Propeller walk

Propeller walk is the term for a propeller's tendency to rotate a boat as well as accelerating it forwards or backwards.

A right-handed propeller (which rotates clockwise [as viewed from the stern] when in forward gear) will tend to push the aft of the boat to starboard.When in reverse gear, the effect will be much greater and opposite. A right-handed propeller will now push the aft of the boat to port.

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.

Propeller walk is a complicated effect which depends on ship geometry, direction of travel, propeller direction, vessel speed and depth of water. Three causes are identified for a vessel in deep water:-

*1. Upward oblique flow at the propeller location.
*2. Vertical wake distribution at the propeller.
*3. Unbalanced lateral forces on the rudder (when set amidships) arising from the propeller slipstream impinging on the rudder blade.

The first of these results from there being a measurable difference in speed of water flowing close to the hull and that at lower depths which has not been affected by the vessel's motion. At low speeds the last effect is most pronounced and when going astern has even more influence.

In shallow water the upwards flow from under the vessel becomes much less strong and ultimately disappears. Model tests carried out show that, at a very small underkeel clearance, screw bias caused a ship to sheer to starboard (rather than port) when moving ahead and that there is an intermediate depth where the sheer from bias is neither one thing nor the other.

Finally, when moving ahead with the propeller moving astern, flow into and around the propeller is very confused. Generally the overall result for a single screw ship when stopping is a sheer to starboard, but this is not always guaranteed; sometimes it may go the other way, depending often on any yaw rate on the vessel when the propeller starts to turn astern.

Other terms for propeller walk are propeller effect, asymmetric thrust, asymmetric blade effect, or simply prop walk.

ee also

*Seamanship

References

*http://www.boats.com/content/default_detail.jsp?contentid=7590
*http://www.boatdocking.com/other/Sternway.htmlDand. I. W.: “Hydrodynamic Aspects of Shallow Water Collisions” Transactions of the Royal Institution of Naval Architects, Volume 118, 1976.


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Propeller — A propeller is essentially a type of fan which transmits power by converting rotational motion into thrust for propulsion of a vehicle such as an aircraft, ship, or submarine through a mass such as water or air, by rotating two or more twisted… …   Wikipedia

  • Walk the Plank (theatre company) — Walk the Plank is a firm who specialize in pyrotechnics and theatre and organizing events. Their shows are on land and on water and can include stage plays, music, lighting, visual images, fire, and fireworks. They were established by John… …   Wikipedia

  • Glossary of nautical terms — This is a glossary of nautical terms; some remain current, many date from the 17th 19th century. See also Wiktionary s nautical terms, Category:Nautical terms, and Nautical metaphors in English. Contents: A B C D E F G H I J K L M N O P Q R …   Wikipedia

  • Seamanship — is the art of operating a ship or boat. It involves a knowledge of a variety of topics and development of specialised skills including: navigation and international maritime law; weather, meteorology and forecasting; watchstanding; ship handling… …   Wikipedia

  • P-factor — P factor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller,[1] that is responsible for asymmetrical relocation of the propeller s center of thrust when aircraft is at …   Wikipedia

  • Bollard pull — is a value that allows the comparison of the pulling power of watercraft, particularly tugboats.BackgroundUnlike in ground vehicles, the statement of installed horsepower is not sufficient to understand how strong a tug is this is because other… …   Wikipedia

  • Neil Armstrong — For other uses, see Neil Armstrong (disambiguation) …   Wikipedia

  • A Kiss Before You Go — Студийн …   Википедия

  • Sasuke (TV series) — Ninja Warrior redirects here. For the unrelated arcade game, see The Ninja Warriors. Sasuke Genre Sports Entertainment, Obstacle Course Narrated by Ichiro Furutachi (1997–fall 2003) …   Wikipedia

  • Control line — Brodak Control Line Aerobatic Strega in flight Control line (also called U Control ) is a simple and light way of controlling a flying model aircraft. The aircraft is connected to the operator by a pair of lines, attached to a handle, that work… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.