"Accidental" Deco

[DuboisP]

Originally Posted by DuboisP
...//...the director is actually a Suunto Vytec DS

I'm using a Suunto Vytec DS for diving Air/Nitrox, with or without O2 for deco.
I'm preparing my runtime with V-Planner when diving Trimix

the V-Planner algorithm is based on decompression physics of deep dives with trimix, where the saturation/desaturation is quicker, so the rules are not the same

ok, it's wrong, it's not only for trimix, it's only for deep dives, and for me, 120 ft is not deep.
sorry.

 

[Kern]

ok, it's wrong, it's not only for trimix, it's only for deep dives, and for me, 120 ft is not deep.
sorry.

No, this is wrong too. VPM-B is fine for shallow air/nitrox dives. Its just a duel phase algo that measures on & off gassing, it really doesn't matter what depth or gases are being used.

If you prefer a Suunto with its single phase algo that's been hacked to behave similarly, but not exactly, like the fully iterative duel phase version of RGBM, that's fine. But to say its better, more accurate, adapted, etc, than VPM-B for any form of diving is just plain wrong.

 

[DuboisP]

If you prefer a Suunto with its single phase algo that's been hacked to behave similarly, but not exactly, like the fully iterative duel phase version of RGBM, that's fine. But to say its better, more accurate, adapted, etc, than VPM-B for any form of diving is just plain wrong.

i didn't tell that Suunto is OK for trimix diving. I use it for air/nitrox, and as a gauge when i dive trimix.
Suunto Vytec DS is conservative and safe when i dive air/nitrox, and i don't see any reason to add a lot of minutes of deco by using VPM-B on air/nitrox.

 

[Kern]

i didn't tell that Suunto is OK for trimix diving. I use it for air/nitrox, and as a gauge when i dive trimix.
Suunto Vytec DS is conservative and safe when i dive air/nitrox, and i don't see any reason to add a lot of minutes of deco by using VPM-B on air/nitrox.

But I'm saying that VPM-B is good for air, nitrox or trimix, shallow or deep.

Here's what V-Planner (VPM-B +2) would have to say about an "oops" recreational Caribbean-style dive (120ft for 22 minutes): 1 min @ 50ft, 1 @ 40ft, 2 @ 30ft, 4 @ 20ft, 7 @ 10ft.

VPlanner VPM-B + 2, tells me : 2 min @ 50 ft, 3 min @ 40 ft, 4 min @ 30 ft, 7 min @ 20 ft, 12 min @ 10 ft, so a deco time of 28 min
VPlanner is not accurate for AIR or Nitrox dives, as it's a software for diving Trimix
with the tables generally used in France for training (and sometimes for diving), calculated for 75 ft, I have 2 min at 18 feet, 19 min at 9 feet, so a deco time of 21 min.

Here you seem to be comparing a deco schedule using VPM-B +2 for a dive to 120' for 22 minutes, with a schedule using another algo, not Suunto recreational RGBM? for a dive to 75'. Is that right, & was the 75' schedule for a 22 minute dive?

I'm asking for clarification, because if we compare apples to apples, for a 75 foot dive for 22 minutes on VPM-B I don't get any deco. Would you actually like to compare a dive to 120' for 22 minutes using VPM-B +2, to the same dive using Suunto's recreational RGBM using a similar conservation setting.

 

[drbill]

I went into deco the first time by accident. I was diving an HP120 plus a pony and had plenty of gas for the dive. However, I spent more time at depth filming and wasn't looking at my computer often. It was on my return from the dive site (the Valiant here on Catalina) that I actually went into deco. I was a little nervous at first since in 40 years on SCUBA I had never knowingly done that (we didn't have dive computers in the early years). My deco obligation cleared up since I usually spend time in the shallows filming before actually making a safety stop. That dive taught me that going into deco was not a life threatening experience and many of my dives after that involved deco obligations, many of them satisfied by my dive profile involving short stops at decreasing depths to film critters.

 

[DuboisP]

But I'm saying that VPM-B is good for air, nitrox or trimix, shallow or deep.
Here you seem to be comparing a deco schedule using VPM-B +2 for a dive to 120' for 22 minutes, with a schedule using another algo, not Suunto recreational RGBM? for a dive to 75'. Is that right, & was the 75' schedule for a 22 minute dive?

