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In a message dated 6/11/00 4:46:03 PM, donburke56@ya*.co* writes: << SB>While I need to emphasize that I am definitely not recommending the use of wrist computers for extended decompression diving, the reasons you are giving for not using them are, IMHO, not valid reasons for eliminating them from consideration. I say again that simply carrying a second computer will protect against any possible failure of your primary unit. DB>Lack of redundancy is the only one you've addressed so far and we aren't out of it yet. >> My present answer > Hi Don, this statement requires no answer. << SB>But "what about informing two computers of my gas changes during the dive?" you say. Well actually, it is not necessary. Consider for example, the Cochran three gas computer. It is not a trimix computer but will handle three nitrox / air mixes and automatically switch to the deco gasses at the correct time. All I need to do is to program into the computer the depth at which I plan to switch to my second deco. gas and the computer then does the rest. In fact, I cannot change the programming of the computer after I have entered the water. DB>Loss of a deco gas would be a real problem here. Actually, you've already planned out the dive in order to set those switch depths (twice!) so I submit you computer is more like a smart bottom timer than a computer. You worked out the deco in order to set them, right? Doesn't that make your computer more of a timer/backup? >> My present answer > Don, as I've discussed in a previous posting, if I loose a gas during a dive, the situation is then the same as if I lost a gas with any predetermined dive plan. I would pull out the waterproof dive tables, use the computers as depth gauges / bottom timers, and figure a worst case (depth and time) plan for deco. with the gasses I have available. Also with the computers, I don't see why there would be a need to plan out the dive in order to set the gas switch depths; they will usually be the depths at which the deco. gasses yield a PPO2 of 1.6; e.g. 20 ft for O2, 70 ft for EAN 50, etc. So I do not understand why the computer is acting simply as a timer. It would be calculating my deco stop times. << SB>Consider for example, a dive to say, 100 feet on air for a long time and EAN 50 and O2 as the deco gasses. I would need to program in 20 feet as the depth to switch to my second deco gas (the O2). The computer would then do the rest. SB>"How does the computer know when to switch to the deco. gasses?" you ask. Good question. Magic!!! No not really, the computer is an air integrated unit connected to the back tanks. It keeps track of my breathing rate during the dive. And when that breathing rate goes to zero, it knows that I am no longer breathing off of the back tanks so it switches to the first deco. gas (the EAN 50 in this example). Then, later in the deco schedule, when I have progressed up to 20 feet, it knows to switch to the second deco. gas (O2 in this case). DB>Ouch! Now we have two computers and a pressure guage hanging off a first stage. >> My present answer > Not really, I would probably position one computer on each post. Of course I would want an SPG on the left post also. And since I envision these as hoseless computers, there would be no additional hoses to contend with. << SB>As you can see, no "informing the computer" during the dive is necessary, so a second computer stowed away conveniently, serves well as a backup should a failure occur in the primary unit. DB>How do you "stow away conveniently" a second air integrated computer? >> My present answer > You might put it in your pocket or pouch. << SB> Of course a set of waterproof deco tables must be taken also (with the computers serving as depth gauges / bottom timers), to serve as a second backup should something unusual occur during the dive. DB>If the computer fails, you probably will lose time reference, depth and probably gas pressure. >> My present answer > I assume you mean "gas pressure readings". That's why the second computer. If one fails, just pull out the other and deco. out the dive. << SB> After all, the well trained and experienced human brain is still the best dive computer around, by far. DB>I'll stick to tables as opposed to this plan. >> My present answer > That, of course, is always your option. << SB>So as I said previously, I need to emphasize that I am certainly not recommending using wrist dive computers for extended decompression dives at this time. But I believe the reasons you are stating for not using them are not valid reasons to preclude their use. I do agree with you however, that some time in the future these computers may have reached the state of maturity where we will be able to depend on them for extended decompression dives. SB>Take care and safe diving, Scott DB>I'll give it a hell of a shot. >> My present answer > You take care now, and thanks for the comments, Scott -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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