Correct. Few folks fully understand what a fin is really doing. My compliments to you.
I fully agree! Fins are hydrofoils and sails are airfoils, both are foils and react in the same way to flow.
When pumping for speed, the fins act exactly like sails to generate directional speed.
Hence the shortboard era was born. Maneuverability allows you to place the board in the proper place on the wave to take advantage of gravity and build speed through climbing and dropping.
But, the planing surface of the longboard allows you to maintain speed you have acquired.
Balance it is. Pumping the board to maintain speed, or maintaining speed through planing.
Somewhere there is a middle ground.
I personally think that fins on a Board can act like sails… Sail can can genarate speed by how air flows over the curved surface creating lift like an airplane wing creates lift. In The case of sails this lift results in directional speed.
Re read, no texture works better than mirror smooth.
Sand finish is a marketing issue. We can skip the gloss coat and polish, knock off a couple of bucks, (far less than a gloss and polish cost) and tell the kids it goes faster. It is lighter, so maybe it is more maneuverable, but not faster.
for me it sounds that it doesn’t matter what you are doing with your bottom-surface.
No more sanding up to 2000…
That’s exactly why finfoil is born!
Exactly, which is why, although as an analytical type, I enjoy and appreciate the efforts put into understanding hydrodynamics and hydrodynamica as a scientific approach to design, I believe it is much less applicable to surfboard design than is thought. Some designs work, others don’t, but 99.9% of surfers are not going fast enough, riding waves good enough, or getting airs quick enough for hydrodynamic or aerodynamic principals to be of anything more than a minimal effect.
Interesting. No sand finish, no grid texture, gloss the bottom and go faster.
Always remember, boat hulls are driven through the(static) water, by the sails. Surfboards, on a wave, are driven by gravity AND the wave(dynamic) itself, impinging on the fin. There is a similarity, BUT a far different physical process is going on, with a surfboard.
I’ve said it before…
In surfing, acceleration beats speed every day, all day…
And, if you really break down what a surfer is talking about when they say a board is “fast” what they really mean is that it accelerates quickly.