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> You bring up a good question of redundancy that has been addressed before on > this forum - how much is enough? > > EX: Your rebreather craps out totally: > > --> You gotta go to your open circuit bailout. > a) How much gas do you carry? Some folks say "enough to complete your deco" > which makes total sense. Others say "Just enough to bail." Some, like > Leon, actually advocate and teach NO open circuit bailout - total reliance on > the unit. > > But say you've decided to carry enough open circuit gas to do your deco up to > 20 ft. where you've got your O2 hung. Now - do you carry ONE second stage > reg, or TWO, in case one craps out? Did you see my presentation at the forum? I carry 80 cf of diluent - usually 30 cf heliox and 50 cf air - which sure as hell isn't enough to get me all the way to my 20 ft stop on a lot of my profiles. The idea is that it is enough to buy me some time to get out of deep water, alert surface support that I need more gas, and allow time for surface support to get that gas down to me. As for the question of 2nd stages, the Mk4 does not run the integrated OC bailout supply through the rebreather gas manifold, which means I have the option of plumbing in a secon gas block (generally a real fustercluck), or having independent 2nd stages on each of the offboards. I have been opting for the latter. The Mk5 will route the integrated OC 2nd stage via the rebreather gas manifold, which means active diluent is always equal to active OC supply (i.e., I can access all onboards, as well as all offboards via quick disconnect, via the integrated OC 2nd stage). Consequently, my philosophy about FFM's may yet change. Nevertheless, I'd still like to maintain my ability to conduct a spirited debate with Allah, if & when he calls my name (when the loop crashes and the integrated 2nd stage goes boom), so I'll probably "T" - off an backup second stage to the Mk5. > If you advocate TWO - then what happens if your first stage blows (which I > have seen happen)? Do you carry a second bottle? If you do, do you use ONE > second stage or TWO? Five bottles (Transportable Pressure Recepticals), five 1st stages, 2 2nd stages would be my preferred configuration. Five TPR's are 30cf Heliox, 30 cf air, 20 cf air, and 2 x 13.5 cf O2. > See where I'm going? Redundancy can be carried to an extreme level. For > total safety, you could carry 2 bailout bottles with 2 regulators each. Then > you'd have a total of 5 regs down there (actually 4, but lets pretend your > mouthpiece is a reg for the moment). This gets even more complex if you > decide to carry bottom mix, and travel mix. Shee-utt. Now you look like me > in one of those stories I write... The goal is to maximize probability of staying alive & healthy while accomplishing the mission, and minimizing the probabiliy of a need to prematurely abort the dive. There is a point where excessive redundancy starts reducing your probability of staying alive and healthy, and certainly starts reducing your ability to accomplish the mission. > When it comes to rebreather bailout, the coolest thing I saw was the "Y" hose > connectors that Leon had for his CCR-1000. It allowed a second set of hoses > and mouthpiece to be worn on the back of the unit. If your unit took a dump, > you would swim over to your buddy (which is required in this particular > scenario), and latch on to his back like an abalone, and start breathing > through that spare pair of hoses, through his breathing loop. Leon states > unequivocally that the CCR-1000 can keep two divers alive this way. I have > no idea if that is completely true, but if so, that's the ultimate "buddy" > system. Sounds like an excellent solution. > As you know, I'm still new to this rebreather game, but I can see that it is > easy to start sliding down the slope of multiple redundant systems to the > point where you are wearing so much gear its impossible to swim, or that the > logistics of hanging bottles is so complex as to make each dive a major > production. That's why you gotta find the ratio that works best for you. The system I outlined above for me (5 bottles, 80 cf diluent) is for dives in excess of about 280 feet. Shallower dives, and dives of shorter duration, may or may not require less. > I know there is a compromise somewhere in here, but I haven't quite found it > yet. I don't think any of us have yet. > BTW, Rich, you missed a great BBQ at my house. Dick King, Rod, John, Pete > Heseltine, Leon Scamahorn, and another fellow whose name escapes me (sorry) > came over, talked rebreathers, ignored the two young women there, ate BBQ > chicken like it was going out of style - drank beer, and walked out the door, > still debating the merits of some rebreather part. All in all, a great > evening. When was that? I went to the Hruska & Lesser deal, which was both free & excellent. Rich
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