What brand of computer do you use?
Posted 06 August 2006 - 09:13 AM
At the end of the day, the question is which computer can we trust? This is after all part of life support.
Canon SD550 - Canon housing (pocket videocam)
Larry Chan -- My Webpage
Posted 06 August 2006 - 10:51 AM
Likes: readable display (nice UI, show info you need while diving), long battery life, good ergonomics (relatively small size, compass mounted at top and angled for easy reading), built-in screen guard, easy download of dive data via IrDA (mac & PC), good algorithm (also see dislikes)
Dislikes: alarm beeping on ascent (very slow ascent rate for last 30 feet/10m; the alarm doesn't go off very often for me; but, can/will go off if you swing the console up to look at it), the software(JTrac) for my mac could use some user interface/features tweeking
UW photo methods
Posted 06 August 2006 - 11:26 AM
I did a dive to the Shark Hole at Tikehau. It's around 40m deep. After less than an hour the dive guide wanted to do a second dive. I managed to delay things so that we got about an hour and ten mins surface interval.
On the way up, I found I had to hang for around 20 minutes. The dive guide took a lot of interest in what my computer said.
Afterwards, back in the boat, she said that she though that ten minutes deco-stop was quite enough and that 20 mins was totally un neccessary. I asked her what here computer said.
Her answer? "I don't have a computer!"
So there's your answer. Dive without one. She seems to be OK - or at least she was when I last saw her.
I buy my own photographic kit. Diving equipment manufacturers and diving services suppliers get even-handed treatment from me whether they choose to advertise in the publications I write for or not. All the equipment I get on loan is returned as soon as it is finished with. Did you know you can now get Diver Mag as an iPad/Android app?
Posted 06 August 2006 - 11:52 AM
Now, as for getting bent, it depends a lot more on the physiology of the person than on what computer one uses. I've seen people get bent when following a suunto blindly, and I've seen people that never used a computer or tables and are still alive. I've done more than 1,000 dives with my uwatec on the least conservative setting (L0) and never had a problem, but it may happen some day, who knows.
Luiz Rocha - www.luizrocha.com
Nikon D800, Aquatica AD800, Ikelite strobes.
Posted 06 August 2006 - 01:58 PM
Thought I'd share some info here.
As part of my veiled past I spent two years in a very dubious corner of eastern Africa. Trying to decide what I would do stuck in the dust bowl of Djibouti for two years (horn of Africa north of Somalia) I turned to Diving. A friend I was working with a crazy diving dude by the name of Yves LeFevre (not the Club Raie Manta from Tahitit Yves) took me aside, I wasn't dive trained, and progressed to introduce me to the basics of SCUBA. He was a trained DM equivalent with the French FFESSM agency.
My first and only lesson was "OK, my Eeenglish friend, eer izz ze regulaator. You breeze wiz ziss. You must never ever 'old your bress and when yoo see zis needle (holding up the SPG) getting low down to zees red areaa zen you must come back to zee surface. D'accord".
A short lesson on equalizing and ascent speeds and I was trained. That was the first and only session I had for diver education in two years. We dived every day if we could, making use of the Red Sea which lapped at our doorstep. I would get tanks filled by the French Marines for free, and they never needed ID so that was great. They also made sure the reserves were open as we were using old J valve tanks.
I dived there for two years. Only a pair of shorts, tshirt, backpack, mask, fins and an air guage. No depth guage or computer. Never had any incident or cause for concern. There were a few muppets who got caught out whilst free diving down to scuba buddies, yanking their regs and fooling around for a couple of minutes then rocketing back to the surface....kaboooom.... But there was no training there, they had no idea of the mechanics of diving.
When I eventually returned to the "real world" I knew what I wanted to do. I embarked on dive training and was already starting to eye up the cameras currently available back then. Going through the education made me cringe. I started my Open Water course with about 600 dives under my belt but was cringeing everyday when the Rule Books were saying "now you can't do this" and You can't do that". We were doing those things with complete abandon in Djibouti. Never had an accident.
So I guess my point is that most dive computers are pretty darn conservative irrespective of their seemingly conservative or liberal allowances. Will the computer manufacturers ever make a computer that is completely on the button so far as true safety margins are concerned? I doubt it. By reading this thread we can see that some people choose to push those limits after having made their decisions based on their own faith and knowledge. With a computer that puts us close to the real safety margins how long would it be before people also try pushing those limits? It's innevitable, we're humans. We wanna push the envelope just a little, see what happens.
