Shearwater Perdix AI

[Diving Dubai]

50 liters/min is not physically sustainable even for a panicked diver at depth --he/she will quickly lapse into unconsciousness after a few minutes due to gas density work-of-breathing leading to dynamic airway collapse, and metabolic CO2 retention and poisoning (Hypercapnia). CO2 also produces cerebral vasodilation which makes a diver more susceptible to Oxygen Toxicity Seizures.

You may well be right. However my numbers will mean we won't run out of air. Also in my location dealing with currents, means that with an emergency, a direct ascent is unlikely to be available. It's quite possible you'll be edging horizontally to a place of some shelter.

I'd rather plan extremely conservatively and get out alive and unbent with my buddy intact then come up short and wish I had more gas

 

[Diving Dubai]

I can give an example when AI would be extremely desirable to me.

When guiding.

Ignoring the Lynx, I wish that there was a computer that monitored my groups gas at a reasonable cost;

When checking gas of my group, young males are the most likely to lie. Their not mistaken, they down right lie about their contents. maybe its their ego' sand them not wanting to be the person that uses the most gas.

Now I have perfected the techniques where I can see the clock position of the needle on their SPG as I ask them a second time (before I grab it and show it to them. But it's not ideal

Also on a 2 tank trip, you don't get time to "learn" you groups consumption. I have to develop a mental picture of each persons gas. That takes bandwidth.

I would love to be able to glance at my wrist and see what gas each person in my my group has. This will NEVER replace the request to each diver of their gas contents, because I think it's important to make 1 on 1 contact with each diver a few times during the (so they're no just following your fins) What is an acceptable frequency (from a clients perspective) differs from person to person. Some look on gas checks as a lack of trust, others are happy that you are "taking an interest"

If AI could drop in price, and we had better technology to read multiple divers that would be a boon. Freeing up my mental bandwidth use that spare for the enhancement of the dive

 

[Kevrumbo]

I had let this go, but since I've let you tempt me into another useless response, let me explain this to you in more simple terms.

I said "25 psi/min from an AL80 is a lower RMV than 25 psi/min from an HP120." You said that is wrong & incorrect [both!].

If your SAC is 25 psi/min and you are using an AL80, then you are consuming 0.64 cu-ft of air per minute (if you are the surface).

If your SAC is 25 psi/min and you are using an HP120, then you are consuming 0.86 cu-ft of air per minute.

Thus, your RMV is higher with an HP120. The same comparison is true no matter what depth you're talking about. It also doesn't matter whether you assume 25 psi/min is corrected for the surface or is the actual rate at depth. I just chose depth of 0 for convenience of the calculations. At any depth and any consumption rate, if the rate of change of tank pressure over time is the same, then using an HP120 means your RMV is higher than if you're using an AL80. 25 psi corresponds to a specific volume of gas from an AL80 and it will always be less than the volume of gas that is correspondent with 25 psi in an HP120. Period.

What I said before is perfectly accurate and correct. Apparently, you are the only one that couldn't understand it, so again I encourage you to seek help with either reading comprehension or basic gas planning. . .

By your logic then @stuartv, this would be analogous to changing my gasoline tank in my truck to a higher volume gallon capacity and expecting my miles/gallon fuel economy rating of my engine to increase -->THAT'S 'EFFIN ABSURD!!!!

• By your logic then, 25psi/min from an AL80 is a lower RMV than 25psi/min in Double AL80's? If your SAC is 25 psi/min and you're using an AL80, then you are consuming 0.64 cuft of air per minute; therefore if you use 25psi/min in Double AL80's you are consuming 1.28 cuft of air per minute?? No!

Stuart, changing to a larger or smaller capacity tank size does not alter the volume SAC rate or RMV of a diver: by definition, a given RMV is constant & consistent across all tank sizes, but it is the pressure SAC rate that changes with tank size, and that's where you confuse the issue because you misunderstand it all bass-ackwards wrong . . .

