CCR Selection priorities

[kierentec]

There have been plenty of "how to choose a rebreather" or "help me choose my first rebreather" type threads over the years, with a couple of great discussions happening recently. So I decided to be completely redundant and start yet another one with what I've deemed some of the most important considerations when choosing a rebreather. I've got a bit of experience over the past 8 years and 1000+ hours on the loop in just about every environment on the planet less the arctic. I've been an instructor a several units, and have diver level training and a fair bit of experience with most rebreathers currently on the market. Based on that, this is what I've come up with as general guidelines. From there, you can get into the nitty-gritty details like the direction of gas flow, where o2 is injected (inhale or exhale side of scrubber), BOV vs DSV, etc.

1. Balance/Trim/overall comfort: This is incredibly important. If the unit is not comfortable to dive, you will have to deal with that every minute of every dive, and with the longer runtimes of CCR dives, it can be a serious issue. If you have to struggle to maintain trim, the loop is uncomfortable in your mouth, etc. dives simply won’t be very enjoyable (which, in my mind, completely defeats the purpose of getting in the water to begin with).
2. Build quality: Rebreathers get used, hard. Make sure to look for things like cheap materials (injection-molded plastic or thin Delrin). Also, look for the overall fit and finish. Units with poor construction are more likely to fail positive/negative checks consistently, making the setup process extremely frustrating and time-consuming. One of my first CCRs used thin cheap Delrin for the canister. If certain components were strapped in too tight, the scrubber not packed “just so”, or things not lined up just right, it would not seal properly. I spent probably 10+ hours tracking down leaks in the setup process in the 200 hours I dove the unit. So when looking at a rebreather, think to yourself, is this thing built like a Mercedes, or a Kia? It will make a significant difference in your longtime enjoyment of the unit. Also, be aware if the rebreather has specific known issues like loop hoses tearing or even coming off the unit entirely mid-dive. And the last point, make SURE common failure points like O2 cells and mushroom valves are quick and easy to replace. If it takes 30 seconds to swap out a cell, you are more likely to do it prior to a dive if something is borderline. If it takes 5 minutes or more, it's easier to convince yourself that "it'll probably be fine".
3. Work of breathing (WOB)/counterlung design: Like overall comfort, work of breathing just has to be great. You have to breathe in and out consistently throughout every dive, and if that’s not easy, it will both lead to increased CO2 buildup, increased strain on your respiratory system, and just be overall uncomfortable. Chest mount counter lungs are a thing of the past. Properly designed back mounted counterlungs have excellent WOB characteristics with an emphasis on ease of exhalation. When you test dive a rebreather, make sure to spend some time evaluating the work of breathing in various positions. Not all dives are spent in perfect horizontal trim all the time, so make sure you will be comfortable breathing slightly head up, head down, on your side, etc.
4. Flood tolerance/recovery: For the types of dives rebreathers are intended for (long, deep, extended range dives), flood tolerance is a critical design attribute that must be considered. Several hours away from the surface is not a place to be regretting the fact that your loop is flooded, scrubber is soaked, and your only option is bailing out. Be aware of the loop design to make sure there are sufficient water traps between the exhale side of the mouthpiece and the scrubber. You drool into the loop, and your moist exhaled gas condenses inside the loop hoses. If the scrubber is directly in line with the exhale side of the mouthpiece, that means it is actually functioning as the water trap. This can significantly affect the work of breathing, scrubber efficiency, and increases the risk of a caustic cocktail.
5. Ease of setup/breakdown: if the unit is super complex to assemble, you will get frustrated putting it together as well as increase your risk of making a mistake. Make sure the assembly process is simple with a streamlined and easy to follow checklist.
6. Flexibility in configuration (on-board tank mounting options, off-board gas addition, etc.): not all dives are equal, and some require or benefit from different tank mounting options. From onboard o2 and diluent as the “standard” CCR configuration, to using the onboard “dil” cylinder as suit inflation and off-boarding your dil from one of your bailout cylinders, to using backmounted bailout, make sure the unit will be able to accommodate a configuration that meets your diving goals. Also, again, rebreathers are designed for long extended range diving. If the unit cannot accommodate a 3L oxygen cylinder, then it’s really not a properly designed unit in my opinion.
7. Travel size/weight: You can always bring extra bags, so this really isn’t at the top of my list. However, a unit that can easily fit in a carry-on is a huge advantage. Luggage gets treated poorly and lost regularly, keeping your rebreather with you on the flight is just an extra warm and fuzzy feeling that makes travel a bit less stressful (and is always fun at security, just be prepared to be inspected every single time and be able to clearly explain what the thing is, in whatever language is appropriate.
8. Manufacturer support: Stuff breaks, make sure that the manufacturer has a track record of responsiveness and good support. Also, be wary of those who make “updates” or “upgrades” to the unit which are extremely costly. For example, has the manufacturer ever phased out an electronics package in a way that required users to spend $4000+ to “upgrade” to a serviceable unit? OR, when a new development was released, did they offer a heavy discount on the upgrade to existing users before phasing the old version out of service?
9. eCCR vs mCCR: this is a personal choice based on your own philosophies.
10. Price: should not be a consideration, don’t be cheap.

