Deep bailout with high SAC VPM & GF deco

Mark Chase

I have been asked to move this here as a new discussion rather than change the course of the Shearwater v VRX thread.

Basicly this is an example of a typical bailout problem id face on a 45min dive to 70m. The discusion was concerning the need as deep CCR divers for a get shallow fast bailout deco profile on our dive computers.

Id be most interested to hear how other CCR divers plan in the 60m+ range.

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Lets look at a practical example of what I am trying to achieve.


If we look at a bailout from a 1.3set point on the bottom at 70m after 45mins on GF 10/90


Bail out gas is 18/45 50% and 100%

I bailout at 70m on to 18/45 and my first stop depth (10/90GF) is showing as 48m and my Time to surface is 133mins.


I am breathing like a sexually aroused hippo so I am in trouble and i switch to my emergency bailout deco plan of 100/100GF


My first stop depth is now 30m and my deco time is 98mins


The first point to note here is I had no idea of haw far i could push it on my first stop. If my computer said 48m and i had no other bailout deco plan, Id have to guess how far above 48m my minumum depth ceiling was. Looking at a 100/100GF profile I would then have a tangible figure in my head as to the minimum depth I can ascend to at 8m-10m/min


In a comparison between the two profiles I have saved eight mins on my ascent to the first stop depth.

Running 10/90GF on a 30sac id need 1533.00 ltrs of gas to make it to 30m and a further 1749ltrs to make it to the 21m gas switch.

Total 3282.00ltrs or 329bar in a 10ltr tank

I am not going to make it I am 932ltrs or to put it another way 10mins short of gas.


So I know I am breathing like a train and wont be able to match mu planned 20SAC plan so I go for bend and mend and switch to 100/100GF bailout.

4mins to 30m = 660ltrs of gas required. Running 100/100 GF it will take me a further 8mins to get to the 21m gas switch costing me a further 843ltrs of gas.


So on my emergency plan I need 1503ltrs of gas and i have 2350ltrs available

Knowing I have a healthy reserve despite my SAC I could slow down the ascent and probably stop at 33 and 36m to soften the blow of 100/100 on trimix.

Id also be aware of the fact i was softening the deco which would boost my confidence and help reduce my SAC further.


By the 21m stop and switch to 50% I would have got through my 2350 ltrs of deep bailout on OC and I hope id be breathing in a much more noraml way so i can manualy pad out the stops between 21m and the surface to compensate for the high gf OR if the new software for the X1 does what i hope, I can folow the less agressive profile also displayed on the screen.

Seeing this information on my screen and knowing I can manipulate the dive from now on to soften the effects of my earlier indiscretions I will have my confidence boosted which will help to calm me down and in doing so further reduce my SAC again. Having it show missed stops / violated ceilings and just a TTS figure based on nothing I can get my head around is going to do the opposite.



I don't have a clue how to do this on VPlanner which is why i have shied away from it in the past.


I looked at this dive running VPMBE 3 and VPMB 0 and it still gave me loads of gas munching deep stops. On VPMBE it gives a first proper stop at 54m and on VPMB 0 its 48m??


Running VPMBe 3 on a 30 SAC id use 4107ltrs of gas

Running my bailout plan of VPMB 0 Id need 3431ltrs


Its simply not possible to run VPM on this dive an carry only 2350ltrs of 18/45 in a 10ltr for bailout, even on my emergency plan.



If any one has any commnets on what they do or how to do this dive using VPM id be very interested to here them.

ATB

Mark

EBT

Team bailout.

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Dive!Dive!

Very interesting post Mark.
It is a very pertinent question. At the moment I use a VR3 set on minimum conservatism. Thats equivalent to VPM +3 or +4 approx as far as I can tell, and for most diving that suits me just fine, but for the deeper stuff when bailing out, yes, you want to be as shallow as possible as quick as you can sensibly, just to conserve gas. Like most folks, I carry tables that are cut much more agressive to do just that, but computers are effectively relegated to bottom timers as you say.
Having a computer which allowed you to switch to pre defiend OC gases (with MINIMAL button pushes/taps etc) and at the same time switch to a predefined minmal deco plan would be very, very interesting.
I only had a very quick look at the VRX but couldnt decide what algorithms it was actually running - real GF's or some sort of hybrid.
Cheers
Steve

Dive!Dive!

Is another thing we do and makes good sense.......but theres maybe gonna come a time, through whatever reason, when you're on your own....

Mark Chase

Like when your heading from 70m to 30m at 10m / min and your buddy thinks, screw you, I am not doing that, your on your own.

Which is roughly what happened to me once except i was ascending at an angle in a cave so no where near 10m/min verticaly but fast enough to make my buddy decide he wasn't going to follow me

Fortunately I got the CCR working again or id be dead right now.

ATB

Mark

EBT

Well, your options are;

1. Carry enough gas
2. Rely on drop gas (bag protocol blah blah)
3. Redundant rebreather
4. Stop breathing so much (not really an option!)
5. SCR the unit.
6. Accept that you're at higher risk

Maybe someone can think of another option for the solo diver.....

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bgpartri

Mark,

Switching to any GF on the fly means pulling it out of your a** because the only way for the profile to be real is to track the first stop on the new profile throughout the dive. It is the definition of a GF profile.

If is completely imaginary anyway, why would the computer's guess be better than yours? In fact, I bet someone with your experience would have a really good guess.

But we could track two profiles throughout the dive.

