WARNING - What you are about to read DOES NOT take the place of qualified training!!
Compass searches have their place in public safety diving and need to be a part of your search pattern arsenal. However, you don't find too many teams using them, even capable of using them. Usually you're either proficient with a compass or you're not. What does it take? You guessed it - training.
Compass searches are used mainly when you have visibility (6 feet or more), have little or no current and are searching for medium size items (bodies) or large items (vehicles) that rest above the silt line (so you can see them). The nice thing about a compass search is that it is quick to set up (no ropes) and easy to conduct if you know what you are doing.
With a little imagination and someone skilled in underwater navigation, you can perform a number of different search patterns. It all depends on the conditions, the environment and your skill level. You can also use natural navigational skills and pace counts as a means of keeping yourself oriented and as a means of checking yourself.
Features of an underwater compass
When selecting an underwater compass, it's important to get yourself one of quality that's designed for underwater navigation. This excludes watchband compasses and land navigation compasses, but you don't have to spend a fortune to get one that will do a good job. Let's go over some features to look for:
Liquid filled - Always select a compass that is liquid filled because the liquid dampens the needle's movement (reduces needle movement) and such compasses can withstand pressure.
North seeking arrow - The north seeking arrow should be "free swinging," enabling the compass even when not held perfectly level to still give you a good reading.
Rotating bezel and numerical degrees - Some types of underwater compasses have the numerical degrees on a rotating bezel and others have the numerical degrees on the base of the compass and an inside rotating bezel. The bezel is used to set your desired heading. You want a compass with numerical degrees rather than cardinal points (North, South, East, and West) for better accuracy in that it allows you to be more specific in your headings.
Lubber line - You are taught that when using the compass you align the center of the compass with the centerline of your body and the point at which you are aiming. To help you do this a North-South lubber line is sometimes painted through the center of the compass or off to one side. Extending the lubber line beyond the center face of the compass will increase your accuracy. This can easily be done by placing the compass in a console and, while the compass is kept oriented to the North, extending the lubber line across the entire console (using the console as a lubber line), or by placing the compass on a compass board and drawing an extended lubber line on the board. A Sharpy pen (permanent ink pen) can be used for this purpose.
Luminous - It's important to use a compass with components like the bezel, numerical degrees and north seeking arrow that are luminous (glow in the dark). This feature will allow you to follow your compass when the lights go out.
Index marks - Index marks are used to set your heading. You use them by pointing the lubber line in the direction you want to go, then rotating the bezel until the index marks are over or under the north seeking arrow, depending on your style of compass. The trick is to follow the lubber line while keeping the north-seeking arrow between the index marks. At first it's like walking, patting your head, rubbing your stomach, and chewing gum all at the same time. Proficiency comes with practice.
In your advanced diving course you should have learned about measuring distance underwater by using your personal kick cycles. An Underwater Criminal Investigator needs to know how many kicks it will take to travel a specific distance. If you're not familiar with your number, or have forgotten it, or never figured it out, the next time you dive, measure off 100 feet along the bottom using your 100-foot measuring tape.
Then carry out the procedure described in the next paragraph.
While hovering off the bottom near your tape, start at zero and kick. Count every time your left or right leg (whichever you prefer ) comes down in your kick cycle, noting the number of kicks it takes you to travel the measured distance. After you reach that distance, remember your ending number of kicks; turn around and start over, heading back to the zero mark. Now average your two kick cycles together and you will have the average number of kicks it takes you to travel 100 feet. Remember, don't hold onto the measuring tape as you kick. Remain relaxed and perform your normal kick.
Natural navigation is simply the use of the environmental features as a means to orient yourself during a dive. Your success depends on your ability to pay attention to the small details of your environment. This is a lot tougher than it sounds. As you know, when you go underwater there are already a lot of "other" things you need to think about. Paying close attention to the features and remembering what you saw and where you saw it could seem to be too much. For some, it is.
Having good natural navigation skills is an important part of your complete underwater navigation ability. You not only can conduct an entire dive using natural navigation, even in conditions of poor visibility, but when it is used along with compass navigation, your accuracy rate can increase tremendously.
Over the last 24 years I have found many cars, motorcycles and bodies by using a compass. The question is, did I cover everything you need to know to get good at searching with a compass? That was just a taste. Get the training you need and add compass searches to your tool box.