RedactedNarrative: OPERATOR OF UNIT 1 WAS WORKING ON THE MOTOR.  THE MOTOR HAD BEEN LEFT IN GEAR WHILE TIED TO THE DOCK.  THE STERN DOCK LINE SNAPPED AND PULLED OUT THE BOW CLEAT.  UNIT 1 STRUCK THE MOTOR OF UNIT 2 CAUSING UNIT 2 TO BREAK FREE AND STRIKE UNIT 3.  THE OPERATOR OF UNIT 1 WAS ABLE TO GET IN UNIT 1 AND REGAIN CONTROL.