I did that on the 2007 EVO 75 and used it with three fins of about equal size (ie not with a big central and two small side fins). My conclusion is that it really didn't improve the board. Upwind got a tiny big better, but it actually got less loose in the turns and felt a bit slower.
I think that with a tri fin setup, it is absolutely vital to get the fin positioning and angle just right and it takes experimentation to get there. If you still want to do it, a starting point could maybe be 1.5-2 degrees toe in of the side fins, shortest distance from rail to box about 1.5-2cm and then the rear edge of the fins contact point with the board 32cms from the tail.
Pretty much all people experienced with tri fin windsurf designs also seem to recommend symmetrical fins. As for boxes, with really small fins you might get away with fcs, but I think Future boxes would be a beter choice. For a full tri fin setup the mini tuttle design that some kite boards uses (and also Withcraft) should be the best option.
Last edited by Ola_H; 16th February 2009 at 03:44 AM.