What's your Low Gradient Factor Selection

[jptaylor9]

I recommend to everybody watch the conference of Dr. Doolittle about deep stops: Check out this video on http://www.rf30.org/presentations/decompression-methods/ ——

Interesting coment right at end of deep stops section, Dr. David Doolette said "...if your using deep stops to control your ascent rate & sliding up 3m at a time is most probably a good thing..."

On my last dive I ascended from 65m to 35m reasonably quickly on a VPM model, then followed the deco ceiling (i.e. not traditional 3m stops), so a slow/controlled ascent rate (X1 does 1m steps to 10m, then 0.5m steps in this mode) until my final stop at 4.5m where I hung around for 25mins of remaining deco time.

Running a GF deco for the dive on a GF of 50/80 would do a first stop at 30m, with less than 1 minute stop at 33m. My first stop was 37m, but reduced to 35m during the ascent. So all this deep stops, VPM, high lower GF settings is splitting hairs at the margin, on this one dive I stoped 5m deeper but it wasn'ta stop as I was soon movig up to 34, 33, 32, 31, .....

 

[DSix36]

Interesting coment right at end of deep stops section, Dr. David Doolette said "...if your using deep stops to control your ascent rate & sliding up 3m at a time is most probably a good thing..."

On my last dive I ascended from 65m to 35m reasonably quickly on a VPM model, then followed the deco ceiling (i.e. not traditional 3m stops), so a slow/controlled ascent rate (X1 does 1m steps to 10m, then 0.5m steps in this mode) until my final stop at 4.5m where I hung around for 25mins of remaining deco time.

Running a GF deco for the dive on a GF of 50/80 would do a first stop at 30m, with less than 1 minute stop at 33m. My first stop was 37m, but reduced to 35m during the ascent. So all this deep stops, VPM, high lower GF settings is splitting hairs at the margin, on this one dive I stoped 5m deeper but it wasn'ta stop as I was soon movig up to 34, 33, 32, 31, .....

When you start doing dives with 5 hours of deco, you can notice a significant difference in both your deco curve and your deco time. Running 30/70 vs 80/90 were the GF's that I actually compared on this same deep cave dive.

 

[jptaylor9]

When you start doing dives with 5 hours of deco, you can notice a significant difference in both your deco curve and your deco time. Running 30/70 vs 80/90 were the GF's that I actually compared on this same deep cave dive.

But I won't be doing dives with 5hrs of deco, so not applicable to me.... Been up to 4hrs/120m but doubt I'll bother with the deeper stuff anymore, 75/80m is most probably my max depth these days & dive boat skippers limit runtimes to 2hrs in most cases anyway!!

But take your point on longer/deeper dives it may make a difference but problem is many rec/tec dives think it make a difference on the typical rec/tec dive

 

[Mark Chase]

But I won't be doing dives with 5hrs of deco, so not applicable to me.... Been up to 4hrs/120m but doubt I'll bother with the deeper stuff anymore, 75/80m is most probably my max depth these days & dive boat skippers limit runtimes to 2hrs in most cases anyway!!

But take your point on longer/deeper dives it may make a difference but problem is many rec/tec dives think it make a difference on the typical rec/tec dive

40mins at 70m theres 10mins in it between 35/90 and 65/90 65/90 being the quickest.

I went 65/80 to soften it and the deco is within 2mins (longer this time) of what i used to run (35/90)

However do deep stops (10GF low) and the deco goes up by 20mins

Now the question is, the deep stop on a 10/90 is 47m, a 65GF is 34m and 20mins less deco

a VPMB2 profile stops at 48m but is 46mins less deco? How does that work?

Personaly I have no idea

ATB

Mark

 

[jptaylor9]

40mins at 70m theres 10mins in it between 35/90 and 65/90 65/90 being the quickest.

I went 65/80 to soften it and the deco is within 2mins (longer this time) of what i used to run (35/90)

However do deep stops (10GF low) and the deco goes up by 20mins

Now the question is, the deep stop on a 10/90 is 47m, a 65GF is 34m and 20mins less deco

a VPMB2 profile stops at 48m but is 46mins less deco? How does that work?

Personaly I have no idea

ATB

Mark

I plugged this dive in MultiDeco, the VPM-B +2 is shorter overall, but not the 46mins you said, only maybe 10mins. You stop deeper but there not really stops, just slowing your ascent. You like to quote John Thraves, on his VPM cards (he used a dive timer only x2) he noted where the first stop was but only wrote down stops > 1mins, the 1 minute stops are just a 3m/min ascent rate, the first real stop is around 33m.

I dive on VBM-B +3 rather than +2, but I also us a surfacing GF of 95% which extends the shallow stop (MultiDeco VPM with GFS model).

