Although the laminate itself came out ok, to my dissapointment the leading edge of the board has a much too big radius. I didn't take into account enough the thickness of the 3 layers C: to get the profile right I should have shaped the leading edge much more precise than I did.
I don't feel ready to throw away the rudder. Instead I'm busy shaping the leading edge again, this time hopefully right, and then re-laminate the front end of the rudder. Because I have to remove almost all the glass from the front till the carbon uniderectional, the carbon won't be totally enclosed by C-glass anymore (I mean: the layers under and above the carbon are not connected to eachother anymore on the front side), so the rudder might be less strong. I'll take the risk.