What's your Low Gradient Factor Selection

[Manu]

The concept of "directing inert gas" was initiated by Pr Gardette Comex, without scientific study to support it, followed by IANTD (south of France Joel Gallien) and spreading around.
To my knowledge, there is no scientific ground in that split, for over 10 year I'm diving deep on CCR Tx10/50 that would be the "worse" gas choice and feel very well.

Hi,

For me, you can not just chose your "GF's" one for all.
Air = one type of GF
Tx<30% He = one type of GF (less than 30% He) "normoxic"
Tx<30% N2 = one type of GF (less than 30% N2) "hypoxic"

Depending of wich is your directing inert gaz the deco profil must be different.
My 2ct

 

[jptaylor9]

Ok, then you are not talking the same thing as everyone else.

What about if you run done other gf that provides you with the intended result but simply starts the stops shallower than vpm?

Sent from my SM-G900I using Tapatalk

I'm out of here, fcuk it I'm off diving......

 

[garethingham]

Not true.... see earlier threads by me/Baron015. We discussed a 60m dive, I do 40mins BT, on GF70/70 I'd have to cut BT to 25mins to stay within 2hr limit set by skipper. So I'd loose 15mins bottom time. Baron015, stated he'd had to reduce his bottom times since changing to a 70/70 profile....

On my next dive (~60m), got blown out due to Hurricane Bertha this w/end, I'm running my X1 on plain VPM-B+2 (shaves a few mins off deco) & the Vision on GF 50/90 as the profiles are broadly comparable (was 35/95)....

Isn't the point that the model has been shown to be flawed more so than GF? Neither are perfect but data does seem to support one more than the other. It seems all you are accepting is a higher risk than others are wiling to accept based on current evidence?

Why don't you just model a higher risk GF deco schedule. Just had a look on Baltic deco at GF 40/85 with 18/45 Bottom Gas @ 1.2, switch to 1.4 at 21m on 50%. Research seems to indicate that changing gases won't really add much value, just lie to the computer about the switch.

Out of the water in 121mins. Let's just leave a minute early .

My experience with VPM on a few hundred OC mix dives between 40 to 90m looks very aggressive shallow, holds you deep for a while (not great for emergencies) and resulted in skin and minor joint bends for myself and a few diving mates. In hindsight, we were not spending enough time shallow on 02. All were resolved with 02 surface deco. Like you we were attracted by the perceived shorter deco times, plus it worked well with GUE ratio deco.

If you can achieve the same BT goals while having some new data points in your pocket supporting the model you are using, why wouldn't you?

What am I missing in your logic apart from the fact you have not been bent yet using the VPM model?

 

[rossh]

Isn't the point that the model has been shown to be flawed more so than GF?

No, the test was of the BVM(3) model, and VPM-B and ZHL with GF were not tested. Nor did they test any profile types in use today, or the profiles in question here.


ZHL with GF is used to emulate VPM-B by 62% of divers in this thread, and ZHL with GF is used by a 73% of divers to make deep stops in general. It seems wrong to isolate VPM-B, when the same profile is being done using ZHL with GF instead.

 

[Hydreliox]

Forgive me for sounding once again a little bit of a layman here.

I am currently set to use VPM+2-GFS 75 at the moment. It my minds seems to give the best of both worlds. Some 'slowing down' a little bit deeper (just changing from 9m/min to 3m/min) followed by a longer stop at 6m. VPM+2 will probably remain first bailout choice. 75 in reality is maybe a tad relaxed.

Comparing all of this with a 35/75 or a VPM+2 - somewhere in the middle of the masses. If anyone else has any feedback on the VPM-GFS approach I would be interested. I've only just made the switch.

I'll be playing around with this in the coming weeks and see how they dive and work for me. VPM+2 has always been the go to.

 

[DeepUnderground]

Forgive me for sounding once again a little bit of a layman here.

I am currently set to use VPM+2-GFS 75 at the moment. It my minds seems to give the best of both worlds. Some 'slowing down' a little bit deeper (just changing from 9m/min to 3m/min) followed by a longer stop at 6m. VPM+2 will probably remain first bailout choice. 75 in reality is maybe a tad relaxed.

Comparing all of this with a 35/75 or a VPM+2 - somewhere in the middle of the masses. If anyone else has any feedback on the VPM-GFS approach I would be interested. I've only just made the switch.

I'll be playing around with this in the coming weeks and see how they dive and work for me. VPM+2 has always been the go to.

I'm in the same boat as you, used to dive vpm +2 but people saying about it being aggressive eventually got to me and for around a year now I've benn using VPN +2 with gradient factor surfacing.

Still do the occasional vpm +2 dive

 

[Hydreliox]

I'm in the same boat as you, used to dive vpm +2 but people saying about it being aggressive eventually got to me and for around a year now I've benn using VPN +2 with gradient factor surfacing.

Still do the occasional vpm +2 dive

DeepUnderground - a few questions if you don't mind.

Which GF have you got set? Any issues at all? What are the typical profiles you run. I would still do a VPM+2 (and I have never had issue with it) however, significantly less time in shallows seems a wee bit strange.

As many have already pointed out we are trying to compare apples with charcoal at best. Therefore figuring the approach to critical radii on bubble formation maybe we just don't need the extra shallow time.

