Shearwater Perdix Air Integrated...Opinions

[Kevrumbo]

Something else to add to the discussion. The screen on my perdix is fairly full of information. It's quite clean and intuitive, but I can see where adding additional information would contribute to cluttering the screen. Again, just my view. YMMV.

Yes . . .information like bottom gas time remaining (GTR) in decompression diving with separate deco mixes like Eanx 50 & O2 would be cluttering and superfluous, when you can easily determine that based on your elapsed dive time, or simply just looking at your SPG. The data that is more useful and that I prefer in that field of the Petrel2/ Perdix display is the delta + 5 and the TTS displays along with the current gas selected. From Shearwater's FAQ:

. . . The GTR display becomes blanked if decompression stops are required (it will return once cleared), so the diver must ensure they have enough gas if they expect to have decompression obligations. The GTR is based on the currently measured Surface Air Consumption (SAC) rate, averaged over the last few minutes. . .

The GTR calculations on the Perdix AI are only for single-tank diving that does not require decompression stops. . .This calculation includes the gas used for the ascent but does not include any safety or decompression stops. . .

GTR is a tool for no-stop (i.e. no decompression) diving. We do not recommend GTR as a tool for decompression diving. Decompressing diving involves significant pre-planning of gas reserves and typically requires multiple tanks and gas mixtures. The complexities due to managing multiple tanks and differing styles of gas management would make setup of GTR too complex for reliable use. We tried this during development, and experienced testers frequently made setup mistakes that resulted in incorrect GTR. Shearwater feels that GTR is a great tool for single-tank, no-stop diving, but unfortunately does not work well for more complex diving.

 

[scubadada]

Yes . . .information like bottom gas time remaining (GTR) in decompression diving would be cluttering and superfluous, when you can easily determine that based on your elapsed dive time, or simply just looking at your SPG. The data that is more useful and that I prefer in that field of the Petrel2/ Perdix display is the delta + 5 and the TTS displays. From Shearwater's FAQ:

. . . The GTR display becomes blanked if decompression stops are required (it will return once cleared), so the diver must ensure they have enough gas if they expect to have decompression obligations. The GTR is based on the currently measured Surface Air Consumption (SAC) rate, averaged over the last few minutes. . .

The GTR calculations on the Perdix AI are only for single-tank diving that does not require decompression stops. . .This calculation includes the gas used for the ascent but does not include any safety or decompression stops. . .

GTR is a tool for no-stop (i.e. no decompression) diving. We do not recommend GTR as a tool for decompression diving. Decompressing diving involves significant pre-planning of gas reserves and typically requires multiple tanks and gas mixtures. The complexities due to managing multiple tanks and differing styles of gas management would make setup of GTR too complex for reliable use. We tried this during development, and experienced testers frequently made setup mistakes that resulted in incorrect GTR. Shearwater feels that GTR is a great tool for single-tank, no-stop diving, but unfortunately does not work well for more complex diving.

Shearwater GTR is not very sophisticated. Oceanic ATR reflects both a SS for NDL diving or deco stops for deco diving. Shearwater could easily improve on this implementation and has been advised to do so.

 

[Kevrumbo]

Shearwater GTR is not very sophisticated. Oceanic ATR reflects both a SS for NDL diving or deco stops for deco diving. Shearwater could easily improve on this implementation and has been advised to do so.

It's not very sophisticated as currently implemented nor would there be any more added value to "improve" this capability with additional transmitters for decompression diving using separate standard deco gas mixes that you've already pre-planned with enough volume to cover set deco profiles and contingencies.

So then again it begs the question (with respect to this forum of Technical Diving Specialties): why would you then use AI over simple SPG's, other than as an extravagant training wheel?

 

[lowviz]

...//... So then again it begs the question (with respect to this forum of Technical Diving Specialties): why would you then use AI over simple SPG's, other than as an extravagant training wheel?

Kevrumbo,

In the most nonconfrontational manner possible, I have an honest question for you.

