Will Air Integration in dive computers replace the SPG?

[stuartv]

Hi Stuart,

Right now I do it manually. Diving an AL 80, if I am shallower than 90', I leave it at 500 reserve. For 90 to 120, I go to 700, and 120 or more, 800--I set it for less if I am on an HP 100 or 120. Maybe more if it is going to be a stressful dive (night dive in a strong current for example) Like boulderjohn said, in a rec diving gas sharing emergency I am not doing a safety stop, as I expect my OOG buddy's first priority is to get to the surface. Similarly, I am heading up at 60'/min until I hit 30 feet when I will slow it down.

What you seem to be posing is a "rock bottom" algorithm, where the computer calculates ATR based on the gas needed for ascent based on two divers using the tank--i.e. double your current real time consumption at the current depth (the only one available to the computer), as predicted through the ascent (like current ATR algorithms). This would be "rock bottom" refined for the real-time conditions of the dive and would replace a pre-set "reserve". That might actually be a good option to offer, especially if you could program the parameters of the ascent (no stops, faster rate as I would do, or true "rock bottom" with standard ascent and the stop).

No, I am not posing a rock bottom algorithm. I am just suggesting that what you described that you do manually could be done automatically. Instead of having 1 hard number for your reserve, it could automatically vary the amount of the reserve based on your current depth and dynamically update your ATR based on that reserve.

E.g., in your case, your computer could use 500psi as the reserve as you descend and swim around at depths down to 90'. If you descend further, it would start increasing the reserve number that it using. So, your ATR would drop as you descend. It would drop as you descend anyway, but what I'm talking about is that it would drop faster than would be accounted for solely by the increase in ambient pressure. It would drop faster than that because the ambient pressure is increasing AND the reserve number it's using is also increasing. Conversely, if you ascend, your ATR might increase (or increase more rapidly) as the reserve number used in the ATR calculation drops.

The more I think about it, the more I like the idea. Currently, my computer has one setting for Reserve, which has a default of 500psi. The "enhancement" would be to add one more setting. The current setting would be the Reserve for any depth of 60' or less. The new setting would be the Reserve for a depth of 130'. The default would be, say, 1000psi.

So, right out of the box, if I dive to 130' and hang out, the ATR calculation will be sending me up to the arrive at the surface with 1000psi. If I dive to somewhere in between, say, 95', it would interpolate the 2 numbers and calculate ATR based on a reserve of 750psi.

Hitting the surface with 1000psi may sound excessive. But, one, that reserve would shrink as you ascend, so you could stay down longer, if you are staying at a shallower depth, and you'd arrive at the surface with that lower reserve. If you ascend at hang out at 60' or less, and then ride your ATR, you'd still arrive at the surface with 500psi.

And, two, you could change the default. So, you could make the reserve for 130' be 800psi or whatever, if you want.

And if you're diving a bigger tank, you could change both numbers to lower values, if you want.

It's really just about eliminating that manual step that you are doing now where you adjust the reserve based on the planned max depth. And for computers that let you enter the cylinder size you're using, it could even automatically compensate for that. If you're set for 500psi on an AL80 and you change the computer to tell it you're using a 100, it would reduce the reserve setting so that you're hitting the surface with the same amount of air left, though it's a lower psi number.

To the Negative Nancys: I have not and am not saying anyone NEEDS any of this. I'm not sure why I'm repeating myself, though. I've said this enough times already that I can only include some people have a fundamental lack of reading comprehension. Either that or PermaGrump. Or both.

 

[stuartv]

Excuse the dive computer n0ob question. Do the Oceanic DC's dynamically display the lower number it calculates between ATR & DTR? Shouldn't the DTR always be lower since it takes the ATR then also adjusts down (safer or more cushion) for oxygen/nitrogen absorption? Is this user settable? I have the Aeris A300 but am just starting to play around with it. Yes I have the PDF manual, in the middle of reading it.

