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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.
From my post on TDS in a similar thread-
Quote:
Originally Posted by jj1987
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.Quote:
Originally Posted by Slüdge
Quote:
Originally Posted by Slüdge
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.
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.Quote:
Originally Posted by Slüdge
Besides, you are only describing a single stage dive, and Andrew was talking about a multi stage 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.Quote:
Originally Posted by techdvr
Quote:
Originally Posted by Slüdge
Quote:
Originally Posted by FW
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.
Andrew - Carrying it further than 1/2+200 in a shallow, or high flow cave DOES increase the safety margin....does it not?
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?Quote:
Originally Posted by techdvr
A catastrophe is a one-in-a-thousand shot. (Assuming quality gear, properly maintained.) A double catastrophe is one-in-a-million.
Maybe we all mean different things by "1/2 + 200" when I say it, I meanQuote:
Originally Posted by aainslie
At a *minimum* I am reserving out of myh doubles, "the amount I exceed thirds by" on the stage. In this case, if I breathe 1300 PSI out of the stage, have "violated" 1/3's by 300 psi in an 80 and must subtract this from the BG before dividing that up (of course on cft not psi :)
For the first stage, I reserve in BG the entire amount I am breathing out of the stage (so if I assume Double 80s on BG for ease of calc :) that means I breathe 1300 out of the stage, so I reserve 650 (so 700) out of my doubles befor calculating my 1/3 or 1/4s etc
For each stage after the first, i would just reserve "the amount I exceed 1/3" or 300 PSI in an 80
This means
- I can suffer OOA at max penetration *and* lose a stage on way back (we did this in class easily)
- my reserve gas is on my back, so I can ditch stages morew quickly in an emergency and dont end up with 3 or 4 80s each with a 1/3 in them
potential downsides ?
- maybe i end up donating a long hose more often (I may not have a stage to pass off) so 2 divers are joined by a hose
- at some point, you "run out" of BG to back up your stages (this would be a different kind of dive :)
This assumes no scootering (out of my area of experience)
just doing 1/2+200 with no other changes does not seem to make any sense.
I never run 1/3s in team of 2, no matter what, but I would in a no-flow cave with a team of 3
Siphons are another matter. I dive "gentle" siphons in Mx, but a fullon siphon is another beast
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.
We dive our stages (AL80) to 1/2 + 200
Take thirds of backgas (dbl95's) 3600/3 = 1200
Deduct 200psi from thirds to allow for the stage 1200 - 200 = 1000psi usable out of backgas.
If we come back and the stage is gone or empty, we have half a stage worth of gas in reserve in backgas to make it out on.
I do not see how you are arriving at half a stage of reserve in your BG. 200psi of 95's is only 14.4 cuft. Half a stage would be 39 cuft. Even if you double it for the other buddy, you still only have 28.8 cuft.Quote:
Originally Posted by Jason B.
Not saying anything is wrong with the approach, just the math. What am I missing?
edit: Are you including your original 1200 reserve in the calculation? If so, you have way more than a stage, but I do not see how that fits into the planning.
I'm subtracting the 200psi from my thirds. That's a net savings of 600psi or 7.2 x 6 = 42ish cu/ft of gas.Quote:
Originally Posted by Marc Bryan
Whats wrong with breathing it down a 1/3 so that it is neutral, not positive, so that it rides properly. Then leave it, and and still reserve an extra 100psi (if diving 104's, and staging an al72, or al80) in your back gas to allow for getting back to it in a catastrophic gas loss (assuming diving with a buddy. solo is an entirely different discussion) at max pen, silt out, etc.... What is out there that that extra 100 psi is so important?
Or just carry it with you as long as possible.
I edited that in while you were responding. Thanks.Quote:
Originally Posted by Jason B.
Yes, this is basically same as I said above, but just for the 1st stage right ? If you had a 2nd or 3rd, you'd reserve less?Quote:
Originally Posted by Jason B.
You dont carry it as long as possible (which I interpret to mean "until empty" as you might in the ocean) as you are then swimming a long way with a stage, which is extra drag and bulk especially if you have multiple or are in small cavesQuote:
Originally Posted by Marc Bryan
If you breathe to 1/3 then, the more stages you have, the more stages with 1/3 of gas you have in them on the way home, so you end up needing to carry them further out of the cave on the exit in an emergency.
If you dive 1/2+200 and reserve what you "break 1/3's" from in your BG, you can ditch empty stages earlier in an emergency and so you aren't dragging them out of the cave as far (you can swim faster and with less bulk)
LOL - I certainly did not mean breathe it as long as possible till empty (who would even think that?).....I meant when you come off of it, carry it with you until such a time as you are entering tight sidemount passages/smaller cave on BM and then leave it. I was referring to one stage, obviously you would not carry five the entire dive.Quote:
Originally Posted by limeyx
I'm really conservative when it comes to gas management. I dive sidemount, so all of my bottles are independent. No stages I dive 1/3 + 100-200, depending on the system. Solo means 1/4. Add a stage and I dive the stage using 1/3s. Side gas is same as without a stage. add a scooter and it's 1/4s. Solo and AL comes along, too (AL doesn't get touched). If I have more than one stage I'm on a scooter. That's too much to be swimming. I drop stages a couple of minutes after I stop breathing them to give me time to clean up the bottle. I know it's really conservative, but I haven't done a dive where I haven't had enough air.
