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Leeway is the amount of drift motion to leeward of an object floating in the water caused by the component of the wind vector that is perpendicular to the object’s forward motion.<ref name="BOWDITCH">Bowditch. (1995). The American Practical Navigator. Pub. No. 9. 1995 Edition. Defense Mapping Agency Hydrographic/Topographic Center. Bethesda, MD. p.116.</ref> The National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual defines leeway as "the movement of a search object through water caused by winds blowing against exposed surfaces".<ref name="IAMSAR">National Search and Rescue Committee, (2000). "U.S. National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual," Washington D.C.</ref> However, the resultant total motion of an object is made up of the leeway drift and the movement of the upper layer of the ocean caused by the surface currents, tidal currents and ocean currents.<ref name="LEEWAYDIVERGENCE">Allen, (2005). Leeway Divergence. Government Report prepared for the U.S. Department of Homeland Security. January 2005. CG-D-05-05. Retrieved from http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA435435.</ref> Objects with a greater exposure to each element will experience more leeway drift and overall movement through the water than ones with less exposure.

A navigator or pilot on a vessel must adjust the ordered course to compensate for the leeway drift and more important set and drift, an all encompassing term for drift that includes the steering error of the vessel.<ref name="BOWDITCH"/> Failure to make these adjustments during a voyage will yield poor navigational results.<ref name="LEEWAYDIVERGENCE"/> Bowditch's American Practical Navigator (1995) offers a comprehensive free guide to navigation principles.

An object can be classified as either an active object like a ship navigating through a waterway or a passive object like a liferaft, drifting debris, or a person in the water (PIW) (Figure 3). A passive object will experience the greatest leeway drift and it is this drift that is of utmost importance to those involved in search and rescue (SAR) upon inland waterways and open oceans.


Leeway sections
Intro  Leeway in Search and Rescue  Leeway in common parlance  References  

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