That's about it for now. Discuss

 

[CptTightPants21]

Thank you for this.

I understand if you are hesitant (or not allowed) to speak about it in depth. You are an instructor on several units, including the XCCR. Over the years, several posters including myself have commented how they enjoyed demoing the XCCR, but the price scared them away. I agree with the comment about not using price as a major consideration, but Megs, JJs, Fathoms, SF2s all seem to be in the 8-9k range and XCCR is around 11K--Granted XCCR packages include tanks so -$500. But going apples to apples as much as possible there is still a considerable variance. Can you go into detail about why this price variance exists and may or may not be justified?

You have some important factors listed above and many rebreathers have pros and cons. Using the number above, could you maybe list out a top 2 or 3 units and "bottom" 2 or 3 for units for each. An example, I am no expert, but revos and Optimas seemed to be a little more complicated to set up vs JJ/Meg. Revos are known to have very poor flood tolerance, which unit has some of the best, why?

I realize my post essentially asked you to dump another thousand word response, but you asked for it.

 

[kierentec]

Thank you for this.

I understand if you are hesitant (or not allowed) to speak about it in depth. You are an instructor on several units, including the XCCR. Over the years, several posters including myself have commented how they enjoyed demoing the XCCR, but the price scared them away. I agree with the comment about not using price as a major consideration, but Megs, JJs, Fathoms, SF2s all seem to be in the 8-9k range and XCCR is around 11K--Granted XCCR packages include tanks so -$500. But going apples to apples as much as possible there is still a considerable variance. Can you go into detail about why this price variance exists and may or may not be justified?

You have some important factors listed above and many rebreathers have pros and cons. Using the number above, could you maybe list out a top 2 or 3 units and "bottom" 2 or 3 for units for each. An example, I am no expert, but revos and Optimas seemed to be a little more complicated to set up vs JJ/Meg. Revos are known to have very poor flood tolerance, which unit has some of the best, why?

I realize my post essentially asked you to dump another thousand word response, but you asked for it.

Haha, happy to discuss, that's why I started the thread

In all honesty, IQ sub builds some of the highest quality stuff in diving. The machining is absolutely stunning, and the fit and finish truly remarkable. My Defender (x-ccr's cousin) has over 1000 hours on the electronics, and well over that on the rest of the unit and gone through major abuse (dropped off the back of trucks, etc) and none of the hardware has ever failed in setup or on a dive. That's really what you're paying for, the extra attention to detail and the increased costs associated with ultra high precision machining with high quality materials. Whether it's worth the extra couple grand to you or not is really a personal choice. A similar unit that comes in at a lower price tag would be the JJ, which of course has it's differences which I find to be cons (o2 injection on the inhale side of the scrubber, heavy and bulky stand, no BOV, axial scrubber (though a radial is available as an option) and a few other things). It's still very similar in function and considerably cheaper.

As for top and "bottom" selections for each, I'm happy to go through some things privately with individuals, but don't think it's appropriate as an instructor to (what some might consider) "bash" any competitors products on a public forum. However, I am happy to provide my top 3 units in the categories listed above:

