I found a very well done video which explains the two different sources of drag:- pressure (or form) drag, basically the "void" created by a wide wake that pulls back
- friction drag, the friction of the air or water alongside the whole cord of the foil
dimples make the flow "stick" longer with the object, closing the wake, reducing the pressure drag but increasing the friction drag
vortex generators on the leading edge have the opposite effect in reducing the friction drag but not trying to reduce the pressure drag
Dimples on a golf ball works because the gold ball shape is not streamlined and has a huge pressure drag but a small friction surface. But they do not work on fins, wings, foils because the pressure drag is so small to begin with.
Dimples on the leading edge can be useful on propellers because of the specific problem of cavitation
But on streamlined foils (airplane wings, wind turbine blades) what works is quobba-like "winglets" inducing vortexes in a way that does not adds lots of friction drag, unlike dimples.
Select to expand quoteMade me think of this shape, The Surator from Laid Hamilton
The most progressive shape on the marketDesigned by Laird and Terry Chung, the patented Surrator is the most progressive shape on the market. Using rail traction technology for performance, the result is stability and responsiveness unlike anything else on the market. Designed for intermediate to advanced surfers, the Surrator uses premium PVC construction with a lightweight EPS Foam, giving the board (and you) the feeling of precision, yet flexibility, in all surf conditions.
The rails have all sorts of dents as it looks
