Double Dive Computer Redundancy (on little T-Rex Arms)

[Mark IV]

Back in the day, when I was in my ill-advised deep-diving phase, I used to wear 2 Aladin Pros (and I owned 3, so I'm sure I've dived with all 3 before). But, I also always had a dive watch, as well as analogue depth guages. I never liked (and still don't) not having the redundancy of an analogue time piece and depth gauge, on top of any electro-gizmos.
When doing "normal" dives, I was content with a single computer, and often times not even that, as I (and most any experienced diver) pretty much knows the single-dive NDL's by heart, and we generally dove predictable, standard times/profiles (boat had to be back for the 1:00 pm trip), plus, it was almost always the customer's air consumption rather than deco limits that started us up.
I've long been a big proponent of veeerrry slow ascents, and extra-long safety stops, and when it seemed appropriate, extra-long surface intervals ( it ususally wasn't too hard to get the customers to go along, by just putting a little of the fear of God into them, especially given that it would've been them that screwed the pooch in the first place !! )
Doing any normal recreational profile, on an Al80, you have to try pretty hard to get a whole minute of deco (I don't think i recall it ever happening on a dive I ran with customers), and a 5+ minute safety stop is sufficient. Unless it was a deep dive with my buddies (or all by my lonesome!)I sure as hell ain't calling a dive because a computer crapped the bed.

 

[boulderjohn]

Think about the dive you are planning, and follow this general rule:

1. Essential for that dive: you need at least one backup, maybe two
2. Nice to have for that dive, but not critical: one will do
3. Not needed for that dive: why bother?

For some NDL dives, if you give it a lot of thought, you will realize that not much is essential. I did a number of muck dives in the Philippines in which I realized I didn't need much at all. The dives were shallow, so I knew I was not going to run out of gas, I would not get near NDL, there was plenty light enough, I was navigating by terrain, there were no possibility of entanglement, etc. I could have done the dives safely without pretty much any instrumentation. On the other hand, a deep decompression dive in a hostile environment needs a lot of careful thought about what you are going to bring.

 

[tbone1004]

1. Do you dive two dive computers?
   1. sometimes
   2. two for big cave dives, trimix dives etc. One for the vast majority of my diving. Sometimes in quarries or whatever I will just use a watch since I know the depth profiles and there is always visual reference. That is typically if someone wants to try one of my computers or whatever.
2. Do you carry backup dive watch, compass, depth gauge, tank air gauge, or just plan to abort the dive in case of DC failure?
   1. Compass is on a navigation slate clipped off typically to my rear crotch strap d-ring.
   2. In event of failure, I will typically ride my buddies computer first, but I do carry a watch and a knotted spool connected to my dsmb.
   3. Tank air gauge is clipped to left hip or shoulder d-ring
3. If two DC are used; are both identical, both same brand, each different brands, each different algorithms?
   1. same brand, same algorithm, different model
4. If using a transmitter, do both computers work with AI, or will one be independent of that potential failure point?
   1. Recently gone to a Perdix AI, the other computer is standalone
5. If different algorithms, do you have to dive the most conservative DC at all times, or dive conservatively on your liberal algorithm DC?
   1. I would not dive with different algorithms. My computer allows me to change conservatism on the fly if I need to, but that is only in case of emergency
6. Are they both on your arm, or can you leave one in a pocket and still have it read ok?
   1. One on each forearm
7. How much does the console become critical, is it never possible to stream line that one hose off the reg?
   1. Console if used should be cross clipped to the right shoulder d-ring. Unless your computer is not WAI, you should have a standard SPG, no need for a console with a dive computer
8. Who has room for an arm-mounted dive slate?
   1. I do. Slate lower on the forearm, computer close to the elbow

 

[Marie13]

I don't have a lot of real estate on my forearms, either. Main computer on wrist, the other is on a D ring on my harness.

 

[ATJ]

@ATJ if your computer is on your camera rig, it seems a little dicey because I hear people lose cameras more frequently, although the money cost of losing a DC doesn’t compare to a camera rig, it still has your dive history.

My camera rig is large and there's no way I'd lose it, plus it's always there in front of me. If I was to lose the camera rig something very serious has gone wrong (like I've nearly lost my life) and I'm not going to care about the dive profile from that one dive.

 

[Bubblesong]

@ATJ I see you are from Sydney, and you have a Rockstar camera, so it stands to reason that you might have some leafy seadragon photos? I know I am hijacking my own thread, but I love those seadragons!
Also, you have a reasonable approach to the valuation of the dive computer, but in the slim chance there is an accident, the doctors might want your computer to help diagnose what treatment to give you, so that is why even if I copied your camera/computer set up, I would still carry a second computer in my thigh pocket. But it would definitely help me to not forget to look at time remaining if it is in front of me while the distraction of Seadragons was claiming my attention.

