Standard gasses

[tbone1004]

What I have in mind is that you do not touch the stages except if you bailout, so you need OC gas only for the exit + problem management (like hypercapnia, but of course there is more depending on the cave: flow, eventual silt out in highly silty caves, restrictions, etc.) when diving in CCR.

For example, imagine a dive with 2 stages in CCR. You can leave the first stage at a distance that you can cover breathing it (it is full when you leave it, since you are breathing from the CCR). Then you can continue the dive based on the amount of gas in your second stage bailout (or backgas if your configuration is GUE style); then you need to come back. Of course, you want to add some safety to deal with problems. And, of course, oxygen and diluent adequate for the dive, but I consider them part of the CCR.

So you cover with 2 stages (or one stage + backgas) + CCR the distance you can cover in OC with the two stages (or one stage + backgas) minus the gas you want to save to solve eventual problems.

Assume open circuit, same dive. You would need for the same dive 4 tanks minus the amount of gas you want to keep for reserve (which is at least one third of backgas).

So basically you are right in this range, because you would bring, assuming doubles, two stages plus the backmounted doubles - which is almost equivalent to a CCR set except if you go for something ultracompact, right?

But if you add another stage in CCR, you need to add two stages in OC. However, assuming shallow caves, and depending on your SAC, we are in the range you mentioned (5000ft+) - and I am rather sure if you add calculation for reserve gas we end up to your result.

Again, I am overly-simplifying the management of problems (we all know, thirds or stricter rules in OC, account for hypercapnia or other problems in CCR, eventual morphology of the cave, flow, etc.), I would never plan a cave dive without taking into account more factors and writing down all I need, but I see an advantage in long penetrations, which is what I meant...

With Cave CCR there is a minimum of 2x bottles to carry, no exception. If you say a "standard" set of doubles are LP104's that hold ~260cf of gas when cave filled that would give you ~174cf of exit/reserve gas and with a CCR with 2x AL80's that gives you ~150cf, so call that close enough. So for anything within the radius of LP104's, you're carrying a LOT more gear because a backmount CCR is effectively equal to a set of doubles and then you need the pair of bailout bottles. On a Sidewinder then you can argue that it's LP85's plus the breather so it's a pretty negligible increase in equipment, or if you have a rack mounted unit then it's pretty comparable.

If we look at LP104's + 2x stages we have a total of ~410cf of gas and would be ~280cf for straight bailout, not including any factors for hypercapnia. 280cf would typically be LP85/HP120 + 1x stage or 4x al80's. Sure we are carrying a bit less CF of gas to your original point, but it's about the same amount of gear, and once we add in the factor for hypercapnia resolution we are at the 2x steels + 2x stages, or 4-5x AL80's and now we are back at nearly the same amount of gas that we started with on OC. The CCR's start making sense from an efficiency point after LP104's + 2x stages, which if we were talking about this in 2015 would have been a BIG dive at around 4000ft penetration in Florida caves. With CCR's and DPV's becoming much more common it is not perceived the same as it was, but that's a long way from the door. Obviously scale that distance up or down based on the depth of the cave, personal kicking speed, or factoring in a backup DPV, but no matter how you skin it, that is not a "normal" cave dive for the vast majority of divers.

If we sidestep over to the ocean, you're still carrying all of the same deco bottles, though you will typically be ditching bottom stages, but it's not really saving a lot of gear in the water.

 

[ginti]

@tbone1004 we are on the same page. When I mentioned doubling the distance I also mentioned it was WITHOUT taking into account problems, that was my way to imply the advantage was smaller but still existing (again, with only BIG dives in mind, and by the way I was considering only shallow caves - cause deco would add deco bailout... Unsure why I didn't mention it).

And yes, in the ocean I see zero advantage in terms of equipment (might even see a disadvantage if the CCR is in a heavy configuration).

I totally agree with your reasoning

 

[kensuf]

With Cave CCR there is a minimum of 2x bottles to carry, no exception. If you say a "standard" set of doubles are LP104's that hold ~260cf of gas when cave filled that would give you ~174cf of exit/reserve gas and with a CCR with 2x AL80's that gives you ~150cf, so call that close enough. So for anything within the radius of LP104's, you're carrying a LOT more gear because a backmount CCR is effectively equal to a set of doubles and then you need the pair of bailout bottles. On a Sidewinder then you can argue that it's LP85's plus the breather so it's a pretty negligible increase in equipment, or if you have a rack mounted unit then it's pretty comparable.

If we look at LP104's + 2x stages we have a total of ~410cf of gas and would be ~280cf for straight bailout, not including any factors for hypercapnia. 280cf would typically be LP85/HP120 + 1x stage or 4x al80's. Sure we are carrying a bit less CF of gas to your original point, but it's about the same amount of gear, and once we add in the factor for hypercapnia resolution we are at the 2x steels + 2x stages, or 4-5x AL80's and now we are back at nearly the same amount of gas that we started with on OC. The CCR's start making sense from an efficiency point after LP104's + 2x stages, which if we were talking about this in 2015 would have been a BIG dive at around 4000ft penetration in Florida caves. With CCR's and DPV's becoming much more common it is not perceived the same as it was, but that's a long way from the door. Obviously scale that distance up or down based on the depth of the cave, personal kicking speed, or factoring in a backup DPV, but no matter how you skin it, that is not a "normal" cave dive for the vast majority of divers.

