The fin shown is a 10.5" low aspect ratio spitfire cutaway fin, other templates include D fins, Hatchet fins, pivot fins or any custom shape of your own.
The elliptical spitfire' fin has the lowest induced drag of any planar fin shape. This means more drive, more power, better control, and greater speed.
http://olosurfer-woodensurfboardsatpipeline.blogspot.com/2010/12/low-aspect-ratio-spitfire-cutaway-box.html
Elliptical wing explanation on wikipedia:
http://en.wikipedia.org/wiki/Elliptical_wing
