Stage Diving: What are you doing?

[marinediver]

Also, partially flooding your drysuit would probably help a bit with excess + buoyancy.

I hear that rocks work well too....

[Meister481]

I understand why you want to carry it with you. But then if you lose 1/2 your BG, you lose 1/2 the "reserve" from the stage that you moved over there. Doesn't that worry you? Doesn't it make more sense to leave it in an independent tank (the stage), and just carry the stage a bit further instead?

The whole point of splitting reserves up is so that the loss of one tank doesn't take a disproportionate percentage of your gas with it.

What if you breathed a couple hundred psi of back gas before you start the stages, and drop them once you get to thirds. Same result IMO.

To me this makes the most sense in a single or double stage swim dive. This would also depend on kit used. If I were back mount I would conserve a bit more back gas in case of a failure with the manifold and carry a stage with me at all times. Side mount has the best case scenario in a solo dive with stages, you are almost guaranteed to keep half the reserve and you will always have at least one tank useable. In Sidemount you could change regs on a bottle if one popped on a stage or you had a failure in a main tank reg. If it were a 3 man team I might sign off on the 1/2 +200 idea. Lots of gas swimming with me.

I guess I'm trying to say this all depends on the situation, kit and once you add a scooter all bets are off. I'm keeping my eggs in all available baskets, and keeping them as close as possible.

well in that scenario I'd have about 100 cuft of gas on my back. between that and my buddy's long hose (assuming 2 man team) I think I'd be in ok shape. if I've done my math right, you're left with more than a third of your starting backgas pressure if you save half the gas during a failure at max penetration.
I'd probably go on the long hose for a big chunk of the trip back to the stages, saving my backgas for gas switches/whatever, then cash the stages and ditch them to get streamlined.

I'll just add that I think the far more likely failure is coming back to an empty stage. or a stage with a bad freeflow once you turn it on. I've had more stages go tits up on me than anything

I don't know about you, but I used to use my OW regs as stage regs. I didn't do as much testing and upkeep as I should. That changed once I started using them in a cave. Would you trust your stage reg as much as your back gas reg? You should!

[LiteHedded]

yea they all get serviced and treated the same

[aainslie]

GUE teaches it. So does NAUI. The latter (which I teach) actually explores several different stage options. All of these options operate within the rule of thirds, but differ as to how you carry that third. I like the 1/2 plus 200 for dives involving a single stage sand use it up to two. After two stages, it starts to get silly subtracting the stages third volume from your back gas before calculating thirds for the latter. Also, I don't have any reason to swim that far anymore. I'm too busy here at work to start down other the road with other options, but I approach managing thirds on the DPV in an entirely different way. For example, it sometimes works out to kick the stages and leave the back gas alone and completely dedicated to contingencies. And there are other ways to approach it, but ALWAYS within thirds at the least. Planning always includes all the what ifs and calculations of swimming distances/times. I know you are a NAUI instructor so look at the article on 1/2 plus 200 in the latest Sources. Distance and time are included in the worst case scenarios there.

Chris

OK, so I got around to reading this article (which, you forgot to mention, you wrote). A couple of questions and comments:

1) What in your mind is so special about "thirds" for a stage? You keep talking about "violating rule of thirds" - but this is a rule designed with backgas in mind. Why do you and/or NAUI believe it should be carried over to stages? (actually why does anyone? It is at best, I believe, a prudent BUT ARBITRARY reserve for SNAFU's on the way out)

2) One of the things that gets thrown at me about my spreadhseet is its complexity. The calculations required to move the "third" in the stage to your BG require quite a bit of calculation. Aren't you worried about errors creeping in?

3) You talk about hte extra dwell time if you were to move the extra reserve over to your BG - but don't you ahve the same dwell time just by carrying the stage further?

4) Do you believe that thirds is the right amount no matter how many stages? So would you reserve a third for the first all the way to the last tank in, say, an 8 stage dive? if so, why?

I sort of get the feeling that you're getting to an answer that looks sensible, but for all the wrong reasons. This is why I believe it's so important when thinking about this stuff to start with Exley's starting point - the rule of DOUBLES. And add a nice margin to that, But not an insane margin.

Here are my caveats and concerns after reading your article:

1) Diving rule of thirds absolutely makes sense on BG - particularly in outflow caves, marginally in still caves - based on reserving double the gas required to exit, in order to reserve for eitehr a catastrophic loss of one partner's gas or half of your own in sidemount. Diving rule of thirds on between 1 and 3 stages after that makes sense (1 in high flow, 3 in no flow) - but it is an arbitrary added margin, and unlike Exley's original rule, has no theoretical basis - unless you're planning to lose half of ALL of your tanks on exit (assuming an even number of tanks), an infinitesimally probable event.

2) By extension, 1/2 + 200 makes perfect sense for the remaining, earlier stages (i.e. those closer to the exit) since the reserve travels with you from the back of the cave. A small caveat - increased SAC rate which might make you go slightly higher than 200 in no flow caves.

3) The reason to move to backgas has little to do with searches, and more to do wtih the relative safety of backgas (Which stays with you) and a stage (which when dropped might freeflow, trickle out, be unfindable in a siltout etc).

[Gary]

Diving rule of thirds on between 1 and 3 stages after that makes sense (1 in high flow, 3 in no flow) - but it is an arbitrary added margin, and unlike Exley's original rule, has no theoretical basis - unless you're planning to lose half of ALL of your tanks on exit.

Loss of tanks is but one of many situations that requires the reservation of gas to cover.

