Yeah Mark,
That hyperbolic cut out significantly effects the length of fin needed at low speeds. I'd say it effectively removes 6cm from a 49cm fin (the exact opposite of what Decrep needs). But once you've got some knots up you don't notice it at all. And because the board is otherwise handling friendly at low speeds it doesn't matter much except in the bumps, oh and upwind too. If you find yourself overpowered and backing off you have the additional nuisance of spinout to contend with. There is an "upwind kit" that came with the board. It comprises a lightweight shaped board that fills in the cutout around the fin root leaving just little cutouts. On the whole I like the deep cutout because I just prefer the way the board trims up like that. Others prefer it with the uwk in.
It just occurred to me that a guerny flap would have the effect of changing the fins aoa. Automatically you get reorientation without having to rebuild the root. But then having the right aoa may not matter if you have a feature free (no v) bottom. However if you do have that stuff it might work to line up the chine with the direction of flow.
I wonder if the effect of the flap would vary quite a bit with speed. So at slow speed your very tiny fin will spin out and at record speed you have to contend with the induced drag of what is effectively an extra huge fin?
