The oldest, most basic – and perhaps most useful – instrument on a boat is the magnetic compass. No matter how much sophisticated electronic gear lines the dashboard, every boat should have one. When the batteries go dead or salt water fries the electronics, the magnetic compass will still work–it will still get you home.

Of course, you have to buy quality equipment, install it properly and maintain it if you plan to call upon your compass to bail you out of a jam. A compass that is not installed correctly can cause more problems than it solves. You also have to learn to use it, and keep those skills sharp. What follows is a primer than will help you do all of the above.Gene BjerkeFew boaters get excited about the compass anymore, but it will get you home when the electronics go dark.

Gaining fluency with a compass will put you in good company. It was the Chinese who discovered that a magnetized steel needle, free to move in a horizontal direction, will always line up on a north-south axis. It was the Europeans who developed the compass as we know it today. By about the 14th century, the modern nautical compass was essentially complete. Today, it is right up there with the rudder and the propeller as one of the few pieces of equipment that comes standard with almost every boat, power or sail.

The nautical compass differs from its land-based counterpart in several ways. Rather than a magnetized needle turning over a background with directions printed on it, the directions are printed on a compass card with small magnets attached underneath. The entire card turns to line up with the magnetic field of the earth. Because vessels pitch and roll, and the compass is secured to the vessel, the card is suspended in gimbals so that it remains level while everything else moves around it. Place all this in a case, add a reference line – called a lubber line – and fill it with fluid to damp the motion, and you have a modern ship's compass. Some compasses have additional lubber lines at 45 degrees either side of the main lubber line, which are useful for sailors who use a tiller and sit on either side of the cockpit.