CCR truths and misconceptions

[Camerone]

On CCR you're not diving by rule of thirds.

As a trained CCR Cave diver (IANTD) I have to disagree. You're diving by a _different_ set of thirds than an OC diver. You have four limiting factors for your loop: Oxygen (which is based on metabolic rate...effectively a constant drain), diluent (not thirds-based, but profile based on the cave), scrubber duration (pure rule of thirds - a three hour scrubber is one hour in, one hour out, and one hour to sort s*** out), and bailout (distance driven, just like regular OC air consumption).

So there is rule of thirds in there, it's just applied differently.

Bailout strategies are possible in several ways. There's the normal "rule of thirds" strategy, which requires a LOT of gas, but is safest. You take your own bailout, and you make sure it follows the rule. There's the "just enough" where you figure your bailout, and you make sure there's just enough to get you to the surface, and you rely on everyone on the team carrying "just enough" for the weakest guy, and then there's full-blown team bailout, where you figure out rule of thirds for the weakest guy and then split up the gas carrying by team so everyone takes a portion.

I prefer the "just enough" strategy. Reasonable gas carry loads, and a fairly good margin for safety.

Note that as a CCR cave diver, you can safely do things that you cannot do on O/C. Most of the time, the limiting factors for a CCR cave dive are either scrubber duration or bailout penetration distance.

If bailout is the limiting factor, when you hit your max pen distance, you can always come back and explore side tunnels until you hit scrubber thirds or another limiting factor. Coming out and going in somewhere else is perfectly fine, as long as you never exceed the distance you can swim out. On O/C, when you hit thirds, you start to exit, and you don't go meandering down side tunnels for kicks.

There's a lot of nuances to CCR cave diving, but I'm a huge fan of having the extra time and flexibility that the unit allows in the overhead environment. You just have to understand what you're doing with it and how the tool has to be applied...

 

[Cave Diver]

As a trained CCR Cave diver (IANTD) I have to disagree. You're diving by a _different_ set of thirds than an OC diver. You have four limiting factors for your loop: Oxygen (which is based on metabolic rate...effectively a constant drain), diluent (not thirds-based, but profile based on the cave), scrubber duration (pure rule of thirds - a three hour scrubber is one hour in, one hour out, and one hour to sort s*** out), and bailout (distance driven, just like regular OC air consumption).

So there is rule of thirds in there, it's just applied differently.

Good points, especially in regard to scrubber duration. On most CCR dives, this is going to be the limiting factor. Personally, I'd rather be about more conservative than this on scrubber duration, because the more of the scrubber bed that has been used, the higher the potential for breakthrough is. My previous response was tailored more to the gas planning questions.

Bailout strategies are possible in several ways. There's the normal "rule of thirds" strategy, which requires a LOT of gas, but is safest. You take your own bailout, and you make sure it follows the rule. There's the "just enough" where you figure your bailout, and you make sure there's just enough to get you to the surface, and you rely on everyone on the team carrying "just enough" for the weakest guy, and then there's full-blown team bailout, where you figure out rule of thirds for the weakest guy and then split up the gas carrying by team so everyone takes a portion.

I prefer the "just enough" strategy. Reasonable gas carry loads, and a fairly good margin for safety.

Agreed.

Note that as a CCR cave diver, you can safely do things that you cannot do on O/C. Most of the time, the limiting factors for a CCR cave dive are either scrubber duration or bailout penetration distance.

If bailout is the limiting factor, when you hit your max pen distance, you can always come back and explore side tunnels until you hit scrubber thirds or another limiting factor. Coming out and going in somewhere else is perfectly fine, as long as you never exceed the distance you can swim out. On O/C, when you hit thirds, you start to exit, and you don't go meandering down side tunnels for kicks.

Agreed.

There's a lot of nuances to CCR cave diving, but I'm a huge fan of having the extra time and flexibility that the unit allows in the overhead environment. You just have to understand what you're doing with it and how the tool has to be applied...

Totally agree.

Have you seen this thread? http://www.scubaboard.com/forums/cave-diving/310989-do-you-have-ccr-cave-training.html

 

[WD8CDH]

Really makes me wonder why bail out rebreathers aren't more common.

 

[Cave Diver]

Really makes me wonder why bail out rebreathers aren't more common.

Cost of owning two rebreathers would be one reason.

 

[wedivebc]

Really makes me wonder why bail out rebreathers aren't more common.

Bulk mainly. For a RB to work well it has to have well placed counterlungs. There is only so much real estate on a divers body to place those counterlungs so for true redundancy you have to either reduce the size of the CLs or place them in a less than optimal position. There are some ingenious solutions people are coming up with but nothing I am ready to use as of yet.

 

[wedivebc]

Cost of owning two rebreathers would be one reason.

I own 3 but I still don't have a BOB

 

[Tegg]

What happens in a max penetration issue for a two person RB team using shared bailout when one has a buddy who is either "lost" or is simply not around? (missed communication, etc)?

I personally have made the clear thought out decision to make sure I carry at least 2/3rds the "required" gas for exit. Meaning that I carry enough gas for the planned max penetration that equates to at least what I would have in gas volume if I did the same dive on OC.

On a RB, there are many issues (such as hypercapnia) that can cause one to use quite a bit of bailout gas to "calm down" and clear the head and I want to be sure that I make it out of the cave whether my buddy is around or not... Thus, if I needed a certain amount of gas in OC (2/3rds) at max penetration, why would things be different when using a tool such as a RB?

Cave divers are not taught to "share" gas reserves when using a DPV with a buddy, why do it with a breather?

 

[Cave Diver]

I own 3 but I still don't have a BOB and this wouldn't fit in most places I go.

If you wanna donate one to me, then we can both have redundancy.

 

[nadwidny]

I own 3 but I still don't have a BOB and this wouldn't fit in most places I go.

Dave, you need to resize this picture to something smaller. It's messing up the format of the forum.

 

[wedivebc]

Dave, you need to resize this picture to something smaller. It's messing up the format of the forum.

Yeah I see. It was ISCs picture so I had to remove it