Thanks guys. Sunvistas reply indeed amazed me a little bit but actually for me it's reality. Thus I damage my rudders ...
Our cat-club has oa. a number of Hobie Tigers and Foxes. For some strange reason they don't seem to have this problem, although system is in principle identical.
Got a spare H17 rudder assembly on which I'm going to do some tests at home. Ideal would we computer animation to determine angles & critical area.
But on the other hand: being the largest cat class world wide >110,000 pcs > 30 years it can not be necessary to invent the wheel again. So surely I must be overlooking something or at least doing not the right way.....
Thanks for comments anyway !!