Shearwater Peregrine TX - Match DSAT?

[BobbiK]

Any recommendations of Shearwater Peregrine TX Gradient factor/Conservatism settings to match older Oceanic/Pelagic/DSAT algorithm? Many buddies have Oceanic/Sherwood/Genesis computers.

 

[scubadada]

Hi @BobbiK

Buhlmann with GF and DSAT do not run exactly the same for 1st clean dive or repetitive dives. DSAT is generally more liberal on 1st clean dive, particularly if deeper. Buhlmann is generally more liberal on repetitive dives, especially if shallower.

A GF high of 95 matches DSAT reasonably well for many dives.

I have posted about this before, including extremes

DSAT vs GF high 95, examples

I have written previously about my experience diving DSAT and Buhlmann ZH-L16C with a GF high of 95. I have an example of what I have previously reported. This dive is a first dive of the day on the Castor in Boynton Beach. It was relatively deep with a max depth of 107 feet and an avg depth of...

scubaboard.com

 

[staggsSevin]

Buhlmann with GF and DSAT do not run exactly the same for 1st clean dive or repetitive dives. DSAT is generally more liberal on 1st clean dive, particularly if deeper. Buhlmann is generally more liberal on repetitive dives, especially if shallower.

A GF high of 95 matches DSAT reasonably well for many dives.

I have posted about this before, including extremes

DSAT vs GF high 95, examples

I have written previously about my experience diving DSAT and Buhlmann ZH-L16C with a GF high of 95. I have an example of what I have previously reported. This dive is a first dive of the day on the Castor in Boynton Beach. It was relatively deep with a max depth of 107 feet and an avg depth of...

scubaboard.com

@scubadada if your oceanic had dual algorithm's would you run your backup as Pelagic Z+ (Buhlman ZHL-16c) vs keeping it on DSAT? I got a new backup computer (cobalt trade up to a proplus x) that has the dual algorithm's and I was planning on using the Z+ (to match my mk3i) but you can also not really adjust the GF on the ProPlus X other than turning on a Conservative option that decrease dive times by 1 altitude level.

I don't know much about the subject, so I always lean towards folks that have a much better ideal than I. I use to just exclusively dive DSAT many moons ago, before I got my atomic cobalt in 2011.

 

[scubadada]

Hi @staggsSevin

I have been running an Oceanic computer with DSAT since 2002. I have run a number of 2nd computers, one running Buhlmann and GF since 2016.

I have no experience with PZ+. I believe it would be reasonably matched with a GF high of 85, maybe 90, you would have to see.

You have 4 choices on an Oceanic computer, from most liberal to most conservative, DSAT, PZ+, DSAT with conservatism, PZ+ with conservatism

 

[John Bantin]

Hi @BobbiK

Buhlmann with GF and DSAT do not run exactly the same for 1st clean dive or repetitive dives. DSAT is generally more liberal on 1st clean dive, particularly if deeper. Buhlmann is generally more liberal on repetitive dives, especially if shallower.

A GF high of 95 matches DSAT reasonably well for many dives.

I have posted about this before, including extremes

DSAT vs GF high 95, examples

I have written previously about my experience diving DSAT and Buhlmann ZH-L16C with a GF high of 95. I have an example of what I have previously reported. This dive is a first dive of the day on the Castor in Boynton Beach. It was relatively deep with a max depth of 107 feet and an avg depth of...

scubaboard.com

Did you know that if you have a recent Oceanic computer, it has dual algorithms, and you can choose to set Pelaic Z+, which is Buhlmann-derived and will be much closer to your Shearwater? Many people buy Oceanic (and clones thereof) computers and are never told about this important feature. The Pelagic DSAT is the default algorithm but it is not intended for anything deeper than no-deco-stop dives shallower than 100-feet.

 

[inquis]

In my experience, Pelagic Z+ is fairly comparable to GFhigh of 90, though it does vary a bit, especially on repetitive dives. There are some proprietary modifications, making it differ from ZHL-16C with a fixed GF.

Although I think the OP has worked things over the last year or so, for the benefit of others: in a backup role, the algorithm choice will likely depend on what you're doing for your primary. (You don't want your backup to be more conservative if it will be rendered unusable when surfacing before it thinks you should.)

Finally, DSAT was designed and tested for repetitive NDL diving, but dives will be limited by gas rather than NDL for many -- especially if you leave a reasonable reserve that will get two stressed divers back to the surface.

 

[MrChen]

I got rid of my Oceanic as a backup to my Perdix 2. For the most part it was fine and had only a little variance from the Perdix 2. I do a lot of diving in the 80-115 ft range. One day after 3 dives, at the end of dive 3, I look at my Oceanic and I was in violation. I looked at my Perdix and my SurfGF was under 70%. It was at that point that I sold the Oceanic and bought another Shearwater computer. I've since got my hands on a Garmin MK2i and now I'm comparing it to the Shearwater. It's performing nearly identical to my shearwater.

 

[BjörnBear]

@inquis out of curiosity what kind of dive profiles were you doing where you found the PZ+ algorithm lining up roughly with GF high of 90?

For NDL diving I never noticed the PZ+ as overly conservative, but when I brought it along as a backup on various planned deco dives with a gas switch it seemed to line up closer to GF hi of 70-ish. Makes me wonder if it adds conservatism when going into deco.

 

[inquis]

For NDL diving I never noticed the PZ+ as overly conservative,

That fits with my experience as well. A buddy used PZ+ on NDL profiles, 70-100 ft max depth, but mostly dual-level to 50-60 ft. It did give a little less time when venturing past 100 ft, but hard to say given the multi-level nature. We typically ended on gas constraints (single AL80): the initial loading off-gassed nicely at 60 ft but the depth excursion took a big chunk out of our gas.

(I have no experience with PZ+ on deco dives.)

 

[Belzelbub]

@scubadada if your oceanic had dual algorithm's would you run your backup as Pelagic Z+ (Buhlman ZHL-16c) vs keeping it on DSAT?

I know not directed at me, but I did just that when my daughters were learning to dive. They had Oceanics, and I was using my Perdix. I set their DCs to use PZ+. For a backup DC, I probably would do that, but you’d probably want to set the GF on your primary so it is more conservative. DSAT can work as well, but it will likely become the more conservative computer on repetitive dives.