Tactical Tailor

SCUBAPRO Sunday – Compasses

Using a Compass on your wrist or on a Navigation/attack board is something that is taught when you first start diving in the military. But how much time have you really spent honing your navigational skills? Using an underwater compass can keep your dive on track, optimizing your bottom time as well as getting you to and from the target safely. I am going to walk thru a handheld compass as it has more parts than most compasses that are on Nav Boards.   

Knowing about your compass what it can and can’t do. Everyone knows that a compass points north. The part that handles that task is called the card. This is the spinning face of the compass that has N, E, S, and W printed on it. The edges of the cards are angled at 45 degrees. Around the perimeter of the compass is a movable ring called a bezel. The bezel has a line (sometimes a double line) running through the center called the lubber line. This line is your directional marker. One of the most important things to remember is to keep the compass as level as posable. Depending on where you are in the world, your compass hand will “dip.” That is caused by the different magnetic fields in the Earth pulling on the arm of the compass. This is different than setting your declination. Declination is where the arrow points. The inclination is the pull on the arm of the compass. All compasses are made for different parts of the world. If you buy a compass in the U.S., it was made for use in the U.S. Some companies produce what are called global compass. Those are made to be used worldwide. They have the least amount of dip of any other compasses. Truly the dip is really only a factor if you are covering long distances.  Most of that info was for a handheld compass. But as far as keeping a compass level, that is true no matter whether if you are on Sea, Air or Land. ( see what I did there) SEAL.


If you are using a compass on your wrist you will use the side window to aim the compass where you want to go or see at what bearing something is at. Once you orient the lubber line, with the side window of the compass, you will see a number on the card through that window. This is where the angled design of the card comes into play. As long as you are seeing this same number through the window, you are heading in the desired direction. If you see a different number, make small adjustments until your number comes back into the window.


You can also use landmarks, like piers, sandbars, rocks, whatever will not move to check your position. You can set these as waypoints or reset points. Look at your heading and then use that to reference a visible landmark that is on a straight line visually. When you arrive at this waypoint, you can look ahead to find the next one. These visual cues will work in conjunction with using an underwater compass and allow you to get where you want to be. It is just like doing it on the land so keep in mind that metal objects can interfere with your compass’s magnet, causing what is known as “deviation,” so if your compass starts to move around a lot, try and stay on heading and your compass will settle down once you pass it. Moving away from the object, either laterally or vertically should correct the problem. Recheck your headings, and you can get back on track.


A lot of younger diver like using a digital compass on Navigation boards. The same priceable apply for using a digital compass. Digital compasses should be calibrated for the area you are diving. Each calibration is basically taking a sample of the magnetic that surrounding the compass. A particular calibration is only valid for that location of the compass. Ferrous materials can cause heading inaccuracy. So, make sure when you do calibrate your compass you are away from metal. Ferrous material can also affect your compass on a dive. Since heading is based on the direction of the Earth’s horizontal field, a digital compass must be able to measure this field with lesser influence from other nearby magnetic sources or movement. A digital compass is like a traditional one. Both compasses use the Earth’s magnetic field to determine which way is North. The difference is that a standard compass can dip because of movement and may encounter interference from strong magnetic sources, so inaccuracy can be a problem. A digital compass is much more accurate because it will only use magnetic North. So, using an excellent waterproof compass can help make you a better combat swimmer.  


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