There and back again
WHEN MY SON GOT MARRIED in Poland, he sent me an address and told me that it was 150 miles from Krakow. I rented a car at Krakow airport and followed the instructions of the on-board GPS.
It worked. Navigation under water appears to be more difficult.
If the water is exceptionally clear and the light good, you can navigate by looking at where you’re going and noting where you’ve been.
Training manuals call it “pilotage” – making a note of any prominent features that you might pass.
If you keep the reef wall to one side, it’s not likely you’ll go the wrong way, although I have known divers overshoot their moored boat on the way back.
When the terrain is less simple, you can always use the position of the sun shining through the surface to give you a clue, but it is only that, a clue.
It makes sense to orientate yourself before getting into the water, and then at least have an inkling of north, south, east and west. This does mean paying attention to the briefing, or studying a map of the site.
Once the visibility drops to British levels, things get a lot more complicated. It’s like being a stranger in town during the famous London smog of 1953. It can even be difficult to know which way is up, and if you follow your bubbles you need to be sure there’s no strong current driving them other ways.
However, the way to the surface is crucial, so let’s assume that you have a delayed SMB or a shotline to guide you. You can then be picked up by your boat, assuming that it finds you. That’s when a surface-marker becomes a potential life-saver.
A depth-gauge or computer that reads ambient depth is also an important navigational instrument for a diver. It will tell you if you are going deeper or shallower.
That leaves getting to and from where you want to go, and navigation certainly is a crucial skill when shore-diving or diving from a moored vessel.
THE COMPASS IS THE DIVER’S FRIEND. Learn how to use it. We often see people practising with compasses in the car parks of inland sites before going into the water and getting hopelessly lost.
The needle or compass card of a magnetic compass needs to be able to swing freely, and to be unaffected by the kit you’re wearing. That big steel tank on your back can cause problems, so hold the compass well away in front of you.
Take a bearing before you set off, and mark the reciprocal bearing before departure too, so that you have a chance of finding your way back.
This should be simple once in the sea, but unfortunately the ocean doesn’t lie still. It has currents and tidal flows that can ensure that you don’t get to where you think you’re going, even if you do everything right.
There was the famous case many years ago of the diving officer of BSAC No 1 branch.
He set off from the Isle of Wight in the club-boat during a fog, headed due north on his compass and managed to miss the British mainland entirely!
Under water, you’re effectively in a fog. You might need to vector your course to account for a current, even a gentle one.
What this means is that you need to use a combination of skills. Your compass can give you a heading, but you need to be aware of the direction in which the water is flowing by looking at marine life such as seaweed or soft coral that might be affected by it.
You also need to look where you’re going, and from time to time look back at where you’ve been to help you memorise the features you pass.
I remember one particular wreck expert organising a group of divers to swim out at different bearings from the anchored dive-boat in order to perform a radial search for a wreck he thought they were near.
The current was so strong that I knew all of them would soon be swimming on the same bearing as the current, regardless of any bearing they tried to follow – apart from the wreck expert, who took the direction of the current directly from the back of the boat.
You also needs to gets to grips with your compass. A reciprocal course is +/-180° of the heading you first take.
You could divide your dive into four roughly equal lengths, turning in the same direction through 90° each time you’ve counted a given number of fin-strokes. That should bring you back to near where you started, allowing for water movement.
Three lengths with two turns of 60° will give you a triangular course. It’s great in theory.
You need to hold a magnetic compass out in front of you and horizontally, preferably with the symmetry of two hands. A simple compass needle will always swing to the north, provided it’s free to swing, so check often that it can do this. If it appears to be locked in place, you’re probably holding it at an angle.
The latest electronic compasses included with many computers are almost all tilt-free and very easy to use, but you must remember to calibrate yours for the part of the world you’re in before you rely on it.
A compass is a useful navigational tool, as long as you’re aware of its limitations.
AT NIGHT, IT’S USUALLY SENSIBLE to leave a marker lamp or strobe light at your point of entry/exit.
Bear in mind that this can become obscured from sight by obstructions such as reef bommies, or a wreck.
Don’t penetrate a wreck at night, even if it was easy during daylight hours, unless you have a lot of reliable marker lamps to leave as a trail, and a reliable guide. Even then, wreck-penetration can be difficult for the unwary.
A moored dive-boat will swing in the wind. Depending on the depth of water and the lengths of the mooring-line and the vessel, it can swing in a very large arc.
Only recently I witnessed a diver miss a wreck entirely during daylight hours in Truk – and we were moored over it!
On wrecks in home waters with poor visibility and no view of the surface, it’s very easy to pass under or into a feature of the wreck without realising it, and be unaware that you have no clear route to the surface. You need to be able to go back the way you came.
Similarly, wrecks that lie on their sides can be disorientating, even in the most benign conditions. Be aware that other divers, or even you, can reduce visibility to zero through poor finning technique.
Because compasses use magnetism to work, they are pretty useless when diving on steel wrecks, in which case it is essential in poor visibility to use a bottom-winder or spool and line.
You’ll probably descend some sort of line from the surface down onto the wreck. Once there, clip off the line at your starting point and unreel it as you go. To ensure that it doesn’t get pulled into cracks and hazards that will make it impossible to follow on the way back, be sure to belay it properly by repeatedly tying it off at points on your way. This is crucial to your survival.
“Line-laying is an art,” a famous cave-diver used to say. Be aware that a long untied length of line can drift into a crevice, making it impossible to follow later. That’s why cave-divers also use the mantra: “Lose the line and lose your life.”
The first recorded line-layer was Theseus in Greek mythology, who used a ball of string to enter the Minotaur’s Labyrinth and find his way out again.
It worked for him!