UNIT 1 WAS UNOCCUPIED, TIED TO A DOCK WHILE REFUELING. OPERATOR OF UNIT 1 WAS INSIDE OF THE MARINA OFFICE PAYING FOR THE FUEL. UNIT 2 WAS A RENTAL VESSEL. V2 LEFT THE FUEL DOCK, ACCELERATED QUICKLY AND STRUCK THE PORT ENGINE OF UNIT 1. UNIT 2 WAS CHARGED FOR NEG. OPERATION.