How To Navigate with a Compass Underwater when you are scuba diving. A photo of a standard diving compass.
A compass assists scuba divers with underwater navigation.

Navigation using maps, even GPS systems, especially in a car has to be among the number one causes for couples arguing. The word compass alone can send shivers down ones’ spine. Now, let’s take all that and recreate a navigation scenario underwater on your third-ever dive in the ocean. Furthermore, your partner is your buddy. Nothing can go wrong, right? So let’s take a look at some tips on how to navigate with a compass underwater which should help alleviate some of the anxiety!

How To Navigate with a Compass Underwater

Truth be told, underwater navigation using a compass is not all that different from compass navigation on land. The primary differences are the addition of vertical space and movement, additional gauge monitoring introducing time pressure, limited visibility, and currents. Using natural navigation scuba diving can also greatly improve your navigating success. Spacial awareness and correct compass positioning are both essential in achieving your goals in underwater navigation.

We will have a look at how we can deal with these additional challenges that arise during underwater navigation. But first, let’s go over the very basics.

How to use a Compass

A compass is similar to a personal computer because it does not interpret what you want and tell you an answer. You need to tell it what you want it to do.

Similarly, a compass does not interpret your navigation needs or tell you where to go. It simply helps you orientate yourself in relation to the magnetic north, which then helps you navigate.

And yes, on a standard underwater compass, the magnetic north needle always points north.

A compass is designed to aid in navigation and has, therefore, the main four cardinal directions painted on it. These are separated by a 90-degree angle.

These are North (N), East (E), South (S), and West (W).

National Geographic has a great little exercise to familiarise yourself with cardinal directions. Practicing on land really helps when learning how to navigate with a compass underwater.

A compass is an essential piece of a Rescue Diver’s Equipment list.

Interpreting this Information

Now, as navigators, we interpret the direction we want to travel in based on our starting point and the cardinal directions. The direction we are facing when looking down at our compass is our travel direction.

Navigation on its most basic level is a vector, or straight line, between point A and point B. The direction of that travel path can be determined by standing on point A and rotating to face point B and reading your compass heading.

Divers avoid complex travel paths underwater and often employ the compass reciprocal heading, keeping it really simple.

This allows divers to go from point A to point B and then back to point A, their starting point, easily. Reciprocal is just a fancy word for going and coming back in equal direction and distance. It is mathematically a 180-degree turn at point B reciprocating the starting travel direction in order to end up at the starting point.

So remember that you are less likely to get lost traveling slowly over a short distance. Furthermore, it is ok to get lost. No need to panic, as we can ascend if we need to. If we employed the former rule we should not be too far from our starting point.

You will learn how to do this in your first level certifications courses with PADI, SSI or RAID.

The Compass Lubber Line

The compass lubber line is usually a red line painted on the face of the compass. This line helps the navigator visualise the directional travel path from their starting point to their desired travel destination. If we wanted to travel not exactly in one of the main four cardinal directions, we can use the lubber line to aid in establishing direction.

Here is an image of three different travel directions and what they look like on our compass.

Compass Lubber Line Travel Direction Example

From left to right, we are traveling North-West, South-West and finally directly West.

Notice how this compass has a lubber line that is about 21 degrees off centre where the wrist straps are?

Offset Compass Lubber Line

This means we do not need to hold it as rigidly at a 90-degree angle. It allows for a more casual glance for more advanced navigators.

As long as we imagine our travel direction along the lubber line (red line) we are traveling in that direction.

Underwater Navigation Challenges

Still, this all sounds a bit technical and complicated. So let’s dive into the added challenges when navigating underwater.

Three dimensional movement

I can also go up and down in the water. This is a common mistake new divers make. The added task of navigation causes them to perceptually narrow on their compass. Meaning the diver will often forget to check their depth, check their air, or even on their buddy.

Maintaining a buddy system is part of safe diving practice. See what else divers can do for their own safety.

In order to avoid ascending or descending while maintaining a travel direction underwater, divers wear their compass and computer on their right wrist and grab their left elbow with their right hand.

Here is what that looks like:

Correct Compass Position when Navigating Underwater

This creates a sort of ‘cockpit’ where they can easily see their dive computer as well as their travel direction indicated by the lubber line. This position also means that they are swimming in the direction of the lubber line as this keeps the lubber line parallel to their bodies.

Holding a compass too casually and not imagining the travel direction line means you will not end up at the desired destination.

Like in this picture below:

Wrong Compass Position

If we use the lubber line to travel North-East in the above situation, we would not end up traveling in the direction of the red line. The green line is the direction we are actually traveling in, which would be directly North.

Monitoring Air and NDL as well as Depth

Underwater divers need to continually monitor their no-decompression limits, remaining air supply, as well as their depth. They also need to maintain a buddy system. Because there is limited time at depth, we cannot park the car on the side of the road and rotate our huge paper map several times around until we realize we didn’t need to rotate it in the first place.

This often causes new divers to commit to a travel direction and stick with it without making sure they are maintaining it and are actually swimming in the right direction.

Limited Visibility and the lack of Peripheral References

On land, once you have established your travel direction and you see a prominent mountain in the distance, you have this peripheral reference to aid you in navigation, even over long distances.

Underwater, visibility is sometimes limited to 10-15 meters and at times much worse at almost zero visibility. This forces divers to focus on and trust their compass direction more. We still use natural navigation scuba diving but in a different fashion.

For example, once I have established my travel direction and I see a distinct coral in that direction, I can then use this coral as a natural reference. Once I reach it, I can find a new natural reference in my travel direction. This will also aid me when returning on my reciprocal heading as I should recognize some of these visual references on my return journey.

Underwater Currents

If you are doing everything correctly but you are swimming perpendicular to a current, it will push you off course. In order to not lose your desired travel direction, you can use natural and visual references. If you are near the bottom, watch for small shells, sea urchins, corals, etc, and imagine your travel direction in a line between these.

If you notice that they are moving left or right away from your imagined line, you know you need to compensate for the current.

My best navigation tip is to always validate where you are as opposed to getting lost and trying to re-establish direction underwater.

What does this mean?

Let’s say I descend on a mooring line, I always turn my body on the surface in my desired travel direction and descend that way.

At the bottom, I find a natural reference before I swim into the dive site and remember the depth. Then I take a heading using my compass and in a roving path follow this direction using natural references and validating my direction using the compass direction.

Once I want to turn around, I simply do a reciprocal heading and travel parallel to my first path to navigate back to the boat.

What about the fancy numbers on top?

These are your degree headings painted on the bezel of your compass. If you needed to travel exactly in a 112-degree heading for a long distance to find a small object, degree heading come in handy. However in scuba diving we almost never travel far or need to travel in very exact directions. We can divide the main four cardinal directions and that normally suffices with the aid of natural navigation.

Keep it simple when learning how to navigate with a compass underwater on your scuba diving adventures.

So, before you navigate yourself into the next argument with your better half underwater, remember these simple steps on how to navigate with a compass underwater.

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