Ongoing discussion of Ratio Deco

[ScubaMilo]

Isn't that what I said?



Let me try again since I guess this may have been misinterpreted...

Ratio is never more than 1 minute LESS than decoplanner. It may be more conservative. And you need to add it the deep stop times.

Did you read the second profile I'll write it again for you.

130fsw for 40 min using 21/35 w/ean50
ratio deco says: 30min
d-plan(set at 30/85 GF) says: 35

Deep stop times would be added equally to both profiles so that part is a wash.
Were talking time on the deco bottle here.

Milo

 

[amascuba]

Try 20min at 160fsw using 21/35 w/ean50
ratio deco says: 25min
d-plan(set at 30/85 GF) says:20min

MV-Plan 1.4.2
Settings: GF=30-85 ppH2O=2.041 ftsw
===================================================
DESC:160ft for 02:25 [ 2] on Trimix 21/35, SP: 1.3, END: 73ft
DIVE:160ft for 17:34 [ 20] on Trimix 21/35, SP: 1.3, END: 73ft
ASC : 70ft for 02:43 [ 23] on Trimix 21/35, SP: 0.0, END: 24ft
DECO: 70ft for 00:16 [ 23] on Nitrox 50, SP: 0.0, END: 32ft M-Value: 65% [02], GF: 38%
DECO: 60ft for 01:00 [ 24] on Nitrox 50, SP: 0.0, END: 26ft M-Value: 70% [03], GF: 46%
DECO: 50ft for 01:00 [ 25] on Nitrox 50, SP: 0.0, END: 20ft M-Value: 73% [03], GF: 54%
DECO: 40ft for 01:00 [ 26] on Nitrox 50, SP: 0.0, END: 13ft M-Value: 77% [04], GF: 61%
DECO: 30ft for 02:00 [ 28] on Nitrox 50, SP: 0.0, END: 7ft M-Value: 82% [04], GF: 69%
DECO: 20ft for 04:00 [ 32] on Nitrox 50, SP: 0.0, END: 1ft M-Value: 86% [05], GF: 77%
DECO: 10ft for 08:00 [ 40] on Nitrox 50, SP: 0.0, END: 0ft M-Value: 90% [06], GF: 85%

and try

130fsw for 40 min using 21/35 w/ean50
ratio deco says: 30min
d-plan(set at 30/85 GF) says: 35

Neither is within 1 min as stated.
ratio deco seems to be inconsistent as to being conservative or liberal depending on the profile.

Hope this helps,
|Milo

MV-Plan 1.4.2
Settings: GF=30-85 ppH2O=2.041 ftsw
===================================================
DESC:130ft for 01:58 [ 2] on Trimix 21/35, SP: 1.3, END: 52ft
DIVE:130ft for 38:01 [ 40] on Trimix 21/35, SP: 1.3, END: 52ft
ASC : 70ft for 01:49 [ 42] on Trimix 21/35, SP: 0.0, END: 24ft
ASC : 60ft for 00:18 [ 42] on Nitrox 50, SP: 0.0, END: 26ft
DECO: 60ft for 00:52 [ 43] on Nitrox 50, SP: 0.0, END: 26ft M-Value: 69% [04], GF: 39%
DECO: 50ft for 01:00 [ 44] on Nitrox 50, SP: 0.0, END: 20ft M-Value: 73% [04], GF: 48%
DECO: 40ft for 02:00 [ 46] on Nitrox 50, SP: 0.0, END: 13ft M-Value: 78% [04], GF: 57%
DECO: 30ft for 04:00 [ 50] on Nitrox 50, SP: 0.0, END: 7ft M-Value: 83% [05], GF: 67%
DECO: 20ft for 07:00 [ 57] on Nitrox 50, SP: 0.0, END: 1ft M-Value: 86% [06], GF: 76%
DECO: 10ft for 13:00 [ 70] on Nitrox 50, SP: 0.0, END: 0ft M-Value: 90% [07], GF: 85%

Both profiles are similar to what ratio deco would call for. With ratio deco you would have some deep stops starting at 80% of average depth and the overall shape would be different. More of an S-shape.