 

[Mark Chase]

I plugged this dive in MultiDeco, the VPM-B +2 is shorter overall, but not the 46mins you said, only maybe 10mins. You stop deeper but there not really stops, just slowing your ascent. You like to quote John Thraves, on his VPM cards (he used a dive timer only x2) he noted where the first stop was but only wrote down stops > 1mins, the 1 minute stops are just a 3m/min ascent rate, the first real stop is around 33m.

I dive on VBM-B +3 rather than +2, but I also us a surfacing GF of 95% which extends the shallow stop (MultiDeco VPM with GFS model).

I just re run it

40mins 70m VPMB2 running 1.3 set point on 15/50 gas

If you run 1 second stops

VPMB 2 is 154.04mins

and GF 10/80 is 190.55

So 34mins not 45 my bad

If you run 1min stops 215 for GF and 189 for VPM 2 so 26mins??

Whats the diferance between a stop and a real stop when doing VPM?


ATB

Mark

 

[rossh]

I just re run it

40mins 70m VPMB2 running 1.3 set point on 15/50 gas

If you run 1 second stops

VPMB 2 is 154.04mins

and GF 10/80 is 190.55

So 34mins not 45 my bad

If you run 1min stops 215 for GF and 189 for VPM 2 so 26mins??

Whats the diferance between a stop and a real stop when doing VPM?


ATB

Mark

Hi Mark. Your run time numbers seem a bit off. Also 10/80 GF is not the equivalent of a VPM-B dive. That 10/80 GF is stretching the ZHL model excessively in both deep and shallow times. It is unlikely that any model will align with such drawn out GF numbers.

Using 40mins 70m, running 1.3 set point on 10/50 gas, using 1 second stops

VPM-B+2 135 mins (1st stop 42m)
ZHL-C GF 40/90 146 mins (1st stop 42m)
ZHL-C GF 40/100 135 mins (1st stop 42m) - same end time

Using realistic 40/90 GF numbers, the differences is 11 minutes. That difference is because ZHL and VPM have different ideas about the allowable gradient in the last part of the dive. Internally the difference is quite small. (last stop max allowed gradient on this dive: VPM-B 173KPa He, ZHL 164KPa He).

 

[Mark Chase]

Hi Mark. Your run time numbers seem a bit off. Also 10/80 GF is not the equivalent of a VPM-B dive. That 10/80 GF is stretching the ZHL model excessively in both deep and shallow times. It is unlikely that any model will align with such drawn out GF numbers.

Using 40mins 70m, running 1.3 set point on 10/50 gas, using 1 second stops

VPM-B+2 135 mins (1st stop 42m)
ZHL-C GF 40/90 146 mins (1st stop 42m)
ZHL-C GF 40/100 135 mins (1st stop 42m) - same end time

Using realistic 40/90 GF numbers, the differences is 11 minutes. That difference is because ZHL and VPM have different ideas about the allowable gradient in the last part of the dive. Internally the difference is quite small. (last stop max allowed gradient on this dive: VPM-B 173KPa He, ZHL 164KPa He).

Sorry Ross I wasn't trying to makle a direcet profile comparison, I was just noting the issue I have always struggled with with VPM (and some other profiles designed arround deep stops) in that it has a lot of deep stops but less shalow stops.

Add deep stops to a GF profile and the deco goes up and up but no so on bubble models.

I am NOT saying thats wrong I am just saying I cant understand it / resolve it in my mind.

I can understand presure gradients and gas transfers in deco running GFs but the concept of the bubble moddel baffels me. Mainly because its counter intuitave to my very basic understanding of deco.


I did the profiles on Multi Deco which is my main deco planning tool thease days and the only issue with that is the extent of the variables you can program in will give diferent results across diferent peoples settings. One thing that occured to me which will influance is my ascent rate setting is 7m/min



ATB

Mark

 

[jptaylor9]

Sorry Ross I wasn't trying to makle a direcet profile comparison, I was just noting the issue I have always struggled with with VPM (and some other profiles designed arround deep stops) in that it has a lot of deep stops but less shalow stops.

Not sure that's strictly true.....

1) A lot of the "deep stops" are 1min stops, these are basically slowing the ascent rate to 3m/min, I dive MultiDeco on my X1, in the water if you have direct ceiling set, your moving steadily up. E.g says 27m, by the time checked handset, it's saying 26m so up you go, you hardly stop as such just move up slowly.

2) Dr David Doolette, said at the end of his deep stops section in his presentation (see earlier post) that these type of deep stops ("to control your ascent rate") were most probably a good thing. As an aside he didn't every say VPM was a bad deco model, as some have implied!

Taking a real world example rather than desktop generated profile, I dived the Arsitos today (only 4 of use o Steve's boat ). Down at the stern, run time 55minutes, running SP=1.25 on my X1 with 12/45 dil. Glanced at the X1 & end of dive time was 122mins, sh!t better get moving as 2hr limit on dive! Popped up onto the top of the wreck & sent my bag up, stuck my SP up to 1.4 on the unit & 1.3 on the X1 (set it to 1.35 once I'd done the initial ascent).

