Will Air Integration in dive computers replace the SPG?

[agilis]

Officiating? We're all adults here.

 

[stuartv]

This is precisely the problem with depending on ATR and SAC information. I will assume that your computer calculates SAC based on gas consumption since the dive started and the average depth.

And you will have assumed wrong. Or purposely misdirected the discussion, a la the people who keep trying to assert that people are saying they NEED AI or an ATR calculation, and the people who keep trying to assert that if you use AI at all then you must use it on every bottle you carry. All false.

The documentation that I have seen for ATR calculations has said (for those computers whose documentation I saw) that ATR is based on consumption rate for something like the previous 1 to 2 minutes. So, if you get into a heavy current and start working hard, the ATR will update to match within 1 to 2 minutes.

 

[KenGordon]

Okay, Netdoc, we need some officiating. I have gone back and counted the number of times Kev has explained his methodology of using data from an SPG. We have seen it explained 13 times and I figure that may actually be some sort of record? Even after I pointed out that he has no audience for what may be a perfectly legitimate system he continues to go out there swinging. I will give him props for determination (or OCD?).

I remember when I was a new teacher and I came up with a lesson that tanked and I would be stuck teaching it over and over..... because for that one topic, I was a one band.

You are very presumptious about the audience.

 

[packrat12]

And you will have assumed wrong. Or purposely misdirected the discussion, a la the people who keep trying to assert that people are saying they NEED AI or an ATR calculation, and the people who keep trying to assert that if you use AI at all then you must use it on every bottle you carry. All false.

The documentation that I have seen for ATR calculations has said (for those computers whose documentation I saw) that ATR is based on consumption rate for something like the previous 1 to 2 minutes. So, if you get into a heavy current and start working hard, the ATR will update to match within 1 to 2 minutes.

Still does not matter. The data I have experienced reflects both. Either way the same result happens. If the outbound leg is 'easier' then the return leg, ATR is off. On a dive of say 100', 1 - 2 minutes is 10% of the dive even at your numbers. The bigger point is that reliance on ATR is not a safe proposition. Changes in depth, current etc can throw a diver off and cause a serious shortage of gas. Using standard principals, such as you should have learned in AN/DP and even OW would illustrate the risks. In the end ATR is information that must not be relied upon during the dive. It is a tool that many divers both inexperienced and some experienced depend on which can lead to an OOA situation.

The same statement also still applies, AI including wireless AI does not offer significant improvement over SPG. Use of information such as ATR is not and should not be depended upon by a diver. It is informational only.

 

[Charles2]

This is precisely the problem with depending on ATR and SAC information. I will assume that your computer calculates SAC based on gas consumption since the dive started and the average depth. ATR is then momentarily calculated based on depth and SAC. I have had tanks heated in the sun to a high temp e.g. high pressure. As soon as we hit the cool water the pressure drops a couple of hundred PSI or more. Our SAC is always high on these dives, which may be good in your situation. Less drastic but the opposite can also happen. But now lets see the issue, you are bouncing up and down in the currents. Your SAC is constantly changing. Your depth may be constantly changing. The amount of effort to get to your start point may have been easier at the outbound and will be harder inbound. And more. Assuming SAC is an average, it will respond slower to current conditions. You might have had great SAC at the beginning of the dive and then terrible SAC in the current. The SAC being used in the calculations will be lower then what it is now. Could also be the opposite here too. Using ATR might return you to the starting point with excess gas (good) or not enough gas (bad). Because you cannot determine the overall situation until back at the starting point, you cannot determine which it will be.

The manual for my computer states the calculation a little differently than your assumption:

"ATR is the time you can remain at your present depth and still safely surface with the tank pressure reserve that you selected during setup (the End Pressure alarm setting).

Tank pressure is measured once each second and an average rate of consumption is calculated over a 90 second period, and used in conjunction with the depth to predict the amount of air required to make a safe controlled ascent, including the No Deco Deep and Safety Stops and any required Deco Stops.

Air consumption and depth are continuously monitored and ATR reflects any change in circumstances, such as beginning to breath more rapidly when swimming against a current which the OCi will recognize as a change and adjust ATR accordingly."

Perhaps your AI computer is an older model. If so, it would seems that the manufacturers are listening to their customers and making improvements in their newer products.

 

[packrat12]

The manual for my computer states the calculation a little differently than your assumption:...

