Poll: GTR to include stops when one gas is active/on for Shearwater’s AI Teric & Perdix computers?

[RainPilot]

This would never happen. If you are in deco, Shearwater does not show you a GTR.

Good point. Replace the 5 min deco with a 5 min safety stop then.

Also, if the OP implementation were to happen, then deco stops may be included.

 

[CWK]

@npole @hammet
I have a feeling after SW sells thousands of Terics to Rec divers, and with the appropriate refinements (inc those driven by all users), their model range will be the best of the best for many years. Thank you Shearwater (in advance!). However, resolutions w.r.t. cop-outs as cited by StuartV above will need to be part of the solution if they're serious about Rec clients in the long-term.

At present GTR counts down to 0 based on your SAC. At 0, your SPG will show 50 bar.

I do recreational diving all the time. Most of the places I dive will tell me to dive to X mins or to 50 bar. Diving to 50 bar is interpreted to mean different things. One boat I was on said very clearly to ascend and do safety once you hit 50 bar, and that everyone should be on the boat with 30 bar. As far as I can recall, most of the time one would end the dive and do SS when one hits 50 bar as opposed to being on the boat with 50 bar.

The present GTR counts down to 0 (50 bar) without taking into account SS. You have 50 bar with which to do your SS. I don't see a problem with this. Based on the places that I dive at, this is what is asked of divers - end your dive when and o a safety stop when you hit 50 bar.

You want GTR to count down to 0 (50 bar) taking SS into the count down. This means that you want 50 bar in your tank when you are at the surface. I don't really recall being asked to be on the surface/boat with 50 bar in the tank.

I don't see any real need to change the GTR calculation.

 

[mderrick]

I think using the GTR calculation as part of any dive plan is questionable practice. There are just too many circumstances, plus some "edge" conditions, that can make a GTR calculation unreliable. If it's unreliable, then relying on it for SCUBA even as some kind of "backup", doesn't seem like safe practice. While it might have some small benefit for newbies, who don't have any feel for gas consumption, but they should be diving using gas rules that provide wide margins of safety.

 

[npole]

Don't think you got the point.. GTR to plan a dive? It doesn't make sense, because if you use the GTR you didn't planned the dive at all (and you're wrong from the start!).
It's more like this:

- I planned my dive and I know my times already;

A) I compare what I already know with what the computer is showing to me and they (approx) matches: great, I'm re-assured and I'm a happy diver;

B) I check what I already know and I compare it with my computer but the data are greatly different. It's time to review it.

B - 1) Well I'm right, the computer is wrong because the GTR sometime can be off due to many assumption;

B - 2) After all the computer may be right, looking at my profile I didn't respected the depth and the times of my plan because I was distracted by that siren and I don't have time to stay at this depth any longer, better to do my deco stops and not risk it.

This is the correct way of conducting a dive IMO, and this is what I do. And I do all the above already with the TTS, but I have to do some mental calculations to interpolate my SAC at deco stops with the TTS, I have a complex and costly computer, I would love that those calculation are performed for me in real time by it.

This is "my" story, and I believe none here would use it differently in an advance diving, and anyway we have a working brain to understand the difference between a real data and an estimated data.

 

[scubadada]

Are some of you saying you believe you are consistently more accurate with estimating your surfacing pressure on a no stop dive with a safety stop using your computer and SPG compared to using a computer with ATR?

I would imagine, like is true with many SB topics, that many have no experience using a computer with an accurate ATR.

If Shearwater thought this technology did not work, they would not have included GTR on the Perdix AI and the Teric. I could simply add 100 psi to my GTR and be almost as accurate as my Oceanic, as I actually only need about 60 psi.

 

[Jay]

This means that you want 50 bar in your tank when you are at the surface.

Correct, and the reason why I'm asking it is because this is the definition of GTR.

I see where you're coming from with a two-birds one stone approach. I too do similar diving as to you and have had similar instructions, but those two birds are very different.

FYI there is a slight typo in your first sentence which might confuse some. You said "At present GTR counts down to 0 based on your SAC. At 0, your SPG will show 50 bar." but what I think you mean is 'At 0 the surface, your SPG will show 50 bar', OR, At 0, your SPG will show 50 bar plus the gas required to get to the surface .

 

[Hatul]

I really don't understand what the big issue is. The Scubapro G2 and the Galileos include mandatory stops in the GTR calculation and no demons come out. It's useful for a recreational diver if you get into accidental deco which usually clears on ascent, but it does help with real time gas management.

