Vessel 1 was pulling the victim on an intertube.  Vessel 1 was going in circles, slinging the tube around faster and faster.  Vessel 1 was approx. 45 to 50 ft. away from the end of the dock.  The tube was attached to a 50 ft. rope.  The victim lost his grip on the tube and fell off.  He "skipped" twice across the water and struck the dock.  The victim died as a result of blunt force head trauma.