Backup deco plan

[ajduplessis]

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.

I would not worry about the second stop allocations, just keep moving. Same for the 1min stops. If you are controlling your ascent speed, they should clear by the time your reach them. The longer stops obviously requires you to spend the time there. Not really needed for such short BT, but I would also reduce the O2 in your back-gas to a 16/35 (18/35) and are you comfortable with a END of 43m?

How many dives have you done past the 50m mark? How many deco dives have you done to date?

---------- Post added June 5th, 2015 at 02:29 PM ----------

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

The default DC settings as shipped by manufacturer. You know there is no standard and implementations may differ between manufactures? Flexing you knowledge muscle????

 

[PfcAJ]

*Print* your deco schedules. With a computer machine.

 

[Pavao]

(snip)
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


(snip)

(snip) However I have (somehow) a hard time reading lots of small numbers in a dark place(snip)

looka, do you really need all those numbers? I think you can do without Mix, pO2 and EAD. If you want/need you can always just highlight the stop of the gas switches.

*Print* your deco schedules. With a computer machine.

And there's also that ^^. I think a printed out version will always be much more clearer to read than the nicest writing you will ever do, certainly true in my case

 

[TSandM]

So, looked at another way, the OP's schedule is 30 fpm from depth to a little shallower than half maximal depth, then 10 fpm from there to 50 feet (15 meters) at which point some short stops ensue, until the majority of the deco is done at 20 feet (6m). If you just think about the 10 fpm ascent rate, you don't have to memorize all those 30 second stops.

It seems like a strange schedule, but then, it seems like an odd dive to begin with.

 

[ajduplessis]

Very odd, short BT and expensive mix, I hope the dive goal is worth it.

 

[Nasser]

Exactly, all those short stops from 30m to around 12m are really just the plan telling you to do a slow controlled ascent until you get to your shallower "proper" deco stops.

You could set it up with variable ascent rates for each portion of your ascent. So from your Max depth to your first "deep stop" you're moving at a rate slightly faster than 10m/min (but no slower), and once you pass the "off gas ceiling" from 30m onwards, you are moving at 10 m/min rate and not faster. Eventually when you get to your shallower stops you might even use a slower ascent rate to move form stop to stop and finally to the surface.

If you're using the Petrel's deco planner then of course you can't program variable ascent rates and the Petrel does your plan based on the fixed 10m/min. rate.

 

[Patoux01]

over 10m/min on trimix? That's something I haven't read very often.

 

[Nasser]

over 10m/min on trimix? That's something I haven't read very often.

The idea is when you leave the bottom phase you don't want to go slower than 10m/min... until you hit the off-gas ceiling and then from your first deep stop onwards you can go 10m/m or slightly slower. The deep stop is where you give a chance for your body to catch up and allow the helium to begin offgassing in some of the faster tissue compartments.

If you want to read more about it check out The Six Skills - by Steve Lewis in the chapter where he discusses way-points and variable ascent rates. Actually, in the book I think he uses 9m/min as the reference.

 

[ajduplessis]

over 10m/min on trimix? That's something I haven't read very often.

What about 20-25m/min coming from 100m trimix dive?

 

[looka]

Thanks everybody, the feedback is very useful.

That's not a real dive, it's an example for discussion, but I can see how one would want to do such a dive on a wall for example. The point of the question was about the apparent redundancy of these deco tables, so I posted an example profile.

Printing the deco plan with an actual printer seems like a good idea. It's quick and easy to read (provided you have a printer)
The ascent rate solution is not dissimilar from 6m-step solution (you would smooth out the steps anyways)
I still use these profiles only in case my petrel fails

Anyways, great feedback, thank you.

To answer some of the questions:
I probably have 20 dives between 50m and 60m, some on air some on trimix and 1 to 65m.
Yes I am comfortable with a short-dip at 43m END provided there is no overhead and/or complex navigation
Yes I could use 16/35 instead. When bottom time is so short, it makes a really small difference

Luca