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CCR Selection priorities

Discussion in 'Rebreather Diving' started by kierentec, Sep 29, 2020.

  1. hroark2112

    hroark2112 Tech Instructor

    # of Dives: 0 - 24
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    I think both should be looked at. If a unit is fairly resistant to water intrusion, but impossible to de-water without disassembly, you take it into consideration. If a unit is easy/not impossible to de-water during a dive, but there are more ways to get water in the unit, you consider that too.

    The “perfect rebreather” for everyone does not exist. Every unit has its pros and cons, so you have to measure them and see which unit has more pros and less cons for you and your type of diving. The more time you spend researching in advance, the less likely you are to go through several units before you find what you like, or the less you have to modify your first unit it to make it work for you.

    It’s kind of a joke, but when people post “what’s the best rebreather?” threads, most of the posts are from people who have one been on one unit...so everyone thinks their unit is the best because no one likes to admit they made a $10,000 mistake.
     
  2. stuartv

    stuartv Seeking the Light ScubaBoard Supporter

    # of Dives: 200 - 499
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    LOL Yeah, I saw a FB post asking that the other day. My reply was "buy a rEvo, then never look at anything else and it will always be The Best." :)

    So, seriously now. What are the various ways that different units can get flooded, and how bad is the result. Ways I know of:

    - torn mouthpiece - I'm guessing that would just result in a slow to very slow flooding that you should be able to detect somewhat early on and turn the dive before it gets to the point where you would have to go off the loop?

    - loose lips - even slower flooding than above. Mitigate by just being aware? You might have gurgling in your loop, but not necessarily a reason to turn a dive.

    - take the DSV/BOV out of your mouth without closing it - could result in a quick, massive flood, requiring you to go to BO for the rest of the dive - unless you have a unit with a good ability to dewater.

    - counterlung OPV fails - could result in a quick, massive flood and probably requires going to BO for the rest of the dive.

    - nut on connection (e.g. T-piece) is loose or has a bad O-ring. Likely a very slow flood (presuming you did a proper pre-dive checklist), allowing time to detect and turn the dive while staying on the loop.

    - scrubber cover or head not on correctly or bad O-ring - same as above.

    - ripped/torn loop hose or counterlung - could be a slow or quick, massive flood. Probably requires going to BO for the rest of the dive.

    - DSV/BOV O-ring failure - likely a slow flood, allowing the diver plenty of time to detect it, turn the dive, and finish on the loop.

    Corrections? Additions?
     
  3. flymolo

    flymolo DIR Practitioner

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    Resistant to flooding- wouldn't that be mostly universal as a unit will likely flood from diver error (letting water in through the mouthpiece) or a problem with the mouthpiece itself?
     
  4. kensuf

    kensuf Cave Instructor

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    I've owned a KISS Classic, SF2 (two of them actually), a JJ, and a Fathom. Additionally, I'm certified on other units including the Optima and Meg.

    NONE of them is absolutely perfect. They all have trade-off's somewhere.

    When deciding on what unit to buy, I think flood tolerance is something that should absolutely be included in the decision tree, but doesn't necessarily mean it's a make or break decision. If I were diving in environments that ample bailout and the buoyancy loss from a flooded unit are simple inconveniences, then a lack of flood tolerance may not be that important, whereas other items like the ability to get manufacturer support and ease of build may be important.

    I think Jon did a pretty good job on identifying factors that should be part of your decision tree back on page 1 of this thread. I don't know if he ranked them by his personal priority, but here is my priority ranking and things I would consider.

    1. Work of breathing & overall comfort. This includes hydrostatic work of breathing, which can be influenced by your trim, the gas flow, which can be influenced by hoses / fittings / scrubber, and the balance / fit of the unit. A unit that breathes like crap or is uncomfortable to dive is useless to me.

    2. Ease of setup/break-down / simplicity of design. I'm a firm believer that if you make it overly complicated, things will be missed on assembly and that can be problematic. I also think regular maintenance should be simple as well. Anything that's overly complex runs the risk of breaking on you -- Keep it simple, stupid.

    BTW, while checklists are important, they can also make a simple build overly complicated (the reality is a Meg is a pretty simple unit to build, but I noted that in Stuart's post about his friend, he was following a 30+ step process to build the unit, egad).

