Your reference to sail area/displacement is not clear. If you mean 20 pounds of displacement per square foot of sail area, then the boat will either be much under canvassed or way over weight. Try for something more on the order of 5 or 6 pounds displacement per sq. ft. if you are anticipating spirited performance. This will be a cat or proa so I suspect that you are thinking go fast. If so, keep the boat light.
Plyboats program is a fun tool to play with. It can save a lot of calculation time. It has a serious flaw that is worth addressing. The program asks for the location of the station with maximum beam. You might tell it station 11 in a 20 station layout. O.K. that is max beam at 55%. The program will also place maximum rocker at 55%. The program has no facility for doing it otherwise. The fact is that you may not want max rocker at that location. Many hot rod type boats have max rocker well forward of that point. One reason for doing so is to keep the angle of the quarter beam buttock as low as practical aft of the deepest part of the hull. Another reason is to retain the ability to tinker with the displacement curves.
I have no doubt that you can use the program to produce a satisfactory boat. Most of the boats built directly from plyboats offsets tend to be less than pleasant to look at. Not ugly maybe, but not beautiful either.
05-28-2009, 02:37 PM
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