Subsurface Rebreather Bailout Planning

[flymolo]

For a CCR bailout you only care about the diver bailing out. There is no sharing, although there may be team bailout where not all the bailout is carried by one person. The SAC for the bailout needs to take into account a CO2 hit, especially for deep bailout, as that is the worst case you are planning for.

Think of CCR divers as solo divers who magically become OC divers at the worst possible moment.

Was going to say this- I was taught that in a non-mixed team (ccr divers only) oc bailout is for one person. However, is 1.0 enough to account fora co2 hit? Or is 2.0 defined as "one person with an rmv of 2"?

 

[grantctobin]

Was going to say this- I was taught that in a non-mixed team (ccr divers only) oc bailout is for one person. However, is 1.0 enough to account fora co2 hit? Or is 2.0 defined as "one person with an rmv of 2"?

I go back to Ainslie’s Rethinking Bailout article in terms of adequate bailout volume. It’s one thing in open water and entirely another in an overhead environment. Most people do not carry enough.

 

[wedivebc]

Just a thought, but if "CC" is selected, perhaps add code based on that flag to allow less than 2.0 SAC factor, and trigger a diffent phraseology in the inadequate gas warning?

I don't know if the SAC factor needs to be changed but the reason for the SAC factor certainly does.

 

[rsingler]

I agree with both comments above. It should also be kept in mind that the SAC factor entered will apply during problem solving, at Bottom SAC. In other words, whether you are positing one diver breathing at double his usual RMV, or two divers sharing gas, this calculation applies during problem solving at depth. But the SAC factor doesn't apply during ascent.
Increased SAC should gradually decline as you settle down during ascent after a CO2 hit. So I run two sets of calculations, one with a problem solving time of zero and my normal SAC, to determine projected normal consumption during ascent, and a second run, again with zero problem solving time, recognizing that I will have a minimum of twice my normal SAC throughout. For a CO2 hit, I'll presume 5x. I then average the two figures that say "X cu ft used during ascent." That gives me a declining consumption, starting (in my case) at 5x and declining to 1x by the time I switch to the next deco bottle.
I have to admit, it would be more convenient to have more control of the SAC, but this roughly works. The high consumption at high ambient pressure (at depth during initial stressed ascent) is counterbalanced by longer time of lower consumption during shallow deco, so a mean value works for me.

And to account for problem-solving gas during a CO2 hit, if I'm really geeking out, I need to do two more runs: one at a SAC of 5 with zero minutes of PST, and one with my hypothetical problem solving time. Comparing "Minimum gas at 0 min PST, with Minimum Gas at "x min" of PST gives me my problem solving consumption during 5x SAC. It's a little bit of a kludge, but it works.

Your thoughts, @atdotde? Please confirm that the SAC factor is not applied to Deco SAC during the ascent? It would be nice to have problem solving gas and ascent gas broken out, with the relevant SAC that was applied listed next to it. Then the "Minimum Gas" total and any warnings you add will make more sense to the occasional user.

 

[p.kiel]

I go back to Ainslie’s Rethinking Bailout article in terms of adequate bailout volume. It’s one thing in open water and entirely another in an overhead environment. Most people do not carry enough.

Definitely a good resource I was shown back in Cave DPV class. Attached here for those that aren't familiar.

The warning is shown if your gas reserve is not sufficient for gas sharing during the ascent (as it says), meaning two divers breathing from the gas resources given at the nominal SAC rate. Why would you want to make this one and a half diver making it to the surface? I am not sure, though how relevant the scenario of bailing out and sharing gas at the same time really is. Please note as well that subsurface does not try to compute your gas consumption while on CCR (as that cannot be reliably computed by a SAC-like computation).

Many oc deco protocols call for 1.5x on the deco gas because if your team of 2 loses a deco bottle, you extend stop times by 1.5 and breathe the respective stop deco gas for half the new time and breathe the next highest 02 content for the other half. Ex. #1) if on 18/45 back gas and 50% deco and you had 4 min stop @ 50' you'd do 6 mins total with 3 on 50% and 3 on backgas. Between 2 buddies you're breathing 6 mins of 50% (1.5x the planned 4 minutes). Ex #2) same dive but additionally have 02. But you lose one 02 bottle in the team. You have 20 mins at 20'. You'd do 30 mins total with 15 on 02 and 15 mins on 50%. Total time on 02 between the 2 buddies is 30 mins (1.5x the planned 20 mins). So no planning 1.5x on deco does not get only 1.5 divers to surface. These OC principles carry into rebreather BO too, I'm going to have multiple BO bottles (of bottom and deco) to play around with to get buddy and I out if SHTF.

