Retroactive gradient factor/tissue saturation calculation

[ChrisMBC]

I've read the materials on T1-level ratio deco (max 51m, 30 mins deco time) from the GUE course material and this InDepth blog. While I conceptually understand ratio deco and the parameters within which it makes sense, I'd like to understand the impact of the deep stop:6m stop rationalization. All the ratio deco material I've seen focuses on total deco time, but particularly as you stretch the envelope of the ratio deco applicability (long 32% dives/ long times at 39m), the differences between Decoplanner and ratio deco on the intermediate stops become quite severe.

To understand the impact better, I'd like to run a bunch of ratio deco profiles through something that can tell me the gradient factors and tissue saturation at different points in the dive (essentially just the GF99 compared to the profile). The problem I'm having is that all the dive planning tools create a dive profile for you, rather than analyzing an existing dive profile. I was thinking of creating spoofed log files and feeding them to Subsurface, but that seems quite difficult. Before I go to that level of effort, does anyone have a better solution for testing a bunch of ratio deco profiles in this manner?

 

[jborg]

You mention Subsurface, and spoofing log files, and I might be missing your point or your problem but it seems to me that Subsurface does what you ask for. In the dive planner, describe your profile in terms of depth/time pairs, and you can read GF & SurfGF from any point in the profile.

 

[L13]

As @jborg said, Subsurface is exactly the tool you are looking for.

 

[Matan]

If you've taken T1 - contact your instructor.
If you haven't taken T1 - contact a GUE instructor to start working on becoming a T1 diver - you won't be disapointed.

To answer to the topic at hand (based on my personal opinion):

All the ratio deco material I've seen focuses on total deco time, but particularly as you stretch the envelope of the ratio deco applicability (long 32% dives/ long times at 39m), the differences between Decoplanner and ratio deco on the intermediate stops become quite severe.

1. GUE SOP - all decompression should be planned based on Decoplanner.
2. GUE divers are taught to use Decoplanner to create an adjustable plan that will fit their dive.
3. regarding long %32 dives AKA 100ft/30m range - where I would deco using Oxygen (for example 50-55' at 100ft/30m with a double 12 and a DPV) - I don't see much difference between Decoplanner and what I want to do in the water.
4. 39m - Use trimix + nitrox 50% - Fits perfectly to T1 level dives as well.

Matan.

 

[rjack321]

Your 1:1 ratio deco lines won't fit outside of the 20-30mins Decoplanner derived/T1 deco parameters. RD is taking a line and drawing it through a curve with some tweaks because deco is always curvilinear. Its close enough (if you accept the 30/85 GFs it's based on) within T1 dives.

If you want to do a dive outside of those parameters (or more conservative/modern than 30/85) then use decoplanner as GUE recommends to come up with a plan.

If you havent taken T1 then you should probably do that first.

 

[rjack321]

You mention Subsurface, and spoofing log files, and I might be missing your point or your problem but it seems to me that Subsurface does what you ask for. In the dive planner, describe your profile in terms of depth/time pairs, and you can read GF & SurfGF from any point in the profile.

View attachment 791464

You can also put the RD profile into something like multideco or decoplanner, and let the software choose how long your 10ft stop needs to be to make up for what RD told you was "enough" deco. This is especially useful if you arent comfortable diving a GF high of 85 and want to plan for something more in line with modern conservative GFhighs. (65-75ish)

 

[ChrisMBC]

If you've taken T1 - contact your instructor.
If you haven't taken T1 - contact a GUE instructor to start working on becoming a T1 diver - you won't be disapointed.

To answer to the topic at hand (based on my personal opinion):

1. GUE SOP - all decompression should be planned based on Decoplanner.
2. GUE divers are taught to use Decoplanner to create an adjustable plan that will fit their dive.
3. regarding long %32 dives AKA 100ft/30m range - where I would deco using Oxygen (for example 50-55' at 100ft/30m with a double 12 and a DPV) - I don't see much difference between Decoplanner and what I want to do in the water.
4. 39m - Use trimix + nitrox 50% - Fits perfectly to T1 level dives as well.

Matan.

I took T1 late last year. I'm not confused about how to plan dives to SOPs (either Decoplanner + pragmatize, or ratio deco) - the part I'm particularly curious about is how much difference we'd see in surfGF for a pragmatic/ratio profile vs a pure Decoplanner profile, given the increase in time spent deeper.