    3. Flexibility. I dive caves. I dive deep ocean stuff. I travel. I'm doing a trip to Bikini in 2022 (covid permitting). I like having the ability to configure my units for the type of diving I'm doing and optimize what I'm doing. Ability to plumb in off-board DIL is a must. Ability to slap twin 50s on the back is a nice thing to have. Ability to use a larger scrubber if I'm going to be doing something that warrants it is important. Something I can carry with me in my carry-on luggage or easily toss into a suitcase is a must. I think ability to add a BOV is also important.

    4. Build quality. Jon waxed poetic on this and I have to agree with almost everything he said. If you're spending your hard earned money on a life support device that you will be taking into a hostile environment, it should be made of appropriate materials that will be robust. You do not need a machine that can crack or break just from the rigors of being on a boat, or can self dis-assemble while you're underwater.

    5. Flood tolerance. I think it's important, especially for the type of diving I find myself doing most frequently (long cave dives where I'm literally miles from the exit), but it's not as critical for all environments.

    6. Manufacturer support. This *SHOULD* be higher on my priority list, but the reality is that for a simple unit that is well built, I should never need the manufacturer support. I think he has a valid point that a manufacturer that has a history of abusing their clients with regularly occurring costly updates should be avoided.

    Now the decision of eCCR vs mCCR is an interesting one. There are pros and cons to both and I believe there are places for both (and I currently own two eCCRs and one mCCR and regularly dive all of them). This really is a personal decision based on your philosophy, but one thing to consider with an eCCR is that you may be stuck with a proprietary electronics package that becomes obsolete (I prefer units with Shearwater controllers).

    If I lived in North America and were in the market for a new backmount rebreather, there's probably only one manufacturer I'd look at, which is the Fathom. If I lived in Europe, I'd probably give a serious look at the JJ. One is an mCCR, the other is an eCCR, both of them hit almost all of the check-boxes in my decision tree. Jon would probably say look at the Defender, he loves it, but I am concerned about long term support for the electronics.
     
  5. stuartv

    stuartv Seeking the Light ScubaBoard Supporter

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    I think it is also influenced by the number of connections that there are - the number of places where there is an O-ring. Just from looking at other CCRs, it seems like some have 8 (or 10?) or more nuts with O-rings that have to be put together just to assemble the breathing loop. One on each side of the DSV, one on each side of a T-piece that attaches to each counterlung (so, is that 2 or 3?), and one on the end where it attaches to the head/scrubber. 8 or 10 O-rings in the loop, each of which is an opportunity to leak.

    In contrast, the rEvo, with the standard DSV, has only 2. One at the end of the inhale hose and one at the end of the exhale hose.
     
    cathal likes this.
  6. Heat Miser

    Heat Miser DIR Practitioner

    # of Dives: 100 - 199
    Location: Perth
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    @kierentec I appreciate your experience in these matters. Taking on @kensuf point about and Defender/Fathom/JJ, maybe you can add some colour to the relevant merits of each CCR.

    What do you think about the merits of GUE soft manifolded D7 litre JJ. It seem to me more dil is better than less. I understand that its heavy, but probably no more heavy than my rEvo with Ally 80 stage.
     
  7. cathal

    cathal Barracuda

    # of Dives: 500 - 999
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    I am a rEvo diver, I do deep wrecks. My buddy is a GUE diver who does caves and deep wrecks, with the twin 7 litre dil cylinder config. On a rocking boat he was not able to manage the extra weight of the JJ CCR with twin 7's dil cylinders. He ended up geting rid of them and going back to the standard JJ configuration of just a single 3 litre dil cylinder. The twin 7 dil cylinder configuration I imagine, works great in caves but in heavy swells on a hard deck boat trying to stand up and walk across the deck or when getting back in the boat when its rolling, they turned out to be too heavy for him. And just to clarify he's a 6ft guy of average build.
     
    stuartv, evandroairton and Heat Miser like this.
  8. kensuf

    kensuf Cave Instructor

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    Jon lives near Tulum, I think he's got other things to be concerned with versus posting on scuba board. It may be a few days before he gets back to you.

    In terms of the "GUE Config" -- I sometimes run my Fathom that way. It's great for diving off boats and decent for cave diving.
     
    Heat Miser likes this.
  9. Heat Miser

    Heat Miser DIR Practitioner

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    So what does the soft manifold do, provide redundant dil if one of the first stages goes?
     
  10. kensuf

    kensuf Cave Instructor

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    Heat Miser likes this.

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