Subsurface Rebreather Bailout Planning

[p.kiel]

Downloaded subsurface recently and playing around with its planning tools and beginning to really like the program and plan to implement it into my dive planning.

When planning some BO deco for CCR diving using the "Bailout: Deco on OC" function, I get the following warnings sometimes: "Warning: not enough reserve for gas sharing on ascent!"

This pops up when it is saying I will need 24cuft of O2 for deco when I am carrying a 40cuft 02 bottle in the plan. If I bump up the fill pressure in the bottle a bit or switch to a bigger bottle, such as an al80, this warning goes away. For this specific plan, the warning goes away once my plan has 46cuft of O2 (1.92x). My question is what is the default setting for reserve/contingency planning and is there any way to change it? I didn't see anything in preferences or dive parameters. General recommendations are to bring 1.5-2x the deco gas you need. 1.92 is almost 2, but not quite. Is Subsurface doing some other calculation to determine how much deco gas I should be bringing rather than a simple 1.5 or 2x factor? Interested in their planning logic behind the warnings.

Patrick

 

[rsingler]

I believe that Subsurface assumes (because of its OC focus), that you are sharing bailout. I may be wrong.
At least, when I'm modeling OC gas failures, the numbers assume my buddy has lost his primary ascent gas, and that I am sharing on the way up to the next deco bottle.

 

[elmo]

I'm not a CCR diver and have not used the planner for a little while (unfortunately have not had the need). But have a look at the 'gas options' choices. There is a 'sac factor' (multiple applied to gas consumption rate) and 'problem solving time' (time it takes before ascending to sort yourself out). If you just want a simple 1.5 factor you should be able to set problem solving time to zero and sac factor to 1.5.

 

[rsingler]

I think the minimum SAC factor is 2.0. Hence my assumptions about sharing gas.

 

[p.kiel]

I'm not a CCR diver and have not used the planner for a little while (unfortunately have not had the need). But have a look at the 'gas options' choices. There is a 'sac factor' (multiple applied to gas consumption rate) and 'problem solving time' (time it takes before ascending to sort yourself out). If you just want a simple 1.5 factor you should be able to set problem solving time to zero and sac factor to 1.5.

I think the minimum SAC factor is 2.0. Hence my assumptions about sharing gas.

Yes. Their min is 2.0. I planned some OC tech dives and they use this in conjunction with sac rates and ascent rates to calculate a min gas. I have used this to mimic GUE CAT min gas planning quite well (10'/min, 0.75 cf/m, 2.0 factor with 1 min problem solving).

So all the program needs to do is use the value in SAC factor to also be a bailout factor and rebrand it as a "conservative factor". The current min of 2.0 falls with my general bailout and deco conservative factors so not a problem, but there are definitely divers out there bringing only 1.5, especially for deco gas. So having it go below 2 would be nice for those calcs (easy enough to do in mental math since it gives raw consumption volumes). But again, using programs like these is to automate all these calculations.

 

[AdamSa]

You can always set you SAC rate to be lower to scale with a factor of 2.0 to whatever you need it to be.

 

[atdotde]

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).

 

[KenGordon]

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).

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.

 

[atdotde]

If you don’t intend to share gas you can simply ignore that warning.

 

[rsingler]

If you don’t intend to share gas you can simply ignore that warning.

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?