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Apr 30, 2019

Dead Reckoning

Your on the water, but where am I?

Hey, Pirates never used chartplotters, and their depth finders were lead lines. But they found their way. Take a lesson from them. Bring along a ruler to use with your chart. Using the chartplotter or a GPS position from a cellphone, plot your position on the paper chart as you go along. To plot your course on paper, simply take the latitude and longitude coordinates from the GPS. Find the corresponding coordinates on the edges of the chart. Typically, the longitude coordinates are on the top and bottom edges, and latitude coordinates are on the left and right edges; some chart books have chart views arranged at other angles for space or clarity purposes. Using a straightedge, make a light pencil mark where the lines intersect.

After you've plotted three or four positions, wait 15 minutes or so, then turn off the chartplotter, paying close attention to the compass heading as you do so. Now try to keep track of your position without it. You may not know where you are at that moment, but you'll know where you were 15 minutes ago, and that'll be a pretty good clue. If you know this, you can "dead reckon," which comes from the phrase "deduced reckoning" and means steering by your compass while taking note of your speed and passing time to determine distance traveled. You'll likely find your way to where you want to go, or at least be close. You can also use landmarks, seamarks, and Aids to Navigation to verify and adjust your dead-reckoning position.

Unlocking the navigational clues scattered across your chart won't only add to your onboard fun — it will keep you safer should something knock out your electronics