Have I understood the basics of decompression theory, GF99 and SurfGF?

[dmaziuk]

from my own simulations of your dives if I set the conservatism really, really low I can with some effort get a dive plan that sort of matches your description of the second dive either without going into NDL or else clearing it on the way up without a required deco stop ...

Cressi, or at least my Leo, is fairly clever in the no-stop part and really dumb once you hit deco: the only way to clear it is to ascend to the deco stop depth and hang there. No amount of "shallowing up" will clear it, it'll only add more deco. If "Z+" is anything like that, I can easily see them getting a "transient" ceiling on dive 2 that would've cleared on ascent -- but send the "dumb" computers into VGM lock-out.

 

[therookie]

Cressi, or at least my Leo, is fairly clever in the no-stop part and really dumb once you hit deco: the only way to clear it is to ascend to the deco stop depth and hang there. No amount of "shallowing up" will clear it, it'll only add more deco. If "Z+" is anything like that, I can easily see them getting a "transient" ceiling on dive 2 that would've cleared on ascent -- but send the "dumb" computers into VGM lock-out.

My Leo, unsurprisingly, is just as clever and as dumb as yours - they really take that "don't go beyond your NDL" thing to a whole new level don't they? I was thinking more of the newer computers like the Garmins etc that have more configurable alarms like a 5 minute NDL warning (if I remember right from reading some of the manuals).

 

[lowwall]

The explanation is about half-way down the page, under "what to do about gradient factors" heading: Gradient Factors in a Post-Deep Stops World

Thanks. Here's what Dr. Doolette had to say in the article:

"In ZH-L16, the average of “b” parameters is 0.83. I choose my GF low to be about 83% of the GF high, for instance GF 70/85. Although the algebra is not exact, this roughly counteracts the slope of the “b” values. This approach allows me to believe I have chosen my GF rationally, is not so large a GF low as I am unable to convince my buddies to use it, and satisfies my preference to follow a relatively shallow stops schedule."

I am not suggesting that something around 83% is unreasonable, but that IMO, there's an unwarranted leap between one person's opinion, no matter how well informed that person is, to the categorical statement I was questioning:

"Decompression experts recommend GFLow = 0.83xGFHigh".

 

[Joemdown]

My Leo, unsurprisingly, is just as clever and as dumb as yours - they really take that "don't go beyond your NDL" thing to a whole new level don't they? I was thinking more of the newer computers like the Garmins etc that have more configurable alarms like a 5 minute NDL warning (if I remember right from reading some of the manuals).

Makes sense.

It’s worth noting none of knew how to use the comps and were just given them, no instructions on use, not even dive briefings were given really.

It didn’t have an audible alarms but possible visible when I wasn’t looking at it.

Wasn’t told we’d need any deco so we all just did the 3min 5m safety stop to clear

As you say. I think bad planning coupled with our ignorance not helpful. Hence the reason for looking into so I can make my own decisions on the future if I want to dive the 3rd!

 

[dmaziuk]

I am not suggesting that something around 83% is unreasonable, but that IMO, there's an unwarranted leap between one person's opinion, no matter how well informed that person is, to the categorical statement I was questioning:

"Decompression experts recommend GFLow = 0.83xGFHigh".

And about as irrelevant to NDL diving as on-gassing in the shallows while watching 99GFs go down. If you don't intend to have a deco stop, you may as well go DSAT set your delta-M slope to 0.

 

[boulderjohn]

I am not suggesting that something around 83% is unreasonable, but that IMO, there's an unwarranted leap between one person's opinion, no matter how well informed that person is, to the categorical statement I was questioning:

"Decompression experts recommend GFLow = 0.83xGFHigh".

Yes, you are correct that this is only one person's opinion, but that is one pretty significant person indeed. I would bet that a lot of people started thinking along those limes right after that article came out. I know that pretty much everyone I dive with was persuaded.

Almost all of the experts I know of are closer to that than to the standard Shearwater presets.

 

[tursiops]

Yes, you are correct that this is only one person's opinion, but that is one pretty significant person indeed. I would bet that a lot of people started thinking along those limes right after that article came out. I know that pretty much everyone I dive with was persuaded.

Almost all of the experts I know of are closer to that than to the standard Shearwater presets.

Cool, I dive 70/85. Does that make me an expert?

 

[dmaziuk]

Almost all of the experts I know of are closer to that than to the standard Shearwater presets.

Fraedrich's analyses show that GF Low should not be set to < 55 so SW presets are really wrong on that side. OTOH if their definition of "recreational" is "no-stop", then GF Low doesn't matter anyway unless set to something ridiculous like 10 IIRC.

 

[MarkA]

Fraedrich's analyses show that GF Low should not be set to < 55 so SW presets are really wrong on that side. OTOH if their definition of "recreational" is "no-stop", then GF Low doesn't matter anyway unless set to something ridiculous like 10 IIRC.

What is "Fraedrich's analyses"? Google doesn't supply anything relevant.

 

[dmaziuk]

What is "Fraedrich's analyses"? Google doesn't supply anything relevant.

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