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propwalk |
While moving ahead a propeller driven ship follows a straight line, but with the engine going astern a vessel's stern decidedly 'walks' to port or starboard depending on the direction of the prop's rotation. A vessel with the usual right-handed propeller can more easily be turned starboard round, conversely a left-handed (counter-clockwise) prop facilitates turning over port, and docking 'starboard to'.
The explanation is somewhat complex; in simple terms: with the engine going astern the revolving prop-wash is thrown forward against the vessel's sides causing different hydrostatic pressure between port and starboard. This pressure difference pushes the stern sideways. |
