How to Use an Underwater Compass
After you’ve done the “square” swim in your advanced course, you may doubt the practical use of the underwater compass. When will you swim squares? So, first the basics, followed by some more practical examples of the techniques used by the dive guides.
Still on the boat, put the lubber line (the fixed red line) in the direction of your destination or parallel to the coastline where you enter the water (in case it's needed only as a general orientation).
While holding the lubber line (actually the whole compass) in it's original position, turn the bezel (the mobile ring with the degrees on them) with the 0° (normally marked) on the North.Now you've set the compass. Take care tonot turn the bezel againor you will lose your setting, unless you are swimming a pattern with calculated angles at predefined turning points (after having covered a measured distance).
You can now find the original position underwater by turning the whole compass (attached to your arm or in a console) until the North is on 0° again.The lubber line now points to your destinationorwill be parallel to the original coastline where you entered the water.
- Another suggestion for the course is to do a triangle, not only a square. In clear water a square can be “guessed” by making more or less 90° turns. With angles of 120° that is a bit more difficult, so precision with the compass becomes more important. Put a teaspoon in the sand at the starting point and see if you find it back.
- Another practical use is the situation of having your dive destination, for example the top of a coral pinnacle, visible from the surface at the entry point, for example a boat or jetty. Point the lubber line to your destination and set the bezel before you enter the water. Once down you know were to go and using the reciprocate direction (180°) you find your entry point back. Many books on the dive sites give a compass heading from the entry point as part of the description to find your way.
- “Swimming in the blue” can be added as an extra exercise in the navigation dive as part of the Advanced course. Set the compass as explained previously. Keep a steady depth, lets say 6–9 meters (19.7–29.5 ft). Swim perpendicular away from the shore or reef until you can’t see it anymore. Turn a few times around your body axe with your eyes closed. After opening your eyes, first try to guess where the shore is and then look at the compass to see if you were right. Now try to swim back with the compass in a straight line to your starting point on the shore or reef. This is also a good buoyancy exercise.
- If diving at a circular shaped coastline or reef, or a cape, the difference between the lubber line and the actual coastline next to you is an indication how far you swum, or if you already rounded the cape.
- Imagine you dive along a steep reef wall. At first sight, you don't need a compass, but then you see a dark area long from the reef. You swim out and find a big branch of barracudas swimming in circles. You and your buddy follow them, circling around with them. When it’s time to head back to the reef, you’re surrounded by the blue. No sight of the reef. Surfacing is the only option, with the risks involved created by boat traffic and surface current.
- If you had a compass this would not have happened. Before the dive you put the lubber line of the compass parallel to the reef or coastline and set the mark on the bezel on the north. You now always know your position respect to the reef or shore. If you even remember the reading of the number of degrees on the bezel at the end of the lubber line, you can set it back to it’s original position if it turns accidentally.
Video: Scuba Diving Lessons : How to Navigate Underwater
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