Drift diving, in some cases is a matter of necessity, as a desired dive site may lie in the midst of tidal waters. However there are other reasons, the effortless diving while being swept along through a dive site can be exhilarating. Many wrecks were lost for the very reason that they were caught in a strong tidal stream and then swept onto rocks. In many other cases the moderate to strong tidal flow keeps a dive site sediment free and reduces the sediment stirred up by other divers.
Added to this, where tidal movement is substantial, the very movement of the water brings suspended organisms as food for larger life forms, the food web is more dynamic and life in these areas is generally very prolific.
Searching out potential drift diving sites it is important to consult charts, tide tables and tidal stream atlases. It is worth mentioning that a tidal stream and a current are two different entities. A tidal stream is governed by the tides (and in turn by the sun and moon), however a current is a movement of water caused by ocean circulation, the wind or even river flow.
Diving in Tidal Streams
A moderate tide is loosely defined as having a speed of up to 2 knots. When planning a dive where one is likely several factors need to be taken into account. Most importantly, we must now always think in terms of movement and not of a static position. If you do nothing at all on a drift dive you will be steadily move along the bottom, so this must be regarded as the norm. This orientation of attitude is the key to successful drift diving.
We must ensure that we have adequate surface cover. Normally this will take the form of an inflatable boat, although in some long, narrow straits it is possible to shore dive in tidal streams and still regain the shore. The best way to maintain contact is to have the divers marked with a surface marker buoy, which can easily, which can easily be followed by the boat.
Surface marker buoys are almost always essential when drift diving. Ensure your the buoy and reel are of good quality. The reel must be convenient to use - it should be fast and easy to reel in and out. There should be enough line (at least twice the intended depth) and the line should be thin to minimise drag. The buoy should be large enough to be visible (inflatable ones are advisable) to the cover boat from a reasonable distance and should have a buoyancy of 10-20 kg (or even more in offshore conditions.
Be careful to enter the water together with your buddy, otherwise you may become separated. The best way to do this is to enter the water holding onto a grabline at the side of the boat, then assemble at a prearranged point, dive together, and say together throughout the dive.
It is very important to keep together while underwater. To do this it is necessary to operate as a team by arranging a plan and sticking to it. You must also realise that holding onto a rock while your buddy drifts on is the equivalent of your finning away hard in the still water.
Try to avoid being swept into eddies or behind rocks or into gullies (i.e into stationary water) while your buddy is still in the tidal stream. You will separate in, literally, a few seconds in these circumstances. Once you are separated by a distance greater that visibility, you will be very lucky to re-establish contact, so take the appropriate care.
If by any chance you do become separated, you should look around for a few seconds to attempt to locate your buddy. Look both for your buddy and also just above the bottom for the slightly lighter colour of your buddy's bubble stream. If you see nothing, drift on for a few more seconds and, if you still see nothing, you must make for the surface alone. Be very careful to maintain an upward direction throughout your solo ascent.
Cover Boat Operations
The team in the cover boat must keep the divers surface marker buoy in sight at all times. The best way to do this is to circle it continuously, so that contact is maintained, especially in rougher seas. As it is difficult to follow more than one diving pair in the water at anytime, unless very similar dive plans have been intentionally organized in advance.
Remember that the divers will expect to find the cover boat close by when they surface. In most circumstances the absence of the cover boat could considerably embarrass and unnerve the divers. For this reason a reliable boat and engine should always be employed.
There is a further danger of separation - separation on the surface due to mist or poor visibility. This can cause buddies to become separated from each other or from the cover boat. It may also cause the cover boat to lose the parent vessel. It is important, therefore, that you only attempt drift dives in conditions of good visibility or, at the most, very light mist, unless you are totally sure of your position. It is also possible for divers to lose sight of the cover boat in a very heavy swell and such conditions are best avoided when drift diving.
While the divers and the cover boat should never become separated the fact remains that this sometimes happens. At such times it is extremely useful (an reassuring) to be able to attract the attention of the cover boat. It may be possible to do this with a whistle, although these are difficult to blow effectively when they are full of water and your lips are cold. A small orange flag wrapped around a collapsible mast is a good alternative, as is an air klaxon which attaches to your inflator system (although it requires a supply of air to operate).
The most effective way of attracting attention is to ignite a flare. Waterproof flares are available with an orange smoke at one end and a red flare at the other, and most BCD pockets can fit them in.
Flares are typically an extreme measure of attracting attention so use them only when it is really necessary. By day it is best to use orange smoke and by night the red flare by night, although opinions do vary. Ensure it is fired off downwind and when it has the best chance of being seen.
If the divers and the cover boat become separated, it is imperative that a sensible procedure is followed in attempting to re-establish contact. The cover vessel should patrol downstream in the direction that the tidal stream is flowing. Note that even a strong wind has only a little effect on divers floating on the surface, even if they have BCDs fully inflated. There may even be some merit in dropping a reference buoy if the cover boat is well offshore - at least you then have a reference buoy if the cover boat is well offshore - at least you then have a reference point for your search. You should have worked out in advance the strengths and the directions of the tidal streams at different times of your dive, partly in anticipation of this possiblity.
If you are one of the pair of divers who are separated from your cover boat, then you are in a tricky position. Remain together (fasten a buddy line between each other) and conserve your air in case you subsequently have to make a difficult exit through heavily foaming breakers. If you are within reach of the shore then you can attempt to reach it - many have! Do not remain tied together during an attempt to get out on a very rough shoreline. It is advisable to retain your weight belt unless buoyancy is a problem, in which case you should jettison it without delay. In some circumstances, it even may be prudent to jettison your scuba unit. If reaching shore is not possible, then remain calm and make yourself as noticeable as possible with whistles, flags and even flares.
From the seriousness of the procedures just described it should be very apparent that you must not become separated from your cover party, so take the precautions to dive sensibly and with prior planning.
Diving from smaller vessels | Diving from larger vessels| Boat Handling| Low Visibility Diving