Use a Compass to Get There and Back

By Bonnie J. Cardone

My 1973 certification class didn't include using a compass. Shortly after the class ended I won a compass in a raffle. Since I had no idea how to use it, I asked a friend. I don't remember what he told me but I remained navigationally impaired. (I was in good shape, though, from all those long surface swims back to the boat.) Nonetheless, I strapped the compass on my arm before every dive, hoping for an epiphany. None came.

Time passed. Someone pointed out the north indicator on my compass was broken (who knew for how long?) and I threw it away. There seemed no point in buying a new one.

Then I was asked to write an article on using a compass for the magazine I edited. I found several manuals with short sections on the subject in the magazine's library. My first thought after reading them was: It can't be that easy. But it was.

A compass is a magnet suspended so it can rotate freely and point toward the earth's magnetic North Pole. All dive compasses have a floating card with an arrow on it that points north. All also have degrees from 0 to 360 marked on them, usually in 30 degree increments. Some dive compasses also have east, west and south indicated on them. The directional symbols are not important. Most of the time divers use compasses to find their way back to the boat or beach from which they entered the water. The direction is usually immaterialit is the heading that is crucial.

All dive compasses are filled with fluid. This serves three purposes: it allows a reading to be obtained even if the compass isn't perfectly level; dampens the movement of the needle so it doesn't swing wildly; and allows the compass to withstand the pressure of water at depth.

Compasses are attracted to ferrous metalsthat is, metals that contain iron. Dive compasses won't be affected by most dive gear because it contains little iron (since iron rusts) and because of the amount of water between the compass and the gear. You can find out what objects affect your compass by holding each object nearby to see if there is a reaction. If there is, just make sure the object is not close to the compass when you are taking a reading. One of the reasons I was navigationally challenged for so long was because I always carried an abalone iron, using the tip of it to keep me off the bottom until I learned buoyancy control. That tool, held in my hand, interfered with the compass reading.

All dive compasses have a lubber line. This is a stationary line that runs straight down the face of the compass and indicates your precise forward direction. Most dive compasses also have a rotating bezel with an index mark (or marks) or an arrow. The bezel is moved to mark the direction the needle is pointing when you take a reading, so you don't have to rely on your memory.

Three things are super important in underwater navigation. Besides keeping ferrous objects away from the compass you must remember to take a reading at the beginning of the dive, to keep the compass level and to align your entire body with the lubber line. For wrist worn compasses the latter is accomplished by placing the hand of the arm on which you are wearing the compass on the elbow of the other arm, which is held straight in front of you. Then line up your head, torso and feet with the lubber line. Hold the compass at eye level so you are sighting over it instead of down on it. If the compass is in a console, hold it in front of you and line your body up with the lubber line.

When you have a heading, rotate the bezel so the arrow or indices mark the direction the needle is pointing. To return to your starting point, turn your body until the compass shows a heading directly opposite (180 degrees) the initial heading. As you swim, monitor your heading frequently and correct it if necessary.

A word to the wise: A compass cannot pinpoint the exact location of an object, just its direction from a given point. Although it will get you back to a beach easily, you might swim right under and beyond a boat before you realize it. (Been there, done that!)

There are two kinds of compasses: direct and indirect. On a direct reading compass the degrees are marked on the rotating bezel; on an indirect reading compass they are not. Many dive compasses are both: degrees are marked on the rotating bezel as well as on the compass card. You can read the degrees marked on the compass card via a window on the side of the compass but must make mathematical calculations to determine your reciprocal heading. I'm sure this is a useful feature, it's just not one I've ever had to use.

Practise on land before taking your compass underwater. A few minutes is all it takes. And, if you remain navigationally challenged, which isn't likely, you can always take a specialty course to help you master this skill.

Ikelite offers two low profile, direct reading compasses. The Pro comes as a wrist mount only. The Modular Pro is available as a module (for insertion in your console) or in a wrist mount. Both the Pro and the Modular Pro have tough polycarbonate cases and the needle, 30 degree markings and bezel indicators are luminescent.