I think scubadada already answered this. But, to be clear, my Oceanic Atom normally displays NDL on the main screen. But, if it calculates that the ATR is less than the NDL, then it automatically switches to showing the ATR (as the DTR) on that main screen instead of the NDL. I would guess the A300 works the same way.

 

[scubadada]

Oceanic end pressure can be set anywhere between 300 and 1500 psi. I dive by myself, I leave my end pressure at 500 psi, I often dive after my ATR is zero. My dives are mostly drift dives where I have direct access to the surface and know exactly how long and how much gas it takes me to get there.

 

[scubadada]

I think scubadada already answered this. But, to be clear, my Oceanic Atom normally displays NDL on the main screen. But, if it calculates that the ATR is less than the NDL, then it automatically switches to showing the ATR (as the DTR) on that main screen instead of the NDL. I would guess the A300 works the same way.

Correct

 

[scubadada]

All my audible alarms, and most of my alarms in general, are disabled, all I have to do is push a button to get rid of any other message my computer is giving me, such as zero air time remaining.

 

[scubadada]

After 1,046 dives with Oceanic computers, Pro Plus, Pro Plus 2, then VT3, I can vouch for the fact that the ATR calculation is quite, quite accurate.

I also have my SRMV for the last 644 dives and it is remarkable constant at 0.37 +/- 0.04 cf/min (mean +/- sd). For me, the most significant frequent variable is being warm or cold. This info is extremely valuable in gas planning. My SRMV is a little less than this for the last couple years, I use 0.75 cf/min for emergency gas planning like required pony volume...

 

[stuartv]

The goal of "achieving maximum dive time while taking no more decompression precautions than required to avoid the bends and while carrying no more air than required to avoid drowning" is intriguing. It reminds me of people who would let the lever pop from a grenade and then hold it for the maximum time possible.

Whether you choose to hold it until there's 0.5 seconds left on the fuse or 5 seconds, more precise and accurate data on when it's going to blow is still a good idea.

I wonder if people who are keen on the idea that the ATR feature (or some smarter future incarnation thereof) might help economize their air supply usage are the same people who seek out "the most liberal" computer (so they have the option of economizing decompression). I guess I'm just a wasteful diver. I often am back at the boat with plenty of no-deco time and gas left.

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, what is your personal formula for determining how much padding you need to apply to what your computer is telling you is safe? And how did you come up with this formula? What are the statistics? Does your padding decrease your chance of DCS by 10%? 1%? 0.1%?

Have you ever been bent? Do you somehow "sense" when you are (or were) close to getting bent?

I can tell when I'm getting close to crashing my motorcycle because I can feel the tires sliding and I (mostly) have the skill to push them to that point and no further, so that I don't crash, but I KNOW that I was right at the limit.

How do you do that with DCS? I have never heard that there is a way to do that. And if you don't/can't KNOW how close you are to getting DCS and you have never had a DCS hit, then why do you think your "feeling" about it is better (in a meaningful, useful way - if you're 0.001% less likely to have a DCS hit, I'd say that's pretty meaningless and not useful) than what your computer is telling you is safe? Are there statistics that show that users of more liberal computers experience DCS more often than users of more conservative computers? Are there statistics that you consulted that indicate people who dive to the last, say, 3 minutes of their NDL are more likely to get a hit than people who only dive to the last 5 minutes or 10 minutes? Got a link or a reference I can look up? I'd really like to see data on the correlation of DCS hits to NDL diving and how close the divers comes to the NDL.

 

[agilis]

Whether you choose to hold it until there's 0.5 seconds left on the fuse or 5 seconds, more precise and accurate data on when it's going to blow is still a good idea.



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, what is your personal formula for determining how much padding you need to apply to what your computer is telling you is safe? And how did you come up with this formula? What are the statistics? Does your padding decrease your chance of DCS by 10%? 1%? 0.1%?

Have you ever been bent? Do you somehow "sense" when you are (or were) close to getting bent?

