Pursuit gradient factors

Mark Chase · 29th March 2008, 20:15

Quote: (Originally Posted by sailor)

I believe 100/100 is a very dangerous profile but still diveable in case of emergency.
I don´t think you can do 10/130 without harm.
The maximum adjustment for my Pursuit is 90/90 or 40/99.

100/100 is straight Buhlman tables. Buhlman tables are the most dived and proven tables in the world.

However Buhlman hit a bit of a problem when he started to look at helium. Principley his work was based on air. End result he looked at the on gassing potential for helium based on molecular size and extrapolated data for off gassing based on nitrogen models.

End result is veryheavy penalty's for diving helium.

Recent research has found that Helium off gasses far more efficiently then predicted. However the shear volume of gas absorbed is an order of magnitude above that expected of Nitrogen.

End result is Buhlman profiles ar not Helium friendly.

Not enough deep stops to control the growth of the helium bubbles and far too long a shallow stop. Getting bent on the way up and doing DCI treatment in the shallow stops. Or "Bend and Mend" is how it was referred to.

WKPP did some serious personal experimentation with rich Helium mixes

After some quite impressive pushes on trimix they concluded it was necessary to do a lot of deep stops to control the helium and that using large gas gradients in the shallow stops was a good idea. The profiles for helium were re written. Lots of deep stops and gradual progression to the shallows and not so long in the shallows as you would expect.

VPMB is probably the pinnacle of this thought process. It is certainly the profile of choice among the loads of helium / heleox divers.

To get GF deco along the same lines you need to look at extending the deep stops and reducing the shallow stops

10/120 10/130 does exactly this.

A significant group of divers actually dive 120-120+ profiles for normal every day dives. Personally I feel its pushing it unnecessarily but it has to be said they are getting away with it.

ATB

Mark

Meng_Tze · 29th March 2008, 20:52

Spot on Mark.
I have been working to get my X1 (VPM) and Shearwater GF match up profiles. The more I get in the 10/110+ range, the more they start to pull together.

Have some greens

**UWSojourner** · 29th March 2008, 20:56

Quote: (Originally Posted by Meng_Tze)

I have been working to get my X1 (VPM) and Shearwater GF match up profiles. The more I get in the 10/110+ range, the more they start to pull together.

By "pull together" do you mean total runtime? or something else?

Meng_Tze · 29th March 2008, 21:03

More RT, I know that pulling the actual ascend profiles is more challenging. I seem to 'bend' my SW GF when I do a dive and follow the X1 out of the water. With adjusted GF's the 'seriousness' of bending it seems less. With that I mean missed stops are less and shorter in time.

Nailer99 · 29th March 2008, 22:26

Quote: (Originally Posted by Ben Field)

Nailer, no offence but PLEASE- go read up on this.... diving Profiles you "think you get" will get you one thing for sure, and that is bent.

Oh- also- I'm not diving profiles I "think I get." My original question was because of the Gradient Factor setting in my computer- which I don't use for deco anyway- I cut multiple tables for deco dives using V-planner, and I pad the heck out of them. All the material I've studied on Gradient factors made sense to me, but I just wasn't clear on the deep stops/ surfacing value progression......I appreciate your concern, but I don't want anyone to think I'm some idiot who monkeys around with his computer and does 300 foot dives with no understanding about what I'm doing, or something like that. Anyway, thanks again for the information- green for you and Chasey!

Andy Del · 30th March 2008, 02:48

Quote: (Originally Posted by Nailer99)

I cut multiple tables for deco dives using V-planner, and I pad the heck out of them.

But where you are padding them out may not be so good for your overall ascent, hence the concern some are expressing. At some stage padding may well introduce on-gassing, or less than optimal off-gassing and then you'll need to be aware of this and adjust accordinglcheers

cheers

Andy

Nailer99 · 30th March 2008, 05:40

Quote: (Originally Posted by Andy Del)

But where you are padding them out may not be so good for your overall ascent, hence the concern some are expressing. At some stage padding may well introduce on-gassing, or less than optimal off-gassing and then you'll need to be aware of this and adjust accordinglcheers

cheers

Andy

Again, thanks- but I pad mine above 60'- where ongassing isn't much of an issue. I DO understand what you're saying, and appreciate your concerns.

