Backup deco plan

[looka]

Most of us who went through a deco course learned how to plan a deco dive, write a custom deco schedule and then follow it with a bottom timer (at least I did). And most of us after getting certified kept planning such dives at the surface, but then mostly flew by their computer once in the water, keeping the pre-planned schedule as a backup/sanity-check in case computer failed (at least I did).

So my thinking is:

I can see the reason to have a refined primary deco schedule, but when I need to resort to a backup, simplicity is gold. Do i really want a deco plan that looks like an ugly matrix of numbers that is impossible to memorize, lengthy to write and difficult to read? I thought I would not like that. I thought that if I have a problem, my computer is dead and I am confused, I would like to have a simple plan, not a very complex one.

So more practically:

I planned a short trimix dive to 75m and the algorithm spit a longish series of deep 30sec / 1min stops (in this case 10 stops from 30m to the surface, helium being the culprit). For obvious reasons I don’t want to skip the deep stops, but what about consolidating them?
So I changed the settings to generate stops on 6m intervals and a minimum duration of 1m: what I got is a 5-stop schedule, with no significant difference in CNS nor time to surface. It seems like a good alternative (I could even “smooth” out the profile while executing it if I really wanted to).

Do you think this could be a good back up plan? Is there something that I am missing? What is the drawback of my simplified plan?
Even if it’s sub-optimal (but safe), do I care? (considering I have a 99.9% probability of following my computer anyways) ?

Your feedback is appreciated.
Looka

 

[ajduplessis]

What algorithm and settings do you use? All deco schedules is a matrix of numbers, they are your friend and should not be "ugly". The plan is what it is!!!! Length should not be an issue and neither should it be difficult to read. You don't want to skimp on things you will heavily depend on. I DEPEND on the easy to read information on my slate/BT and trust it fully. Do not tweak any plans unless you fully understand the impact.

I would not do a 75m dive with additional deep stops (suunto?), just the stops as per software (vpm or gf based). If the software uses deep stop function like suunto, rather switch it off, you will be in the water forever. My profile for a dive like this would have the first stop at around half the total pressure (40m or so) no longer than 1min and then follow the algorithm out.

Why don't you share your planned run? It might be helpful.

 

[looka]

What algorithm and settings do you use? All deco schedules is a matrix of numbers, they are your friend and should not be "ugly". The plan is what it is!!!! Length should not be an issue and neither should it be difficult to read. You don't want to skimp on things you will heavily depend on. I DEPEND on the easy to read information on my slate/BT and trust it fully. Do not tweak any plans unless you fully understand the impact.

I would not do a 75m dive with additional deep stops (suunto?), just the stops as per software (vpm or gf based). If the software uses deep stop function like suunto, rather switch it off, you will be in the water forever. My profile for a dive like this would have the first stop at around half the total pressure (40m or so) no longer than 1min and then follow the algorithm out.

Why don't you share your planned run? It might be helpful.

Thanks for your response

I am using ZHL-C with GF set to 70/30, that's what's on my Petrel. By "deep stops" i mean the stops artificially generated by the low gradient factor, NOT additional stops. The issue i meantioned with 6m steps-size vs 3m applies to VPM too: in both cases, using 6m steps would reduce the number of stops without a significant change in total deco time. Not only I find it easier to write/read in a small space, but I also find it hard to follow 30sec stops, most computers do not even show seconds.

Let me share the ZHL-C plan with 3m steps and 6m steps:

3m steps

Depth Stop Run Mix pO2 EAD
Lvl 75 4:15 8:00 18/35 1.52 40
Stp 30 0:30 13:00 18/35 0.72 13
Stp 27 0:30 13:30 18/35 0.66 11
Stp 24 0:30 14:00 18/35 0.61 10
Stp 21 0:30 14:30 50 1.54 9
Stp 18 0:30 15:00 50 1.39 7
Stp 15 1:00 16:00 50 1.24 5
Stp 12 1:30 17:30 50 1.10 3
Stp 9 2:00 19:30 50 0.95 1
Stp 6 9:00 28:30 100 1.60 0


Dive # 1, ZHL-C+GF 30/70
Elevation = 0 m
CNS = 26%
OTU's = 42
Decozone start = 43 m
Gas 18/35 = 1476 ltr.
Gas 50 = 186 ltr.
Gas 100 = 189 ltr.

