Swinging the Compass

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You can employ a compass adjuster to swing your compass or you can do it yourself quite easily. There are several ways to do it, but the quickest and easiest is to have the helmsman steer due north (000°C) on the steering compass while another person uses a hand bearing compass to sight along the centerline of the boat while standing at the stern, well clear of any magnetic interference.

Make sure there is no deviation at your chosen spot, by taking a bearing of a chartered transit and checking it on the chart. Note the course steered and the reading from the hand bearing compass, then turn to 030°C and repeat the procedure.

Continue recording bearings every 30° until you have completed a full 360°. Plot the results on graph paper to produce a curve giving the amount and direction of deviation for each course steered.

If deviation exceeds about 6° on any course, employ a compass adjuster to correct the compass.

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Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him at darrellnicholson.com.