Riding GF99 instead of mandatory/safety stops

[grantmac]

Shearwater will let you adjust GFHi, not GFLo

 

[rjack321]

Shearwater will let you adjust GFHi, not GFLo

Correct, in large part cause that would be going back into your deco curve and starting it over somewhere else. Deco time travel lol

 

[Wallowa]

Well I just got swept up in this thread.....all 15 pages...very interesting; but honestly as several have said I am wondering "why"?

Is the objective to dive and not generate ANY micro bubbles or nuclei? Or to not become symptomatic with DCS? Or is the purpose to accomplish a reduction in decompression times while optimizing [subjective] BT? What is the goal?

I admit to getting tangled up in the endless discussion of what constituted "total gas pressure" vs 'ambient pressure' vs 'tissue pressure'....since in my limited understanding any breathing gas pressure classed as total or ambient should be at the pressure generated by the hydrostatic pressure, and to a minute degree atmospheric pressure, at a specific depth...while tissue pressures are just that, the 'pressure' of any gas within a tissue and subject to variances in 'on or off gassing' [entering or leaving the tissue] depending on the partial pressure of the specific gas in question within the circulatory system, serum or cells...gradient driven with non-metabolic gas such as nitrogen [He] but not entirely with metabolically utilized oxygen....which throws in another wrinkle...surfacing at altitude while diving in fresh water and how the GFs/M-limits [values] are affected, if at all. My stops are shallower when I dive at altitude [6K and above are a norm for me], and in fresh water, than they would be in at sea level and in salt water. Significant? GFSurf is of importance when atmospheric pressure drops the absolute ambient [ATM] and tissue pressures are still elevated from dive...hence shallower stops [ATA] "push" slow tissue off gassing to compensate for the ATM reduction when surfacing.....but is all this voodoo? Supposedly my Peregrine adjusts the profile parameters based on altitude [fresh water P-delta is insignificant]. I am using the "most conservative" pre-set GF settings and voiding my usual "trust with verification" mantra. Weakness I see is in riding the correct slower ascents.

For an old fart like me who still loves to dive deep and solo I am trying for the most conservative profiles possible and still assuming with all my physiological foibles hyperbaric/hypobaric will do damage; hopefully not enough to require treatment or stop my diving.

Ps....I have a double Jumbo-D D.A.N. oxygen kit at dive sites and will soon be rigging an EAN 40 small bottle at shallow safety stop combined with an extended stop time on EAN40. Plan my dives with no-decompression profiles but prepared for decon if needed.

Appreciated all the dialogue in this thread....

 

[Wallowa]

PPs....While nitrogen/helium and oxygen are mentioned in this thread another more insidious and overlooked gas is COs.....it can play a big part in gas exchange and bubble formation/DCS; I assume it was included in profile modeling.

 

[old frogman]

Sure Shearwater let's you can change your GFs throughout a dive. I've done it myself. In theory you could change them at every stop.

What are you trying to accomplish though?

Objective - flexibility. On a multi-level deep dive, you may want to change depth and time durations e.g. you find something interesting at a particular depth and wish to stay there longer (within the available gas logistics). Or perhaps an unplanned event occurs requiring the dive duration to be increased or reduced. Kevin's article suggests VGM may be more suitable. It appears that on a VR3/VRX the GF parameters change automatically. While on a Shearwater, the GF parameters have to be manually changed (requiring an educated decision to be made by the diver driving the computer).

 

[Wallowa]

OK....I understand that "plans change" but knowing that something 'might be suitable' to accommodate a changing profile in my world is not an option for staying pain and DCS free....my understanding is that Shearwater parameters do change regardless of the profile....whether it keeps the diver below the magic bubble supersat level is up to the diver....since any computer only can sense pressure and time then adjust to meet the device mapping; the diver makes the profile decisions not the computer [but of course even close to that line you fizz a little and the 'little' damage may be asymptomatic, but still damages tissue].

So each must determine if the price of 'flexibility' when freestyling the profile on-the-fly, when balanced against injury is worth the risk. Same, same with trying to eek out more bottom, less stop time or faster ascents. Is the risk worth the 'reward'. There are so damn many physical and physiological variables that can determine whether a diver is injured during and after a hyperbaric/hypobaric exposure that to try and juggle them based on extemporaneous assumptions/educated decisions is not in my play book. But to each their own. Like I said...too old to roll those dice.

 

[old frogman]

OK....I understand that "plans change" but knowing that something 'might be suitable' to accommodate a changing profile in my world is not an option for staying pain and DCS free....my understanding is that Shearwater parameters do change regardless of the profile....whether it keeps the diver below the magic bubble supersat level is up to the diver....since any computer only can sense pressure and time then adjust to meet the device mapping; the diver makes the profile decisions not the computer [but of course even close to that line you fizz a little and the 'little' damage may be asymptomatic, but still damages tissue].