PnL · 30th March 2008, 06:22

Quote: (Originally Posted by Meng_Tze)

Spot on Mark.
I have been working to get my X1 (VPM) and Shearwater GF match up profiles. The more I get in the 10/110+ range, the more they start to pull together.

Have some greens

I find that a single GF setting does not match up with VPM-B for all profiles. For example, 10/90 tends to be more conservative on deeper dives (>250 fsw), but can be more aggressive on shallower dives (<150 fsw) compared to VPM-B/+2. You have to remember that VPM calculates the deco obligation differently that Buhlman does, even though GF does adjust the M-values to help reflect He loading/unloading.

My 0.02 cents.

Mark Chase · 30th March 2008, 15:51

Quote: (Originally Posted by PnL)

I find that a single GF setting does not match up with VPM-B for all profiles. For example, 10/90 tends to be more conservative on deeper dives (>250 fsw), but can be more aggressive on shallower dives (<150 fsw) compared to VPM-B/+2. You have to remember that VPM calculates the deco obligation differently that Buhlman does, even though GF does adjust the M-values to help reflect He loading/unloading.

My 0.02 cents.

I personally have not attempted to match VPMB profiles. What i try to achieve is a different shape to the conventional Buhlman off gas curve.

However I only do this if there is a need to. IE if I am pushing the limits of bailout or if i am doing bigger than average dives where the in water time on a 20/80 or 10/90 is just too long for comfort.

My attitude is that occasionally i push my luck but I don't need to do that all the time. On a dive where 20/80 or 10/90 gets me out of the water in under three hours and results in adequate bottom time, Ill just run that.

I am probably doing wayyyyy to much deco, but then no one ever got bent from doing too much deco

ATB

Mark

PnL · 30th March 2008, 19:00

Quote: (Originally Posted by Mark Chase)

I personally have not attempted to match VPMB profiles. What i try to achieve is a different shape to the conventional Buhlman off gas curve.

However I only do this if there is a need to. IE if I am pushing the limits of bailout or if i am doing bigger than average dives where the in water time on a 20/80 or 10/90 is just too long for comfort.

My attitude is that occasionally i push my luck but I don't need to do that all the time. On a dive where 20/80 or 10/90 gets me out of the water in under three hours and results in adequate bottom time, Ill just run that.

I am probably doing wayyyyy to much deco, but then no one ever got bent from doing too much deco

ATB

Mark

Hi Mark,

I think its interesting that there are such discussions about matching GF to VPM. I'm not sure why others do it, but for me its because I have been diving with VPM for such a long time that I feel much more intimate with it. Therefore, when I'm diving GF, I look at what the various GF does to my deco profile compared to what I would normally do using VPM-B. I think for me it helps in getting a better understanding of exactly what adjusting those M-values does for my deco profile for various depths and bottom times compared to profiles I have safely used before. Its been a worthwhile exercise for me. But in the end, getting to the surface without getting bent is the goal of all these algorithms and I agree, a longer stop at 20 fsw won't kill you unless you run out of gas or die of the boredom factor

(I suppose there are plenty games one could play to offset the boredom!)

