Tech computer: Perdix or Petrel 2?

[Lorenzoid]

Part of the reason why the Petrel also catches my eye is most tech divers I know still use their Petrels and swear by them. And those guys have plenty of money on hand so its not as though they couldn't afford the Perdix if they wanted it..

"Those guys have plenty of money" that they would rather spend on dive trips, helium, or whatever than replace a perfectly good computer with "the latest model." Continual upgrading for the sake of upgrading doesn't seem to be part of the tech diver mindset. Sure, some have replaced their Petrels with Perdixes, but others seem to have the mindset that the computer is just another tool, and if it works fine, upgrading it not as much a priority as other things.

If cost is an issue, buy a used Petrel. I can't imagine international shipping from the US or Canada would cost that much. Used Petrels have been coming up for sale often here on ScubaBoard. If saving 100 USD or more is not a priority, buy a new Perdix. There are even used non-air-integrated Perdixes coming up for sale at good prices. I'm tempted to get one myself as a backup.

 

[boulderjohn]

Like some others on the thread, I have both the Petrel (not Petrel 2) and the Perdix, and I dive with both for technical diving. I don't have a strong preference for one over the other.

If you go the tech route using a computer, you will eventually have to decide how you will make your backup decompression plans. Some people use a computer and then back it up with other instruments to measure depth and time and a set of written contingency schedules. Others use a second computer. If you choose the latter method, you can just get both the Petrel 2 and the Perdix and avoid the decision altogether.

 

[Caveman]

Like some others on the thread, I have both the Petrel (not Petrel 2) and the Perdix, and I dive with both for technical diving. I don't have a strong preference for one over the other.

If you go the tech route using a computer, you will eventually have to decide how you will make your backup decompression plans. Some people use a computer and then back it up with other instruments to measure depth and time and a set of written contingency schedules. Others use a second computer. If you choose the latter method, you can just get both the Petrel 2 and the Perdix and avoid the decision altogether.

I was thinking the same. Whatever I don't buy first, I will probably buy later on down the line and by that point, there might even be more improved Shearwater computers.

But for my first choice, either one will do just fine?

 

[dulinor]

So, I don't do tech diving so my opinion is worth exactly nothing in this realm, BUT...

I do software resilience and continuity work in my "real" life and I would worry that the Perdix and the Petrel are so similar on the inside as to likely be identical with respect to any potential software failure modes. Both have been bullet proof in my experience, but generally I suggest different equipment from different vendors / stacks if possible.

The equivalent could be - we have backup network switches to protect against hardware failure, but they have the same firmware so they both go down from the same software bug. Ask me how I know that can happen...

It'd be a pretty minor difference, but if starting from scratch it's something to consider.

 

[rjack321]

"Those guys have plenty of money" that they would rather spend on dive trips, helium, or whatever than replace a perfectly good computer with "the latest model." Continual upgrading for the sake of upgrading doesn't seem to be part of the tech diver mindset. Sure, some have replaced their Petrels with Perdixes, but others seem to have the mindset that the computer is just another tool, and if it works fine, upgrading it not as much a priority as other things.

If cost is an issue, buy a used Petrel. I can't imagine international shipping from the US or Canada would cost that much. Used Petrels have been coming up for sale often here on ScubaBoard. If saving 100 USD or more is not a priority, buy a new Perdix. There are even used non-air-integrated Perdixes coming up for sale at good prices. I'm tempted to get one myself as a backup.

Shoot the predator is still a fine computer too, chunky with special saft batteries but functionally it does all the same stuff (minus a few bells and whistles like the compass). A used predator would be a good way to save money as you're starting out.

 

[Caveman]

So, I don't do tech diving so my opinion is worth exactly nothing in this realm, BUT...

I do software resilience and continuity work in my "real" life and I would worry that the Perdix and the Petrel are so similar on the inside as to likely be identical with respect to any potential software failure modes. Both have been bullet proof in my experience, but generally I suggest different equipment from different vendors / stacks if possible.

The equivalent could be - we have backup network switches to protect against hardware failure, but they have the same firmware so they both go down from the same software bug. Ask me how I know that can happen...

It'd be a pretty minor difference, but if starting from scratch it's something to consider.

That is a good piece of advice. Ill take it into consideration. In the end I think Ill go for the Petrel as my first.

 

[boulderjohn]

The equivalent could be - we have backup network switches to protect against hardware failure, but they have the same firmware so they both go down from the same software bug. Ask me how I know that can happen...

It'd be a pretty minor difference, but if starting from scratch it's something to consider.

When a dive team is doing decompression dives using computers, they stay together on the ascent by ascending when the most conservative computer says it is OK to ascend to the next deco stop. That usually means one diver signals that his or her computer has given the OK to ascend, and once everyone's computer says it is OK, the team ascends. If you as an individual are using two computers with the same algorithm and the same settings, both of your computers will agree within a few seconds. If your teammates are using the same computers with the same settings you are, you will all usually be within a minute or two of each other. Everything goes smoothly.

If you are using different make computers, the one on your left wrist may be giving very different information from the one on your right. One of them could be telling you it is time to ascend while the other is telling you to stop at that depth for another 5 minutes--maybe more. It is very frustrating when the computer you trust the most disagrees with your backup, but you have no choice but to follow your backup. It is even more frustrating for your teammates when their computers agree with the one you trust the most, but they have to follow your backup, too.

 

[dulinor]

Yeah that would be a totally valid reason to take the risk of a minor edge case - although possibly mitigated by finding similar algorithms.

 

[rjack321]

Yeah that would be a totally valid reason to take the risk of a minor edge case - although possibly mitigated by finding similar algorithms.

Or you could bring tables.
Or have a basic understanding of the relationships between depth and time to come up with a "just get me out of the water" plan.

Sometimes not bringing an extra piece of electronics is simpler and more robust.

 

[dulinor]

Well, when I dive I take my old computer (VT3) with me "just in case" - if I have a bad battery or something happens that make my primary freak out and put me into Deco when it shouldn't have (as happened to a friend on day 2 of a liveaboard week on my last trip) I don't want to be locked out of diving till it clears. Bad battery (or user error sealing the compartment back up) seems like an entirely foreseeable problem.

(Yes, you can use your judgement but the operator in those circumstances has liability concerns and overall final say on who dives and who doesn't.)