Where should I start to approach the rebreather world

[Celt]

I started at 70. Now Helitrox CCR building time for Mod 2. I can't tell you how much warmer and easier and more fun it is! Yeah, there are complications, and it's a PITA relearning buoyancy control, and post-dive cleanup is long. But it is very much worth it, at any age.
Post in thread Advanced penetration of the Spiegel Grove Wreck

I just wouldn’t get the use out of it now if I wasn’t going deep or long multi hour dives. Some divers enjoy the technical side of gear, I’m the opposite. I like doing stuff with the least amount of gear and fuss.

 

[beester]

Hi everyone,

I am a diver with about twenty years of dives on my back and I am starting to consider a future step towards the rebreather.
For several years I have been certified for diving at 60mt with 2 decompression gases and I stopped at this level (GUE and CMAS certifications).
I would like to go further, not so much in terms of depth (even that, why not) but in terms of knowledge, I would like to explore and learn about the rebreather world and then evaluate this leap. In the recent years, with the current prices of helium, the cost of technical dives has increased a lot, at least where I am diving (Italy, Croatia) and certainly this is an aspect that makes me think.
For a serious dive at 60m, considering everything, we are now talking about 200/250 € (dive+boat+gasses+bottles)

I am aware of the fact that an objective saving on gas is obtained with the reb, but at the same time there are new costs to consider for maintenance, etc.
The first question I would like to ask therefore is whether with the transition to the reb we can actually speak of an economic saving compared to the open circuit, considering the same range of depth and frequency of dives. This minus the cost of the rebreather, which I consider to be an (expensive) investment to continue my passion.

I realize that in recent years I reduced the number of dives because of the cost of gas and I feel very limited and stopped by this.
What I think is that rebreather could therefore give new imputs and goals to my diving career.

I know several people who have switched to the reb, but I rarely dive with them due to the difference in equipment and the groups / interests that inevitably arise.
In my area, but I think almost everywhere, marrying a type / model of reb means marrying an agency, which I ideally don't like, even if I can understand.
Where I live for the most part I see JJ (GUE) and Tres Presidentes (UTR), along with some groups with SF2 (I ignore the agency). Other rebreathers very rarely (maybe there are, but I don't the people/ groups).

The second question I ask myself is therefore how much importance you give to the team (a team of divers with the same reb) rather than to the rebreather itself due to its technical / constructive characteristics. Practical example: in your opinion the Revo is the best rebreather, but all your friends have the JJ. Would you still rate the Revo? Why? It's not a simple question, but I'm curious to have points of view.

I also have many doubts about the type of reb, for example if in my case a PSCR is convenient, rather than a CCR (that I see as the future), with much higher and important costs from what I understand, which for my pockets would not be exactly painless.
I mainly dive in lakes, to find a good sea with interesting depths and wrecks I have about 4 hours by car, so I usually stop all weekend with my buddies, when possible, but I cannot do it all weekends.

I am definitely ignorant in terms of rebreathers, types and pros and cons of the various models, so I ask you how in your opinion I should start deepening this world to understand the choice to make. The feeling is that if I involve instructors now, they will push for the agency more than the rest.

Thanks for all your comments
N

Seems I'm late to the party, but let me comment since my situation is reasonably similar.

Background: I'm a GUE diver (T2,C2) and IANTD instructor. Been diving JJ since 2017, from Belgium but currently living in Italy on the wrong side of good diving ;-) (Veneto). Go to Croatia (Krnica) reasonably often.

My advice is to first look at the dives you are going to do and with who. If all your buddies are diving a JJ, get a JJ (irrelevant if they are GUE or not GUE divers) if they dive REVO's get a revo. There is a lot of advantages diving the same breathers (shared spareparts, shared experience and advice, shared procedures).

If you ever plan on participating in GUE (official) projects, you are going to be limited. I don't see them accepting other rebreathers than a JJ. However there is no issue diving the JJ in a non GUE setup. One of my close buddies switched from RB80 to JJ, and after diving it for a couple of years in GUE setup decided to switch it back to standard setup and dive more sidemounted bail out. This mixed diving is possible with a bit of discussion.

