Dive Computer + Air Integration – Yay or Nay?

[drrich2]

When I saw the article, I saw 2 separate issues:

1.) Should you have backup redundancy for your tank pressure gauge, whatever that is?

2.) If so, should that backup device be an SPG, as they are presumably cheaper than having a 2nd dive computer.

The SDI Solo Diver course advised a diver use 2 dive computers. I do this; when I bought an Atomic Aquatics Cobalt (which they later replaced with a Cobalt 2 after the Cobalt has an out-of-warranty pressure failure; kudos to Atomic!), I already had an Oceanic Worldwide VT3.

While having a second computer (in this case, 1 console, 1 wrist) is more expensive than an SPG (unless like in my case you wanted a new computer and already had the old one), there are other benefits.

If your computer craps out, you've got a backup that's been storing your profiles, nitrogen loading, logging the dives for download to your computer (if your model supports that), etc... An SPG doesn't have any of that.

If later, looking at your downloaded dive log, you see data obviously way off due to some unknown glitch, you have another source. On one trip, the VT3 gave me some kind of bizarre reading; on a recent trip, it inexplicably gave data that showed up in MacDive as a ridiculously low starting tank pressure (the Cobalt 2 handled it fine). But the Cobalts are notorious for giving temp. low readings considerably higher than other brands, and the VT3 I trust more for dive temp. lows. By having a console (with a nice, intuitive interface) and a wrist unit (more convenient to consult on the dive), I get the best of both worlds.

If you want tank pressure redundancy, an SPG is an option worth considering, but not the only one, and not always the best for everyone's agenda.

 

[AfterDark]

Same here. That doesn’t really make sense. If the reason is redundancy, I wonder how many divers are running two SPGs off of a single first stage.

Both SPGs and *transmitters are very reliable. So, for most recreational dives, carrying a backup SPG or transmitter is just not required. In either case, it woul be a good idea to carry a backup pressure reading device in your save a dive kit.

*Some transmitter types are more reliable than others. PPS are probably the simplest, and seem to have the fewest complaints. They turn on with pressure and that’s it. Other types use power saving features that are pretty much unnecessary and add complexity and opportunities for things to go wrong.

It wasn't until AI that I've heard/read so much about redundancy of tank pressure monitors/indicators. Since the advent of SPGs I don't think I ever saw anyone with 2 hose mounted SPGs unless it was on IDs or SM rigs. Now it's AI and SPG for some, for "redundancy". Probably just a coincident.
I have an entire spare regulator setup with me including SPG and octo, but I don't bring it into water with me.
I do rarely use 2 PDC on a dive.

 

[AfterDark]

In over four decades, I have yet to have a conventional SPG fail on me, or not jibe with other electronic equipment readings -- nor have I ever witnessed it; but the same cannot be said for air-integrated and non-AI computers, of which I have scuttled quite a few -- something about saltwater, electronics, and the rubber bands that keep everything together . . .

I've had 1 SPG failure in 53 years and it was pre-dive, when I turned the air on, the spool failed.

 

[Bigbella]

I've had 1 SPG failure in 53 years and it was pre-dive, when I turned the air on, the spool failed.

I, too once sprung a leak before a dive, on a 300 bar fill -- also a spent spool issue; heh, what we do for nice swiveling action. Took two minutes to correct it, along with some colorful language; but I wouldn't consider that an outright failure . . .

 

[AfterDark]

I, too once sprung a leak before a dive, on a 300 bar fill -- also a spent spool issue; heh, what we do for nice swiveling action. Took two minutes to correct it, along with some colorful language; but I wouldn't consider that an outright failure . . .

Well it didn't work so in my world that's a failure. I just grabbed my backup set and went diving, replaced the spool the next day.

 

[Blackcrusader]

If your computer craps out, you've got a backup that's been storing your profiles, nitrogen loading, logging the dives for download to your computer (if your model supports that), etc... An SPG doesn't have any of that.

Cressi Digi2 SPG keeps a back up of previous dive and the dive you have just completed. It does not calculate nitrogen loading though and how many DC's do that? I can use this SPG for bottom time diving where I need a backup to my Perdix AI.

 

[drrich2]

It does not calculate nitrogen loading though and how many DC's do that?

What I'm referring to is, if you do, oh, say, 2 morning dives in a live-aboard, and your dive computer craps out, you may be looking at 2 or 3 more dives that day (2 afternoon, 1 night). But...your body has accumulated nitrogen from your first 2 dives of the day.

If you were wearing a second dive computer, odds are good it's got that info. Granted, it can't directly measure nitrogen loading across tissue compartments, but it serves the same function as our old pre-computer dive tables (plus factors in multi-level diving much more easily), that assigned us pressure groups that improved over time as nitrogen was calculated to leave our bodies.

So it factors your prior nitrogen loading into calculating NDLs for your dives the rest of the day.

Most basic mechanical SPGs don't do that. So the person relying on his computer to log his dives, who doesn't recall the max. and average depths of his first 2 dives and has a computer failure, has a choice...

1.) Stop diving for the day.
2.) Keep diving (whether applying some educated guess work with tables).
3.) Or the politically incorrect alternative of assuming if he hasn't been hitting NDLs on the usual dive regimen, he'll just take his chances).

 

[lexvil]

I like all the computer things that happen when my computer knows how much air is there.

 

[Centrals]

Cressi Digi2 SPG keeps a back up of previous dive and the dive you have just completed. It does not calculate nitrogen loading though and how many DC's do that? I can use this SPG for bottom time diving where I need a backup to my Perdix AI.


View attachment 712049

It is NOT a computer.
Absolutely useless as a back up to a computer.
Do you understand the meaning of back up?

 

[Blackcrusader]

It is NOT a computer.
Absolutely useless as a back up to a computer.
Do you understand the meaning of back up?

Nobody claimed it was a computer. It is called a console for a reason. Any device that keeps a record of time & depth can be used as a backup. How did you ever learn to plan a dive using tables without a device that knows your depth and a device for dive time. Good thing I learned to dive before dive computers came along and made people lazy.