Peregrine NDL Questions

[Belzelbub]

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?

I'm going to go with your settings are fine. The algorithm Suunto uses tends to get more conservative as the dive count racks up. Especially if the surface interval may have been less than Suunto wishes. Oceanics do tend to be quite liberal on the first dive (DSAT), but this changes on subsequent dives and it moves more conservative when compared to Buhlmann.

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.

21/00 not 21/100. 2nd number is the Helium %. Peregrine doesn't have helium capability, but the firmware is the same as Perdix and Petrel, so it displays that way. 21% is air, but air is Nitrox as well. Just not enriched. Plus as mentioned, Nitrox is the mode. Nitrox mode makes sense, though you could also use Air. Setting it at 21% when in Nitrox mode is considering your mix as air.

Your computer is set at 40/85, which is moderate conservatism. I noticed on both my Perdix and Garmin that doing long shallow dives doesn't do much to my SurfGF. It's generally in low single digits, so not likely to exceed NDL anytime soon. Even on multiple dives over an hour each.

 

[Divin'Papaw]

I noticed on both my Perdix and Garmin that doing long shallow dives doesn't do much to my SurfGF. It's generally in low single digits, so not likely to exceed NDL anytime soon. Even on multiple dives over an hour each.

I've noticed the same. Pretty much all of my Blue Heron Bridge dives regardless of length (2-3 hours typically), my End SurfGF is always 1.

 

[scubadada]

Hi @Kimela

What did your husband's computer show for a NDL? Was he diving DSAT or PZ+? Was conservatism off or on?

In general, I would expect DSAT without conservatism to be more liberal than Buhlmann ZH-L16C set at 40/85. However, I have seen some wild NDLs on my Teric with repetitive dives, when they are shallow, compared to DSAT. Somewhere on SB I posted an extreme example, I will try to find it.

Edit: It was easy to find with the SB search. See the 2nd example in this post, I found it startling DSAT vs GF high 95, examples

 

[rhwestfall]

I can't remember if it is true with SW, but there are/were some computers that wouldn't let you change the mix from air to a nitrox mixture if it was calculating an offgassing. The work-around was to put the computer in nitrox mode and set the percentage to 21. You then could change to a different mix for an additional dive.

 

[Belzelbub]

View attachment 739879
I forgot to add one thing I noticed. This won't affect NDL in any way, but could affect your depth reading. Looks like your Peregrine is set to EN13319. Should have 3 options for salinity. Fresh, Salt, and EN13319. EN13319 is a standard between Fresh and salt. The only thing this will change is how deep your DC displays. If this dive was in salt, the actual depth would be shallower than the 32.5' listed. In fresh, it would be a bit deeper. Just thought you might like to know.

Again, won't affect NDL calculations in any way as that comes from the pressure readings.

 

[Divin'Papaw]

I can't remember if it is true with SW, but there are/were some computers that wouldn't let you change the mix from air to a nitrox mixture if it was calculating an offgassing. The work-around was to put the computer in nitrox mode and set the percentage to 21. You then could change to a different mix for an additional dive.

That is exactly the kind of nonsense you DON'T see with Shearwater. One of the reasons they have such a loyal following.

 

[Kimela]

Hi @Kimela

What did your husband's computer show for a NDL? Was he diving DSAT or PZ+? Was conservatism off or on?

In general, I would expect DSAT without conservatism to be more liberal than Buhlmann ZH-L16C set at 40/85. However, I have seen some wild NDLs on my Teric with repetitive dives, when they are shallow, compared to DSAT. Somewhere on SB I posted an extreme example, I will try to find it.

Edit: It was easy to find with the SB search. See the 2nd example in this post, I found it startling DSAT vs GF high 95, examples

R was showing 5 minutes NDL and he was diving DSAT. I think conservatism was on, but I'll have to double check.

Thanks!

 

[asher102]

I just ran this scenario with MultiDeco using ZHL-16C 40/85, and for 3 90 min dives with 1 hour SI you are still within your NDL.

 

[DanFromDownUnder]

I will normally run a dive plan on the computer to compare it to what my buddy has, he dives a Garmin I dive a Perdix AI and then we tweaked our settings so we had a similar NDL"

 

[Kimela]

So ... I went into the System Setup mode and found where I can change it from Nitrox to Guage or something else or Air and I changed it to Air. At that point it is permanently set at 21% and I no longer have a menu to change my gas from air to nitrox! So if I want to be able to change my gas from air to nitrox without going into System Setup, I guess I leave it on Nitrox so I still have access to the Gas menu. It will stay on Nitrox, even when diving 21%.

I'm finding out some interesting things along the way. I appreciate all the input and help.