Strategy for bailout calculation

[LFMarm]

I have been playing with developing bailout plans for CCR dives. The approach I was trained on is to calculate gas required for safe ascent to surface taking into account all deco obligations from the worst possible point of the dive (typically the end of the bottom part of the dive). I would like to hear what is the approach/strategy that experienced CCR divers take to build their bailout plans (e.g., what is the sequence of decisions you take?, what conservatism do you embed in the calculations?, what tools do you use or have built to approach this?, etc.).

Some specifics of my diving that may or may not have any influence on the bailout planning:

1. I plan to be self sufficient for bailout even if diving with others (i.e., no team bailout),
2. I am always carrying at least 2x AL80 as part of my sidemount CCR setup (1 tank is the dil/dilout, the other one dedicated to bailout)
3. With few exceptions, the bailout is planned to be carried and not staged

 

[inquis]

Plus hypercapnia allowance.

 

[beldridg]

IMHO, there are really (at least) three different "buckets" of situations. The proviso for the second two is, as always, "it depends."

1) "Simple" MOD1 and even shallow or short MOD2 dives that don't have a large deco obligation associated with them and no penetration. In this case, as mentioned above, plan a large (double?) normal SAC rate for your deep bailout for a number of different reasons and then carry another cylinder for accelerated deco (e.g., Nx50). Calculate appropriate safety margins. Generally, in most cases, for a MOD2 dive, you will be okay with a couple AL80 tanks. For simple MOD1 dives without a deco obligation, an AL40 will usually work.

2) MOD3 dives without penetration and with deco obligations 90 minutes or less. In this case, you are likely to need a third cylinder and there are many ways to plan that. I personally usually take a deep bailout, a Nx50 and a AL40 of O2. It can vary, but that is "normal" for me. If needed, I'll take an intermediate but I try to avoid it.

This is where the "it depends" really starts to kick in. Do you have a dive buddy? Are you comfortable with them (i.e., can you plan team bailout for the O2 bottle and just take one and maybe one of the team carries an intermediate)? What are conditions like -- i.e., can you "leave" the O2 on the line or do you need to carry it for the whole dive? Etc.

These dives normally need to have a custom plan but they are pretty well understood by divers who regularly do MOD2-MOD3 dives.

3) MOD2 / MOD3 and/or extensive penetration -- sorry, but when these are combined, you really need to build a custom plan. I don't think there are "formulas" for these dives and it is likely you are going to have to use some combination of pre-staged tanks (e.g., cave) or team bailout, safety divers, etc.

It is just my take.

- brett

 

[LFMarm]

This is where the "it depends" really starts to kick in. Do you have a dive buddy? Are you comfortable with them (i.e., can you plan team bailout for the O2 bottle and just take one and maybe one of the team carries an intermediate)? What are conditions like -- i.e., can you "leave" the O2 on the line or do you need to carry it for the whole dive? Etc.

Thanks - I edited the original post to specify that I am not doing bailout team planning and normally I need to carry all gas including O2 when used.

1) "Simple" MOD1 and even shallow or short MOD2 dives that don't have a large deco obligation associated with them and no penetration. In this case, as mentioned above, plan a large (double?) normal SAC rate for your deep bailout for a number of different reasons and then carry another cylinder for accelerated deco (e.g., Nx50). Calculate appropriate safety margins. Generally, in most cases, for a MOD2 dive, you will be okay with a couple AL80 tanks. For simple MOD1 dives without a deco obligation, an AL40 will usually work.

I am focusing the planning exercise on dives with significant deco obligations (70+ minutes)

 

[beldridg]

Thanks - I edited the original post to specify that I am not doing bailout team planning and normally I need to carry all gas including O2 when used.


I am focusing the planning exercise on dives with significant deco obligations (70+ minutes)

The problem with trying to answer that question is that "70+" implies a significant variance and you are starting to get into the zip code of custom planning the dive.

For example, for a 70 minute obligation, in most cases I'd be comfortable with two AL80 cylinders (deep and Nx50) and really wouldn't do too much planning. I've done enough of those dives to just "know" what works.

For 90-ish minutes of deco, I'd also bring an AL40 (or more) of O2 -- especially if I'm not relying on team gas.

When you start to get into the two hour deco obligation range then you are likely to need a custom plan depending upon the situation. It will likely involve four tanks and it is starting to get unwieldy (at least for ocean diving).

Past 120 minutes of deco obligation and you are likely going to have to rely on team bailout or staging tanks or safety divers, etc. That is just the reality of the amount of gas you need to bring.

All the above also assumes no penetration.

If you take a MOD2 and especially a MOD3 course, your instructor should spend a significant amount of time discussing various strategies for bailout.

I would say that thinking in terms of the deco obligation (and not just "what is the max depth") is the approach I usually take. But, without specifics on the dive plan, it is a bit hard to give specifics on a bailout plan.

- brett

 

[Dsix36]

This is short, sweet, and simple BUT there is much more to really consider when planning and all plans should be done with personal abilities and preferences included.

Plan the dive and calculate the bailout that is needed. 1.5 x that, is what I carry as a minimum.
Remember to take into consideration any other mitigating factors that might pose additional time and/or resources.