Feedback on recent two-tank and dive limits

[old frogman]

My takeaway from this discussion is as follows:
1. If I have just completed an open water or advanced open water dive course and have no intention of advancing into technical diving, I would stay well away from any computer using GFs. I would stick to recreational level dive computers with Bhulmann and/or DSAT algorithms.
2. If I have completed an advanced open water dive course and are looking at the possibility of advancing to advanced nitrox and decompression procedure course, a dive computer such which incorporates GFs would be a serious contender.

However, when using the dive computer (with GF) for recreational level NDL dives, I would avoid GFs lower than 70/70. My view is that GFs such as 45/95, 40/85 and 35/75 are designed more for planned decompression dives. If you use them for NDL recreational dives you may find yourself being told by the computer to do unplanned decompression, and there lies the risk.

As a further risk mitigation strategy, I would check at the dive plan screen on the computer before committing to the dive. This reduces the risk for square dives but for multilevel dives the risk may still be unknown.

 

[inquis]

when using the dive computer (with GF) for recreational level NDL dives, I would avoid GFs lower than 70/70. My view is that GFs such as 45/95, 40/85 and 35/75 are designed more for planned decompression dives

I can't tell what you're trying to say. Your first sentence says you would use a GFhigh above 70 for recreational diving. Then you state GFhighs of 75, 85, and 95 -- all above 70 -- are more designed for planned deco dives, which is NOT recreational diving by most people's definition. (Yes, the BSAC folks blur that line, but let's go with the majority view world-wide.)

In fact, DSAT was designed for repetitive NDL dives, and is fairly comparable to a GFhigh of 95 (and perhaps 90ish on later dives).

 

[inquis]

If you use them for NDL recreational dives you may find yourself being told by the computer to do unplanned decompression, and there lies the risk

In my view, that's a lack of awareness. If it tells you to do unplanned mandatory decompression, you screwed up long before that point.

 

[old frogman]

I can't tell what you're trying to say. Your first sentence says you would use a GFhigh above 70 for recreational diving. Then you state GFhighs of 75, 85, and 95 -- all above 70 -- are more designed for planned deco dives, which is NOT recreational diving by most people's definition. (Yes, the BSAC folks blur that line, but let's go with the majority view world-wide.)

In fact, DSAT was designed for repetitive NDL dives, and is fairly comparable to a GFhigh of 95 (and perhaps 90ish on later dives).

It appears that you have misunderstood what I said. I understand, you may lack nuance of the King's English. Please let me rephrase it simpler for you.

Recreational NDL diving - anywhere between 100/100 to 70/70.
Planned decompression diving - below 70/70, for example, 45/90, 40/85, 35/75. These GFs will give you deeper stops and over all longer ascent profiles.

 

[JMarc]

1. If I have just completed an open water or advanced open water dive course and have no intention of advancing into technical diving, I would stay well away from any computer using GFs. I would stick to recreational level dive computers with Bhulmann and/or DSAT algorithms.

I'm not aware of any computer proposing Buehlmann ZHL-16 outside GF. Scubapro proposes a series of adaptive algorithms named ZHL-8 something, the initial design was done by Pr Buehlmann after ZHL-16 was completed but the details are not published and Scubapro seems to continue to make the method evolve.1

RGBM seems on the EOL curve since Wienke's death, at least recent models of Suunto and Mares are using ZHL-16 + GF (and in the case of Mares some optional additional automatic adjustment, I don't know if and how Suunto has their own tweaks).

However, when using the dive computer (with GF) for recreational level NDL dives, I would avoid GFs lower than 70/70. My view is that GFs such as 45/95, 40/85 and 35/75 are designed more for planned decompression dives.

When ordering GF pairs, the usage I'm familiar with is to use GFhigh has the most significant member of the pair, thus 70/70 is lower than 45/90. And that ordering make sense as GFhigh is the main driver of the total stop time.

And again about the value of GHlow, 45/95, 40/85 and 35/75 seems to date from the time when aggressively deep stops were though to be useful, something which is not the current consensus for air and nitrox.

Planned decompression diving - below 70/70, for example, 45/90, 40/85, 35/75. These GFs will give you deeper stops and over all longer ascent profiles.

I've no planner available here to double check, but I'm pretty sure that 45/90 will give you less total stop time than 70/70.