Your Gradient Factors?

[rjack321]

This thread has been enlightening because I was not expecting 90s and 95s to be this common. Some have been diving past 100!

Long long ago (1990s and early 2000s, 20 years might as well be the dark ages of decompression) when people thought Buhlmann was bunkus, they padded the deeper stops and ran >100 high. This was after Yount's paper (late 1980s), but before VPM was widely published or usable commercial code was written.

 

[kensuf]

Why is that Kensuf

Because my experience has taught me that on super short decompressions (<10 minute mandatory deco), adding a little conservatism isn't a bad thing, and that on super long decompression (4+ hours), it's not necessary.

 

[gbirch]

OK, I'll bite, what is the rationale for GF High of >100?

 

[nadwidny]

OK, I'll bite, what is the rationale for GF High of >100?

The thinking was that with deep stops, time at the shallow stops could be shaved off.

 

[_Ralph]

I have no idea what my average depth is when surfacing, I don't really look at average depth or see why I would. Sometimes I look at surfGF to pad the conservatism beyond my normal plan, if there's no pressing reason to get out I'll hang out until it drops to 60 or something. That may parallel your average depth method. What's the trend you're referencing?

Anyway, it's possible I was misreading your post, but what I was calling crazy wasn't anything to do with average depth or gradient factors. It was the act of rocketing up to the surface from 6m and breaching yourself onto the swim platform. Those last several meters are the part of the ascent where pressure change (and gas expansion, aka bubble formation) is greatest and you should go the slowest. I make a point of going extremely slow between the last stop to the surface, especially with demanding or multiple dives.

What does GF impact regarding depth?
What does changing a value change regarding depth?

_R

 

[tursiops]

No idea... I just like to Polaris missile myself from 6m onto the swim grid once my average depth hits 21m again.... DM’s dig it!

What’s your average depth when you get out of the water for a deco dive?

Notice any trends?

What does GF impact regarding depth?
What does changing a value change regarding depth?

What are you talking about? How does average depth relate to GFs? How does GF affect depth?

You seem to have something in mind, but can you please be a little less cryptic? Maybe, just come out and say it instead of playing guessing games?

 

[JonG1]

Because my experience has taught me that on super short decompressions (<10 minute mandatory deco), adding a little conservatism isn't a bad thing, and that on super long decompression (4+ hours), it's not necessary.

How did you arrive at this conclusion pls, obvious signs of stress, Doppler etc?

Also any difference in thinking depending on profile, so 4 hours could accumulate over a really long dive at shallowish depth, versus a deep "bounce"?

 

[beester]

Typical normoxic dives (35-55m) I'll run 80-85. Deeper and longer 90. Shallower (but longer) I run very conservatively (60-70), I've seen too many hits on 30-40m dives vs 60-90m.

The ideal answer would be to experiment yourself, because your body is different from everybody elses, and decompression is a complex biochemical reaction. However... I struggle to get a significant baseline (enough dives) to get a good guideline. On 40-60m dives I've done enough dives to know how I react (close to 200), but deeper longer dives I don't... but that's also where it becomes more complicated and a general doesn't apply anymore... so it stays a bit black magic.

Next to deco plan and/or shearwater I also check the average depth at certain depths to see if I'm on deco target, meaning on deeper dives I don't want to get out of the water with an avg depth of more than x and I also don't want to move up from 9 to 6m before my avg depth reaches a certain depth even if the plan or computer says I can move up.

I'm not going to mention the depths I use, because I don't want to feel responsible for someone elses experimenting, but I'm sure if you do enough dives you'll see a certain correlation.

cheers

B

PS: I see someone else already mentioned avg depth (Ralph) ;-)

 

[tursiops]

Typical normoxic dives (35-55m) I'll run 80-85. Deeper and longer 90. Shallower (but longer) I run very conservatively (60-70), I've seen too many hits on 30-40m dives vs 60-90m.

The ideal answer would be to experiment yourself, because your body is different from everybody elses, and decompression is a complex biochemical reaction. However... I struggle to get a significant baseline (enough dives) to get a good guideline. On 40-60m dives I've done enough dives to know how I react (close to 200), but deeper longer dives I don't... but that's also where it becomes more complicated and a general doesn't apply anymore... so it stays a bit black magic.

Next to deco plan and/or shearwater I also check the average depth at certain depths to see if I'm on deco target, meaning on deeper dives I don't want to get out of the water with an avg depth of more than x and I also don't want to move up from 9 to 6m before my avg depth reaches a certain depth even if the plan or computer says I can move up.

I'm not going to mention the depths I use, because I don't want to feel responsible for someone elses experimenting, but I'm sure if you do enough dives you'll see a certain correlation.

cheers

B

PS: I see someone else already mentioned avg depth (Ralph) ;-)

What, exactly, does average depth have to do with nitrogen uptake?

 

[100days-a-year]

Hi @100days-a-year

You're right, the Orca Edge appears to run a GF high of around 90-95 on 1st, clean dive. Do you have any idea how it performs on repetitive dives? I've never been able to find any information on this. For example, DSAT is generally a bit more liberal than a GF high of 95 on the 1st dive. On repetitive dives, a GF high of 95 tends to become more liberal than DSAT, particularly at shallower depths.

View attachment 625528 View attachment 625531

They tend to be extremely liberal for shorter repetitive dives.
Running against older Cochrans it seemed they were only a little more conservative than a 0 setting. The guys doing similar BTs would have a higher incidence of getting bent with Cochrans with no conservatism.
In the range we preferred, 120' to 180' , it was pretty easy to get a lot more actual bottom time doing multiple shorter dives vs a couple longer. Often you would nearly clear on your ascent if you didn't overstay. This also helped the other divers as we got paid on production and lengthy decos were frowned on.
Shallower than 120' and you would be better served diving most modern liberal nitrox computers.
It sounds sketchy and is but over a lot of years and 10s of thousands of dives or more guys got a sense of what worked empirically.
My personal rule was to run BTs that me an RT of ~ 25 minutes all day for days on end.
I think with a Shearwater in parallel I could have downloaded all those profiles to see how they compared to GFs.
I do know my heaviest trips were 6-7 dives up to 7 days in a row doing ~25 min RTs on ~2hr SIs in depths up to 180' without incident and several guys exceeded that.