Did you not bend yourself badly doing ratio deco maths in your head? Would it have had any worth at all to have all the details of that dive both presented in real time and recorded? From past posts, you seem to be an analytical kind of guy. What is your problem with more data?

 

[Scared Silly]

From the peanut nut gallery. I am lazy, damn lazy, real lazy. I know my gas usage but I rarely record it now that I have sold my old AI computer. I am so lazy, so damn lazy, so real lazy I thought about buying another AI computer again so to record my gas usage while using it in either gauge mode or as a backup. Given that I have bottom timer as well that would be three devices. With the Perdix AI I can get what I need without buying another computer. Being lazy, damn lazy, real lazy I like that option.

As for the discussion on GTR. As my niece would say whatever. Based on my experience with my previous AI computer I have found that calculation to be less than useful. I have watch it go up and down more times than French whore from Marseille. So hopefully Shearwater will make that optional information.

As for the reliability of WAI, I had dropped signals twice in 100+ dives. Mostly because I was about to splash, forgot to pair it, and being lazy, damn lazy, real lazy I did not want wait. So I splashed anyways and used my SPG.

Oh and for those of us with aging eyes, reading our gas off our wrist via a nice bright color display is great. I am not so feeble as not to be unable to unclip, read, and reclip my SPG if necessary. But being lazy, damn lazy, real lazy I'd rather read the gas pressure off my wrist.

 

[Kevrumbo]

Kevrumbo,

In the most nonconfrontational manner possible, I have an honest question for you.

Did you not bend yourself badly doing ratio deco maths in your head? Would it have had any worth at all to have all the details of that dive both presented in real time and recorded?

Non sequitur. . . But a nonconfrontational answer and a honest reply & account all covered in the link: 2008 Incident.

From past posts, you seem to be an analytical kind of guy. What is your problem with more data?

It's not a "problem with more data" per se --I just prefer reliable practical mechanical instrumentation that gives me pertinent vital pressure information without requiring a battery power source.

I once had a Suunto Vytec WAI (2005) connected to backmount double AL80's and it never gave a reliable sync pre-dive; it would not register a valid reading at all at depth especially if I was coming off of a stage bottle and switching to backgas (frustrated, I got rid of that unit after only using it for three months). So I learned how to utilize the SPG again along with switching to the Metric System --it's not difficult at all working with multiples of 1 or 2 bar per minute pressure SAC rate. You really don't need an AI/GTR function to do these pressure calculations at all in either recreational or technical diving.

Metric or Imperial?

 

[lowviz]

Non sequitur. . . But a nonconfrontational answer and a honest reply & account all covered in the link: 2008 Incident. ...//...

That was funny on at least two levels!

I'm good with that answer. Back to lurking...


Edit:
I know that I'm guilty of making light of this current post, Oh well, but Kevrumbo's epic thread really should be re-read now and again. It truly falls under "keeping things in perspective".

 

[lowviz]

And now, not so funny:

...//...it felt all wrong to me intuitively ("Deer in-the-Headlights Syndrome": you're overwhelmed cognitively and fail to act decisively, despite realizing an immediate threat to your safety.

Exactly, precisely my point. I want a kick in the ribs if I ever should stray this far afield...

 

[clownfishsydney]

If I had the money I would run a perdix AI, but it wouldn't replace my spg. I would like to have it simply for tracking my gas consumption when logging my dives. I currently dive a petrel 2 that replaced a vyper air and that is the only thing I miss from the vyper. Since at the level I am currently at I would never have more than backgas and 1 deco bottle, 2 transmitters would work.

You can easily work out gas consumption without an AI computer. All you need to do is download your dive data to a suitable software (Subsurface is perfect) and enter your starting and ending pressures and the size of the tank. Simple. So simple, I have been doing this with Subsurface and other software for 10 years.

The computer itself will not tell you your air consumption since it does not know the size of your tank, it will only tell you how many bar (well, psi for Americans and North Koreans) you used.

My very old Uwatec Aladin AirX (and then AirZ to replace the dead one) could give you the time you could continue diving based on your air use rate and amount left even if you went into deco. This was handy, but did not tell me anything really that I did not already know. Why cannot the Perdix AI do this? That was 1993 technology.