Regarding cost. If your diving is mainly shore diving, and you are planning a sufficient amount of diver per year your annual mainenance cost per dive obviously will be lower and you'll see a bigger return on investment (gas cost vs OC). However if most of your dives requires charters (which will cost on average already half of your cost per dive) the return will be lower. My annual cost on the JJ is ~500€. The cost reduction per dive on a typical T1 dive is on a chartered wreckdive about 50-60€ per dive. T2 dives you can add 100€ more in reduction. So you need to do at least 10 T1 dives per year to just balance the annual maintenance cost before any return on investment. A JJ + training will set you back 10000€ euro, so it'll be a couple of dives before it's written off.

However all this cost calculation is a bit of "false economy". You should decide on a rebreather mainly not as a cost saving device but as a device that enables you to expand your diving horizon.

I'm off to Krnica this evening for some diving until Sunday. Will be all OC, because I'm taking a friend who 's taking her first normoxic baby steps...

Cheers

 

[Teleopsis]

Seems I'm late to the party, but let me comment since my situation is reasonably similar.

Background: I'm a GUE diver (T2,C2) and IANTD instructor. Been diving JJ since 2017, from Belgium but currently living in Italy on the wrong side of good diving ;-) (Veneto). Go to Croatia (Krnica) reasonably often.

My advice is to first look at the dives you are going to do and with who. If all your buddies are diving a JJ, get a JJ (irrelevant if they are GUE or not GUE divers) if they dive REVO's get a revo. There is a lot of advantages diving the same breathers (shared spareparts, shared experience and advice, shared procedures).

If you ever plan on participating in GUE (official) projects, you are going to be limited. I don't see them accepting other rebreathers than a JJ. However there is no issue diving the JJ in a non GUE setup. One of my close buddies switched from RB80 to JJ, and after diving it for a couple of years in GUE setup decided to switch it back to standard setup and dive more sidemounted bail out. This mixed diving is possible with a bit of discussion.

Regarding cost. If your diving is mainly shore diving, and you are planning a sufficient amount of diver per year your annual mainenance cost per dive obviously will be lower and you'll see a bigger return on investment (gas cost vs OC). However if most of your dives requires charters (which will cost on average already half of your cost per dive) the return will be lower. My annual cost on the JJ is ~500€. The cost reduction per dive on a typical T1 dive is on a chartered wreckdive about 50-60€ per dive. T2 dives you can add 100€ more in reduction. So you need to do at least 10 T1 dives per year to just balance the annual maintenance cost before any return on investment. A JJ + training will set you back 10000€ euro, so it'll be a couple of dives before it's written off.

However all this cost calculation is a bit of "false economy". You should decide on a rebreather mainly not as a cost saving device but as a device that enables you to expand your diving horizon.

I'm off to Krnica this evening for some diving until Sunday. Will be all OC, because I'm taking a friend who 's taking her first normoxic baby steps...

Cheers

Enjoy Krnica, I did my T1 there. Fantastic diving.

 

[Nico-ITA]

Seems I'm late to the party, but let me comment since my situation is reasonably similar.

Background: I'm a GUE diver (T2,C2) and IANTD instructor. Been diving JJ since 2017, from Belgium but currently living in Italy on the wrong side of good diving ;-) (Veneto). Go to Croatia (Krnica) reasonably often.

My advice is to first look at the dives you are going to do and with who. If all your buddies are diving a JJ, get a JJ (irrelevant if they are GUE or not GUE divers) if they dive REVO's get a revo. There is a lot of advantages diving the same breathers (shared spareparts, shared experience and advice, shared procedures).

If you ever plan on participating in GUE (official) projects, you are going to be limited. I don't see them accepting other rebreathers than a JJ. However there is no issue diving the JJ in a non GUE setup. One of my close buddies switched from RB80 to JJ, and after diving it for a couple of years in GUE setup decided to switch it back to standard setup and dive more sidemounted bail out. This mixed diving is possible with a bit of discussion.

