How important are smooth foils

Actually, no. A laminar flow section operating in its laminar flow bucket will have lower drag than a similar turbulent-flow section. One way to illustrate this is to think of all the small-scale movements inherent in a turbulent flow. The energy to create these movements must have come from somewhere, and it is extracted from the kinetic energy of the foil as drag.

The big deal with laminar sections is that they can get a lot draggier outside the laminar flow bucket, so there's a real incentive to keep them within it. With a turbulent-flow section you don't get the same step change (even though it may be more efficient than the laminar flow section outside its bucket) so the incremental cost of imperfections is smaller.

Dave

Yeah do have to argee with the weed thing. soo annoying.

And if you've got crap lumpy foils - you'll never know how fast you could be going.
But this also may partly explain boat speed difference between the ends of the fleet.
If you have nice foils you can tell when they are not working right ( ie weed!) but the problem in a fleet is deciding whether to stop and clear the weed, or continue at a slower speed without stopping.