Who should use a CCR?

[bamafan]

There is a very very small number of people who actually need a rebreather to make the dive safer. I mainly cave dive so that is how I look at things. There are very few people who are doing sub 300' dives with runtimes of 6+ hours. I am certainly not one of these and hate doing that much deco. If only people who "needed" a breather bought one the industry couldn't survive. I personally don't see much value in them for shallow diving if you carry the proper bailout. I see people skimping on bailout because they don't want to essentially drag as many tanks as it would take to do the dive on oc. This is especially true with the sidemount breather crowd and their single tank as dil / bailout. Dive what makes you happy.

 

[kensuf]

You don't need to go below 300' to have 6 hour dives.

But I defer to your vast experience and accomplishments as a cave explorer.

 

[RainPilot]

That must have been a Devil of a dive Ken, judging by the dive number...

 

[PfcAJ]

I have a number of buddies who use them because they dive regularly with Trimix and it's the right tool for that job in terms of keeping your deco obligations optimal and your gas prices within reason and logic. Personally, for all of the Trimix diving I do I'll just stick with OC and do the extra hang-time unless I ever move somewhere with a dive site or two that makes using Trimix on a regular basis really compelling.

I've been doin some diving lately with guys on CCRs, and I've come to the conclusion that the "less deco time" thing is a myth. Never not ONCE has a CCR guy had less deco on his computer than I had. Same or similar gradient factors, same dives (obvi). At best they're equal.

 

[PfcAJ]

You don't need to go below 300' to have 6 hour dives.

View attachment 407476

But I defer to your vast experience and accomplishments as a cave explorer.

idk man 183ft is purdy deep

 

[stuartv]

I've been doin some diving lately with guys on CCRs, and I've come to the conclusion that the "less deco time" thing is a myth. Never not ONCE has a CCR guy had less deco on his computer than I had. Same or similar gradient factors, same dives (obvi). At best they're equal.

I've done some diving with a buddy that dives CCR. AFAIK, when diving square(-ish) profiles, deco is about the same either way. On the bottom, you're both breathing about the same ppO2, so you're both ongassing about the same over the whole dive.

The difference comes in multi-level dives. If you choose your OC gas for a max depth of (say) 180, and then you spend a lot of your dive at 150, you will have a lot of your dive with a ppO2 that is less than optimum. Which means a higher ppN2 than is necessary. Your buddy on CCR may choose that same gas for dil that you chose for back gas, but when you're both hanging out at 150, his CCR will bump up his ppO2 to higher than what you are breathing, keeping his on-gassing at a reduced level compared to you. That's when the CCR will result in less deco time.

 

[PfcAJ]

I've done some diving with a buddy that dives CCR. AFAIK, when diving square(-ish) profiles, deco is about the same either way. On the bottom, you're both breathing about the same ppO2, so you're both ongassing about the same over the whole dive.

The difference comes in multi-level dives. If you choose your OC gas for a max depth of (say) 180, and then you spend a lot of your dive at 150, you will have a lot of your dive with a ppO2 that is less than optimum. Which means a higher ppN2 than is necessary. Your buddy on CCR may choose that same gas for dil that you chose for back gas, but when you're both hanging out at 150, his CCR will bump up his ppO2 to higher than what you are breathing, keeping his on-gassing at a reduced level compared to you. That's when the CCR will result in less deco time.

That's the academic reason everyone brings up, but it just doesn't seem to pan out in reality.

 

[wedivebc]

I've been doin some diving lately with guys on CCRs, and I've come to the conclusion that the "less deco time" thing is a myth. Never not ONCE has a CCR guy had less deco on his computer than I had. Same or similar gradient factors, same dives (obvi). At best they're equal.

depends on the depth. Multi level rebreather will always win, square profile below 150ft OC will likely win unless RB is running at 1.4 setpoint then it will win. I may not dive OC anymore but I always run OC bailout profiles as backup and between 150 and 200ft they are similar. The one advantage on OC diver has over a RB on bailout is I have to carry a bottom bailout mix whereas the OC guy has an optimized deco mix for the same number of stages.

 

[wedivebc]

That's the academic reason everyone brings up, but it just doesn't seem to pan out in reality.

Just caught this. Nothing academic about it. This is my real world experience from about a dozen years on rebreathers. I was also OC trimix instructor before I discovered rebreathers so I believe I may be qualified to make that observation.

 

[The Chairman]

But I defer to your vast experience and accomplishments as a cave explorer.