Hi Patrik,
I did not answer your second question about the ARC21 in my previous response so here goes.
"Also I wonder if there are any examples of the "shared lift" theory employed on the ARC-21. How does that work more precisely. ( Board placement, areas, rudder sections aso.)"
The ARC21 employs "shared lift" to a very large degree. The daggerboard is in front of the main beam. At this forward location it is exposed to only 70% of the side force from the sail plan. Therefore the daggerboard is downsized to 70% of the size it would have been if it were located in the classical position, roughly at the shroud chainplate, carrying 97% of the side force from the sails. The area that was removed from the daggerboard has been added to the rudder. The distribution of carrying the side force from the sail has been changed from 97% CB and 3% rudder to 70%CB and 30% rudder. For the CB to carry 97% of the side force from the sail, the CB trunk is located near the shroud chainplate. For the CB to carry only 70% of the side force from the sail, the CB trunk is located just in front of the main beam. The final "center of laterial resistance" from these two systems is the same location along the hull. Sailing on main and jib, the boat doesn't know the difference.
The advantage of having the daggerboard so far forward is that the center of effort from the sail plan "with a full size spinnaker up" will not migrate to infront of the daggerboard and cause leehelm which is additional rudder drag and therefore slows the boat down.
Bill





All input appriciated!


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