Diving techniques.

Despite the BS-AC's excellent diver training programme, there appears to be a number of areas which aren't taught about sufficiently, and which I find myself having to impress upon up-and-coming divers time and time again. These are techniques which I believe to be good diving practice, and good advice to junior and intermediate divers, (but I do not in these columns intend to preach to senior divers who have thought the issues through, and whose practices are different to those that I am advocating. They have in most cases many years more experience than I, and have sound reasons for diving as they do.) Nevertheless, for my target audience I shall continue.

Drysuits.

Novice divers under training are taught to use their BCD as their prime source of buoyancy, and some continue to do so when using a drysuit in open water. There are arguments which say 'I put air in my drysuit for comfort', then use my BCD for buoyancy' which I'm afraid that I do not go along with. As a less than fully experienced diver, I do not believe that it is easier and more automatic to control two sources of buoyancy in an emergency when you could be controlling only one. If it is more complicated for you, then think how much more complicated it would be for your rescuer.

My firm advice is that as a novice, or junior sports diver, you dive ONLY on your drysuit. As you gain more experience, you may find that at depths in excess of 30 metres, your suit cannot hold enough air to compensate for suit compression in neoprene drysuits, and that you have to use your BCD as well below these depths, but only at below these depths. Those in membrane drysuits, (or some compressed neoprene drysuits) should never need to use their BCD if they are properly weighted.

Neutral buoyancy

My observations lead me to believe that certain intermediate divers seem to think that neutral buoyancy is the state where one neither increases nor decreases one's depth in the water. This is not the case.

A 25kg lump of lead dangling on 5 metres of rope over the side of a boat does not change its depth, but cannot, with any stretching of the imagination, be classed as being neutrally buoyant. Nor can, to my mind, a diver who is oriented vertically in the water, and finning for all he is worth, who happens to stay at the same depth.

If you want to demonstrate neutral buoyancy, hang vertically in the water, cross your ankles (you can't fin that way) and then adjust your buoyancy until you don't go up or down. Anything else, and you are just fooling yourself that you have control of your buoyancy. Why don't you try it?

Shot lines

Many less-than-experienced divers, in my observations, do not properly understand the characteristics and limitations of shot lines.

These long thin items are an immense boon to diving, but have severe limitations which frequently catch divers out. There are three main assumptions about shot lines which are repeatedly proved wrong.

1. The shot is super-glued to the seabed/wreck

Wrong! The bottom of a shotline, even on hardboats, is usually a small shot, which has limited weight and can easily be pulled off the bottom/wreck even by the tide. let alone by divers pulling themselves down the line.

2. The buoy is super-glued to the surface

Wrong! While buoys are usually more secure than the shot, those who dived the M2 submarine in Dorset will never forget the experience of meeting the small marker buoy at depths in excess of 6 metres.

3. No matter what, the line remains straight.

Oddly enough, this only occurs with lazy shots, which are seldom used. Usually what happens, in a slackish tide, is that inexperienced divers, on descent, hit the bottom, then have to swim quite some distance horizontally, following the line, to find the wreck. (Think about it!). The converse is that divers ascending either

A. Drag from the bottom, leaving long loops to tangle themselves up in at the stop depth, .. or

B. Hang from the top, leaving long loops below them to tangle the next pair up.

Of course the only obvious answer to all of these is to treat the shot line as a reference guide, neither dragging nor hanging onto it, but using it as a spacial reference to reach your objective. In the ideal world you would be able to swim down, and up the shot line, without ever touching it, using it merely as a reference, and this is the ideal that you should be aiming for. So - the rules for using a shot line are;

1. Never drag a shot line down or up.

2. Use it only as a guide

3. Look below you, then above you, and aim to keep the shotline straight by adjusting your buoyancy to be neutral and swimming along the shotline at all times.

Ideally, you should be able to make an 'OK' sign in one hand, put the line in the middle of the 'O', and descend or ascent the shot line without the rope ever touching the inside of your fingers. However, in a running current, it's every man for himself - but don't be diverted from the ideal when conditions are right.

This page was last updated on : 06 Sep 2011