Regardless of what planning and team protocol you choose to adhere to, would be nice for Subsurface to allow changing of the conservative factor and allow independent conservative factors for deco and back gas. Back to my original example in post #1. I need 24cuft of 02 for the stop. I'd like it to give me warning only if I had less than 36 ft available. I'd only share this 02 bottle if both my rebreather and buddies rebreather are dead AND buddy lost 02, a really bad day. Again, this is only a minor inconvenience. It accurately gives me the raw consumption volumes which I can apply whatever conservative factors I seem appropriate for the segment. Just a small feature request.

Shearwater doesn't do this at all. They just give you raw consumptions volumes for each gas just like Subsurface. But if you are going to put in a warning like they do here, I'd like to have a bit of control over it.

 

[flymolo]

Definitely a good resource. Attached here for those that aren't familiar.

Many oc deco protocols call for 1.5x on the deco gas because if your team of 2 loses a deco bottle, you extend stop times by 1.5 and breathe the respective stop deco gas for half the new time and breathe the next highest 02 content for the other half. Ex. #1) if on 18/45 back gas and 50% deco and you had 4 min stop @ 50' you'd do 6 mins total with 3 on 50% and 3 on backgas. Between 2 buddies you're breathing 6 mins of 50% (1.5x the planned 4 minutes). Ex #2) same dive but additionally have 02. But you lose one 02 bottle in the team. You have 20 mins at 20'. You'd do 30 mins total with 15 on 02 and 15 mins on 50%. Total time on 02 between the 2 buddies is 30 mins (1.5x the planned 20 mins). So no planning 1.5x on deco does not get only 1.5 divers to surface. These OC principles carry into rebreather BO too, I'm going to have multiple BO bottles (of bottom and deco) to play around with to get buddy and I out if SHTF.

Regardless of what planning and team protocol you choose to adhere to, would be nice for Subsurface to allow changing of the conservative factor and allow independent conservative factors for deco and back gas. Back to my original example in post #1. I need 24cuft of 02 for the stop. I'd like it to give me warning only if I had less than 36 ft available. I'd only share this 02 bottle if both my rebreather and buddies rebreather are dead AND buddy lost 02, a really bad day. Again, this is only a minor inconvenience. It accurately gives me the raw consumption volumes which I can apply whatever conservative factors I seem appropriate for the segment. Just a small feature request.

good read- thanks for posting this

 

[atdotde]

The problem with adding configurable options to the Subsurface planner is that there are already far too many. The user interface in its current state is so baroque that it scares off quite a few new users even with sane default values. And experience shows, with these kinds of contingency plans, different people will have very different ideas how to do them so making everybody happy will require not only those additional controls you will need for your way of doing it but easily a multiple of those. We had similar discussions around computing alternative plans for lost gas or different depths or bottom times but in the end settled for a way that allows you to do it semi-automatically: An easy way to disable a gas and the "plan variations" giving you a first order approximation how to change the total runtime for different bottom times or depths (but without specifying how to distribute the additional time over stops).

That said, I believe you should simply use the settings for SAC (which is ignored for the CCR parts of the dive anyway) to reflect what you want to use during bailout (applying a factor of 1.5 or whatever compared to your normal rate) and manually add a problem solving interval to the end of your bottom time. The problem solving time and SAC factor are only used to compute minimum gas which does not make sense in a CCR context anyway. So maybe it would make sense to grey out those options for rebreather dives.

But I am open to other suggestions as long as they take into account that other divers will have different preferences and every additional configurable setting makes realization more unlikely.

 

[kelemvor]

The problem with adding configurable options to the Subsurface planner is that there are already far too many. The user interface in its current state is so baroque that it scares off quite a few new users even with sane default values.

A lot of projects are tackling that issue by having an unlockable "advanced" configuration. For example in Android OS, a lot of the configuration is completely hidden unless a user completes a sequence of touches in the right place. Other projects, such as Firefox, choose to use a config file that most users will be completely unaware of.

That gives you the best of both worlds. Simplicity for those users that would be turned off by complex software while retaining the flexibility needed for power users.

 

[KenGordon]

But I am open to other suggestions as long as they take into account that other divers will have different preferences and every additional configurable setting makes realization more unlikely.

It is tempting to suggest that they can already get the sources and change it. If they can’t manage that then should they be diving a rebreather?

 

[rsingler]

It is tempting to suggest that they can already get the sources and change it. If they can’t manage that then should they be diving a rebreather?

Yeah, you're right. But everybody likes convenience. I can make my kludge work. It's all good.