I modified one of my two Black Skimmer sea kayaks for wing paddle racing by making the cockpit longer for paddling in the knees up position and adding a rudder. The Black Skimmer is my own design and was originally intended for Greenland style kayaking competitions, which included racing, rolling, and throwing a harpoon. But it converted nicely and is about as fast as the 19" wide stable surfskis. I'm really liking it for paddling at night when it's colder or when there is a lot of rain run off. The butt stays warm and dry, unlike in my surfskis.

More photos are here:

http://duane.smugmug.com/Other/Black-Skimmer-Race/27140812_vHCmxm#!i=2278275957&k=6h37H2K