We are going to offer a couple of things in the new year. I'm not exactly sure what will final offering will be, but the plan is to display the current GF compared to 100/100 Buhlmann. The second is to track a second profile for OC. That would allow a diver to switch to the second GF with the switch to OC.

This would allow you to set an agressive OC GF, but to temper it by actually doing the bailout on a normal GF by following the "current gradient" number.

By the way, the only way I would follow a 100/100 profile while I was working hard (high SAC) is if death from drowning or great white shark was the only other alternative.

Bruce

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Mark Chase

Bruce what you describe is exactly what I have been asking you for from day one. Id given up on getting this implemented on the Shearwater.

So basically your telling me I spent all that money on my X1 for nothing :D

I could go off you you know :D

And Yes 100/100 would be the base line and yes i'd only follow it if it meant that or drown, but for the purpose of this discussion 100/100 showed the most dramatic comparison.

Id most probably back calculate my bailout on a 30SAC to find the GF at max run time and set my OC bailout at what ever GF that came out at.

What I cant understand is your comment about pulling a profile out of your a**?

Surely if you stop a dive at any point and switch to a new GF the profile will take all of whats gone before as just a multi level dive?

I had assumed the program would know the tissue loadings at any single point in the dive and could calculate a decompression from that point so long as the tissues had not exceeded theoretical M value during the dive to that point?


As for me making it up my self? You over estimate my abuility. What I am doing at the moment is using my knowledge of ratio deco to plan the bailout but its only working because I do a lot of diving in quite a small depth range (60-70m) and pretty much always do 45mins so its easy to sit in front of a lap top and figue out how to play with the numbers.

A dive to 80+ is outside my comfort zone for working it out myself but i do do dives to 80 and much deeper

So a bit of help from my £1000 dive computer would be much appreciated :D


The second interesting point of this thread is how on earth do you plan deep bailout running VPM?

ATB

Mark

single tank numpty

Hi Mark

Great idea for product development.

On OC I dive tables anyway, more or less (Finger in the air adjustments have been known ). If I'm doing a dive like this, then I usually bring tables that are telling me a minimum deco based on differing conservatism. I plan on V Planner for all contingencies other than this extreme one (Lost Deco, deeper, longer). For this extreme one I also plan with DecoPlan with minimum gradient factors, not sure that I've ever dropped it to 100/100 though!.

But at the end of the day, a good deco schedule is a good deco schedule. If the shit hits the fan, I want to be doing what I believe to be a good deco schedule. That is what gives me comfort.

So I'm not sure how much comfort I would get from having a deco schedule on my computer that tells me that everything is hunky dory, when in fact it is giving me info that I normally wouldn't touch with a barge pole. I'd still be thinking 'what the chuff am I doing following this load of old billocks'.

So it comes down to carrying enough gas doesn't it?

On any OC dive in the 70m range I'm carrying 3 tanks, and for one of this length it will be 4. Either with a deep ascent gas from 51 ish, or with a shallower one from 36 ish, depending on the dive.

So although I'm not close to dives like this on Rebreather yet, I'm not planning on carrying any less for emergencies than I would have done for OC. If anything I was expecting to usually have to carry one more tank than on OC due to the need for bailout plus 'normal' deco gases.

Mike

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"If CCR diving hasn't profoundly shocked you, then clearly you haven't fully understood it." Tony Bridge (Well known fountain of plagiarism)

Mark Chase

Hi Mike

The "enough gas" thing is interesting because I have dived with a reasonable number of different divers all doing 70m+ dives and I have never seen anyone take in four tanks.

The fact is when you do the math on the 30SAC as trained you would either have to carry a huge amount or cut the bottom time short. Most of the bloks I dive with arn't interested in 15-20mins on the wreck if its only 70m.

I take a third tank when my deep bailout goes beyond the range of 18/45 However this is often a smaller 7ltr with 250bar in plumbed directly to the BOV for initial bailout with the intent on getting on the 10ltr 18/45 as soon as its breathable. Shallow gas is on drop tanks via the deco station or yellow bag so we dot carry that.

The 7ltrs is more about getting me back to the shot line (Up line) than it is about meaningful deco. Missing the shot and ascending in the current is adding a whole new set of problems.

I never factor in the 7ltr to my bailout calculations as really its just bottom time and maybe 2mins of ascent time below the off gassing level.

There comes a point where unless you have the luxury of kitting up in the water or having safety divers de kit you, managing a large number of very heavy stages becomes more of a problem than the one it solves.

Reaching the surface and realizing its choppy as hell (it wasn't three hours ago when you got in) and you have four Ali80s or 10ltr steels strapped to you, is not a fun place to be.

Another reason for having the option to accelerate deco is the issue of bailing out and missing the shot. If I am free ascending i may be comfortably inside my max planned run time but find i don't have any shallow deco gas on the yellow bag. As a result i have to do the minimum possible deco on my 50%

When i plan a dive I have three levels of risk to consider.

1st is max bottom time possible to deco out on gas i am actually carrying.

2nd level is max bottom time on gas I carry + the drop tank

3rd Level is modified deco due to elevated SAC (C02 hit). This can affect carried gas and overall gas.

I try not to include my buddy in the equation as I have had too many unreliable buddies in the past but its a reason I prefer not to dive solo on a CCR. If i start the dive with a buddy theres a possibility he might be able to help out with spare gas.

A solo dive for me would always be within the limits of deco on carried gas. A buddy dive will be to the limits of carried gas and the drop tank with my buddies gas as a final fall back position.


ATB

Mark