 

[Kevrumbo]

You can easily work out gas consumption without an AI computer. All you need to do is download your dive data to a suitable software (Subsurface is perfect) and enter your starting and ending pressures and the size of the tank. Simple. So simple, I have been doing this with Subsurface and other software for 10 years.

The computer itself will not tell you your air consumption since it does not know the size of your tank, it will only tell you how many bar (well, psi for Americans and North Koreans) you used.

My very old Uwatec Aladin AirX (and then AirZ to replace the dead one) could give you the time you could continue diving based on your air use rate and amount left even if you went into deco. This was handy, but did not tell me anything really that I did not already know. Why cannot the Perdix AI do this? That was 1993 technology.

You really don't even need the software. . . Once again, how hard is it rounding to and working with multiples of 1 bar/min or even 2 bar/min pressure Sac rate??

Example:
Given a Volume Sac Rate of 22 liters/min*ATA, divide it by the Tank Factor Rating of the Cylinder in use. For an AL80 cylinder with a tank factor rating of 11 liters/bar:

22 liters/min*ATA divided-by 11 liters/bar = 2 bar/min*ATA Pressure Sac Rate

Now instead of a single AL80 with an 11 liters/bar tank factor rating, use a twinset (double AL80's) for a total of 22 liters/bar tank factor rating, and let's see what happens to the Pressure Sac Rate:

22 liters/min*ATA divided-by 22 liters/bar = 1 bar/min*ATA Pressure Sac Rate.

So your Volume Sac Rate of 22 liters/min is constant across all tank sizes & capacities, but it is your Pressure Sac Rate that will change with the sizes & capacities (i.e. tank rating factors) of the cylinders that you actually use. . .

Below are some pressure Surface Consumption Rate (SCR) values for a variety of common cylinders with a given arbitrary volume SCR (also known as volume SAC rate or RMV):

Given a arbitrary nominal volume SCR of 22 liters/min per ATA (that's 0.78 cuft/min per ATA in US Imperial Units, a reasonable & achievable volume SCR for most novice divers):

Cylinder Size | Pressure SCR
11L/bar tank (AL80): 2bar/min per ATA;
12L/bar tank (Steel HP100): 1.8bar/min per ATA;
13L/bar tank (AL100): 1.7bar/min per ATA;
15L/bar tank (Steel HP119): 1.5bar/min per ATA;
16L/bar tank (Steel HP130): 1.4bar/min per ATA;
11L Twins (Double AL80's): 1bar/min per ATA;
12L Twins (Double HP100's): 0.9bar/min per ATA;
16L Twins (Double HP130's): 0.7bar/min per ATA.

Given a arbitrary nominal volume SCR of 15 liters/min per ATA (0.53 cuft/min per ATA in US Imperial Units):

11L/bar tank (AL80): 1.4bar/min per ATA;
12L/bar tank (Steel HP100): 1.3bar/min per ATA;
13L/bar tank (AL100): 1.2bar/min per ATA;
15L/bar tank (Steel HP119): 1bar/min per ATA;
16L/bar tank (Steel HP130): 0.9bar/min per ATA;
11L Twins (Double AL80's): 0.7bar/min per ATA;
12L Twins (Double HP100's): 0.6bar/min per ATA;
16L Twins (Double HP130's): 0.5bar/min per ATA.

Given a arbitrary nominal volume SCR of 11 liters/min per ATA (0.39 cuft/min per ATA in US Imperial Units):

11L/bar tank (AL80): 1bar/min per ATA;
12L/bar tank (Steel HP100): 0.9bar/min per ATA;
13L/bar tank (AL100): 0.8bar/min per ATA;
15L/bar tank (Steel HP119): 0.73bar/min per ATA;
16L/bar tank (Steel HP130): 0.68bar/min per ATA;
11L Twins (Double AL80's): 0.5bar/min per ATA;
12L Twins (Double HP100's): 0.45bar/min per ATA;
16L Twins (Double HP130's): 0.3bar/min per ATA.