Surfboard Fin Design - Greenlight Surfboard Design Guide
Here is a short writeup focusing on fin cant and toe in... check back soon for a full explanation of all fin design and placement aspects.
Fin cant and toe is actually quite simple.
Toe-in affects the way the board surfs through balancing turning ability and drag. More tow-in = more turning, more drag (slower board), less toe-in = less turning, less drag (faster board).
Toe-in is the angle the fin is pointing towards the nose. It is usually measured in fractions of an inch relative to a line parallel to the stringer over a distance of 4 1/2" inches (for trigonometry's sake).
Common toe-in values are 1/4", 3/16", and 1/8"
Tri fin set ups normally have 1/4" toe in the front fins but can be less for big wave boards where speed is more important than turning.
Quads normally have 1/4" in the front for pivot and 3/16" or 1/8" in the rear fins for drive.
Twins are 3/16" or 1/8" since there is no center fin to stabilize and the set up is already more prone to turning than drive..
Fin Cant is the same principles as tow-in. Turning vs. drag but in a different plane. Cant allows the fin to "stick into the wave" at an angle and acts as a pivot to turn the board.
More cant = more turning, more drag. Less cant = less turning, more drive in the board.
Tri fin set ups are normally 7-9* in the front for turning but 5* is used for bigger waves or more down the line surfing.
Quads are 7-9* in the front and 3-5* in the rear. The front fins act as pivots for turning and the rear fins are the driving mechanism.
Twins are set at the lower range of cant angle and classic double foiled keel fins are normally set at 0* cant for all speed and little turning.