I am using a SAC based on a longer average. It can be a misunderstanding on my part for the specific ATR but Oceanic (mine) indicates "Patented Air Time Remaining algorithm provides extremely accurate time based on current depth and your personal air consumption". This leads me to believe it is a hybrid of Instant and long term. But it really does not matter because an instant, e.g. 90 second SAC may be even more off then your overall average anyway. Think about it, when you are reading it, was it during a resting period or an over active period..... Like the instant MPG in a car, it is a poor reflection on your actual MPG..... Either way the ATR is not and should not be depended on for information. It is information or what I would call for reference only. The real number of interest is the tank pressure. All other data that can be provided is not safe to depend on. When at an anchor line or getting ready to blow a bag, ATR will be good. But if I have a swim to the exit point, ATR might be really really off. That is why my primary point is that some decided upon rule, e.g. rule of thirds, rock bottom etc is what really needs to be used. These rules are based only on tank pressure. That is also why AI does not add much to the divers tool box. As I have said before, a dive computer gives a diver tremendous amounts of information and planning capability on their arm. AI just gives tank pressure. All other data is just neat information but is irrelevant during the dive. Post dive, I will analyze the AI data but this is more for trend information. I do this will all my dives.

Same statement applies... AI is not adding much to the diver's toolbox. Unless more information can be gleaned in the future, it is not that important of an improvement. As a result, I do think it eventually will overtake B&G SPGs for recreational divers but it is not more reliable/better then B&G SPGs. Because of this, I do not think AI will overtake SPGs in technical for a long time.

 

[DiveNav]

.....Kev has explained his methodology of using data from an SPG. We have seen it explained 13 times....

Sorry for asking .... could you explain it again?
I still haven't figure out on how to use it during a multi-level (with a lot of levels ....) dive

 

[Charles2]

These rules are based only on tank pressure.

That's because tank pressure was all that was available when the rules were made.

Years of tradition, unhampered by progress, will always be a viable fallback strategy for many. I would still be comfortable using a J-valve and one double hose regulator, but I really do enjoy the advances that technology has provided and remain confident that the future holds even greater strides in the enjoyment of life underwater.

 

[packrat12]

That's because tank pressure was all that was available when the rules were made.

Years of tradition, unhampered by progress, will always be a viable fallback strategy for many. I would still be comfortable using a J-valve and one double hose regulator, but I really do enjoy the advances that technology has provided and remain confident that the future holds even greater strides in the enjoyment of life underwater.

Funny - I have both dove with and around many J-Valves (Old diver here) including a J-Valve regulator (US Diver Calypso) I had. Lets see, the J valve was a mechanical spring prone to possible failure using a position that was prone to being bumped to the other position or even forget to being set. You typically had a metal bar coming down your harness that always got in the way. The pressure was sub 500 PSI that it would indicate which is not safe even for a deeper dive ascent. Even considering we did not do safety stops back then. So you would be comfortable doing an ascent from 125' with 500 PSI and a safety stop - oh and the restriction kicked in when you were on the other end of the wreck??? A bump could mean that you were at the regulator minimum and out of gas before you knew it. You would be comfortable doing your ascent from 125' with 200 PSI and a safety stop while still at the other end of the wreck????

I see the HUGE benefit of SPG at that point. I know my pressure at any time, not just after they J-Valve tripped. That is light years ahead. I also can start doing restrictive diving like Cave Diving which is the group that championed most of our gear including SPGs. Sorry this analogy does not hold water and I doubt you would do any deeper dives with that configuration without an alternative.

Double hose regulator - Not really a good design. Been around them at the end of their main existence, never used one. The single hose regulator replaced them as they were a simply better design in most cases. I do not know enough about them but that there are major advantages to the design. Everything from WOB to free flow problems to adjustability to adding an octopus etc. Again, the single hose regulator had significant enough improvements to justify the replacement. One of the few exceptions is where the back exhaust was more important for the diver. Again this analogy does not hold water.

AI just does not have this. I can easily say that NO diver should dive based on ATR no matter how it is calculated. Things change throughout the dive. No algorithm can predict this change. AI is just a SPG with a little bit more information. I can easily spell it out: 1 - Logging of gas use, 2 - ATR, 3 - SAC calculation (automatic). I cannot think of any more information that it can present. There is nothing here that can be depended on in a dive and the same basic principals still apply. You base your dive profile on time (NDL/Gas Supply), depth and pressure. All turns should only be based on that information.

