Stage Diving: What are you doing?

[atedeschi]

Ok, so not to completely hijack the other thread lets start a new one. How are you diving stages and why? Please be more specific then just 3rds or 1/2 +200, say what you plan for your stage and your BG. I would like to see what you are doing for a swimming single stage dive, swimming multiple stage dive, scooter single stage and scooter multiple stage dive. Let’s see how this goes.

[jj1987]

From my post on TDS in a similar thread-

Here's how I see it. I haven't taken a stage course though, so you're probly more qualified to answer your own question than I am.

My numbers MIGHT be off here, I didn't double check them, and I barely escaped Physics 1 with a C, struggled through Calc 1, and had to retake discrete math, so be warned that math isn't my thing.

Let's do the math with cave filled 104's-
* Penetration cu ft = Volume / Rated Pressure * (Fill Pressure / 3) * 2 (since we’re using doubles)
* Penetration cu ft = 104/2650*(3600/3) * 2
* Penetration cu ft = 104/2650*1200*2
* Penetration cu ft = 94.19 cu ft

OK now let’s apply that to stage diving:

A single AL80 holds 77cu ft of gas @ 3000psi (rated pressure), and a cave filled set of double 104’s holds 282 cu ft of gas as shown earlier.

* Total gas = 77+282 = 359 cu ft

At turn pressure, you have 2/3 of 282cu ft to share, So 188cu ft of sharable gas since the stage doesn't have any way to share it with a buddy, and at this point, your backgas is *in theory* empty. Let's hope your buddy didn't drop his stage before you did, or this could get bad, at least mathmatically....

Let’s do this the 1/2+200 way that caused all the controversy earlier this year.

* Total gas = 77+282 = 359 cu ft
* We will use 1300psi of the stage, or 33.36 cu ft, dropping it at 1700psi (1/2+200)

Now, let’s subtract 300psi from back gas before figuring our penetration gas (because this is roughly how far we went over 1/3rds on the stage).

* (3600-300)/3 = 3300/3 = 1100psi for penetration gas.
* 104/2650*1100*2 = 86.34 cu ft for penetration gas.

So, we’re using 86.34+33.36cu ft (119.69) for penetration gas, out of a total of 359cu ft.

* 359/3 = 119.667 cu ft. This means we’re within .03 cu ft of 1/3 of or total gas volume.

By diving to 1/2+200 instead of 1/3 of the stage, you’ve increased the volume of gas that you can share exiting the cave by 11 or 12 cuft, AND you’ll have more gas to deal with issues such as entanglement, silt out, a navigational error, etc in the BACK of the cave, where you're most likely to need it.

I prefer to breathe the stage on the way out as well to ensure I have as much gas as possible in backgas, since it's the only source that the team can share.

I still think that carrying your stages 100-200ft further than you breathe them instead of dropping them as soon as they hit drop pressure can result in a huge safety margin.

[Sludge]

I was taught that half plus two and thirds on backgas is as safe as diving thirds and no stages. I'll make the following assumptions for my example:

Two divers, roughly the same SAC, with the same size doubles filled to 3600, one AL80 apiece filled to 3000, and they drop their stages near each other. Obviously, any differences in these givens will require alterations to the dive plan.

Worst case scenario: the divers breathe their 80s to 1700 and drop them. They continue on, breathing backgas until 2400. As they turn their dive, one has a total gas failure. The other has 1200psi on his back for each diver. This gets them to their stages, where they breathe them and exit with 400psi left each.

Obviously this cuts it very close. But so does just plain diving doubles to thirds. This is how I dived for years, and how everybody I dived with did it. Yet people are saying it is unsafe.

Someone please point out the recklessness. Obviously, the prudent diver will add a little for a fudge factor. But why is this less safe than doubles to thirds?

[atedeschi]

I was taught that half plus two and thirds on backgas is as safe as diving thirds and no stages. I'll make the following assumptions for my example:

Two divers, roughly the same SAC, with the same size doubles filled to 3600, one AL80 apiece filled to 3000, and they drop their stages near each other. Obviously, any differences in these givens will require alterations to the dive plan.

Worst case scenario: the divers breathe their 80s to 1700 and drop them. They continue on, breathing backgas until 2400. As they turn their dive, one has a total gas failure. The other has 1200psi on his back for each diver. This gets them to their stages, where they breathe them and exit with 400psi left each.

Obviously this cuts it very close. But so does just plain diving doubles to thirds. This is how I dived for years, and how everybody I dived with did it. Yet people are saying it is unsafe.

Someone please point out the recklessness. Obviously, the prudent diver will add a little for a fudge factor. But why is this less safe than doubles to thirds?

Its how I am diving but I bring the stage farther in then when I breathe it and it more stages I use a little more reserve in the last stage tank.

[techdvr]

I was taught that half plus two and thirds on backgas is as safe as diving thirds and no stages. I'll make the following assumptions for my example:

Two divers, roughly the same SAC, with the same size doubles filled to 3600, one AL80 apiece filled to 3000, and they drop their stages near each other. Obviously, any differences in these givens will require alterations to the dive plan.

Worst case scenario: the divers breathe their 80s to 1700 and drop them. They continue on, breathing backgas until 2400. As they turn their dive, one has a total gas failure. The other has 1200psi on his back for each diver. This gets them to their stages, where they breathe them and exit with 400psi left each.

