The All New ...DeltaMax .👍👅

Meh said..
What's the angle?

45 deg. It’s for big sails , shallow water ,not heavy weed.

Basalt cover with black resin for a sensual look.

various thoughts on that, depends who you listen to. I think it depends on the R number. and how smooth the foil.

A good boundary layer helps the flow stay in contact, and the theory is it's a water on water friction.
The boundary layer is created by slight friction on the surface, starts water tumbling over itself.

A polished surface can give laminar flow, so no turbulence, and any foil irregularities can cause separation and stalling.

the slower the speed the rougher the wet and dry. higher speeds benefit from finer wet and dry. a rule of thumb for us is anything between 400 and 1000.

However Fangy's latest experiment was straight out of the 3D printer with no smoothing and he said it went surprisingly well.

Personally I haven't noticed any difference.

No same argument, laminar flow or boundary layer.

I forget the name of the guy, but he did some tests, with dinghys, towed 2 behind him and found the polished boat had less drag than the wet and dry one, but that was at a very slow speed.
I've no idea really, as you say it's a **** fight, people on both sides of the fence believing there argument is better.

My boards finished with 600 go well enough

Imax1 said..

Imax1 said..
Ok 400 it is. 🤔 Thats the finish I give my boards. It’s a big fin for grip not so much speed. I suppose there could be difference in finishes of being fast and slippery apposed to grippy. But then a slower grippier fin could end up faster because you can push off it more with confidence. Cranking upwind or bearing off , must act differently on a fin. My head hurts.

ps, I have a beautiful carbon Curtice fin which is a shiny piece of art. It’s horrible. Like Elmo’s shiny fins , it violently spins out and I have to virtually stop to get it to regrip.

This is all good info, and makes sense.
Sanded fins induce a boundary layer, consisting of small rotations in the water next to the fin, (turbulence)
I guess these keep weed away from the surface of the fin.
The turbulence also travels around curves mu better than a laminar flow associated with polished fins.
Too much pressure, angle of attack on a polished fin will produce separation of the flow from the fin, this will drag air down and kill lift.

So conclusion from this thread is, a sanded fin is much more user friendly than a polished one.
Any difference in speed is undetermined.