Ongoing discussion of Ratio Deco

[amascuba]

Yeah, absolutely. If RD is based on standard gas mixes, but produces results that can only be duplicated with other algorithms using nonstandard mixes, what conclusions do you draw?

I'm not entirely sure that I understand what you are saying here?

That somebody used a decompression application and ran profiles using air as backgas and 36% as deco and concluded that those results would work for somebody using RD using 30/30 and 50% deco?

If that's what your saying, where did you get that from?

 

[rjack321]

Rjack,

You were on a roll until you failed to harmonize your bogus assertion to Scuba Milo's demonstration of a profile where RD is 500% less conservative than D Plan (GF=30/85). What's 5 minutes more or less? Did you just clock out on that one? Until Milo shot it down, you had me convinced that RD is a close approximation of the other scientifically derived algorithms. As can be readily observed by working out a few profiles on D Plan, sometimes RD produces a close approximation and sometimes it doesn't. It's frequently validated as an approximation of other algorithms, which means that it's an approximation of an approximation.

Every once in awhile I get called away to work So yes I get behind. And no I'm not that vested in this whole thing.

Furthermore, you haven't addressed the limitations on dive planning caused by RD's reliance on standard gas mixtures or does your adherence to RD go so far as to supplant any thought of a mission where optimal BT/DT requires customized mixes? Using RD can you give me a schedule for 8 repetitive gas dives over 3 days with a max depth of 250fsw on Trimix 16/55 EAN36 and 100 O2. SIT(1) three hours and thereafter increasing 2 hours between subsequent dives assuming a dive SAC =.80/deco SAC = .30?

As far as nonstandard gases go: 1st why are you using them?

Then maybe there's some merit in discussing the myriad of ways you could come up with a deco schedule that won't kill you. Although I see lots of ways you aren't diving DIR on the bottom to start with.

EG
why are you pushing ppO2s at 250ft with a 16% mix?
what's your rock bottom to get up to that 36% bottle?
your dive SAC is pretty high IMO, can you even carry enough gas?
you decoing deep at >1.4 ppO2? why?

I see alot of non-dir issues in the gases selected and thus I don't think a schedule for these choices is appropriate for this forum. Whether the WKPP or EKPP uses non-standard gases I don't know and don't really care. I'm not doing those dives and I don't know the rationale for their mix selections.

I 100% agree that RD is just one set of tea leaves, Buhlmann, VPM, RGBM, GAP, etc. being other flavors of tea.

 

[amascuba]

I believe Phil K. is just trying to point out the limitations of ratio deco.
And, believe it or not non standard gases can be DIR (Take a look at some deep cave explorations ie: WKPP, EKPP).
Standard gases can be determined by the team who is doing the dives.
These guys are using "nonstandard" gases to fit the profile of the dive.

So I believe that talking about "non standard gases" is is not outside the realm of this forum.

Unless you would say the WKPP is not DIR?

Milo

The concept of 'standard gas' comes from the need to keep the team on the same playing field decompression wise and the need to simplify dive planning, execution, and decompression logistics.

I'm quite aware that non-standard GUE gases can be DIR. It all depends on your location, your team, and your environment. Example: A dive team may consider the adoption of a standard gas that's not apart of GUE's standard gas lists, because of their environment.

AG's RD document states that the calculations are based on using standard gases. So anybody reading the document or taking his class can clearly see that using a standard gas is a limitation of using RD based on the information provided by AG. At that same time though, anybody can decide that they want to use xyz as a standard back gas and abc as a standard deco gas, run multiple profiles through v-planner, decoplanner, etc and make their own version of RD based on their own rules. I'm sure it wouldn't really be that hard. It would be time consuming and allot of analysis of profiles.

Phil's question was about the limitations of RD using nonstandard gases. It's quiet obvious that AG's RD wouldn't correlate with the profiles that he used as examples and I don't think anybody would rebut that. Since this IS the DIR forum, and per forum rules, only DIR answers are allowed, then it really makes phils question null, since it doesn't really follow what people are taught about standard gases from GUE.

 

[cool_hardware52]

Finaly we agree on something, Tobin!!!

Thanks, Clare for helping clearify what we have been saying.

Milo

Clare's post was well written, polite, free of bluster and unnecessary scolding. Not a single :no

I found it informative, and a welcome contribution, in short helpful and classy. Exactly what I'd hope the "DIR curious" might see.

I hope to see more contributions of like kind.

Tobin

 

[rjack321]

The only thing I have to add to James' synopsis is that we don't push ppO2s deep. None of the "best mix" concept (e.g. up to 1.4 consistently on the bottom) enters into a DIR team's planning.

