Contingency Deco Plan

[PfcAJ]

multiple reasons where you may want to take a 50% bottle to accelerate deco depending on the cave profile, and yeah, you could have a valve failure after you've lost your buddy. In that case you steal his gas, but you could also be diving solo and got stuck, or something else. You don't plan for it, but if it happens, I at least want to know I have options to get out with minimal risk of being bent

No. there's zero reason to do a bottom time/profile that requires 2 deco gases but only take 1 deco gas.

Rules 1,2, and 3 in full effect here.

 

[tbone1004]

read the damn post AJ, you wouldn't take one, you would take both of them, but if you have a valve failure on the O2 bottle, you can't use it. ergo you have to finish deco on the other gasses you have with you.

 

[PfcAJ]

You can totally use the o2 bottle. Take a 50% reg and slap it on there.

Good grief.

 

[tbone1004]

You can totally use the o2 bottle. Take a 50% reg and slap it on there.

Good grief.

read the damned posts AJ! you can't take the f*cking 50% regulator off and put it on a 100% bottle with a VALVE failure! regulator failures are annoying because you can swap, valve failures mean no access to gas, PERIOD. It's either already gone if the neck O-ring or burst disc failed, or you can't access it because it's coming out of the hand wheel. Ergo, you can't use that gas and have to deco on something else.

 

[PfcAJ]

so you've got 50% leftover and backgas left over. Do the required time.

There's just no excuse to not plan your gas reserves properly. Even worse when you try to justify it with things like simultaneously losing your buddy.

Do people really dive like this? Is this real life?

If you're plan is such that you're depending on having oxygen then put another bottle in the water. It's not hard, guys.

 

[kensuf]

I'm going with AJ on this one, but personally, I prefer 2x the deco gas rather than 1.5x. I just like having the warm fuzzies of having more gas.

The only reason I could see to alter your GF's to cut your stop time short is a medical. In that case, I hope you have support to alert them then go back and finish your deco.

 

[Jack Hammer]

Whats the point of messing with gfs mid dive, If you feel gf95 is perfectly "safe" why not just plan your dive using it and stay longer if you want extra conservatism? might as well just wing it and make everything else up as you go along...

 

[packrat12]

Medical or extreme need is the only reason to change the GF up for me. With Shearwater, I can also follow the GF99 in extreme emergencies. I have miss-planned, planning went south, medical etc. This is a quote directly from Shearwater with regard to GF99: "In extreme conditions, decompression risk can be traded for operational risk by using the GF99 display. For example, in a low-gas situation or perhaps a bailout or injury, you may want to get to the surface faster, but not blow off all the remaining decompression stops." This can also be accomplished by modifying your GF.

Whats the point of messing with gfs mid dive...

With regard to 'messing' with the GF mid dive, what if my dive has been more 'stressful' then planned, maybe 30/85 is not so good and I want to go to 20/60..... or perhaps I went the other way. Stress can be temperature, workload, overall feeling etc. The option is available to adjust GF as needed with Shearwaters. At my current diving, I have not felt the need to adjust it either way.

 

[boulderjohn]

Whats the point of messing with gfs mid dive, If you feel gf95 is perfectly "safe" why not just plan your dive using it and stay longer if you want extra conservatism? might as well just wing it and make everything else up as you go along...

I once dived with a very experienced diver who used a GF of 85 and then stayed for a while after it was done, with the extra length depending upon his judgment on how much additional safety was warranted after the dive. He generally stayed 5 extra minutes, but it might be longer. He said he liked to know that the algorithm considered him done and ready to ascend at any time he felt was right.

 

[Remy B.]

Air on diver, 2x 12L-300 + 2x 6.8L-300 + 1x 5.6L-200 50%O2 + 1x 7L-230 80%O2

This is what I'm thinking about


Decompression model: ZHL16-B + GF

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 35/65

Dec to 60m (3) Trimix 18/40 18m/min descent.
Level 60m 26:40 (30) Trimix 18/40 1.25 ppO2, 27m ead, 32m end
Asc to 36m (33) Trimix 18/40 -8m/min ascent.
Stop at 36m 1:00 (34) Trimix 18/40 0.82 ppO2, 14m ead, 18m end
Stop at 30m 2:00 (36) Trimix 18/40 0.72 ppO2, 11m ead, 14m end
Stop at 27m 2:00 (38) Trimix 18/40 0.66 ppO2, 10m ead, 12m end
Stop at 24m 3:00 (41) Trimix 18/40 0.61 ppO2, 8m ead, 10m end
Stop at 21m 3:00 (44) Nitrox 50 1.54 ppO2, 10m ead
Stop at 18m 2:00 (46) Nitrox 50 1.39 ppO2, 8m ead
Stop at 15m 5:00 (51) Nitrox 50 1.24 ppO2, 6m ead
Stop at 12m 6:00 (57) Nitrox 50 1.10 ppO2, 4m ead
Stop at 9m 8:00 (65) Nitrox 80 1.51 ppO2, 0m ead
Stop at 6m 40:00 (105) Nitrox 80 1.28 ppO2, 0m ead
Surface (106) Nitrox 80 -6m/min ascent.

OTU's this dive: 142
CNS Total: 54.6%

4834.6 ltr Trimix 18/40
681.9 ltr Nitrox 50
1349.5 ltr Nitrox 80
6866 ltr TOTAL

===========================================================================================

Backup Plan.

Decompression model: VPM - B

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = Nominal

Dec to 60m (3) Trimix 18/40 18m/min descent.
Level 60m 46:40 (50) Trimix 18/40 1.25 ppO2, 27m ead, 32m end
Asc to 42m (52) Trimix 18/40 -8m/min ascent.
Stop at 42m 0:45 (53) Trimix 18/40 0.93 ppO2, 18m ead, 21m end
Stop at 36m 4:00 (57) Trimix 18/40 0.82 ppO2, 14m ead, 18m end
Stop at 30m 3:00 (60) Trimix 18/40 0.72 ppO2, 11m ead, 14m end
Stop at 27m 3:00 (63) Trimix 18/40 0.66 ppO2, 10m ead, 12m end
Stop at 24m 6:00 (69) Trimix 18/40 0.61 ppO2, 8m ead, 10m end
Stop at 21m 3:00 (72) Nitrox 50 1.54 ppO2, 10m ead
Stop at 18m 4:00 (76) Nitrox 50 1.39 ppO2, 8m ead
Stop at 15m 6:00 (82) Nitrox 50 1.24 ppO2, 6m ead
Stop at 12m 7:00 (89) Nitrox 50 1.10 ppO2, 4m ead
Stop at 9m 10:00 (99) Nitrox 80 1.51 ppO2, 0m ead
Stop at 6m 41:00 (140) Nitrox 80 1.28 ppO2, 0m ead
Surface (141) Nitrox 80 -6m/min ascent.

Off gassing starts at 46.8m

OTU's this dive: 184
CNS Total: 71.0%

8120.7 ltr Trimix 18/40
856.2 ltr Nitrox 50
1441.0 ltr Nitrox 80
10417.9 ltr TOTAL