What's your Low Gradient Factor Selection

[jptaylor9]

Well, in David Doolette's case you are unfortunately quite wrong. Although he is a world-renowned decompression physiologist who works at NEDU and knows more about the subject than almost anyone else on the planet, he also is a very accomplished technical diver who has done some pretty outstanding cave exploration with the WKPP. So he does know exactly how we dive, and has enough insight into the inevitable limitations of the scientific evidence that he can produce a pretty well-argued opinion about most decompression topics that technical divers talk about. If you haven't already, try reading some of his posts in the infamous 'Deep Stops' thread on the other forum.

I am away of David Doolette's personal diving experience & respect his opinion, did listed to the interesting presentation referenced in this thread. However, will NEDU give him the time/budget to test the gases we dive? I doubt it, that was the point I was making...

 

[Igor P]

I am away of David Doolette's personal diving experience & respect his opinion, did listed to the interesting presentation referenced in this thread. However, will NEDU give him the time/budget to test the gases we dive? I doubt it, that was the point I was making...

The seccond question is: will NEDU geave him money to test true profiles we dive? My opignion is probably not.

Back to main question, which GF do divers use in their diving? I see most numbers arround 30 for GF-lo.... this tells me something.

Waiting to see if this changes throught time.... usualy practices tells what is good and what is bad.



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[garethingham]

True profiles? The Navy is funded by the taxpayer, they spend money like every other govt organisation on the the things that benefit them/taxpayer/USA. Last time I checked, trimix wreck diving and cave diving were not high on the list of Navy Divers, Seal Teams.

If we are all serious about this stuff we should tip our own dollars into a big pool so we can fund our own research.

 

[jptaylor9]

True profiles? The Navy is funded by the taxpayer, they spend money like every other govt organisation on the the things that benefit them/taxpayer/USA. Last time I checked, trimix wreck diving and cave diving were not high on the list of Navy Divers, Seal Teams.

My point exactly....

If we are all serious about this stuff we should tip our own dollars into a big pool so we can fund our own research.

We don't need to, just use VPM..:devilban:

 

[Mark Chase]

We don't need to, just use VPM..:devilban:

Ignorance is bliss

ATB

Mark

 

[Simon Mitchell]

We don't need to, just use VPM

You seem genuinely interested in this issue. The reasons why there is a growing trend to de-emphasise deep stops, the justification for such a trend, and the explanation as to why David's work is already highly relevant to technical diving can be found in the threads on RBW. The issue was exhaustively debated and the outcome in the court of opinion among participants (many of whom were extremely well informed people) is clear.

The main thread can be found here:

http://www.rebreatherworld.com/gene...6994-deep-stops-debate-split-ascent-rate.html

A follow-up thread which in some ways is even more informative can be found here:

http://www.rebreatherworld.com/gene.../48083-deep-stops-rebreather-dive-charts.html

And a post by me attempting to summarise important points and direct the reader to key posts can be found here:

http://www.rebreatherworld.com/447844-post131.html

Simon M

 

[dmainou]

Amen

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[jptaylor9]

You seem genuinely interested in this issue. The reasons why there is a growing trend to de-emphasise deep stops, the justification for such a trend, and the explanation as to why David's work is already highly relevant to technical diving can be found in the threads on RBW. The issue was exhaustively debated and the outcome in the court of opinion among participants (many of whom were extremely well informed people) is clear.

Interesting discussion, but I don't intend to change my decompression style. I'd rather base my descision on my own first hand experience, rather than experts, no matter how well qualified they are. My buddy & me have done many dives using VPM without issue & feel good after the dive.... that's me signing off this thread.

Amen

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If you don't have anything to contribute, don't bother posting this shite!

 

[Baron015]

Interesting discussion, but I don't intend to change my decompression style. I'd rather base my descision on my own first hand experience, rather than experts, no matter how well qualified they are. My buddy & me have done many dives using VPM without issue & feel good after the dive.... that's me signing off this thread.

You will accept that some of us want to consider new information as it becomes available and integrate it into our diving. I used to be a deep stopping VPM advocate myself, and frequently felt like I'd been run over by a bus after a deep/long dive, but since moving to Buhlman/GFs and increasing GF-lo and reducing GF-hi I've done many dives without issue and feel better than ever after the dive. So seems like an improvement for me, although sample of 1 and psychosomatic effects not ruled out.


---
The first principle is that you must not fool yourself - and you are the easiest person to fool.