1. Fathom MKII CCR (literally excels in all of my criteria, but here’s the breakdown)
   1. Excellent, and I mean, EXCELLENT balance and trim in all configurations, loop and mouthpiece is also very comfortable
   2. Excellent build quality, thing is extremely solid with very tight machining tolerances. Definitely a “Mercedes”
   3. Great WOB
   4. Great water tolerance and flood recovery
   5. VERY easy setup and breakdown
   6. Very flexible in configuration.
   7. Very compact to travel with (30lbs and fits in a carryon with room to spare)
   8. Great customer service, factory is in gainesville and the owner is full-time.
   9. mCCR only
   10. Other plus’:
       1. HUGE scrubber capacity (9lb is standard, so about 9 hours of functional duration)
       2. The depth compensating needle valve allows you to adjust oxygen flow rate to match the metabolic needs in real time on the dive, but does NOT require adjustment based on depth changes like most needle valves.
       3. Super simple operation. Analogue electronics, easy to service, very few failure points.
       4. Unit is actively being used for some of the biggest cave exploration dives being conducted right now.
2. Defender/X-CCR: my second pick (I dive the defender, not the X as I prefer the simplicity of the electronics over all of the bells and whistles of the X, but the following points cover both units)
   1. Good balance and trim in a drysuit, but still a bit butt-heavy, harder to dive in a wetsuit than the fathom but still possible. Loop and mouthpiece are comfortable.
   2. Best build quality on the market, no question.
   3. Great WOB
   4. Great water tolerance and flood recovery
   5. Very easy setup and breakdown
   6. Fairly flexible in configuration, though requires quite a bit of fiddling and re-routing of things.
   7. The full-size canister fits in a carryon, but you need to pack the head in your personal item like a backpack. However, if you have a travel canister, the whole thing fits in a carryon. Much heavier travel weight than the fathom, though.
   8. Good customer service. The Thorntons of SubGravity really care about their customers and always try their hardest to make things right if there is a problem.
   9. eCCR only, but 2 electronics packages. Either the X-CCR with Shearwater diveCAN with CO2 monitoring and dil and O2 high pressure sensing in the handset, OR the defender’s proprietary electronics (analogue, simple, robust).
3. Flex CCR Sidemount: in all honesty, I highly discourage looking at side mount CCRs as your first unit. Even I RARELY do dives where a side mount CCR is required. But, if someone really needs a side mount CCR, I think the Flex is the best option available.
   1. Sidemount CCRs just take a lot of fiddling to get them dialed in, but the flex is overall pretty easy to configure to your liking to get it comfortable. It trims out like a full AL80, so you can dive it in your normal aluminum tank sidemount kit comfortably without any adjustments.
   2. Same build quality as the defender/x as it is built in the same factory and uses many of the same components.
   3. For a side mount CCR, excellent WOB
   4. For a side mount CCR, great flood recovery and water tolerance
   5. Very easy setup and breakdown
   6. Very flexible in sidemount configurations. Can wear it on the left or right, with several options for plumbing in dil. Also allows for a 3L O2 cylinder
   7. Light for travel, but needs to be in checked luggage
   8. Distributer is Golem Gear, whome I've always had good experiences with. However, others have not and a quick look around you'll find a few postings about.
   9. mCCR (my preference for a side mount unit) eCCR, or hybrid options are available. eCCR and hybrid options use shearwater diveCAN electronics.

 

[rjack321]

re: "Great WOB"
Its a shame the Fathom has no third party WOB or scrubber duration testing and no CE either. Plus running the loop through the radial inside to outside is just silly as it negates the value of the canister as a water trap before wetting the sorb.

The Flex in its fully rigged configuration is enormous as SM CCR. It also often leads to some "less than ideal" choices about BO - namely only having one source of dil/BO on the opposite side.

 

[kierentec]

re: "Great WOB"
Its a shame the Fathom has no third party WOB or scrubber duration testing and no CE either. Plus running the loop through the radial inside to outside is just silly as it negates the value of the canister as a water trap before wetting the sorb.

The Flex in its fully rigged configuration is enormous as SM CCR. It also often leads to some "less than ideal" choices about BO - namely only having one source of dil/BO on the opposite side.

not going to lie, the inside out flowpath if the scrubber was a big concern of mine and one of the main reasons I held off on buying a unit of my own. I spent a good deal of time on it, putting 8+hours on a scrubber and noticed no noticeable difference in moisture in the sorb vs my essentially identical (but backwards) defender can. The exhale counterlung is the primary water trap and most of the moisture condenses in that lung before the gas hits the inside of the hot scrubber. When that gas passes to the outside of the scrubber, the moisture it picks up via the reaction in the sorb then condenses on the inside of the can and drops out into the bottom of the can. When I was sure it was a non-issue, I pulled the trigger and got one.

The idea behind the inside out flow was based on duration testing dating back quite a ways (steam machine’s prizm) where there was a slight increase in efficiency. The unit was built for extreme duration dives, and the gas flowpath was decided to suit that need.

más for the Flex, I should have clarified I’m on the Flex2, which is the pretty much the same size as an AL80, and sits pretty much just like one. Properly rigged (2 bailout bottles, one side mounted opposite the CCR, the other carried as a stage, is the exact same profile as OC sidemount with a stage. Super easy to configure it to switch between the 2 as drive bottles, allowing you to easily remove one or both cylinders. It’s actually not a big drama to remove the ccr for no-mount stuff as well. You’re just juggling 3 items at that point, but again, no more than OC sidemount with a stage. You can also easily mount a 2L drive bottle to your butt as well, and not be tied to both bailout cylinders (not a fan personally)

With sidemount CCRs, there is no great solution out there right now. For me, the slightly larger profile of carrying the stage is a non-issue. Easy to pull gear off when dealing with restrictions, nothing new there. The build quality, piece of mind that the unit will stay together in even the tightest spots and WOB are my personal primary focus.

