Abstract: A method and apparatus for the performance testing of a ship's engine while the ship is moored in a harbor, and even when the ship is being refitted or before the ship is completely built. To facilitate stationary testing of the ship's engine, a zero-thrust controllable-pitch propeller substitute, designed in the manner of a water-braking device, is installed. The propeller substitute attaches to the propeller shaft of the ship and replaces the regular controllable-pitch propeller during testing. The water-braking device has controllable a drag which can be adjusted to correspond to the engine output, and is preferably designed to accept the controls and fittings of the regular propeller. The water-braking device produces substantially zero thrust on the propeller shaft and the hull of the ship at all speeds of operation thereof, thereby producing far less currents at the site of the mooring of the ship during testing than the prior art methods.