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In a message dated 6/11/00 3:03:53 PM, se2schul@uw*.ca* writes: << Scott, What if you lose a gas? You can't reprogram you computer in the water. You computer schedule becomes invalid. What then? >> Hi Steve, Thanks for raising some good points that are worth discussing. If you loose a gas during a dive, the situation is then the same as if you lose a gas with any predetermined dive plan. You 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 you have available. << 2 computers sounds pretty expensive, and about as useful as diving with 2 wings. You just fixed a problem (unreliable dive computer) by adding a second computer. Now the problems are compounded. >> I really don't think anything is compounded. One computer can be tucked away in a pocket so it is not even seen unless it is needed. And if it is needed, then the other computer has failed and so is ignored. Both computers contain the same information so what's to compound? And as far as expense is concerned, when the cost of life support equipment becomes a strong consideration in technical diving, then perhaps it's time to consider some other avocation. << How useful are your 2 computers when the deco that the computers suggests is wrong anyway? Steve >> Remember please that I'm not proposing the use of wrist computers at this time, for extended decompression diving. I'm only pointing out that a number of the arguments against them are really not valid. However, I do completely agree with this last point of yours in many cases. But it has been my experience that the wrist computers are simply more conservative, rather than being "wrong." And as time goes on, I imagine the algorithms employed in these units will get more realistic and then perhaps the wrist computers can be useful. I just don't like eliminating their use with a wave of the hand and a number of invalid arguments. Thanks for the response to my thoughts. Take care and safe diving, Scott ----- Original Message ----- From: <ScottBonis@ao*.co*> To: <donburke56@ya*.co*>; <techdiver@aquanaut.com> Sent: Sunday, June 11, 2000 1:00 PM Subject: Re: Oxygen Toxicity - using 100% in open water > Hi Don, again, > > 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. > > 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. > > Consider for example, a dive to say, 100 feet on air for a long time and EAN50 > 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. > > "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). > > 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. 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. After all, the well trained and experienced human brain is still > the best dive computer around, by far. > > 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 > sometime 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. > > Take care and safe diving, Scott > > > > In a message dated 6/11/00 8:08:25 AM, donburke56@ya*.co* writes: > > << DB>A computer failure on a deco stop dive isn't nearly > that easy in that vital information about your deco > obligation went away with the computer. Perhaps one > day there will be a computer with an independent, > redundant system that can fix this properly. There > are other issues as well. > > SB> I can't speak to the "other issues", but this one > is a non-problem. Simply take a second computer. And > remember, there may be no significant difference > between the failure rate of dive computers and the > failure rate of the electronic depth gauges / bottom > timers commonly used in technical diving. > > > Scott, > The rub here is the gas changes. The Nitrex (I > think that was the name) computer needs to be told > about each gas change. IMO doing this on two > computers during a dive is a bit much. Two computers > in the same case, (but independent pressure housings) > operated by a double set of switches might fill the > bill. > > Make no mistake, I _really_ like the display on my > Oceanic but I have been screwed by electronic devices > too often to bet my life on one. > > The digital depth guages can be backed up with your > reel and bottom timers can be backed up with your > watch. It's also pretty easy to find a home for an > extra watch or an extra depth guage (like maybe on > your buddy). Since you don't need to look at these > devices until the primary fails, they can be stashed > away. Not so with a computer that must be informed of > gas changes. > > There are some watches out there that can give you > depth, so there's a possible backup to backup. > > The fact that I'm paranoid doesn't mean these devices > aren't out to get me. :) > > SB>Take care and safe diving > > Same to ya >> >> -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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