If we sidestep over to the ocean, you're still carrying all of the same deco bottles, though you will typically be ditching bottom stages, but it's not really saving a lot of gear in the water.

As TBone said, CCRs don't give you a "less gear" advantage unless you're willing to skimp out and go with an inappropriate amount of bailout (or use a BOB). But there are some serious advantages while cave diving, especially when it comes to working dives. Being able to go to a spot in the cave and stay there for extended periods of time to do things like shoot photos, collect water samples, count critters, maintain navigational aids (line/markers), survey, etc can be worth it's weight in gold.

 

[tbone1004]

As TBone said, CCRs don't give you a "less gear" advantage unless you're willing to skimp out and go with an inappropriate amount of bailout (or use a BOB). But there are some serious advantages while cave diving, especially when it comes to working dives. Being able to go to a spot in the cave and stay there for extended periods of time to do things like shoot photos, collect water samples, count critters, maintain navigational aids (line/markers), survey, etc can be worth it's weight in gold.

aside from the practical aspects, moving to radius based cave diving instead of time based cave diving is life changing! I'd also argue it's immensely safer as well, but it's so relaxing to just plot out on a map and say "I can't go past 3700ft" and then draw a big arc and then not have to worry about how long it takes to get anywhere or how slow you make the exit. When time constraints become how bored am I going to get on deco or how hungry am I going to be at the end vs. tick tock tick tock on the gas clock it makes the whole experience much more enjoyable.

 

[grantctobin]

how bored am I going to get on deco or how hungry am I going to be at the end vs. tick tock tick tock on the gas clock it makes the whole experience much more enjoyable.

Hangry*

 

[InWay2Deep]

aside from the practical aspects, moving to radius based cave diving instead of time based cave diving is life changing! I'd also argue it's immensely safer as well, but it's so relaxing to just plot out on a map and say "I can't go past 3700ft" and then draw a big arc and then not have to worry about how long it takes to get anywhere or how slow you make the exit. When time constraints become how bored am I going to get on deco or how hungry am I going to be at the end vs. tick tock tick tock on the gas clock it makes the whole experience much more enjoyable.

and THAT is the payoff for CCR Cave diving and less gear. You can spend ALL DAMN DAY in your BO radius on CCR, OC buddies can't do that. If your goal is max penetration you will be carrying more gear, always, stages, deco, extra DPVs, etc. It just comes to a point where OC isn't practical. I did a dive a few weeks ago over 6,000ft of penetration, took just about 3hrs total. Would have been at the limits on OC w/o a setup dive.

 

[rjack321]

For cave diving too? Assuming you don't use the stages and they are for bailout only, and assuming no reserve to solve problems, you should be able to double the distance compared to an OC dive... Although, sure, depending on the cave, how much reserve for problems you want, etc.

But overall it seems to me in caves you actually bring less gas for the same dive. Am I missing something?

I bring smaller bottles - but as a general rule I am not going any further distance than I would on OC. I am staying at that distance range longer (or it's taking me longer to find the way on in the cave at all).

 

[rjack321]

With Cave CCR there is a minimum of 2x bottles to carry, no exception. If you say a "standard" set of doubles are LP104's that hold ~260cf of gas when cave filled that would give you ~174cf of exit/reserve gas and with a CCR with 2x AL80's that gives you ~150cf, so call that close enough. So for anything within the radius of LP104's, you're carrying a LOT more gear because a backmount CCR is effectively equal to a set of doubles and then you need the pair of bailout bottles. On a Sidewinder then you can argue that it's LP85's plus the breather so it's a pretty negligible increase in equipment, or if you have a rack mounted unit then it's pretty comparable.

If we look at LP104's + 2x stages we have a total of ~410cf of gas and would be ~280cf for straight bailout, not including any factors for hypercapnia. 280cf would typically be LP85/HP120 + 1x stage or 4x al80's. Sure we are carrying a bit less CF of gas to your original point, but it's about the same amount of gear, and once we add in the factor for hypercapnia resolution we are at the 2x steels + 2x stages, or 4-5x AL80's and now we are back at nearly the same amount of gas that we started with on OC. The CCR's start making sense from an efficiency point after LP104's + 2x stages, which if we were talking about this in 2015 would have been a BIG dive at around 4000ft penetration in Florida caves. With CCR's and DPV's becoming much more common it is not perceived the same as it was, but that's a long way from the door. Obviously scale that distance up or down based on the depth of the cave, personal kicking speed, or factoring in a backup DPV, but no matter how you skin it, that is not a "normal" cave dive for the vast majority of divers.

If we sidestep over to the ocean, you're still carrying all of the same deco bottles, though you will typically be ditching bottom stages, but it's not really saving a lot of gear in the water.

In your FL centric universe sure...
In MX there are next to no 104s at all and the "standard" cave doubles are al80s.
A "standard" set of OC bottles in my neighborhood is a set of lp45s

 

[tbone1004]

In your FL centric universe sure...
In MX there are next to no 104s at all and the "standard" cave doubles are al80s.
A "standard" set of OC bottles in my neighborhood is a set of lp45s

Zoom out from the specifics of the math. If you are doing straight line penetration, you have to carry the same amount of gas in effectively the same number of bottles. You do get a bonus if you are just doing radius limit meandering which is more typical in Mexico, but if you redo the math for AL80's or LP45's then it's still fundamentally the same