Recently a builder of fiberglass boats said that aluminum as a hull material is way inferior to fiberglass because:
1. Aluminum suffers from fatigue–the older the boat the greater chance for structure failure. 2. Aluminum boats are prone to failure by stress corrosion and weld corrosion.
Based on your research and experience, these statements seem to misrepresent scientific fact. In your book, Offshore Cruising, your thoughts are very clear about the superiority of aluminum for cruising boats. We would be interested in your prospective on items 1& 2 and what the best welding process is for aluminum hulls. Thanks, John and Ruth
Hi John and Ruth: We swing both ways, as you probably know–we do aluminum and fiberglass–and have experience going back 22+ years with both. Both materials can be long-lived, if done properly, and both can have problems if not done correctly.
Regarding the specific questions raised:
1. Fatigue is an issue with all structures–FRP and Alu. This starts with the material choice, how hard spots are handled, and the usual general engineering approaches. We have always used the same philosophical approach with Alu. and FRP, and have seen no difference in the longevity of the two materials.
Regarding the risk of fatigue in older boats, as long as the aluminum is properly engineered, I do not think this is a major issue. Certainly no more of an issue than with fiberglass–where you also have to be concerned with osmotic blistering, interlaminary shear failure, etc.
2. Stress and weld corrosion can take place with any metal–and can be particularly severe with stainless steel. With aluminum, the main issue is proper welding wire and proper welding environment. Where there have been weld problems, in our experience these have shown up during manufacturing, and the contaminated welds have been cut out and re-welded. In our experience this has not been a problem associated with age.
3. I’ll mention a third issue which your FRP builder did not–galvanic corrosion. This can be a major problem with aluminum and steel hulls. But only if they are not correctly wired. However, it is certainly less of a problem than osmotic blistering in FRP. Once again, in our own experience we have not seen problems with galvanic corrosion. Steve Dashew
Posted by Steve Dashew (November 30, 1999)
January 17th, 2012 at 1:26 pm
Steve,
I used to own a 52 foot aluminum flush-decked power boat designed by Phil Rhodes. The boat had isolation transformers and a Capac monitoring and impressed-current system. Protecting that boat from corrosion was a major part of my life. All the way down to through hulls and the use of nylon bushings to separate metals.
The boat was constructed in Holland almost 40 years ago, so I’m wondering how technology and construction has improved since then, and how much time and attention you have to pay to the problem of corrosion today.
Rick Shutes
January 23rd, 2012 at 11:57 pm
Hi Rick:
We have stayed away from impressed current systems. Too many risks if t hings go wrong. Passive zincs, with a monitoring system work well, are simple, and super reliable.