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Tuesday, January 27, 2009

Pssst! Hey.... Wanna Buy a Couple Masts??

The continuing saga of "what to do with these damned masts!"... Last week, on the way to the Seattle Boat Show, we stopped by Mr. Perry's place and discussed rigs and sailplans (amongst other things anarchic) to help determine a course of action on the masts. The short and skinny version: we will be going with a new, taller, main mast, keel stepped. And, the existing mizzen (too short) will be replaced, and will be deck stepped. Ugly Details... Bob gave us a pencil and his RPN calculator and called out some numbers from the drawing and Skene's Elements of Yacht Design (I felt I was back in college, in my very last class, taking a final exam for which I hadn't studied. My worst nightmare). After computing and double checking some calculations based on the original W42 drawings, we determined the existing main mast in possession, given it's cross-section and wall thickness, is a bit on the "light" side. Light in terms of strength, for a cruising boat of this size (particularly for a deck stepped mast). Furthermore, the total sail area with the "short" 50 foot mast, was a bit conservative when considering sail area/displacement ratios. He wasn't surprised when I mentioned some W42s were offered with the tall 55 foot mast option, and indicated he would go at least 55 feet. But the key point was the lightness of the existing mast. As with things like hulls and rudders, you really only get ONE CHANCE to do this right. Changing it after the fact would be quite an effort. And, while you are replacing the main mast, might as well go double spreaders and keel stepped for stability and strength. Anyway, turns out my wife had a copy of Skene's (8th Edition). I now need to go back and review what we computed, just for my own knowledge and understanding. I did graduate from college, right? That wasn't a dream? I might post more of the technical details later...

4 comments:

Anonymous said...

Yes - go for it! I don't regret buying a new mast at all for our w32 project. Everytime I look at it I get a nice warm fuzzy feeling :)

Gary

rj said...

Thanks Gary,

One more thing I thought of. With all these "discoveries" and additional "uncertainties", in the end, I cant be sure these are original "factory" masts. For all I know, they could have been "swapped" for whatever reason, by the one of the two previous owners.

A quick look at another W42 Ketch on the hard, here in town, shows still a DIFFERENT main mast than what we have got. Were these swapped? Was there a change in production? etc. etc.

I'd rather be certain. At this time, new masts are the best we can do.

The Incredible Hull said...

Very curious to hear more about the mast cross section and wall thickness calculation. Would also appreciate if you could pitch it at 5th grade level.

rj said...

I'll see if I can recap the calculations, one of these nights when I cant get to sleep (or wake up too early).