GPS current compensation
Jan 1, 2003
From Ocean Navigator #120 March/April 2002
To the editor: Theodore Davis provides excellent advice when caught without a working GPS (Nav Toolbox, Issue 119, Jan.⁄Feb. 2002). However, if one does have a working GPS, there is a straightforward way of determining the correct heading even without having any waypoint to aim for. All GPS units have a primary page, which in addition to displaying one's present position, displays track and speed. Track is the direction relative to the ground (otherwise known as course over ground), not course through the water. Knowing this, it is easy to compensate for the set and drift of a current:
1. From your chart, measure the course you wish to make good, which would be your track if there were no current.
2. Using your GPS, adjust your heading, i.e., compass course, until your GPS track is the same as your charted course.
Presto! You have compensated for any current without any plotting or calculation.
Brian Pollard has sailed a Hinckley Pilot 35 for nearly 30 years along the Northeast coast from Connecticut to Maine. He lives in Mt. Desert, Maine.