Or maybe we should not even dive stages. The extra drag caused by carrying the stage uses more gas to get to the same point of penetration. If you get really crazy conservative, you are probably better off not carrying one to begin with. At some point you have to balance the complexity and drag adding a stage creates with the percieved gains, it becomes a double edged sword. No stage diving is by far the simplest and cleanest - so maybe work more on technique and to get the most out of the gas you have.
FWIW - In normal outflow systems such as Ginnie, I dive 1/2 + 200 (no flow or siphon - totally different animal). By the time I get things prepped for drop while swimming and find a nice cave and diver friendly place to drop it, it is naturally in a bit further and you gain the benefit of the extra gas in the stage. Keep in mind, the extra 200 is really at least 400 more than you need to exit. So this does add a decent cushion. But I would not carry it much further because then I have to carry it out further and that will slow my exit which is not what I want under the circumstances.
I have to agree with Sludge, the odds of a double failure are extremely low. Even lower that the BG failure will occur at your planned turning pressure. Most likely, if you did have two failures - they would not BOTH be total. Lets say your stage failed completely but your 2nd failure was not complete and total... somehow you managed to retain at least 500 psi in you BG or it occurred 500psi before your turn and it was total - well, that is equivalent to the 1/2 a stage you also lost...
Bob
High flow yes (although I always get yelled at for pointing that out). Why shallow? I lost you there.Quote:
Originally Posted by jj1987
Here's an idea: why not carry six stages and breathe 100psi out of each? That way we'll have LOTS of gas in reserve.:roll:
For me it all depends on what kind of dive we are doing. I usually dive with a three man team, so there is always lots of air.
On a no stage high flow I will go to 1/3 - 200.
With 1 stage, backgas 1/3-200, stage 1/3
Two stages 1st stage 1/2 plus 200, 2nd stage 1/3, backgas 1/3, or 1/3 - 200. depending on location, and penetration, and mood.
For low flow 1/3 on everything, as there are three of us.
If i only have 1 buddy I tend to like more reserve.
On a no stage high flow I go to 1/3.
With 1 stage backgas 1/3, stage 1/3
Two stages 1st stage 1/3 -100, 2nd stage 1/3, backgas 1/3 plus 100
For low flow I go 1/3 plus 100 on everything
Bob Klauck
With 130s, 200 psi of backgas = 1300psi of a stage.Quote:
Originally Posted by limeyx
subtract 200 from backgas for every stage, calculate 1/3rds on the remainder.
Ok so this looks to be what I thought, people are doing all different things, sounds kinda how I believe scooter gas managment is? What do the agencies say?
I may overly conservative but is it not unsafe to breath all your stages to half+200? If you were to loose all your gas at max penetration, now sharing with your buddy and had staged 4-5 al 80's, it would cut it a bit close I would imagine.
In all the stage dives Thomas & I have done we never breath any stages or tanks past thirds ever.
I went over this many times in planning my dives, and we really find that this is the safest way to plan our gas.
The caves here have no flow so it seems the safest way.
Half +200 seems like cutting it real close for me even if the cave's had flow.
I agree with sludge, that a set of doubles to thirds is really cutting it close too, loose all your air at max penetration and I think you have exactly enough to get out if everything goes exactly the same on the way out, which it wont so you will probably not be enough.
That's probably true for everyone still with us...Quote:
Originally Posted by RN
but thats not what jason said he does. Jason said do 1/3 then take off 200, which is like reserving 600 in BG ?Quote:
Originally Posted by rjack
unless i misunderstood
The 1/2 plus 200 approach to stage diving does not violate the rule of thirds. The rule of thirds applies to the total gas supply used for penetration. This means 1/3 of your total gas supply (back gas and stage or stages) is available for penetration, 1/3 or less for exiting, and 1/3 for contingencies. If you use 1/3 of a stage and then do the same with back gas you are adhering to the rule of 3rds and keeping the math simple. The rule of thirds, however, is subject to diminishing returns at maximum penetration. If it hits the fan at that point in a dive, you may or may not have enough gas to solve the problem.
Using the 1/2 plus 200 rule provides you with more of (actually all of) your emergency third at maximum penetration if you need it. If you use the 1/2 plus 200 rule for a stage, then you must transfer your stage's third to your back gas before calculating 3rds for your back gas supply. For example, with my double 95's and an 80 stage, I'll plan to use 1300 psi (26 ft3) from the stage swimming into the cave. I must therefore subtract 26 ft3 (361 pisg) from my double 95 starting pressure BEFORE I calculate 3rds for my back gas. So if I start this dive with 3500 psi in my back gas, then I first subtract (put in reserve) 361 psi and figure my back gas 3rds from 3139 psi. That's 1000 psi I can use from my back for penetration. If I have a problem at maximum penetration, then I have the 1000 psi emergency 3rd available AND the additional 361 psi or 26 ft3 to deal with the problem. If it was a lost line, lost buddy, or gas sharing you have something like 17 to 20% more gas to deal with the problem. You are still operating within the rule of 1/3's, and you have ALL of the gas remaining in your doubles and stage when you return to it for exiting the cave. Other advantages include the fact that you can return to the parked stage sahring gas like you trained for it, move quicker, etc.
