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Underwater Navigation: How to use a SCUBA Compass

By Carlos Sagaro

I remember when I first started SCUBA diving. My instructor told me I should always have an underwater compass with me when I go diving. He “went over” compass navigation in my basic SCUBA class but, by the time I received my certification, I had little more than a BASIC understanding of how to use a SCUBA compass. If you feel the same way I did, then read on because in this article we are going to go over the compass and how to use it as a SCUBA navigation device.

Parts of the Compass

The most commonly known SCUBA navigation device is the compass. All divers have one and should carry it with them whenever they go underwater. After all, we all know that there is no such thing as an underwater GPS for Divers! However, many of us, including myself when I first started, do not really know how to use the compass correctly to navigate underwater.

 

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Before we get into how to navigate underwater, I want to review the parts of the compass:

The Card:

This is the part of the compass that has the degrees (from 0 to 359 and the letters that determine direction

It rotates inside of a closed chamber that is full of liquid, which allows us to use it underwater.​

SCUBA navigation device, best underwater compass, underwater navigation
SCUBA navigation device, best underwater compass, underwater navigation

The Bezel:

This a rotating piece of plastic on the outside of the compass which can be moved around to help us read our heading

The Lubber Line:

This line is used to determine the direction you are heading in.  It is fixed on the compass' face.

SCUBA navigation device, best underwater compass, underwater navigation

The Side Window

This is a window on the side of the compass that makes it easier for us to see our heading when we are pointing the compass.

    It is important that you become familiar with the different parts of the compass and how to use them before you attempt to use a compass to navigate. Not doing so can cause you to get lost, which I am sure you do not want to have happen! **Note that a digital compass does not have all these parts**

    How to Use a Compass for Underwater Navigation

    The first thing we need to go over is how to hold your compass when underwater. This is important because different compasses are mounted in different ways. Determining what the best underwater compass for you to use is a personal preference but, it is important for you to understand how to hold them so you get the correct heading. Not knowing how to hold a compass can cause you to get an incorrect heading

    Hand-held compass

    When diving with a hand-held or pocket compass, you must hold the compass in front of you, with both hands and in a center line to your body when getting a heading. This will ensure that you are not off center and will allow the card to move freely

    SCUBA navigation device, best underwater compass, underwater navigation

    Wrist-mounted compass

    When using a wrist-mounted compass or a digital compass that is incorporated into a dive computer, you must hold the hand the compass is not mounted on in front of you pointing in the direction that you want to go while grabbing the arm that is pointing ahead in a ninety degree angle so that the wrist that the compass is mounted on goes across your body. This provides you with a fixed position for your compass and ensures that the card does not become stuck so you can get an accurate reading.

    Console-mounted compass

    This works just like the hand-held compass. The major difference is that you will hold the console the compass is attached to in front of you rather than just the compass. One thing that you need to be aware of is that often times compasses that are attached to consoles are placed there at an angle. This is done to allow the diver to have access to the window at the bottom of the compass. You must make sure you are holding your console in an orientation that allows the card to be free to move so that you can get an accurate reading.

    SCUBA navigation device, best underwater compass, underwater navigation

    Taking a heading

    A heading is the numerical description attached to the direction you are traveling in. This will always be between 0 and 360. It is common knows as degrees.

    Now that you know how to hold your compass, the next thing you need to be able to do is take a heading. You will take your heading by pointing the compass in the direction you are travelling in. The lubber line is fixed and will always point forward. The card will rotate in a manner that will always have the “N” pointing north. When you look through the window you will see a number, that number is your heading.

    If you would like to learn more about taking a heading, check out or video below.  In it we go over this as well as a few other aspects of compass navigation.

    How do I get back to where I am came from underwater?

    Introducing The Reciprocal course

    This is a very common question. Because we take headings in a circle from 0 to 360 degrees, it is possible to calculate your reciprocal, or opposite heading. To do this we use something called the add/subtract 180 rule. It requires a little math, but it is not difficult.

    Before I explain this, I want to point out that it is not uncommon for people to round either up or down when they take headings to make their calculations easier and there is nothing wrong with you doing that when you are calculating your headings.

    How this rule works is simple: If your heading is above 180 or higher, you subtract 180 to get your reciprocal heading. If your heading is below 179, you add 180 to get your reciprocal course.

    Example 1: Subtract 180

    You are heading 240 degrees west-southwest. In order for you to calculate your reciprocal course, you would subtract 180 degrees from that heading. 240 – 180 = 60 degrees east-northeast.

