When is ZH-L16C GF not ZH-L16C GF? When it is a G2 Tek computer

[Sevenrider860]

The thing that I was wondering about what happened with my student is if there is some setting for the G2Tek that tells it to apply SP's adaptive algorithm junk to the ascent plan that is calculated using GFs. I.e. it calculates your ascent based on your chosen GFs, but then, if the adaptive setting is turned on, it will make your ascent more conservative based on whatever parameters it monitors (e.g. SAC rate, water temp, etc.).

In order to answer that question, I found the G2 Tek manual and looked. What I found says that the G2 Tek will log your heart rate and skin temp, if you connect those sensors, but it doesn't use that data for the ascent algorithm. So, in theory, my theory is not the explanation. I still don't know why my student's G2Tek gave her all that deco on that one dive.

BUT, in reading through the manual I found these other things:

This is from page 13 of the G2 Tek manual, available here:

https://scubapro.johnsonoutdoors.com/sites/default/files/2022-10/SP_G2TEK_manual_EN.pdf

View attachment 829087

So, if you skip a deco stop, the G2Tek will lock you out for 24 hours.

Not today, Satan!

And this is from page 36:

View attachment 829088

WHAAAT?!? It will change your gradient factors during a dive?!?!

Well, what could possibly go wrong there?

And this is from page 70:

View attachment 829089

It calculates your deco based on a variable ascent rate? W. T. F?!?!

Anybody got any suggestions on what deco planning software you could use before your dive to calculate your dive plan - so that it will match what your G2Tek actually does in the water?

I mean, I use Subsurface for dive planning. It will allow me to specify 4 different ascent rates, if I want to, based on:

Below 75% avg depth
75% to 50% avg depth
50% avg depth to 20ft
20ft to surface

But, as my actual dive computer doesn't have the same options, I use the same ascent rate for all 4 parameters, so that my plan matches what my Shearwater says during the dive.

I don't know of any software that will plan with a variable ascent rate like the G2Tek manual shows.

Bottom line: In my personal opinion, the ScubaPro G2Tek dive computer absolutely SUCKS as a technical diving computer. I sure hope they at least get it sorted out so the GF implementation actually works correctly (i.e. like Shearwater computers and all the dive planning software everyone uses work). Including at least an option for it to calculated based on a more standard ascent rate.

The G2 Tek does not enter SOS mode if you skip a Deco stop. It will go into SOS mode if you ascend above 3 feet for 3 minutes. You can miss every deco stop and as long as you do not ascend above 3 feet for 3 minutes the computer will not enter SOS mode and you have the option to go back down and satisfy those stops. I have verified this through pressure pot testing.

The only missed deco stops that would results in this SOS condition are the the GF 100/100 stops. As you point out, if you ascend more than 5 feet from the set stop, the G2 Tek will increase the GF to the next possible value that would not have you missing a stop. It will then show you the new GF you are operating under. You can bust GF deco stops until you end up at GF 100/100...and now those missed stops will count. I am not overly concerned over the adjustment of the GF because you missed a stop. I don't find it ideal, but it is a way of adjusting things given that you already broke the ceiling of your defined stop in the first place.

Of course I have now learned that 100/100 on the G2 is not the same as 100/100 on the Shearwater based on Scubapro's own statement from Tech Services - "I will note that our unit is more conservative intentionally". That will be something I will try to test in the future. Set both the Shearwater and G2 Tek to 100/100 and compare.

Some issues I have with the G2 Tek in CCR mode is that there are no auto setpoints. I don't use auto set points on my controller, but I do like them on the backup computer that is not connected to the O2 cells. Those calculations are just estimates anyway.

I don't see it documented that the G2 TEK uses the variable ascent rates in its deco/stop calculations...I guess that can be implied, but it is never stated as such that I can find. There is this additional Scubapro Gem...

"In the event of a too-fast ascent, the G2TEK may require a decompression stop even within the no-stop phase because of the danger of microbubble formation."

 

[tursiops]

The thing that I was wondering about what happened with my student is if there is some setting for the G2Tek that tells it to apply SP's adaptive algorithm junk to the ascent plan that is calculated using GFs. I.e. it calculates your ascent based on your chosen GFs, but then, if the adaptive setting is turned on, it will make your ascent more conservative based on whatever parameters it monitors (e.g. SAC rate, water temp, etc.).

