fin placement

Does the (slight) distance of side fins off the rail make a lot of difference? I’ve been spacing my shortboards 1.25" off the rail, and as I move up to gun size I’ve been closer to 1.0" off the rail. The research I have done seems to indicate that this creates a difference in drive off the turn, but can anyone give me a qualified opinion?

Well, I can only say from my own limited experience, but it does seem to create more drive the closer the fin is set to the rail, within reason of course. I redid - reshaped/glassed - an old board earlier this year, and in reshaping the tail, the fins moved from 1.25" to roughly 7/8" to the trailing edge. I couldn’t move them as they were fcs plugs in the foam, and i didn’t want to fill holes… I have noticed a remarkable difference in drive out of turns. I was originally worried it would have a negative impact on straight line speed too, but that hasn’t happened either.

I hope this helps, and maybe one of the masters here can provide a less vague explanation.