SPG vs. Air Integrated

[Peter Guy]

My "buddy" and I are having this "discussion" -- she's becoming a "mindless DIR lemming" (her phrase) and wants to be as "DIR Compliant" as possible.

We both have Cobra air integrated computers as well as Mosquitos. As a recreational diver, she has no desire/intention of giving up her Mosquito to be totally "DIR Compliant" -- but she wants to replace her Cobra with an SPG. As far as I can tell, the two reasons are:

1. The Cobra isn't "DIR" and gives her too much information -- i.e., it will display remaining air time in addition to NDL's and remaining pressure; and

2. An SPG is analog and it is easier to tell at a glance approximately how much air she has left because the arrow is easier to read than the Cobra's digital readout.

WITHOUT GETTING INTO A DISCUSSION OF WHY DO I CARE WHAT MY BUDDY DOES WITH HER GEAR....

I'd like to hear the pro's/con's of having an SPG plus wrist computer as opposed to wrist computer plus air integrated computer.

BTW -- To me, getting rid of the "backup" computer (Cobra) to go with an SPG doesn't make sense because you are giving up information that CAN be valuable.

Note -- I did NOT put this in the DIR forum because this is related to recreational, not techinical, diving AND I hoped the whole spectrum of divers would add their 2 cents worth of advice.

 

[H20Bubbles]

Being fairly new to all of this, I don't quite know what DIR actually stands for.

But for us, we decided to go the SPG, wrist computer route simply as a matter of fail-over. As the SPG is mechanical (analog) it is always nice to have. The wrist computer allows for the benefits of having the dive computer. With a console integrated computer with, or without, air integration we realized that given a computer failure, we would be giving up not only the depth but possibly the air guage as well.

 

[Diver0001]

It's all about context, Peter. Having the computer on the console will become an issue when she starts to carry stages for the following reasons:

- The console will be bulky and in the way and it will take alot of abuse when it's hung under a stage (or stages). The AI coupling of the cobra could be vulnerable to damge and/or leaking.

- Although you only need to refer to pressure a few times during the dive, you need to see your run-time very frequently (constantly?). Having it all on the console is a major PITA in that context. Hanging it up over the stage is an option if you can get used to it but it makes an already cluttered zone more cluttered (and it's not DIR )

As far as I'm concerned there's no reason to replace the cobra until carrying stages gets in the way and makes it a PITA. Meanwhile, just hang it on the left shoulder D ring. That's not DIR but it's a clean solution regardless.

R..

 

[Doc Intrepid]

Ah Peter, you're a good man. And patient.

In a recreational environment, its kinda sorta six of one half dozen of the other.

SPG's in a technical application offer less bulk, less dangle, are more streamlined clipped off, and large clunky items get trapped beneath the two deco tanks slung off your left side - e.g. they're a PITA to take out and put back. Which is one reason why the rest of the instruments go on the wrists. (Yeah, I know that reaching into holes after lobsters is tough with wrist mounted gauges, but most hunters don't hunt on helium...)

Moreover, on a technical dive the SPG is often somewhat superfluous. You've got a good idea of your consumption rate and planned time (exposure) at depth, so you've already got a pretty good sense of how much gas you'll have remaining at any given number of minutes into the dive. Assuming all goes as planned. The timing device and the compass, however, will be referenced much more frequently.

You're right however, if you're using a digital timing device with helium mixes most instructors would suggest using two - if one timing device craps out and you've got 40 minutes of deco remaining to do, you're going to get tired of counting off 2400 seconds going "one-onethousand-two-onethousand..." etc.

But in a recreational environment carrying two computers on each dive seems a bit redundant - if one craps out the dive is over. If you're not planning deco dive profiles to begin with, uh, head up. I can see carrying two on a liveaboard, such that if one craps out you need the other to do the rest of the vacation, but two for every dive as a matter of habit? If you want to, go for it...but some may consider that technology-overkill Basically your buddy's "backup computer" would be yours, and vice versa.

For recreational diving many divers like consoles. No problems. In terms of pros and cons, for recreational diving some might say it comes down to fashion and personal preference. Consoles are in fact larger, clunky, dangle down, and all too often get entangled on the boat or hooked on things with unfortunate results. SPG's still offer less bulk, less dangle, and are more streamlined clipped off. The gauges on your wrists still tell you whatever you need to know.

So eBay her Cobra, and let her get an SPG!

You'll both be happy. Life is good!

Happy New Year to both of you.

Doc

 

[countryboy]

2 words:

Yes Dear..

 

[Dan Gibson]

What valuable information is given up by eliminating the backup computer(i.e. the Cobra)?

BTW -- To me, getting rid of the "backup" computer (Cobra) to go with an SPG doesn't make sense because you are giving up information that CAN be valuable.

 

[DA Aquamaster]

I still take a computer (Sherwood Wisdom) along but it is pretty compact and not much bigger than an SPG alone. But the computer is just a back up timing device and depth gauge and also a bailout decompression device in the event I abort a dive exceptionally early.

In my experience, for technical diving it works best if the dive plan / deco schecule and several contingencies are carried on a slate. The dive timer is carried on the wrist and is the primary instrument for measuring elapsed time and depth. Doing that forces you to do a significant amount of planning prior to the dive and avoids the temptation to just jump in an go.

The electronic spg function of an air integrated computer is more failure prone, but if you monitor it properly, you will never be left in doubt about how much gas you have left and will in any event end the dive at that point knowing you have more than enough gas for a normal ascent.

One way a mechanical SPG can fail is to stick. That should again not catch you off guard as the unchanged or higher than expected reading should be noticed, But it is none the less a far more subtle error to detect than a blank electronic SPG. So to some ectent the greater potential for failure in an electronic SPG/air integrated computer is somewhat offset by the higher likelyhood that you will notice the failure sooner than a stuck spg needle.

 

[jsmith89]

I have dove with air integrated computers before when researching different computers and I see them as a point of failure for just rec divers. I don't like the idea of anything that requires anything outside my actual essential dive gear to operate (ie. a battery) unless there is a backup. I do use a computer but back it up by using tables. If I were to dive an air integrated computer I would have to carry a regular spg with me as well.

-Jacobi

 

[bradshsi]

I'd like to hear the pro's/con's of having an SPG plus wrist computer as opposed to wrist computer plus air integrated computer.

BTW -- To me, getting rid of the "backup" computer (Cobra) to go with an SPG doesn't make sense because you are giving up information that CAN be valuable.

My view is that the second computer is almost redundant for recreational diving.

I would ask what information are you giving up by not having 2 computers ? Both computers are going to display different NDL's and time remaining. Since one computer is likely to be more conservative and the other less conservative which one do you pick ? If you pick the same computer each time (to determine your NDL's), what purpose does the backup computer have ?

The one time a backup computer might be of use and "save a dive" would be if one of your computers failed (assuming you were happy to use the NDL's on the second computer). But if the computer that failed was the AI computer you'd still have to call the dive as you would have no tank pressure readout.

To me the advantages to the single computer and spg are:

1) The SPG is likely to be more reliable than the AI computer it replaces. This should mean fewer lost dives

2) You don't get conflicting information from the two computers.

 

[Diver Dennis]

Redundancy is my middle name! I have exactly the same computer set up as you, Mosquito and Cobra, PLUS an mini SPG and depth guage that tucks neatly into the back of my right hand BC pocket. All very trim. Yes, I know that folks will not agree with my set up, I've heard it many times, but the most important thing is that you are comfortable with YOUR set up and very familiar with it. I'm very happy and am not about to change.