 

[kierentec]

re: "Great WOB"
Its a shame the Fathom has no third party WOB or scrubber duration testing and no CE either. Plus running the loop through the radial inside to outside is just silly as it negates the value of the canister as a water trap before wetting the sorb.

The Flex in its fully rigged configuration is enormous as SM CCR. It also often leads to some "less than ideal" choices about BO - namely only having one source of dil/BO on the opposite side.

As for the third party testing, sure, it would be good to have the numbers, but not really very important. None of the individual components In the loop are new design, there’s data out there on the components in similar configurations, which all perform very well.

 

[rjack321]

As for the third party testing, sure, it would be good to have the numbers, but not really very important. None of the individual components In the loop are new design, there’s data out there on the components in similar configurations, which all perform very well.

The old Golem DSVs illustrate the problem with this line of thinking. They used drager flapper valves which in the original drager DSVs were fine. When used in the Golem DSV or with the Golem spiders they were horrible and failed CE WOB requirements.

It's not important to you. But the unit cannot be sold in the EU and in some places its probably iffy to advertise to shops and clubs you're even diving it (France in particular). Saying the "WOB is great" without any data is just your anecdote. Ditto scrubber duration which is a mystery even under standard 4C, 1.6L CO2 conditions.

 

[broncobowsher]

Very good.

I remember doing my shopping years ago. There was a new one out that on paper looked really good. When I saw it in person it was a different story. Not that the build quality was bad. But the pure complexity and how many parts it had was way above anything else. And you want all that to work perfectly, every time, while being dunked in salt water. I do still admire it and the craftsmanship, but don't want to own it.

There was another that was extremely proud of everything made in house. They can control the quality of all the parts. And they sure looked like good parts. But they are the only source of there parts. Made any future repairs very dependent on that single source of parts. Little too dependent for my tastes. But in recent years Mares has stepped in with rEvo (yes, that is what I own and dive) and that supply chain has got a LOT better. Was a single source, now just about anyplace that can get Mares parts can get you most anything for a rEvo. They have also opened up a few more service centers as well.

 

[rjack321]

más for the Flex, I should have clarified I’m on the Flex2, which is the pretty much the same size as an AL80, and sits pretty much just like one. Properly rigged (2 bailout bottles, one side mounted opposite the CCR, the other carried as a stage, is the exact same profile as OC sidemount with a stage. Super easy to configure it to switch between the 2 as drive bottles, allowing you to easily remove one or both cylinders. It’s actually not a big drama to remove the ccr for no-mount stuff as well. You’re just juggling 3 items at that point, but again, no more than OC sidemount with a stage. You can also easily mount a 2L drive bottle to your butt as well, and not be tied to both bailout cylinders (not a fan personally)

With sidemount CCRs, there is no great solution out there right now. For me, the slightly larger profile of carrying the stage is a non-issue. Easy to pull gear off when dealing with restrictions, nothing new there. The build quality, piece of mind that the unit will stay together in even the tightest spots and WOB are my personal primary focus.

The sidewinder is nice in the BO regard - sucks in pretty much every other category though. I put my 1st deco gas underneath on the left and it makes me at least as thick as SM + a stage. The 2nd deco gas on a leash is not really any fun. I don't dive this unit with 2 deco gases when there is no way to drop them.

I don't find 2L of o2 (on my butt) inadequate for even my longest exploration dives. But I am thermally limited by 3-7C water far more than O2 limited. Even if I use my 8lb scrubber in my Meg I would still be in the <5hr range for these temps. And only 5hrs for the 7-8C dives. 3-4C really puts a damper on runtime. If I had Finnish blood perhaps I'd be bolder.

 

[kierentec]

The old Golem DSVs illustrate the problem with this line of thinking. They used drager flapper valves which in the original drager DSVs were fine. When used in the Golem DSV or with the Golem spiders they were horrible and failed CE WOB requirements.

It's not important to you. But the unit cannot be sold in the EU and in some places its probably iffy to advertise to shops and clubs you're even diving it (France in particular). Saying the "WOB is great" without any data is just your anecdote. Ditto scrubber duration which is a mystery even under standard 4C, 1.6L CO2 conditions.

there’s no arguing that saying “work of breathing is great” without testing and data to back it up is anything other than subjective. However, having dealt with several manufacturers at the training agency level who were trying to get through the CE process, I can promise that a CE certification (at least for a rebreather) has very little to do with actual performance or safety. At some point I’m sure someone will pop up here with a bunch of PDFs to prove me wrong, though... but I still agree with your point. For me, the way the unit breathes on my back and in the water is what’s important, which, I suppose, is my point in the original post.