    Example 2: Add 180

    You are heading 160 degrees east-southeast. In order for you to calculate your reciprocal course, you would add 180 degrees from that heading. 160 + 180 = 340 degrees west-northwest.

     

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    How about natural navigation? How to use your compass to assist in natural navigation.

    SCUBA navigation device, best underwater compass, underwater navigation

    It is a very good idea to use your compass in conjunction with natural navigation. This is a very good way of avoiding tunnel vision, this is when you are so singular focused on your compass that you do not notice what is happening around you. I have seen it happen more than once that a student will focus so diligently on their compass that they will swim right passed the ascent line of the boat without even noticing it.

    By fixing your heading on something on the sea floor. A part of the reef or some other fixed object, you can focus on that object and your surroundings and then fix your heading on another object to continue swimming in your desired direction. This also allows you to continue to enjoy your dive. 

    What if there is a cross current?

    There are times when you will be swimming with a current coming across your body rather than in front or behind you. The idea here is to slightly deviate your swimming directing into to current to compensate. Of course, this is not an exact science, but it will allow you to compensate for the current and get you closer to your desired destination.

    Is the compass the primary / only navigational tool I need?

    Great question! While the compass is what is often emphasized in most beginner SCUBA courses it is not the only navigational tool, nor is it the only way to navigate underwater. Natural Navigation (using the environment itself as a navigational tool) is actually the type of navigation used most often. The reason why compass navigation is emphasized over Natural Navigation is two-fold.

    The first reason why compass navigation is prioritized is because it is incredibly important for performing boat checks. A boat check is what you do when you are unsure of your position underwater (more on that in a moment). During a boat check you ascend to the surface take the bearing on where the boat you need to return to is, and then descend back underwater to follow the heading which you took on the surface. This skill is critical to ensuring you make it back to the dive boat safely. This is why it is critical that you learn how to read and use the compass.

    The second reason why compass navigation is prioritized in most SCUBA classes is because it generally is easier and simpler to teach.

    So how do I perform a boat check using my compass?

    SCUBA navigation device, best underwater compass, underwater navigation

    The boat check is usually only done on shallow reefs. if you ever feel lost or unsure about your position on a reef, provided that there is not a strong current then you can perform a boat check.

    The idea is to go to the surface, take the heading of where the boat is, and then return underwater and swim in the direction of the boat. The reason for returning underwater is because by doing so you avoid stronger currents, waves and boats which are on the surface.

    To perform a boat check you'll need to follow these 6 simple steps:

    1. Ensure that there are no running boats in the area before ascending to perform a boat check. If you hear the sound of an engine, wait for it to go away. Sound travels 4 times faster underwater than it does on land so establishing where the sound is coming from is impossible while diving.
    2. Determine who will be the dive leader. This is the person who will be taking a bearing leading the group back to the boat.
    3. Ascend to the surface slowly to check for the position of the boat.
    4. Inflate your BCD and begin scanning the horizon for the dive boat. You may need to do a full circle sometimes before locating the dive boat.
    5. Once you've located the dive boat, point your compass in its direction and take note of the bearing by looking through the side window. You can use the bezel to lock in the reading you just took.
    6. Deflate your BCD and descend back to the reef / wreck.
    7. Swim back to the dive boat while following the heading that was taken on the surface.

    About dive leaders

    You probably remember from your entry level course that you should decide on a dive leader for the dive. This is especially true with compass navigation. The reason is because it is very easy for 2 different compasses to read slightly differently from each other. It's also very easy for 2 divers each paying attention to their own compass to become easily separated. For this reason it's incredibly important for just one person to be the dive leader and for that person to both follow the heading of the compass and continue to monitor their buddy and dive team while navigating underwater.

    How to Use Your Buddy To Take a Heading

    There are times when you are just going to have to do a boat check. Maybe you got turned around or you were busy paying attention to a turtle or other interesting sea creature.

    When your buddy ascends to do a boat check you can use him or her to take a bearing so you can also get an idea on the direction of the boat.​

    It is important to remember that the person who ascends and takes the bearing is the one who will lead the group back.

    Another good idea is to double check what bearing your buddy took when they get back down.

    ​Click below to check out our video explaining how we do this.

    I hope this has helped you understand the ins and outs of using a compass as a SCUBA navigation device. Keep in mind that the compass is only one of 8 different tools you can use to help you to navigate. If you'd like to learn more about the other 7 tools you can do so by clicking here to get our FREE guide "The 8 Navigational Tools You Should Never Dive Without"