Rolf

In terms of classical fluid dynamics, it's laminar. In CFD, it's laminar or transition to laminar.

The test data I have seen, has always been about the same.

Special surface finish makes a small difference (bumps grooves, etc)

Fair and smooth makes a difference.

Drag continues to decreases with polish. An English test of foils showed drag continued to decrease up to 3200 grit (test limit). Also the higher the polish, the better flow stayed attached. I have never seen enough data to say where the area of diminishing returns is. I used to say 400 grit, now I polish my boat the best I can.

The biggest factor is clean. Everything else is trivial compared to this. It does not take many grains of 40 grit beach sand stuck to your hull to offset everything else.

Carl