Standard gases avoid that too. 30/30 being the bucktooth stepchild. And not so oddly off Mr RDs radar.

 

[Meng_Tze]

An approximation of an approximation can't be more accurate than what it's trying to approximate.

Actually it can sometimes...... some call it 'lucky shot'. Not sure if that applies here, this is all 'black magic ' to me....
I mean. We don't know how deco works, but we do know empirically what does/does not work. We have mathematical models that approximate our body's reactions to thei diving thing and some come close to empirical data, others are tweaked (GF, deep stops, more compartments, new compartments, dissolved gas etc). But what RD seems to do is merely shape the rough edges out of the profile based on empirical data. This sometimes works, and sometimes doesn't. By closing variables as gas selection and ratio's between stop times.... you get ever closer. A wrapper around something that is not exactly predictable and computable (analogous to circular integral calculation of a point charge effect on a space contained in a sphere...... ) . I admire the findings (not only RD, but deco models in general), but do think that things are too polarized around this.

Back to lurking

 

[vbcoachchris]

Here is an email I sent to AG about RD and his reply. You can see he does not think that the Back Gas mix matters that much.


"I have read a lot of information about exceeding MDL in the 80 -110 fsw range on 30 /30 and 21/ 35 in the 120 -150 fsw range. NAUI Helitrox however is only 26 -30 % oxygen and 13 - 17 % helium, and you still receive certification to 150 fsw. How can you apply ratio deco to these mixes? Looking at the NAUI Helitrox course description for 5th D X, I gathered you talk about ratio deco in your course. "

His reply

"Chris

Excellent question. In reallity Ratio is designed to be, backgas (Exponential curve with deep stops) or 1 deco gas - 1:1 (S-curve and deep stops) or 2 deco gases - 1:2 (s-curve, exponential curve and deep stops) and so on. Not really worried about bottom mix percentages. Meaning if you dive 130' with a 26/17 and use back gas only then just use a standard 130' is 5min NDL and deco using backgas with exponential curve beyond that. If you add a deco gas then use 1:1 at 130' for bottom time. would you like examples?

Andrew"

 

[lamont]

You were on a roll until you failed to harmonize your bogus assertion to Scuba Milo's demonstration of a profile where RD is 500% less conservative than D Plan (GF=30/85). What's 5 minutes more or less? Did you just clock out on that one? Until Milo shot it down, you had me convinced that RD is a close approximation of the other scientifically derived algorithms.

I would not consider gradient factors to be scientifically derived.

 

[amascuba]

"Chris

Excellent question. In reallity Ratio is designed to be, backgas (Exponential curve with deep stops) or 1 deco gas - 1:1 (S-curve and deep stops) or 2 deco gases - 1:2 (s-curve, exponential curve and deep stops) and so on. Not really worried about bottom mix percentages. Meaning if you dive 130' with a 26/17 and use back gas only then just use a standard 130' is 5min NDL and deco using backgas with exponential curve beyond that. If you add a deco gas then use 1:1 at 130' for bottom time. would you like examples?

Andrew"

What he is describing here is basically the same concept as "Diving EAN32 using Air tables". It gives you a conservative deco profile for using a non-standard mix.

 

[grazie42]

I, amascuba and data have managed to put together what I/we(?) think is a mostly correct comparison between V-planner +2, RD & GF30/85 on another board, thought it might be of some interest here too (yes I´m stuck inside because there´s a snowstorm outside...I will dive next weekend!)
Here you go:

profiles:
T1-range(?) 21/35 with 50%______V-plan +2________GF30/85__________RD_____________Diff
35m/120ft_________________________18mins__________22mi n_________15mins_____+3 (v-plan) +7(GF30/85)
40m/135ft_________________________25mins__________19mi n_________25mins_____+0 (v-plan) -6(GF30/85)
45m/150ft_________________________32mins__________27mi n_________30mins_____+2 (v-plan) -3(GF30/85)
50m/170ft_________________________39mins___________38m in________40mins_____-1(v-plan) -2(GF30/85)

T2-range(?) 18/45 with 50% +O2____V-plan +2________GF30/85_________RD_____________Diff
55m/180ft_________________________45mins___________41m in_________40mins_____+5(v-plan) +1(GF30/85)
60m/200ft_________________________56mins___________55m in_________50mins_____+6 (v-plan) +5(GF30/85)
65m/220ft_________________________65mins___________69m in_________ 60mins_____+5 (v-plan) +9(GF30/85)
70m/235ft_________________________74mins___________83m in_________ 70mins_____+4(v-plan) +13(GF30/85)