UWSojourner:
"Your unit will have catistrophic failures once in a while so train for bailout."
How does one "bailout" of a dive where you spent 2 hours at, lets say, 150 ft? Don't you have quite a decompression obligation?
I'm with Rob on that one.
A 'catastrophic failure' refers to a complete loop failure, it means you
have to get off the loop, using the rebreather is impossible. This is indeed a rare occurance, either due to damage (e.g. tearing or cutting a breathing hose) or sloppy pre-dive (e.g. missing a major seal).
A minor problem that can turn major (and yes, even fatal) if left unattended is much more likely (e.g. one of the valves getting stuck). There are ways to manage many if not most problems without bailing out to OC (for the rest of the dive, anyway) which, as Rob said, should be covered during training.
You'll spend most of the training time flying the rebreather manually to be able to use the rebreather if the electronics and automated systems fail for example.
In any event you'll need enough bailout gas to safely return to the surface, and safely includes any deco obligation you may incurr.
But for starters you aren't supposed to do deco dive with your initial RB certification and training. That is
advanced RB diving, just as it would be on OC. When you accumulated the rec profile experience on your RB, and diving with it is second nature, you seek further instruction for deco procedures and planning. Simple as that. If you look at accident reports you'll find many a diver switching from from OC to CC after having done very advanced dives on the former. They frequently proceed to fast back to their old profiles even though they're still CC newbies ... sometimes with fatal consequences. That's one of the reason's why I believe it to be a good idea to first become proficient on the RB, then take technical training. Less to unlearn, less strain on the ego.
"What sounded good, 2 1/2 hours, 250' or both?"
Mostly the longer time. I am actually very cautious, so I'm not looking for depth for depth's sake.
Most any available RB will give you two hours of dive time. As gas is used sparely, the scrubber duration is generally the limit on CCRs. Most are rated at 3 hrs, with smaller 'travel' units between 2 and 2 1/2 hrs, and a few rigs 5 hrs or more. Depth rating is generally between 150 ft and 300 ft, with a few models rated deeper than that.
The 7, 8 and more hrs dives to 500 plus feet you hear about every once in a while are for the exploration minded and fall in the 'good luck' category.
"Study and read as much as possible."
Besides Jeff Bozanic's "Mastering Rebreathers" which was listed, what else?
There was another good book, by Steve Barsky, 'Simple Guide to Rebreathers'.
Well done and easier to read than Jeff's book (which is used as the RB textbook by NAUI). It's out of print, but you should be able to find a copy on the web.
Here a couple of links that'll get you plenty of info and even more links.
Rebreathers Worldwide - a huge collection of pictures and info, ranging from early rebreathers to the latest from Dive Shows.
http://www.therebreathersite.nl/
Furthermore you'll find links there to every RB manufacturer and many home builders. Also look out for Howard Hall's rebreather blunders on what not to do.
Richard Pyle's Learner's Guide to Rebreathers
http://www.bishopmuseum.org/research/treks/palautz97/lgrb.html
Ron Micjan's tmi website - here you find his own Dolphin CCR conversion (very thorough write-up) as well as tear-downs of the KISS, Sport Kiss, Prism, Inspiration, Megalodon and MK-5p. Ron just added a very good article regarding partial pressure that'll help understand how CCRs work.
http://www.tmishop.com/
The Golem Gear website - it has a very detailed tear-down and excellent graphics explaining the RB80 passive addition SCR
http://www.golemgear.com/scr/scrteardown.htm
Madmole's Inspiration Buddy site - Stephen dives that CCR and has a pretty intresting website regarding it. The owners survey is worth a look, and so is the accident section. Much to be learned there.
http://www.btinternet.com/~madmole/divemole.htm
And what do you guys think about the Megalodon?
I never used one, but I've seen them a couple of times and Leon talked me through it ... in a few words, capable, high end CCR. Beautifully but expensively machined, very solidly build. Electronics are in the middle of the pack, some good features (like the HUD) are optional.
I like the flexibility of different scrubber sizes and ability to use different tank sizes.
It's an expensive rebreather, though, and production has been pretty slow (machining most every part does take its time). I'm not aware of any independent testing or test results being available.