 

[jptaylor9]

You will accept that some of us want to consider new information as it becomes available and integrate it into our diving. I used to be a deep stopping VPM advocate myself, and frequently felt like I'd been run over by a bus after a deep/long dive, but since moving to Buhlman/GFs and increasing GF-lo and reducing GF-hi I've done many dives without issue and feel better than ever after the dive. So seems like an improvement for me, although sample of 1 and psychosomatic effects not ruled out.

If you read my posts I don't see that the first stop on VPM are much/if at all deeper than a GF profile & I feel fine after the dive. I don't feel like I've been run over by a bus. I initially dive 15/85 (Vision default) then moved to 10/90, then 10/95. Now I dive VBM-B/GFS (note the shallow GF that extends the shallow stop) with my Vision on 30/95. I don't dive a "pure" VPM profile it's a hybrid VPM/GF profile.

As I don't get bent & feel great after a dive, why should I change my deco, as change involves risk?

 

[matt]

The issue was exhaustively debated and the outcome in the court of opinion among participants (many of whom were extremely well informed people) is clear.

...since moving to Buhlman/GFs and increasing GF-lo and reducing GF-hi I've done many dives without issue and feel better than ever

What's the "consensus" on GF settings?

I'm broadly following this table from the APD manual, BTW:

Cheers
Matt.

 

[Baron015]

If you read my posts I don't see that the first stop on VPM are much/if at all deeper than a GF profile & I feel fine after the dive. I don't feel like I've been run over by a bus. I initially dive 15/85 (Vision default) then moved to 10/90, then 10/95. Now I dive VBM-B/GFS (note the shallow GF that extends the shallow stop) with my Vision on 30/95. I don't dive a "pure" VPM profile it's a hybrid VPM/GF profile.

As I don't get bent & feel great after a dive, why should I change my deco, as change involves risk?

Yes, but there are other people diving apart from you. They might want to change based on new information.


---
The first principle is that you must not fool yourself - and you are the easiest person to fool.

 

[jptaylor9]

Yes, but there are other people diving apart from you. They might want to change based on new information.

There was me thinking a forum is a place for discussion & folks are free to post different/opposing opinions/arguments

Next you'll say you believe in global warming because of all the experts that back it, even though there are other experts that say it isn't happening....

 

[Igor P]

Yes, but there are other people diving apart from you. They might want to change based on new information.


---
The first principle is that you must not fool yourself - and you are the easiest person to fool.

I think he nowere wrote others should do what he does.
Everyone should model his deco based on his state after dives....
What works for me not necesarely works for you and vice versa....


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[Baron015]

What's the "consensus" on GF settings?

I'm broadly following this table from the APD manual, BTW:

Cheers
Matt.

I've moved to 70/70 on trimix dil to 80m. I'm still alive and happy, and feel better after my dives as far as I can tell. Eg yesterday after diving the Duke I happily drove to Wales wide awake, in the past I used to be micro-sleeping just going back to south London.

Deeper than that I'd be tempted to use 50/70 but that would be just fear of change, rather than any actual evidence, after some time I would plan to increase lo GF for that too.

120m 4hrs+ who f'ing knows, but I'm thinking of not doing too much of that any more as the long deco tests my mental willingness to remain in the water for that extra hour.


---
The first principle is that you must not fool yourself - and you are the easiest person to fool.

 

[dmainou]

If you don't have anything to contribute, don't bother posting this shite!

Yeah mate, problem is that I did read the whole thread posted by Simon. It's all there. You can continue to deco however you want but the numbers are there and essentially there is strong evidence that indicates that vpm is not the most efficient model around. Research continues into what is the most efficient model, however, we KNOW what's not.

Not planning to start a re run of the above quoted threads. Up to you if you dig your head in the sand.

D



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[matt]

The problem with the thread on the other place is that it is too long! Luckily Simon took the time to summarise in post 106 - now that is very useful.

I think I'm going to move from 15/85 to 50/80 or 50/85 (maybe 70/70, who knows!) - but first I'm going to check out some profiles out and see if they seem right.

Personally I've never dived VPM as the profile didn't look good to me - but that was 10 years ago. I think now the profiles are pretty similar and from what Jon says VBM-B/GFS and 30/95 are, at least.

Good thing about GF is that you can dial what deco you like.

Matt.

 

[jptaylor9]

I've moved to 70/70 on trimix dil to 80m. I'm still alive and happy, and feel better after my dives as far as I can tell. Eg yesterday after diving the Duke I happily drove to Wales wide awake, in the past I used to be micro-sleeping just going back to south London.

