Thanks Jeremy. Drilled holes and tested rudder blade (5 Bft). As it happens to be the heavy (cheapest ??) "plastic" version it flexed and bent incredibly causing a large number of spin outs. As windsurfer I knew this when using cheap fins - stiffened high tech fins cause seldom trouble...
Gonna fix the other TheMightyHobie18 blade as well now drilling turned out not to difficult. Have high expectations while better blade.
Nevertheless I anticipate I'll buy 2 new carbon rudder blades in the USA....