The reason for not including the stops in GTR was revealed once by someone from Sherwater. The way they see it, the main benefit of AI is to have the gas pressure in one display. The GTR is incidental.

 

[stuartv]

Bear in mind that not all divers use T1+T2 for sidemount, some use it for buddy gas checking and some for backgas and a deco stage. Also, if you have any issues with one of the tanks, then the GTR could lead to a false high reading and that would not be great. Right now, I have GTR for 1 tank, so I can double it and get a rough idea of how long I still have. If a tank has failed then I know how much I had on a single tank and that helps crosscheck my contingency gas planning.

I would not change the SM implementation.

I don't understand. The point of "sidemount mode" (T.SM, as Jay put it), would be that in that mode, the computer has a pressure reading for each tank and it assumes that they are the same size. Thus, a GTR calculation would be as accurate as in any other mode.

If the user has T1 and T2 being used for buddy gas checking or back gas and deco gas, then they wouldn't use T.SM. They would use the T1+2 mode that already exists.

In other words, preserve the existing modes, exactly as they are now, but add a sidemount mode.

I can't see how this would have a risk of a false high reading or any other problem.

I believe that 2 ways of displaying GTR , differentiated by which mode you are in, would be simple. They already do this with the way NDL is dealt with.

I personally wouldn't use GTR in the sense that the OP is wanting but I can definitely see why some would, I would have no issue with a change.

The notion that there would be 2 ways of displaying GTR is part of the problem. There should only be one way of displaying GTR - the time you have until you must start your ascent, doing all stops that the computer will prompt for, in order to arrive at the surface with your pre-configured reserve. Pretty effing simple. It works, whether you have mandatory deco stops or an optional safety stop or none of the above. If the computer is going to prompt for it, it is included in the TTS and should be included in the GTR calculation.

As noted earlier, the GTR accuracy depends on the assumptions that the diver ascends at precisely the speed that the computer expects and stops at precisely the depth the computer wants, for precisely the time prescribed, and continues to breathe the same as they have been. It sounds like so much that GTR would not be very accurate. But, Oceanic has been doing it for years and, in my mind anyway, it has proven to be pretty darn accurate - at least for divers of even modest experience who have even modest dive skills.

Nobody seems to be concerned about the accuracy of TTS. Yet the only additional variable in calculating GTR is the diver's breathing rate. If the diver continues to breathe at the same rate, GTR would be precisely as accurate as TTS.

 

[Hatul]

I don't understand. The point of "sidemount mode" (T.SM, as Jay put it), would be that in that mode, the computer has a pressure reading for each tank and it assumes that they are the same size. Thus, a GTR calculation would be as accurate as in any other mode.

If the user has T1 and T2 being used for buddy gas checking or back gas and deco gas, then they wouldn't use T.SM. They would use the T1+2 mode that already exists.

In other words, preserve the existing modes, exactly as they are now, but add a sidemount mode.

I can't see how this would have a risk of a false high reading or any other problem.



The notion that there would be 2 ways of displaying GTR is part of the problem. There should only be one way of displaying GTR - the time you have until you must start your ascent, doing all stops that the computer will prompt for, in order to arrive at the surface with your pre-configured reserve. Pretty effing simple. It works, whether you have mandatory deco stops or an optional safety stop or none of the above. If the computer is going to prompt for it, it is included in the TTS and should be included in the GTR calculation.

As noted earlier, the GTR accuracy depends on the assumptions that the diver ascends at precisely the speed that the computer expects and stops at precisely the depth the computer wants, for precisely the time prescribed, and continues to breathe the same as they have been. It sounds like so much that GTR would not be very accurate. But, Oceanic has been doing it for years and, in my mind anyway, it has proven to be pretty darn accurate - at least for divers of even modest experience who have even modest dive skills.

Nobody seems to be concerned about the accuracy of TTS. Yet the only additional variable in calculating GTR is the diver's breathing rate. If the diver continues to breathe at the same rate, GTR would be precisely as accurate as TTS.

Both Oceanic and Scubapro have been doing it. On the other hand Suunto had the worst implementation of air time as it did not take into account the ascent at all. Sherwater is somewhere in the middle.

 

[Jay]

Both Oceanic and Scubapro have been doing it. On the other hand Suunto had the worst implementation of air time as it did not take into account the ascent at all. Sherwater is somewhere in the middle.

FYI: you can also add these brands to the list doing GTR with stops incorporated: Aeris, Hollis, Sherwood, and Tusa. and probably Aqua Lung.