The Weekend Navigator, tip #2


    Excerpted from The Weekend Navigator, Second Edition, Bob Sweet

    Double-Checking Your Navigation

    Quick Comparisons with the GPS

    A quick comparison of visual bearings with their corresponding GPS bearings isn’t precise, but it will give you confidence in what your GPS is telling you. This very simple technique will encourage you to make regular checks.

    Your GPS Map Screen displays nearby landmarks and buoys whose waypoints you have programmed into your unit. You may need to zoom out to bring them into the field of view, and you need to get yourself oriented. Generally you will be using a North-Up display on the GPS, and your direction of travel will be indicated by the orientation of the boat symbol (usually a sharp triangle). If you are sighting quick relative bearings, such as a beam bearing, simply look to see whether the chosen landmark appears to be abeam of the symbol on the screen. If the GPS has truly failed, it is unlikely that the two will agree; if the two agree, it is unlikely that the GPS has failed. If you are still uncertain, take some more precise bearings for comparison.

    If youve sighted a bearing across the compass, you need a numeric GPS bearing to compare it with. Using the cursor key on a newer model GPS, scroll to that buoy or landmark on the Map Screen; when it is highlighted, the GPS will show its bearing in a data window. Simply compare the GPS reported bearing with your visual observation. Assuming you set up your GPS to magnetic direction, no conversion is required. If the GPS bearing and your observation match, at least within about three to five degrees, your GPS appears to be working properly.

    If any of your quick observations do not match, its a time for a more detailed approach.

    For more advice on navigating with your GPS and other electronics, purchase The Weekend Navigator from Practical Sailor.

    Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. 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.


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