Shearwater Perdix AI

[C Dub]

snort!

 

[AJ]

Yeah, all I know is that my understanding of the philosophy is that everyone on the team has the same gear, in the same config, so that everyone not only knows where their own SPG/knife/compass/xyz is, but they also know where all those things are on their teammates, too. With that philosophy, I would think that everyone would have an SPG and it be located in the same place.

The real question is: does having an SPG or AI matter in a GUE team? I would have no problem with a diver that uses AI and does not even have an SPG attached in my team. He/she must be able to monitor his/her gas and that's what AI does as well as an SPG. However, during training an instructor might want you to use an SPG for training purposes (i.e. task loading). That's a different situation than a normal dive.

What would bother me is a diver who has not enough knowledge and skills to contribute to the team effort for instance making a gas plan but instead relies on his/her computer to make his/her own gas plan for him/her. This diver is no longer part of the team effort and therfore no longer a team member. In my opinion GUE is about team diving and not about standard rig/skills or AI/SPG choices.

 

[scubadada]

Why? @stuartv will be constantly staring at the AI trying to sort out a turn pressure . . .and your MGR too @Lorenzoid. . .

Just can't help yourself, can you?

 

[savsuds]

As a Rec diver, I am not sure why people are concerned about the GTR.

Back Story: The dive boats I ride limit each dive to an hour and you have to return with >= 500 PSI.

I always set my AI computer to 1000 PSI. I can do an hour dive at 60ft and come up to the surface after my safety stop with 1200-1500 PSI left in the tank.

To account for those dives with a differing stress level, I set the pressure alarm at 1000 to give me an idea for the latest I should start my ascent. I always want to be back on the boat with 500-800 PSI. From my understanding the GTR is calculated from the pressure alarm I set. (I have not read the Perdix AI manual yet). I don't use GTR as a count down to getting out of the water, but as a warning for when I hit my predetermined pressure. If I am not drift diving, I set the pressure alarm at my turn point. It is just a tool to follow my dive plan (hop in the ocean and not die).

 

[stuartv]

As a Rec diver, I am not sure why people are concerned about the GTR.

Because not everyone dives the same way you do? Not everyone dives off boats? Not all boats limit your dive time?

If I used an AL80 on the dives I normally do, I would often have to ascend because I was getting low on gas before i got low on NDL time.

To account for those dives with a differing stress level, I set the pressure alarm at 1000 to give me an idea for the latest I should start my ascent. I always want to be back on the boat with 500-800 PSI. From my understanding the GTR is calculated from the pressure alarm I set. (I have not read the Perdix AI manual yet). I don't use GTR as a count down to getting out of the water, but as a warning for when I hit my predetermined pressure. If I am not drift diving, I set the pressure alarm at my turn point. It is just a tool to follow my dive plan (hop in the ocean and not die).

Most AI computers use ATR/GTR to tell you when to start your ascent, so that you arrive at the surface with your desired reserve left. The Perdix AI works almost that way - it just doesn't account for gas you'll use during a safety stop. So, with the PAI, if you do a safety stop, you'll hit the surface with a little less gas than you set for your reserve. That is assuming, of course, that you ascend at exactly 30 ft/min.

So, GTR is not a countdown to getting out of the water. It's a countdown to starting your ascent. Possibly more accurate than your estimate of when you should start to ascend in order to have 500 (or 800 or whatever it is you want) psi left when you get to the surface.

 

[savsuds]

Most AI computers use ATR/GTR to tell you when to start your ascent, so that you arrive at the surface with your desired reserve left.

I have or have owned 2 AI dive computers in addition to my Perdix AI (have not dove with it yet) the Aeris A300CS OLED and the Hollis TX1 AI dive computers. Aeris calls it Air Time Remaining (ATR) and Hollis calls it Gas Time Remaining (GTR).

Aeris Manual pg 25. "ATR is the time you can remain at the present Depth and still safely surface with the Tank Pressure reserve that you selected during setup (End Pressure Alarm Setting)."

Hollis TX1 Manual pg 39. "GTR is the time your current selected gas will last at the present Depth with the Tank Pressure reserve that you selected during setup (End Pressure Alarm Setting)."

Perdix AI manual Pg 10. "Gas Time Remaining (GTR) is the time in minutes that can be spent at the current depth and SAC rate until a direct ascent to the surface at a rate of 33 feet/min (10 m/min) would result in surfacing with the reserve pressure."

I guess dive computer companies choose to define it however they seem fit.

I am accustomed to the Hollis variant of GTR, which could explain my confusion about the GTR differences.

I would be perfectly happy with GTR defined how Hollis does it.

