Pursuit gradient factors

**UWSojourner** · 28th March 2008, 23:27

Article in the library that might be helpful.

http://www.rebreatherworld.com/gener...r-dummies.html

**Dsix36** · 29th March 2008, 00:13

Quote: (Originally Posted by Nailer99)

Here's the part I'm still confused about- I understand that GF= percent of M value, and that the first number equals the deeper portion, and the second number equals the surfacing value......but where is the "/" part? I mean, at what depth do we transition from the "10" to the "90" with a GF of "10/90" ?

(mine is set for 15/85, only because my instructor reccomended it, not because I fully understood the damn thing.....)

The first number DOES NOT equal the deeper portion. It is the percent of difference from the M value for the first stop. The lower the number means the deeper the first stop.

The second number is at what percent of difference of M value upon surfacing. 100 is right on the edge of being bent.

10/100 will give deeper deco stops and get you out of the water the fastest.
25/85 will be shallower deco stops and keep you in the water a little longer.

This is very simplified, but it will give you an idea to work from.

Nailer99 · 29th March 2008, 03:47

Quote: (Originally Posted by Dsix36)

The first number DOES NOT equal the deeper portion. It is the percent of difference from the M value for the first stop. The lower the number means the deeper the first stop.

The second number is at what percent of difference of M value upon surfacing. 100 is right on the edge of being bent.

10/100 will give deeper deco stops and get you out of the water the fastest.
25/85 will be shallower deco stops and keep you in the water a little longer.

This is very simplified, but it will give you an idea to work from.

OK- yeah, I think I get that. Thanks. I just don't see a lot of difference between, say, 10/90 and 15/85. Seems like splitting hairs. I guess the difference would be more pronounced on deeper profiles.....

sailor · 29th March 2008, 07:06

Quote: (Originally Posted by Nailer99)

Here's the part I'm still confused about- I understand that GF= percent of M value, and that the first number equals the deeper portion, and the second number equals the surfacing value......but where is the "/" part? I mean, at what depth do we transition from the "10" to the "90" with a GF of "10/90" ?

(mine is set for 15/85, only because my instructor reccomended it, not because I fully understood the damn thing.....)

When you use 15/85 that means you start with 15% of the M-value and then you constantly increase the M-value to 85% during your ascent.

Lets say your software´s or computer´s first stop with a GF of 15% is at 45 meter / 150 ft for a given dive and 85% when surfacing then your GF is 50% at roughly 18 meter / 60 ft.

The upper 100% line is with zero safety margin, the lower 0% line will virtually not offgas at all.
When using GF15/85 you are moving along the middle line.

Mark Chase · 29th March 2008, 07:18

Hears an example of the same dive dive on two diferent GFs 20/85 (nice soft profile) and 10/110 (about what ratio deco gives you for this dive. Deep stops to handle the helium and agresive shalow stops because they reckon you dont need them)

As you can see theres 40 odd mins diference. The bottom profile is my emergancy last ditch bailout option for this dive on carried gas. 10ltr 18/45 and 11ltr 50% both blown to 250bar

Ben Field · 29th March 2008, 07:48

Quote: (Originally Posted by Nailer99)

OK- yeah, I think I get that. Thanks. I just don't see a lot of difference between, say, 10/90 and 15/85. Seems like splitting hairs. I guess the difference would be more pronounced on deeper profiles.....

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.

IMO the important bit it the "Gradient" part, the shift from low to high value that controls the stops/ascent rate and how this relates to the depth, workload and mix you've been diving with.

Decompression is one element (of many

) I'm not sure you should try to learn about on a forum- you need to do the paper work on this one.... IMVHO anyway.

Mark Chase · 29th March 2008, 12:33

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.

IMO the important bit it the "Gradient" part, the shift from low to high value that controls the stops/ascent rate and how this relates to the depth, workload and mix you've been diving with.

Decompression is one element (of many

) I'm not sure you should try to learn about on a forum- you need to do the paper work on this one.... IMVHO anyway.

Nailer,

As you can see above the difference between 20/85 and 10/130GFs is almost 100%. If I had added 100% 02 to the last profile it would be at least 100%.

I like GF deco because I can see even with my feeble brain ways to soften the ascent. I can mentaly figure out what to add where to do this. With VPMB I have not the first clue how to best go about this I would have to folow pre cut tables.

Ben is absolutely right the best way is to learn as much as you can on this but I have to say I spent a LOT of time trying to get my head round it all and I fairly quickly went past my feeble brain power limits.

Hear is a good link to quality info:

ftp://ftp.decompression.org/pub/

In the end I concluded there were four profiles worth worrying about:

NOTE: some of these will most likely bend you and ALL of them could potentially bend you.

20/80 or 20/85 if your using an Inspo or other fixed GF computer

General purpose soft deco. I use this a lot when I am not pushing bailout limits or ding silly long deco.

10/90

Good profile for dives with lots of helium in the mix and fairly long run times ie over 120mins. Pad the last stop to soften the deco if your feeling like it IE dive was hard work, you know you have a ladder to climb, not feeling 100% physical etc.

