THE EE WAS IN THE PROCESS OF LOWERING A 700 LB DEWATERING PUMP, WHICH WAS SUSPENDED FR5OM A MANUALLY OPERATED WINCH. THE EE LOWERED THE PUMP A SHORT DISTANCE AND THEN FLIPPED THE STOP DOG TO E NGAGE A SPROCKET TOOTH WHICH WOULD HOLD THE PUMP IN POSITION. THE STOP DOG DID NOT COMPLETELY ENGAGE THE SPROCKET, ALLOWING THE PUMP TO FREE FAL. WHEN THIS HAPPENED, IT CAUSED THE WINCH LEVER