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Old 06-24-2006
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I am afraid that there is nothing on Carl's Calculator http://www.image-ination.com/sailcalc.html that actually tells you anything meaningful about stability, or motion comfort.

Carl’s calculators provides a useful service but the Capsize Screen Formula and the Motion Comfort provide no useful information in evaluating a boat for either motion or stability. I know that I have explained this on this forum before but here it is again, both of these formulas were developed at a time when boats were a lot more similar to each other than they are today. These formulas have limited utility in comparing boats that otherwise are very similar.

Neither formula contains almost any of the real factors that control motion comfort or seaworthiness. Neither formula contains such factors as the vertical center of gravity or buoyancy, neither contains weight or buoyancy distribution, and neither contains any data on dampening all of which really are the major factors that control motion comfort or the likelihood of capsize. Weight alone has no bearing on motion comfort and stability.

I typically give this extreme example to explain just how useless and dangerously misleading these formulas can be. If we had two boats that were virtually identical except that one had a 500 pound weight at the top of the mast. (Yes, I know that no one would install a 500 lb weight at the top of the mast but if we compare a boat with teak decks, heavy decks, wooden or steel spars to the opposite extreme at the other end, a boat with a deep bulb keel those differences can easily have that kind of impact.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize screen formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth. That is why I see these formulas as being worse than useless.

Jeff

Last edited by Jeff_H; 07-31-2009 at 04:30 PM.