A good dive route starts with a plan
Underwater you cannot always see your surroundings well. Landmarks may be less obvious than expected and it is not always easy to tell exactly where you are.
That is why it helps to think about the route before the dive. Where do you start? Which points do you want to reach? Which direction do you follow between those points, and how do you navigate back?
A route does not have to be complicated. An entry point, a few clear points and a description of the stretches in between can already be a useful starting point.
Decide beforehand which heading you want to swim, roughly how far apart the next points are and which landmarks you expect to come across. Also think about the way back and about what you will do if you cannot find a point.
Navigating with a dive compass
A dive compass helps you hold a chosen direction underwater. You set a heading and use the compass card and the marks on the compass to check that you keep following it.
A compass tells you which direction you are pointing, but not automatically where you are. Current can also push you sideways while your compass still shows the same heading. That is why you combine the compass heading with the distance covered and with landmarks.
How do you hold a dive compass?
Hold the compass in front of you, at about chest height, with the lubber line in line with the centre line of your body. Keep the compass as level as possible, so the card can turn freely and stays easy to read.
Look in the direction you are swimming and keep your arms and compass as steady as possible. Turn your whole body to change direction, rather than only turning your wrist while your body points another way.
Practise this in calm water first. You will notice that even a small change in the position of your wrist or body affects how easily you follow the heading.
Watch out for metal objects and magnetic equipment close by. They can affect what a compass shows. If your compass gives unexpected or changing directions, check that you are holding it correctly and whether there is a possible source of interference nearby.
The main parts of a dive compass
To use a dive compass, it helps to know which parts help you set and follow a heading.
- The lubber line
- The fixed, usually bright red line running across the middle of the compass housing. While diving it shows your swimming direction and lies parallel to the centre line of your body. You use it to read the heading you are following.
- The compass card or needle
- The moving magnetic disc in the compass. North (N) points to magnetic north. The card shows the degrees from 0° to 360° and often the cardinal points. The liquid in the compass damps the movement of the card.
- The bezel
- The rotating ring on the outside of the compass housing. You use it to set a heading. The marks on the ring help you check while swimming that you are holding the chosen direction.
- The index marks
- On many dive compasses one mark consists of two lines or dots that together look like a small house. On the opposite side, 180 degrees away, there is a single line. The marks help you keep the compass card in the right position while following a set heading. The opposite mark can also help you hold the return heading.
- The compass housing
- The transparent, liquid-filled capsule that holds the compass card. The liquid damps quick movements, so the card is calmer to read. The housing protects the parts and is made for use underwater.
- The side-view window
- Some dive compasses have a small window on the side of the housing. It lets you read the heading in degrees straight ahead while holding the compass in your swimming direction. Not every model has one.
How do you set a heading?
You set the bezel before you start swimming, or while facing the right direction. The order is:
- Point the lubber line at your target: the landmark or the direction you want to go.
- Turn the bezel until the north needle falls exactly inside the little house.
- Swim forward and keep the north needle in the house.
Following a heading from a route, such as 120°? First turn the bezel until 120° sits at the lubber line. Then turn your body until the north needle falls in the house and swim in that direction.
The exact operation differs per type of compass. The key principle is that you follow the set heading by watching the position of the compass card relative to the marks.
Do not look only at the compass while swimming. Look ahead too and watch your surroundings. Following your heading and observing your surroundings go together.
What is a compass heading?
A compass heading is a direction expressed in degrees. A full circle has 360 degrees.
- 0° or 360° north
- 90° east
- 180° south
- 270° west
A route often consists of several legs. For example, you first swim 60 metres on a heading of 110° and then change direction to reach the next point.
Recording the heading and distance of each leg makes clear how the route is built up. That helps during the dive, but also when you look at the route on a map beforehand or discuss it with another diver.
Map and compass: declination
A map points to true north, a compass to magnetic north. The difference is called declination. In the Netherlands it is currently about 2 to 3° east: a direction of 220° on the map is 218° on the compass. Every route on Duiken Centraal already includes declination, so you can set its headings directly on your compass.
