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post #1 of Old 02-08-2011 Thread Starter
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Precision 15 with or without keel

I'm considering getting a Precision 15. Basically I want something small (and stable) that will fit the family to head out on light days on iowa lakes. Goal 1 is fun but a close second is to help my wife get the "feel" for sailing so we both feel comfortable to take bareboat vacations to the great lakes or the gulf. I also want something that a friend and I could take out on windy days and have some fun.

I think the precision 15 fits the bill pretty good. The only thing I'm not sure of is if I should get the keel or centerboard version. The center board draws 3' 8" and the keel 1' 9". I don't have a depth problem at any local lakes with either boat. The keel will be harder to launch, but still should be pretty easy at normal boat ramps and will still fit through my garage door.

I know I'll be sacraficing some windward performance with the short keel on moderate days and will be dragging around more weight on the really light days, but I should get more "stability" (valuable with family on board). Problem is, the keel only weights 250 lbs and is short. I've run some rough numbers based on a hand sketch and at 10 heel me and my wife (~350 lbs total) sitting on the coaming are a 8x bigger righting moment than the keel. At 20 we are about 4x bigger.

So the question is... will this little keel really give me that much more stability?? The nice thing about the keel is, the more it heels, the more the righting moment, but the problem is the magnitude is so small. Our weight (assuming we don't move our bodies) actually provides less righting moment as the boat heels. Of course, we can move our bodies and we don't have to move very much to make a big change in moment.

Any comments? do my numbers sound about right? Is there a good reference out there that talks about this kind of stuff (short of a 500 page text book on nautical engineering)?

By the way... I'm an engineer, a normal person would just go out and sail them both and figure out which one felt best. It would, however, be kinda cool to predict which one will be better
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