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.