottom of the tank, which is what you are looking at, is quite excessive. Now a look at the installation and why it failed.
The tank was resting on a series of 1/4″ thick Delran strips that had been glued to the bottom of the tank with 3M 5200 or similar. This complies with the recommendations in ABYC H-24. The idea is to provide an air space under the tank so that water won’t get trapped between the mounting surface and the aluminum tank. The installer had done all that just fine. The problem here was that there was a wooden strip that was installed on the mounting surface that was run the length of the tank at the lower edge to help position the tank on it’s mounting surface. Water had found its was under the tank between the Delran strips and became trapped by the wooden strip. The net result? What we know as Poultice corrosion set in and perforated the fuel tank.
So, what’s the lesson here? You need to make sure that with an aluminum fuel tank it is surrounded by air and will never risk sitting in standing water under **ANY **circumstances. If positioning blocks are needed as part of the installation, make sure they are not continuous and perhaps even have some limber holes drilled in them so water won’t get trapped.