On a NDL dive, which computers' NDLs are not affected by GFLo?

[atdotde]

PS it doesn't "leave out" the 4-minute TC, you have to choose the 4 or 5-minute one for your implementation (again according to Baker). Of course in computer-minutes that's 20% (or 25, dep. on which way you count 'em) difference in the key value in your TC that's first to react to ambient pressure changes...

At some point, we played around with it and used the 4 minute compartment. As it is both on- and off-gassing faster, the effects cancel out to some degree and this compartment is determining at best the very first part of your deco (as you can see for example in Subsurface when plotting the individual tissues) that the actual effect on deco schedules is very minimal.

 

[dmaziuk]

At some point, we played around with it and used the 4 minute compartment ... the actual effect on deco schedules is very minimal.

On deco schedules, I'm sure it is. Have you tried using something like 10/90 and running it to 0 NDL to see where your first stop suddenly appears, as @huwporter did? He got a 9m stop, would one get a 9m + 20% rounded down to the next 3m = 12m deco stop w/ the 4-minute 1st TC?

 

[Jay]

ok redone check for AV1
air, 25M, 20min, 90/90, 24min total
air, 25M, 20min, 10/90, 24min total listing stops from 15M but with 0min stop.
Same.
For
air, 30M, 15min, 90/90, 21min total with 1min at 3M
air, 30M, 15min, 10/90, 20min total listing stops from 18M but with 0min stop.
1min less with 10/90.
And for
32%, 25M, 20min, 90/90, 22min
32%, 25M, 20min, 10/90, 24min total listing stops from 12M but with 0min stop.
2min more with 10/90
32%, 30M, 15min, 90/90, 18min
32%, 30M, 15min, 10/90, 20min total listing stops from 12M but with 0min stop.
2min more with 10/90
So, looks like it depends... or maybe the delta is too small for being pertinent...

Thanks for doing that. It all seems more or less consistent with what StuartV found in post #126.

I've updated the updated list:

Here's an updated list ... not many to go now.

GFLo basically* does not affect NDL on a NDL dive (source)
Shearwater
Dive Rite's discontinued Nitek - Q (post#2)
Deep 6 (post#93 and via PM)
Garmin Descent (from a Descent diver via PM)
TDC-3 (email and post#69)
Seabear H3 (the link in post#126)
Heinrichs Weikamp (post #4 of StuartV's link in post#126)
Dive Soft (post#122)
AV1 (post#123) <--?provisional (post#135)

GF Lo affects NDL on a NDL Dive
none yet

Unknown (yet) but do have custom GFs (i.e. easy to know if GFLo affects NDL)
Mares - Genius (awaiting email response - if someone's near a shop with one feel free ....
Ratio/SEAC (Tech+ has custom GFs)
Scubapro - HUD (anyone got access to play with one?)
Suunto EON Steel <-- need to wait for 16C implementation (?post launch of the D5)

Unknown but doesn't have custom GFs (probably impossible to discover)
Liquivision Lynx



Thanks for that @stuartv. A very interesting and relevant thread.

*basically means for all intents and purposes e.g: stops clear as you arrive at them, or, there is only a small unique window (e.g. a few meters to the surface) etc etc .... and rather than making a blanket statement which could be argued is technically incorrect ... leading to ambiguity of what the results practically mean for other divers that haven't read the whole thread in detail.

 

[atdotde]

On deco schedules, I'm sure it is. Have you tried using something like 10/90 and running it to 0 NDL to see where your first stop suddenly appears, as @huwporter did? He got a 9m stop, would one get a 9m + 20% rounded down to the next 3m = 12m deco stop w/ the 4-minute 1st TC?

No, this is not how it works. At least at first approximation, it does not lead to deeper stops but it could create such a stop after a shorter bottom time. But on the other hand, it also desaturates faster and thus the corresponding stop tends to be shorter by 20% (assuming all the other compartments don't create additional deco obligation).

But the main point is that such very short stops are virtually indistinguishable from non-stop dives with slightly lower ascent rate (as the very fast tissues already desaturate during the ascent). In fact, with sufficiently slow ascent rate the very fast tissues will not be dominant for very long (or at all) for your deco stops.

Take this example of a dive to 40m with air. I have set the ascent rate to 10m/min and used the kind of extreme gradient factors 10/90 as you suggest:

You can see that the fastest tissue creates a massive ceiling as deep as almost 20m. But it recedes almost as fast as the ascent creating a minimal length stop in fact at 12m. But if I decrease the ascent rate to 9m/min, this stop is gone and I am left only with the shallower stops created by the somewhat slower tissues.

 

[KenGordon]

This raises a question about what a no stop dive is for. Is it to avoid stops in an otherwise normal ascent or to keep a diver safe in the event of an accidental, and faster than normal, ascent? Should a no stop dive be one which never has a ceiling?

 

[scubadada]

This raises a question about what a no stop dive is for. Is it to avoid stops in an otherwise normal ascent or to keep a diver safe in the event of an accidental, and faster than normal, ascent? Should a no stop dive be one which never has a ceiling?

This is an interesting question. Has anyone ever left the bottom at, or very near, the NDL and had a stop appear during the ascent? I have started my ascent on numerous occasions at NDL=0, but not yet into deco, on both my DSAT and Buhlmann computers, and have never had this occur. However, I don't recall ever doing this with a faster than normal ascent.

On the other hand, I would imagine many of us have started the ascent with a very small deco obligation and had it disappear before reaching the stop depth.

 

[dmaziuk]

In fact, with sufficiently slow ascent rate the very fast tissues will not be dominant for very long (or at all) for your deco stops.

Good. So the choice of 2.5 minutes for the 1st TC in my computer will possibly maybe penalize me more for faster ascents, but nothing more than that.

IIRC Baker in decolessons picks the 5-minute TC "to be compatible with other planning tools" and because "it won't make practical difference except on short bounce dives" (as you've demonstrated). I have no context for that statement: what are those "other tools" and do I care about compatibility with them today? Would a no-stop dive to 40 m fit Erik's definition of "short bounce dive"? Maybe I want the 4-minute TC, rather than 5-minute, in my recreational dive computer.

 

[dmaziuk]

This is an interesting question. Has anyone ever left the bottom at, or very near, the NDL and had a stop appear during the ascent?

Theoretically it may be possible but that should come from slower tissues. They won't be affected by ascent speed so much. At a guess the way to get there would be to dive 6 tanks/day to DSAT limits on both NDLs and SIs.

(Don't do that at home, it's how they bent their test diver on day 2.)

 

[dmaziuk]

This raises a question about what a no stop dive is for. Is it to avoid stops in an otherwise normal ascent or to keep a diver safe in the event of an accidental, and faster than normal, ascent? Should a no stop dive be one which never has a ceiling?

I think this goes back to the idea that if you understand how this works, you don't really give a toss about exact NDL number. If your no-stop dive goes as planned, the only time it needs to be greater than zero is at the end of your highly-recommended-not-decompression 3 m stop. If the dive goes sideways you hopefully did some risk assessment before splashing and have some kind of plan...

 

[Jay]

This raises a question about what a no stop dive is for. Is it to avoid stops in an otherwise normal ascent or to keep a diver safe in the event of an accidental, and faster than normal, ascent?

Does it need to be either or, why not both?