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Coastal Navigation iPad eLearning App

How to use a Breton (Portland) Plotter

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Using a Breton Plotter aka Portland Plotter (aka rotating protractor) to determine a course

They say a picture is worth a thousand words – we say an animation is worth infinity! Check this out.

Here is an animation of how to use the Breton Plotter to determine a course. We use the Long Island Sound chart to determine a course from a buoy we are passing close to – to the entrance buoy to New London Harbor. We want to know the true and magnetic course. Note this is not equivalent to your heading. Heading will take into account the leeway and current. We cover how to determine your heading using the known course in our Coastal Navigation course.

Have fun with this animation and please share with your friends.

We have found that this animation is best experienced with Google Chrome.

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Author

  • Grant Headifen

    Grant Headifen is a USCG-certified Master Mariner (50-Ton), founder of NauticEd, and one of the sailing world's most recognized educators. With 46 years on the water, charters across 40+ global destinations, 5 sailing books, 30+ online courses, and 300,000+ students worldwide, Grant brings real-world expertise to every article. He pioneered fractional boat ownership through SailTime and serves on the Texas Boater Safety Advisory Board. NauticEd is the only U.S. sailing education body recognized by the U.S. Coast Guard under American National Standards.

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Last updated on June 29th, 2025
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