So then, what do people think is the best shape on the base of the board, flat, concave, double concave? and what difference does each make?
It'll be good to hear peoples views on what they think is best.

Any idea of what Sroka is using under the water? Fins and bottom?

HAHAHA, sorry man but this is now the one guy that you cant even ask that question. Bruno doesn't have a hull with fins. he has a hand full of boards with a boatload of fins and changes combination of boards and fins up accoring to the days conditions and location.
I guess the only answer to this could be he is on Paolo boards and fins.

hi,
that is what i would expect. There was a time when windsurfers carrier more than 10 boards and 20 fins to a race event.
The question is what is the design he is using that works so well. Of course he is not going to be the one to tell.
See you!

to my knowledge he uses a board with 4 fins, rides the board flat driving off the fins for upwind ability rather than using the board edge

Here we can see the tip of the iceberg. Jesse won all races in Morroco, with the exception of one. And Sroka was there.

I think that this one supports a windsurf sail