29th March 2008, 20:15	#21 (permalink)
Mark Chase RBW Member Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,867	Re: Pursuit gradient factors Quote: (Originally Posted by sailor) I believe 100/100 is a very dangerous profile but still diveable in case of emergency. I don´t think you can do 10/130 without harm. The maximum adjustment for my Pursuit is 90/90 or 40/99. 100/100 is straight Buhlman tables. Buhlman tables are the most dived and proven tables in the world. However Buhlman hit a bit of a problem when he started to look at helium. Principley his work was based on air. End result he looked at the on gassing potential for helium based on molecular size and extrapolated data for off gassing based on nitrogen models. End result is veryheavy penalty's for diving helium. Recent research has found that Helium off gasses far more efficiently then predicted. However the shear volume of gas absorbed is an order of magnitude above that expected of Nitrogen. End result is Buhlman profiles ar not Helium friendly. Not enough deep stops to control the growth of the helium bubbles and far too long a shallow stop. Getting bent on the way up and doing DCI treatment in the shallow stops. Or "Bend and Mend" is how it was referred to. WKPP did some serious personal experimentation with rich Helium mixes After some quite impressive pushes on trimix they concluded it was necessary to do a lot of deep stops to control the helium and that using large gas gradients in the shallow stops was a good idea. The profiles for helium were re written. Lots of deep stops and gradual progression to the shallows and not so long in the shallows as you would expect. VPMB is probably the pinnacle of this thought process. It is certainly the profile of choice among the loads of helium / heleox divers. To get GF deco along the same lines you need to look at extending the deep stops and reducing the shallow stops 10/120 10/130 does exactly this. A significant group of divers actually dive 120-120+ profiles for normal every day dives. Personally I feel its pushing it unnecessarily but it has to be said they are getting away with it. ATB Mark __________________ See my "Doing It Chasey" video where I'm locked into a padded room, naked, with two ball bearings and within an Hour, I manage to lose one and break the other!!! Kevin Juergensen 16/11/08 [/quote] Last edited by Mark Chase : 30th March 2008 at 05:44.
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29th March 2008, 20:52	#22 (permalink)
Meng_Tze 246 Bubbleless Cove Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jan 2007 Location: FL, USA Posts: 111	Re: Pursuit gradient factors Spot on Mark. I have been working to get my X1 (VPM) and Shearwater GF match up profiles. The more I get in the 10/110+ range, the more they start to pull together. Have some greens __________________ Homo Bonae Voluntatis
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29th March 2008, 20:56	#23 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 558	Re: Pursuit gradient factors Quote: (Originally Posted by Meng_Tze) I have been working to get my X1 (VPM) and Shearwater GF match up profiles. The more I get in the 10/110+ range, the more they start to pull together. By "pull together" do you mean total runtime? or something else?
(Online)

29th March 2008, 21:03	#24 (permalink)
Meng_Tze 246 Bubbleless Cove Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jan 2007 Location: FL, USA Posts: 111	Re: Pursuit gradient factors More RT, I know that pulling the actual ascend profiles is more challenging. I seem to 'bend' my SW GF when I do a dive and follow the X1 out of the water. With adjusted GF's the 'seriousness' of bending it seems less. With that I mean missed stops are less and shorter in time. __________________ Homo Bonae Voluntatis
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29th March 2008, 22:26	#25 (permalink)
Nailer99 RBW Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jan 2007 Location: Seattle, WA, USA Posts: 280	Re: Pursuit gradient factors Quote: (Originally Posted by Ben Field) Nailer, no offence but PLEASE- go read up on this.... diving Profiles you "think you get" will get you one thing for sure, and that is bent. Oh- also- I'm not diving profiles I "think I get." My original question was because of the Gradient Factor setting in my computer- which I don't use for deco anyway- I cut multiple tables for deco dives using V-planner, and I pad the heck out of them. All the material I've studied on Gradient factors made sense to me, but I just wasn't clear on the deep stops/ surfacing value progression......I appreciate your concern, but I don't want anyone to think I'm some idiot who monkeys around with his computer and does 300 foot dives with no understanding about what I'm doing, or something like that. Anyway, thanks again for the information- green for you and Chasey!
(Online)

30th March 2008, 02:48	#26 (permalink)
Andy Del Classic KISSer Current Rebreather/s: Sport Kiss Classic Kiss Other Rebreather/s: Join Date: Feb 2005 Location: Australia, Sunny Sydney Posts: 439	Re: Pursuit gradient factors Quote: (Originally Posted by Nailer99) I cut multiple tables for deco dives using V-planner, and I pad the heck out of them. But where you are padding them out may not be so good for your overall ascent, hence the concern some are expressing. At some stage padding may well introduce on-gassing, or less than optimal off-gassing and then you'll need to be aware of this and adjust accordinglcheers cheers Andy __________________ Yellow - the colour of greatness!
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30th March 2008, 05:40	#27 (permalink)
Nailer99 RBW Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jan 2007 Location: Seattle, WA, USA Posts: 280	Re: Pursuit gradient factors Quote: (Originally Posted by Andy Del) But where you are padding them out may not be so good for your overall ascent, hence the concern some are expressing. At some stage padding may well introduce on-gassing, or less than optimal off-gassing and then you'll need to be aware of this and adjust accordinglcheers cheers Andy Again, thanks- but I pad mine above 60'- where ongassing isn't much of an issue. I DO understand what you're saying, and appreciate your concerns.
(Online)