Regarding cost. If your diving is mainly shore diving, and you are planning a sufficient amount of diver per year your annual mainenance cost per dive obviously will be lower and you'll see a bigger return on investment (gas cost vs OC). However if most of your dives requires charters (which will cost on average already half of your cost per dive) the return will be lower. My annual cost on the JJ is ~500€. The cost reduction per dive on a typical T1 dive is on a chartered wreckdive about 50-60€ per dive. T2 dives you can add 100€ more in reduction. So you need to do at least 10 T1 dives per year to just balance the annual maintenance cost before any return on investment. A JJ + training will set you back 10000€ euro, so it'll be a couple of dives before it's written off.

However all this cost calculation is a bit of "false economy". You should decide on a rebreather mainly not as a cost saving device but as a device that enables you to expand your diving horizon.

I'm off to Krnica this evening for some diving until Sunday. Will be all OC, because I'm taking a friend who 's taking her first normoxic baby steps...

Cheers

The similarities don't stop there, because I also live in Veneto!

My buddies are mostly GUE, but OC. I barely know JJ GUE divers (2 or 3 people with which I did a few dives years ago in OC) and in general rebreather divers, just because I am used to dive with OC people.
I am an OC GUE diver, but by jumping on the rebreather I will surely have to look for new buddies, for this I want to do a wide evaluation and try to understand, in addition to JJ, which are the most common rebreathers in the part of Veneto where I live and honesty I have no idea right now.

At the moment participating in projects is not my goal, I have always seen this as something distant. Who knows, maybe things could change in the future. I was just wondering how hard it can be to "get accepted" in a group with a different reb, but I think this depends a lot on the people in the end.

Thanks
N

Ps. sometimes I go to Krinca, for sure the most tech-diving-friendly of the area, together with the Shark diving

 

[stuartv]

A fully configured Revo Mini titanium with 3 litre oxygen and diluent cylinders, a steel 2 litre suit inflate cylinder, a stainless stand, umbilical torch, two full scrubbers, it weighs 44kg. You can reduce this, but need additional weight with a drysuit.

Add the bailouts (single ali7 <35m, two ali7's to 50m, two ali80s to 70m).

Just saw this thread. This info may be no longer relevant. But...

My rEvo III Micro (which is titanium, as all Micros are), with 2 x 3L steel cylinders, rEvo factory (steel) stand, packed scrubber baskets, Dive Rite Nomad XT wing (instead of factory rEvo wing), rEvo BOV, Predator controller, NERD2 monitor, and 2 x AI transmitters (no Dreams or SPGs):

66 # or 30kg.

I just weighed it with my digital luggage scale.

I dive it like this in fresh water, in a drysuit with medium weight undergarments, and no additional lead. That is, with a drysuit inflation bottle clipped on the side that is not there now. Or, in a 5mm wetsuit, in the ocean, with no drysuit inflator (obviously) - and no additional lead.

The rEvo Micro is really nice for flying with (as CCRs go, anyway).

 

[Degenerate]

A fully configured Revo Mini titanium with 3 litre oxygen and diluent cylinders, a steel 2 litre suit inflate cylinder, a stainless stand, umbilical torch, two full scrubbers, it weighs 44kg. You can reduce this, but need additional weight with a drysuit.

Add the bailouts (single ali7 <35m, two ali7's to 50m, two ali80s to 70m).

Did they make it out of lead?
That is heavy AF for something that is marketed as a "mini", damn.

 

[rsingler]

66 # or 30kg

I don't think my JJ weighs much more than @stuartv 's Revo weight. It's spec'ed at 34kg with backplate, steel tanks and sorb.

 

[Degenerate]

I don't think my JJ weighs much more than @stuartv 's Revo weight.

My AP in stock config is also around the 30kg mark.
I've added a 6kg backplate and a Gbox so it's a little bit heavier, but still lighter than a Revo "mini" apparently
Would be interesting to know why there is such a huuuge difference in weight between them IMO, know very little about Revos as they are not especially popular here in Europe.

