Surface smoothness

[Panos_na]

In the windsurf industry, some boards have a nery smooth hull and others have a hull surface which is mat.

My question is, how much does the hull surface smoothness affect the resistance, boundary layer, etc?

Some say that the mat surface has better performance, while some others insist that a very smooth surface is better.

I think that everything has to do with laminar flow, turbulent flow, boundary layer, etc.
Can someone give me more information..?

[Knut Sand]

Golf....

http://ffden-2.phys.uaf.edu/211_fall...ts/flight.html

Now, joke aside, some of the physics that are valid for a golf ball will probably be valid for a board too. But then they wax the boards and I've never heard about anybody waxing their balls.... (Now I got the wrong picture...)......

[kazik_four]

There`s some information you were searched. It is common but useful
http://www.sailtoronto.com/racetraining/bottom.pdf

[kach22i]

Originally Posted by kazik_four

There`s some information you were searched. It is common but useful
http://www.sailtoronto.com/racetraining/bottom.pdf

Nice paper on the topic, thanks for posting it.

[Knut Sand]

But that paper want the hull to be without dents, some theories I've heard say that at planing speed or above, you get air under the board, the bubbles get trapped in the dimples and dents, redusing the wetted surface, and therefore the friction. However I agree that a smooth surface is the best alround solution, as the dimples will probably have quite the oposite effect (to be read as "a brake") at speeds outside the optimum, with regard to speed and waves.

[tspeer]

Originally Posted by Knut Sand

But that paper want the hull to be without dents, some theories I've heard say that at planing speed or above, you get air under the board, the bubbles get trapped in the dimples and dents, redusing the wetted surface, and therefore the friction. ...

It's also been said that air bubbles stuck to the surface are bumps that increase the drag, hence the concern about wetting or not wetting the surface.

In "High Performance Sailing," Frank Bethwaite reports the tests he did towing full scale planing dinghies to measure the effect of different surface preparations. His finding was the bottom cannot be too smooth. Polished is better than anything else.