This is a center fin for a longboard, it can be used as a single fin or in a thruster setup. I am still working on the lower tab for proper insertion in a standard fin box. The tab can easily be removed to glass the fin on.
Also check out my shortboard fins at http://www.thingiverse.com/thing:12495
and my longboard side bites at http://www.thingiverse.com/thing:12497
If you like these checkout mesheldrake's Cardboard Surfboard thingiverse.com/thing:4764 or his other boards at sheldrake.net/cardboards/
His most excellent work on these cardboard surfboards inspired this creation.
For the center trailing fin use 1/8" or 3mm stock and cut one of each then glue them together. Set red to vector cut and black to raster. The foil will be made by the black raster, so run it at full power and very slow. I used a 60 Watt Universal laser cutter with power at 100%, speed at 1.5%, and 1000 ppi for 1/4" birch plywood. With a little sanding and maybe some epoxy or polyester resin you can make and surf your own fins.
I have not installed a completed fin in a box yet. But all that should be needed are two holes drilled for a small 3/4" long bar and set screw.