Deep Diving 108 feet w/ a single AL 80 (Air.) No redundancy.

[boulderjohn]

BTW, what are the PADI or DAN recommended ascent profiles now?

Nothing has changed recently. They recommend divers ascend at a rate consistent with the instruction of the computer they are using and doing a 3-minute safety stop at about 15 feet. If people are using tables, PADI says they should not exceed 60 FPM, which was the standard ascent rate when the tables were created. They emphasize slow, though, so slower is better. DAN's publications are pretty much the same, emphasizing slow ascents. They do not identify an ascent rate that is too slow, and that is because there is no literature suggesting that an NDL dive can be too slow, unless the diver goes slow enough to violate NDLs.

In theory, a diver should be able to ascend at a normal rate from any depth at any point in an NDL dive and go directly to the surface without harm. The safety stop provides an extra level of protection.

 

[Storker]

For a 100'/30 m dive, MG calculates as 40 cf of gas or about 1500 psi or 100 bar with a full 80 cf tank.
That's it. It doesn't change.

It doesn't change as long as you're at 30m. With the caveat that it depends somewhat on the individual divers' RMV.

But if you go to 20m, the required reserve changes. If your min gas calc doesn't account for that, it seems to me to be a rather inflexible parameter, not particularly suitable for real diving but more of an academic exercise.

 

[Ayisha]

...and they are?

As you know, I am not a GUE instructor or authorized, so I will refrain from going into specifics. The formulas may be openly available, I'm not sure.

I believe the OP is GUE trained in MD, but he probably didn’t intend for it to go into course specifics.

 

[Storker]

As you know

I didn't, but thanks for the heads-up. I am in no way associated with GUE; the closest I've been to that agency is that my CMAS 3* instructor also held a GUE T2C2 cert.

Which in itself is a good argument for cross-pollination between agencies. IMNSHO, of course.

 

[Ayisha]

It doesn't change as long as you're at 30m. With the caveat that it depends somewhat on the individual divers' RMV.

But if you go to 20m, the required reserve changes. If your min gas calc doesn't account for that, it seems to me to be a rather inflexible parameter, not particularly suitable for real diving but more of an academic exercise.

The SCR that is to be used for 2 stressed divers only changes if one of the team has a known massive consumption rate when stressed. It isn't an individual exercise and takes into account that both may be stressed or one may be more stressed than the other.

MG doesn't change when you ascend from 30 m to 20 m on the same dive.
Yes, it would probably be considered too inflexible for many or most divers.

I suspect it would be more of an issue for those with a higher SCR. Mine is very low and my tank is usually almost half full anyway diving to the MD or NDL limits.

The ones with higher consumption rates routinely go quickly into doubles, so no worries for them.

 

[Storker]

The SCR that is to be used for 2 stressed divers only changes if one of the team has a known massive consumption rate when stressed. It isn't an individual exercise and takes into account that both may be stressed or one may be more stressed than the other.

MG doesn't change when you ascend from 30 m to 20 m on the same dive.
Yes, it would probably be considered too inflexible for many or most divers.

I suspect it would be more of an issue for those with a higher SCR. Mine is very low and my tank is usually almost half full anyway diving to the MD or NDL limits.

The ones with higher consumption rates routinely go quickly into doubles, so no worries for them.

Sorry, does not compute. At least not to me.

Is your required reserve different at 20m (or 10m) than at 30m? Yes, of course. Does that change your math? No, it shouldn't. Does calculating a necessary reserve at 30m differ fundamentally from calculating a necessary reserve at 20m (or 10m)? Why should the depth you're at change what you choose to call your calculation of your necessary reserve?

 

[Ayisha]

Nothing has changed recently. They recommend divers ascend at a rate consistent with the instruction of the computer they are using and doing a 3-minute safety stop at about 15 feet. If people are using tables, PADI says they should not exceed 60 FPM, which was the standard ascent rate when the tables were created. They emphasize slow, though, so slower is better. DAN's publications are pretty much the same, emphasizing slow ascents. They do not identify an ascent rate that is too slow, and that is because there is no literature suggesting that an NDL dive can be too slow, unless the diver goes slow enough to violate NDLs.

In theory, a diver should be able to ascend at a normal rate from any depth at any point in an NDL dive and go directly to the surface without harm. The safety stop provides an extra level of protection.

This is what DAN has published about ascent rates: in Alert Diver | Ascent Rates

"Despite the lack of definitive consensus on what ascent rate divers should use, "slow" is a good way to go. The U.S. Navy and the National Oceanic and Atmospheric Administration (NOAA) use a rate of 30 feet per minute, and recreational dive-training-agency recommendations range from 30 to 60 feet per minute. Regardless of the ascent rate you choose, it is most important that your ascents be well under control".

They are in the middle of an Ascent Rate study.

Since you mentioned the PADI 3 minute safety stop, notice that GUE does not have a 3 minute safety stop. It is replaced by 3 one minute stops/slides.
Add the one minute at 40 feet, and you have a one minute longer ascent time.

 

[Storker]

This is what DAN has published about ascent rates: in Alert Diver | Ascent Rates

"Despite the lack of definitive consensus on what ascent rate divers should use, "slow" is a good way to go. The U.S. Navy and the National Oceanic and Atmospheric Administration (NOAA) use a rate of 30 feet per minute, and recreational dive-training-agency recommendations range from 30 to 60 feet per minute. Regardless of the ascent rate you choose, it is most important that your ascents be well under control".

During my 3* class sessions, we were tasked to ascend at pretty close to 10 m/min (30 fpm). That was a lot faster than I usually ascend and, frankly, a bit difficult to do.

I'd be hard pressed to ascend at 10 m/min unless I'm close to an uncontrolled ascent in free water. Following the bottom up on a shore dive? No effing way unless I'm working hard at it. 60 fpm (20 m/min)? You'd have to haul me up on a line.

 

[Ayisha]

Sorry, does not compute. At least not to me.

Is your required reserve different at 20m (or 10m) than at 30m? Yes, of course. Does that change your math? No, it shouldn't. Does calculating a necessary reserve at 30m differ fundamentally from calculating a necessary reserve at 20m (or 10m)? Why should the depth you're at change what you choose to call your calculation of your necessary reserve?

That is a misunderstanding.
MG is a different formula from RB.
The formula to calculate MG for a 30 m dive or a 20 m dive is the same. The calculated end result is of course, different.

DIR/GUE went from using RB, to a newer RB, to MG. I imagine GUE must have had reasons to shift deco strategies.

15 - 20 years ago, people complained to no end that RB was way too conservative. Now, people still use RB who weren't even trained in it.
People say that MG is way too conservative, yet quite a lot of people use it even beyond those formally trained in it.
Will the paradigms keep shifting? Don't know.

 

[Storker]

Again, I'm not understanding the difference I understand that you claim there is between min gas and rock bottom. In any case, the goal should be to be able to estimate what the minimum reserve is at your current depth, no? How does it matter what you call it, min gas or rock bottom? How does that change with max or current depth (except what the necessary reserve is?). And how do the formulae differ? I'm fine with mathematical definitions, please bring on the formulae!