10/130

About as aggressive as I ever want to intentionally plan for. Base line rich helium mix deco for when my bailout gas wasn't enough due to unforeseen circumstances. More likely to bend you with a type 1 hit DCI pain only bent but by no means guaranteed not to put you in a wheel chair.

Can be adapted on ascent as required by adding time to all stops above 21m assuming gas will allow it.

100/100GF

The final option is what I call rock bottom. Where the choices are do this or drown. This option gets you shallow ASAP and out of the water quickly. The only reason to use it for me would be to conserve bailout gas due to totaly inadequate levels. Getting shallow fast with a lot of Helium in the mix holds a far greater risk of serious Helium bends Type 2 in the brain and spine.

As with the previous deco plan, you pad as much as you can with available gas by adding deep stops and extending shallow stops. This sort of profile on a 120min plus profile would see me on o2 on the boat straight away and probably calling for the chopper.

I try and stick to the top three and worry more about hydration and electrolyte levels. No smoking at least an hour before the dive and proper food when I can.

ATB

Mark

Nailer99 · 29th March 2008, 14:38

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.

IMO the important bit it the "Gradient" part, the shift from low to high value that controls the stops/ascent rate and how this relates to the depth, workload and mix you've been diving with.

Decompression is one element (of many

) I'm not sure you should try to learn about on a forum- you need to do the paper work on this one.... IMVHO anyway.

None taken- please don't worry, I'm not doing anything crazy. And I have to respectfully disagree about learning gradient factors from an online forum- I've had lectures from instructors about them, I've read textbooks about them, and I was still not clear as to what they were- I just learned a lot reading all your posts, thank you, everyone!

Meng_Tze · 29th March 2008, 14:44

Quote: (Originally Posted by Nailer99)

..... I've had lectures from instructors about them,... and I was still not clear as to what they were- ...

get your money back!

sailor · 29th March 2008, 17:37

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.