I place the stage in a smart and convenient place, not necessarily where I hit the 1/2 plus 200. Many of you have noted the advantage of parking it further in, i.e., closer to you on exit. That may not be advantageous, however, relative to restrictions, passage configuration, line placement, mud and silt etc. Where I leave a stage always, "depends".
A final observation - divers using the 1/2 plus 200 ruke usually penetrate about the same or slightly less distance than those using 1/3's. he advantage is simply the fact that you have your entire contingency third with you at maximum penetration in case a problem arises.
Cheers,
Chris
Andrew's Response from the other thread, incase others were not following both:
"Always carry excessive gas at the deepest point of penetration. if you're going to go to the edge, do it on stages nearer the exit.
On a catastrophic gas loss at the deepest point of penetration, you need the gast THERE, NOT near the entrance. However, you now carry that surplus back with you, so it's always available everywhere else.
So if you want to do 1/2 + 200, ONLY do it on a multi stage dive on cylinders nearest the exit, and DO NOT DO IT on the last few cylinders that you use. Be more conservative at the deepest point of penetration. Note that on a single stage dive, that means your ONLY stage should not be dived to 1/2 + 200 as it IS at your deepest point of penetration. I personally go to thirds in high flow, and reserve more than 2/3 in no flow on backgas and my last 2 stages.
Scooters add to the complication. Do as above BUT additionally calculate reserves based on your SWIMMING rate of exit, such that you have at least double the gas needed to exit on your backgas and last couple of stages. I like to drop full stages along the way for a swimming exit. This often needs a setup/setdown dive in addition to the normal dive.
Here's an example. A single stage at 1/2 + 200 may get you to the furthest point you're allowed to scooter in Ginnie... but good luck swimming out on 1700! It may be doable but it'll be close, and you won't have any reserves. So if you swim from the Henkel on thirds, and have a catastrophic loss at thirds, you'll just get back to your stage... find your scooter flooded/stolen/dead/drifted off... and be on the ragged edge the whole way out. Not pretty. Alternatively if you'd dropped a full stage there or at Stage Rock, you'd be fine.
And the nice thing is, that stage at Stage Rock can sit there for days while you play around, ready for an emergency. No need to redump it every dive. In essence you're using a rebreather approach to reserve for your scooter.
(Now I'm going to get yelled at for teaching people to dive on the internet. Like half the people at Little River even have a DPV card! Isn't it better to teach them on the internet than let them go in and dive it to thirds on their shiny new scooter with no further thought?)"
You understood me.Quote:
Originally Posted by limeyx
I think rjack was pointing out another method which looks to gives similar results?
What do you do for additional stages ? Surely the *minimum* you have to reserve "extra" in your backgas is just the amount you have "violated" 1/3's by.Quote:
Originally Posted by Chris Laughrey
In this case, going in on the stage, you violate 1/3's by 300 psi in an 80, which is 7cft of gas.
Therefore, the min you need is to subtract out 7.5 cft from your start volume in doubles before calculating your 1/3's right ?
I was trained to reserve the entire 1300 psi from first stage into BG (which I make to be 32.5 cft) and then just the amount which you exceed 1/3s from additional stages
Which is why I asked Jason as he seemed to be reserving a lot of gas for additional stages (and actually quite a bit on 1st stage unless I dont get it) not a problem at all, but I was wondering
I *think* richard saysQuote:
Originally Posted by Jason B.
(Start Pressure - #of stages * 200) then third it which reserves 200 psi for each stage in BG
you said
Start pressure, 1/3 it then take out 200 * # of stages which (I think) is 600 psi per stage ? which is way more.
but again, I could be mis understanding :)
Gas failure is only one way to have problems. Simply getting chilled, or getting a cramp can impede one's exit. Possibly enough to render that into a fatal accident without needing a gear failure.Quote:
Originally Posted by Slüdge
Diving to 1/2+200 on the stage and 3rds on backgas. If someone had a gas failure, shared air and made it back to their stage. They quite likely would find themselves light and floating (as in several accident examples including Sheck's) and not utilizing gas as efficiently. In fact there could be dozens of reasons to be less efficient on a return after an air share back to the stages.
----
Sheck's air share in "Caverns Measureless to Man" (p145+) would have probably been a double fatality had they been diving 1/2+200 on the stages.
They weren't even to 3rds on backgas and Sheck's buddy wasn't even completely out of gas. They didn't have a loss of vis and they still ran out of gas before reaching their stages.
They dove to 3rds on the stages. Once back to the stages they should have had twice the gas they needed to exit. Instead they were almost out and one of them had to abandon deco temporarily to surface to yell for help.
If they'd dived 1/2+200 on the stages they wouldn't have gotten back at all.
no I botched it.Quote:
Originally Posted by Jason B.
1300psi in an AL80 = 400psi in 104/130s.
13*2.5 = 32.5cf
4*8 = 32cf
close enough, manufacturing tolerances aren't this close.
plan:
2 stages to 1/2+200 and "thirds" of 104s
3600 in 104s - 800psi for the 2 stages = 2800 available
2800/3 = 900psi penetration
drop stage 1 at 1700
drop stage 2 at 1700
turn on backgas at 2700
I have enough gas to cover loss of both my stages and a OOA buddy (who still has stages) at maximum penetration.
