Shearwater Perdix AI

[stuartv]

What do you spend all that extra time on during your dives that you saved by not having to look at a separate SPG? The day I miss the whaleshark because I spent an extra three seconds looking at my SPG when I could have been glancing at my wrist is the day I will switch to AI.

I like the BC analogy. It's interesting that there are divers who buy into the "minimalism" aspect of the BP/W, but are gung-ho on AI. I don't see AI as completely incompatible with minimalism, but between a mechanical system and an electrical system, I would argue the mechanical system is simpler, though I know the other side of the argument.

By the way, you ARE the Scubanati now.

As for the BC/minimalism thing, I feel like I have totally bought into that. My first BC purchase was right after OW and was a BP/W with a Hogarthian harness. I want nothing more. In my mind, I'm going to wear a computer (2, in fact), so there is no reduction towards "less" to be had there. Given that my computers are staying, replacing a HP hose, gauge, and bolt snap with a small transmitter does jibe, in my mind, with the concept of minimalism.

"That's a maintenance issue that you should have taken care of before you got in the water" is an argument that has been used many times to dismiss reliability issues for physical SPGs. I think that argument applies equally well to batteries and battery compartment O-rings.

With my SPG, I need to periodically check the connection to the 1st stage to make sure the O-ring is good and the hose is screwed in tight. And I need to check that the gauge is connected to the other end of the hose tightly and that the O-rings on the spool are good. I also need to check to make sure the bolt snap is solidly attached to the SPG, the cave line (or whatever) holding it on is not about to break. And check the bolt snap gate to make sure it still slides easily, possibly lubing it every now and then. I need to check the HP hose itself to make sure I don't see any signs of damage or bubbling, etc.. And I need to check the calibration periodically to make sure, for example, that it's not sticking when the pressure gets low, so it continues to read 250 (for example) even when the pressure has dropped past that.

With an AI transmitter, I have 1 battery, 2 O-rings, and the battery compartment cover to check and to make sure the transmitter is still screwed into the 1st stage tightly. I am unaware of any issues with failure modes of the transmitters that would require a person to check the calibration periodically. There is no concern that I know of to suggest that an AI transmitter would read correctly from 3500 psi down to 500, but then stick at a number even while the pressure drops past that.

Replacing an SPG with a transmitter also seems to jibe with the concept of minimalism from a maintenance point of view as well.

 

[Kevrumbo]

It is very kind of you to say "Stuart and other experienced divers" but I consider myself to be not all THAT experienced as a recreational diver and very INexperienced as a tech diver. I've just barely gotten started in tech diving.

I made a comment a while back, in a thread about integrated BCDs versus BP/W setups. It boiled down to saying that newer dives often perceive things with more options as being better. As they gain experience, they learn which of those extra features are ones they will actually take advantage and which ones turn out to be never used. Thus why an integrated BCD often looks better to newer divers who, later, realize that a BP/W with Hogarthian harness is all they have a use for and the simplicity, durability, and reduced cost are more important to them than all those BCD features (which they turn out to never use).

I can totally see AI as being ALMOST the same thing. Data logging and evaluating my gas consumption on many different dives in different conditions is important to me - right now. I have already learned that my SAC is pretty different on tech dives (in a drysuit, in cold water) than it is on rec dives (thin wetsuit, single tank, etc.). That has been really handy. Will it continue to offer me so much value as a get more experienced in tech diving? Probably not. But.... so what?

The reason I said AI is "almost" the same as the BCD/BPW debate is that there is one important difference. While the data logging, like the BCD "features", may become less and less important over time, the convenience of seeing my gas data on my wrist, with my other data, will always be there. Many have said that they rarely look at their SPG and, when they do, it is just to confirm what they already know. Okay. If I check my computer two or three times for every one time I check my SPG, it is still quicker and easier to note the pressure reading when I check my computer than it is to check my computer and then reach down, unclip, hold it up, then put it back and re-clip. It is even easier than looking down at a gauge that is clipped to a chest D-ring (though the difference is not as great). It is also easier for my aging eyes to read a number on my wrist than a gauge that is clipped to my chest. My wrist is further away from my eyes...

