and a really skilled Indian can shoot a crooked arrow, but for the rest of us a little help is not a bad thing. Then with more practice will come more skill.
I only really know two things about this, but they are important points to consider.
First a fin is surface and VOLUME. So if we don’t spray it with a hose or move it through a tub of water, what happens when we put that fin into water? The water displaces an equal amount in the direction that water tends to go. And it’s not pretty, cause water will get out of the way , but we call it turbulence and swirls and drag and chaos and on and on. And that’s before we even put that fin IN MOTION!
Second I met Forrest and Bill Thrailkill at the Cerritos College get together, and just hearing Bill’s theory about fins, in particular his two fin beauty, enlightened me to something that we really don’t think about but it is a huge consideration. That is, our boards are the only thing out in the ocean that don’t change their angle of attack in relation to direction of movement, ie; TURNS. Any fishes that you can think of that are rigid front to back in the vertical plane? Bill was telling me all the facts on why the fin design worked because the water is moving this way and the nose of the board is headed this way and there is low pressure on this side of the fin and on this side push and - the man is a genius. But I finally saw that a rigid board is really just SKIDDING around on the water surface, pivoting on the fin (combinations) and rigid rocker and foil and rail shape is just balancing flat planing SPEED surfaces and rounded displacing CONTROL surfaces.
Look at Greenough’s spoon again. Why the hey was he always free-falling on takeoff? Cause that board is just pure release?! All flats and thin (volume) for flex/spring return in the downward direction. The tail of that board is just a big spring to snap him up onto the surface of the water. When moving at speed the spooned nose acts more like a rounded skipping stone to keep the rails high and out of the way, but can you imagine the drag at flipper speed, just before he gets to his knees? He needed speed to get that tuna fin working. So there was an awkward point in time, basically whenever the board is not at top speed, where the board is not at dynamic balance with it’s design and function. Also when going hard into a turn, the flex would curve the rail shape and aid in the direction change. Dynamic - flat rocker for speed with curved rocker for turns. Plus positive spring return of energy loaded in the turn. Sweet!
AND that is the shapers and fin foilers purpose and that is why molded fins and popouts and “one” designs will not provide the magic elixir, no matter how nice a guy Bob Bolen or Randy French or Karl Pope is, or how sound their theroies or construction techniques are. Dynamic, man. NEVER the same, infinite in possibility.
The good news is that in certain conditions these fins will work as advertised…