On the first profile ratio deco would actually be more conservative.

 

[Meng_Tze]

And that's why I asked Heather....:-0

 

[limeyx]

MV-Plan 1.4.2
Settings: GF=30-85 ppH2O=2.041 ftsw

Both profiles are similar to what ratio deco would call for. With ratio deco you would have some deep stops starting at 80% of average depth and the overall shape would be different. More of an S-shape.

On the first profile ratio deco would actually be more conservative.

EDIT: Duh, didnt read your post properly. nevermind

 

[FishTaco]

MV-Plan 1.4.2
Settings: GF=30-85 ppH2O=2.041 ftsw
===================================================
DESC:160ft for 02:25 [ 2] on Trimix 21/35, SP: 1.3, END: 73ft
DIVE:160ft for 17:34 [ 20] on Trimix 21/35, SP: 1.3, END: 73ft
ASC : 70ft for 02:43 [ 23] on Trimix 21/35, SP: 0.0, END: 24ft
DECO: 70ft for 00:16 [ 23] on Nitrox 50, SP: 0.0, END: 32ft M-Value: 65% [02], GF: 38%
DECO: 60ft for 01:00 [ 24] on Nitrox 50, SP: 0.0, END: 26ft M-Value: 70% [03], GF: 46%
DECO: 50ft for 01:00 [ 25] on Nitrox 50, SP: 0.0, END: 20ft M-Value: 73% [03], GF: 54%
DECO: 40ft for 01:00 [ 26] on Nitrox 50, SP: 0.0, END: 13ft M-Value: 77% [04], GF: 61%
DECO: 30ft for 02:00 [ 28] on Nitrox 50, SP: 0.0, END: 7ft M-Value: 82% [04], GF: 69%
DECO: 20ft for 04:00 [ 32] on Nitrox 50, SP: 0.0, END: 1ft M-Value: 86% [05], GF: 77%
DECO: 10ft for 08:00 [ 40] on Nitrox 50, SP: 0.0, END: 0ft M-Value: 90% [06], GF: 85%



MV-Plan 1.4.2
Settings: GF=30-85 ppH2O=2.041 ftsw
===================================================
DESC:130ft for 01:58 [ 2] on Trimix 21/35, SP: 1.3, END: 52ft
DIVE:130ft for 38:01 [ 40] on Trimix 21/35, SP: 1.3, END: 52ft
ASC : 70ft for 01:49 [ 42] on Trimix 21/35, SP: 0.0, END: 24ft
ASC : 60ft for 00:18 [ 42] on Nitrox 50, SP: 0.0, END: 26ft
DECO: 60ft for 00:52 [ 43] on Nitrox 50, SP: 0.0, END: 26ft M-Value: 69% [04], GF: 39%
DECO: 50ft for 01:00 [ 44] on Nitrox 50, SP: 0.0, END: 20ft M-Value: 73% [04], GF: 48%
DECO: 40ft for 02:00 [ 46] on Nitrox 50, SP: 0.0, END: 13ft M-Value: 78% [04], GF: 57%
DECO: 30ft for 04:00 [ 50] on Nitrox 50, SP: 0.0, END: 7ft M-Value: 83% [05], GF: 67%
DECO: 20ft for 07:00 [ 57] on Nitrox 50, SP: 0.0, END: 1ft M-Value: 86% [06], GF: 76%
DECO: 10ft for 13:00 [ 70] on Nitrox 50, SP: 0.0, END: 0ft M-Value: 90% [07], GF: 85%

Both profiles are similar to what ratio deco would call for. With ratio deco you would have some deep stops starting at 80% of average depth and the overall shape would be different. More of an S-shape.

On the first profile ratio deco would actually be more conservative.

