NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: leeway
From: Buck Godwin
Date: 2001 Dec 06, 7:45 PM
From: Buck Godwin
Date: 2001 Dec 06, 7:45 PM
Ross Garrett wrote that leeway is proportional to the sine of the heel angle and inversely to the square of the boat speed. He cites a proportionality constant of 464 based on model tests of for a particular 12.2 meter boat when using leeway in degrees and boat speed in knots. In section 3.5.3 he presents a graph that shows good agreement between the model test data of the actual leeway and the leeway calculated from full-scale trial data. He recommends the proper constant be determined for each boat from trials. It is fairly independent of sail area, unless heavily reefed. I believe the constant would depend on the hull bottom condition. Rather than measure leeway by your wake, steer a steady course from a floating marker dropped overboard and take a bearing on that marker. Leeway is taken as the difference in the relative bearing and 180 degrees. Don't use a tethered buoy, unless there is no current. Measure heel angle and boat speed as well, to determine your boat's constant of proportionality. I am quoting from "The Symmetry of Sailing" by Ross Garrett, Adlard Coles Limited, 1987 Buck Godwin > -- --from Ocean Navigator #45 p. 72 > >58.5*heel/boatspeed^3 > >Is an approximation of leeway. > >Steve Tripp