Hello Mr. Roberts,

Thank you for your reply!

To see if I could learn something from your reply I did a rough calculation of the size the rudders would need to be to operate in the bucket. I considered a catamaran of similar dimensions to the SC-17 sailing upwind at 6 meters per second, and looked at the effect of rudder area on resistance (assumed NACA 63-009 section).

I learned that while increasing the area (and span) of the rudders would reduce resistance, the effect of operating in the low drag bucket was minimal (~ 10 N) compared to the total resistance. The rudders also would need to be impractically large to provide the required lift at a Cl of only .20. Did not see any obvious minima to optimize around, but I did not (could not) consider the effect of leeway angle on hull residuary resistance.

So, my rudder question was a rather silly one.

The 63-0xxx are nice sections for avoiding ventilation at high speed and load, which is a much more important consideration in this case (guessing that's why it was chosen).


Thank you for indulging an amateur with your explanation.

-colin pitts