28th March 2008, 23:27	#11 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 556	Re: Pursuit gradient factors Article in the library that might be helpful. http://www.rebreatherworld.com/gener...r-dummies.html
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29th March 2008, 00:13	#12 (permalink)
Dsix36 Going Down? Current Rebreather/s: Optima Other Rebreather/s: Join Date: Aug 2007 Location: Deerfield Beach, Florida Posts: 1,052	Re: Pursuit gradient factors Quote: (Originally Posted by Nailer99) Here's the part I'm still confused about- I understand that GF= percent of M value, and that the first number equals the deeper portion, and the second number equals the surfacing value......but where is the "/" part? I mean, at what depth do we transition from the "10" to the "90" with a GF of "10/90" ? (mine is set for 15/85, only because my instructor reccomended it, not because I fully understood the damn thing.....) The first number DOES NOT equal the deeper portion. It is the percent of difference from the M value for the first stop. The lower the number means the deeper the first stop. The second number is at what percent of difference of M value upon surfacing. 100 is right on the edge of being bent. 10/100 will give deeper deco stops and get you out of the water the fastest. 25/85 will be shallower deco stops and keep you in the water a little longer. This is very simplified, but it will give you an idea to work from. __________________ THE MORE THAT I LEARN, THE MORE THAT I STILL NEED TO LEARN!!!!!!
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29th March 2008, 03:47	#13 (permalink)
Nailer99 Joshua Smith Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jan 2007 Location: Seattle, WA, USA Posts: 220	Re: Pursuit gradient factors Quote: (Originally Posted by Dsix36) The first number DOES NOT equal the deeper portion. It is the percent of difference from the M value for the first stop. The lower the number means the deeper the first stop. The second number is at what percent of difference of M value upon surfacing. 100 is right on the edge of being bent. 10/100 will give deeper deco stops and get you out of the water the fastest. 25/85 will be shallower deco stops and keep you in the water a little longer. This is very simplified, but it will give you an idea to work from. OK- yeah, I think I get that. Thanks. I just don't see a lot of difference between, say, 10/90 and 15/85. Seems like splitting hairs. I guess the difference would be more pronounced on deeper profiles.....
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29th March 2008, 07:18	#15 (permalink)
Mark Chase I go down for ages Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,693	Re: Pursuit gradient factors Hears an example of the same dive dive on two diferent GFs 20/85 (nice soft profile) and 10/110 (about what ratio deco gives you for this dive. Deep stops to handle the helium and agresive shalow stops because they reckon you dont need them) As you can see theres 40 odd mins diference. The bottom profile is my emergancy last ditch bailout option for this dive on carried gas. 10ltr 18/45 and 11ltr 50% both blown to 250bar __________________ Is it supposed to make that noise ? I took my unit to the dive shop and demanded they bolt on every thing that would fit. Join my elite diving teem and get a Tshirt "Doing It Chasey"Hammerhead Eccr Advanced Diving System Last edited by Mark Chase : 29th March 2008 at 07:29.
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29th March 2008, 07:48	#16 (permalink)
Ben Field CK+Shearwater Current Rebreather/s: Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Aug 2005 Location: London, England Posts: 1,632	Re: Pursuit gradient factors Quote: (Originally Posted by Nailer99) OK- yeah, I think I get that. Thanks. I just don't see a lot of difference between, say, 10/90 and 15/85. Seems like splitting hairs. I guess the difference would be more pronounced on deeper profiles..... 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. IMO the important bit it the "Gradient" part, the shift from low to high value that controls the stops/ascent rate and how this relates to the depth, workload and mix you've been diving with. Decompression is one element (of many ) I'm not sure you should try to learn about on a forum- you need to do the paper work on this one.... IMVHO anyway. __________________ Know your PPO2, Pre-breath, Use checklists, Validate cells at 6mtrs, Use pure O2 at or near surface, Use a BOV, Don't dive Solo, Change Slime and Cells as recommended by Manufacturer and RTFM! Beware Fridge Suck! www.hugsac.org.uk
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29th March 2008, 12:33	#17 (permalink)
Mark Chase I go down for ages Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,693	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. IMO the important bit it the "Gradient" part, the shift from low to high value that controls the stops/ascent rate and how this relates to the depth, workload and mix you've been diving with. Decompression is one element (of many ) I'm not sure you should try to learn about on a forum- you need to do the paper work on this one.... IMVHO anyway. Nailer, As you can see above the difference between 20/85 and 10/130GFs is almost 100%. If I had added 100% 02 to the last profile it would be at least 100%. I like GF deco because I can see even with my feeble brain ways to soften the ascent. I can mentaly figure out what to add where to do this. With VPMB I have not the first clue how to best go about this I would have to folow pre cut tables. Ben is absolutely right the best way is to learn as much as you can on this but I have to say I spent a LOT of time trying to get my head round it all and I fairly quickly went past my feeble brain power limits. Hear is a good link to quality info: ftp://ftp.decompression.org/pub/ In the end I concluded there were four profiles worth worrying about: NOTE: some of these will most likely bend you and ALL of them could potentially bend you. 20/80 or 20/85 if your using an Inspo or other fixed GF computer General purpose soft deco. I use this a lot when I am not pushing bailout limits or ding silly long deco. 10/90 Good profile for dives with lots of helium in the mix and fairly long run times ie over 120mins. Pad the last stop to soften the deco if your feeling like it IE dive was hard work, you know you have a ladder to climb, not feeling 100% physical etc. 10/130 About as aggressive as I ever want to intentionally plan for. Base line rich helium mix deco for when my bailout gas wasn't enough due to unforeseen circumstances. More likely to bend you with a type 1 hit DCI pain only bent but by no means guaranteed not to put you in a wheel chair. Can be adapted on ascent as required by adding time to all stops above 21m assuming gas will allow it. 100/100GF The final option is what I call rock bottom. Where the choices are do this or drown. This option gets you shallow ASAP and out of the water quickly. The only reason to use it for me would be to conserve bailout gas due to totaly inadequate levels. Getting shallow fast with a lot of Helium in the mix holds a far greater risk of serious Helium bends Type 2 in the brain and spine. As with the previous deco plan, you pad as much as you can with available gas by adding deep stops and extending shallow stops. This sort of profile on a 120min plus profile would see me on o2 on the boat straight away and probably calling for the chopper. I try and stick to the top three and worry more about hydration and electrolyte levels. No smoking at least an hour before the dive and proper food when I can. ATB Mark __________________ Is it supposed to make that noise ? I took my unit to the dive shop and demanded they bolt on every thing that would fit. Join my elite diving teem and get a Tshirt "Doing It Chasey"Hammerhead Eccr Advanced Diving System Last edited by Mark Chase : 29th March 2008 at 12:57.
(Online)

29th March 2008, 14:38	#18 (permalink)
Nailer99 Joshua Smith Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jan 2007 Location: Seattle, WA, USA Posts: 220	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. IMO the important bit it the "Gradient" part, the shift from low to high value that controls the stops/ascent rate and how this relates to the depth, workload and mix you've been diving with. Decompression is one element (of many ) I'm not sure you should try to learn about on a forum- you need to do the paper work on this one.... IMVHO anyway. None taken- please don't worry, I'm not doing anything crazy. And I have to respectfully disagree about learning gradient factors from an online forum- I've had lectures from instructors about them, I've read textbooks about them, and I was still not clear as to what they were- I just learned a lot reading all your posts, thank you, everyone!
(Online)

29th March 2008, 14:44	#19 (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 Quote: (Originally Posted by Nailer99) ..... I've had lectures from instructors about them,... and I was still not clear as to what they were- ... get your money back! __________________ Homo Bonae Voluntatis
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29th March 2008, 17:37	#20 (permalink)
sailor New Member Current Rebreather/s: Inspiration Vision Other CCR Dolphin Other Rebreather/s: Other CCR Dolphin Join Date: Jul 2006 Location: UAE Posts: 64	Re: Pursuit gradient factors 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.
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