COMPUTERS & TIMERS

GUE has long been skeptical of dive computers. In most cases, these reservations have been justly deserved— computers have historically produced ill-conceived and sometimes potentially dangerous profiles. Inconsistent reliability was also a common problem for many years. More recently, the technical capacity and reliability of dive computers have greatly improved, and today’s decompression computers can very closely approximate current GUE diving protocols.

Historically, GUE divers were reluctant to embrace dive computers; the devices were imperfectly designed, and divers’ blind trust in them (despite their inconsistency and undesirable decompression algorithms) was unsettling. Modern-day computers, however, have become more reliable and, to a reasonable extent, have incorporated improved decompression algorithms.

The devices still aren’t perfect, and their overall increased reliability has potentially made the impacts of the remaining malfunctions even more severe. After just a few positive experiences using them, divers could become more reliant upon their computers and grow complacent. Because of this, GUE allows divers to use computers as a backup but adamantly discour- ages using these devices without first understanding how to dive without them. GUE courses continue to teach important decompression techniques that give divers a full grasp of the concepts, which lets divers remain entirely independent of any decompression computer.

Many divers choose to run their computer in gauge mode (displaying just time and depth) to use it as a bottom timer. Instruments with clearly readable screens are the norm.

Bottom timers

If all you need is an accurate indication of depth and time, a bottom timer can do the trick. With accurate depth and run time information, divers can calculate the proper decompression obligation if required. Digital gauges with large displays are preferable, and interfaces should be easily readable in low light conditions. An easily understood, minimalist interface is also ideal, but a stopwatch function is a useful additional feature. The instrument should be attached to your right wrist so that you can illuminate it with your primary light (held in your left hand) while operating a diver propulsion vehicle (DPV).

Modern dive computers have large, easy-to-read displays and many useful functions, such as digital compasses and resettable average depth.

GUE divers always wear the primary instrument on the right wrist, which can be illuminated with a light held in the left hand if necessary.

There are numerous excellent bottom timers available on the market today, and most computers can be used in gauge mode and exclusively function as a bottom timer. Many action watches or smart watches (including Apple Ultra) also give time and depth, secondary information (like temperature), and additional functions (like logging).

Tables

While breathing underwater, gas accumulates in a diver’s tissues. The volume of gas absorbed and the way it is removed are complex interactions involving a range of variables—most of which are related to the time spent at a given depth. Decompression modeling attempts to capture these variables by using algorithms that anticipate gas accumulation at a given gas mixture, a specific depth, and over a particular time period. Decompression tables provide a simplified way to track this process, but for the sake of simplicity, they round time and depth into categories that sometimes create fairly conservative decompression estimates. While divers have been using these tables successfully for years, they have done so by accepting limitations that—for the most part—make dives shorter or require longer decompression profiles. These limitations were created primarily by a lack of precision in assessing time at various throughout a profile. For example, while a diver might spend only a few minutes at the deepest depth, the tables may show the entire profile at this depth.

Compelling features

When dive computers were introduced and their early reliability problems were solved, they slowly became a preferred decompression management strategy for most divers. They provided divers a device that could closely monitor depth-time profile and calculate in real time, allowing more precise calculations for a given profile. Manufacturers offered a variety of products. Most of the earliest models had no customization options, and they produced quite conservative—and sometimes oddly shaped— decompression profiles. Despite these issues, most divers migrated to using computers. The convenience, ease of use, and real-time monitoring were compelling features.

Blind followers

With these advantages came a new problem. Divers became complacent, trusting the output from computers and paying little attention to their own awareness of their current decompression status—and ignoring the tactics they learned in training. Divers gradually began to disregard decompression planning. At the same time, traditional training agencies and instructors de-emphasized the importance of using diving tables and even the need to under- and agree on the plan with your team. If you agree to follow your dive computer’s recommendation, be sure it mirrors your pre-planned expectations and that the team agrees with this strategy. your stand the nuances of decompression science. In other words, divers started to blindly follow a number on a screen without developing a fundamental understanding of what that number represented, its origin, or how it could change during a dive. Furthermore, different brands and models followed different decompression algorithms, produced different versions of the same algorithm, and offered different results for the same depth and dive profile. This complicated team operations and led to confusion.

Desktop software

The lack of flexibility, concerns over reliability, inefficient decompression profiles, and differing profiles in the team—among other factors—were major influences in GUE’s reluctance to embrace dive computers as their primary means of decompression planning and monitoring. GUE instead chose to use desktop decompression software as the primary method of decompression planning. This allowed the creation of standardized deco strategies that could be tailored to the dive plan’s specific variables, including the type of dive, experience of the team, profile of the environment, and various other contingencies.

