Safety stop feature request

[tbone1004]

educate me here what does GF lo have to do with NDL dives? am I missisng something. As I under stand It gf lo is moot until NDL is over stayed and only the gf hi is of value of being used. That for a rec ndl dive there is no difference between 30/70 and 70/70. that gf hi of 70 adjusts the NDL so you can directly surface and hit the surface with a GF of 70 with no stops assuming you did not exceed 70 on the ascent. 30 being first stop and 70 being the max allowed GF through out the dive. Max or the highest GF is expected as you hit the surface.

Using deco planner.
100ft on EAN32, all plus or minus a minute, so don't be pedantic
With 30/70, you get 10 mins on the bottom
With 70/70, you get 20 mins on the bottom
With 99/99, you get 30 mins on the bottom

The gf-lo sets the threshold not to exceed for the first stop which is how it controls the stop depth. That will absolutely change your bottom time when that "first stop depth" becomes shallower than the surface.
Now what is worth noting and why I don't agree with what you guys are doing is this. If you do what you're doing when you say I want to surface at GF70, you are still exceeding GF70 during your ascend. If you're ok with ascending at GF99, then you may as well get the rest of the way to the surface since you offgas faster at the surface than you do at 15ft since the partial pressure of inert gas is still higher than 0.8.

 

[rsingler]

educate me here what does GF lo have to do with NDL dives? am I missisng something. As I under stand It gf lo is moot until NDL is over stayed and only the gf hi is of value of being used. That for a rec ndl dive there is no difference between 30/70 and 70/70. that gf hi of 70 adjusts the NDL so you can directly surface and hit the surface with a GF of 70 with no stops assuming you did not exceed 70 on the ascent. 30 being first stop and 70 being the max allowed GF through out the dive. Max or the highest GF is expected as you hit the surface.

You're absolutely right. GFLo has nothing to do with NDL, but GFHi does. So a reverse profile wouldn't help, would it?
Having said that, I'm intrigued by @tbone1004's comment above that GF30/70 has a significantly shorter NDL than GF70/70. I'll have to look at that.

What I'm really doing is the same as @CWK : changing my GFHi on the fly. And I have a workaround based on TTS that allows me to gas plan, and a relatively known extension of safety stop time based on rate of SurGF decrease.
What he's asking for, I already do. It's just not displayed actively.

 

[rsingler]

you are still exceeding GF70 during your ascend. If you're ok with ascending at GF99, then you may as well get the rest of the way to the surface

This is where we disagree. Too much is happening with slower compartments after repetitive dives between 20 ft and the surface for me to dive xx/99. Slowing it down on final ascent has been a discussion item in another thread.

 

[tbone1004]

This is where we disagree. Too much is happening with slower compartments after repetitive dives between 20 ft and the surface for me to dive xx/99. Slowing it down on final ascent has been a discussion item in another thread.

but you still ride the /99 during the ascent. Look at the graphs that your planner generates. This is the 99/99 dive, 100ft for 30 minutes on EAN32 with a 5 minute stop at 15ft. Displaying % of M Ratios

This is doing the same dive at 70/70 which gives you 8 minutes of mandatory deco at 10ft and I gave an 8 minute stop at 15ft to normalize.

I don't see why you wouldn't just run 70/70. How on earth would the boat know if you went into deco or not? Since this is about a Shearwater computer, there is no notification that would remain on the screen that you violated a deco stop, so they'd have no idea. The only way they'd know is if they were looking at your computer specifically.
Dive the GF's that you believe in, and quit trying to manipulate the damned computer. The only reason I see for this is the fear mongering that the industry has put into the word decompression. It only leads to everyone trying to bend the rules to "stay out of deco" when they don't understand how or why it works, pun intended. Remember that pure buhlmann is theoretical, remember that most of the test subjects were 20yr old hot shots in the best shape imaginable, and also remember that anyone in commercial or military diving has a surprisingly high acceptable rate of DCS because they have chambers on board.

 

[CWK]

Some of us have been doing this manualy for some time.
.
.
You want this automated so you know your SS time in advance?

Yes. SS time based on surface gf.

 

[rsingler]

but you still ride the /99 during the ascent. Look at the graphs that your planner generates. This is the 99/99 dive, 100ft for 30 minutes on EAN32 with a 5 minute stop at 15ft. Displaying % of M Ratios
View attachment 599717
This is doing the same dive at 70/70 which gives you 8 minutes of mandatory deco at 10ft and I gave an 8 minute stop at 15ft to normalize.
View attachment 599723

I don't see why you wouldn't just run 70/70. How on earth would the boat know if you went into deco or not? Since this is about a Shearwater computer, there is no notification that would remain on the screen that you violated a deco stop, so they'd have no idea. The only way they'd know is if they were looking at your computer specifically.
Dive the GF's that you believe in, and quit trying to manipulate the damned computer. The only reason I see for this is the fear mongering that the industry has put into the word decompression. It only leads to everyone trying to bend the rules to "stay out of deco" when they don't understand how or why it works, pun intended. Remember that pure buhlmann is theoretical, remember that most of the test subjects were 20yr old hot shots in the best shape imaginable, and also remember that anyone in commercial or military diving has a surprisingly high acceptable rate of DCS because they have chambers on board.

You have a point, Tom. Lemme look at your graphs and see how long (how shallow) I'm pushing 99. If, to get my desired bottom time, I have to throw in a minute at 30 feet, I have no problem hiding that from the boat.

 

[tursiops]

Sorry, I've lost the bubble, starting at Tom's post #61. I thought the idea was to stay OUT of deco, not to compare how long you are IN deco with various GF pairs. 30 mins at 100 ft is only an NDL dive for a GFhi of 99, maybe 95. So what is the discussion about doing that dive with a GFhi of 70, for which it IS a deco dive and therefore the 30/70 and 70/70 bottom times WILL be different. Seems like a bunch of apples and oranges.

 

[KenGordon]

This is were we differ. To me, m-value is set by the algorithm such as Buhlman’s zhl 16c. The gf high allows you to set a conservatism or safety margin away from m-value. But to set a conservative value such as 75 and have the computer say that you are in deco because your surface gf is 76 is, to my mind, incorrect and erroneous.

The whole point of GF Is that 100/100 is too aggressive.

It sounds like you don’t think pure Buhlmann is too aggressive but then it sounds like you don’t want to actually dive it.

I do the opposite of you, I have one computer set to a conservative GF and one to 95/95. I do the deco as required by the conservative one but in a mild emergency, such as bailing out, I am prepared to follow the 95/95 one. It would be nice if bailout having different GF was supported.

Maybe you should look at an OSTC as they are a bit more advanced with how they handle this kind of thing, I believe.

 

[KenGordon]

Sorry, I've lost the bubble, starting at Tom's post #61. I thought the idea was to stay OUT of deco, not to compare how long you are IN deco with various GF pairs. 30 mins at 100 ft is only an NDL dive for a GFhi of 99, maybe 95. So what is the discussion about doing that dive with a GFhi of 70, for which it IS a deco dive and therefore the 30/70 and 70/70 bottom times WILL be different. Seems like a bunch of apples and oranges.

He wants to do the 30 minutes at 100ft and the stop called for by 70/70 but label the dive as NDL because he didn’t exceed 99/99 at the surface. Tom is pointing out he will exceed 70/70 on the way to the surface.

Meanwhile the point of safety stops has been lost and everyone is gaming the computer because they don’t like diving PADI style after all.

When developing software you have to think how it will be abused. SurfGF is being abused here.

 

[KenGordon]

You know Suunto changes the length of the safety stop depending on aspects of the profile and get slated on SB an FB for that?