Matthew, I think the roughness thing really isn't that tricky. It is only having an effect on the boundary layer. Once its turbulent there is very little effect. You can quite easily calculate the thickness of the boundary layer. It correlates well with the grain size of 600 grit, close to the leading edge. Hence my opinion that wet sanding is causing early transition which prevents laminar separation, and delays stall. Which is why it feels good on the water.

Dings will even stick out of a turbulent boundary layer, especially near the leading edge. So best to clean those up.

I did the EE thing too, but was not paying attention to the fluid mech stuff in 1st year. Only got interested last year when I discovered it was useful for speedsailing...

As for the fin design thing, I think a more calculated approach is warranted. Learning about, and understanding the underlying mechanisms, designing to account for the most critical of these for the desired performance outcome, and then testing on the water is my approach. I know a few guys working to this- Boogie (C3), Mal Wright, and Andrew McDougal have all been delving into the theory. CFD might be useful to determine whether you got the balance of those design elements right. We are using 2D panel methods for now. For the Reynolds numbers we are running in, most of the standard foil design approaches remain valid.

Mr Lang, yes a flexy fin can be a fun thing to sail, but it aint going to break any records...

Alby has it spot on. A good fin will help you to find 6th gear with confidence. If you are scared of spinning out at speed, then maybe its time for an upgrade. I've found that speed perception goes in increments of about 2 knots. Every 2 knots gained feels like an extra gear. Its very rewarding to find 2 more knots, even if its 'only' from 30 to 32...

hi guys,

i thought i would move away from fins and ask about wet and dry on the hull of the board?

is the principle the same as with the fins. ie. 400-600 grit or should it be smoother?

thanks for any help..

gestalt.