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

[npole]

GTR and TTS are backups, this is what we're talking about, neither of the two are accurate, a diver should know how much time he has because (it's supposed) he have planned the dive, and if he didn't it's because of a recreational dive, so it's supposed he can go up anytime he wants. They will never substitute the remaining pressure and depth gauges, they will provide you a value that you can compare with what you should already know.

If Shearwater is worried to provide the wrong value, then it should worried about it with the TTS: it says 10 minutes, but your stop is slight off or your ascent time isn't the one "imagined" by the software, and you'll figure that you needed 12 minutes instead.

And the same could happen without deco, when the GTR is available, the diver know to have 10 minutes of air, but then he start to breath faster due to the presence of a current, and he'll find that his GTR got reduced to 5 minutes and he's far from the boat or wherever he was supposed to finish his dive.

I find it more "dangerous" to give the GTR to a recreational diver that could trust it like the bible, than to a more experienced diver for a more advanced dive (with deco stops) that could understand better its function and how that value is calculated.

 

[wKkaY]

Another thing to consider is that GTR is not linear once NDL is exceeded.

An extra N minutes spent at depth doesn't reduce the GTR by N minutes, it reduces by more than that because of the additional deco required.

 

[scubadada]

GTR and TTS are backups, this is what we're talking about, neither of the two are accurate...

After over 1500 dives (95% no stop, 5% light deco, <15 minutes) in the last 16 years, I can confidently say that the Oceanic ATR is quite accurate.

 

[npole]

Another thing to consider is that GTR is not linear once NDL is exceeded.

An extra N minutes spent at depth doesn't reduce the GTR by N minutes, it reduces by more than that because of the additional deco required.

So the TTS.. again: the GTR is nothing more than TTS data (deco stops and ascend time) + SAC at given depth (air consumption at given ATA).

 

[npole]

After over 1500 dives (95% no stop, 5% light deco, <15 minutes) in the last 16 years, I can confidently say that the Oceanic ATR is quite accurate.

They are all calculated the same: they do an average according to air (pressure) sucked from the bottle, it is a pretty easy calculation. Is it accurate? It depends.. if you are a diver with a constant breath rate it could be pretty accurate, if you're a diver that could double or quadruple the air consumption because of an unexpected event, it will not. That's why I said the GTR could be more dangerous if read by a diver with less experience than interpreted by a diver with more knowledge.

 

[stuartv]

Note that even Rec divers may carry more than one bottle of gas, and in OC Rec mode, Shearwater not only allows more than one bottle of the same gas but also 3 different gases.

KISS?

Irrelevant. The OP is about what the computer does when you only have 1 gas enabled. To KISS.

I already asked Shearwater, they said that it is a decision (intentional) because the computer couldn't know how many tanks you may carry and if you have stages the GTR will mislead you.

..

I then learned to use the TTS and comparing it with my SAC and gas left... however I still find a unnecessary operation that the computer could calculate for me, hence the proposed solution above.

Very disingenuous from Shearwater. The current GTR is based solely on the one tank you are breathing. Besides, if you are carrying additional, that just means you have longer than what GTR says - which erring way on the safe side.

I think the problem with including safety stops in GTR would be how it is calculated DURING the stop.
Before, the stop, it is easy to apply your current SAC rate to an specific time and depth (say 3:00 and 15 feet or whatever your settings are) to calculate how much gas time is required.
However, once you are at the stop, you may no longer be at 15 feet. You could be higher or lower.

So? Oceanic manages to calculate it quite accurately. Are you saying Shearwater can't do the same?

The point I'm trying to make is that GTR calculations during a safety stop would have to make an ASSUMPTION that you are going to stay at an precise depth for the calculation to be accurate.

What assumption is the TTS countdown making other than a value for a safe ascent rate?

It would assume a 30fpm ascent, that you make every stop at the precise depth the computer tells you to (including whatever safety stop depth is prescribed, and that your breathing stays the same. I think it's pretty easy for a diver to understand that the GTR is only as accurate as the diver is accurate is performing the ascent that is expected by the computer.

Another thing to consider is that GTR is not linear once NDL is exceeded.

An extra N minutes spent at depth doesn't reduce the GTR by N minutes, it reduces by more than that because of the additional deco required.

Non sequitur. Linearity has no bearing on the question. The computer calculates TTS, even when you're in deco. So, it knows your SAC and it knows exactly how long you will be at every 1 foot increment of depth. That last part is exactly how it knows your TTS. So, with knowing those two things, if it assumes you will continue to breathe the current tank, it can calculate GTR just as accurately as it calculates TTS. Whether you are in deco or not.