 

[kelemvor]

1)Do you dive two dive computers?
Yes
2)Do you carry backup dive watch, compass, depth gauge, tank air gauge, or just plan to abort the dive in case of DC failure?
I thought that was clear after answering #1. Yes, It's in the second dive computer.
3) If two DC are used; are both identical, both same brand, each different brands, each different algorithms?
Same
3)If using a transmitter, do both computers work with AI, or will one be independent of that potential failure point?
AI
4) If different algorithms, do you have to dive the most conservative DC at all times, or dive conservatively on your liberal algorithm DC?
N/A
5)Are they both on your arm, or can you leave one in a pocket and still have it read ok?
Arm is easiest.
6) How much does the console become critical, is it never possible to stream line that one hose off the reg?
Umm hose off the reg? What part of AI aren't you getting. AI eliminates that failure point.
7) Who has room for an arm-mounted dive slate?
Not you, from the look of that photo. Look into a couple AI shearwater DC's.

 

[stuartv]

Not Just the double dive computers, but all the other arm mounted devices, (see photo), where does all this stuff go?
Other Questions:
1)Do you dive two dive computers?
2)Do you carry backup dive watch, compass, depth gauge, tank air gauge, or just plan to abort the dive in case of DC failure?
3) If two DC are used; are both identical, both same brand, each different brands, each different algorithms?
3)If using a transmitter, do both computers work with AI, or will one be independent of that potential failure point?
4) If different algorithms, do you have to dive the most conservative DC at all times, or dive conservatively on your liberal algorithm DC?
5)Are they both on your arm, or can you leave one in a pocket and still have it read ok?
6) How much does the console become critical, is it never possible to stream line that one hose off the reg?
7) Who has room for an arm-mounted dive slate?

I always dive 2 computers. One on each arm. I have 3 computers. Which 2 I use depends on the dive. 2 of them support wireless AI, so I always have at least 1 on me that is wireless AI.

2 of my computers have electronic compasses, so I always have at least 1. But, if I expect to really use a compass, then I take a separate compass and bungee mount it to the back of my right hand. That is much easier to follow than an electronic compass that is mounted on my forearm.

None of my computers are the same brand. 2 of them run the Buhlmann ZHL-16C with Gradient Factors algorithm. The 3rd runs DSAT. When I use the DSAT computer, it is because I'm doing a recreational dive (e.g. diving from a boat where the rule is "no deco"). I start up before I run out of NDL (according to DSAT), but then I will do any deco stops that may be shown by my other computer. For technical dives, I use the 2 computers that run Buhlmann, and have them set to the same GF.

I only use AI. No physical SPG. If my AI dies during a dive, then I will probably end my dive early.

I have an arm slate and room for it on my left arm, next to the one computer that is there. I have never used it, myself. If I anticipate wanting to be able to write, I carry a wetnotes notebook in a thigh pocket.

 

[scubadada]

AI primary computer and compass on my left arm, backup computer on my right arm, SPG on my left shoulder strap

 

[ATJ]

@ATJ I see you are from Sydney, and you have a Rockstar camera, so it stands to reason that you might have some leafy seadragon photos? I know I am hijacking my own thread, but I love those seadragons!

In Sydney we get weedy (or common) seadragons. You have to go to South Australia for the leafy seadragons. I have thousands of photographs of weedy seadragons but have only gone to South Australia once for the leafy seadragons and only have a few photographs.

@ATJAlso, you have a reasonable approach to the valuation of the dive computer, but in the slim chance there is an accident, the doctors might want your computer to help diagnose what treatment to give you, so that is why even if I copied your camera/computer set up, I would still carry a second computer in my thigh pocket. But it would definitely help me to not forget to look at time remaining if it is in front of me while the distraction of Seadragons was claiming my attention.

Yeah, I have considered that, and agree it is a possibility, however:

• My camera rig is tethered to my BCD and is slightly buoyant and is likely to be recovered
• I suspect most medical professionals would struggle to work out how to get any data off a dive computer, especially some of those one button pucks. I know my Oceanic Atom 3.0 is very difficult without the manual and the manual doesn't help a lot.
• There is not a lot of useful information you could get off a dive computer that would help with treatment options. Breathing gas(es) might be of use, although duration of each gas may not be obvious. Dive duration and maximum depth alone would not tell you a whole lot as you may have been at the maximum depth for 10 seconds or the whole dive. I would think pulling all the data off the computer would be of more use for the coroner.
• I would hope that the doctors base my treatment options on the signs I'm displaying

That said, it is likely I will have a Garmin Descent MK1 in the next month or so and I will be wearing that on my wrist where it will have other benefits.