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Hello all, I need some advice. I'm doing a science project on the shape of surfboard fins in relation to the drag generated. I need to choose on variable to change in the design of the fins (Rake, Hieght, Base length, Thickness, ect.), but this variable needs to affect the drag of the board so that I can get results. So what so you guys think I should do, what single variable greatest affects the drag of the board?
the longer the base of the fin, the more turbulance is created. That increases drag. Keel fins have a lot of base. Some builders are now putting cutaways on the trailing edge of keel fins to shorten up the base of the fin and hopefully reduce turbulenece generated at the base of the fin, without dramitacally changing the template of the fin. Fin height will also increase drag. There are tons of threads about fins and drag that get pretty involved in the archives. Many of them talk all about the different kinds of drag and lift that fins generate. Hopefully people with more knowledge on this subject will chime in. Good luck with your project!
You didn't list it but the angle for the toe of the fin leads to huge differences in drag
Its good to be young, I have more time to fix my mistakes.
stoke the fire
Hi Ryan,
I would agree with the above post by "Jcyr". the toe angle of the side fins has not commonly been recognized for its effect on drag especially as this relates to the straight center fin in a thruster set up. More toe gives the board greater lateral lift at lower speeds, but at higher speeds, the counteracting influence on drag necessitates a lesser degree of toe in. But what has been overlooked is the effect of the, what I call, snow plow effect: the directional friction created between the different angles of attack of the down rail side fin and the center fin.
The problem described above is the impetus for my invention the TunaFin. I've just received a patent on the technology that drives the TunaFin. Basically, TunaFin allows the surfer to control the center fin's angle of attack (3-5 degrees), to match the toe in angle of the down rail side fin, therby reducing drag. This is acheived by way of a mechanism on the deck of the board to engage the riders back foot in the same way that a traction pad does, only rather than just providing for an increase in parrallel friction to keep the rider's foot from slipping off, the device acts as a pressure plate tiller, deflecting in response to the parrallel force of the riders back foot to drive the angle of the center fin much as a tiller and rudder assembly steers a sailboat.
The reduced drag of TunaFin has been clearly perceptible. I would be very interested to measure the reduction in drag.
Look for my upcoming posts on this and other discussion forums.