Over the last ten years or so, the popularity of the dive computer has increased substantially, but has this made the good old dive watch redundant?
It is often said that time is important but to the diver it’s critical; overstaying your planned bottom time (the time from the start of your descent to the start of your continuous ascent to a safety stop or the surface) can have dire consequences in the form of D.C.I. (De-Compression Illness) or ‘The bends’ as it used to be known. The dive watch is used in conjunction with a set of dive tables and a depth gauge; the tables telling the diver the maximum amount of time that can be spent at a certain depth, the dive watch giving the diver the means by which to measure the bottom time accurately and the depth gauge to record the maximum depth during the dive.
The Dive Computer
These come in all shapes, sizes and types depending on what your intended use will be. The main function of the dive computer is to replace the dive tables and because it has an in-built timer many divers are now diving with no dive watch. The dive computer does so much more than dive tables and is infinitely flexible; dive tables are quite inflexible and should only be used underwater as an emergency measure, hence the old saying ‘Plan the dive and dive the plan’. The dive computer monitors the depth and time extremely accurately, its various algorithm converts this into the ‘on gassing’ and ‘off gassing’ of nitrogen during the dive. A dive plan is still made but if it is changed during the dive the dive computer will automatically update the N.D.L. (No Decompression Limit) constantly, often giving an extended safe N.D.L. on the vast majority of dives. It also monitors safe ascent speeds, safety stops and in the event of exceeding the N.D.L. it will plan the safest way to surface; advising of any emergency decompression stops that may be required. They are often linked electronically to your gas supply, under normal circumstances this would be breathing air but modern dive computers can easily handle dives using enriched air (Nitrox) or the more technical mixed gas dives.
The Dive Watch
Not so many years ago it was often said that there were ‘old divers and bold divers but no old, bold divers’ as any mistakes in the planning and subsequent execution of a dive could and often did result in tragedy. The dive watch therefore was an extremely important piece of equipment and its reliability paramount. The conditions in which a dive watch must perform are severe; constantly under pressure, being knocked about and often in extremely cold water. Through all this, the divers life is reliant on its ability to keep accurate time. Rolex sum it up with their iconic ‘Submariner’, advertising it as a ‘Self-winding, diver proof, time recorder’. The diver needs a number of things from a dive watch.
- It needs to be able to function under water.
- For the no-decompression diving limit of 40m the timepiece should be rated at a minimum static pressure of 20 bar (200m).
- It has to have a second hand; this is not for precision timing but to give an instant visual confirmation that the timepiece is still running.
- An elapsed time bezel that can be set to the minute hand at the start of the descent; it is extremely important that it rotates counter-clockwise only so that if it is knocked it can only reduce your actual bottom time, increasing the safety of the dive.
- A robust strap that can be extended to go over a ‘wetsuit’ or ‘drysuit’.
- It must be easily legible in all conditions including complete darkness with no torch.
The Sensible Option?
For normal no-decompression diving down to 40m, I always plan the dive on dive tables, wear a dive watch and set the time elapsed bezel at the start of the descent; I then use the computer to monitor the dive. The tables will give you a no-decompression ‘bottom time’ whereas dive computers generally calculate and update maximum no-decompression time at all depths as you ascend; this being more of a maximum no-decompression ‘dive time’ in reality. The computer calculates every dive as a complex ‘multi-level’ dive, this being where the extra time comes from over that of the tables. As a diver, you are always looking at your computer and gauge console every minute or so and should the computer suddenly stop working you are in a strong position to control the situation safely using your watch and depth gauge. It’s always good to have a back-up plan and although I would go diving without my dive computer I certainly wouldn’t go without my dive watch.