Anonymous wrote:
Hello Valentin,
I was hoping that a Sunbird 32 owner would come in, and and help from first hand experience. In their absence, I can say, from memory, that there have been two broken foremasts: Sabra (Newsletter no 26) and Lexia. There may be others. Having been aboard Lexia when she was being prepared for the OSTAR, my opinion is that both masts are undersized, too weak and too flexible. What I would want to do before starting a lengthy passage (if the size of the partners makes it possible), is to take out the foremast and replace it with the mainmast cut down to a suitable length, then put in a new mainmast, larger in diameter.
I've worked with aluminum a lot over the years, and found that there really is only one readily available alloy & temper I would consider suitable for a mast. That is 6061 T6 (not T651 which is brittle), nor is 6063 suitable, as it is far weaker. 2024 or 7075 in the proper tempers are incredibly strong and resilient, but not normally available in shapes and dimensions suitable for a mast. 6061 T6 is resistant to cracking unless it has been welded. All aluminum (or steel) that is subject to high stresses...... such as the portion of the mast near the partner, should be free from scratches or gouges.... any that exist should be polished out, as they are always the origin of failures. Look at wing root failures in aircraft, for examples of this..... there is good reason that they use generous radii and are highly polished, and it has nothing to do with looks. The beam failures in the new San Francisco transit center.... massive welded steel I beams were traced to torch cut access holes made after the fact not polished out or stress relieved, in what should have been massively over strength beams. I see the same thing in my work on a frequent basis, and as a result, I clean up surfaces, edges, cuts, and holes and stress relieve welds, and I try to eliminate stress concentrations wherever I can.
If and when I step an aluminum mast in a boat of my own, I will approach it in the same way, avoiding all defects or penetrations near the partner or between it and the step, and probably using elastomer wedges made from something like Devcon Flexane 80, with a high durometer modifier (stiffer) so there is no hard point at the partner, but rather some give......... But I'm an extremist. I've seen enough failure that I will go to considerable lengths to minimize it.
H.W.