 

[stuartv]

@Wibble please explain how your logic works? If you follow the Revo recommendation of replace them when they die instead of on some arbitrary time interval *which I fully agree with*, you have 5 cells that are going to fail at some point vs. 2 or 3 from another unit, it is impossible that you are replacing less cells per year than a unit with less cells.
I fully agree with most of what's in those papers you linked in terms of how we check cells and how we determine when they're dead, but I don't believe that having 5 cells makes it inherently better. I also don't think that 3 cell voting logic is a good thing, but I think 5 is excessive and that there are better ways to skin that cat.
I haven't refuted anything about the twin cans, the RMS, or anything else, just the quantity of cells. I will never dive a Revo, it does not work for my diving and it never will, but that doesn't mean it isn't a good unit.

I thought we were talking about operating the units based on the manufacturer recommendations.

If you dive your 3 cell unit and follow the instructions, you'll probably be replacing 3 cells per year.

If you dive a rEvo with 5, you will probably actually only be replacing 2 cells per year (assuming you buy top quality sensors, anyway, like the rEvo ones).

@Wibble if you start a dive without all of the cells, then you are starting with a malfunctioning rebreather. My mCCR has 3 cells in it and if one dies, it is removed and I conduct the dive on 2 cells. I use a Divesoft Freedom and I can manually disable a cell in the middle of the dive if it cooks itself, no issue. Carry one spare cell and you are fine. I don't call the dive if a single cell fails on the mCCR. I keep 1 spare, when one cell dies, I put the spare in and get another spare. I don't follow any time schedule and do not pay attention to the dates on my cells. The dates are in the spreadsheet I use to track the cell health, but I don't care if it's 30 days old or 30 months old, if it is still behaving linearly and isn't current limited, then I don't mess with it. I do not like moving cells around either, they get put in a slot and stay there until they die.
If you have Shearwater electronics, you can't do override the voting logic and that is very scary to me and people have died because of it. This alone is a HUGE benefit of the Divesoft electronics platform. If you have a cell fail that is on the solenoid side with a Shearwater controller you really need to call the dive.

If you are okay with diving your mCCR with only 2 cells working, then how can you possibly knock somebody with a rEvo for diving with 4 cells working? In fact, rEvo has more than one officially acknowledged configuration, so diving with 4 cells is not remotely "starting with a malfunctioning rebreather." That is just pure fake news.

Additionally, you can be scared of the rEvo's Shearwater electronics if you want to, but I think that statement is also really just fake news. Has anyone died because of Shearwater electronics voting logic, that was using 5 cells?

If a rEvo has 2 cells on the controller that both go out and hose the voting logic (which could just as easily happen on a 3 cell unit, too - so why specifically knock the rEvo?), then (unlike 3 cell units) you can set the controller to the low set point and drive it manually using the 2 completely independent cells that are showing on your monitor.

If your 3 cell unit has 2 cells that go out and screw your voting logic, what are you going to do? Set it to your low SP and fly it manually, right? And how are you going to know what your deco obligation is, now that your controller is computing your deco based on bad data from your screwed voting logic? Well, obviously, you are going to use your backup computer that is set to a fixed SP, right? You may have a NERD monitor, but you can't use that, either, since it is getting the same bad data from your 3 sensors. If you DO have a NERD as a monitor, you can change it on the fly to not use External sensors, and use a fixed SP, so you could use that - if you noticed the bad sensors in time to keep the NERD from already having too much bad data included in its calculations. Otherwise, you have a 3rd computer, that it totally standalone, right?

Still doesn't seem as good as having a NERD monitor on a rEvo that is using 2 completely independent sensors to still do valid, real-time deco calculations.

Or, in your specific case, I guess you'll disable the 2 bad cells in the Divesoft and let it calculate your deco based on the one good cell. That still doesn't sound as good as having 2 good cells that are completely independent that are being used for your deco calculation. Especially if your Divesoft ran for a few minutes slurping bad sensor data into its record of what your current tissue load is before you noticed.

How comfortable would you REALLY be being 10,000 feet back in a cave and now having to finish your dive with only 1 good cell? Having 1 good one shown on your controller and 2 completely independent good ones shown on your monitor seems like a much nicer situation to be in....