Fortunately, dive computer technology is evolving, and current models offer similar advantages to those sought in desktop technologies. These computers allow the user a reasonable level of customization, offering them the chance to model GUE’s tailored ascent—this means that they can produce similarly successful results to GUE’s DecoPlanner desktop decompression software. See page 42 in this issue of Quest for a full article on the past, present, and future of DecoPlanner.

Supporting role

Despite technological advances in dive computer technology, one critically important consideration remains: Divers should not be overly reliant on dive computers, using them in a supporting capacity to augment knowledge and planning. Blindly following a computer is irresponsible and can be dangerous.

All GUE divers should consider the following recommendations when using dive computers. Choose a computer model that uses the same algorithm as GUE’s DecoPlanner (Bühlmann ZHL16), which has a customizable conservatism factor (preferably gradient factors). This way, your dive profile (MDLs, decompression obligations, and variable ascent rates) will closely match the planning you can do with desktop software or a smart phone app. This enhances flexibility, supports dive planning, and helps maintain team coherence.

Choose a computer model that offers a resettable average depth indicator function as well as a timer. This will allow you to accurately monitor your average depth and easily compare the computer suggestion with expecta- tions set during dive planning. It will also help to maintain GUE standard protocols, such as pragmatic MDL.

Adequately plan your dive and agree on the plan with your team. If you agree to follow your dive computer’s recommendation, be sure it mirrors your pre-planned expectations and that the team agrees with this strategy.

Always follow the GUE ascent profile, even if you are using a computer to calculate MDL or decompression obligations. Consistent implementation of GUE’s standard ascent profile supports better ascent control, allows time for ascent-related tasks (e.g., SMB, primary light stowage, and team communication), and is consistent with ascent practices followed in more advanced types of diving. Your dive computer monitors your ascent rate and takes into consideration any additional time spent during the ascent.

Take control

Do not reduce your level of situational awareness. Dive computers can’t predict the future— always remain aware of the environment and the team. Diving while blindly following a dive computer often results in a false feeling of safety. Many dive computers offer a TTS (Time to Surface) calculation, but you should keep in mind that this calculation does not account for factors such as cold, current, and equipment malfunctions which can affect the dive plan and your decompression profile.

Remember that dive computers can perform calculations quickly, and they can offer accurate suggestions, but they can’t make decisions. The diver needs to make the decision, and for this, you need enough knowledge about both diving concepts and your device. Make sure you understand the concepts of gas absorption, gas elimination, and basic decompression theory; discuss any questions you have with a GUE instructor.

If your particular computer model has a deep stop function implemented, it is recommended you disable it when following a GUE ascent profile. A GUE ascent profile already incorporates strategies for addressing bubble formation and reduction of asymptomatic bubbles.

Use DecoPlanner

Read the manual and understand the functions of your dive computer before using it. Take the time to set the computer properly and input all necessary data: conservatism levels, gas used (travel, bottom, and decompression gases), last stop depths, salt or freshwater, when the computer will start to count time of a surface interval, and when it will start to count dive time. Learn your computer progressively. Do not rely on it while using it for the first time or on a difficult, challenging dive. Become familiar with how it behaves—which information it indicates and how it’s displayed. It will require awareness and concentration to understand the information the device is displaying, at least during the first few dives.

When multi-day diving, like on a liveaboard, use GUE DecoPlanner as your primary planning tool, using your dive computer as a backup verification tool. This strategy offers the best of both worlds—you benefit from the value and flexibility of standard protocols as well as the precise data collection capacity of a dive computer. Pragmatic or other planning tools have limitations, especially over extended diving events, and your computer can mitigate these risks.

Ensure all team members use the same settings on their computers. Do not allow a dive-computer-generated profile to separate the team.

Another layer of safety

When used by properly trained, thinking divers, dive computers can simplify decompression tracking and provide another layer of safety for the team. All divers should strive to understand and learn about the latest decompression theory and always use sound diving practices and protocols, no matter which tools they choose for underwater support.

Next time: stage/deco cylinders

Dimitris Fifis

Born in Athens, Greece, Dimitris Fifis started diving in 1991 and became an instructor in 1998. In 2009, after 23 years of service in the Greek Navy (most of them in the aviation branch), he retired and decided to pursue a fulltime career in diving. Since then he has managed diving operations in various diving centers in Greece as well as on mega-yachts. Dimitris discovered GUE in 2007 and never looked back. He currently lives and works in Dubai, and is involved in various wreck exploration and underwater filming projects in the area. Because of his strong interest in increasing dive safety through quality education, he also produces training videos for GUE.