I can tell when I'm getting close to crashing my motorcycle because I can feel the tires sliding and I (mostly) have the skill to push them to that point and no further, so that I don't crash, but I KNOW that I was right at the limit.

How do you do that with DCS? I have never heard that there is a way to do that. And if you don't/can't KNOW how close you are to getting DCS and you have never had a DCS hit, then why do you think your "feeling" about it is better (in a meaningful, useful way - if you're 0.001% less likely to have a DCS hit, I'd say that's pretty meaningless and not useful) than what your computer is telling you is safe? Are there statistics that show that users of more liberal computers experience DCS more often than users of more conservative computers? Are there statistics that you consulted that indicate people who dive to the last, say, 3 minutes of their NDL are more likely to get a hit than people who only dive to the last 5 minutes or 10 minutes? Got a link or a reference I can look up? I'd really like to see data on the correlation of DCS hits to NDL diving and how close the divers comes to the NDL.

 

[agilis]

The same logic applies to injecting heroin. There are so many variables, human and drug, that precision is impossible. If you don't leave a wide safety margin they find you with the needle still in your arm and a beatific expression on your dead face.

Dancing on the edge of DCS is exactly the same kind of multiple variable situation with some of those variables unknowable. The classic 'things we don't know that we don't know we don't know'. People get bent for all sorts of reasons, but you can bet your life that running close to the limits greatly enhances the likelihood. Statistical data does not exist for most hazardous activity.

Coming back with a lot of gas does get annoying,especially on a tourist head boat, when the inexperienced divers set the end time by getting down to six or seven hundred pounds when you still have eleven or twelve hundred pounds. But that's just how it is.

I hope your experience with grenades has been strictly theoretical.

 

[stuartv]

The same logic applies to injecting heroin. There are so many variables, human and drug, that precision is impossible. If you don't leave a wide safety margin they find you with the needle still in your arm and a beatific expression on your dead face.

Dancing on the edge of DCS is exactly the same kind of multiple variable situation with some of those variables unknowable. The classic 'things we don't know that we don't know we don't know'. People get bent for all sorts of reasons, but you can bet your life that running close to the limits greatly enhances the likelihood. Statistical data does not exist for most hazardous activity.

Coming back with a lot of gas does get annoying,especially on a tourist head boat, when the inexperienced divers set the end time by getting down to six or seven hundred pounds when you still have eleven or twelve hundred pounds. But that's just how it is.

I hope your experience with grenades has been strictly theoretical.

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

You speak of running close to the limits of DCS, but how do you know you are to the limits of DCS unless you are able to sense when a DCS hit is about to happen, or you actual have a hit? Do you mean running close to the limits that your computer tells you? If so, then how do you know how close the computer's proscribed limit is to your actual limit? What is YOUR formula for determining the safety margin you set? What data is it based on? How much safer is your chosen margin making you? If you don't know, then what is your basis for telling anyone that they are "running close to the limit" of DCS if they stay within the NDL their computer tells them (which, as I understand it, is always less than the NDL that PADI or USN or NOAA tables would say, when comparing apples to apples)? It's your "feeling"? A "feeling" that is based on how much experience actually FINDING the limit (by having a DCS hit)?

What if I assert that the margin of safety that you use to pad your NDLs is only making you 0.001% less likely to experience a DCS hit? In practical terms, that would be an assertion that it's not making you any safer. Do you have data to refute that assertion with? Or you just "know" that it's making you safer, but you don't know how much?

When you drive across a multi-lane bridge, do you always make sure you're in the centermost lane, too? That IS safer, right? Less likely to go over the edge, right?

By the way, notice that I haven't said a single thing about how I think anyone (including myself) should dive, relative to their NDL. I'm just asking you to explain exactly how you do it and the basis for your decisions on the safety margins you use. I have not said that I would hold the grenade until 0.5 seconds left. I just said that no matter how long you choose to hold it, having a more precise and accurate measurement of the fuse is better than having a less precise or accurate measurement.