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tbone1004

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First, you are ignoring the fact that some oxygen will be introduced along with the DIL. The amount of course, will depend on how hypoxic the DIL is. Second, when it comes to live or dead situations, going from a safety margin from 90 second to 5+ minutes is a whole world of a diference.

I specifically said that I was ignoring any dil being added because it adds 4-5 lines to the equation and I'm not going to bother doing that since you shouldn't be adding dil back into the loop in this situation, you should be adding O2 because that is what you are consuming, and most importantly you should be using a dil that is matched to your ideal bottom mixes and I firmly believe in standard gases, i.e. 100ft=EAN32, 30/30, 35/25, etc. not air and certainly not 12/70. In either instance though the choice to ignore the addition of dil was to emphasize how important it is to actually understand how the rebreathers work and when you follow minloop volume, you aren't going to go hypoxic if you are not ascending.
 

JonG1

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On the subject of de-watering, I am wondering how many situations can be recovered, plus the impact on the sorb from a single or repeated flooding issue must have an effect?

I guess an accidental dropping of the loop, or loose lips could be 1, or if it was a gradual slow leak that could be purged repeatedly, but a loop tear, catastrophic failure leading to a flood, o ring failure, build error etc. would still require bailout anyway to cover the exit.

If it was a slow but continuous leak that required repeated purging, I'd be concerned about the sorb, reduced scrubbing potential, WOB, caustic etc.

All a bit moot because I don't do dives where this would be an issue, but curious never the less.
 

tbone1004

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I have a question on this. What if you're an well educated (mod 2 or 3) accomplished diver (lot's of hours) on a CCR. Will this argument still hold in your opinion? I understand learning to dive a CCR and doing Cave is not wise and you should be an accomplished OC diver to be able to bailout safely.

Just curious what's your opinion on this.

arguably more so because cave diving with a CCR is WAY different than diving it in the ocean and the skills that are emphasized in a good cave CCR course are either going to be new or very different than you would be using in the ocean, particularly with regards to SCR mode. There are also configuration changes that have a lot more benefit in a cave than they do in open water, mainly the concept of dilout/bailuent instead of using an onboard 3l for diluent. The instructors can't get to that until you are comfortable with line work, 0 viz, lost line/buddy, reading flow, likely fixing all sorts of trim and propulsion issues etc. Being an accomplished CCR divers means that the CCR isn't going to task load you in terms of actually running the rebreather, but diving a CCR in a cave can and IMO should be very different than the "traditional" CCR configurations in open water. It is actually very similar to going from a stab jacket with a "golden triangle" regulator setup to a bp/w with a primary donate setup. With setups like the RB80, GUE JJ, Fathom, and all of the homebuilt rack mounted units that many of us are using for the backmounted breathers or going to sidemount instead of a single bottle following the dilout/bailuent concept, staying on SCR mode when in 0 vis or with failed cells/ppO2 readouts, etc. is all new skills that the CCR diver has to contend with. Most open water CCR divers have a fairly head up trim position because the rebreathers breathe better up there than they do when in a flatter position which has to be contended with, and almost all of them need a LOT of small modifications to get them to be anything close to what we would consider streamlined for a cave. If you have the basic cave skills sorted, then the cave CCR class can focus on getting you to the point where you can really use the CCR for where it shines in a cave and breaking the class up into two sections can really help. TDI now has a CCR intro to cave which at least lets the course get broken up and can help, but it is also highly likely that an accomplished CCR diver is spending much if any time doing technical diving on OC so it forces you back to that mindset for bailout swims.
 

flymolo

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cave ccr unlocks a lot of doors right from the get-go. going oc cave first is a more conservative path that i imagine would lead to a better cave diver overall
 

Garth

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My take on rebreather purchase.

1. If this will be your first rebreather and you aren’t planning a mission requiring sidemount I would choose backmount.

2. (Maybe unpopular opinion) but I think running a fully eCCR manually is ridiculous. Set point control is not as good manually as the eCCR or maybe the hammerhead controls were that good but the solenoid control was pretty impressive. Did it get you complacent? Yes, but this is why I would choose a hybrid personally now that I’ve dove both eCCR and manual.

3. There is nothing wrong with front mounted counterlungs as a first setup. You will like how they breath better but as you get more experience and want less clutter up front you will accept the trade off to go backmounted… but deep down there is nothing that breaths like front mounted counter lungs IMO.

4. Sidewinder is awesome, but it’s not as forgiving as backmounted units with radial scrubbers like the XCCR and defender. I would start there personally. The other backmounted units are nice but knowing what I have done to my hammerhead it’s built like a tank, no need for a shield or any weird thing like that.

Summary:
Every decision is a trade off - if you aren’t doing tight cave, aren’t exploring and are going deep a backmounted unit should work.

I’m pretty happy I have a backmounted hammerhead unit and a sidewinder.

I don’t know if I’ll get rid of the front mounted counterlungs…
 

rjack321

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Have been diving a Kiss Classic since 14 years ago. Even with a clogged orifice, I do not think that going from 1.3 to under 0.2 would happen in 90 seconds, but waaaaaaaaaaaay more time.
Shrugs
Start at 1.1 or 1.2 at 30ft
Ascend to the surface
Have the loop collapse and the ADV squirt in some low ppO2 dil on the way
Breathe there are minute or two on the loop

Running manually with a clogged orifice is a lot dicier than you realize and there are several ways to go from breathable to NOT in a pretty short amount of time.

Despite what you "think" Nadwidny has the shearwater logs to prove his point. You'll have to read alertdiver when his case study is released. In the meantime, watch your O2 gauge, don't use slider shut offs, and don't dive with clogged orifices. There have been 3 hypoxia events, 2 fatalities and one very near miss - one each from these causes in less than a year.
 

andrespp

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Shrugs
Start at 1.1 or 1.2 at 30ft
Ascend to the surface
Have the loop collapse and the ADV squirt in some low ppO2 dil on the way
Breathe there are minute or two on the loop
.

Sorry for pointing the evident, but if you are going from 30 ft to surface you REALLY need to be on top of your ppO2, no matter if the CMF leaky valve is working or not.

Being close to surface, both when starting the dive or acending is ALWAYS a critical spot when diving CCR.
 

Dsix36

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I may be the only person that disagrees with the OC first for cave training. Personally I have absolutely zero OC technical training. I have never had a set of doubles on my back and I hope to goodness that I never do.
BUT
I think you need a lot of time and experience (read as problems underwater) on OC so that you are so completely comfortable that it is second nature to you before you ever even consider a rebreather in the first place. Then you need another entire boat load of experience on the rebreather before you head into the caves. Your last chance for survival in the event of a rebreather failure is OC, so you darn well better have the skill set in place and practiced extensively before you need to use it in anger.

Dewatering the rEvo can be done very simply and effectively if done via the way the original rEvo was made. My unit is old enough to have this and it works just fine.
 

macado

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Dewatering the rEvo can be done very simply and effectively if done via the way the original rEvo was made. My unit is old enough to have this and it works just fine.

Didn't you reverse the direction of your loop on the rEvo so that your bottom counterlung is the exhale lung with the original OPV on the bottom? I thought I remember reading something like that but I don't recall if you ever posted the specifics online.
 
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