In order to answer that question, I found the G2 Tek manual and looked. What I found says that the G2 Tek will log your heart rate and skin temp, if you connect those sensors, but it doesn't use that data for the ascent algorithm. So, in theory, my theory is not the explanation. I still don't know why my student's G2Tek gave her all that deco on that one dive.

BUT, in reading through the manual I found these other things:

This is from page 13 of the G2 Tek manual, available here:

https://scubapro.johnsonoutdoors.com/sites/default/files/2022-10/SP_G2TEK_manual_EN.pdf

View attachment 829087

So, if you skip a deco stop, the G2Tek will lock you out for 24 hours.

Not today, Satan!

And this is from page 36:

View attachment 829088

WHAAAT?!? It will change your gradient factors during a dive?!?!

Well, what could possibly go wrong there?

And this is from page 70:

View attachment 829089

It calculates your deco based on a variable ascent rate? W. T. F?!?!

Anybody got any suggestions on what deco planning software you could use before your dive to calculate your dive plan - so that it will match what your G2Tek actually does in the water?

I mean, I use Subsurface for dive planning. It will allow me to specify 4 different ascent rates, if I want to, based on:

Below 75% avg depth
75% to 50% avg depth
50% avg depth to 20ft
20ft to surface

But, as my actual dive computer doesn't have the same options, I use the same ascent rate for all 4 parameters, so that my plan matches what my Shearwater says during the dive.

I don't know of any software that will plan with a variable ascent rate like the G2Tek manual shows.

Bottom line: In my personal opinion, the ScubaPro G2Tek dive computer absolutely SUCKS as a technical diving computer. I sure hope they at least get it sorted out so the GF implementation actually works correctly (i.e. like Shearwater computers and all the dive planning software everyone uses work). Including at least an option for it to calculated based on a more standard ascent rate.

I sure hope ChrisDee does not see this thread. You are criticizing his baby!

 

[stuartv]

The G2 Tek does not enter SOS mode if you skip a Deco stop. It will go into SOS mode if you ascend above 3 feet for 3 minutes. You can miss every deco stop and as long as you do not ascend above 3 feet for 3 minutes the computer will not enter SOS mode and you have the option to go back down and satisfy those stops. I have verified this through pressure pot testing.

I did understand that. I wrote about it poorly.

There are conditions where it will lock you out. I need care no further.

The only missed deco stops that would results in this SOS condition are the the GF 100/100 stops. As you point out, if you ascend more than 5 feet from the set stop, the G2 Tek will increase the GF to the next possible value that would not have you missing a stop. It will then show you the new GF you are operating under. You can bust GF deco stops until you end up at GF 100/100...and now those missed stops will count. I am not overly concerned over the adjustment of the GF because you missed a stop. I don't find it ideal, but it is a way of adjusting things given that you already broke the ceiling of your defined stop in the first place.

I understood (inferred) that as well. I rank that feature right up there with the Oceanic computers that reset your gas to Air 24 hours after the end of your last dive.

Of course I have now learned that 100/100 on the G2 is not the same as 100/100 on the Shearwater based on Scubapro's own statement from Tech Services - "I will note that our unit is more conservative intentionally". That will be something I will try to test in the future. Set both the Shearwater and G2 Tek to 100/100 and compare.

Some issues I have with the G2 Tek in CCR mode is that there are no auto setpoints. I don't use auto set points on my controller, but I do like them on the backup computer that is not connected to the O2 cells. Those calculations are just estimates anyway.

I don't see it documented that the G2 TEK uses the variable ascent rates in its deco/stop calculations...I guess that can be implied, but it is never stated as such that I can find. There is this additional Scubapro Gem...

"In the event of a too-fast ascent, the G2TEK may require a decompression stop even within the no-stop phase because of the danger of microbubble formation."

I missed that one. And perhaps that is what happened to my student on the one dive. I HAD emphasized that I wanted her to ascend at exactly 30 feet per minute (to the best of her ability, of course). Maybe on that ascent, where the SP thinks an ideal ascent rate is slower, she went up even faster than 30 (for a short amount of time) and it gave her a fast-ascent penalty.

