Klaus,

I agree with your analysis, laminar foil sections tend to make little sense for this application, the drag reduction is minimal to non-existent, any benefits are instantly lost if the surface finish isn't perfect and they stall at 5 degrees lower angle of attack. Plus the drag outside the bucket is significantly higher than in the bucket. I could see there use on dagger boards but on rudders that operate outside the bucket for >50% of the time, I don't see the point.

Out of curiosity, how are you modelling cavitation effects?

I can very easily cut foam to the proper shape for a rudder and daggerboard. By easily I mean all 4 foils can be done in one eight hour session with the hot wire bow. I don't think cutting wood to an airfoil section will take that little time. I can vacuum bagged the next day, paint on the third day-its a very quick process for me as I've done it a lot. Concerns of crushing the foam core are valid, I would use Dow High Load 100 as it is the highest density foam that I can relatively easily acquire and most importantly still cut with the bow-going to Rohacell IG 71 would double the crush resistance (231 PSI vs. 100 psi) , but drive the cost up and I would need CNC equipment to get the proper shape. My experience with the high load foams is it isn't too bad in dent resistance with 1 light layer of fiberglass. Considering I'm going to 4 layers of 5.7oz carbon minimum to handle the bending loads, I'm not too worried about it. If the core is getting crushed at high speeds, the number of skin layers is insufficient to handle the loads.