Obviously this cuts it very close. But so does just plain diving doubles to thirds. This is how I dived for years, and how everybody I dived with did it. Yet people are saying it is unsafe.

Someone please point out the recklessness. Obviously, the prudent diver will add a little for a fudge factor. But why is this less safe than doubles to thirds?

That's not the worst case scenario. What if one of the divers has a gas failure on the stage bottle as well. If you knock the stage down to breathing a third on the way in (or less), if the team were to use all of one diver's backgas to get back to the stages, they could buddy breath off the one stage to get out.

If I'm staging while with a team, I'll breath my stage down 1/3 then drop it (or leave it on depending on the cave) that way on the way out, I have the option to just pass that bottle to another person. If I'm staging on a solo dive, I'll double stage it, breath both bottles down a 1/3, then drop them together. I treat it like having two sets of sidemounts for one dive.

[atedeschi]

That's not the worst case scenario. What if one of the divers has a gas failure on the stage bottle as well. If you knock the stage down to breathing a third on the way in (or less), if the team were to use all of one diver's backgas to get back to the stages, they could buddy breath off the one stage to get out.

If I'm staging while with a team, I'll breath my stage down 1/3 then drop it (or leave it on depending on the cave) that way on the way out, I have the option to just pass that bottle to another person. If I'm staging on a solo dive, I'll double stage it, breath both bottles down a 1/3, then drop them together. I treat it like having two sets of sidemounts for one dive.

It depends on the dive and how many failures you plan for. For a single stage diving swimming I plan single failure. If you are planning bigger dives, or smaller tighter passages you can be more conservative, but I would do it on my BG that is with me, not my stages. BTW have to tried to buddy breath on an exit? It sounds good but I think buddy breathing would slow your exit a good amount.

[aainslie]

I was taught that half plus two and thirds on backgas is as safe as diving thirds and no stages. I'll make the following assumptions for my example:

Two divers, roughly the same SAC, with the same size doubles filled to 3600, one AL80 apiece filled to 3000, and they drop their stages near each other. Obviously, any differences in these givens will require alterations to the dive plan.

Worst case scenario: the divers breathe their 80s to 1700 and drop them. They continue on, breathing backgas until 2400. As they turn their dive, one has a total gas failure. The other has 1200psi on his back for each diver. This gets them to their stages, where they breathe them and exit with 400psi left each.

Obviously this cuts it very close. But so does just plain diving doubles to thirds. This is how I dived for years, and how everybody I dived with did it. Yet people are saying it is unsafe.

Someone please point out the recklessness. Obviously, the prudent diver will add a little for a fudge factor. But why is this less safe than doubles to thirds?

Remember that thirds is only marginally safe anyway. If you have a failure at maximum penetration, Your buddy only has enough gas to barely get you back out.

Besides, you are only describing a single stage dive, and Andrew was talking about a multi stage dive.

Actually Forrest, i think that SINGLE stage dives are particularly dangerous for 1/2 + 200,e because it's easy for people to be complacent there. They're arguably just as dangerous as a 5 stage dive.

Here's the scenario. With thirds, you have JUST enough to get out of the cave. With thirds and 1/2 + 200, you have just enough to get back to your stage... where the emergency now continues. In essence you've now massively increased the period during which resources are critical. There's the old argument that SAC's tend to be high during emergenceis - I've definitely found that to be true. So having a critical resource at that point for the continuation really sucks. You want wiggle room on that tank.

However if everything goes well and you've reserved more than thirds in that last stage, you either get out... if it's single tank... or you get to the next tank, where hopefully you've now built up a small reserve since you won't ALSO deplete that stage. Hence you have a bit of fat, which you take with you all the way out.

But it helps to have that bit of fat, whether on one stage or many stages, when furthest back.

On a related topic - Steve Bogaerts and many other instructors teach to take your stage FURTHER than where you stop breathing it, for two reasons - a) it's available deeper in the cave in an emergency, and b) you can be tidying it up and shutting it down while swimming instead of while stationary. However, there's no point carrying it further if you only have 1/2 + 200 since now you're back on a resource taht won't last you out. So while carrying the stage a bit further makes a LOT of sense, it only makes sense if it has more than 1/2+200 in it.

[Sludge]

What if one of the divers has a gas failure on the stage bottle as well.

You're talking a double catastrophe. I answer that with what if you're diving no stages, and you have a total gas failure so you turn and share air out. What if your buddy then has a total gas failure?

A catastrophe is a one-in-a-thousand shot. (Assuming quality gear, properly maintained.) A double catastrophe is one-in-a-million.

[phillip1]

Now I guess you guys do way more stage diving than me, but I do a fair amount of stage diving involving up to 5 al80's, sometimes more.
I take my lowest tank pressure and use that to calculate third for all my other tanks and I have always breathed my stages to thirds plus 20bar (for bonus air) and dropped them a bit past that point to overlap. It may be overkill but I feel way safer having way more than enough air for me or my buddy should an ooa emergency arise.
Having only enough air to get to my next stages and then to the the next set of stages etc.. till you get out is too close for comfort for me.

[FW]

...But why is this less safe than doubles to thirds?...

Remember that thirds is only marginally safe anyway. If you have a failure at maximum penetration, Your buddy only has enough gas to barely get you back out.

Besides, you are only describing a single stage dive, and Andrew was talking about a multi stage dive.