Will Air Integration in dive computers replace the SPG?

[guyharrisonphoto]

I think it is some confusion in linking ATR to NDL. Each of these is an independent limit on dive time, with the shortest controlling.

I choose my NDL by selecting a computer with an established algorithm (Buhlman, which is generally regarded as middle of the road) and using the "standard" conservatism setting. Thus, when I dive to the NDL, I am not "diving to the limit" or "pushing the edge" but am just diving the conservatism of my plan and getting the most out of that plan instead of cutting the dive short.

Similarly, when I do my ATR settings, I choose a reserve that experience suggests will be adequate for a fast emergency air sharing ascent with no stop. Thus, when I dive to the ATR, I am not "pushing the edge" either, but diving the conservatism of my gas plan.

These are two different things. I don't want to cut myself short on either, so I dive the limit of my pre-planned conservatism, but that is not the same as the "limit" of DCS (not an exact science of course) or OOG.

Usually, I run out of NDL before I run out of ATR (thank heavens big steels are available where I dive!). But, if the particular dive got me to ATR first, I would follow that. The shortest of the two is the limit on my dive time.

No "grenades" for this diver!

 

[Lorenzoid]

Back on the boat with plenty of NDL and gas left does seem wasteful, to me. I like boats, but when I spend the money for a scuba charter, I want to dive, not just be out on the water.

If being out of the water with "plenty" of NDL left is your way of ensuring (as best you can) that you don't get bent, . . . .

No, it's not so much about not getting bent as it is that the length of my dives tends to depend on factors other than how conservative my computer may be with NDLs and, for that matter, how much gas I carry. I have mentioned this before in the context of those discussions about seeking the most liberal dive computer. The boat rule may be "be back in 50 minutes." I may get chilly, tired, crampy or otherwise uncomfortable. Or my buddy may. Sometimes, one of us looks at the other and shrugs as if to say "I feel I've seen what I came here to see, and I'm happy to call the dive if you are." When I get out of the water, it's usually--maybe not always, but usually--because I want to. I just feel like I'm done, and I'm ready to get out, get dry, have something to drink, etc. There's always another dive, today or another day. I don't feel like I need to cram it all in right now. (We'll see if my attitude changes after I start diving with my new drysuit.)

We're all different. Those of you who want to squeeze out every possible minute may even be the majority--I don't know. I can certainly imagine that if one's goal for the dive is something like spearing fish, and you want to remain down there until you've bagged what you came for, then maximizing dive time is important. Having the precision or accuracy that you mentioned--whether for gas or decompression--may be important to you and others. But I know there are others like me, because I often take dive trips with a group of like-minded people. So, to tie this back to the original question, the plain ol' SPG will remain just fine for us.

 

[stuartv]

No, it's not so much about not getting bent as it is that the length of my dives tends to depend on factors other than how conservative my computer may be with NDLs and, for that matter, how much gas I carry. I have mentioned this before in the context of those discussions about seeking the most liberal dive computer. The boat rule may be "be back in 50 minutes." I may get chilly, tired, crampy or otherwise uncomfortable. Or my buddy may. Sometimes, one of us looks at the other and shrugs as if to say "I feel I've seen what I came here to see, and I'm happy to call the dive if you are." When I get out of the water, it's usually--maybe not always, but usually--because I want to. I just feel like I'm done, and I'm ready to get out, get dry, have something to drink, etc. There's always another dive, today or another day. I don't feel like I need to cram it all in right now. (We'll see if my attitude changes after I start diving with my new drysuit.)

We're all different. Those of you who want to squeeze out every possible minute may even be the majority--I don't know. I can certainly imagine that if one's goal for the dive is something like spearing fish, and you want to remain down there until you've bagged what you came for, then maximizing dive time is important. Having the precision or accuracy that you mentioned--whether for gas or decompression--may be important to you and others. But I know there are others like me, because I often take dive trips with a group of like-minded people. So, to tie this back to the original question, the plain ol' SPG will remain just fine for us.

