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OSTC 2958
Sorry for this question...is possible to set the deep stop? because for example my buddy and I goes to 60 mt. depth with trimix + ean50 + oxygen...my ostc say that my first step is 21 mt. whitout deep stop...my buddy 2 min. at 45 mt....what I can do...thank you

Change to a GF deco model and set a low low GF (CF32 like 10%). It's not actually a deep stop in the meaning of pyle stops but it gets you near to this...

HTH,
Jan

Hi,

in order to generate kind of "deep stops" with Buehlmann you have to use the GF-mode and in order to do that you need to know some basics about that mode.
There's no such thing like Pyle for the present firmware.
There's plenty of threads here about that, use the search-function.

Here a very brief introduction ( you still have to read more about it, this is not enough to safely use GF ! ):

GF ( Gradient Factor ) is controlled by 2 values which are set by CF32 and CF33.
In order to have a deeper first stop you have to adjust CF 32.
You can go as low as 5 but 10 is a good value to start with, the default is 30.
CF 33 ( the second GF-value ) is controlling the conservatism to simplify it, a lower setting will increase the time on the shallow stops.

This is only very basic info on GF, look for more info here or use google.
Make sure not to exceed 30 for the first value and 90 for the second value.
I use 10/85 or 15/80 in general.

Be safe,Reiner

Upps, to slow

Hello,

For this stile of dive (20min @ 60m, Tx 21/35, Nx50): 10/85% looks fine (see the attached plot).
But understand that security factors have to be adapted to your mix and profile (and conditions).

Regards,

To have a similar deco planing like your buddy you may check the GF% displayed by you OSTC when your buddy is doing the 1st deep stop and use a value like this for CF32.

disregard

sailor Wrote:
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> Make sure not to exceed 30 for the first value and
> 90 for the second value.

Hi,

I have read a fair bit about GF figures and I understand the reason for adding them and also how they work. However, I see no need to keep the GF(Lo) factor at 30% or less. The GF(Lo) figure is the percentage of your M-Value which you first stop at, with a deco profile generated on the basis that your head towards GF(Hi) by the time you surface. Surely, any figure less than 100% is acceptable? If you were to run GF(hi) and GF(lo) at 100% you would simply be running a straight algorithm without gradient factors, so anything inbetween is more conservative surely?

I have run two profiles on GAP Software (sorry, but it's all I have!) (50m for 20mins, air, with EanX50 for deco) They were very similar in run times but one of the profiles was GF(lo) = 50%, the other GF(Lo) = 20% (both have GF(hi) = 90%).The lower GF factor got me out the water in 43mins, the other 41mins. With the low GF giving me 8 stops starting at 27m whereas the higher GF factor gave me 5 stops with the first being at 18m. So both looked sensible dive profiles to me and my own diving experiences suggest loading up slow compartments whilst stopping quite deep doesn't help (for me personally..on the type of dives I do)

I apologise if I am on the wrong topic for this dicussion but I would be very keen to hear why most advice on this topic is based on a GF(lo) of around 30% or less. The OSTC allows up to 90% before warning.

I should also say I am not an expert on this subject so I'm happy to take constructive critisism. But I did think it was relevant to Alex's original question of setting up the OSTC to provide deep stops that he would find useful.

Thanks
Nick

@JeanDo: Which software did you use to generate this diagram?

Nick Fleming Wrote:
-------------------------------------------------------
> sailor Wrote:
> --------------------------------------------------
> -----
> > Make sure not to exceed 30 for the first value
> and
> > 90 for the second value.
>
> Hi,
>
> I have read a fair bit about GF figures and I
> understand the reason for adding them and also how
> they work. However, I see no need to keep the
> GF(Lo) factor at 30% or less. The GF(Lo) figure is
> the percentage of your M-Value which you first
> stop at, with a deco profile generated on the
> basis that your head towards GF(Hi) by the time
> you surface. Surely, any figure less than 100% is
> acceptable? If you were to run GF(hi) and GF(lo)
> at 100% you would simply be running a straight
> algorithm without gradient factors, so anything
> inbetween is more conservative surely?
>
> I have run two profiles on GAP Software (sorry,
> but it's all I have!) (50m for 20mins, air, with
> EanX50 for deco) They were very similar in run
> times but one of the profiles was GF(lo) = 50%,
> the other GF(Lo) = 20% (both have GF(hi) =
> 90%).The lower GF factor got me out the water in
> 43mins, the other 41mins. With the low GF giving
> me 8 stops starting at 27m whereas the higher GF
> factor gave me 5 stops with the first being at
> 18m. So both looked sensible dive profiles to me
> and my own diving experiences suggest loading up
> slow compartments whilst stopping quite deep
> doesn't help (for me personally..on the type of
> dives I do)
>
> I apologise if I am on the wrong topic for this
> dicussion but I would be very keen to hear why
> most advice on this topic is based on a GF(lo) of
> around 30% or less. The OSTC allows up to 90%
> before warning.
>
> I should also say I am not an expert on this
> subject so I'm happy to take constructive
> critisism. But I did think it was relevant to
> Alex's original question of setting up the OSTC to
> provide deep stops that he would find useful.
>
> Thanks
> Nick


