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> I'm *very* curious, which habits need to be deprogrammed? One of the > biggest differences that I can think of is that you can no longer use > breath control to affect bouyancy changes because of the counterlung. > A second difference is that sawtooth profiles that require you to > add/dump gas to maintain neutral bouyancy will use up your diluent too > quickly Those are two. Breathing pattern is another one. Scuba cylider duration is a function of breathing rate, so people tend to take long slow rhythmic breaths and hold them for a couple of seconds (even though they're not supposed to - come on...admit it...). It takes a while to learn to just breathe "normally" when underwater. Another thing is frequent mask clearing, which I did as an OC diver. Also, you have to learn not to make sudden descents (causes PO2 spikes). There are a few other things I had to unlearn - nothing really major or life threatening. I think the overconfidence an experienced trimix diver might have is a more serious concern. I was an experienced trimix diver when I started on rebreathers, and I had this sort-of elitist attitude that "well, hell...if anyone can rebreather dive, *I* can rebreather dive..." But the humbling thing is that my overconfidence nearly got me into serious trouble on several occassions. Much more useful...*MUCH* more useful than my skills as a trimix diver have been my solid grasp of gas physics, and my "tinkering"/mechanical thought patterns. > I'm sure there are differences, but any diver that's been around and > has progressed from standard openwater dives to more difficult and > technical dives has had to modify and relearn things continuously. I > think the ability to adapt is probably the most important ability in > this case and most of the more experienced divers around have shown > this ability. Yeah, I sort of agree with this. In a similar post I made a while ago, I mentioned that one of the qualities trimix divers *tend* to have (at least experienced trimix divers) is a good sense of discipline and caution about approaching new things. I like to think I had this discipline as a trimix diver, and I think I did. But I still got humbled. Also, rebreathers are VERY different - not like moving from air diving to trimix diving. With any OC dive, you calculate the PO2 before you get in the water, and you don't need to worry about it. With a rebreather (fully-closed) the PO2 is a dynamic variable. It takes a lot to grasp this conceptually and functuinally during a dive. Also, unless the rebreather has onboeard real-time decompression calculations, then fluctuating PO2 means a corresponding fluctuating diluent partial pressure, which means decompression calculation is even fuzzier than it already is for OC diving. PO2 management becomes the biggest concern. > As far as confidence, you're obviously right. I approach each and > every dive as if my life depended on it, mostly because it does. I > have seen too casual an attitude among two groups of divers, those > with very few dives (<100) and somewhere in a mid-range that probably > happens somewhere after the 2nd year of diving, which really depends > on how many dives you do... Ahhh...the old bell-curve syndrome... > >While it is true that the amount of training required by a non-diver to > >become a qualified rebreather diver is much greater than the amount of > >training for a non-diver to become a qualified (not certified) scuba > >diver; it is NOT necessarily true that the amount of training required by > >a non-diver to become a qualified rebreather diver is much greater than > >the amount of training required by an experience trimix diver to become a > >qualified rebreather diver. > > I would like to discuss this point with you. What you're saying is > that not many skills translate from OC to CC. Some do - the basic ones do. I'm not saying that a skilled diver and a non-diver have an *equal* footing at the outset; I'm just saying that the advantage the skilled diver has may not be as great as many people would assume. > Let me attempt to make > some points. Well trained and proficient divers already have > experience with and knowledge of diving in general, much of which can > be translated to rebreather diving with appropriate modifications. The basic things, yes. > They will have discipline, patience, knowledge of appropriate physics > and physiology, good emergency plans, be able to adapt quickly and > have experience with a variety of OC scuba (especially exposure suits > which can take quite a while to get used to), and, hopefully know how > they react to situations underwater. > The rebreather diver still needs to have all of these qualities and > abilities and have a knowledge of OC scuba and be proficient in its > use (in case of an OC bailout either with on board gas or with > appropriately placed stage bottles). So, I think that indeed, being a > proficient OC scuba diver is actually a prerequisite to becoming a > rebreather diver. Well...yes and no. I don't think the gas physics is emphasized enough -- even in trimix training. The physics becomes much more important on the rebreather becasue the diver needs to understand the various consequences of different counterlung volume (not in