5mins later I'm at 21m, initial ceiling was 27m, but that reduced to 25m on the ascent & droped to 21m as I ascended slowly, didn't feel I actually stopped for an appreciable amount of time until I gotto 18m

Running the dive profile thru MultiDeco & using a GF of 40/90 it has a first stop at 27m, and the runtime is comparable. On the actual dive the X1 would have tracked me ascending/descending on the wreck.

For the types of dives I do I don't see any appreciable difference & don't feel that I'm adding any more deep stops than I would on currently fashionable GF profile....

 

[Igor P]

Sorry Ross I wasn't trying to makle a direcet profile comparison, I was just noting the issue I have always struggled with with VPM (and some other profiles designed arround deep stops) in that it has a lot of deep stops but less shalow stops.

Add deep stops to a GF profile and the deco goes up and up but no so on bubble models.

I am NOT saying thats wrong I am just saying I cant understand it / resolve it in my mind.

I can understand presure gradients and gas transfers in deco running GFs but the concept of the bubble moddel baffels me. Mainly because its counter intuitave to my very basic understanding of deco.


I did the profiles on Multi Deco which is my main deco planning tool thease days and the only issue with that is the extent of the variables you can program in will give different results across diferent peoples settings. One thing that occured to me which will influance is my ascent rate setting is 7m/min



ATB

Mark

Mark, you try again to put both types of algorithms in same box, but they can not be. They work differently, tush different profiles etc... for same BT....sure depend on yoursettings too.

You can not expect same road on the way back home on two different GPS navigation systems with different algorithms - sometimes it can be, sometimes not. It is the same here. Some profiles are quite similar, some are not.

 

[jptaylor9]

I'd caution against simply removing the deep stops rather than redistributing the time to shallower depths, i think that's probably reading abit too much into the NEDU study. That said it's the high GF number that dictates the majority of the deco anyway.

I've got an excel spreadsheet (linked below) that will compute run times and total tissue supersaturation for a large range of Gradient factors for a given depth and time. You can play about with different dil's, bottom times and most importantly time on the surface post dive to see how they change things.

http://bit.ly/QCvyew

My main concern with talks by these experts working for commercial/military diving & shown in Dr Doolette's presentation is that they don't test the stuff we dive!

Commercial/Military divers dive a breathing mix of oxygen + ONE inert gas be that Air/Nitrox (O2/N2) or Heliox (O2/He). They can afford to use lots of Helium...

They don't test dives where your trying to control TWO inert gases which enter/leave your body at different rates. They never will unless commie/military divers start to use Trimix/HeliAir gases which is very unlikely.

Personally I don't see the need for deep stops if diving Air/Nitrox, I'd happily dive a 90/95 gradient, did lots of Air diving/deco on an Aladin Pro (basically an 8 compartment Buhlmann model w/out gradient factors).

From memory I added deeper stops to handle the Helium off-gassing, deeper stops/slower ascent to allow the Helium out, by the time you got to the to the shallower stops Helium was effectively dealt with & you now have to deal with the Nitrogen. That's why I used 10/95 on a series of 120m dives back in the day....

I like VPM as it deals with both cases OK, just set your overall levelof conservitism & away you go....

(Actually use VBM-B with GFS to add a bit of time on the last stop & sync up with the Vision deco)

 

[matt]

What do you set on the Vision, Jon, to make it match the VPM-B?

Matt.

 

[Mark Chase]

Mark, you try again to put both types of algorithms in same box, but they can not be. They work differently, tush different profiles etc... for same BT....sure depend on yoursettings too.

You can not expect same road on the way back home on two different GPS navigation systems with different algorithms - sometimes it can be, sometimes not. It is the same here. Some profiles are quite similar, some are not.

Never said you could but the core concern remains

How can you spend so much more time deep with VPM and still end up with greatly reduced shalow stops?


The control of bubbles and bubble tension giving such significant improvements in deco just leaves me with too many questions unanswered.

My greatest concern is that people who previously ran 30/85 type profiles switch to vpm and stard running VPMB-2 because they dont really understand the levels of agression they are accepting. Personaly I wouldn't do a normal dive on anything more agressive than VPMB-4 and then theres little or no advantage over the run times I was getting with GF30/90

However as I have said many times my main reasion for not experimenting with VPM is CCR bailout for which I need to get shalow quickly to conserve gas.

ATB

Mark

 

[jptaylor9]

What do you set on the Vision, Jon, to make it match the VPM-B?

Matt.

30/95 (EDIT: more like 30/100 for dives I do, say 30/98 on Vision)

However as I have said many times my main reasion for not experimenting with VPM is CCR bailout for which I need to get shalow quickly to conserve gas.

