Peregrine NDL Questions

[Kimela]

I just did two days of meg tooth hunting and used my Peregrine. The dives were 35 ft max and I averaged 105 minutes per dive - 3 dives per day, so total of 6 dives. I was set on Air at 21%, moderate conserv, and had the same dive profile as everyone else (because you literally could NOT go deeper than 35ft).

After the last dive everyone was commenting that they had to end the dive because they were at between 2 and 5 minutes of NDL. My computer still said 99! I sent a message to Shearwater this morning and we'll see what they say, but I'm really curious. I know someone was diving a Suunto, and Roger was diving an Oceanic (and his might be set on conservative). I'm wondering if there's a setting I missed? My alarm works fine. I watched my ascent rate - not that that would change my NDL, just trying to show that I really am paying attention. I also looked at my tissue saturation rate during that last dive because I was wondering if I was getting close and I was still a-ok. Had an impromptu discussion with the other divers and they all said 'maybe you're still set on nitrox?' - nope. I'm not bent, all is ok. Just super curious.

If you have any ideas or suggestions please let me know.

 

[Wayward Son]

Watching

 

[jborg]

I threw three 105-minutes-to-10m dives into Subsurface, not paying too much attention to surface intervals or details, and the final dive looks like it ends with a SurfGF of 69% and NDL of 74 min (for GF45/85). If your actual dives were even a little shallower, 99 min NDL doesn't sound implausible.

If the dives where to 11 m instead (36 ft), which they won't have been in your case, SurfGF ends at 81% with an NDL of 14 min. So getting a bit deeper than 35 ft makes a lot of difference. Perhaps the other computers' different algorithms make a larger difference. Perhaps the next day there's enough residual nitrogen to penalize them.

In any case, you could import them into Subsurface and see what its calculations are, as a form of second opinion.

 

[tursiops]

I just did two days of meg tooth hunting and used my Peregrine. The dives were 35 ft max and I averaged 105 minutes per dive - 3 dives per day, so total of 6 dives. I was set on Air at 21%, moderate conserv, and had the same dive profile as everyone else (because you literally could NOT go deeper than 35ft).

After the last dive everyone was commenting that they had to end the dive because they were at between 2 and 5 minutes of NDL. My computer still said 99! I sent a message to Shearwater this morning and we'll see what they say, but I'm really curious. I know someone was diving a Suunto, and Roger was diving an Oceanic (and his might be set on conservative). I'm wondering if there's a setting I missed? My alarm works fine. I watched my ascent rate - not that that would change my NDL, just trying to show that I really am paying attention. I also looked at my tissue saturation rate during that last dive because I was wondering if I was getting close and I was still a-ok. Had an impromptu discussion with the other divers and they all said 'maybe you're still set on nitrox?' - nope. I'm not bent, all is ok. Just super curious.

If you have any ideas or suggestions please let me know.

Even the PADI RDP would allow those dives to 35 ft, given a 1h SI between them.
I don't see a problem.

 

[inquis]

I watched my ascent rate - not that that would change my NDL

But it might change that of others. Suunto penalizes rapid ascents (perhaps on earlier dives).

 

[rongoodman]

Did you look at the tissue loading graph after the dives?

 

[Kimela]

Even the PADI RDP would allow those dives to 35 ft, given a 1h SI between them.
I don't see a problem.

I wasn't paying attention to how much time our surface intervals were - and I'm not finding that on the computer or on the app. I suspect they were less than an hour. And again - the mystery is why my computer is so very different than the other 5 divers.

Also, I have checked, double checked (with R looking over my shoulder - on the boat and again today) and made sure I'm at 21%. BUT there is screen on the app version that shows my Computer settings and it looks like even though it says 21/100 it says NITROX. I'm flummoxed.

 

[wnissen]

I wasn't paying attention to how much time our surface intervals were - and I'm not finding that on the computer or on the app. I suspect they were less than an hour. And again - the mystery is why my computer is so very different than the other 5 divers.

Also, I have checked, double checked (with R looking over my shoulder - on the boat and again today) and made sure I'm at 21%. BUT there is screen on the app version that shows my Computer settings and it looks like even though it says 21/100 it says NITROX. I'm flummoxed.
View attachment 739878View attachment 739879

I'm pretty sure that's just the computer's mode. If you ever dive Nitrox it should be set to Nitrox.
From https://www.shearwater.com/wp-content/uploads/2020/07/Peregrine_Manual-metric.pdf

4.2. Dive Mode Differentiation
Each dive mode is designed to best suit a particular
type of diving.
Air
Designed for use during recreational, air only,
no-decompression diving activities.

• Air (21% oxygen) only, not switchable underwater​

• Simplified Info Rows​

• Enhanced warnings​

Nitrox (Single Gas)
Designed for use during recreational, Nitrox,
no-decompression diving activities.

• Single Gas Nitrox up to 40% oxygen​

• No gas switching underwater​

• Simplified Info Rows​

• Enhanced warnings​

 

[Divin'Papaw]

I wasn't paying attention to how much time our surface intervals were - and I'm not finding that on the computer or on the app. I suspect they were less than an hour. And again - the mystery is why my computer is so very different than the other 5 divers.

Also, I have checked, double checked (with R looking over my shoulder - on the boat and again today) and made sure I'm at 21%. BUT there is screen on the app version that shows my Computer settings and it looks like even though it says 21/100 it says NITROX. I'm flummoxed.
View attachment 739878View attachment 739879

Surface interval is in the right column partway down. Nitrox is just the mode. It is set at 21% so you've set it correctly. My guess would be that the other computers are either bubble models instead of Buhlmann with GFs or penalizing the divers for something. Rapid ascents, surface intervals too short, etc. Shearwaters run the straight algorithm according to your settings as a computer should. It doesn't build in penalties that I'm aware of.

 

[rhwestfall]

"Air" is "21% Nitrox".... no difference.