--------------------------------------------------------
6m steps

Depth Stop Run Mix pO2 EAD
Lvl 75 4:15 8:00 18/35 1.52 40
Stp 30 0:30 13:00 18/35 0.72 13
Stp 24 1:00 14:00 18/35 0.61 10
Stp 18 2:00 16:00 50 1.39 7
Stp 12 4:00 20:00 50 1.10 3
Stp 6 9:00 29:00 100 1.60 0


Dive # 1, ZHL-C+GF 30/70
Elevation = 0 m
CNS = 26%
OTU's = 42
Decozone start = 43 m
Gas 18/35 = 1478 ltr.
Gas 50 = 213 ltr.
Gas 100 = 189 ltr.

I like the simplified plan -> 0.5, 1, 2, 4, 8 + safety = I'll write it down, but I remember it already

What do you think?

 

[PCoetzee]

I still use "old-school" IANTD dive tables for calculating backup plans in case my computer dies. I prefer tables because I instruct and like to stay fresh in their use. I normally take 3 plans with me on a slate:
1) Normal Run
2) Too Deep (Next depth bracket on the table.)
3) Too Long (Next time bracket on the table.)

If you need a plan for too deep and too long then you shouldn't be a technical diver.

IANTD tables are derived of Buhlman and VPM algorithms and gives very similar profiles to software like V-Planner. It is just easier to get it wrong. Especially when making altitude adjustments.

Concerning Complexity:
Technical diving is inherently more complex than other forms of diving and if you have trouble interpreting complex runs then you really have only 3 options:
1) Simplify the runs as you suggested. (This will be more dangerous especially when He is involved. By having less stops and bigger jumps you will be stressing the tissue compartments more than necessary.)
2) Practice complex runs until you become more proficient and comfortable with it. (This will be my suggestion.)
3) Dive shallow reefs with a single cylinder within the No-Deco limits.

Hope this helps.

 

[Dr. Lecter]

Read some of the new thinking on deep stops, as well as whether helium really requires significally lower GF low settings. While it's admittedly on CC, most of the guys I know are diving 60-70% helium mixes with GFs closer to 60/80 all the way up to 80/85 and lengthier shallow stops as they see fit. There's also the question of what helium mix one runs on the SW versus what's actually in the tank, but that's a different question.

 

[looka]

Interesting. Thank for your answer.

I also have 3 plans , they are: normal, lost gas1, lost gas2. I try to leave the bottom a couple of minutes early, so I automatically have a time/conservatism buffer. I don't plan for deeper, I just don't go deeper.

Your comments about tissue stress are interesting. I assumed tissue stress would come from the gradient factor and not the step size, but it makes sense, they probably both have an impact. That's the answer I was looking for.

To clarify: I do not have a problem following a complex plan. However I have (somehow) a hard time reading lots of small numbers in a dark place and I find tedious counting seconds in my head because my bottom timer does not show seconds, so i find stops that 30 seconds only a bit annoying.

Anyways, thank you for your feedback!

 

[tomfcrist]

If you need a plan for too deep and too long then you shouldn't be a technical diver.

Sometimes it's nice to have a plan for too deep, especially for those of us who drop on unknown wrecks for exploratory purposes. If you are diving a wreck that nobody has been to before, and doing penetrations, there is no telling how deep you may end up while inside the wreck...especially since you may end up deeper than the depth of the actual bottom.

 

[Nasser]

I think that your plan should be dictated by how you feel when you get out of the water... and tweaking your conservatism / GF settings accordingly. Having those as your basic framework, you could have deeper/longer and lost gas contingencies but dive within the plan... riding your computer.

If you are making frequent dives to certain depths and maxing out at similar bottom times, after a while you're going to end up with a standard set of tables you've cut as the outermost limits ( contingent plans / backups) based on your GF's and you won't have to keep re-cutting tables as long as you keep diving freely within the limits you've set.

 

[PCoetzee]

Read some of the new thinking on deep stops, as well as whether helium really requires significally lower GF low settings. While it's admittedly on CC, most of the guys I know are diving 60-70% helium mixes with GFs closer to 60/80 all the way up to 80/85 and lengthier shallow stops as they see fit. There's also the question of what helium mix one runs on the SW versus what's actually in the tank, but that's a different question.

I am a huge fan when it comes to the advancement of knowledge and we do a lot of reading ourselves...

My only reservation is that experimentation amongst inexperienced people can lead to trouble. It is my opinion that you need a relatively good understanding of diving physiology and algorithms paired with a lot of personal experience before you decide to do significant algorithm tweaking.

I try not to change the basic algorithms simply because I'm scared of students thinking it is OK and safe to do the same. Also because the existing tables and algorithms work...

 

[Dr. Lecter]

And what, in your opinion, is "the basic algorithm" for GF settings?