Yes I agree, I want that reserve 3rd with me and not subject to possible loss via officer Gibson or otherwise. Despite this, I have almost never dived thirds. Mostly because I have done most of my cave diving with only 1 buddy and we reserve more gas in these cases.Quote:
Originally Posted by Chris Laughrey
Quote:
Originally Posted by rjack
Yes. And if you were open to the additional risk, you can reserve "what you exceed thirds" from stages after the first, and still be within 1/3's (or similar for whatever gas plan you chose)
so in those cases, you take off 400 psi for 1 stage, and just 7.5cft (300 psi in stage and whatever that is in BG) for subsequent stages, if you are OK assuming just one will fail
Yes, I got that he's doing it different than me, but our end results are similar.Quote:
Originally Posted by limeyx
One difference is Rjack was talking 104's and I was talking 95's. Other than that (for one stage) we are tit for tat the same end result in gas use. For additional stages I'd deduct 100psi.
I could (and sometimes do) subtract only 100psi for the single stage but that is only a 300 psi reserve of about 24cu/ft of gas vs the 32.5 I need if the stage is missing. (Ainslie's Flow Law at work ;)).
It''s just an easy method. Take thirds, then subtract from thirds for various items, such as stages and scooters.
Quote:
Originally Posted by rjack
1300psi in an AL80 = 460ish-psi in 95s.
13*2,5 = 32.5cf
6*7 = 42cf
(a little extra gas!)
plan:
2 stages to 1/2+200 and "thirds" of 95s
3600 in 95s
3600/3 = 1200psi penetration
1200psi-200 for 1st stage = 1000psi
1000psi-100psi for 2nd stage = 900psi
3600-900 = 2700psi turn pressure.
drop stage 1 at 1700
drop stage 2 at 1700
turn on backgas at 2700
I have enough gas to cover loss of both my stages and a OOA buddy (who still has stages) at maximum penetration.
:D
Ok so here is what I am going:
Single Stage Dive:
lp85s filled to 3600psi
AL80 filled to 3000psi
Breath stage to 1700psi
Breath 85s to 2600psi then turn dive
If I lost half my gas at max distance in and can still get out and have 7.32 cu ft in reserve.
Double Stage Dive:
lp85s filled to 3600psi
AL80 filled to 3000psi
AL80 filled to 3000psi
Breath stage to 1700psi
Breath stage to 1900psi
Breath lp85s to 2600psi
Still have 3.32 cu ft in reserve if lost half of all my gas at max pen.
This is for a no flow cave, i would make adjustment for things like restrictions, low silty nasty areas, etc. But for normal swimming no flow caves this is the plan. If you look at the total gas avalible and used i still more conservative then 3rds. Now for flow my numbers will be different for the lp85s but if you use this for caves with flow you will be even more conservative with this plan or you could adjust the lp85s to get more out of them and keep the conservatism the same, but thats another beast and could be search in a previous thread.
No I am assuming all the stages are all going to go bye bye for whatever reason. They are not on me so I don't plan on having that gas available on return. I am just a baby cave diver and haven't gotten to the point where the required backgas reserves exceed my backgas capacity (>4 stages with AL80 backgas, >9 stages with 104s).Quote:
Originally Posted by limeyx
after 2 stages its not worth the effort swimming and gas usage, a scooter would be involed then the planing is a different ball game.Quote:
Originally Posted by rjack
agree, 600psi reserved in lp85s covers loss of the stage.Quote:
Originally Posted by atedeschi
32cf used from the stage, 6*6cf = 36cf extra reserved in backgas
I would breath both stages to 1700 but turn on backgas at 2800 (thirds of usable)Quote:
Originally Posted by atedeschi
oh I realize that, I have swum 2 stages a few times and its a pita. just illustrating where the logic eventually takes you. to not touching backgas at all and eventually adding safeties.Quote:
Originally Posted by atedeschi
So it seems a common approach is to breathe the stage below 2/3 BUT reserve the extra in BG. I like it. Couple of questions:
Is this an official GUE and/or UTD approach? Does anyone else officially teach this?
Why do that rather than just go to 1/3 and then carry a bit further? Woudln't it make for identical redundancy plus easier planning?
I like having the extra with me, because maybe I need it after I drop the stage or if the stage bottle is gone, empty (not likely), or some other reason, I can use it up and dump it on the way out if needed. I also carry a wrist slate for deco, making notes for flow and Sac calculations and wear jumps and features are at, so I can add to the maps. So if I have multiple bottles with different drop pressures I right that on there as well.
I know it's what GUE teaches but I'm not sure about UTD. I would assume it's the same.Quote:
Originally Posted by aainslie
I like having that reserve on my back where I have more flexibility with it.
the planning is pretty easy with 104/108s/130s. it works out to about 100 psi off your backgas thirds (per stage) to keep yourself under total thirds.
so half+200 on the stage and 1100 instead of 1200 for backgas penetration gas. of course, you're free to get more conservative from there. but I like to keep that gas on my back and not in the stage(s).
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.
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.Quote:
Originally Posted by aainslie
Chris
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 agree that adding the buddy changes things. Personally I always plan solo - but as soon as you plan in teams of two or 3, gas planning definitely gets way the heck safer.
Solo, I'd prefer to distribute the gas rather than putting it all on my back. The extra carry achieves the same thing, while the gas distribution decreases gas lost in a worst case emergency.
