UNIT 1 HAD REPAIRS DONE TO THE CONTROLS AND WAS BEING MOVED OUTSIDE OF DOCK. OPERATOR OF UNIT 1 WAS ASKED FOR ASSISTANCE MOVING VESSEL AND WAS TOLD BY MECHANIC THAT CONTROLS WERE REPAIRED. WHILE MOVING THE VESSEL THE OPERATOR PUT UNIT 1 IN REVERSE. UPON PUTTING UNIT 1 IN NETURAL ONE ENGINE REMAINED IN REVERSE SWINGING UNIT 1 OUT AWAY FROM DOCK AND INTO UNIT 2 PORTSIDE PLATFORM OF UNIT 1HIT PORTSIDE REAR OF UNIT 2 WHICH WAS DOCKED.