Getting your bearings
Its surprising how often divers go off at a tangent under water - even those who should know better, says John Liddiard. He provides his own guide to the art of diving navigation Divernet

A DIVER HAS A BEARING TO FOLLOW. He raises his compass arm, turns the bezel to set the bearing, takes an initial sighting, lines up - and then swims off at a tangent. Its a common sight under water, and not just among inexperienced divers. I have seen dive guides and even instructors, supposedly qualified to teach underwater navigation, make the same mistake.
The problem begins with the way divers wrist compasses are marked with a big direction arrow across the wrist. Such arrows are almost contrived to lead them astray. The diver holds his wrist across the body and lines up with the arrow but, alas, the wrist is rarely square to the direction of travel, the arrow points off to one side and, without thinking further, he swims in the wrong direction.
If applied consistently, such a fundamental mistake will even pass the usual compass navigation exercises of diver training. A diver can swim off the bearing out, then the reciprocal off the bearing back, ending up perfectly at his starting point. He can even swim a perfectly wrong square and end up back at his starting point. But given an accurately measured bearing to follow to the dive site, he will miss it by 45 or so every time.
So lets start by solving this basic error. A technique often taught is that a diver can keep his compass arm square by holding his opposite arm close to the elbow.
Its another technique that is wonderful for training exercises, but on a real dive you have other things to keep your hands busy. With your arm square, its hard to read the compass. Divers attempting this method on a real dive invariably slip up, letting their arm stray off-square, failing to make any correction, and getting back to the basic mistake without realising it.
A more realistic solution for using a wrist compass is simply to be constantly aware of the pitfalls and make a mental adjustment to the direction of travel.
Rather than lining the bearing up for the direction arrow across the wrist, line it up for an imaginary arrow 45 (or whatever your personal correction factor is) off line with the course mark.
The same principle applies with a compass that is part of a console. While it is easier for a diver to hold a console square to the body, square can be awkward and soon slip. However, with a little ingenuity a console can sometimes be taken apart and reassembled with the body of a compass rotated to put the direction arrow at a more convenient angle.
For serious accuracy, the best solution is to hold the compass by hand. A diver can take the compass off his wrist and hold it across the palm of his hand with the direction arrow accurate for his direction of travel.
Removing a compass from your wrist and then putting it back again repeatedly is inconvenient, which in the long run leads back to the original sloppy navigation problem.
An alternative is to attach the compass to the end of a shoulder-strap. In many cases this is just the right length to be able to pull the compass up and sight across the direction arrow.
I am not a great fan of introducing extra dangly bits. Anything with the potential for dangling will invariably get in the way at some point. For occasional use it is easier simply to keep a compass in a BC pocket, perhaps attached to a lanyard, or even attached to a retractable lanyard. Thats one device of which Im not a great fan, but in this case I will admit that it has merits.
On an average UK dive, I already have enough dangly bits with camera, sketch-pad and ppO2 monitors for a rebreather, so attaching a compass to a shoulder strap is not the answer for me. My personal solution is to attach a compass to another bit of kit that is already on a lanyard, perhaps a reel or a camera lanyard.

Button compasses
If absolute bearing accuracy is not essential, a tiny button compass can be convenient in this role. I also carry a button compass attached to my BC crinkly hose. It is discreetly out of the way, barely noticeable, and easy to hold and use when I need it.
A word of caution here: wrapping a compass around a dive light is not such a good idea. The metal in the light and electric current will cause an incorrect reading, either dragging the needle off north or, if strong enough, just lining it up with the light.
So its back to basics again. I usually carry only a button compass, which in my experience is good for holding a course to within 20Â or so with careful use.
It is extremely rare for me to need to follow a bearing more accurately than that under water. Higher accuracy is relevant only to compass training, not to practical diving. So why trouble myself with a more expensive, bulkier and more awkward-to-use compass with a false sense of security in the resolution of the bezel
For the purists, my choice rests in the difference between accuracy and resolution. I would rather follow accurately a device of resolution just good enough for the job, than follow inaccurately a device of resolution much higher than that required.

