Ive been seeing quite a few Closed Circuit Rebreathers on boats lately and finding the technology and diving approach quite fascinating. I know very little about rebreathers except for a very basic understanding of the concept and designs. I've done a search but couldn't really find any specific threads or answers to some of these questions, so perhaps some of you rebreather pilots can share your knowledge:
1. I understand that CCRs basically come in three flavors - eCCR or mCCR or hybridCCR
what kind do you choose to currently dive and why? Also what brand of CCR do you use?
I dive an Inspiration Vision - an eCCR - for a number of reasons. It was recommended to me as a unit that demonstrably (because they were used for extended periods in Vanuatu) survive the electronics-hostile conditions in the South Pacific. It's been around for long enough to be a proven, reliable loop. And lots of people are getting rid of them and upgrading to fancier units, so you can pick one up for a decent price
Although it's an eCCR, I mostly dive it manually and use the electronic setpoint control as a back-up if I get distracted. I'm only a baby CCR diver, but I've found that my brain is much better at predicting what the loop ppO2 will be in a moment or two than the unit is, since I know what I'm about to do, so manual addition of O2 is more efficient. The electronics are handy if you're doing three things at once during an ascent, though, or get completely side-tracked by the half-dozen curious sharks circling you.
2. How different do you find CCR to Open Circuit in terms of the actual diving technique ? was it a huge learning curve?
Monstrous learning curve, as others have said. Gone - at least for the moment - are the days of unthinking, pinpont buoyancy control. And there's a lot more to monitor than just depth, time and gas: now I'm doing the rounds of cell readings, is controller 2 in synch with controller 1, do any of the cells appear to be falling out of step, am I breathing too hard, do I feel normal or is that CO2 bypass/breakthrough, why did the solenoid just fire for longer than I expected, is that gurgling noise coming from the exhale hose or counterlung (ok) or from the scrubber can (very not ok), oh, and depth, time and gas. And still having the odd buoyancy catastrophe, although they're getting further apart.
3. Is there anything that you still prefer in open circuit over CCR?
Once I get proficient enough with the CCR to just do the dives I bought it for - deep mixed-gas and overhead diving - I'll be more than happy to go back to OC for anything shallower than 180 feet or so (in the tropics), NDL diving, etc. Other than keeping motor memory current, practising skills or photographing skittish animals, I'm a bit bemused as to why anyone would want to dive CCR (relatively) shallow when they could just grab a tank or three and jump in. Especially given that post-dive care for OC is
Rinse. As opposed to sterilise, rinse, repack scrubber, dismantle head to work out why battery 2 is showing low voltage when you know it's good, etc etc.
4. Finally
how safe do you find CCRs in general? are there any brands or types (electronic vs. manual) that you find safer over the other?
As others have said, CCR safety is user-dependent. There are more ways for it to go wrong than there are with OC, but careful set-up, doing the pre-dive checklist by the numbers, carrying sufficient bailout and monitoring the system properly during the dive all help to ameliorate those risks. The kind of diver who so overestimates their abilities as to strap on a CCR and plummet off to 200 feet without proper training and experience is just as likely to put themselves in an unsurvivable position on OC, in my opinion. Arrogance and/or complacency are more likely to kill you than your chosen system for delivering breathing gas.
I merely pose these questions for my own better understanding of CCRs and am not looking to start any debates
just interested in your own personal experiences.
Many thanks
cheers,
nasser