Dan,



The answer to your question is, of course, very complicated. In an attempt to assist in your understanding, I would suggest that you consider the following conditions:



The rudder's center of lift or center of force is not in the middle of the rudder, but farther forward.



The center of mass of the rudder is far ahead of the center of the length of the chord. The center of the length of the chord may be what you call the center of the rudder, but it is not the working center of it.



The angle of attack of the leading portion of the rudder is much sharper than the portion of the rudder that lies behind the thickest portion of the rudder. The trailing portion (of the attacking side) of the foil is somewhat parallel to the angle of attack.



Do not forget to consider the angle of attack is not parallel to the rudder's center of thickness. In fact, the angle of attack is somewhat inline with the trailing end of high pressure side of the rudder.



I hope that this can help. I am not a teacher, nor a hydrodayamic/aerodynamic scientist. I only hope that I can lend some insight and help you to question any ideas that you, I, or we can come up with.



GARY