So each must determine if the price of 'flexibility' when freestyling the profile on-the-fly, when balanced against injury is worth the risk. Same, same with trying to eek out more bottom, less stop time or faster ascents. Is the risk worth the 'reward'. There are so damn many physical and physiological variables that can determine whether a diver is injured during and after a hyperbaric/hypobaric exposure that to try and juggle them based on extemporaneous assumptions/educated decisions is not in my play book. But to each their own. Like I said...too old to roll those dice.

Have you read the article "Variable Gradient Model: An approach to create more efficient decompressions".
By Kevin Gurr? It's published in the In Depth Magazine 2017. It's not about reaching the surface as fast as possible. It's about reaching the surface more efficiently. Read it and then tell me what you think about it.


indepthmag.com
https://indepthmag.com › create-more-efficient-decompr…

 

[Wallowa]

Have you read the article "Variable Gradient Model: An approach to create more efficient decompressions".
By Kevin Gurr? It's published in the In Depth Magazine 2017. It's not about reaching the surface as fast as possible. It's about reaching the surface more efficiently. Read it and then tell me what you think about it.


indepthmag.com
https://indepthmag.com › create-more-efficient-decompr…

Thanks ....will do.

 

[Wallowa]

Ok...read the article and it was very detailed and interesting but unconvincing for me in establishing VGM as a safer method of decompressing. "Stochastic modeling forecasts the probability of various outcomes under different conditions, using random variables." was referenced though out and is merely another statement of methodology not of verified modeling. Noted that the author also used his concepts commercially within the computer industry; not dismissing his veracity but he has a dog in the fight. Baker et al do acknowledge that more is unknown on the true mechanisms and variables that produce DCS than are currently known or modeled into decompression dives [all dives are decompression dives].

Great respect for Gurr, Baker and all those searching for methods to lessen DCS. My view is that a diver never really eliminates injurious circulatory and tissue damage on any hyperbaric/hypobaric cycle. Regardless of profile. So little is actually known of nuclei establishment and persistence; along with extent and nature of cellular damage after dives.... all dives.

OK...just for me....I put my money on the bar and called my shot....is my Peregrine or previously used Orca computer going to prevent either symptomatic or asymptomatic DCS? Carp shoot at best. Will the the largely unknown risk factors stop me from diving? At my age any damage is already done after 70 years of diving; so no I am in a penny, in a pound. I WILL dive more conservative profiles regardless of engaging computer manipulations and take experientially verified steps to lessen or prevent damage. Such as staying a long way from NDL/M values, slowing ascents in shallow, staying hydrated, using the "oxygen window" to hastening N2 elimination by lessening N2 inspired and increasing N2 expired by the use of EAN40 at extended safety stops [staged not carried], moderated physical exertion to lessen CO2 tensions and limit post dive core/limb temp increases and circulatory increases from exertion.

Only my approach and definitely "one size doesn't fit all"..... hopefully I can continue to blow bubbles and enjoy the serenity of being underwater without limiting injuries. We divers are a privileged lot.

Thanks again for the article; good read.

 

[tursiops]

Ok...read the article and it was very detailed and interesting but unconvincing for me in establishing VGM as a safer method of decompressing. "Stochastic modeling forecasts the probability of various outcomes under different conditions, using random variables." was referenced though out and is merely another statement of methodology not of verified modeling. Noted that the author also used his concepts commercially within the computer industry; not dismissing his veracity but he has a dog in the fight. Baker et al do acknowledge that more is unknown on the true mechanisms and variables that produce DCS than are currently known or modeled into decompression dives [all dives are decompression dives].

Great respect for Gurr, Baker and all those searching for methods to lessen DCS. My view is that a diver never really eliminates injurious circulatory and tissue damage on any hyperbaric/hypobaric cycle. Regardless of profile. So little is actually known of nuclei establishment and persistence; along with extent and nature of cellular damage after dives.... all dives.

OK...just for me....I put my money on the bar and called my shot....is my Peregrine or previously used Orca computer going to prevent either symptomatic or asymptomatic DCS? Carp shoot at best. Will the the largely unknown risk factors stop me from diving? At my age any damage is already done after 70 years of diving; so no I am in a penny, in a pound. I WILL dive more conservative profiles regardless of engaging computer manipulations and take experientially verified steps to lessen or prevent damage. Such as staying a long way from NDL/M values, slowing ascents in shallow, staying hydrated, using the "oxygen window" to hastening N2 elimination by lessening N2 inspired and increasing N2 expired by the use of EAN40 at extended safety stops [staged not carried], moderated physical exertion to lessen CO2 tensions and limit post dive core/limb temp increases and circulatory increases from exertion.

Only my approach and definitely "one size doesn't fit all"..... hopefully I can continue to blow bubbles and enjoy the serenity of being underwater without limiting injuries. We divers are a privileged lot.

Thanks again for the article; good read.

You are trying to have it both ways, aren't you?
You say it's all a crap shoot, then you list all the things you are going to do to improve your odds even further than your Peregrine suggests. Why not just admit that there is some real value in the Peregrine calculations, and in your mitigation measures, and that the current models and experience-based behaviors are FAR BETTER than "just a crap shoot."