I would also like to ask of others how these deco approach decisions affect you O2 CNS considerations. So far 115% is where I have maxed out. Looking at anything deeper and it is tough to decide where the concern should be placed. Sorry if this is a little OT - maybe I should start a new thread.

 

[DeepUnderground]

DeepUnderground - a few questions if you don't mind.

Which GF have you got set? Any issues at all? What are the typical profiles you run. I would still do a VPM+2 (and I have never had issue with it) however, significantly less time in shallows seems a wee bit strange.

As many have already pointed out we are trying to compare apples with charcoal at best. Therefore figuring the approach to critical radii on bubble formation maybe we just don't need the extra shallow time.

I would also like to ask of others how these deco approach decisions affect you O2 CNS considerations. So far 115% is where I have maxed out. Looking at anything deeper and it is tough to decide where the concern should be placed. Sorry if this is a little OT - maybe I should start a new thread.

Currently have the gfs set at 85

Never any Deco issues to date, (I'm young and keep fit)

Typical dive would be 50m ish 40 minute bottom time.

 

[matt]

Why not? I tried it yesterday and did not die. But also did not go deep or for very long! I'm going to use it on my upcoming trip; if I do not post again then it is obviously not to be advised!

Matt.

OK, I'm back from my trip where I took the opportunity to experiment. It's scooby diving, a picturesque wall down to 7,000m.

I can post some profile's if anyone is interested, but basically a few mini-bounces up to 70m on air using 90/95. Did a couple of 2-3hr runs, but did the deco all at 20m. I think I got to 22mins max deco, so nothing exciting. 22 dives, no problem. Most dives 60 mins, 2 a day.

I also tried the Inspo's "gradual" set-point setting. It's pretty cool. For this diving you can get away with using 20 bar O2 per dive. Deco goes up as you ascend, which is a bit weird.

I also experimented with how the temp-stick worked with the CO2 monitor. No CO2 alarms, even at only "2-blocks" left on the stick (7 dives, a tad over 7 hours, 28C). I have a trip in December where gas and lime are limited - so I'm going 3 days per fill on that one, wish me luck.

I'm moving to 50/85 for gas diving. Wish me more more luck.

Cheers
Matt.

 

[Mr fish]

thanks matt

 

[Manu]

matt an you please post some of your most engaged profiles.
Thanks

 

[matt]

matt an you please post some of your most engaged profiles.
Thanks

Not sure engaged can be used for this scooby diving, but here you go. This is where we were at with the Temp Stick after dive 7, 427 minutes, minimum water temperature is 29.6C:

And here is a typical profile down the wall. The deco is paltry, as you can see with GF90/95, Air:

Matt.

 

[Manu]

Thanks Matt, appreciate your posting.
I'm also moving from GF 30/85 to GF 90/90 for 70m dive total time around 60min on Tx 10/58 and I'm still alive.
This thread is quite disturbing as it shakes years of belief in slower ascent and shorter deco time near the surface.
We are back to the fundamental Haldanian deco profile. Not talking about the extreme dive >100m ...

 

[rossh]

for 70m dive total time around 60min

If I'm reading this correctly, its about 12 or 15 minutes on the bottom? That's not much of a dive or a test. Any kind of deco would work just fine for such relatively small gas loads.

I would expect all deco times derived from a model with conservatism, or extra time added (like all examples being discussed here), will work perfectly well. No one is really pushing the envelope here.

 

[matt]

No one is really pushing the envelope here.

No one is claiming to.
Matt.

 

[Baron015]

I'm moving to 50/85 for gas diving. Wish me more more luck.

Cheers
Matt.

Matt, just done 8 UK gas dives 50m-80m over the last two weeks using 75/75 GFs. Not exactly a statistically significant sample but I am still alive and felt good after the dives.

I've used Multideco to illustrate how the profiles were different from my normal 30/85 GFs.

[table="width: 500, class: grid, align: left"]
[tr]
[td]Depth/m[/td]
[td]Gas[/td]
[td]GFs[/td]
[td]BT/mins[/td]
[td]First Stop/m[/td]
[td]6m Stop/mins[/td]
[td]Runtime/mins[/td]
[/tr]
[tr]
[td]60m[/td]
[td]16/50[/td]
[td]30/85[/td]
[td]35[/td]
[td]33[/td]
[td]40[/td]
[td]113[/td]
[/tr]
[tr]
[td]60m[/td]
[td]16/50[/td]
[td]75/75[/td]
[td]35[/td]
[td]24[/td]
[td]45[/td]
[td]115[/td]
[/tr]
[tr]
[td]75m[/td]
[td]9/54[/td]
[td]30/85[/td]
[td]30[/td]
[td]48[/td]
[td]52[/td]
[td]137[/td]
[/tr]
[tr]
[td]75M[/td]
[td]9/54[/td]
[td]75/75[/td]
[td]30[/td]
[td]30[/td]
[td]56[/td]
[td]136[/td]
[/tr]
[/table]

So the main points I noted were:
- for the same bottom time the total dive time was roughly the same
- but with the first stop significantly shallower
- and with more time spent shallower stops esp 9m and 6m

In general I am happy with the profiles I was diving for these depths and times. Clearly might think again when doing some deeper dives with correspondingly longer runtimes but right now will probably continue this experiment and see how it goes.

Disclaimer: no one claiming that this is new or different or not been done already or that I have learned anything, just posting for forum / internet diving purposes

TB.