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post #7 of Old 07-08-2011
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Originally Posted by hdra View Post
So I just went up to Santa Barbara today to look at this islander 36. Everything on it seems pretty good, except for one big weirdness - Some prior owner took a perfectly good keel stepped mast, cut it in half at the deck, and installed a big aluminum plate as a tabernacle so they could raise and lower it. The lower section of the mast is still intact inside the boat, functioning as a compression post - the top of the bottom half of the mast goes through the partners and rests against this aluminum plate that they installed to hold the tabernacle. Now, my first thought was that this was pretty ridiculous, but am I right in thinking that this setup significantly weakens the mast? I like the rest of the boat, but I don't want to have the rig come down because someone took a sawzalll to it years ago...
I seem to recall sailing aboard a number of Islanders with deck-stepped masts while we lived in San Francisco. As I recall, the mast sections did not seem to be any heavier than did the sections on the keel stepped yachts and it's likely that Islander used the same mast on both versions of the boat. The only change in the structure of the mast is the "effective unsupported length" of the "column" between the deck and the lower spreaders in the calculation of Euler Buckling loads as the column (mast) goes from a fixed end condition to a pinned end. It is not a big deal to calculate the buckling loading if you can come up with the mast section and I suspect that would not be difficult (check RigRite). Further, I am reasonably confident that there is no problem.

In SoCal it was not uncommon to see yachts transformed from keel stepped masts to tabernacle based masts, particularly around Huntington Beach and Long Beach where there were/are relatively low fixed bridges between waterfront homes with docks and the ocean and it was not unusual to see a yacht with its mast angled forward at 45º or more to make it under these bridges (although this would be problematic with roller furling). In some respects, there is much to recommend the design in areas where there are low bridges. In my own case, it only takes one bridge less than 65' to make a section of the ICW entirely unusable.

I suggest you have a structural engineer take a look at your prospective yacht as you may/likely have a non-issue.


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