Lastly, a buddy took his X to Bikini. 1 of the cells quit working, but it wasn't the cell. It turned out to be a connector somewhere that had gotten corroded and picked that time to fail. They couldn't repair it. The part that was bad was not part of his normal spares kit. He ended up diving the rest of his time there using only 2 cells. He has not knocked the rEvo's 5 sensors since that happened.

It's not like I'll throw out my entire scrubber after one dive unless it's a pretty long/deep/cold one.
Easily do two 50-60m dives with 40-50 min bottom time on a fill of sorb, can you do that on the Revo and only use up one of your two scrubbers?
Because if not, then you are definitely not "saving a fortune" on sorb.

Or to phrase it another way, would you feel comfortable doing the two dives I mentioned above with just one of your scrubbers packed with sorb?
No, you wouldn't because you would most likely have a very bad time somewhere during dive #2.

If it's in one or two scrubbers should not make much of a difference, X kilos of sorb can absorb Y amount of co2, no?

Do a 60m dive for 50 minutes bottom time, then do the same thing again tomorrow?

If my rMS said I was still in the top basket after the first dive (which it would), then I would dump the top basket and cycle the other one to the top. You would be dumping your whole scrubber.

Result: You would use 2 full loads of sorb. I would use 1.5 loads of sorb. Perfectly safely. While you spend 33% more on sorb.

If you are OK with diving a non-fully functioning unit...

Actually functioning completely - in a 4 sensor config, per factory instructions, unlike your plan to dive your unit starting with only 2 good sensors.

I never doubted that you can do that on a full load of sorb.

The claim was that the dual scrubber system of the Revo would save you a ton of money on sorb because you typically only replace the sorb in one canister at the time.

I said that is bollocks because it is.
If you do a fresh fill of sorb in a Revo and do two 50-60m dives 40-50 mins of bottom time, would you throw out all out all of your sorb after that or would you keep the sorb in your secondary scrubber for your next (similar profile) dive?

If the second option is your go to then you are a lot braver than I am

I already explained why it was your statement about it that is bollocks.

And, it is not about bravery. It's about having a better, more modern system than what you have. A system that reliably tells us when we have actually used up all the sorb in the top basket. It may get used faster, on a dive in really cold water. But, the system will still measure it and tell us that.

MAYBE on a 60m dive for 50 minutes in truly cold water, just MAYBE that would consume all of the top basket and get into the 2nd basket in one dive. In that case, then yes, we would use the same amount of sorb if we did the same dive again the next day. But, I am highly skeptical that I would consume all of the top basket in that first dive. The manufacturer specs for the rEvo (and ALL units) are very conservative. The rMS system works well and regularly allows us to far exceed the manufacturer's specs for sorb life. Because we are diving based on actual real-time data - not on a spec that had to be published as a worst-case, very conservative statement.

You are driving a car with no fuel gauge and a manufacturer's statement that says it will go 200 miles on a full tank. And you can't tell how much fuel it used when you get to your destination. You have to drain your fuel tank without seeing how much comes out, then fill it all the way up every time. If you know you are driving at a slow but steady speed, with no stop and go, and all flat ground, you might somehow "know" that you can really go 300 miles before stopping to fill up. But, that's about the best you can do.

With rEvo rMS, we are driving a car with a working, accurate fuel gauge. The manufacturer still says it will go 200 miles on a full tank. But, with our gauge, we drive 200 miles, see that we still have 3/4 of a tank, and continue on for quite a ways. And if we stop for gas before it gets to 1/2 tank on the gauge, we can just add 1/2 a tank of fuel and continue with a full tank, rather than draining the whole tank before refilling. Safely and without having to "make an educated guess".

 

[stuartv]

You may save "a ton of money on sorb" and *only* replace 0.65 extra cells per year on a Revo... Alas, all of those savings will be wiped out when it has to go in for obscenely overpriced factory service to replace the counterlungs.

