Ancient navigation equipment still works


It was the year 1120 AD, and even in this overcast night hiding the stars, the helmsman knew which way to steer. He had a lodestone which pointed north-south. Soon, the fires from the village at his harbor came into view and his crew cheered.

The Earth’s magnetic field has been guiding sailors, armies, etc for centuries. Who first came up with this simple but ingenious idea? The Chinese are credited with the first systematic use of the basic compass, about 250 BC, with magnetic lodestone shaped into a spoon which was spun on a plate and came to rest on a north-south line. Surprisingly, the first widespread use of compasses was to align buildings to be in harmony with the universe - Feng shui. Later it was used in digging tunnels to provide direction when surface landmarks could not be seen from underground. From a lodestone spoon to a hanging magnetized needle to a floating needle the Earth’s magnetic field has long been used for directions over land to aid troops etc. It took over 1000 years for helmsmen to see the value of adding the compass to their navigation by the stars.

Who cares? All this is pretty obsolete with the electronic navigation, right? No! GPS – plotters – are such a great advancement that many boaters get the idea they no longer need a compass! All USCG inspected vessels – ferries, tankers, cargo ships, cruise ships, etc., are required to carry a compass. Electronic navigation instruments like plotters, auto pilots, and radar can and eventually will fail. There must be a back-up that relies on the Earth’s magnetic field which will not fail. Any professional navigator will not leave the dock without a fathometer, a watch, and a compass.

A compass needs care, and may need adjustment. How can you tell? With the boat tied to the dock, note your compass heading. Then bring a piece of steel near the compass and move it left and right. Remove the metal and see if the compass returns to the same heading. If it does not, then most likely the jewel that keeps your compass card swinging easily is damaged and you will need to get it repaired or buy a new compass. Also, check your compass against your GPS. Compute a course to steer and if you notice the heading on your compass is different from your GPS, your compass needs to be recalibrated by a compass adjuster. Another thing that can affect your compass’s accuracy is any magnetism. People have found changes when they bring their pots and pans and silverware aboard, and huge discrepancies due to stereo speakers.

The larger the compass, the more accurate and the better the dampening motion which lets you read the compass even when the boat is bouncing around. In the winter, it is a good idea to bring the compass home and store it well away from metal, especially magnets. If you subject it to extreme variation in temperature the seals can leak, and you may lose oil, leaving a bubble. This makes it hard to read the compass card which depends on the oil refraction of light for you to read the numbers. Loss of compass oil also diminishes the dampening effects that stabilizes the card. You can buy more oil at a marine store.

If you are the occasional boater whose knowledge of navigation is just plugging a number in your plotter and following a line, you are risking the safety of your passengers. There is nothing wrong with using a plotter if you have a compass to back you up, and if you know how to use it. Take a USCG Auxiliary course and learn what you need to know. There are three starting Feb. 27 in Warwick. Call Nick at 401-739-6028, or go to to get information or to register.


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