Reading rocks
So how do I get away with a small compass that cant be read more accurately than 20, and still manage to navigate successfully A flippant answer would be that much of my UK diving is on wrecks, so a compass would be useless anyway. Wreck navigation is all about recognising features, understanding the way ships are built and how they collapse. Have a look through your pile of old magazines for March 2002 and Anatomy of a Shipwreck, or look it up on Net.
Successful navigation when not on a wreck has many similarities to the techniques that work on one.
A lot of it has to do with understanding the shape and geology of the seabed, noting depths and reading clues through the dive, to build a mental picture of the dive site and surrounding area.
Rocks are rarely random. Its not unusual for them to be lined up in ledges, often of varying depth, but overall providing some regular structure to a reef or system of reefs. For example, part-submerged rocks running parallel to a cliff-face usually indicate the lines of gullies and canyons running parallel to the cliff-face.
A compass is needed only to give the basic direction of which way to follow a gully in the rocks.
Another clue may be provided by the layering of rocks. Some layers are softer than others, so under water have eroded faster to leave lines of ledges. Once the general direction of those ledges is understood, they can be used as a navigation guide with little further reference to a compass.
On a larger scale, softer areas of rock can be eroded and cut into a cliff face, leaving a series of ridges and valleys running perpendicular to that face. Directions to a dive site can be a simple Head roughly east to the second valley at about 12m.

Sandy ripples
On a sandy seabed, the prevailing wave pattern often leaves ripples, which run along the waves. Sand ripples may change with the direction of a storm, but are hardly likely to change during a dive, so can provide a guide to direction.
Look closely, particularly in shallow water, and the actual direction of the waves gives a different shape to the leading and trailing edge of a ripple.
The surge from waves themselves can also provide a clue to direction, but will not necessarily line up perfectly with the sand ripples. It is easy to line up with the surge or across it, but keeping a constant course at a diagonal takes a bit more practice.
As with sand ripples having a different shape on the leading and trailing edge, wave surge feels different depending on whether you are heading with or against the waves, and can also provide clues of an approaching constriction or barrier.

Current clues
Among kelpy rocks, even if you cant feel the wave surge, look up and the kelp will be flowing back and forth with the waves. A more uniform direction to fronds of kelp shows the direction of the current.
OK, so divers should be able to feel the current directly, but on an uneven seabed current tends to swirl round rocks, giving back-eddies and funnels along gullies. As a diver, you can feel what the current is doing here, but kelp indicates what it is doing there and what it is doing above.
To use current successfully to aid navigation requires building a mental picture of how it swirls and eddies about more complicated dive sites. Divers must also bear in mind that on a dive close to slack water the currents direction could change through 180.

Sun and shadows
Another direction indicator, particularly on a bright day in shallow water, is the direction of the sun. One catch to navigating by the sun is that refraction at the surface of the sea puts the sun higher in the sky than it would appear from the boat or shore.
The physics term for this is Snells Window. Even so, the sun can be used to give a direction to east, south or west, depending on the time of day.
In very strong sunlight you dont even need to look up, as even under water the direction of shadows provides the direction of the sun.
Overall, I think I subconsciously sum up and filter clues from all these sources, though I do have to think twice about the midday sun when diving in the southern hemisphere. Somehow, a sun from the north just doesnt feel right.



A
A compass attached to a shoulder strap can be lifted and used accurately
left
left hand holds right arm close to elbow, keeping the left wrist and compass square to direction of travel
compass
compass removed from wrist and hand held, the direction arrow now lined up with divers body
Three
Three ways of attaching your button compass, 1
2
2
3
3
Rocks
Rocks in layers running parallel to the cliff face are repeated under water
Look
Look below the kelp to see seams in the rock running parallel to the cliff
Drifting
Drifting across ledges - note the gravel-filled gully running from the right of the picture, indicating the direction of the shore
Waves
Waves above sand often carve ridges below
Flying
Flying kelp indicates current or wave surge
In
In the afternoon, the sun moves round from south to west

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