A simple though experiment here.... Please try it if you are so confident on your ATR information.

1 - Swim downstream in a current until your ATR matches your elapse time. This implies that you should have enough gas to return to the start point, ascend, complete your safety stop and exit with x PSI.
2 - Turn your dive when ATR matches your elapse time and see how far you get.

Repeat the same dive following the rule of thirds.
1 - Swim downstream in a current until you use 1/3 gas supply.
2 - Turn dive and return. See how far you get.

The odds are much higher that you will return on the second dive then the first. Neither may make it (watching the current may have been more important here) but I would bet on the second one.

This simple experiment shows why ATR is not a panacea solution and why even in the future, this data will still be useless as a controlling part of the dive.

 

[DevonDiver]

Anyway, does anyone have any more creative ideas about WAI? What they would like to see from WAI in the future? Perhaps, we can even entertain some creative thought and talk about the types of procedures a tech diver could implement when using WAI with multiple transmitters.

Reliability and cost issues aside... (but not forgotten)...

AI could be useful for the technical diver if it provided a warning that compared available gas against planned dive and deco schedule. It'd be a purely baseline safeguard... as the tech diver should have plenty sufficient gas. Nonetheless, the unanticipated can occur and divers have been left with insufficient deco gas before.

I'm not sure whether tech divers would want that comparison using ATR or pre-designated SAC/s. These could be: deco/resting (low), working (med), and elevated (hi). The computer could default to 'med' on the bottom and 'low' in deco...or the diver could pre-designate. The diver could also amend the SAC in-water as the situation dictated.

I think I'd prefer a pre-designated SACs... but an AI computer could simply warn if actual consumption deviated from that pre-designated SAC by a significant margin.

How I envision that'd work... The tech diver would have to program each transmitter into their computer, to include the gas type and volume of the tank. That'd be a timely process and would demand some personal and team protocol to prevent human errors in the pre-dive phase. The programming of the computer would need to be confirmed, as would the syncing of the correct transmitter to the correct input gas. The functionality of each transmitter would also need to be confirmed (maybe the computer could cycle through a battery check - as per modern CCR electronic checks)

As the dive progresses, the computer calculates the deco schedule as per normal, based on the gasses it knows the diver is carrying (this already happens with computers like the Petrel). At the same time, it predicts the necessary gas consumption/volume for each available gas needed to perform the real-time scheduled deco ascent. When the predicted gas consumption reaches 2/3rds of the known gas carried (rule of 1/3rds), it issues a warning.

Should any gas lose volume, or the SAC rise beyond pre-inputted predictions, then the computer would issue a warning. If a gas became entirely unavailable, then the diver would immediately de-select that gas from the computer. The computer would, as normal, recalculate the decompression schedule based on the new gas situation.

If the available (selected) gasses were predicted to be insufficient to allow the calculated decompression, then the computer could ask/suggest whether the diver wanted a bailout strategy - yes or no.

The diver would select 'no' if they could complete the designated deco using an 'off-sensor' gas supply (i.e. gas donation from team member).

If the diver had no 'off-sensor' gas supply, they'd select 'yes'. That strategy could then provide the 'best-chance' decompression based on what gas/ses were available. This could include:

1. Re-planning deco using other available gasses.
2. Changing the deco curve to allow shallower stops, if that extended gas supply sufficiently to allow acceptable deco.
3. Reducing conservatism to permit the best possible deco given limited gas.

Or a combination of all 3. Basically, it'd be an exercise in shifting Gradient Factors intelligently to allow the best off-gassing with what gas the diver had at their disposal.

However... the bulk of this could be done without AI on a current generation tech computer. It'd be relatively easy to provide a software solution to gas versus time; where the diver simply input the volumes of the gasses carried and their SAC rate/s. The computer can work out the rest, as it knows the depth and deco obligation. AI would still only provide a benefit if the actual SAC varied (unnoticed) from the predicted SAC or, potentially, where a partial loss of gas occurred.

Until now, tech divers have to do this mentally. The hardest tangible is predicting the best possible decompression based on an insufficient gas supply. There'd be considerable debate in the tech community on any algorithm that attempted to provide a solution to that. Honestly, I don't know if any computer manufacturer would want that liability....

I will leave it to the reader to decide whether they feel 'technical' AI would adhere to the K.I.S.S. principle.