EDIT: GTR how Aeris and Shearwater defines it seems to leave the calculations more subject to variables than the Hollis variant.

 

[stuartv]

I have or have owned 2 AI dive computers in addition to my Perdix AI (have not dove with it yet) the Aeris A300CS OLED and the Hollis TX1 AI dive computers. Aeris calls it Air Time Remaining (ATR) and Hollis calls it Gas Time Remaining (GTR).

Aeris Manual pg 25. "ATR is the time you can remain at the present Depth and still safely surface with the Tank Pressure reserve that you selected during setup (End Pressure Alarm Setting)."

Hollis TX1 Manual pg 39. "GTR is the time your current selected gas will last at the present Depth with the Tank Pressure reserve that you selected during setup (End Pressure Alarm Setting)."

Perdix AI manual Pg 10. "Gas Time Remaining (GTR) is the time in minutes that can be spent at the current depth and SAC rate until a direct ascent to the surface at a rate of 33 feet/min (10 m/min) would result in surfacing with the reserve pressure."

I guess dive computer companies choose to define it however they seem fit.

I am accustomed to the Hollis variant of GTR, which could explain my confusion about the GTR differences.

I would be perfectly happy with GTR defined how Hollis does it.

EDIT: GTR how Aeris and Shearwater defines it seems to leave the calculations more subject to variables than the Hollis variant.

Interesting! Thanks for posting that! I have an Oceanic Atom w/AI and a Hollis TX-1. The Atom works the way your Aeris does. I haven't had the TX-1 very long and I only use it for tech dives, where I have no use for GTR, but I have been just assuming that the TX-1 worked the same way as my Atom. My bad for assuming!

As for how Aeris, Oceanic, and Shearwater do it, the only real variable is your ascent rate. The computers know your depth and where they want you to stop. I definitely prefer the way Aeris/Oceanic does it. If I'm going to look at my computer to tell me how long I have, why have it do half the math for me and leave the other half up to me? If I'm using it to do any of the math, may as well have it do it all. I can look at the remaining pressure and my current depth to do all the math myself, to sanity check what the computer says. And, for that matter, the math for remaining time at current depth is easier than the math for how much gas I need for the ascent, so why have the computer do the easy part of the math and leave the harder part up to me?

Obviously, none of it is hard. You don't need a computer to do any of it. But, IF you choose to let the computer do some, why not let it do it all? That's all I'm saying.

 

[savsuds]

Interesting! Thanks for posting that! I have an Oceanic Atom w/AI and a Hollis TX-1. The Atom works the way your Aeris does. I haven't had the TX-1 very long and I only use it for tech dives, where I have no use for GTR, but I have been just assuming that the TX-1 worked the same way as my Atom. My bad for assuming!

As for how Aeris, Oceanic, and Shearwater do it, the only real variable is your ascent rate. The computers know your depth and where they want you to stop. I definitely prefer the way Aeris/Oceanic does it. If I'm going to look at my computer to tell me how long I have, why have it do half the math for me and leave the other half up to me? If I'm using it to do any of the math, may as well have it do it all. I can look at the remaining pressure and my current depth to do all the math myself, to sanity check what the computer says. And, for that matter, the math for remaining time at current depth is easier than the math for how much gas I need for the ascent, so why have the computer do the easy part of the math and leave the harder part up to me?

Obviously, none of it is hard. You don't need a computer to do any of it. But, IF you choose to let the computer do some, why not let it do it all? That's all I'm saying.

Good points.

I have learned today that both my computers will be telling my something different when they display GTR. I guess I will be using my Perdix and Perdix AI when I dive. TX1 goes to the closet. Gotta have both defining GTR the same for safety sake.

 

[jd950]

Duplicate, sorry.

 

[jd950]

As a Rec diver, I am not sure why people are concerned about the GTR.

Clearly you have not spent much time reading posts by members of the Authoritarian Divers Party (a secret society who fears technology, change or individualism in the scuba diving world and travels under various three-letter acronyms whose names (acronyms) I will not mention. They pray at the alter of Halcyon (a long dead right wing dive god) and worship all things Hogarthian (an ancient cult into weird forms of bondage using nylon webbing). Ultimately, these folks subscribe to the principle that "You must dive the vay vee do and you vill only use dive gear vee approve of...or you vill die!" They can at times be held at bay by holding up a PADI dive traininig book and chanting "air integration is God's will!" It is rumored that wrapping one of them in a poodle jacket BCD will cause them to do whatever you say and answer any questions put them. Unfortunately, doing this banned by various international treaties on enhanced interrogation.

I have put my life at risk by even revealing their existence, but if I can save you from imminent death by Perdix by doing so, then I must...

Long Live the Resistance!