I'm not arguing if one method is more conserative or not. Just that Ratio Deco is not consistent; If you take Ratio Deco to its set point extremes you'll find even greater inconsistencies, at least at the T1 level.

BTW, every DIR diver I know modifies the shape of the ascent and adds in deep stops.

Chris

 

[amascuba]

I'm not arguing if one method is more conserative or not. Just that Ratio Deco is not consistent; If you take Ratio Deco to its set point extremes you'll find even greater inconsistencies, at least at the T1 level.

BTW, every DIR diver I know modifies the shape of the ascent and adds in deep stops.

Chris

Actually I think that Ratio Deco is actually more consistent. You have set rules for say within the 180fsw range of deco 1:1 of BT at 150 and +/- 5min. +/- 10fsw beyond that. All this on a standard back gas of 21/35 or 18/45 with a single deco gas of 50%.

I guess what I'm saying is that if you give a person the tools to do it they should come up with the same answers as somebody else, but the actual deco programs may vary some from program to program.

Does Ratio Deco give different answer then the decompression software? Yes, and it shouldn't really be a surprise that it does. You should know that it's going to vary some or maybe allot depending on the decompression application and algorithm.

It's like comparing the VPM model to the navy tables and saying that the VPM model is inconsistent because they don't closely match what the navy tables say.

 

[MaxBottomtime]

Its the ignorant who are critical by and large.

If you read George Irvine's Gavin scooter list you would find several examples of GI arguing with AG over Ratio Deco. Irvine showed some examples of dives in the 250-300 feet range where ratio deco didn't come close to his minimum deco that he and J.J. came up with after years of diving Wakulla. J.J. said he told Andrew about minimum deco during a plane ride back from Europe but Andrew dumbed it down in such a way that GI says it should not be considered DIR.

 

[ScubaMilo]

Actually I think that Ratio Deco is actually more consistent. You have set rules for say within the 180fsw range of deco 1:1 of BT at 150 and +/- 5min. +/- 10fsw beyond that. All this on a standard back gas of 21/35 or 18/45 with a single deco gas of 50%.

I guess what I'm saying is that if you give a person the tools to do it they should come up with the same answers as somebody else, but the actual deco programs may vary some from program to program.

Does Ratio Deco give different answer then the decompression software? Yes, and it shouldn't really be a surprise that it does. You should know that it's going to vary some or maybe allot depending on the decompression application and algorithm.

It's like comparing the VPM model to the navy tables and saying that the VPM model is inconsistent because they don't closely match what the navy tables say.

If ratio deco was consistently conservative or consistently liberal I could see your point.
But it has a tendancy to swing from one end of things to the other.
Also I am not saying it is not a usefull tool.
Just not the primary planing tool.

Milo

 

[FishTaco]

Anyway, I have found ratio deco quite reliable. Total stop time is never less than 1 minute from decoplanner.

amascuba, I was only questioning rjack's comment.
Like I said before, I've used ratio deco effectively, and for certain profiles will continue its use. I just have more faith in a deco program backed by science.

Take care,
Chris

 

[amascuba]

If you read George Irvine's Gavin scooter list you would find several examples of GI arguing with AG over Ratio Deco. Irvine showed some examples of dives in the 250-300 feet range where ratio deco didn't come close to his minimum deco that he and J.J. came up with after years of diving Wakulla. J.J. said he told Andrew about minimum deco during a plane ride back from Europe but Andrew dumbed it down in such a way that GI says it should not be considered DIR.

Don't you mean Maximum Deco? At any rate, it's pointless to fuss with terming semantics.

Ratio Deco by default is fairly conservative. Over a period of time, as a diver/team gains experience, and knows his/her limits then changing aspects of ratio deco is up to the individual or team.

Beyond that, since you read the gavin scooters list, When does George Irvine EVER AGREE with anything that AG does or says, whether it be Ratio Deco or even how to make a quality scooter?