Recreational Ascent Rate in the last 15 feet

[scubadada]

Nice table, did you do one for Air too?

 

[scubadada]

I forgot to mention, for the tables I posted, I used the Saul Recreational Dive Planner to calculate the probability of DCS from the bottom time. If you know the risk you are willing to take, you can also calculate the bottom time from the P(DCS). For instance, if you are diving to 100 feet on air and are willing to take a risk of 0.2% (1/500), your bottom time is 16:48

 

[FreeFlyFreak]

I have enjoyed this thread very much. @rsingler's simulations were particularly interesting. You get a 0-1% decrease in your SurfGF for increasing your SS from 3 to 5 minutes. You get an additional 1-4% for the extra 4 1/2 minutes with the slow ascent. With both the 5 min SS and the slow ascent, you reduce your SurfGF by 2-5%. Overall, these changes seem relatively small.

@dmaziuk pointed out the SAUL probabilistic decompression algorithm. It has been brought up several times previously on SB, I have been following the development over the last 7-8 years. The following table shows the probability of DCS in % for diving up to the NDL using 3 different decompression algorithms. This is with 32% nitrox, depth is in feet, NDL in minutes.The SAUL algorithm includes a 3 min SS

View attachment 551923

So, for a clean, 1st dive, with a 3 min SS, the probability of DCS varies by dive time, or GF high, if you will. To put this into perspective, 0.5% is 1/200. 0.25% is 1/400, 0.1% is 1/1,000, and 0.01% is 1/10,000. Zero in the table is <0.01%

My impression is that we all have to choose a SurfGF range that we are comfortable with. We can continue to debate exactly how we get there.

It appears that the PDCS are off for the 32% GF times, at least when I run them through the SAUL website calculator myself.
I'm getting all zeros PDCS for 75GF
And all zeros at the 80%GF NDL times that I got from my Petrel I haven't dug into your 85 and 95 times yet though.

Maybe I'm doing something wrong??
The air table looks right for the little checking I did @ 80GF times

 

[rsingler]

Nice table, did you do one for Air too?

Similar results, with slightly higher SurGF.
Right now I'm working on a comparison with SubSurface, because my recollection was of a faster improvement in SurGF both when ascending and during a Safety Stop. My mental expectation was of a 1.5-2% improvement in SurGF per minute of near-surface time. That didn't occur using EFX' spreadsheet, so I want to compare. Will report back later today.

 

[Brett Hatch]

It appears that the PDCS are off for the 32% GF times, at least when I run them through the SAUL website calculator myself.
I'm getting all zeros PDCS for 75GF
And all zeros at the 80%GF NDL times that I got from my Petrel I haven't dug into your 85 and 95 times yet though.

Maybe I'm doing something wrong??
The air table looks right for the little checking I did @ 80GF times

Just squinting at scubadada's chart, every P(DCS) is <0.1% in the GFHi=75 column. Perhaps your calculations are rounding off 0.1% (1/1,000) to zero, where scubadada's rounded 0.01% (1/10,000) to zero?

 

[FreeFlyFreak]

Just squinting at scubadada's chart, every P(DCS) is <0.1% in the GFHi=75 column. Perhaps your calculations are rounding off 0.1% (1/1,000) to zero, where scubadada's rounded 0.01% (1/10,000) to zero?

Nope.
The chart posted for 32x GF75 shows 0.03, 0.04, 0.04, 0.02, 0.01 to start
When i run those respective times/depths thru Saul they all come up less than 0.01

Feel free to try it yourself :
SAUL Recreational Dive Planner | Modern Decompression

 

[rsingler]

As promised, here is a comparison of the SurGF numbers from EFX versus SubSurface. I used the dive with the most significant surfacing GF. That is, medium depth for max duration.

At GF 50/75, I dived Air down to an NDL of 1 minute at 48ft. The variables are only Safety Stop duration and ascent rate from 15' to the surface. Ascent rate from depth to SS was 30 fpm for all dives.

The results below are leading compartment (LC) number and compartment half-time, and Surfacing GF (SurGF) from @EFX and from SubSurface.
I can't explain the discrepancy, but I have a PM in to the authors to explore this.

At 48 ft x 57 min:
3min SS; 30 fpm ascent from SS to surface:
EFX: LC #6 (38 min); GF 86
SubSurface GF: 68

5min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 85
SubSurface GF: 65

3min SS; 3 fpm ascent from SS to surface:
EGX:LC #6 (38 min); GF 82
SubSurface GF: 60

5min SS; 3 fpm ascent from SS to surface:
EFX: LC #6 (38 min); GF 81
SubSurface GF: 58

10min SS; 3 fpm ascent from SS to surface:
EGX: LC #6 (38 min); GF 80
SubSurface GF: 54

Subsurface is showing both a lower finishing GF, and a greater improvement with time during the stops/ascents. Obviously, I'd prefer to be at 54 instead of 86, so let's wait to hear from @EFX and @atdotde as to whether we're comparing apples and oranges, or whether there's a calculation issue.

 

[dmaziuk]

Nope. The ascent was very slow. Well below the ascent rate.
Mares Nemo Wide.

Weird. I suppose single-digit NDL is not unusual below 90 feet, but the computer has a sampling interval and a re-calculation interval. If you're coming up slowly, I find it hard to believe it wouldn't re-read the pressure sensor and re-compute your NDL at least a couple of times between "4" and "99". Mares may have programmed in some "interesting" fudge factors I suppose...

 

[scubadada]

It appears that the PDCS are off for the 32% GF times, at least when I run them through the SAUL website calculator myself.
I'm getting all zeros PDCS for 75GF
And all zeros at the 80%GF NDL times that I got from my Petrel I haven't dug into your 85 and 95 times yet though.

Maybe I'm doing something wrong??
The air table looks right for the little checking I did @ 80GF times

I get all the values I posted

 

[FreeFlyFreak]

I get all the values I posted

Weird
You are using the website right, not some app or program that i am unaware of?