How to use a compass underwater

Finding your way underwater, preventing getting lost, and not having to navigate with aids like coral heads and sand ripples makes carrying a compass on every dive extremely important. But carrying the compass is only half the battle; you also have to know how to use the compass. Using a compass underwater is different than on land. There are many influences underwater that can cause problems when trying to swim in a straight line or when returning to the boat.

Many people are intimidated by compasses and think they are difficult to use, but that isn’t true at all; they are actually very easy to use and anyone can learn.

A majority of the compasses on the market today are what is called needle direct compasses. The compass has a magnetic needle that points north and a bezel that can be rotated around the needle. The bezel is marked from 0 to 360 degrees in a clockwise direction. The compass also has a line on its face, known as a lubber line, which is used to ensure that the compass is pointed in the same direction that your are going.

There are many different compasses on the market, but it’s a must that you use a quality compass for underwater navigation. A small, watchband compass or one attached to your console is not going to work very well. You need a large, easy to read, liquid filled compass that has a well-marked face. Some of the higher-end compasses have a window on the side that enables you to read a heading easier and a bubble level that helps to make sure you keep the compass level when navigating underwater.

Compasses are used in two basic ways: to determine the direction you are going and to follow a predetermined heading toward a certain destination.

To determine the direction you are going once underwater, you must align the compass to the direction you would like to go. Many training agencies teach to wear your compass on your left wrist, so to use the compass in this manner, you need to extend your left wrist in the direction you are going, bend your left arm 90 degrees, and hold your right arm at the elbow with your left hand. This aligns the compass with the direction you want to go. The most important thing is to make sure the lubber line is accurately lined up with the direction you are going.

Another method is to use a hand held compass or mount your compass to a slate. With this method, you can easily orient the compass by holding it with both hands in front of you.

The compass must also be level. If your compass has a bubble level, make sure the bubble is in the center of the compass. When the compass is tilted, the bubble will be towards the higher side of the compass. Also, when the compass is tilted, the needle may jam rendering the compass useless. The two most prominent reasons why divers have difficulty using a compass underwater are from either failing to line up the lubber line in the right direction or not holding the compass level so that the needle swings freely. It’s a good idea to practice with your compass on land before taking it underwater. Practice holding the compass level and navigating around your house or yard and get a feel for reading the dial and using the lubber line.

Now that you’ve practiced around your house, you’re ready to hit the water. Let’s run through a basic scenario on a dive. You have descended to the anchor at the bottom of the ocean, oriented the compass in the direction you want to go, leveled the compass, and made sure the needle is floating freely. The compass needle is pointing at a 90-degree angle to the right of where you intend on going. Now, rotate the bezel until the “0” on the bezel aligns with the compass needle. Read the heading. This is the heading, in degrees, for the direction you’re planning to go.

After swimming and exploring for a while in a certain direction, you eventually have to turn around and return to the dive boat. If you want to swim underwater without surfacing all the way back to the boat, you must use your compass the right way. The best way to do this is to turn around until the compass needle points to 180 degrees. Keep the needle aligned with 180 degrees while you return from the direction you came. This will bring you back to the anchor, where you started your dive. This new heading is called the reciprocal course. You can repeat this process over and over, each time exploring a new section of reef or area you’re diving.

To follow a predetermined heading towards a destination, you must first have a fixed point that you want to go to. The fixed point can be anything you want to see on your dive. You may already now the bearing of the object you want to see, either from a map or maybe the boat captain told you. Let’s say that the bearing is 130 degrees from the boat. The first thing you want to do is rotate the compass bezel until “130” lines up with the lubber line. Next, rotate your body and the compass until the compass needle lines up with “0” on the bezel. Finally, keeping the compass needle on “0,” swim towards your destination. You can easily see your return heading by reading the number at the bottom of the lubber line.

You may not always know the bearing you need to go, but you may be able to see a portion of the object you want to go to. For example, you may have surfaced a good distance from the boat. You can see the boat, but you don’t want to swim on the surface all the way back. In this situation, pull out your compass and point it in the direction of the boat. Turn the compass bezel until the lines on the bezel line up with the lubber line (north). Read the heading at the top of the compass. This is the heading back to the boat. You can now descend and swim back to the boat using your compass.

Mastering these two compass uses will allow you to easily and safely navigate underwater. As mentioned, it’s a good idea to practice these procedures on land before going diving. Once you have the steps down and are familiar with how your compass works, you’re ready to use it diving. Good luck and happy exploring.


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