30th March 2008, 06:22	#28 (permalink)
PnL RBW Member Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Mar 2007 Location: San Diego, CA Posts: 188	Re: Pursuit gradient factors Quote: (Originally Posted by Meng_Tze) Spot on Mark. I have been working to get my X1 (VPM) and Shearwater GF match up profiles. The more I get in the 10/110+ range, the more they start to pull together. Have some greens I find that a single GF setting does not match up with VPM-B for all profiles. For example, 10/90 tends to be more conservative on deeper dives (>250 fsw), but can be more aggressive on shallower dives (<150 fsw) compared to VPM-B/+2. You have to remember that VPM calculates the deco obligation differently that Buhlman does, even though GF does adjust the M-values to help reflect He loading/unloading. My 0.02 cents. __________________ SDTechDiving.com - A San Diego Technical Diving Community
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30th March 2008, 15:51	#29 (permalink)
Mark Chase RBW Member Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,867	Re: Pursuit gradient factors Quote: (Originally Posted by PnL) I find that a single GF setting does not match up with VPM-B for all profiles. For example, 10/90 tends to be more conservative on deeper dives (>250 fsw), but can be more aggressive on shallower dives (<150 fsw) compared to VPM-B/+2. You have to remember that VPM calculates the deco obligation differently that Buhlman does, even though GF does adjust the M-values to help reflect He loading/unloading. My 0.02 cents. I personally have not attempted to match VPMB profiles. What i try to achieve is a different shape to the conventional Buhlman off gas curve. However I only do this if there is a need to. IE if I am pushing the limits of bailout or if i am doing bigger than average dives where the in water time on a 20/80 or 10/90 is just too long for comfort. My attitude is that occasionally i push my luck but I don't need to do that all the time. On a dive where 20/80 or 10/90 gets me out of the water in under three hours and results in adequate bottom time, Ill just run that. I am probably doing wayyyyy to much deco, but then no one ever got bent from doing too much deco ATB Mark __________________ See my "Doing It Chasey" video where I'm locked into a padded room, naked, with two ball bearings and within an Hour, I manage to lose one and break the other!!! Kevin Juergensen 16/11/08 [/quote]
(Online)

30th March 2008, 19:00	#30 (permalink)
PnL RBW Member Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Mar 2007 Location: San Diego, CA Posts: 188	Re: Pursuit gradient factors Quote: (Originally Posted by Mark Chase) I personally have not attempted to match VPMB profiles. What i try to achieve is a different shape to the conventional Buhlman off gas curve. However I only do this if there is a need to. IE if I am pushing the limits of bailout or if i am doing bigger than average dives where the in water time on a 20/80 or 10/90 is just too long for comfort. My attitude is that occasionally i push my luck but I don't need to do that all the time. On a dive where 20/80 or 10/90 gets me out of the water in under three hours and results in adequate bottom time, Ill just run that. I am probably doing wayyyyy to much deco, but then no one ever got bent from doing too much deco ATB Mark Hi Mark, I think its interesting that there are such discussions about matching GF to VPM. I'm not sure why others do it, but for me its because I have been diving with VPM for such a long time that I feel much more intimate with it. Therefore, when I'm diving GF, I look at what the various GF does to my deco profile compared to what I would normally do using VPM-B. I think for me it helps in getting a better understanding of exactly what adjusting those M-values does for my deco profile for various depths and bottom times compared to profiles I have safely used before. Its been a worthwhile exercise for me. But in the end, getting to the surface without getting bent is the goal of all these algorithms and I agree, a longer stop at 20 fsw won't kill you unless you run out of gas or die of the boredom factor (I suppose there are plenty games one could play to offset the boredom!) __________________ SDTechDiving.com - A San Diego Technical Diving Community
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