Refusing to show GTR just because the diver has exceeded their NDL is a cop-out. Not including time spent at a stop the computer will prompt for (e.g. a Safety Stop or a mandatory deco stop) is also a cop-out.

The fact that Oceanic includes the safety stop in their GTR calculation and the result is that Oceanic gives a MORE ACCURATE GTR than Shearwater does (even on an Oceanic computer that supports 3 gases) OUGHT to be enough to shame Shearwater into doing it. But, apparently, it's not.

Doing deco on back gas is a lot more challenging math, when you are trying to figure out how much longer you can stay down, than the math when you are just doing an NDL dive. I have done a number of dives where I went into a few minutes of deco and then did my deco on just my back gas. Having the computer do that math for me, so that I can have a sanity check that I have calculated correctly would be really nice. And easy for the computer to do. I really do not get why Shearwater won't give us this feature (GTR even when in deco).

 

[Jay]

@npole @hammet some aspects of your discussion are more about 'how' rather than 'if' and it's the latter that is the OP focus. Agreed the two are somewhat related. The remaining 'how (to implement)' aspects can be thrashed out later, or as @stuartv says above (post#26) re its accuracy versus TTS' accuracy then it seems like a moot point.

Please for for the proposal if you think it has merit (and assume nothing will be implemented if it doesn't safely work in an clear and simple manner - SW wouldn't implement anything dodgy).

I would like to note that a SS countdown is not part of OC Tec even though it may be in OC Rec. Any change to GTR would have to take OC Tec into consideration.

Thanks for noting that CWK. I 100% agree that this proposal must consider OC Tec. Given there's no SS in OC Tec then the GTR (proposal) wouldn't have any effect on OC Tec in that regard?

However, if you're talking about Tec-Rec on one gas doing light deco, then this proposal would affect GTR. I'm wondering if the no-votes are from those divers. CWK, you're the only one so far to articulate your reasons, so please do let me know if this guess of mine is a concern and if so how or if there are other remaining concerns.

@CWKI think the real problem here is that these are technical computers that have been adapted to recreational use as a second thought. The technical bias overrides the recreational use/function. This would not prevent me from buying a Teric today if my trusty VT3 died, I already have the transmitter. Thank you Shearwater

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.

 

[RainPilot]

For GTR Sidemount mode, it would assume that T1 and T2 are both connected to the same-sized tanks filled with the same gas. So, it would apply the current measured SAC to both tank pressures to calculate the total GTR (copied from @Stuartv’s earlier post from Perdix AI wishlist). T1/2 would display T.SM (/whatever named) being the sum of all active tanks.

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.

TTS includes stops. Just compare GTR to TTS.

The snag there is that the two may be wildly different and thus possible to misinterpret. If you are at 40m, with say a 5 min deco stop incurred, you may have a TTS of 10 min. However, you have enough gas to remain at depth for 1 more minute before ascending. A TTS of 10 and a GTR of 1 may lead a novice rec diver to confusion and possible panic if they think they don't have enough gas to get to the surface. This is going to be more of an issue with the Teric, as SW positions itself in the rec market more and more.

There is really no need to add a 3 minute safety stop on top of a GF that you have chosen. So in terms of KISS, I think keep it as it is. Divers should just understand GF if they want to use a GF based computer.

My understanding of the safety stop is that it is most useful in the sense of reducing the average ascent rate. A GF value does give you conservancy but it is based on assumptions of ascent rate. If you exceed the ascent rate average direct to the surface, then you may surface with a higher GF99 than you planned for. Again, this is an issue with newer rec divers more than with tec divers.

Any change to GTR would have to take OC Tec into consideration.

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.

 

[scubadada]

...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.

The Rec mode was added to the Petrel, then carried over to the Perdix, Perdix AI, and then the Teric. The Tech lineage was never lost. No doubt Shearwater has significantly penetrated the Rec market. Including Rec features that have been available on other brand's computers for many years would further solidify their position. If they had GTR, including all stops, even for only 1 transmitter, that would be great. I would also like the download software to be able to auto-calculate my RMV after input of cylinder information. Oceanlog has a simple dropdown list including all the cylinders you use. One can only wish and hope.

 

[CWK]

The snag there is that the two may be wildly different and thus possible to misinterpret. If you are at 40m, with say a 5 min deco stop incurred, you may have a TTS of 10 min. However, you have enough gas to remain at depth for 1 more minute before ascending. A TTS of 10 and a GTR of 1 may lead a novice rec diver to confusion and possible panic if they think they don't have enough gas to get to the surface. This is going to be more of an issue with the Teric, as SW positions itself in the rec market more and more.

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