As for SAC and tech diving, I made this observation the other day: I can write out my dive plan and note expected tank pressures at my various waypoints, and I can check my consumption along the way to confirm that my actual consumption matches my planned consumption. But, if I'm on a tech dive that I planned for 0.8 cu-ft/min RMV and I work that out to XX psi/min, then having a SAC displayed on my wrist that I can monitor lets me have a continuous, precise, and accurate monitor of whether my dive is going to plan, versus either having to wait for a waypoint to know or do mental math based on a less precise readings from a 2" dial SPG. I don't see this as a necessity, of course. Like having an SPG on my wrist, it is merely a convenience that lets me spend more time paying attention to my dive and less time spent on my safety checks (while, at the same time, doing them more often).

Stuart, you really don't need the precision of an AI.

Here are some pressure SAC rate values for your volume SAC rate (or volume SCR, or RMV) of 0.8 cuft/min:

Given an 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), some pressure SCR (pressure SAC rates) for common dive cylinder tanks are:

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.

The point is: For nominal dives on single tank, just round your pressure SCR to 2 bar/min (30 psi/min in US Imperial Units); on doubles, use 1 bar/min (15 psi/min).

If your SAC rate increases any more than this due to exertion, then stop whatever physical activity is causing it, or if you cannot --consider thumbing the dive. IOW, if you're breathing hard and you're spiraling into Hypercapnia, whatever instantaneous info an AI is giving you is moot & superfluous, because your body is already telling long before of an unsustainable physical condition at depth (hyperventilation, increased WOB, and CO2 narcosis). . .

 

[dmaziuk]

I don't see AI as completely incompatible with minimalism, but between a mechanical system and an electrical system, I would argue the mechanical system is simpler, though I know the other side of the argument.

You're thinking in terms of what's under the hood. Why? In terms of usage, you have a hose (more often then not dragging behind you with a 3-instrument console ploughing through the coral) and 2 instruments to check. How tf is that simpler than everything on one screen and no drag?

 

[Lorenzoid]

@stuartv, yep that's the other side of the argument. It's far from settled whether the SPG or the AI system is the more "minimal" or simpler. Also, a nitpick, but I would not count the bolt snap as a potential failure point.

Electronics rules our lives these days. A lot of people expect as a matter of course that everything is to be electronic. To a new diver, especially a younger person, a mechanical gauge must seem bonkers. But when there is a time-tested, arguably simpler alternative, I am open to the idea of using it. Maybe it's not objectively "better," but rather just as good, albeit in different ways. I believe I recall that when you were a new SB member and had just finished (or maybe hadn't even finished) your OW class, the first thing you focused on was a computer. You had a huge number of posts about computers. If I recall, some replies suggested that while a computer is a wonderful, modern convenience, and more affordable than ever, and we should all be using one, it should not be the focal point in our diving. You have asked a lot of great questions and participated in a lot of great conversations, but I suspect computers and AI constitute a surprisingly large percentage of your posts. Admit it, you just love this stuff.

You're thinking in terms of what's under the hood. Why? In terms of usage, you have a hose (more often then not dragging behind you with a 3-instrument console ploughing through the coral) and 2 instruments to check. How tf is that simpler than everything on one screen and no drag?

My comments are assuming not a console but a plain old SPG, clipped off to a D-ring, with the hose streamlined against my body. I would maintain that having more numbers crowded onto a screen, when some of those numbers are only useful at longer intervals than others, is not inherently more "convenient." I like that my Shearwater screen displays only what is most important to me and doesn't distract me with extra information unless I want it. I CAN check my SPG, quickly and easily, now and then, when I feel I need to. I'm not going to argue it's actually MORE convenient than AI, but it is no LESS convenient for me.

 

[Kevrumbo]

You're thinking in terms of what's under the hood. Why? In terms of usage, you have a hose (more often then not dragging behind you with a 3-instrument console ploughing through the coral) and 2 instruments to check. How tf is that simpler than everything on one screen and no drag?

Because you don't need complex remote RF telemetry to monitor pressure of a tank mounted on your back or side, when a simple more reliably connected analog SPG can be directly hosed attached and utilized, with minimal streamlined length of 24 to 26 inches.

Even if wireless AI is ever accepted & utilized as augmented instrumentation for students in basic open water courses such that the instructor can also monitor the student divers' remaining pressure as well, it will never supersede the economy, practicality and back-up reliability of the analog SPG.