the sense of different rebreather designs, but in the sense of loop volume management during the course of the dive) and injecting oxygen and diluent manually, and figuring out how to ensure the loop gas is breathable (life-sustainable) even when all the sensors crap out, and knowing how to verify the sensors are giving correct readings, etc. In my experience, many experienced divers don't really *understand* the physics; they've just sort-of memorized some of the formulae. When asked to calculate a partial pressure, they crank out their calculators and plug in the numbers. On rebreathers, you need to have (or at least should have) a conceptual grasp of what a partial pressure really means. For example: Imagine a one-liter container (open at the bottom) filled with air at 130 feet. The PO2 is just about 1.0 and the PN2 is about 3.9. Now take that container to a depth of 300 feet and top it off with helium (so it's still one liter of gas). What's the PO2? What's the PN2? What's the PO2? (no calculators allowed, unless you happen to have one that you can take on a 300-foot dive with you). Now, take it to 1000 feet and top-off with hydrogen. Quick, what are the PO2 and PN2? You should be able to answer without hesitation. What's the PHe? You should be able to figure that out quickly without a calculator. Go back to 130 feet, allowing the excess gas to bubble away. What are the PN2, PO2, PHe, and PH2? Again, this should be something you can do in your head in a couple of seconds. Here's another way to look at it: What are some of the most important skills an experienced trimix divers has?: 1) Knowing what rig configuration is best for a given dive. Rebreather: Whole new ballgame. 2) Excellnt bouyancy control while ascending from a deep dive in blue water, or preventing a silt-out in a cave or wreck. Rebreather: Whole new ballgame. 3) Comprehension of decompression dynamics, allowing itelligent alterations of dive profile to avoid DCS when something goes wrong. Rebreather: Whole new ballgame. 4) Intimate understanding of one's SAC to calculate a given rig's duration. Rebreather: Whole new ballgame. 5) Correllary to above: calculation of how much time is remaining with a give tank pressure, when the dive parameters change unexpectedly. Rebreather: Whole new ballgame. 6) Sharing gas supplies with buddies. Rebreather: Whole new ballgame. 7) Gas switching techniques during decompression. Rebreather: Whole new ballgame. 8) Effective backup (bailout) systems Rebreather: Whole new ballgame. I could go on.... Yes, sure, the skills of an OC diver and a CC diver overlap to a certain degree. However, the overlap is just traininng stuff. My point is that an experienced diver might be tempted to believe that he or she requires less time getting trained on a rebreather than a non-diving person who has good discipline and a solid grasp of gas physics. The non diver will have to be taught basic scuba skills, which would total about 5-10% of the time needed to master rebreather-specific skills. In other words, the experienced scuba diver needs to do about 90-95% of the training that a non-diver needs. This assumes that a grasp of physics and good discipline are indepentent of dive experience (which, in my estimation, is generally the case). > Lets just go over your points... > > >1) Enormous discipline > >2) Humility > >3) Solid comprehension of gas physics > >4) More discipline > >5) Patience > >6) Good mechanical abilities (and brain) > >7) Yet more discipline > > Everything you've listed is also a quality of a good OC scuba diver, > you are obviously attempting to emphasis discipline, but, there *are* > plenty of OC divers that meet your definition. Of course there are. There are also plenty of skydivers who meet my definitions, plenty of rock climbers who meet it, plenty of bike-riders who meet it, plenty of accountants who meet it, plenty salesemen who meet it, plenty of constructions workers who meet it, plenty of high-school teachers who meet it.... A lot of J.Q. Public DO NOT meet it. A lot of certified, even experienced divers DO NOT meet it. I think the dangerous assumption is that experienced diver = disciplined diver, or that experienced diver = a diver who grasps gas physics. I've yet to be convinced that such correlations exist in the real world, at least on a population-wide basis. > I hope you don't mind an opinion from a non-rebreather diver. Of course not! (You already knew that). I'm especially interested in your thoughts, because your experience in training and teaching people vastly exceeds mine. I really don't have a lot of experience teaching. My motivation for taking the stance I have taken comes from my own transition from being a reasonably experienced trimix diver to a rebreather diver (work still in progress...). My rebreather diving companion, whose experience as a diver vastly exceeds mine, would agree. Rod Farb seems to agree. I suspect Bill Gavin might agree. I can't speak for semi-closed rebreathers because I've never used one; I'd like to know what people with experience on those think about it. > In closing, I appeal to *all* people on this list, please stop the > rampant flaming, it really doesn't do any of us justice... Agreed. Aloha, Rich
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