Example: along the Zeeland Bridge
| Leg | Distance | Compass heading |
|---|
| Pier 1 → Pier 2 | 95 m | 218° |
| Pier 2 → Pier 3 | 95 m | 218° |
| Pier 3 → Pier 1 | 190 m | 038° |
The positions come from the Dutch large-scale topographic register (BGT); the headings are compass headings corrected for the 2026 declination. Right at the piers the compass is unreliable because of the steel; there the row of piers is the landmark and the heading is the check.
How do you measure distance underwater?
A heading tells you which way to go. Distance helps you judge when you should roughly reach the next point. Underwater you cannot always read that distance easily, but there are several ways to learn to work with it.
Practise with your fin kicks
A practical method is to count your fin kicks. First you need to know how far you travel on average with a certain number of kicks. You can practise this in a pool with a known distance:
- Swim a fixed distance, for example 25 metres, at a calm and even pace.
- Count how many fin kicks you need to cover that distance.
- Repeat the exercise a few times and work out your average.
- Use that average to estimate a distance during a dive.
Say you need 40 fin kicks on average to swim 25 metres. Then one kick in that exercise is about 0.6 metres. For a 60-metre leg you would expect about 100 kicks.
This is an example, not a fixed conversion. Your kick changes with current, fatigue, trim, equipment and speed. So also practise with the equipment you dive with, and treat the result as an estimate.
Use an even pace
You can also learn to estimate distance by practising an even swimming pace. If you know how long you normally take over a certain distance, you can use that experience to plan legs.
This method is less reliable when your pace changes or when you swim against the current. So do not use time as your only way to judge your position.
Combine distance with landmarks
No distance method is exact in all conditions. That is why navigation works best when you combine several cues.
Do you expect a change in the bottom or a recognisable object after about 60 metres? Then use both your estimated distance and that landmark to judge whether you have arrived at the right spot.
Do not forget the return heading
The way back is part of planning a dive route too. On a straight line over the same stretch, the opposite heading is 180 degrees from the outbound heading.
If you swim on 70°, for example, the opposite heading is 250°. On a route with several legs, you reverse the order of the points and work out the opposite heading for each leg.
Say you first swim on 70° to point A and then on 140° to point B. For the straight way back you follow the legs in reverse order: from B on 320° back to A, then on 250° to the starting point.
The return heading is an aid, not a guarantee that you will end up exactly at the entry point. Current, deviations while swimming and changing conditions can all affect your position.
So plan not only how to reach a point, but also how to return safely. Take your experience, your buddy and the conditions at the dive site into account.
Allow for current
A compass helps you hold a direction, but it does not tell you which path you are taking over the bottom. On dive sites with current that difference matters.
Swimming against the current may take more effort and you may cover less distance than expected. With the current you can be carried along faster. A cross-current can also mean you do not end up where your heading and fin kicks suggested.
A few practical points:
- Check the conditions beforehand. Take the expected current into account and decide whether the planned route suits your experience.
- Use landmarks. Where possible, check that your surroundings match what you expected along the way.
- Do not rely on fin kicks alone. The same number of kicks can cover a different distance in different current.
- Plan the way back carefully. Swimming back against the current can take more effort than expected.
- Adjust your plan when needed. The actual conditions and your own safety matter more than finishing a planned route.
In the Oosterschelde the current turns around slack water, so the current on the way back may run differently than on the way out. Plan your dive around the moment the current stops.
Read when slack water falls →A recorded route gives you a starting point for navigation. It is no guarantee that you can follow the route exactly in all conditions.
Landmarks make the difference
A heading and a distance are useful, but what if you are not sure you have reached the right point?
So also describe what you can recognise along the way. That can be a pier, an object, a change in the bottom or another clear feature of the dive site.
A good route tells you not only where you swim to, but also what to look out for. Photos and short notes help with that. Another diver can then picture the route and the points they will come across before the dive.
Landmarks are not always visible or unchanged. Use them as a supplement to your navigation and take visibility and conditions into account.
