thanks, Rabidric, that's the keyword i was waiting for.
the next idea that struck me was the twist cut fins. i don't want to go deeper into this topic cause it led to a too conventional design which worked upwind totally grand. downwind was, well, let's say, no fun. see this for more info.
viewtopic.php?f=159&t=2364350
then i said to myself, f*** it, follow the very early idea of a retractable centreboad. can't be that tough to build. well and here it is. i used two backfins, because i think that it delivers more stability. later i want to try a single back fin. there was one testrun so far. the cernterboard is 36 cm in length. when set vertically (90°) the board is not stable at all. the problem i know too well by now. if i angle the board to one side the board will turn to the other side. at around 60° the board will not react to leaning to eighter side. it starts to work around 50°. at this angle the centerboards tip is around 30 cm away from the board. seams to be the magic number. anyways, for this angle the straps were mounted to far to the front. also i think i can use bigger back fins. i have not found the right setup yet, but i hope this concept works. why? because downwind is just awesome! it totally feels like a waveboard. i installed a mechanism to retract the centerboard with rubberbandrope that extracts the centerboard and a rope that pulls the centerboard back into the board. the rope runs through a clamcleat so the centerboard can be set to any position. plus when running aground it will give way.
more to come...
i call it raveboard.
h.