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Propeller walk (also known as propeller effect, wheeling effect,
A propeller is called right-handed if it rotates clockwise in forward gear (when viewed from the
Propeller walk (also known as propeller effect, wheeling effect, paddle wheel
A paddle wheel is a form of waterwheel or impeller in which a number of paddles are set around the periphery of the wheel. It has several uses, of which some are:
* Very low-lift water pumping, such as flooding paddy fields at no more than abou ...
effect, asymmetric thrust, asymmetric blade effect, transverse thrust, prop walk) is the term for a propeller
A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
's tendency to rotate about a vertical axis (also known as yaw motion). The rotation is in addition to the forward or backward acceleration.
Knowing of and understanding propeller walk is important when maneuvering in small spaces. It can be used to one's advantage while mooring off, or it can complicate a maneuver if the effect works against the pilot.
Effect
A propeller is called right-handed if it rotates clockwise in forward gear (when viewed from the stern
The stern is the back or aft-most part of a ship or boat, technically defined as the area built up over the sternpost, extending upwards from the counter rail to the taffrail. The stern lies opposite the bow, the foremost part of a ship. Ori ...
). A right-handed propeller in forward gear will tend to push the stern of the boat to starboard
Port and starboard are nautical terms for watercraft and aircraft, referring respectively to the left and right sides of the vessel, when aboard and facing the bow (front).
Vessels with bilateral symmetry have left and right halves which a ...
(thereby pushing the bow to port
A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as ...
and turning the boat counter-clockwise) unless the rotation is corrected for. In reverse gear, the turning effect will be much stronger and with opposite direction (pushing the aft to port
A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as ...
). A left-handed propeller acts analogically to the right-handed but with all rotation directions reversed.
Cause
Propeller walk is caused by the water, moved by the propeller in an axial direction and in a rotation. The water, coming from the propeller, gets a cone shape, widening when it leaves the propeller. If the rotating water cone contacts the ship's hull, a sideways force is generated. Propeller walk is hardly noticeable when sailing forward, since the propeller water will not hit a large surface of the ship's hull and corrections to the ship's course can easily be made with the rudder. When in reverse gear, the water will hit the hull directly, resulting in propeller walk.See also
* *References
*https://web.archive.org/web/20050402035644/http://boatdocking.com/other/Sternway.html Dand. I. W.: “Hydrodynamic Aspects of Shallow Water Collisions” Transactions of the Royal Institution of Naval Architects, Volume 118, 1976. {{Seamanship Propellers Marine propulsion