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centerboard design


JeffM

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Needing to install a second pair of seat stringers in my CS20 (mismeasured in the original installation), has given me an idea. Graham told me that the correct seat stringer height was important for getting the correct centerboard trunk height -- since the seat tops come out level with the top of the trunk.

My idea is this: if I used my original stringers (or lowered the new ones), the cb trunk would indeed come out lower, and leave the leading edge of the board protruding from the bottom of the boat even when fully raised. Wouldn't this be a good thing in shallow water, since I would have some control of lateral plane even with the board all the way up? Also, I'd get more board for each inch I lowered it, owing to the longer triangle of board being exposed at any given depth.

I know it's not that simple a mod, since lowering the stringers would change many other things well: the seats would be lower, the stepped portion of the mizzen mast shorter, the tanks smaller in volume, and so on.

On the other hand, the board itself could be lowered by the simpler expedient of hinging it with a pin located higher up in the board, and altering that pokey bit at the top.

Or I could just shut and trust that Graham had a reason for designing it the way he did, and build it to spec!

Jeff

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Just some random ramblings on the subject since we are in the Design Forum:

I guess the question is how much help would it give you for lateral resistance? Probably some, but I'm not at all sure an inch or two of a board being down would help all that much. I'm sure there's a formula for the area of the board and its effectiveness, but I wonder if a couple of inches right below the hull even counts.

My Weekender has no centerboard, but has a deep forefoot that, combined with the high aspect rudder, provides the lateral resistance (that's my theory anyway ... people always wonder why the Weekender doesn't just blow sideways in the wind without a centerboard). It rows pretty well because of the keel, that acts as a skeg. I suspect the board being down a couple of inches would act more like a skeg than a true centerboard.

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