Underwater navigation

In short

Navigating underwater means knowing where you are, where you came from and how to get back to the exit point. You combine natural landmarks (relief, depth, sand, light, current) and, when they are not enough, the compass. You estimate the distance covered by fin kicks or by time. It all starts at the surface: study the site and agree on the route at the briefing. And when in doubt, ascend safely rather than search for a long time.

Why it matters

A team that knows where it is going uses less air, avoids long surface swims and returns to the boat without stress. A lost team, on the other hand, worries, gets out of breath and may end up far from the boat, sometimes in a busy or current-swept area. Navigation is also a skill you build gradually: practise it with a guide first before diving independently.

Preparing your navigation

• Study the site: chart, club map, the guide's description, depths and shape of the relief.
• Locate the mooring: from the surface, look at where the boat is in relation to the coast and the sun; on the way down, observe the bottom around the mooring.
• Agree on the route at the briefing: direction of the dive, turning point at a given pressure or time, expected landmarks, ascent point.
• Plan a fallback: if returning to the mooring is not possible, where and how to ascend.

Natural landmarks

• Relief and depth: follow a wall, a crack, a line of rocks; the depth tells you which side is offshore or towards the coast.
• Wall on the right or on the left: on the way out, the wall is on one side; on the way back, it should be on the other.
• Sand ripples: they usually run parallel to the coast, shaped by the swell.
• Light: the position of the sun gives a general direction, especially in shallow water; the water is often clearer towards the open sea.
• Current: its direction is a landmark, as long as it does not change during the dive.
• Notable marine life and rocks: a large gorgonian, an anchor, a wreck, a school of fish that stays in the same place.

Look back regularly: a landmark does not look the same on the way out and on the way back.

The compass

Reading and holding it

The compass shows magnetic north. You use it with its lubber line, the mark that shows the direction of travel.

• Hold the compass level, arm outstretched or close to the body, with the lubber line aligned with the axis of your body.
• Keep it away from metal objects and lights, which deflect the needle.
• Move forward keeping the needle in the set marks, looking ahead and not only at the compass.

Taking a heading and returning

• Taking a heading: aim in the desired direction with the lubber line, then turn the bezel to place its marks on the needle.
• Reciprocal heading: to come back, add or subtract 180°; most compasses have a return mark.
• Standard patterns: out-and-back (heading, then reciprocal), square (four sides at 90°) and triangle (three sides at 120°) let you return to the starting point with a simple plan.

Common mistakes

• compass tilted or not aligned with the body;
• needle disturbed by a light, a cylinder, a wreck;
• drift caused by the current, which pushes the team sideways even when the heading is held;
• losing track of time or distance covered.

Estimating distance

• Fin kick cycles: count your cycles over a known distance, for example in a pool or along a line; you will know how many cycles make 10 m.
• Time: at a steady speed, a duration matches a distance.
• Air used: coming back the same way, you use roughly as much air as on the way out, which also helps decide when to turn around.

What to do when in doubt

• Stop, gather the team and look for a known landmark.
• Do not prolong the search: it costs air and time.
• Ascend vertically and safely, with a stop, rather than swimming a long way underwater. At the surface, signal to the boat and wait for it to come.
• If you have lost your team, follow the procedure agreed at the briefing (see the safety guide).

Key takeaways

• Study the site and agree on the route at the briefing.
• Combine natural landmarks and compass; look back to see the way home.
• Compass level, aligned with the body, away from metal objects.
• Estimate distance by fin kicks, time and air used.
• When in doubt, ascend safely rather than search for a long time.

Further reading

During a dive, the watch shows a compass, a return heading and the GPS status. GPS does not work underwater: the position is recorded at the surface when a signal is available, which lets you review the entry and exit points in the session. Compass pattern diagrams will be added from the guide image library. The current guide complements this one.