A sentiment that I've heard a lot locally is that total deco time is the important thing, and the ratio/pragmatic tendency to have a higher proportion of deco time being deeper doesn't make much of a real difference. I absolutely don't deny that for T1 dives to T1 depths, it's probably not making a huge difference - I am just academically interested in understanding the effectiveness of those deco strategies, as evaluated by the algorithm (B-16C) that GUE uses. If, on the margins, a pragmatic or ratio deco strategy resulted in a surfacing GF of 105 rather than 85%, I'd be interested to know that. If it results in a surfGF of 87, even better.

You mention Subsurface, and spoofing log files, and I might be missing your point or your problem but it seems to me that Subsurface does what you ask for. In the dive planner, describe your profile in terms of depth/time pairs, and you can read GF & SurfGF from any point in the profile.

View attachment 791464

I feel like an idiot....I'm not a frequent Subsurface user, and I didn't realize that you can see the GF/SurfGF for a planned dive. This is exactly what I was looking for. Thanks!

 

[L13]

A sentiment that I've heard a lot locally is that total deco time is the important thing, and the ratio/pragmatic tendency to have a higher proportion of deco time being deeper doesn't make much of a real difference.

This is absolutely NOT true. The depth of the deco stops do mater (if you care about GF's at all), and deeper stops require more time at shallow stops to surface at the same GF's. For short deco dives, the difference is minimal the longer and deeper the deco starts, the more of a difference it makes.

This is easily proved with Subsurface (provide you buy into GFs at all).
I put in a somewhat silly example dive, 130 ft for 1 hour, on air with 80% for deco.

With VPM-B+1 (a deep stop algo) deco time was 58 min with a surfacing GF of 104% (peak GF on stops of 87%).

With B-16C+GFs you get the same 58 min deco time with 80/85 surfacing at GF of 82% (Peak GF on stops of 76%).

It took VPM-B+4, with an extra 15 min of deco, to get surfacing GF down to the B-16C GF80/85 level of 82%.


Unless you believe that Micro-Bubble formation is much more critical than supersaturation(GF), you will not spend any more time at deeper stops than absolutely necessary to limit the GF peak at the next stop.

 

[rjack321]

This is absolutely NOT true. The depth of the deco stops do mater (if you care about GF's at all), and deeper stops require more time at shallow stops to surface at the same GF's. For short deco dives, the difference is minimal the longer and deeper the deco starts, the more of a difference it makes.

This is easily proved with Subsurface (provide you buy into GFs at all).
I put in a somewhat silly example dive, 130 ft for 1 hour, on air with 80% for deco.

With VPM-B+1 (a deep stop algo) deco time was 58 min with a surfacing GF of 104% (peak GF on stops of 87%).

With B-16C+GFs you get the same 58 min deco time with 80/85 surfacing at GF of 82% (Peak GF on stops of 76%).

It took VPM-B+4, with an extra 15 min of deco, to get surfacing GF down to the B-16C GF80/85 level of 82%.


Unless you believe that Micro-Bubble formation is much more critical than supersaturation(GF), you will not spend any more time at deeper stops than absolutely necessary to limit the GF peak at the next stop.

Could you at least make at least a *teeny tiny* effort to stick to the T1 parameters that were brought up here in the first place? 30mins Max deco, one deco gas, GUE (or humor us and use UTD's at least) standard gasses.

 

[L13]

Could you at least make at least a *teeny tiny* effort to stick to the T1 parameters that were brought up here in the first place? 30mins Max deco, one deco gas, GUE (or humor us and use UTD's at least) standard gasses.

I did only have 1 deco gas. Not worth the effort to implement any of those to demonstrate the point: If you consider super-saturation (GF) significant then deep stop profiles will either have longer deco times, or higher GFs, or both.

Droping to a 30min max deco wont change that fact. changing deco gases wont change that fact.

But here you go. 34 min dive to 130ft on 21/35 with 100% deco gas:

• VPM-B deco time 30 min, surface GF 90% max stop GF 73%.
• 
  
• B-16C GF70/75 deco time 30 min, surface GF 74%, max stop GF 67%.
• 
  
• To match surfacing GF, VPM-B+4 deco time 44 min, surface GF 73%.

Of course if you are more concerned about Micro-Bubble formation, none of this matters. But in that case, why bother with any kind of science at all if you are going to ignore recent research anyway.