If any readers do decide to push their own personal limits and those limits set down by dive computer manufacturers then they do so based on their own assumption of risk. No one can say, don't do it. Its down to the individual. Hopefully they will live to tell the tale.
- A Natural History Documentary -
Posted 06 August 2006 - 06:02 PM
After this discussion between Kriptap and Frogfish, I think the most interesting part is the wide variety of conservative to not so conservative models out there. My LDS sells a lot of Oceanics. They are a big shop, and thus many people here in San Jose have these computers. We are not seeing more people going into DCS, or at least nobody is reporting them. ... At the end of the day, the question is which computer can we trust? This is after all part of life support.
Interesting point in an interesting discussion, one in which I hope nobody has been offended. I don't think that anyone here is saying that, say, Oceanic or Cochrane computers are intrinsically unsafe. Nobody intentionally designs unsafe decompression algorithms or manufactures unsafe dive computers, but there are clearly different ideas in the industry and among consumers about what constitutes "conservative enough".
The venerable US Navy Tables (ancestral to PADI's) were never designed to prevent DCS in all combat divers all of the time; the objective was to reduce the incidence of DCS in a population of young, fit, carefully screened and trained individuals to an "acceptable" level. An expected DCS incidence ratio of one hit in 500 dives might look reasonably safe to some people in certain situations, but not others. How comfortable should someone with more than 999 dives be with a more conservative algorithm expected to reduce the hit ratio to only 1 in 1000 dives? Or 1 in 2000?
Dive computer or decompression algorithm cannot directly measure dissolved and gaseous phase nitrogen in our tissues, nor can they take variations in susceptibility to DCS into consideration. These are mathematical models. Some of us are persuaded that RGBM can better model the actual physical processes involved than a Haldane-based algorithm, but that doesn't make it 100% safe. We all know things that are supposedly risk factors for individuals - age, lack of cardiovascular fitness, % body fat, alcohol consumption, dehydration, lack of rest, etc. And I suspect most of us also know someone like Drew, who is considerably younger, fitter, thinner than I am, and who doesn't drink, but who has taken an "undeserved" hit doing a dive with the same kind of dive profile that I have done many times.
We all have to decide what level of risk is appropriate for us, but also keep in mind others who rely on our judgment or may be tempted to follow our example. Kriptak made it clear in his 2nd post in this thread that he wasn't advocating that anyone else play with the EANX % setting on their computer to increase bottom time. But I did want to say loud and clear to others reading this that there are divers here who would consider this an unsafe practice. I have a friend who dives pure DIR rules. He believes that I'm crazy because I do things like dive beyond 30 meters on air instead of trimix, do more than two dives a day, and do dives that require mandatory deco stops without using twin tanks and deco gas, following the rule of thirds, etc.
LChan mentioned diving in the San Francisco Bay Area. I could be wrong, but it's my impression that recreational diving there is often limited to two dives a day, rarely extends over more than two or three sequential days, and that generous or at least adequate surface intervals are the norm, if only to get warm.
As the discussion here has highlighted, the difference between RGBM (modified or full-up) and Buhlmann-based algorithms in terms of bottom time and/or deco stop time is most noticeable on multiple day repetitive diving and when surface intervals are cut short.
This, of course, is the kind of diving we are most likely to be doing on trips on a live-aboard or at a full-out dive-oriented resort, especially in the tropics, and some of those liveaboards will be operating in remote areas of the world far from hyperbaric facilities.
Personally, I don't really think it matters much what computer is used for simple 2 or 3 tanks a day recreational diving over only one or two days. But I think it may matter a lot on a liveaboard when people are doing 3, 4, and even 5 dives a day for up to twelve days, or even longer. I'm afraid that these situations - when having a computer that is sensitive to the heightened DCS risks posed by repetitive multiple-day diving is most important - are also likely to be the situations where some divers will be tempted to cut corners with N2 % settings or else intentionally select a dive computer because it gives him or her more bottom time than other computers rather than for maximal safety. If this discussion only serves to make anyone in this situation think twice before buying a computer because it is generous with bottom time, then it will have been well worthwhile.
