[quote=GLOC;882174]Sorry for the delay Mark in replying, been busy with the kids.
Quote:
A couple of points on what you have said above.
1. Ratio Deco works because, within a certain window of operation, a certain increase in bottom time, increases the deco obligation by the same amount. I ran through some examples last night using 45m (limit of DP qualification) and 25% & 50% alongside 21/35 & 50%, GF 30/85, to see what figures came out. You are correct that the times are very similar but if you the depths are changed the deco time changes are not quite linear (and neither are the standard gas deco times) but the way the times are spread/change would be harder to do from memory. As you increase times from 30mins to 50mins at 39m using 25% & 50%, the change becomes closer to 2:1 rather than 1:1 at 30mins whereas 21/35 and 50% still remains at 1:1.
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To save time you could point me at the profile you think dosent work?
You can't realy use 30/85 to mimic ratio deco you need to use 10/100. I know they tell you to use 30/85 for comparison but it will only confuse people
The 30/85 GF deco for 45mins at 50m is 73mins with a first stop at 30m and 45mins at 6m. How on earth does that give you a comparison with the ratio deco profile which starts at 36m, 26 at 6 and a total of 57mins deco?
For the 39m dive your on the wrong gas. We use 1.4 at planned max depth so we would be on 28% Nitrox
45min @ 39m 28% and 50% 10/100GF
1 @ 15
3 @ 12
3 @ 9
17 @ 6
45mins @ 39 21/35 and 50% 10/100GF
1 @ 24
1 @ 21
1 @ 18
1 @ 15
3 @ 12
4 @ 9
24 @ 6
Ratio deco set point 45m - 5min for every 3m
39 m therefore take away 10
45mins @ 39m on 21/35 & 50 % Ratio deco
1@27
1@24
4@21
3@18
2@12
9 @ 9
18@6
If you look at RD for this dive compaired to the 28% profile you can see its much closer than the GF comparison with 21/35
OK if you say you dont want to dive 1.4 at max depth we could use 25%
1 @21
1 @18
1 @15
2 @12
4 @ 9
20 @6
Still prety good
The long and short of it is its close enough for jazz.
MUCH more importantly I was taught on my DP course to look at at least two generated profiles and compair notes. I used to use Proplanner and Decoplanner to pre plan deco.
Back in the day before DOTF was made public I had already figured out there was a ratio between depth bottom time and deco. I did this by looking at the profiles put out by the software. However I thought the ratio was more like 1.5/1 because I used more conservative settings.
I use ratio deco today on dives to 70m on CCR. I estimate my max and min bottom times and put the numbers in the computer then i work out the ratio. I see where its aggressive or not and make a mental note to run straight ration or to pad.
Then on the actual dive if my computer fails I switch to ratio deco but i already know to add 20% or what ever to my shallow stop times. Its a shotgun approach to deco but these days it doesn't bother me at all. The days where i felt deco was an exact science are long gone.
Nothing wrong with what your saying generally in the thread its all good stuff. I am just highlighting the issue of using RD for gas sets outside of GUE standards. For me this meant using 50% as a deco gas and best mix for the bottom and clearing deco before doing a 6min ascent from 6m to the surface.
If you do this it either works close enough or its very conservitave. Thats good enough for me.
ATB
Mark