Kneeboarding

Kneeboarding is an aquatic sport where the participant is towed on a buoyant, convex, and hydrodynamically shapedboard at a planing speed behind a motorboat. Kneeboarding can also be done, in waves at the beach. In the usual configuration of a tow-sport kneeboard, riders sit on their heels on the board, and secure themselves to the deck with an adjustable strap over their thighs. As in wakeboarding or water skiing, the rider hangs onto a tow-rope. The forte of kneeboarding vis-a-vis other tow-sports seems to be an easier learning curve and a sense of being closer to the water when falls occur.

Reference: Wikipedia Kneeboarding