Not sure of the specific circumstances, but a ship in the water, even with all motors off, doesn't sit still unless you drop the anchor, and even then it can swing on the chain. It would drift with the current, and it would have momentum from wherever it was headed before the power cut out. Unlike a car with brakes. Even if they had power and slammed the engine into reverse, it's not instantaneous. There's just too much mass and not enough friction.