Imo, diving a stage (as a proper stage, with reserves in your backgas) is better than a "buddy bottle", which is unsharable (for all practical purposes) and can be rendered somewhat useless by a simple failure.
I'll dive 1/3s in shallow no flow caves that I a) know relatively well and b) have a solid team with me. If we're going to be pokin around in tight areas, I'll back it off some, sure.
For more complex dives, I start to think less in terms of "thirds" or "quarters" and more in terms of "how much time do I have". Time becomes a real issue, especially in the deeper stuff. 10mins to sort out some snafu in 80ft uses a lot less gas (deco and bottom) than 10mins to sort out the same snafu in a 200' cave. Clearly, these simple rules of thumb break down, and different logic needs to be applied.
Agreed. Once you start getting far in a cave, you've also got to consider how much stress and fatigue is caused by carrying extra unneeded gas (and I use that term meaning it's not needed if things go as planned), and what the chances are that the extra task loading causes a problem that wouldn't exist without it. You and I discussed this yesterday via phone, and I don't think we see eye to eye on where the line is, but it's safe to see that we both agree there's a happy medium.
I'm hesitant about responding as its a touchy subject and one where people have in the past jumped to conclusions - and in fact those hasty conclusions are what results in what Marci is referring to in terms of getting beat with both ends of the stick.
Let me start with the fact that I agree that you need to consider the logistics and the effort rerquired to carry excess gas into a cave. The bigger the dive, the bigger the issue becomes. On the other hand, we all agree there are significant donwsides to diving thirds, and that diving on a two person team reduces the reserve gas available compared to three person team in the event of a total gas loss failure.
With that in mind, and applying it to Peacock, there are longer dives where we will use a stage and carry all of the reserve gas in the primary tanks (sidemount at this point). In that case we are not diving anywhere near thirds but are doing a dive that would either not be possible on thirds, would push thirds a bit too hard, or would leave no time to enjoy the dive. In that case, with the extra brought and used via the stage we are effectively not diving anywhere near thirds. The costs of that are the need to haul to more stages to the water and for each of us to carry them in the cave for a portion of the dive.
There are other dives we do that we may push close to thirds (to about 100 psi short of thirds) where neither of us are comfortable a) being that close to thirds on the dive, and b) not comfortable on a two person team without the reserve that a third team member may have offerred. In that case, one of us may carry a stage and then cache it 1500 ft or so into the cave as gas that is not figured in the plan but is just extra reserve gas. The cost of that is the need to carry one tank to the sink and for one of us to swim it in the cave for a portion of the dive.
It is true that the same dive could be staged instead, but the increased logistics of the dive argue against that. If we are not going to need the gas in the event a failure does not occur, then why have both of us carry and breathe stages?
If you extend that to 2 dives per day in the average 60-90 ft deep florida cave, by the end of the day we will have swam a stage upwards of 3000-4000', hauled 4 stages to and from the water, and will need to fill 4 stages at the end of the day. In contrast carrying a stage as a buddy bottle for additonal emergency gas not included in the gas plan reduces the distance a stage needs to be carried, reduces the number of stages needed in the vehicle by 1/4th and reduces the stages carried to the water by 1/2. And at the end of the day, no stages need to be filled.
So it's largely a matter of perspective, but you can't condem the practice and be on both the "be conservative" and "don't haul uneccesary gas" sides of the fence. The reality is that the practice is a compromise suited to specific dives where a stage is not required under normal circumstances, but where thirds, while do-able is less than optimum in terms of reserve gas. It is also true that a single stage is hard to share in an emergency, but the need to share a single remaining stage would assume a double failure and you can plan yourself right out of doing the dive if you go down that road.
Another thing I think people often forget, is how much deco gas do you have? I see an awful lot of people going to the far reaches of Ginnie (ie Heinkle Swim) with just an AL40, but backgas well within 1/3rds. There's also the risk of thinking that you're going to swim out of JB from EOL when the flow is down and deco out on a single AL40 with no redundancy. Also have heard of several cave divers skimping on deep deco bottles and not reserving enough backgas to get them to o2 if they had a true failure or delay at max penetration. That's something that's poorly taught at the full cave and even DPV specialty level. When we're doing long penetrations @ Manatee Springs, we'll carry an extra AL40 just so there's some redundant deco gas. You don't want to be buddy breathing a bottle for 30+ minutes.
I agree. When depth, and the steep deco penalties any delay imposes, comes into play the reserve needs to be increased, not just to allow more time at depth to resolve problems but also to handle the additional deco that may be needed, often even before the diver reaches the first deco bottle dropped in a cave.
I think you are absolutely correct that this is something that is not well addressed in the average full cave class, especially when the full cave candidate may not have already had AN/DP and ideally an extended range or a trimix course. Without that lead in training, the average full cave candidate is not well versed in lost gas and contigency planning.
The longer this discussion goes on, the more obvious it becomes-- these rules just don't hold up well outside of the common tourist caves. HOWEVER, history proves that they get most divers out of the cave safely until they gain experience and tackle dives where experience is needed to plan them. However, having said that, I think with the rise of side mount diving with new full cave divers, that we're over due for a few deaths in tight silty passages where these rules aren't conservative enough.
I think that is an accurate assessment. It's one thing when feeling your way out on the line is just a full cave drill, but it is something entirely different when exiting from a tight cave in low viz or no viz, in condtions where the low viz or no viz may persist for several hundred feet. If the diver is not prepared for that or planning for that, they can get themselves into a potentially lethal situation even before a failure occurs.