Chris, thanks for blowing my cover!! I'm only an OW instructor, and rarely use those privileges. I did it mainly for the learning.
oh I agree. I can't speak to solo diving. it's just not my cup-o-tea.Quote:
Originally Posted by aainslie
but with team diving I think the reserves make the most sense being on your back so you can ditch the stages as they become empty. and having access to that reserve with two regulators (one of which is on a long hose) is certainly preferable.
Here is my reasoning, and if you see something faulty I am open to change.
From my example I posted before:
On the way IN:
AL80 used 33.8 cu ft
LP85s used 64 cu ft
Lose Half BG I would only have 83.2 cu ft minus the 64 cu ft need to get back to stage, which leaves me 19.2 cu ft.
This should give me enough reserve incase of a slower exit, or lost line, or light failure.
OK but say I lost half my gas and made it back to the stage, turn it on, and its freeflowing. I have 44.2 cu ft but say by feathering I will waste half, which leaves me 22.1 cu ft to use out of the stage, plus the 19.2 cu ft left in my 85 which gives me 41.3 cu ft to exit when I only need 33.8 cu ft. Therefore I should still have a reserve of 7.5 cu ft.
Now I plan as a solo diver so a buddy will just give me more gas, also I dive SM so I should be able to feather the tank that is losing gas, if not a bursk disk, and I when i get to the stage i can always change the regs since i have reserve of 19.2 to keep breathing off while i swap regs.
You in a sense this is planning for 1.5 major failures. If you try to plan for everything you would need so much gas you would not go far or carry to many tanks. Just my thoughts.
As others have said, this is (currently :) what GUE teaches which is my only experience.Quote:
Originally Posted by aainslie
One benefit of not keeping the extra 1/3 in the stage but in BG is that in an emergency exit you dont have a bunch of 1/3 full stages you need to carry to get out of the cave so you can ditch empty stages earlier. You can also more easily share gas in your BG
You wouldnt really lose more of that reserve gas exactly if your BG goes, because you are *already* assuming loss of 1 BG at max penetration + total loss of 1 or more stages (depending on your planning)
Anything more than that going wrong, and I really should have taken up golf!
The "problem" with the independent tank is that its all alone in the cave. And the gremlins like the cave police can screw with it. Any problem with that dropped stage and is likely going to vent until its dry. Unlike with backgas that you at least know what's going on. So the risk is balancing losing all of a stage vs. a portion of backgas (cause you can at least shut it down isolate etc)Quote:
Originally Posted by aainslie
I have "lost" stages in classes and getting out without them is trival. In a team of 2, I "lost" all backgas at maximum penetration (1/2+200 from the stage + 700psi of backgas in AL80s in MX) and my buddy lost his stage when we returned to it. I exited on his long hose back to the stage, and he had to remain on backgas all the way out. He still had 1000psi in AL80s at the O2. I had about 500psi in my stage and no backgas. So even with a fairly significant double failure and we had roughly ~65cf left and almost no stress. This was in Mayan Blue, essentially a no-flow system. Sure it was a class, but I think it illustrates the strength of "reserving the stage" from backgas when you're a long way from 1ATA.
We did same with team of 3 (slightly more penetration gas) and with similar results. Over 1000 psi in all remaining doubles, still gas in both stages.Quote:
Originally Posted by rjack
I'm unsure how a stage could lose gas while unattended if it is shut down when dropped with 2/3 left in it. An independent cylinder (when used in conjunction with another cylinder) such as back mounted independents and side mounts) is much more safe that manifolded double cylinders any day.Quote:
Originally Posted by rjack
If a burst disc goes on a stage tank you lose the gas. If a burst disc goes on a set of manifolded doubles (back gas), you lose the gas on that side, PLUS any gas that escapes from the "good side" up until the point of closing the isolator valve. Manifolded doubles are not redundant until the isolator is closed... IF you can close it fast enough...if you realize what is happening soon enough and which valve needs closing....if the cave configuration allows easy access and if you have continued with muscle memory training for your valve drills.
If you are planning your emergency gas thinking that all of the gas in the "good side" of a BG set of doubles will be there after a burst disc or even freeflow from the bad side, you will be fatally mistaken.
I see not a single "problem" with dropping an independent cylinder other that some idiot who may carry it away while unattended....at which point a 9mm should solve any reoccurance if you survive the dive.
Safe diving,
Brian
has anyone ever had a doubled burst disk blow during a dive? ever?
I had a set that was double disked have one of the tank neck o-rings extrude. After 45 minutes of air spewing out, it was decided to open a valve and drain the tanks down as it was clear it was not going to be a quick process draining via the extruded o-ring (this was on land).Quote:
Originally Posted by LiteHedded
YMMV
The real salient questions are,Quote:
Originally Posted by LiteHedded
Has anyone ever screwed with a dropped bottle: yes
Has anyone ever forgetten to shut off a stage: yes
AND it has all the failure modes of backgas except the manifold crossbar/orings.
Gas in dropped stages is IMHO alot more subject to loss than backgas. Thus, I would not sprinkle my reserves around the cave in stages, 1000psi here and 1000psi there. Since I don't solo dive I don't need for buddy bottles and I'm not to the point of needing safeties.
