I came across this patented fin design [link below] and just curious of its feedback. The article makes clear solid points in terms of flaws in fin design relating to shape and placement in regards to the evolution of fish.
It’s noted however with prior fish design, fins are places too close to rail making for loose less controllable ride. Albeit for speed, it’s since been adapted to toe-in at the expense of considerable drag.
The theory states that parallel fins can work efficiently [with 3 degree cant for hold through turns] when set at 15% boards length from tail and no greater than 1/3 the width of the tail from the stringer.
As for fin foil, concave inside undoubtably produces less drag and more responsiveness when place in aforementioned positioning. The article goes on to reveal its multi-fin design (picture attached).
MY QUESTION:
Going back to the classic keel fish, 2 fins, would it be crazy to incorporate the fins as recommended for placement only with outer concave foils and inner convex foil?
I’m making another fish, starting with the fins (concave inside, convex outside) and willing to glass them what seems to be opposite in the name of experimentation.
Any and all feedback is appreciated.
Surfperception,
Contact Swaylock’s member, lankameese. He has considerable ‘‘in the water’’ experience, with Fish style surfboards, and fin foils similar to what you are addressing. Experience, always trumps theory.
I’m not sure what to make of the diagrams but would encourage you to think about what is happening with the outer foil of the outer fin during rail to rail transitions. By “outer” I mean the side of the board away from the turn direction. A flat or concave surface on the outside will ‘catch’ as you try to break that side of the board free. There is a good reason why the outside surfaces (or both) of practically all fins are foiled as they are. There is also a good reason why some fins are ‘hooked’ - and it is basically the same principle… increasing the curvature of that outer surface to allow easier break away effect of the outer fin during rail to rail transitions. With hooked fins the inner surface of the inner fin will really take hold while the outer surface of the outer fin will break away. These fin elements do not begin to consider the effect of toe-in and cant but I know that there are some pretty good reasons why most fin layouts are designed as they are - at this stage of the game, it isn’t exactly guess work. Most fin theories have been tested and in spite of some far out attempts, for the most part, things keep coming back to tried and true.
