Hi Eric
At the risk of sounding like a cliche',-
balance , is the key , like most things in life , excess or too much of anything is often not benificial ,-
Balance in cat design is found by measuring the CE [CENTER OF EFFORT} of the sail plan in relationship to the CLR {CENTER OF LATERAL RESISTANCE}
If you take a scematic side profile view of the design, a center of the mainsail area and jib can be found by various means ,-some simply draw lines from the foot and clew corners up 2/3 on the luff and lech ,where they intersect is the approx. center ,-or center of effort --AVERAGE AREA from main and jib to a total CE point,
good pic of a 20 here w spin for visual
http://www.fastlanesailing.com/hobie20.html The center of lateral resistance is the underwater profile of hull plus boards , to find this center calc the underwater area and av to its center,-its difficult as this underwater area of hulls and boards changes with sail forces ,hull depression -crew weight etc .
Designers calc this out and factor things like sail fullness ,-mast rake ,-board effectivness ,-bow down tendancies etc and generally set the CE ahead of the CLR by 10 % or more , this due to mast effects mainly ,the goal being to produce a boat that tracks well with balanced helm to weather.
Non board type cat designs often use extreme mast rake to move the CE back which loads up the rudders more . These types also track much better to windward in higher winds when more hull is depressed into the underwater profile than they are able in lighter winds often seen drifting or sideslipping much more to windward than board types.
o k ,--now add a 270 sq ft spin into the mix ,-this set forward of the bows a distance on a pole ,--How drastically does this change the original designed CE and CLR ,-
If you draw a diagram or visualize this you note the CE way ahead of the CLR ,-though sail heading is now changed to downwind mode with resulting change in side forces from 45 to 90 plus and the need to track .
Most cats w spin are sailed with boards half down and all have some lee helm with spin up which results from the CE being forward of the CLR , the trick now is to find an acceptable amount and also offset it as much as possible with added mast rake .
The earlier Worrell 1000 N 6/0s w spin developed by Randy used huge amounts of mast rake and a 14 ft pole in an attempt to get as large a spin as possible set .
Some tried 15 ft poles but found they were fighting excessive lee helm ,-the result was the constant turning of rudders and course corrections were slower , not to mention the lack of control .
The Inter 20 with its more forward front crossbeam location uses a 12.5 ft pole ,-these boats are noticibley faster downwind with more mast rake ,-the more the better ,but the effect upwind with rake is it being slower due again to design effects and balance , so most opt for a happy medium between the two .
The ideal cat design would have a smaller forward board used with the spin to balance it that would change the CLR to corespond to the CE being more forward with spin set ,--maybe also an adjustable rig ,--these design features can now be found on a number of the 60 ft racing tris ,-no surprise.
My guess is the H-20 optimum pole may be very similar to the I-20 that combined with added mast rake ,
If you used a 16 ft pole some type of forward board or molded in foil would be needed to balance out the forces and CE CLR relationship.
There is more to it of course ,but these are the basics ,
You might experiment with different pole lengths and mast rake ,--fun stuff -