For example the Exley and buddy out of air example where once on stages they required most of the 2/3s of the gas that remained in their stages to exit. At that point of the dive the only special situation they were compensating for was buoyancy.

Cold, low vis, reverse of flow, buoyancy problems, mask problems, broken fin straps, unease/medical (cramps, dizziness, whatever), line entanglements, entrapments, loss of direction, loss of buddy. Each of these is a reason for reserve, often more than one can plague any specific dive. Having half a dozen of these happen during the exit on a single dive is more likely than loosing half of one's stages. In some cases having even one or two occur could be enough to utilized more gas than "thirds" allows for.

That's not just a "theoretical basis" it is a "realistic basis". Something that should carry more weight.

[aainslie]

Loss of tanks is but one of many situations that requires the reservation of gas to cover.

For example the Exley and buddy out of air example where once on stages they required most of the 2/3s of the gas that remained in their stages to exit. At that point of the dive the only special situation they were compensating for was buoyancy.

Cold, low vis, reverse of flow, buoyancy problems, mask problems, broken fin straps, unease/medical (cramps, dizziness, whatever), line entanglements, entrapments, loss of direction, loss of buddy. Each of these is a reason for reserve, often more than one can plague any specific dive. Having half a dozen of these happen during the exit on a single dive is more likely than loosing half of one's stages. In some cases having even one or two occur could be enough to utilized more gas than "thirds" allows for.

That's not just a "theoretical basis" it is a "realistic basis". Something that should carry more weight.

Why is DOUBLE the right amount for these other problems?

On your specific issues: I've had all of those except the medical and the reverse flow (the latter is rare beyond belief). None - not even the lost fin - should slow you to half exit speed. An entrapment or entanglement should stump you only for a couple of minutes. Loss of buddy and/or direction is ONLY affected by the gas reserves at teh furthest point - you can't magically get gas out of a tank 1000 feet away to help your search.

And it always cracks me up when I see pure empiricists. Your computer - radio - car - scuba tank - hell, ANYTHING invented after the 1800's depends at some point upon someone's "theory". Being anti theory is just admitting to not being very clever. Empiricism unaided by theory is just a stupidly wasteful way to advance knowledge.

[jj1987]

Would you trust your stage reg as much as your back gas reg? You should!

I would if I didn't have to leave them. Unfortunately as soon as you drop the stage, you're opening yourself up to people touching them, draining them, stealing them etc. Don't think for a minute that stages don't get drained, I've heard from a few people where multiple staged safety bottles were empty when they came back to dive the same area a few days later. This isn't the WKPP most of us are diving where everyone is on the same team, or indian springs where it's guided and safety bottles can be relied on, we're talking open access caves that it's happened in, including one that I bet most everyone on this board has dove.

I know if I were nearly OOA and about to die, I'd take a stage that wasn't mine. I bet 99.99999% of other cave divers would too, excluding the 0.00001% that would lie on the survey. It's worth considering that fact when you start planning stage dives.

[aainslie]

I would if I didn't have to leave them. Unfortunately as soon as you drop the stage, you're opening yourself up to people touching them, draining them, stealing them etc. Don't think for a minute that stages don't get drained, I've heard from a few people where multiple staged safety bottles were empty when they came back to dive the same area a few days later. This isn't the WKPP most of us are diving where everyone is on the same team, or indian springs where it's guided and safety bottles can be relied on, we're talking open access caves that it's happened in, including one that I bet most everyone on this board has dove.

I know if I were nearly OOA and about to die, I'd take a stage that wasn't mine. I bet 99.99999% of other cave divers would too, excluding the 0.00001% that would lie on the survey. It's worth considering that fact when you start planning stage dives.

A key point - check safeties on the way IN. Every time. Pressurise, read gauge, purge, close valve.

I particularly do this when certain locals who think they own Ginnie are around. Well, actually it's just one person... but you get the point.

(Actually he made me paranoid enough that I HID a couple of safeties. Which sucks since it makes them harder to find in an emergency. But it helped reduce the number of people who knew where I was going... )

[Gary]

Why is DOUBLE the right amount for these other problems?

Sometimes double is not enough. Sometimes six times is not enough.

There is no point where anyone has "enough" gas to protect them absolutely from an accident. There are accidents that are severe enough to overwhelm the most conservative gas reserve.

Theory is for every 100 psi more or less then thirds the chances of a fatal accident increase/decrease by a factor of 5-10.

Thirds gives about a 1 in 10,000 chance of fatal accident. Most would probably prefer to shift their chances in the direction of 1 in 100,000 or 1 in 1,000,000 than in the other direction (1 in 1000 or 1 in 100).

[aainslie]

Sometimes double is not enough. Sometimes six times is not enough.

There is no point where anyone has "enough" gas to protect them absolutely from an accident. There are accidents that are severe enough to overwhelm the most conservative gas reserve.

Not sure what your point is here - other perhaps that **** happens... or that double ISN'T the right number. I certainly didn't feel a wave of elucidation after reading that sentence.

Theory is for every 100 psi more or less then thirds the chances of a fatal accident increase/decrease by a factor of 5-10.

a) That's empiricism not theory, and b) do you have ANY evidence to support that, or are you just making that up?

Thirds gives about a 1 in 10,000 chance of fatal accident. Most would probably prefer to shift their chances in the direction of 1 in 100,000 or 1 in 1,000,000 than in the other direction (1 in 1000 or 1 in 100).

Ditto on support/source. Plus too generic - stage? No stage? Scooter? Flow? These are not very useful statistics, even if they did come form anywhere other than a part of your anatomy that would result in three stars.