Dive Computers -

Dive Computers

Article by Jose Mir

The old times

Before the widespread use of dive computers, dive tables were the only tools recreational divers had for planning dive times and depths.

Even if we use dive computers instead of tables for our plans, and regardless of our level of knowledge and experience, we should all know how to use the tables that the type of diving we do might require. In this context, tables are a great educational tool that graphically represents the relationship between depths, times, and ascent profiles.

Different organizations have produced their versions of tables. Some share models and algorithms, while others are more proprietary. However, the decompression profiles they allow us to plan are generally similar (some more similar than others). And every dive has a decompression profile, even those performed within the non-decompression limits.

60/60

Let’s look at a practical example: for a simple dive of 60 minutes at a depth of 60 feet or 18 meters -do you see where the 60/60 comes from?- we see both tables indicate it is a non-deco dive. See Figures 1 and 2 -non-deco and deco tables.

While some divers are satisfied with that answer, many others are not. Mostly, throughout the industry, it is considered that the default values of the different tables lead to planning dives with overly aggressive decompression profiles, especially when considering the contexts in which they take place and the individual reality most recreational divers, like myself, have.

Picture 1, non-deco table

Picture 2, Navy Air deco table

Conservatism

Moving away from the limits indicated in the tables we can add as much conservatism as we want to our dive plans and executions. However, this empirical process is still being determined for many divers. Is subtracting 5 minutes from the limits and times indicated in such tables sufficient? What about 10 minutes? How much then? Resorting to trial and error can have unpleasant consequences.

Fortunately, dive computers provide greater flexibility in this regard, also allowing us to establish different levels of conservatism during the planning and execution phases.

While it is true that decompression models are still a work in progress, and conservatism levels also follow empirical patterns similar to table cases, dive computers and their algorithms allow us to handle these levels more rationally and quantifiably.

One of the most commonly used modes to modify the conservatism level of our dive computers are the Gradient Factors – usually abbreviated as GF. Both technical and sport divers can benefit from using them.

With a medium level of conservatism -Figure 3- the dive computer’s planning function in Figure 4 shows us that the non-decompression limit (NDL) for an Air dive at 60 feet or 18 meters is only 33 minutes, not 60, as the tables indicated above. A 27-minute difference is significant. What happened? Well, the selected profile is more conservative than the tables, giving us a much less aggressive decompression.

Our computer would plan the dive with mandatory decompression stops if we were into technical diving. In this 60/60 case, as shown in Figure 5, the computer indicates that a 17-minute stop at 10 feet or 3 meters is required. 17 minutes! This is a lot of decompression time to skip.

Picture 3, Computer in GF setup screen

Picture 4, computer’s Dive Planning screen

Picture 5, deco computer’s Dive Planning screen

The slate

It is unnecessary to point out the possible severe consequences of not sticking to the plan; we have read and heard about them countless times. This is why our plan must include the necessary flexibility: to avoid deviating from a plan that is too strict or incomplete when unplanned situations arise.

Regarding the decompression profile, when planning with tables, carrying a slate with different depth and time profiles will help us cope with situations where we have failed to respect the limits we had set for ourselves. However, it is easy to imagine that such flexibility will be limited by practical considerations, both in planning and in carrying the numerous alternative notes that some dives may require. Once again, dive computers offer a better alternative.

Interactivity

We might think that dive computers are just interactive tables, but they are much more than that. They are diving with us, descending and ascending by our side, recording times, and recalculating on the fly the decompression profiles that best fit the conservatism settings we have previously configured. In some models, we can modify conservatism levels during the dive execution phases, allowing us to adapt decompression profiles to sudden situations.

For example, if we have exerted too much due to encountering a current stronger than expected, we may want to make our ascent profile a bit more conservative. On the other hand, if an event requires us to accelerate our exit from the water as much as possible, we may want to make the profile more aggressive. Of course, for this, it is necessary to know what we are doing and the implications this may have on the success of the dive -that is, our safe and sound return.

Additional Information

Modern dive computers provide a wide range of additional information -SurfGF, GF99, @+5, etc.- that can help us make the most of each dive, while making it safer.

SDI and TDI have been pioneers in using dive computers since the early open water courses. But despite recognizing their value and the great help they provide, we remain faithful to our spirit of forming thinking divers, not just obedient ones.

As Descartes might have said: “Think, then dive”.

What about the cost?

Today, dive computers have become quite accessible in terms of cost. They are no longer the luxury accessory they could have been years ago but rather an essential and moderately priced tool within reach of everyone.

In a more general context, the computer that best suits the type of diving we want to do will likely have a minor cost when compared to the rest of the necessary gear.

In fact, the computer, regulators, thermal protection, and mask – and the plate and wing, for those divers using this system – are usually the first elements to acquire, even if we are used to renting the rest.

Redundancy

Regardless of how good our dive computer’s quality is, we must be aware that it can fail. Moreover, for good planning, we should assume that it will fail at the worst moment of our next dive. And now what? The answer is redundancy.

Whether you take precautions and decide to carry more than one computer or your redundancy is your dive buddy, you must be prepared for the failure. If it happens, you must have the peace of mind that you have planned for it, that your strategy is the most suitable given the circumstances, and that you can effectively implement the appropriate procedure.

For most divers, the era of backing up their dive computer with a depth gauge and a watch is long gone. Nowadays, the price difference between those two implements and a second high-quality computer is minimal. The only real reason that persists for opting for a depth gauge and a watch is the peer pressure we may experience from whoever may insist on that obsolete, limiting, and higher-risk practice.

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