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Old 01-12-2006, 06:57   #1
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Dynamic/Static Stability

Hi Everyone,

I found this article very interesting http://www.johnsboatstuff.com/Articles/dynamic.htm

I am curious what everyones thoughts are on this.

Best,
Jackie
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Old 01-12-2006, 07:38   #2
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Two solutions for both. Catamaran, Trimaran.

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Old 01-12-2006, 15:13   #3
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Jackie,

This one has a bit more to it but still it's mostly junk science. Just little bit more math to dress it up to impress the reader. Sometimes being better still isn't enough. You are still left with the idea that the assertions don't lead you there by the formulas. The formulas may indeed be correct but why are they the critical numbers out of 100's of equations that might have been considered? They happen to be the ones they could compute so they must be the right ones.

My personal choice:

f = ma

It's simple Newtonian Physics - any object pushed hard enough will fall over. Get a bigger boat.

There seems to be this idea that you can just compute a few numbers and get the numerical expression of stability for any boat relative to another. People want it so bad that in the end all you have is - junk science. The ability to prove things that people want to believe are true.
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Old 02-12-2006, 08:11   #4
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Jackie,

While I agree with Pblais that the author of the article picked his parameters carefully I do not agree that this is junk science. Every boat design should (if it is designed by a reputable NA) include an evaluation of static stability. Dynamic satability is another animal and it is hard (but not impossible) to quantify.

I do find the author's lack of mention of GM (distance of center of gravity to metacenter) rather troubling when it is the accepted method for determining roll period and is the starting point for any dynamic stability investigation.

Suffice it to say that the article does not open any new ground and just enhances the conclusions drawn from the 1979 Fastnet race, penalizing light displacement shallow draft beamy boats on empirical grounds.

Richard
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Old 06-12-2006, 19:40   #5
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Plank on edge theory in a new dress? And still forgets that a plank floats flat, and is very stable that way.

While I love the model and would *die* to own a hollow wave theory hull, the fact is that's it's simply not the best choice for a sailboat. It's extreme, and unrealistic. The same is true of the results of this model: they don't show the reality of a boat which is *always* a compromise.
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Old 16-12-2006, 13:32   #6
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What Should Be Regarded as Essential Design Data
by Michael Kasten
kastenmarine.com/design_calcs.htm
Essential Design Data
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Old 17-12-2006, 21:12   #7
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I like big heavy keel boats. go ahead knock me down, in 30 seconds I am up again resetting sails and on my way wondering where my sunglasses went and pissed because all my smokes are wet.
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