Hi Luiz,
- Rudder's turning forces (LIFT) occur and are measured for optimization at HIGH angles of attack.
Yes, for the sectional coefficients, it would be clmax/cd0. And the planform would be close to rectangular. The rational is a combination between elliptical (low induced drag) and low cl close at the surface to avoid cavitation.
- Board's lateral forces (also LIFT) occur and are measured for optimization at LOW angles of attack.
- Hull's DRAG forces occur at LOW angles of attack and are usually measured for optimization at NO angle of attack.
I think that the angles are around 6° or so? Do you have any numbers?
Optimizing a foil's surface at HIGH or LOW angles of attack are two different things.
Optimizing for minimum absolute DRAG is not the same as optimizing for MAXIMUM LIFT or for BEST LIFT/DRAG RATIO.
Yes, and foil optimisation is only one part, planform, area and span are even more important. As you wrote already in the asymmetric foil posting, hull friction dominates over foil friction effects. Hence the optimisation should not be a pure daggerboard optimisation, but a complete drag optimisation. In general this leads to a cLmax optimisation for both rudder and daggerboard and a minimisation of lateral area. However you will be able to optimse either for light wind or strong wind but not for all the range of possible wind speeds and courses. Or you make a fair compromise between the two, so you have neither a light wind design nor a strong wind design. I would go for the compromise.
Cheers,
Klaus