The net conclusion for me is that I'll keep reserves with me and at least have the potential to shut down a leaking reg, burst disk, or valve.
agreed. I've had issues with stage bottles more than onceQuote:
Originally Posted by rjack
Fair enough. It is indeed feasible to swim past a stage in zero vis (I posted elsewhere about a dumb thing I did that resulted in me doing this), so I buy that argument, IN situations like high traffic or low vis where a tank might "go missing". I've also once had a problem with a tank that decided not to repressurize nicely - it blew an O ring. So I'm beginning to buy into the "on your back" strategy more.
lol. Well that's good to know :-) Hence, the reason you're able to make this post.Quote:
Originally Posted by RN
mine always seem to go at the SPG :smt013Quote:
Originally Posted by aainslie
The only ones I've seen "lost" (outside of a class) were orings on lp hoses that came loose, extruded and then were useless.Quote:
Originally Posted by LiteHedded
Gary posted a while back a thought that most people should try before you are satisfied that you can make a "low-stress" air share out of the cave. Try making a dive at Ginnie with 100 PSI in your doubles (use stages for gas.) I think most underestimate the difficulties involved in overly light tanks- particularly the sidemounters who cannot add a v-weight.
Jason
yes, thats right... During one dive I hade to stay down for a bit longer... and I discovered that LP 85's will get positiv when thay get under ~40 bars (and around 50~60 bar they get neutral), so don't count for the tanks to get you enough ballast. I did the dive in SM. A god thing was that the dive was in a iron ore mine so I could just fill the pockets with iron ore rocks...Quote:
Originally Posted by rchrds
It's yet another reason to drain stages first, and then dump them, in an emergency. You're leaving positive buoyancy behind you.Quote:
Originally Posted by rchrds
Also, partially flooding your drysuit would probably help a bit with excess + buoyancy.
Would that actually save gas though? If you got cold enough you could double your gas use - it could be as bad as being bouyant.Quote:
Originally Posted by aainslie
I hear that rocks work well too....Quote:
Originally Posted by aainslie
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.Quote:
Originally Posted by aainslie
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.
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!Quote:
Originally Posted by LiteHedded
yea they all get serviced and treated the same
OK, so I got around to reading this article (which, you forgot to mention, you wrote). A couple of questions and comments:Quote:
Originally Posted by Chris Laughrey
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).
Loss of tanks is but one of many situations that requires the reservation of gas to cover.Quote:
Originally Posted by aainslie
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?Quote:
Originally Posted by Gary
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.
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.Quote:
Originally Posted by Meister481
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.Quote:
Originally Posted by jj1987
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... :) )
Sometimes double is not enough. Sometimes six times is not enough.Quote:
Originally Posted by aainslie
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).
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.Quote:
Originally Posted by Gary
a) That's empiricism not theory, and b) do you have ANY evidence to support that, or are you just making that up?Quote:
Originally Posted by Gary
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.Quote:
Originally Posted by Gary
Amazing that 100psi in AL80's at 300ft increases the safety margin by the same amount as 100psi in LP104's at 20ft.Quote:
Originally Posted by Gary
I admit I suck at statistics, so I'd love to see the study that produced those numbers if you wouldn't mind linking to it so I could give it a read over. :D
I get the normalized to 1 accident numerator, but where did this 10,000 (dive?) denominator come from???
I am also rather concerned that Exley's buddy, being a tad narked and not realizing that his own doubes were venting gas, and eventually losing backgas somehow is now turned into a "rule" for stages - which Exley HIMSELF didn't recommend even after being part of the accident in question. That kinda says somethin...
http://www.cavediver.net/forum/showthread.php?t=9180Quote:
Originally Posted by jj1987
Interesting, so the following factors don't really change the safety factor calculation?Quote:
Originally Posted by Gary
- Solo vs non solo
- Scooter vs Swimming
- Depth (and as a result, time)
- High flow vs Low flow
- Silty vs Not Silty
- Low/Small/Tight vs Big Cave
- Diver Experience
- Equipment Shape (IE serviced regularly)
- Familiar vs Unfamiliar Cave
- Divers physical fitness level
I DO use that as a factor when considering reserves, If I'm at JB on the weekend I won't drop a stage until I'm past the trash room. If I'm alone during the week I might drop it just past kings bypass. In LR I will dump my stage and scoot at the end of the FL room. Heck, if the place is full enough I'll tow it a bit off the main line and then clip it off.Quote:
Originally Posted by jj1987
Among many others.... I see no basis for survivability. I get what he's trying to get at, but an odds based algorithm has to have many input factors and more data points than total # of dives and a fraction of PSI. Empirical testing like was done in the journal this quarter would be a requirement.Quote:
Originally Posted by jj1987
Exactly how much training do you have in probability theory and statistics?Quote:
Originally Posted by Gary
Why is a Normal distribution appropriate? Why would probabilities be symmetric about 50% consumption?
Gauss would be rolling in his grave if he read that "theory".
Let me give you an example of why it doesn't work. According to your "theory", if I entered at 3000 psi and turned at 1350, I'd still have about a 10% chance of surviving.
Do you believe that? Try THAT empirically and see how it works out. heck, I'll even allow you a safety diver. Do 20 dives to 1350, and see if you survive 2, in a no flow cave.
Fitting a normal CDF the way you did is completely arbitrary and NOT based in any sensible model of air consumption distributions.
Next, the value of 1 in 10k is totally arbitrary. So you're fitting the curve to TWO points (already a dicey thing to do), one of which is a reasonable assumption and one of which is a total guess - and NEITHER of which are based on data. You simply can't do that in any adult audience with lukewarm IQ's.
Finally, there's no reason this would also apply to stages, or scooters, or anything other than backgas.