That all makes perfect sense. My most common scenario (so far, in my world famous on ScubaBoard limited experience) has been running out of NDL well before I run out of air (meaning, reach my TP). And it's often diving a wreck where the NDL is relatively short because of the depth. So, I almost always want to stay as long as I can. So, whether I choose to start my ascent with 5 minutes of NDL left, or set my Conservatism to +2 or whatever, the fact remains that a more liberal computer will still allow me to stay down longer without violating the margin of safety I have given myself. And a more precise and accurate ATR is helpful because I set a reasonably conservative reserve (say, arrive back to the surface with 800 psi) and the ATR will then often come close to being my limiting factor versus NDL. I watch my actual pressure reading AND my ATR, so that I can limit myself and start my ascent if either one gets too low. E.g. I decide on a TP of 1000psi. I haven't hit that yet. But, I'm working against a heavy current and my ATR tells me that I'm blowing through my air faster than I counted on when I made my plan, so I decide to ascend earlier than planned. The alternative would be to actually note my SPG readings regularly and do the arithmetic to determine if my SAC is actually higher than I counted on. Doable, but the ATR is a lot more convenient and being narc'ed won't cause it to calculate incorrectly.

 

[agilis]

Computer algorithms are based on some variation of Navy and successor tables. Since human experimentation is not generally permitted their basis is, as i understand it, experiential and technical. The data from tunnel workers, for example, operating in compressed air environments is utilized, along with elements of physics and medical research.

What is being measured are non-organic variables, in effect what the computer is experiencing, not what is happening to the diver. If you were dead and being transported through the stages of a dive the computer would still let your corpse know what was safe and what was not.

I've never heard of 'feeling' anything during a dive that might suggest the approach of DCS. The notion of a physical sensation in that context is exceedingly bizarre. On the other hand, I do not hesitate to call a dive if I'm feeling at all unwell.

I do not have any formulas of my own. I use tables primarily, and a conservative computer secondarily, and in both cases stay far away from the limits set by either. As I get older, the distance increases. I know that this does not protect me in any comprehensive manner but I believe, based on the experiences of many others over a long period of time, that it does reduce some risk. I also understand that, at 73 years old, every dive is a risk.

I follow guidelines that reduce some of the risk factors, received guidelines that my research indicates are based on good science and careful analysis. I know that even under the best of circumstances I am a high risk diver. I accept that risk, but try to minimize it; I'd be a fool not to.

Crossing a multilane bridge at high speed can be exciting. I tend to drive in the lane closest to oncoming traffic. I once saw a tire fly off an oncoming truck and strike a car on my side in the slow lane, killing the driver. Life is like that, filled with little surprises.

 

[DiveNav]

...... Do the Oceanic DC's dynamically display the lower number it calculates between ATR & DTR? .....

Yes .... DTR is the lower between ATR, NDL and O2 accumulation.

If you jump in the water for a first dive after more than 24 hours (almost no accumulated Nitrogen and no CNS clock) with a tank almost empty, ATR will be the one in charge. Don't do that in real life ... just in eDiving.

Take the A300 online class (free when you register your A300 with Oceanic) and take your A300 for a spin in our simulators so you can get familiar with it before getting wet

 

[Ghosty]

Yes .... DTR is the lower between ATR, NDL and O2 accumulation.

If you jump in the water for a first dive after more than 24 hours (almost no accumulated Nitrogen and no CNS clock) with a tank almost empty, ATR will be the one in charge. Don't do that in real life ... just in eDiving.

Take the A300 online class (free when you register your A300 with Oceanic) and take your A300 for a spin in our simulators so you can get familiar with it before getting wet

Thanks @DiveNav, will do! I have the ACI software, and upgraded the firmware to the latest. Halfway through reading the PDF manual. Next step is your class and any Youtubes I can find.

 

[Bennno]

The alternative would be to actually note my SPG readings regularly and do the arithmetic to determine if my SAC is actually higher than I counted on.

So you need to note your SPG readings and do arithmetic to figure out that your breathing rate has increased?
Usually, an aware diver will notice that he is going through air faster by looking at the SPG and because you are actually the one breathing.

See, this is what I mean, you make up problems that don't exist and then you look for computer features to fix those 'issues'.
Awareness of you breathing and of your surroundings is an important skill in diving that needs to be developed.

The alternative to having a computer to tell you your 'rest air time' or 'noting SPG' read outs is working on your awareness and doing deeper dives as you get better, instead of rushing into stuff.
It's better to work on your skills instead of buying more unnecessary gear to fix things, IMHO.

 

[Centrals]

I bet there is a fair amount of statistical data on heroin usage and the correlation between usage and dependency.

I bet there is none on the purity or the impurity present.