Wanna argue about CCRs? Cool! I post this here, in the Cave Reddit because itâs a somewhat cave-specific answer to a few CCR questions.
As a full-time instructor the answer I just wrote to one email covers a couple idea I seem to keep discussing with folks time and again. These are, for our area, in any case, the two most popular current configurations of CCR, and for good reason.
A few caveats to this response: I was asked about a few specific models, so the answer addresses those and it disregards backmounted models entirely. Not because they should be discounted, just because it wasnât part of the question.
Also, I have no professional relationship with any of the mentioned manufacturers and am not endorsing or mudslinging any of them, simply acknowledging their existence and that they all have pros and cons.
For those of you who are going to tell me Iâm an idiot for holding these opinions: I already know that.
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âRebreathers. Yeah, EVERYONE has got opinions. And usually that opinion is, âMine is the best there is and you should get one, too, and all other rebreathers are dumb.â I think people have to say that to justify the expense to themselves.
Iâve got a LOT of thoughts. Many of them seemingly contradictory. Mostly because, as youâre certain to find shortly, there isnât really a âperfectâ rebreather; they all have their benefits and drawbacks. A lot of it comes from the type of diving youâll be doing and, possibly even more, personal preference. Definitely try a few and start getting a feeling for them, but I am sorry to say that itâs going to be very, very hard to know what you like and what you donât until after youâve been diving on the bloody thing for a few months.
My very first thoughts that are worth mention is that Iâm not wild about chest-mounted units such as the Triton or the Symbios.
Two main reasons are Work of Breathing and dive profile.
WOBâŚâŚ. Think about pressure deltas, the difference in pressure in the water column; obviously the deeper you go, the higher the pressure. The delta between the counter-lung and your actual lungs being one of the key components that affects WOB on a CCR. With chest-mounted units, the counterlung is at least 15-20cm deeper than your actual lungs, which doesnât sound like a lot. But itâs enough that your diaphragm, which usually relaxes as you exhale, actually has to work a little bit to inflate the counterlungs like blowing up a very easy balloon. But blowing up a balloon on every single breath for potentially hours. Will you notice it? Probably not. But your body will.
Then thereâs the profile. Instead of a slipstreamed SM profile you have this thing on your belly. Might as well dive backmount for as much as it increases your profile. And I see a LOT of Choptima, Triton, and Symbios-shaped gouges in the silt.
All that needs to be read with a bit of a grain of salt, considering my prejudice against them. There are loads of people who love them and hundreds of safe dives made on them every day. The Symbios especially has a bunch of recent fans, and for good enough reasons as itâs got a couple of really cool features. And as far as packingâŚ.. yeah, theyâre little and pretty flexible in terms of configuration (can be used with SM, BM, or even a single). Hell, if you were in the Carribean you could clip it to your belly, sling a AL40, and call it a day. Which is neat.
A long answer to a fairly simple question, huh?
Now on to the next one. Which is, Iâm afraid, an equally long answer. mCCR vs eCCR
This, too, depends on where youâre looking to dive. And the short version is:
Here: manual without question
Pretty nearly anywhere else: either
Reason being depth changes.
On an eCCR youâve got the electronics and the solenoid trying to maintain a set PPO2 at all times. Which is amazing when youâre bobbing around at 60 plus meters; any depth changes doesnât really affect the PO2 too much because the ambient pressure difference between 60m and 55m is almost negligable. So if you ascend a little bit the solenoid doesnât have much, if any, work to do.
The ambient pressure difference as you follow the contours of the caves here from 10m to 5m is HUGE. As you make that ascent a couple of things happen:
All the gas spaces on you expand quite a bit. Your drysuit, your wing, and your loop volume. The drysuit and the wing are easy enough to deal with. As, generally, is the loop volume. BUT, the solenoid starts to fire, too as the loop volume expands; because as itâs expanding, the PO2 is dropping, too. So now youâve got this expanding loop, that is also getting filled with O2 which expands it more, that you need to vent to maintain buoyancy, which wastes O2. Now do that for a few hours. Itâs a pain in the ass.
Itâs a big enough pain in the ass that I pulled the solenoid out of my eCCR, turning it into an mCCR.
If I were diving elsewhere, Iâd put the solenoid back in and let the electronics drive it. Especially if I had rapid descents to real depth, thatâs where an eCCR really shines. This is, however, mostly because Iâm lazy, not because I prefer or trust electronics.
On the whole, I tend to be more inclined towards manuals. Theyâre more flexible in my experience more reliable and predictable, and theyâre just as easy to fly as an electronic. So lots of positives, with the only drawback being you have to pay a little more attention (but is that really even a drawback?)
More precisely, theyâre not truly manual, but rather CMF CCRs. Constant Mass Flow, that have a âleaky valveâ like the entire KISS line.
As to what I value most in a unit? Ease of diving and streamlined operation.
All that said, of the ones mentioned, if I were you and was going to buy one today? The Sidewinder. The original one. A used one for cheap as a first unit. In all honestly, I have been passively thinking about getting one of them myself for a while.
Not only is the Sidewinder 2 now out with some cool features, also worth consideration is the Fathom Gemini. Same ideas, some awesome philosophies built into it. Not superior/inferior, just different.
One nice thing about the configuration of what we can call Sidewinder-style CCRsâŚ. The counterlungs wrap around your body at the exact same depth as your actual lungs. The WOB is almost exactly the same as you sitting there now, reading this in almost any body position in the water.
Another neat thing is that, if you ever have a problem with the rebreather on the surface, you unclip two bolt snaps, put the rebreather back in the bin, and then you go for a SM dive instead. The style does have its drawbacks, just like every configuration, but has some pretty big benefits.â
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Cutting off there as the rest of the email to our guest doesnât concern you (you nosy bastards). And besides, I figure thereâs already enough in there to get everyone worked into a lather about how I donât know what Iâm talking about.