OK, I've put my last 62m dive (38mins BT), 12/42 diluent, SP=1.30 thru MultiDeco on a GF plan of 70/70. On that plan the first stop is at 27m & the overall runtime is 130mins with 51mins @ 6m.

Using VPM-B+3 / GFS 95% (what I dive), the first stop is at 39m, but the're only 1min stops so just a 3m/min ascent rate to 30m where there is a 2min stop (only 3m deeper than 70/70). the overall runtime is 120mins (10mins shorter) with 40mins @ 6m. My ascent rate to the first stop is like Chasey's about 7m/min, 10m/min is just too fast on a RB especially when reeling up (doable if coming up a shot line).

On 70/70 your at 27m by RT=43, on my VPM/GFS it's 5mins later at 48m.

By the time I get to 39m I'm happy to have a rest as I ascend slowly to 27m, allowing my unit to stabalise the set-point/loop volume after the initial ascent from the bottom.

Each to there own, but the difference is marginal IMO, & if your using a real-time computer to calc it rather than desktop tables the diffence will most likely get lost in the real-time adjustments...

To stay within the 2hr runtime limit set by our skippers, I'd have to reduce my bottom time to 25mins on GF 70/70 rather than the 38mins I did (i.e. 13mins more bottom time)

 

[Baron015]

OK, I've put my last 62m dive (38mins BT), 12/42 diluent, SP=1.30 thru MultiDeco on a GF plan of 70/70. On that plan the first stop is at 27m & the overall runtime is 130mins with 51mins @ 6m.

Using VPM-B+3 / GFS 95% (what I dive), the first stop is at 39m, but the're only 1min stops so just a 3m/min ascent rate to 30m where there is a 2min stop (only 3m deeper than 70/70). the overall runtime is 120mins (10mins shorter) with 40mins @ 6m. My ascent rate to the first stop is like Chasey's about 7m/min, 10m/min is just too fast on a RB especially when reeling up (doable if coming up a shot line).

On 70/70 your at 27m by RT=43, on my VPM/GFS it's 5mins later at 48m.

By the time I get to 39m I'm happy to have a rest as I ascend slowly to 27m, allowing my unit to stabalise the set-point/loop volume after the initial ascent from the bottom.

Each to there own, but the difference is marginal IMO, & if your using a real-time computer to calc it rather than desktop tables the diffence will most likely get lost in the real-time adjustments...

To stay within the 2hr runtime limit set by our skippers, I'd have to reduce my bottom time to 25mins on GF 70/70 rather than the 38mins I did (i.e. 13mins more bottom time)

As you say, changing the parameters makes only small changes to the profile. But maybe these small changes are important, maybe not.

Yes I've had to cut my bottom times since changing to new GFs, but I feel miles better. I think these are connected. And it's not so bad since profiles typically multilevel anyway.

I may revise this and move the GF-hi to 75 after a bit and see if I still feel as full of beans afterwards, that will allow a smaller reduction in bottom times which would be nice.

Someone who shall remain nameless (and not me) not only blatantly put down a runtime of 130 mins on Choppy's boat yesterday when filling in his details on the dive sheet, he was late and actually did 145 mins, and rightfully got a stern bollocking from Steve on surfacing. So I am with you on trying to maximise the value you get out of a two hour limit.

 

[dmainou]

Each to there own, but the difference is marginal IMO, & if your using a real-time computer to calc it rather than desktop tables the diffence will most likely get lost in the real-time adjustments...

To stay within the 2hr runtime limit set by our skippers, I'd have to reduce my bottom time to 25mins on GF 70/70 rather than the 38mins I did (i.e. 13mins more bottom time)

I would read at least the summary post from Simon. You do not have to have a longer run time. In fact, that is most of the discussion on the thread. Essentially the summary of the summary is like this. Every minute that you spend on gassing your slow compartments during a deep stop is detrimental to the overall decompression when compared to a profile that swaps that minute to a shallow stop. Now the question is where to start the stops? The answer is we don't know but somewhere in between the known shallow stop models and the deep stop models.

In practice. Play with your GF'S to obtain a profile which you are comfortable with that has a run time of two hours and bottom time of 38 minutes which starts the stops shallower than vpm but no shallower than plain zhl. That profile is likely to produce less decompression stress than a profile generated by vpm

**** Please read more than my post above as there is a lot I've just brushed over and I'm likely wrong / I'm not an expert, etc *****


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