Sorry Gary - this just isn't either empirically or theoretically sound. It's total garbage.
I was always curious Andrew what would you do beyond the last stage depot. Lets say a cave becomes too small to carry stages and the only option is your two primary sm bottles. Lets say you are 2 stage legs after scootering in the cave at this point. What rule would you use for your "side gas" for penetration? Lets say up to this point you enjoyed the company of your buddy. Would you take him with your further, how does your gas plan change?
For a double scooter stage then drop and swimming, you would not only plan for a swimming exit but have safeties dropped along the way as well.
Kinda how they were doing exploreration dives past the hinkel.
Turning at starting at 3000 and turning at 1500 is assumed as 50% - a 10% chance of making it turning at 1350 doesn't sound at all unreasonable.Quote:
Originally Posted by aainslie
There is really nothing questionable about the general numbers. Using 3rds chances are about 1 in 10000 - turning at half in no flow 1 in 2 is as close to surety as one can get without actually running testing that would be illegal and unethical.
Depending on your tanks the difference between 3rds and half is about 400 to 500 psi. If you don't like normal distribution the only other way to divvy up the chances gives the same answer.
5 to 10 times the chance of fatality per 100 psi more/less than 3rds.
Solo/buddy, gear config, skills, dive difficulty, flow, etc of course all have their own contributions modifying the initial assumed risk at 3rds and the 1/2 point but it's not going to significantly change the basic answer: 5 to 10 times the chance of fatality per 100 psi.
I push cylinders - so I don't necessarily stop having stages past a tight restriction. It's rare that a thght restriction carries on for hundreds of feet - bu if it does, of course you can only do this so far.Quote:
Originally Posted by ARY
So nothing really changes. I go to thirds in flow (less in no flow).
And I can rarely find anyonw dumb enough to join me so the second question doesn't really come into play.
No matter how you cut it, you're fitting an arbitrary curve to two untested, assumed, pseudo data points.Quote:
Originally Posted by Gary
What empirical data are you using to come up with the 50% turn gives you a 50% chance of survival? If I were to test this, say at little river, I'm willing to bet in 10 tries I would make it out 10 times without going to a stage, breaking your chart.Quote:
Originally Posted by Gary
My problem with those numbers is that they don't account for ANY factors. In a low flow/no flow/siphon system they would skew high on the fatality per event side, and in a high flow cave they would skew low. If I swam in without a light or guideline and followed those numbers would my chances change? yes. The options are endless and without any baseline runs or testing it's really just a pretty graph. You have a great idea, just need to get all the factors and facets down. The fact that you're thinking about the correlation between deaths and turn pressure shows you are looking for an answer to "How Much Is Enough". We all want to know the answer, but I'm sure the answer changes each time we enter the water.
You might want to pick up this quarter's NACD Journal, They did specific gas management tests from back in 02? and 2 out of 3 tests they "died". Testing is possible, prudent and might save some lives. Guessing won't unless you can prove the outcome.
I was taught to be a thinking diver, and I do like to consider what my options are before I develop a proper gas management plan for a given dive. I don't base my survival on an arbitrary psi, but cubes required to exit the cave with 2 major malfunctions. Oddly enough that's always been more conservative than thirds for most dives. If it's just a short swim dive with a buddy I've got plenty at thirds due to my lower RMV than all my buddies. I normally have turn pressure at the safety stop.
Really? If it takes you 100psi per 100ft, you're going to get 1650ft in, and only have enough gas to swim 1350ft. That's simply not possible without extreme flow, possibly even more than mainline @ Devil's system.Quote:
Originally Posted by Gary
How so? The majority of cave dives I take less gas to get out than to go in. Unless you have something to slow your exit when diving halves 1 in 2 times, this stat doesn't add up. We're not planning gas in best case scenario, but statistics need to take it into account. I guarantee the odds of making it out of an average tourist cave like Madison, Ginnie, Peacock, etc with well maintained gear are better than 1 in 100 and maybe even 1 in 1000 when diving halves. That's not good enough odds to bet your life on, but your saying that you have a better chance playing Russian roulette with a 6 shot revolver than diving 1/2's at Ginnie, which simply isn't true at all.Quote:
Originally Posted by Gary
How can depth not effect this answer? Someone with a .65 sac at Wakulla is going to use about 784psi per minute, meaning he can't even support a buddy for 30 seconds with that extra 100psi. The same diver at Peacock is going to use 207psi per minute, and can support a buddy for almost 4-5x as long.Quote:
Originally Posted by Gary
Either we have a huge misunderstanding of what you're trying to convey or one of us is terrible at statistics :-/
It was specified as "no flow" (flow changes the starting and ending points to unknowns.)Quote:
Originally Posted by Meister481
If you swim in to half you swim out the same gas. Your efficiency will be more, less or equal with about equal chance of being better or worse. If better - live. If worse - die.
50%
The assumptions are simple enough to be very safe but even if the chances were significantly off (say 1 in 10 instead of 1 in 2) it would have very little effect of the calculation starting at aprox 1 in 10000 and dividing over 400-500 psi.
4th root (10000/10) = 5.62
4th root (10000/2) = 8.41
5th root (10000/2) = 5.49
And though the starting point may change based on flow, gear, etc there is little reason to assume the factor changes overmuch.
