Scuba Dead Reckoning Navigation or How to Use a Compass

Let me tell you a story before diving into dive reckoning navigation.

I still remember how I felt the first time a Divemaster brought us back to the boat after a complex dive.

It happened some years ago, in the Red Sea. I was lucky enough to do a wreck graveyard recreational dive in Abu Nuhas, whose name means “The father of bad luck” in Egyptian. It is a shallow reef barely distinguishable in the distance. Imagine the number of ships that have sunk in its waters.  The experience was incredible, even more for a discovery lover like me.

At this time, I was still a novice in diving.

There I was, with my brand-new Open Water certification and about to be shocked by the possibilities of dead reckoning navigation applied to diving.

We jumped into the sea right on top of the first wreck. After visiting it, we followed the guide to the second wreck. Then, we changed direction to get to a third wreck. We also faced a slight cross current from the third sunk ship to the fourth. By this time, I was at my wit’s end. If I had to go home alone, I would have cried. But the group guide signaled us to ascend, and when we stuck our heads out of the water, there was our transport. How the hell had he done it?

Magic? No, dead reckoning navigation.

1. What Is Dead Reckoning Navigation

If we understand navigation as the art of finding the way, dead reckoning navigation estimates our situation at a given time.

For that, it needs to consider the departure point, the direction, and the distance navigated.

It is useful for nautical navigation, aviation, and robotic navigation on land.

2. What Does It Mean to Navigate by Dead Reckoning in Diving

 Well, but…, How can I do it scuba diving? The answer is simple: using a diving compass.

Yes, dead reckoning navigation and compass diving navigation are synonymous.

A ship crew has to do very difficult calculations for traveling long distances, but for a diver, they are much simpler. So, don’t worry, sailing by estimation is much easier than you might think.

In diving, we use two types of navigation.

1. Natural navigation

It consists of recognizing natural markers along the way, so we can plot a path back home and relocate if we get distracted.

We pass the hat-shaped rock, reach the abandoned anchor and continue to the brain-shaped coral with tube sponges on the sides and we return. 🤔 🤔👌

2. Dead reckoning or compass diving

It is used on more complicated dives, where you are not moving in a straight line, there is poor visibility, and you are crossing currents or moving in complex navigation conditions.

3. Dead Reckoning or Compass Diving Uses

Most of us hire the services of a dive guide to conducting our dives, but as we gain skills in diving, we also seek more autonomy. At this point, dead reckoning is very useful.

1. Litoral dead reckoning

When we do shore dives, many times the dive starts at one beach and ends at another. So, we use the services of an escort car, which picks up the divers at the agreed beach.

We don’t want to end up on the wrong beach, do we? Much less ascending and finding ourselves in the middle of a cliff where we can’t get out.

2. Dead reckoning marine navigation in low visibility conditions

I have a scuba diver friend who works for the police. It is often an unpleasant job where they spend hours searching for drug bales or missing persons in zero visibility conditions. The compass is a great ally for him.

3. Drift dive compass navigation

In Medas Islands, there is a chasm full of lobsters.

It is 4 minutes of swimming at a 90-degree angle from the Cow cave.

However, very few can reach it.

What is the problem?

To go from the cave to the chasm, the diver has to cross a current. It goes from his or her right to the left. So, it is necessary to calculate displacement caused by the current to follow the right direction. This is another dead reckoning navigation example.

4. Dead reckoning navigation from a boat

Do you remember the story of my wreck graveyard dive? It is a good example of how the diving compass helps us with navigation when you are not moving in a straight line and still have to return to the starting point or the agreed extraction point.

4. How to Do Dead Reckoning Navigation

To write this part of the article, we have consulted our expert, Course Director, and technical diver with more than 30 years of experience Víctor Córdoba.

First, Victor’s advice is to know the parts of a compass. For this, we recommend you read the article The Importance of The Compass in Diving

Although it would be better to take the specialization course Navigation Dive

When the navigation depends on you, preparing for the dive is vital. So, getting a local guide or diver to brief you on the dive will be very helpful. – Says our expert.

Surface orientation is going to be vital. – Mr. Cordoba states –

For example, at first sight, you know the reef is 50 meters away and covering this distance takes you 4 minutes. If you have been flapping your fins for 10 minutes, you’ve made a mistake.

Using the compass for dead reckoning does not mean forgetting natural navigation. Take key points as references when visibility allows. Also, take depth references with the dive computer.

As we said before, dead reckoning marine navigation takes into account the direction and the distance.

We have 5 ways to measure the distance:

• kick cycles,
• elapsed time,
• bottle pressure,
• arm span measures
• measuring line or tape.

Undoubtedly, the most accurate method is to use a tape measure. However, it is only good for measuring short distances on relatively flat terrain. The same goes for arm spans, you can’t go 200 meters pivoting on your outstretched arm.

The most commonly used methods in diving are kick cycles and elapsed time.

For kick cycles, we need to measure the length of our kick cycle. So, we swim 30 meters and count the number of kick cycles it has taken us. If to swim 30 meters, you need 30 cycles; you will know that with each kick cycle, you advance 1m.

We can do something similar to estimate distance as a function of time. You swim 30 m and measure how long it takes you to swim it. In this way, you can calculate the distance by timing yourself as you swim.

By the way, all methods of estimating speed and distance involve an error rate. Probably, tank pressure is the less reliable of all of them. It is only good enough when we bustle in the same way, and even in this case, most of the time, we come back less deep than when we went. In addition, as you know, the pressure drop in your tank depends on the depth and diver’s effort. Therefore, we should estimate distance using any other method and always control tank pressure to ensure you won’t run out of air.

5. Dead Reckoning Navigation using a compass properly

 Our Course Director gives us 3 tips:

1. The compass is just a navigation aid, don’t get obsessed with it

There is no point in moving forward, looking only at the compass. Because the compass depends on you, and you can make mistakes. Doing so is like driving by looking at the GPS and continuing to listen to it when it tells you to drive off a bridge. Therefore, be careful, watch where you are going, and use common sense.

2. Keep the compass in line with your body

Perhaps you have seen this in a photograph of a student during a Navigation dive course. He or she extends an arm and placing the one with the compass on top in a 90º angle. They are not imitating Superman. They are learning to use the compass.

The lubber line of the compass, which is the line that indicates the direction we are going to take, should be right in front of us always. In this way, we will not deviate from our path.

Holding the compass with both hands and keeping your arms close to your body is another good way to keep the compass aligned with you.

3. Make sure the magnetic needle rotates freely

Your compass must be kept in a horizontal position and not bring the compass close to magnetic devices.

My advice is to check often that the needle is free by turning your compass and checking that it is still pointing north. – Says Victor Cordoba –

We cannot finish this article without giving you one last piece of advice about dead reckoning navigation. The best way to learn it is to get your Advanced Diver Certification. Taking it you will learn to:

• how to use a diving compass;
• navigate making multiple turns;
• dead reckoning navigation estimating distance underwater.