Additionally please note that REAL aerodynamics along sails can be very different from what theory predicts. Not many aerospace are great experts on beheviour of low velocity flow over rough (seams ?) and 2-dimensional curved planes. Yes I said 2 dimensional and not 3 dim. Because cloth is so thin that it does not always compare well with NACA 3 dimensional test wing sections. I've read up on Speers article and the optimal angle of attack analyses he presents may be scientic well done but does NOT square out well with pointing angles of soft sail boats. I will not go into detail that will take up much space, I only want to say that you should Speer article as a learning basis and understand that it diverges from real life experience in some important area's.

Wouter