That is the best hypothesis I have at this point, anyway.

 

[Kendall Raine]

I missed that one. And perhaps that is what happened to my student on the one dive. I HAD emphasized that I wanted her to ascend at exactly 30 feet per minute (to the best of her ability, of course). Maybe on that ascent, where the SP thinks an ideal ascent rate is slower, she went up even faster than 30 (for a short amount of time) and it gave her a fast-ascent penalty.

That is the best hypothesis I have at this point, anyway.

That's the thing. With a modified algorithm (ZHL16 ADT MD) whatever that is, you don't know. Coefficients are proprietary. The computer is altering the curve in real time based on coefficients that aren't disclosed and may not even be tested (who knows how many times times they've been changed). Doesn't mean it's wrong (or worse than whatever straight ZHL-16 C + GF) is prescribing. It's just black box time. Anathema to those who think GF's proffer a measure of control/informed consent and hard to use in team dive planning. This has been floating around since the early 90's with Uwatec and the Aladdin. Not to be a cynic, but perhaps the best model is one you can't test. At least the curves are likely more conservatives than straight whatever.

 

[Belzelbub]

There are conditions where it will lock you out. I need care no further.

Same. Mostly. I'm no fan of lockouts. My primary DC (SW) will not lockout. My backup (Garmin) gives the diver the ability to disable the lockout. Both of those are acceptable to me.

A lockout against the M value (GF 100/100) is a lot more understandable to me. At least compared to some other lockouts where it will apply at a user selected more conservative setting. The SP approach appears more understandable to me, though I still dislike it on principle.

Of course, it seems that there may be a possibility that SP GF 100/100 is not actually 100/100.

 

[stuartv]

That's the thing. With a modified algorithm (ZHL16 ADT MD) whatever that is, you don't know. Coefficients are proprietary. The computer is altering the curve in real time based on coefficients that aren't disclosed and may not even be tested (who knows how many times times they've been changed). Doesn't mean it's wrong (or worse than whatever straight ZHL-16 C + GF) is prescribing. It's just black box time. Anathema to those who think GF's proffer a measure of control/informed consent and hard to use in team dive planning. This has been floating around since the early 90's with Uwatec and the Aladdin. Not to be a cynic, but perhaps the best model is one you can't test. At least the curves are likely more conservatives than straight whatever.

It's not just about control/informed consent, and it is nothing to do with teams.

It's about being able to reliably predict how much gas I need, even if I'm diving solo.

If the dive computer can change the ascent plan based on factors outside the scope of my planning (and planning software), then that means it can assign me stops and times that will require more gas than I planned for.

That is unacceptable in a technical diving computer. Unacceptable to me, anyway.

 

[inquis]

that means it can assign me stops and times that will require more gas than I planned for

It will only increase GFs, resulting in less stop time and therefore less gas. I still find it unacceptable as well but for other reasons.

 

[lexvil]

Random question; if you plan a dive so tight why do you need a computer?

 

[stuartv]

It will only increase GFs, resulting in less stop time and therefore less gas. I still find it unacceptable as well but for other reasons.

Except for this:

There is this additional Scubapro Gem...

"In the event of a too-fast ascent, the G2TEK may require a decompression stop even within the no-stop phase because of the danger of microbubble formation."

That reads to me as "it may require stops that require more gas than you planned for."

Which behavior is my only current candidate for explaining why my student had a 17 minute deco stop at the end of a dive where I and the other diver had no deco at all.

 

[stuartv]

Random question; if you plan a dive so tight why do you need a computer?

To tell me depth and time and calculate a better (shorter) ascent for me than what I planned in advance?

The plan is always to get out of the water with a lot of gas left.

The plan also accommodates things like having to share air with a buddy, or deal with a lost deco gas scenario.

I have never yet had one of those things happen in real life - and always gotten out with plenty of gas left.

But, if "shtuff" happens and I'm now highly stressed and also sharing gas with a buddy (who is also highly stressed), then the last thing I want is an ascent that my computer thinks was "too fast" causing my computer to give me an extra bunch of minutes of deco beyond what I planned for. In THAT scenario, the extra deco MIGHT result in not having enough gas.