I'm asking for clarification, because if we compare apples to apples, for a 75 foot dive for 22 minutes on VPM-B I don't get any deco. Would you actually like to compare a dive to 120' for 22 minutes using VPM-B +2, to the same dive using Suunto's recreational RGBM using a similar conservation setting.

why i keyed 75 ft ? hummmmmmmmm.

these numbers are for a dive of 131 ft 25 min : 2 min @ 20 ft, 19 min @ 10 ft, so a deco time of 21 min
for 120 ft 22 min, i have 9 min @ 10 ft
these tables are called "MN90" (Marine Nationale / French Navy 1990)

for Suunto P0 (default setting) , I have 1 min @ 65 ft, 2 min @ 37 ft, 13 min @ 10 ft, so a deco time of 16 min

 

[Kern]

Thanx for the clarification on the depths , times, algo's, makes a lot more sense now.

I'll stick with the VPM-B schedule though. It's not so much the times on the MN90 & DS algo's, but the profile as a whole that I have issues with.

By the way, as you ran the recreational RGBM at P0, it's nominal conservatism, might be interesting to run the dive through V Planner with nominal conservation.

PS. Do the ascent times between those largely spaced deco stops need to be added in, or are they a part of the stop times in the rec RGBM profile.

 

[DuboisP]

Thanx for the clarification on the depths , times, algo's, makes a lot more sense now.

I'll stick with the VPM-B schedule though. It's not so much the times on the MN90 & DS algo's, but the profile as a whole that I have issues with.

By the way, as you ran the recreational RGBM at P0, it's nominal conservatism, might be interesting to run the dive through V Planner with nominal conservation.

PS. Do the ascent times between those largely spaced deco stops need to be added in, or are they a part of the stop times in the rec RGBM profile.

VPM-B nominal : 40 s @ 50 ft, 2 min @ 40 ft, 4 min @ 30 ft, 5 min @ 20 ft, 10 min @ 10 ft, so a deco time/ascent time of 24 min, surface @ 46 min

Suunto P0 : total ascent time must be added : 3 min, so going up after 22 min, surface @ 41 min

 

[Piccola]

I have had a few 'accidental' deco's, (no, not exactly!) All of them occurred while diving over seas where you get into much deeper clearer waters than we usually get here at home (New England area). I will say I have compared my computer to others during a dive and mine (factory set) runs on the conservative side. When my bottom time is getting low I may ascend a bit above my group to increase my remaining time but in the end I follow my computer and perform the necessary stops which usually equates to some extra obligation at the safety stop. I manage my air fairly well and have not been in a situation that additional obligation compromised my safety BUT I watch my computers (I carry 2) very closely all the time. When I am diving with similarly skilled divers I am not concerned, but I have been on dives with divers who I never see even look at their gauges! In this case I would encourage the group to ascend long before approaching the max BT is reached. No one likes sharing air 15' under the boat! (jk)

 

[SailNaked]

Maybe the divers were trained for Deco and the accident was posting the question here.

I will give my not so sage wisdom and thoughts on the issue since it seems to be near and dear to my heart lately.

New divers can exceed the limits but I think it is rare, they mostly use there air too fast and watch their almighty computer really closely. many threads would prove this statistically.

when you have a few hundred dives I think the thinking goes something like "well it did not matter last time" what is a little deco, I am going to do a safety stop anyway just this one is required.

So the difference is not really inattention to gauges, because most people with hundreds of dives know what their air is, and about how much time they have left, they seem to make a conscious choice to ride the line a little tight because if they dont they will be on the boat with 1200# of air.

For me it seems important to think about the gear that people use to do Deco diving and how it is different from the gear that I usually wear on a recreational dive.

Double tanks? double regulators (4+ for the dive team), deco gas?
A buddy that is not only close but knows to look for me and knows how much air I have and my obligations and has reserve air for me.

the problem with accidental Deco is not the deco or the inaccurate computer used to signify it,
the problem is that if you have a problem and you have an actual deco obligation you may be totally and avoidably screwed without good backup planning and execution.

I have done it, I am not preaching, and I had a discussion with my wife on this last trip and we agreed that we would not accept any deco, and we still had a minute or two on one or two dives.
We had more than enough air to complete the obligation even if one of us had a total failure of one tank and as soon as I get within 5 minutes of deco I start swimming right next to her.
but with over 1k of air I am not going to stress too much if my wife wants to watch a ray on the sand for a few minutes, with one exception,

if I am about to go into deco at 35ft, seems the math is bad on this one, and the time required at 10 ft builds up fast really a bad idea.