Agree, I don't use VPM-B for bailout, to much time in mid depth. On the X1 I have VPB-B/GFS as my main deco with two bailout plans. One is VPM-FBO (fast bailout) VPM altered to get you to 21m more quickly, but you pay the price with longer shallow stops, I could switch to a GF bailout instead. The other bailout plan is VPM-B+1 in CCR mode, need to get out quick, but can stay on unit, manually add extra shallow stops manually as req'd.

 

[Igor P]

Mark, we were already discusing about CCR bailout and absence of easy VPM-B use for it. As already discused, only VPM-B FBO that Ross implemented geaves some chance to get shallow faster with VPM. Personaly I have two Bailout settings, one is VPM-B FBO +2 on my X-1 and the other is GF 60/90 on my DIY CCR Computer with ppo2 monitoring. Well I have a third option on my SW Pursuit with GF99 to get shallow realy fast . Sure all this "shallow fast" options incorporate their own risks, which I am accepting to run in bailout situation.

You get nothing without paying in something.

 

[rossh]

Never said you could but the core concern remains

How can you spend so much more time deep with VPM and still end up with greatly reduced shalow stops?


The control of bubbles and bubble tension giving such significant improvements in deco just leaves me with too many questions unanswered.

My greatest concern is that people who previously ran 30/85 type profiles switch to vpm and stard running VPMB-2 because they dont really understand the levels of agression they are accepting. Personaly I wouldn't do a normal dive on anything more agressive than VPMB-4 and then theres little or no advantage over the run times I was getting with GF30/90

However as I have said many times my main reasion for not experimenting with VPM is CCR bailout for which I need to get shalow quickly to conserve gas.

ATB

Mark

Mark. You keep making this same assertion about a great difference. It's not there. Here you have extend the ZHL plan with added GF by some significant amount, meddling with the way in which the ZHL model wants to make a plan. Then the assumption is that this extended GF time is a datum or base line, and then look around and pose the question "why isn't every other model this long"?

Sorry Mark, but all this GF fiddling and comparing, amounts to nothing more than "my fudge is bigger or different to your fudge".

To compare real models, use real models times and outputs and see the differences intended by the model design and that the model theory will produce.


Back to your example:

VPM-B 126 mins (1st stop 42m)
ZHL-C 126 mins (1st stop 30m)
Last stop variance 5 mins.


You wrote "greatly reduced shallow stops". It's not there. They have the same end time and VPM has a slightly higher allowable surfacing pressure. When we look at real model outputs, we see the model design differences. Here the ZHL is favoring stops in mid and shallow times. VPM has stops distributed across deep, mid and shallow. That design difference in models is reflected in the stop distribution.

VPM doesn't think it needs as much shallow time as ZHL, because the model theory is working to control the ascent across a wider depth range, and VPM also considers post dive conditions. VPM computes this in terms of tissue micro bubble conditions, and arrives at maximum allowable pressure conditions for that dive. But, ZHL has far less data to work with and is limited to broad predefined limits of maximums only, to be applied to all dives and conditions.

ZHL pressure levels are NOT the standard or maximum for others to follow. Other models have higher and lower internal allowable pressure levels as maximums. No two models will agree on any value much.

 

[Brad_Horn]

My main concern with talks by these experts working for commercial/military diving & shown in Dr Doolette's presentation is that they don't test the stuff we dive!
Commercial/Military divers dive a breathing mix of oxygen + ONE inert gas be that Air/Nitrox (O2/N2) or Heliox (O2/He). They can afford to use lots of Helium...
They don't test dives where your trying to control TWO inert gases which enter/leave your body at different rates. They never will unless commie/military divers start to use Trimix/HeliAir gases which is very unlikely.

You sure about that!

 

[jptaylor9]

You sure about that!

No, why not make a positive reply & say where commie/military are using gases with more than one inert gas unless your referring to O2/Helium/Hydrogen.... which is for dives well out of our depth range as I understand it.

 

[MeRodent]

No, why not make a positive reply & say where commie/military are using gases with more than one inert gas unless your referring to O2/Helium/Hydrogen....

Ooh ooh ooh!

I can answer that one.

Brad has signed non-disclosure agreements. All you need to do is order 30 UBA's and sign an NDC and you too will be privileged with that data.

 

[apitkin]

My main concern with talks by these experts working for commercial/military diving & shown in Dr Doolette's presentation is that they don't test the stuff we dive!

Commercial/Military divers dive a breathing mix of oxygen + ONE inert gas be that Air/Nitrox (O2/N2) or Heliox (O2/He). They can afford to use lots of Helium...

They don't test dives where your trying to control TWO inert gases which enter/leave your body at different rates. They never will unless commie/military divers start to use Trimix/HeliAir gases which is very unlikely.

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.

Andy