Nikon D2X in Subal housing.
Tabula Int'l Ltd.
Posted 07 August 2006 - 09:34 AM
If the computer modeled reality perfectly (including prior alcohol consumption, phase of the moon ...) then it could give us the absolute maximum safe bottom time for each and every dive. When factors are left out of the modeling equation then, with lifes and law-suites at stake, a worst-case scenario of a drunk, cold, dehydrated, elderly, obese diver must be assumed
Well perhaps not that extreme but algorithms must err on the side of caution and penalize bottom time more than typically needed.
So if older algorithms don't explicitly model the effects of microbubbles they should implicitly account for it by always adding an extra safety margin. In contrast, the RGBM model will know when microbubbles have interfered with off-gassing and only penalize the diver when it is needed.
So, why is RGBM more conservative???
One option is that older models are truly dangerous, but I find that a bit hard to believe.
Based on some of the earlier comments given in this discussion I think it is more likely that the current RGBM implementation is mostly the old model with microbubble-penalties added. Because the old model implicitly accounted for microbubbles by adding an extra safety margin you now account from microbubbles twice, resulting in a very conservative computer. Reality may be somewhere in between, where they have added the penalties but removed only part of the old model's safety margin. Alex's experience that RGBM is actally a bit more aggressive than the older models when you use long surface intervals could be the result of this.
If this is the case then we shouldn't blame the RGBM algorithm itself, just the way the early computers have implemented it. If RGBM is really a more realistic model of reality then, once implemented properly, it should start giving us more bottom time without increased risk. Untill such time I'll happily dive with my simple Genesis Resource computer and use its N2-loading bar graph to stay within my own safety comfort zone.
Sea&Sea 110a, iTorch, GoPro3 BE
Posted 07 August 2006 - 10:18 AM
I think it has been widely observed that the older models (USN, "raw" Buhlmann, etc.) are indeed if not outright dangerous, at least less reliable for a population of average divers (I sem to remember Mr. Buhlmann himself has adviced agaist the "raw" version of the algorithm). For this reason various corrections have been added. The most widely used have been "Pyle" stops and Gradient Factors for Buhlmann (For GF implementation over Buhlmann, see Eric Baker's excellent paper at http://www.gap-softw...ingMvalues.pdf).
Now, the bubble models (RGBM, VPM, etc.) DO model reality better than Haldanean models (see for example http://www.decompres...Strategies.htm). I suppose there is no disagreement on this. But they are still models and the probability of an undeserved hit is still significant. There have been several studies showing that the susceptibility of an individual to DCS varies widely within short periods of time. Therefore, the only way to fully avoid DCS is not to dive. Building a better computer is not the answer since perfectly modelling the human physiology will for some time be outside the capabilities of computer science.
I personally plan all my tech dives using VPM-B (V-Planner SW) and in most cases it comes very close to what I did using Buhlmann and GF (or GAP RGBM with similar parameters). However, it is true that for long dives and especially repetitive long dives it is more conservative than my diving computer. I even add a factor or two of more conservatism if the water is very cold (<5C), if the dive will be stenuous, etc. For me, that extra conservatism is a good thing. Spending the extra 10 minutes doing deco is better than an airlift to a chamber any day.
For recreational stuff, I use a computer with a Buhlmann-based algorithm set to +1 altitude compensation, which brings it quite close to VPM-B for no-stop dives in the 30 meter range using air or nitrox. The major difference being that VPM (and RGBM) make you stop deeper as suggested already by Pyle based on empirical evidence and later by Baker based on theory.
If we look at what Suunto, Uwatec and other computer makers are doing, they are introducing "deep stop" algorithms more and more in their lineup. So, no matter what, bubble model concepts are filtering into the way we do decompression using mainstream computers no matter what algorithm we actually are using. If you do not like it, there are and will be computers out there that can do raw buhlmann and let you do max. bottom times and min. deco. For some, this is probably a wise move, for others not so.
I did a fair bit of studying on this when I started on tech. diving because having a family to support I wanted to know what I'm doing. My conclusions are probably apparent from my choices of computers/SW and I strongly encourage anyone to do a similar study so that you know what risk level you are at. Deco theory is no black art, neither is it rocket science.
Posted 08 August 2006 - 06:55 AM