Low Visibility Diving
Low visibility is the reality for much of the diving that takes place in coastal and inland waters in Britain and northern Europe. There are many reasons why the visibility is restricted. Some of these are seasonal and others depend on the location.
Reasons for Low Visibility Diving
Many professional and commercial divers have no choice in the matter. The work they are contracted to carry out may occur in waters which have naturally low visibility or the act of working itself may cause a disturbance which reduces visibility. Sport divers, however, have a choice as to where they dive and consequently they may or may not want to dive in low visibility waters.
Techniques for Low-Visibility Diving
The major problems that low visibility diving causes to the diver is that it reduces his ability to communicate with his buddy and, unless steps are taken to compensate for this, both the diver and his buddy are put at increased risk.
In good visibility the diver and his buddy can swim up to several meters apart if they wish and still maintain good contact and communication. As visibility is reduced, maintaining contact between the divers becomes an increasing problem.
With visibility of above 5 meters there should be no problem for the divers.
Below 2 meters a buddy line is essential for maintaining contact and below 1 meter seriously consider a lifeline from the surface tethered to either yourself or buddy.
There are a number of techniques which can reduce disturbance of the bottom, and hence increase visibility. The first is to master the art of buoyancy control so that the diver can move along above the bottom. Secondly, avoid using legs and fins for propulsion as this causes severe bottom disturbance. Pull yourself along using hands and arms. Boulders, kelp, etc, make good anchor points to pull yourself along. Keeping your fins still has the added advantage that your buddy, following close behind and trying to maintain contact , is less likely to have his mask dislodged by them.
Descents and ascents need special care in low visibility water. Many divers descend feet first to avoid banging into the bottom with their head. Surfacing is usually performed cautiously, with a hand above the head, to avoid bumping into surface objects such as jetties or moored boats.
The use of the buddy line between divers in no way conflicts with the use of a lifeline to the surface and a surface marker buoy. The two lines serve quite distinct roles. The first allows constant communication between the diving pair. The second keeps the surface party in contact with the divers.
There is a temptation to simplify matters and dispense with the buddy line by allowing the second diver to hold on to the surface marker buoy line some distance away from the diver with the reel. This method suffers from the fact that a diver holding onto the line makes the surface marker buoy even more difficult to control, and the natural tugging of the buoy on the line makes it very difficult for either diver to know whether messages are being sent or not.
Navigation while using a buddy line can be much more difficult. It is very easy for the leading diver to be drawn off course by a constant pull on the buddy line from his buddy. In low visibility it is very difficult to realize that this is happening. The effect on navigation is exactly the same as that of a tidal stream onto one side of the divers and needs to be allowed for or guarded against.
Buddy lines have limited application for low-visibility diving in confined spaces or where there are obstructions on the bottom. Divers should carry a knife in case of inextricable entanglement, but in using it contact with the buddy and surface is likely to be lost. In these conditions other techniques may be more appropriate.
For diving in very low visibility of 1 meter or less it is wise to consider replacing independent swimming divers with a diver secured by a lifeline to the surface and tended by another experienced diver.
The line must be securely tied to the roped diver. The rope should be passed round the body under all the equipment. The diver should be able to jettison BCD and weight belt without having to remove the rope. The other end of the line should be in the hands of the tender, but the tender should tie the free end to an appropriate object (e.g tree, boat, etc) so that if it is jerked from his hands it is not lost.
The tender should be prepared to give all his attention to the diver while he is in the water. If he is not paying attention, he may miss some signals. The tender should ensure that the line is kept free of obstructions and that the line does not become tangled. Coiling and uncoiling the line as it comes in and out is good practice. The line should be neither too tight nor too slack. In the first case, the diver's progress will be impeded, while in the second, signals are difficult to pass on.
The tender must be prepared to react to any obvious difficulty or if signals remain unanswered or confused. The best action is to mobilize the stand-by diver, who will go down the lifeline of the diver in trouble, but secured by his own line and tender. Trying to haul a diver to the surface on his lifeline may only compound the situation if the line is caught on an obstruction, it is therefore something of a gamble attempting this method of recovery.
The tender should remember that the safety and comfort of the diver is his responsibility. It is bad practice to change tenders while the diver is down as signals may be lost or the diver be otherwise confused by the change.
From the diver's viewpoint, patience is the keyword. He must be prepared to wait until the line is right and the appropriate signals given before proceeding. Swimming against a taut line will only exhaust the diver. Similarly, if he returns faster than the line is recovered, he may miss a vital signal. If he should become entangled in the line, it is imperative that he remains calm and then quietly sorts it out.