Hi Wout -Bill -John and all ,-great thread ,-just sat back and read others on this one though very interested ,
like John P posts and Bill,s as active designers of existing cats in the marketplace .
Wout your perspective is from a main objective and goal of building a Formula class {worthy endeavor } but in discussions it often makes you {talk past another} as they say .
An interesting project > I have a SC 15 that I,d like to modify w spin {experimented a little already with one on the sc } and have it comply with F-16 rules for future racing ,--I,m not sure if I,ll add boards or a smaller molded in skeg or just use more rake and load up the large rudders more on this non boarded design .
I may add a little foam expoxy v shaped {for rudder movement} fairing plate off the stern to make it a full 16 ft .
The problem earlier on migrating CE forward with the spin up is the problem I,ll face in adding the spin .
In looking at a side view diagram of any cat -
http://www.parlier.org/site02/images/vue-face.jpg The CLR -{area of underwater profile inc boards & rudders}
has been designed in older non spin cats without consideration of the spin area which when raised moves the CE way forward .
Most racing sailors have found that when you rake the mast aft more under spin the better your speed and handling characteristics. In effect moving the total CE back -
but how much ?
The spin pole is a certain distance from the bows per rules ,-the mast base in located the same ,-an extreme amount of added or extreme mast rake may be a meter or little more ,--thats all .
Draw this out on a particular design with accurate sail area mast height and general specifications in the normal position {without spin} and with extreme mast rake and spin area in calculation of CE to CLR .
Spin are av equal to or larger than the main &jib area
spin tacked out forward on the spin pole.
The CE evan with extreme rake is still way ahead of the CLR ,
tHIS NECCESITATES the moving of the board forward ,near or at front crossbeam location as noted , for spin boats .
One other interesting option would be an evan more forward located smaller angled lifting foil or skeg to change the CLR to CE .
for other readers -
CLR is Center of Lateral Resistance =side view underwater profile under sail and center of area inc boards foils and rudders .
C E is the Center of Effort = center of areas of the sail plan -main -main jib -or main jib spin combinations .
Generally the CLR leads the CE by a small percent ,-allowing for mast effects and wanting some weather helm designed in or nearly nuetral helm .
The forward lifting canted foil nearer the bow to balance the spin CE would create added drag , offset by its ability to lift at higher speed and balance the helm under spin.
In upwind mode this would load the rudders evan more ,
requiring a smaller aft board as well ,-this type of for and aft board configuration is very versitile under many different sail combinations ,--thinking of larger cats -reefing jibs and mains ,-stormjibsails,-and cats with adjustable rigs ,- etc .
An ideal cat design would have an ajustable mast rake ability under sail ,-forward position in normal windstrengths upwind ,--then raked back to an extreme downwind .
The 60 tris have adjustable rigs ,-the first I saw it on beach cats was the 87 Worrell 1000 ,-It was Reg Whites son on a 12 beam Hurricane that had attached a 3 to one block system and cleat at the base of all stays with about 6 ft of adjustment ,-it could be raked back ,--and also to windward a little if desired .
Small inward canted forward lifting foils particularly for 16 ft cats that counteract forward forces -used on the 60 tris so well to carry their huge sail plans ,may be the ideal development for them allowing them to be pressed much harder in high wind speed conditions .
fun to theoretically go through design options and potential variation to explore .
good winds
