Using a Compass Underwater

Many divers stop learning about underwater navigation after their first open-water course. But using a compass underwater properly is a vital skill.

 Many people stop learning about underwater navigation as soon as their open-water course ends. It’s often far easier to follow a guide or divemaster on dives than to find your own way. Underwater navigation is nonetheless a vital skill. In a previous article, we addressed general ways to improve your underwater navigation techniques. Here, we’ll discuss specific techniques for using a compass underwater. 

Carrying and using a compass underwater

Often, a compass works best on a retractor or extender. This means you can clip the unit to your equipment wherever it suits you best. Divers commonly mount their compass on a retractor on the right chest D-ring. This placement means you can extend and read your compass with your right arm, leaving the left arm free to make buoyancy adjustments or check your pressure gauge. When you don’t need it anymore the compass will retract back to your chest or shoulder.

Once in the water, descend gently at the pace of the slowest member of the dive team. If possible, face in your intended direction of travel. In good visibility, you may get an overview of the site as you begin your descent. Beneath the surface, once you’ve checked in with your dive team, here are some tips for using a compass underwater.

  1. Sort out your buoyancy first 

    Adjust your buoyancy before you redirect some of your valuable attention to the compass. Many novice divers can become so preoccupied with the compass that they unwittingly rise or sink in the water column, or drift away from the dive group. This is particularly dangerous on a wall dive with a sheer drop beneath you or, conversely, if you float back to the surface unknowingly. Before worrying about which direction you’re going, get yourself in a neutrally buoyant, horizontal position and check in with your buddies.

  2. Give the compass time 

    The traditional analog compass floats in fluid, and it takes a few seconds to stabilize and give an accurate reading when you extend it. First, make sure the compass is level. Give it a little shake, and then a few seconds to settle into its natural Magnetic North position before setting your first bearing. Keep the compass level while on the move for an accurate reading. Don’t be afraid to give it a gentle shake from time to time to ensure it’s not “stuck” in a position.

  3. Don’t obsess over the compass 

    Spend an appropriate amount of time checking the compass. Once on the move, remember that using a compass underwater is only one aspect of your dive. Glance at it periodically to check your course, just as you would the speedometer on a car. Keep an eye on your buddy, depth and buoyancy too, and don’t forget to enjoy your surroundings. However, you should trust the compass. Sometimes in mid-water your mind can play tricks on you, but the compass is rarely wrong.

  4. Share responsibilities and stay together 

    If you’re new to navigating, as outlined earlier, agree pre-dive with your buddy on how you’ll share responsibilities in-water. Perhaps your buddy will track depth and time while you concentrate on compass directions. Work as a team.Also, be mindful to stay together. New navigators tend to swim at speed, leaving their buddies furiously finning to keep up. Slow down. Take it easy. Check in with your buddy regularly.

  5. Beware shipwrecks 

    Beautiful, intriguing and awesome as shipwrecks are, they can play havoc with your compass. If the wreck is made significantly of metal, it can make your compass give you false readings. On wrecks, opt for feature reference and follow the ship’s layout where possible — your compass may not tell you the truth.

In our next and final installment on underwater navigation techniques, we’ll cover natural navigation underwater.