Early Toy Boat 2


Boat-buying season is coming up! Winter and early Spring could mean boat shows and a lighter checkbook are in your future.

If you’re a first-time boat owner, here are 5 things I learned about boats that you really ought to know…Trust me!

They aren’t meant to talk you out of buying a boat. They’re meant to give you a “heads up” on some things that could come back to bite you if you’re not keeping an eye out…

And by the way…here are 5 Things I Learned About Trailers.

No. 1 – Fuel tanks are not forever

The ocean is a hostile environment, especially for mechanical things. Salt water intrusion can wreak havoc on your boat in ways you probably can’t imagine. 

Your fuel tank is one of the areas to keep your eye on. If your boat has an aluminum under-deck fuel tank, it is not unusual to have to replace it every 10-15 years. Note: if your boat has a polyethylene fuel tank, you can safely ignore the rest of this topic. 

Death from the Outside!

The culprit is something called “crevice corrosion“. There are lots of articles that describe the chemistry behind it, so we’re not going to cover it here. One of the best “regular English” articles on this topic is available on yachtsurvey.com. David Pascoe does an excellent job explaining the various types of corrosion.

Suffice to say that it results from salt water being trapped in a small crevice, between one or more surfaces that can corrode (like aluminum or steel), that has little to no exposure to the atmosphere. It often occurs with stainless screws or aluminum fittings in your hull. Or, if your boat has a below-deck fuel tank, it can occur between the aluminum fuel tank and the foam flotation in the hull, or a hull stringer. If you have an above deck aluminum tank, that would be where your tank rests on the deck.

It is a slow-moving process that could takes years do its damage. If you have an above-deck aluminum fuel tank, you can avoid the problem by periodically checking under the tank and letting it air dry. For under-deck tank installs, it’s not that simple

How Does this Happen?

Many boat manufacturers add flotation by injecting an expanding polyurethane foam into the void spaces in their hulls. In under-deck fuel tank installations, the foam is often used to fix the fuel tank in place as well. This would be OK if the tank was completely sealed by the foam, and there was no way for water to reach the tank.

However, in practice, the top of the tank has to be left uncovered to allow connection of the filler and engine fuel hoses and the wires for the fuel level sensor. Add a little vibration and expansion / contraction due to heat or cold, and you have crevices between the tank and the foam.

Sooner or later the crevices will come into contact with salt water. The water might come from the bilge, or through rod holders, deck plates or hatches. After that, it’s just a matter of time until trouble appears.

Toy Boat 2 – A Case Study

Toy Boat 2's old tank.

Note the water leaking from the side! (Click for a larger image)

In the case of Toy Boat 2, that took about 15 years. We first noticed a strong gasoline smell, which we thought was due to leaky fuel hoses. After replacing the hoses, the smell did not go away, and we started seeing an oily sheen in the bilge water. Then we actually started getting measurable fuel in the bilge.

We finally faced up to the fact that we needed a new fuel tank, and had the tank replaced. The shop sent us a few pictures of the old tank after it was removed, and you can see pretty clearly where the holes were. I guess we were lucky that the range of explosive fuel/air mix is actually pretty narrow!

Death from the Inside?

A lot has been written about fuel system problems in boats using E10 gasoline (gasoline that has 10% ethanol mixed in). One of the issues identified early on was that the ethanol in E10 gasoline is capable of dissolving the resins used in fiberglass gas tanks. Fortunately for skiff owners, fiberglass tanks are rare in smaller boats. 

What to do?

After the tank was removed, before cleanup

After the tank was removed, before cleanup. (Click for a larger image)

If you keep your boat long enough, you will be forced to replace the gas tank. On boats with above-deck fuel tanks, that’s easy.

If you have an under-deck tank (like most fiberglass skiffs), you will be forced to cut the deck open to get to the tank. Because the foam flotation surrounding the tank will probably be soaked with water and gas, it will also have to be removed and replaced. Then the deck will need to be put back into place, and the cut repaired.

On some skiffs, the tank is mounted beneath a removable hatch, but this is uncommon, as it increases the hull cost quite a bit. And even if you have easy access to the tank, the other repair work will still have to be done.

Any way you look at it, this is major surgery, and will not be cheap. Because you’re dealing with lots of gasoline and some pretty complex fiberglass work, most people leave the work to professionals

Do Not Repeat the Sins of the Past 

Deck cut for tank replacement

Ready to pop the deck out and start the tank replacement. (Click for a larger image)

If you can find a polyethylene replacement tank that is the right size and shape, that will be the easiest route out. Polyethylene is not affected by crevice corrosion, and is unaffected by E10 or higher fuels. Polyethylene tanks can be foamed back in place like the original tank.

If you have to use an aluminum replacement tank, make sure the new tank is mounted with a gap around the tank that will allow water to drip off and air to circulate around the tank. The tank should also be mounted off the bottom of the hull, in order to allow bilge water to pass underneath. 

On Toy Boat 2, we had to go with an aluminum replacement tank. In addition to the above precautions, our installer covered the outside of the tank with an industrial plastic coating to help shed water.