JJ: are you saying there is no chance a person can swim out more efficiently than they swam in? Is there no variability in human performance? That swimming to half they can swim out successfully every time but 1 psi past half they have no chance whatsoever?
Clearly that isn't the case. Even if they swam in until they hit 1000psi they'd have some chance of swimming out on half what they swam in on - even if the chance is immeasurably small. They may have had something slow them down going in - but not on the way out. And on the other side they may not be able to swim out on the same that they went in on. They could get a good run in and have a number of delays getting out.
No flow, I can still beat it every time. You use more gas going in because of the drysuit and/or wing inflation going in. I know if I'm marginal on gas I'm going into conserve and I guarantee I'll make it out on less than half the gas. I still say you need to do a study. Test it!Quote:
Originally Posted by Gary
There's going to be a point where you have a zero survival rate within those 2-400 psi. These tests will only prove that x amount of times a diver will swim out to a certain footage and return with x amount of gas or none. The amount will skew with depth as well because of wing and drysuit inflation. It has to be tested at a steady depth in a controlled environment with several different divers of different competency before the number will be viable.
The idea is sound but the differences between individuals will wreck your theory's curve. From this test you can begin to overlay situational data points such as flow, vis, etc. There are several people here with a much better understanding of how to calculate the flow and consumption rates at odds with the rate of travel. This can be done if given the proper amount of data in the proper environment.
I'm saying that there's better than 50/50 odds of making it out alive if you dive halves. I'm guessing the chance is more like 999/1000 or at the very least 99/100. Sure you can pickup speed on the exit, we've all proven that by diving Ginine, Manatee, JB, Maidson, etc.....even Peacock we often exit faster than we enter with as light of flow as there is there, especially when you factor in lighter stage bottles and such.Quote:
Originally Posted by Gary
But since you've acknowledged that, that further proves that the odds of diving halves and getting away with it are a LOT better than 50/50. The higher flow the system, the better chance you have here...but your statistics didn't factor in flow, either in how it helps speed your exit, or how it slows your entrance (and increases sac).
Also, could you comment on why 100psi is a 5x safety factor in both 20ft mexico caves, as well as 300ft deep WKPP or west FL caves?
I think you're onto a key component here, James.Quote:
Originally Posted by jj1987
Some issues slow you down by a percentage of your normal exit time. Losing a fin, or bad vis, are examples of this. For such events, reserving a MULTIPLE of your gas makes sense - for example, reserving double the amount used in to exit (i.e. thirds). Depth doesn't enter the equation.
For other issues, like looking for a buddy, briefly losing the line, running a jumpreel across a line entrapment in a silt out, or an entanglement, one needs to assume a fixed time period to sort the problem out. You might decide to allow 5 minutes for one of these events. Here, the gas reserve DOES depend on depth, and one whould have to increase the amount as one got deeper, based on SAC rate, depth, time required and tank size (we can all do the calculation from there).
For this reason, thirds may be insufficient at (say) 300 ft to handle even one entanglement, given how quickly we use our gas at depth, whereas it may be enough to handle a whole bunch of them in 20 ft caves.
Exactly. Let's say you're in a 300ft deep cave and swim the wrong way, 100ft until you see a line arrow that corrects you. That 100psi barely helps, since barely a minute of gas, where as in peacock, you could easily swim 100ft and back on 100psi (about 5 minutes IIRC from when I calculated it earlier).Quote:
Originally Posted by aainslie
I really wish more majors required discrete math courses. They really force you to think about "hidden" variables that can really change the T/F value of your statement.
For example-
Today I was talking to a customer at work, he ships 1in x 1in items (replacement parts for compressors), so I programmed his shopping cart to add the items end-to-end, thinking this would give the smallest possible box size, so that UPS's online tools api would give the best estimate on shipping as possible when you combine boxes. However, if you order 100 items that are 1in x 1in, my original solution would result in a package that's 1in x 1in x 100in, which due to the length, is a MUCH higher shipping cost.
The correct answer is to add 1in at a time to each dimension to the box, and check to see if you can fit the items, and if not, add 1in to the next dimension, continuing this until everything fits. This results in shipping 100 items in a 10in x 10in x 10in box, which actually winds up costing the same as a 1in x 1in box, other than the weight difference, and literally less than half of what it costs to ship a 1in x 1in x 100in item.
Even this fails. You then need to check to see if the items fit in a flat rate box, and compare the shipping cost for the smallest possible box, and the flat rate box, and choose the cheaper of the two, since it varies depending on location.
But wait, even that fails. You need to estimate the cost of cardboard since flat rate boxes are free, and make sure that the shipping price for the best sized box doesn't exceed the cost of flat rate when you include the cost of packing materials.
Point being - it's nearly impossible to think of all cases in a simple linear formula. It took over a year for us to find this bug in the software I wrote, but after finding it, you feel stupid that you even thought it would work in the first case. I think Gary's idea might work with a small number of test cases if it started with accurate data and appropriate limitations (maybe 60-90ft deep caves with moderate flow, without stages, without scooters, with a buddy), but there's just not enough input to expect it to be even remotely accurate as it was presented.
To answer the original question, I dive my stages differently depending on the dive and have fun doing it.... :)
Safe diving,
Rich
Right, depends on cave, dive plan, buddy/solo, sidemount/backmount, scootering/swimming, etc. Make a plan taking into account the variables and go from there. No one rule takes care of everything.Quote:
Originally Posted by Rich