I currently have a Sunnto Zoop. It has been fine for recreational diving, but I'm plan on starting to Tec training in late spring. I've acquired most of the gear I will be needing except for a dive computer that will handle gas switching. I know that there are those on here that are anti-dive computer and I do plan to make extensive use of the tables, but I see a dive computer as reduntacy for my onboard grey matter computer.
When discussing this with a potential GUE fundie instructor he stated that one of the big drawbacks to computers is you cannot adjust the dive plan on the computer on the fly. For instance if you lost a deco gas your computer would not be able to handle the fact that you are now using your reserve backgas for deco. At least I think that is what he was saying. I was under the impresson that both the X1 and the predator had this functionality. Am I incorrect about this?
In the past computers were not tech friendly. Today, several computers have been designed with the needs of the technical diver in mind. It's not that people are anti-computer and pro tables, but rather those who dislike computers are often better educated regarding ascent strategy. They want to take advantage of the cumulative knowledge we have about safe ascents and employ various concepts at differing depths without a computer punishing them in some way or driving them to the surface.
A dive can be broken down into 4 phases:
1) Bottom Phase
2) Deep Stop Phase
3) Middle Stop Phase with or without Gas Switch
4) Shallow Stop Phase with or without Gas Switch
For tech divers, every minute spent at depth enjoying a dive will result in having to pay the penalty of decompression. Decompression requires time and time uses gas. Gas is life so we want to try to surface with plenty life support. Time also exposes us to cold and cold reduces the effectiveness of decompression. With this in mind, once a dive is over on the bottom we want to keep our decompression as short as possible, yet have it be effective so we don't get bent.
Once the decision is made to head home we just want to get off the bottom where our tissues are loading gas and ascend to a point where we start to off-gas. The ascent strategy for the bottom phase of a dive is simply to begin to ascend fast enough to get out of there and slow enough to off-gas. This is often the standard ascent rate of 30 ft./min.
Once we ascend to a depth where the pressure reduction allows our bodies to off-gas, we want to take advantage of Pyle Deep Stops (first proposed by a marine biologist who noticed he experienced less DCS when he stopped at various deep depths to empty the swim bladders of fish with a hypodermic needle he was collecting) and bubble formation and growth theories. These deep stops are simply 30 second pauses with 30 second slides to the next higher depth. (Some computers would punish you rather than credit you for these stops.)
Most divers will employ a gas switch once they reach a mid-range depth. Some bubble model theory software and some dive computers will credit you for the pressure gradient change that occurs when you switch to a deco gas, but ignore the speed at which our blood circulates throughout the body and how gradient and blood gases work together to create a better theoretical strategy called the "oxygen window effect." Divers may want to hang 3 - 5 minutes longer at the gas switch to take advantage of the high PPO2 at the deepest safe oxygen pressure and remain for a couple of circulatory cycles allowing for the time it takes blood to fully circulate through our bodies to begin to wash out more inert gas. Some computers might punish you for this by adding more deco time in shallow water.
After the switch, we begin to ascend through a short series of stops between where our bodies began to off-gas and the shallow water that lies above. These mid-range stops take into consideration bubble modeling, dissolved gas modeling, overall ascent time to shape a gradual ascent profile and may even include an "air break" at the last mid-range stop. These stops may be 50% of the decompression time and some computers would penalize you for it by adding time up top.
Finally, we enter shallow water where we may or may not employ another gas switch. For most divers the shallow phase begins at 20 feet with a switch to oxygen. Most traditional computers would employ a Buhlmann model and you'd be stuck in the shallows for a long time waiting for the computer to clear having been punished for all the safety stops you made as part of a safer strategy. You can either hang in the shallows for a long time waiting for the computer to clear, or not use a computer knowing how you financed your deco debt to the water column.
Once you train your brain and find deco strategies you like, a modern technical computer can be a great back-up! Sit in any tech class and most divers are coming up with different answers to math questions while sipping coffee and using calculators. Now, these same people are expected to do perfect math underwater while task-loaded every time? In theory ... sounds awesome! In practice ... maybe not so much. Most tech divers who use computers don't believe that they should just let the computer control the dive, but they remember how many times their numbers didn't add up the last time they did their taxes. They know that the IRS can be mean, but "mother nature" - even meaner.
