Maintaining an Aluminum Hull

“Steve and Linda, prefer natural aluminum because it doesn’t demand the incessant maintenance of a painted boat. In fact, the aluminum oxide that eventually coats the exterior is tougher than any paint.”
–Yachting Magazine

We’ve built about half our clients’ (custom) boats in aluminum, and half in fiberglass. During the material selection process, we’re always asked about the maintenance of both.

Each material has its good sides and things to be watched.

In the process leading up to building FPB series, we looked hard at both materials. We even went so far as to do a very detailed engineering study in fiberglass going through the process of sample laminates, types of materials, varieties of cores, etc. In the end we went to aluminum for several reasons. One reason is that we like the way unpainted aluminum looks – the “workboat” effect is pleasing to our eye, and we think stands out less in third world countries than a high-gloss finish. Metal gives you the ability to have integral fuel tanks much more efficiently than does fiberglass. Finally, in extremis, if we make a mistake with navigation or are involved in a collision, the metal boat is likely to survive more abuse than fiberglass.

When we did our first aluminum hull, back in 1980, we did not know nearly as much as we do now about the material or its longevity, or for that matter how to construct in such a way as to keep the aluminum happy in old age. We’ve learned a lot along the way. But at the end of the day, our earliest boats are still floating, some in spite of severe neglect at points in their lives. So we think that aluminum will tolerate a lot more inattention in the maintenance department than we realized 20 years ago.

What do we do for maintenance with an aluminum hull? Let’s start with the exterior. What we do (or what we don’t do) is a function of aesthetics. If we want to stay low key, we do nothing. Over the first nine months to a year that we’re in the water, the aluminum will take on a dull patina as it self-anodizes. It will actually create a self-protecting surface. We can leave that for the rest of the boat’s life. Or, if we get tired of the look, the bare metal can be polished using Scotchbrite grinding pads. We had Beowulf polished this way in the US – topsides and coamings for about US$5000. This also included using a wire wheel on the deck to roughen and brighten the treadplate finish. This is a fraction of the maintenance required for a painted hull. We could put the boat in the yard to polish every six months and still be many thousands of dollars ahead of the game financially!

Bottom paint is a different story. In the past we’ve used TBTF paints, which are compatible with aluminum. These are now banned in most parts of the world. The workboats and commercial fish boats have switched to a new system using a very high quality series of barrier coats, one of which acts as an anode if any electrolysis is going on; this is then covered with a bottom paint containing a less reactive form of copper. We’ve followed these developments now for the last five years and are convinced they are safe. This is the approach are using on the new boat – this is an Ameron-Devoe system and after almost three years in the water it is working quite well.

The big question we’ve asked is, what happens when (not if) we hit something and the barrier coat is rubbed off? Will the copper in the anti-fouling paint go after the aluminum? We’ve asked painters and commercial boat owners, and done our own tests; all indicate that this is not a problem. When these bare spots are touched up, you do have to re-coat first with the barrier. But otherwise, it is just like a fiberglass hull.

This leaves us with repair of the aluminum structure. We used to carry our own portable welding gear which would run off the batteries with the alternators going. We’d then carry spare rolls of welding wire, and bits of plate, channel, angles, etc. We have rudimentary welding skills – and good welders can always be found in the cruising fleet, or ashore – but not always the proper welding wire, plate or inert gas. After dragging this material around for many years and never needing it (when we did the odd bit of welding we were always able to find someone who could do the job for us), we stopped carrying it.

For more information on the FPB Series, e-mailĀ Sue Grant: Sue.Grant@Berthon.Co.UK.

Posted by Steve Dashew  (October 15, 2011)

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