Replacing Powerboat Fuel Tank (part 2)

If the tank is aluminum, you will have far fewer choices. If the manufacturer of your boat is still in business, you might be able to purchase a direct replacement tank from them. Don’t look for it to be cheap, however. If your boatbuilder is out of business, there is a slim chance that a marine consignment store may have purchased their old inventory. It’s worth checking, perhaps online.

Failing that, it’s back to the Internet or your favorite boating magazine to find a custom fuel tank builder. There are many of them, and shipping can be expensive, so try to find one near you. Look for a tank maker that builds to ABYC (American Boat & Yacht Council) standards and make sure they pressure-test it. Then go to the bank and take out a loan. You’ll have to take detailed, accurate measurements, and digital photos may help. You can’t ship the old tank to the fabricator to use as a template; UPS and other couriers won’t accept it for shipping. If the shape is complex, you might consider building a replica out of artist’s foam board, tape, and glue, and shipping that to the tank maker. If your fuel is diesel, check your old tank. Diesel engines sometimes have a fuel return line back to the tank. If so, make sure the tank you get has a fitting for that return line.

While you’re waiting for the new tank to arrive, clean out the area where the old tank resided. Clear out all traces of the foam to ready the space for the tank installation. It’s a good time to check the stringers and floors for any structural issues such as rotted or waterlogged wood. If the old tank was foamed in place in a center compartment, there should have been a pipe or conduit installed beneath it to allow easy movement of bilge water between the compartments forward and aft of the tank. If the pipe or conduit needs to be replaced, PVC pipe works well. You can cut a piece of PVC pipe in half and glue it in place, concave side down. Be careful to seal all the edges and ends so the new foam won’t sneak in and seal off the channel, and so that bilge water won’t come in contact with the foam. Be careful to maintain the original mounting height of the fuel tank. Clearance is often limited under the deck area, and you will need that clearance for running the fuel hoses. Tanks are often secured to the stringers or placed on temporary wood supports. This is just to properly locate the tank, not to fully support it and its load of fuel.

The foam around the tank is used to support the tank and keep it firmly in place. Foam with a 4-pound density is recommended for use around fuel tanks. The foam comes as two separate liquids, Part A and Part B. Mixing the two together starts a chemical reaction that produces the foam. This reaction happens quickly! You have a limited time to mix the foam and pour it into place. Be sure to follow the foam supplier’s recommendation for the proper temperature range for application. Colder temperatures mean slower foaming and longer hardening times.

Mix the foam in small batches using a wire mixer in a drill to ensure that both components are thoroughly mixed. Use disposable containers. I usually measure out several sets of small containers so I can mix batches without having to go back and pour out more chemicals. Start by pouring the liquid foam under the tank. The idea is to fill all the voids under the tank. Pour a batch and then wait fifteen to twenty minutes for the foam to fully expand and harden. If you pour too much foam at once, it could push the tank out of position or even cave the tank in or damage the boat’s structure. Once the area under the tank is filled and the foam has hardened, you can pour along the sides and ends of the tank. Try to replicate the same distribution and amount of foam as it was installed around the original tank. Be careful to keep access to the fuel sender and the tank inlet and outlets clear of foam. If the foam rises above the level of the stringers or deck mounts, let it harden and then trim it level with a handsaw, being careful to avoid cutting your new tank.

Once the foam has finished hardening, you can install the new fuel lines. Do not use just any hose you find at a building supply store. Fuel line hoses must be rated for use with fuel and must be installed with two hose clamps at every connection. Replace the deck and finish it off.