You are somehow right.

The OSTC will warn when exceeding 30/90, at least it used to do it before.
The warning at 90 you are mentioning is the upper second value, not the lower first value.

When switching to plain Buehlmann you will have a value of 90/90 and not 100/100 as there's some safety margin in the plain Buehlmann aswell ( if i'm right ).

Alex was asking how to generate a deeper first stop and in order to do that you have to select less then 30 for the first lower value.
I tried to answer his question and i wanted to make sure he is still safe!

I've heard about some grazy guys using GF-Values exceeding 100.
That might be ok for some navy-seals with a chamber in stanby.
For sure 100/100 is not ok for the average tec diver.

My half cent, Reiner

Hi Reiner,

Thanks for your half cent! I thought the OSTC alarmed above 30% for GF(lo) until I read the following in the 'Custom Functions'list

CF32:GF low value (GF Extension)
The value sets the GF low setting (GF method extension (Erik Baker))
Recommend range: 20 ... 30 (20% ... 30%)
Default setting: 30 (30%)
Example: CF32=30 - GF low = 30% or 0,3

This is critical custom function! If the value is above 90 (90%) a warning symbol is displayed permanently during Surface- and Divemode. Do NOT dive with a OSTC configured that way!

I haven't actually checked my own OSTC to see what it does if I set this above 30% but this then made me wonder why 30% is the number to stick to. I was going to start a new topic but thought it might be relevant here. But as far as deep stops go, in general, the lower the GF(lo) number, the deeper your first stop will be. But like everyone else says... you should read up on what GF factoring actually does in terms of tissue compartment saturation and M-Values to make sense of it. As there are members here that understand the mathematics behind it far better than me I was hoping that there might be a straight forward answer to maintaining a low GF(lo)%

Happy to move this to a new topic if it's worth further discussion.

Nick

@PeterK: I used OSTC Planner... See its thread.

There is no real such think as "Plain Bühlmann" model... Because Her Doctor always said that security margin should be added to the raw model...

In the OSTC you have 4 of them:
- Saturation (>100%) and desaturation (<100%), only when you are in the BH model.
- GF low and GF high, only when you are in GF mode.
- Deco offset: runtime and TTS are predicted assuming you lay 1m deeper than the stop.
- Infinite speed: descent time is counted at bottom depth, and you are allowed to ascent only when going (instantly) to the next stop is allowed by the model. But ascent speed (10m/mn) is used to add to the whole TTS.

Furthermore:
- Setting GF or Bühlmann ratios to 100/100% will led to the same runtime. But this is risky and not recommended by anyone. And will make the OSTC turning red.
- In the code, it is assumed that GF_low <= GF_high.
- Good values depend of your mileage. Personally, I use 40/80 or 50/85 when diving with air/nitrox. I was recommended 50/80 for light trimix (He ~25%) in tek-light configurations. If you do hypoxic, deep dive, you probably want more stops...


About GF/deep stop strategie:
Richard L. Pyle deep stop where somewhat arbitrary. Eric Baker's gradient factor method (tracking GF of the leading tissue) is smoother, and I never see them produce meaningfull on-gasing of any tissue.
See the attached graph: it uses very deep stops (GF 10/85). And there is indeed some tissues doing gas-loading during the first deep stops. But they are way below the decompression threshold...
Even if you push this dive way beyond the limit (bottom 45minutes, which means 4hours of deco and CNS ~ 270%), you seed in that graph that on-gasing tissues are not in the dangerous zone.

Regards,

JeanDo,

Thanks for the graphs and info. Much appreciated.

Nick

JeanDo Wrote:
-------------------------------------------------------
> There is no real such think as "Plain Bühlmann"
> model... Because Her Doctor always said that
> security margin should be added to the raw
> model...

Hi,

when i mentioned "plain Buehlmann" i was refering to the non-GF-modes of the MK2.
Sorry for that.

Reiner