I've sent 2 rEvos for their 10 year factory service (after no prior factory service in their history). Both still with original CLs. Both came back in less than a week. Neither one needed the CLs replaced. Both factory services were something like $500 - except for the one that needed a new dil reg (or was it an O2 reg? I can't remember right now) due to the previous owner getting salt water in it then letting it sit. The new reg added something like $300 to that bill.

If they HAD needed both CLs replaced, it would have probably added - well, the 2 CLs are less than $220, total, for both. Additional labor to install them while the unit was being serviced? I don't know. But, I honestly cannot imagine the bill qualifying as "obscene" - to me, anyway.

What is the cost for 10 years of factory maintenance on a JJ or a Meg or an X?

@rjack321 and for whatever reason is really foot heavy and doesn't play nice when you're in thin wetsuits or a bathing suit

I dive my rEvo in flat trim. I have no lead on it at all, normally, and I do have the factory stainless steel stand on the bottom. And that is also with Hollis F1 fins (i.e. very negative) when I'm in a drysuit. Deep6 Eddy fins (neutral) when I'm in a wetsuit or no suit. Flat trim. No lead. No problem.

What unit are you talking about that is foot heavy? A buddy that used to dive a JJ complained that it was very tail heavy. My friends with Megs mount the cylinders up really high on the sides of the can to try and counteract being tail heavy.

I wish people would just be honest about the time it takes to prep a rebreather. There is no way you are filling both scrubbers, analyzing all your gases, checking your batteries, flow check on your MAV if a mCCR, doing a stereo check, build, positive-negative, calibrate etc in 30mins on any CCR. A full 5mins each at positive and negative alone are minimum 10mins

If you have a bunch of stuff done ahead of time or you skip steps, then sure you can get it down to under an hour. But from scratch let's not mislead people. 60mins is fast, 90mins is normal, 2 hours isnt anything to be ashamed of.

I fill my cylinders and analyze them before I leave the shop. I wouldn't count time filling or analyzing in what I count as CCR prep time.

If I were to compare that aspect of prep between CCR and OC, I would be filling and analyzing a dil, an O2, and, say 2 BO/deco cylinders. On OC, I would be filling and analyzing a set of BM doubles and 2 deco cylinders. So, 4 analyses versus 3. The next day, I would fill and analyze the BM doubles again, and both the deco cylinders. On CC, I would fill and analyze the dil and O2. Now it's a wash - I've analyzed 6 tanks, either way. Diving a 3rd day? Now I'm ahead on the CCR.

Assuming I start with cylinders that are all already analyzed, and empty scrubber baskets, it takes about 10 - 15 minutes to pack my scrubbers (assuming I am starting from scratch, not prepping for a second day in a row of diving). Then, 10 - 15 minutes to assemble my rEvo and do the post-build checklist.

I don't usually spend a full 5 minutes on a Positive test. A Negative test, I do like to give 5 minutes or more. But, I can start those tests and continue with other things, so they don't just add their time to the total.

For example: Start Negative Test. Program gases in computers. Check BO gas cylinder pressures. Complete Negative Test. The Negative test may run for 10 minutes, but it only takes about 30 seconds of actual time.

30 minutes to assemble the unit and do the build check list seems about right for my rEvo. That is from "I haven't dived it in a while" to "ready to put in the truck and transport to the boat or dive site."

Side by side with a buddy with a Meg, the rEvo is just faster. There is less to do. Less things to put together, which means less things to check and less places for the loop to leak, which means less things to fail.

Once I'm on the boat and it's time to get ready to dive, doing the unit's pre-dive checklist adds maybe 5 minutes to the time it takes for me to be ready to splash. I don't have to pre-breathe for 5 full minutes. I only have to pre-breathe until my rMS says that my scrubber is working and showing at least 45 minutes of cycle time available. That usually only takes 1 to 2 minutes of pre-breathing.

If only doing 1 dive, I reckon OC is a little less time spent on the boat. If doing 2 dives, then OC starts to lose out again (or be a wash) by virtue of needing to change tanks. Unless you're doing a 2nd dive on the same BM doubles.