Captain John’s Tips: The “Rule of 36”

Published on July 1st, 2013

No sailing navigation tool tops a great magnetic compass for simplicity and reliability–without the hassle of power or batteries. But you need to be aware of one secret rule that can cause any compass to go haywire!

If you are anything like me, it’s easy to forget about the metal and electronics that may surround your sailing compass. Or the crew that sets their cell phone, knife, or some other magnetic influence near your compass.

Imagine that you are able to turn your compass card over. On the back of the card you would find small magnets attached that help keep the compass aligned to the magnetic north pole.

Set some metal gear or electrical gadget near the compass, and you can bet those magnets will “follow the metal” and no longer align the card to magnetic north. This compass error – called deviation – can cause you to end up several miles off course.

Warn your crew to keep all materials at least 36″ away from any magnetic compass. That includes knives in sheaths on your belt, cell phones in cases on your belt or pocket, IPods, metal rimmed glasses, watches, or any other possible influence. Even a small compass error could cause you to miss a landfall or lose your way in pea-soup fog.

Do you know how many miles you will be off course with a 2 degree error? Read on

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