 

[dmaziuk]

@stuartvMy comments are assuming not a console but a plain old SPG, clipped off to a D-ring, with the hose streamlined against my body ... is no LESS convenient for me.

Well, my mileage does vary: when I have it in a hose keeper on the belt d-ring and clipped to chest d-ring, it is streamlined all right but I have to crane my neck and grab the spg and turn it so I can see the dial. WAY less convenient than glancing at my wrist.

@Kevrumbo: I don't care if it's a needle onna stick or quantum magic fuelled by pixies inside. As long as it does what I need when I need it for the money I'm willing to pay, why, again, should I give a crap what's under the hood.

 

[Lorenzoid]

Well, my mileage does vary: when I have it in a hose keeper on the belt d-ring and clipped to chest d-ring, it is streamlined all right but I have to crane my neck and grab the spg and turn it so I can see the dial. WAY less convenient than glancing at my wrist.

Unclip and avoid the neck-craning? That's what the clip is for.

When I started adopting bolt snaps in my rig, I was pretty clumsy with them. My instructor handed me a practice bolt snap with a bit of hose attached and told me to practice clipping and unclipping without looking, while watching TV or whatever. After a few hours of that, I could do it without thinking about it, and a few hundred dives later it is literally nothing. I don't have to crane my neck. I unclip, look at it it, and re-clip in just a few seconds, without thinking about it or fumbling, as if my hand were robotically controlled. (Granted, I don't dive with gloves.)

 

[Kevrumbo]

Well, my mileage does vary: when I have it in a hose keeper on the belt d-ring and clipped to chest d-ring, it is streamlined all right but I have to crane my neck and grab the spg and turn it so I can see the dial. WAY less convenient than glancing at my wrist.

@Kevrumbo: I don't care if it's a needle onna stick or quantum magic fuelled by pixies inside. As long as it does what I need when I need it for the money I'm willing to pay, why, again, should I give a crap what's under the hood.

Then you need one of these:

For Sale - Aeris CompuMask and transmitter, $400

Because you gotta have that digital display convenience, so you have one on your left wrist and one on your right wrist, and with Data Mask receiver too so you'll have the display right in front of your face at all times, together with the double redundancy of your wrist AI/PDC's and their data logging functions -because you have the money to pay to not give a crap what's under the hood. . .

 

[guyharrisonphoto]

I am amazed the thread recently got off the track of why not implement GTR to account for all stops? That is a simple issue, really.

Instead, once again, the endless drone of "to AI or not to AI". Pointless.

I get why Shearwater did not go "the full monty" and try and implement GTR across all tanks. Very complex and big margin for user error. But, I think they might have gone just a little too conservative the other way by only giving you GTR to your reserve "on the bottom" and not on the surface after all stops. It should be easy to do that change to change it to "GTR on the bottom to reach the surface after "x" stops with "Y" psi (or bar) left over.". As Stuart has noted, all Hollis/Oceanic and now U.S. Divers etc computers do it. I can add that Scubapro/Uwatec computers do it also, and very accurately in my experience.

Is AI with the "proper" GTR essential?--no. Is AI with it valuable?--yes. Let me give you my own example.

For me as a photographer, it is very useful/valuable to have all the info on my wrist as I use a big rig that takes two hands. Snapping and unsnapping an SPG is a real pain, especially if I am dealing with a strong current as well.

Also, like "real time" NDL based on multi-level diving, properly implemented GTR gives me "real time" GTR based on "multi-effort" diving. If I am in unexpected current and working hard to compose scenics, or kicking a lot harder than usual keeping up with big animals, or colder than usual, or bounce deeper than planned after a subject, or am otherwise off of my usual SAC, (or if I would go into unplanned deco due to very bad circumstances which thankfully has not happened to me) the computer gives me very useful and (in my experience) accurate feedback as to my GTR, and even a handy warning or alert with a couple minutes to spare without guesswork-- or, if you prefer,"mental math"--at depth, exerting myself, and no doubt affected by the unperceived narcosis that can hit everyone and slows thought processes down.

Now, to be sure, Shearwater's approach gives you these benefits as to time on the bottom before you are eating into your reserve. And, sure, you could add a couple hundred pounds to your reserve as an estimate for your safety stop (but this would not account for unplanned deco where the GTR including stops would be by far the most valuable).

