To go back a bit none of this matters if the sail plan isn't balanced with the center board. I set my mast rake to get the boat to sail to weather with the jib and main sheeted firm and the traveler out a few inches and the rudders up.
For what it's worth the Nacra rudders are seven (in the water) inches shorter than the Mystere's. The boat steers like a sports car with power steering and only time I ever get lee helm is when I try to go upwind with the chute.
This is my point exactly. If the sail plan is balanced with the hull/foil combination, the rudders are only needed to add fine control...and of course major control in tactical situations. I think the better the balance, the smaller the rudder needs to be. Hence the NACRA "pin heads".
The problem is, down wind with a spinnaker, the sail plan is in a different balance configuration, so more rudder influence is needed to maintain control. In fact, with the spinnaker moving around so much under sheeting input, the balance centers are constantly changing. You need more rudder input to make course corrections. Y'all know what happens when the sail's steering power overcomes the rudder's ability to compensate!
Perhaps we need a computer and trim winglets for better off-wind control.
Adjusting rudder area ahead or behind the pivot affects "feel" on the helm. Too far back and it "feels" heavy, especially when the sail plan is not balanced. Too far forward and you go "over center" and it gets away from you.
<<<<<Controls are sometimes dynamically balanced to assist the pilot to move them. By having some of the control surface in front of the hinge, the air striking the forward portion helps to move the control surface in the required direction. The design also helps to counteract adverse yaw when used in aileron design.>>>>
Sail boats are just like airplanes in that the better balance you can achieve without control surface input, the lower the drag. Then the control surface is only needed for major corrections.