So, there is no reason not to have this benefit based on the real time conditions of the dive and without the need for diver mental estimation during the dive.

For those who don't want it--get the non-AI Perdix, do your mental math, and revel in your skills, but don't get on my case.

 

[stuartv]

@stuartv, yep that's the other side of the argument. It's far from settled whether the SPG or the AI system is the more "minimal" or simpler. Also, a nitpick, but I would not count the bolt snap as a potential failure point.

Admit it, you just love this stuff.

My comments are assuming not a console but a plain old SPG, clipped off to a D-ring, with the hose streamlined against my body. I would maintain that having more numbers crowded onto a screen, when some of those numbers are only useful at longer intervals than others, is not inherently more "convenient." I like that my Shearwater screen displays only what is most important to me and doesn't distract me with extra information unless I want it. I CAN check my SPG, quickly and easily, now and then, when I feel I need to. I'm not going to argue it's actually MORE convenient than AI, but it is no LESS convenient for me.

How can you not count the bolt snap? I haven't even been diving that long and I've already experienced: Cave line holding a bolt snap to a light frayed and let loose during a dive and I lost that light. A bolt snap gate got so stiff that I clipped it on without really registering a problem, but when I went to unclip it in the water, I fought with it and was finally bare able to get it open. The bolt snap is certainly a low risk source of trouble, but then so is the HP hose, the O-rings, and the SPG itself. If you're counting any of those, I would count them all.

Guilty on all counts.

If you use your Shearwater with any of the middle row fields set to not display (i.e. blank), then your point is fair. Otherwise, with the PAI, you would be replacing a middle row number with your pressure reading. So, no MORE numbers than before - only 1 different number. When I had a Petrel 2, I always used all the middle row configurable fields to show something, but I did find some of what was displayed to really be needless. I didn't need to see it. I only had it displayed because the field was there and I'd rather show more data than less, in the case of the Petrel display. My H3 doesn't have as many fields on the screen and I have NEVER missed the pieces of data that I lost going from the Petrel to the H3. But I never found those extra pieces of data on the Petrel screen to ever be inconvenient in any way.

Regardless, do you ever do anything while diving that requires 2 hands for more than a moment? Say, hold onto something with one hand while taking a picture with the other? Or use both hands to hold a camera rig? If you never have both hands tied up at the same time for more than a few seconds, then I'll buy your final point. But, when you ARE using both hands, please tell me how cylinder pressure on computer is not MORE convenient than a clipped off SPG.

And just 'cause I know how I can sound, please understand that I'm not trying to argue with you (I'd call it having an enjoyable conversation discussing the fine points) or change the way you're doing things. But, I'm not convinced that your sweeping generalization (that an SPG is no less convenient for you) is true - at all times during all your dives.

Even if wireless AI is ever accepted ... it will never supersede the economy, practicality and back-up reliability of the analog SPG.

Granted on economy.

When economy is not a component of practicality, then I'd say the Perdix AI setup has already exceeded the practicality of an SPG. It's pretty darn easy and practical to screw a transmitter into a 1st stage, enter the serial number into a computer, and go diving. It's pretty darn practical to see cylinder pressure on your wrist instead of spending a lot of time developing muscle memory to make unclipping/reclipping an SPG effortless. It's pretty darn practical to have a computer tell you how much time you have left on your current cylinder as a confirmation to what you already figured in your head. It is the ESSENCE of practicality to be able to read your cylinder pressure while using both hands to hold a camera or do anything else that requires two hands.

Please provide data to backup your implicit assertion that modern AI, using current generation PPS transmitters, is not as reliable or more reliable than an analog SPG. My personal experience is that my AI has always worked, but I've had one SPG failure (the SPG unscrewed from the HP hose and blew an O-ring on the spool). I've seen posts from at least one person working at a shop that they see more SPG failures than AI failures. And I'm sure you can provide anecdotes in favor of SPGs. So, how about we both dispense with anecdotes and you give actual data to support your statement?

Oh, and as for the Datamask, well, if there were a HUD like that that would work with any mask, I would definitely be considering it. I would not pay a lot extra for it, versus a Perdix AI. And I wouldn't want something that is built into a mask that may not fit me well or may have to be replaced. But, something like that, that would clip onto the masks I have and work with my gauge reader lenses sounds great!