You've been schooled son: go back to basic open water class without your AI (it rots your brain). . .

 

[stuartv]

Stuart, changing to a larger or smaller capacity tank size does not alter the volume SAC rate or RMV of a diver:

Seriously? Have you ever taken a Reading class? Is English your native language?

This is a thread about the Shearwater Perdix AI. The Perdix AI manual clearly defines SAC - which is the definition I am using in this thread, and I have posted SW's definition in this thread. It also happens to be the definition most people I know of use, too.

SAC is the rate of change of the tank pressure over time, normalized to 1 ATA. Let me try to put that in simple enough terms for you. SAC is the number of PSI that your tank drops in 1 minute, converted to what it would be if you were at the surface. If you're at 33' (which is 2ATA) and your tank drops 50 psi in 1 minute, then that's a SAC of 25 psi/min.

So, yes, as a matter of fact, SAC DOES change, for a given diver, if they change to a larger or smaller tank.

And where did I EVER say that a given diver's RMV changes based on tank size? I said that a SAC of 25 means a lower RMV if you're using an AL80 vs an HP120. I didn't say a given person's RMV was going to change if they get a bigger tank. I said IF their SAC is 25 with an AL80, then their RMV is lower than IF their SAC is 25 with an HP120.

And my original post that you have been jumping all over - but never quite hitting - was in response to another poster who said something about needing to enter tank sizes into the Perdix AI in order for it to tell you your SAC. I was explaining why you didn't need to do that and why you would need to, if you wanted the Perdix to tell you RMV.

That's as simple as I can make it for you. You don't seem to understand pretty simple high school level (or lower) English. And you think that using expensive electronics with batteries and O-rings on the battery covers is okay for the most critical dive data, but less expensive electronics (with a years long track record already, I might add) is not okay for less important data because it's not reliable enough. And the expensive electronics can be trusted to calculate your average depth, but not your ascent plan, and that doing it in your head is more reliable. Good luck with all that. Maybe you should take a basic Logic class, too. I won't be surprised to read that you seriously bend yourself someday operating like that.

Anyway, like I said, I've given it my best shot in explaining it to you. I can't do any better. So, I'm done responding to you.

 

[C Dub]

nevermind

 

[Texas Torpedo]

Add another lazy side-mounter to the list.. I'll enjoy the digital + analog...

 

[Kevrumbo]

Seriously? Have you ever taken a Reading class? Is English your native language?

This is a thread about the Shearwater Perdix AI. The Perdix AI manual clearly defines SAC - which is the definition I am using in this thread, and I have posted SW's definition in this thread. It also happens to be the definition most people I know of use, too.

SAC is the rate of change of the tank pressure over time, normalized to 1 ATA. Let me try to put that in simple enough terms for you. SAC is the number of PSI that your tank drops in 1 minute, converted to what it would be if you were at the surface. If you're at 33' (which is 2ATA) and your tank drops 50 psi in 1 minute, then that's a SAC of 25 psi/min.

So, yes, as a matter of fact, SAC DOES change, for a given diver, if they change to a larger or smaller tank.

And where did I EVER say that a given diver's RMV changes based on tank size? I said that a SAC of 25 means a lower RMV if you're using an AL80 vs an HP120. I didn't say a given person's RMV was going to change if they get a bigger tank. I said IF their SAC is 25 with an AL80, then their RMV is lower than IF their SAC is 25 with an HP120.

And my original post that you have been jumping all over - but never quite hitting - was in response to another poster who said something about needing to enter tank sizes into the Perdix AI in order for it to tell you your SAC. I was explaining why you didn't need to do that and why you would need to, if you wanted the Perdix to tell you RMV.

That's as simple as I can make it for you. You don't seem to understand pretty simple high school level (or lower) English. And you think that using expensive electronics with batteries and O-rings on the battery covers is okay for the most critical dive data, but less expensive electronics (with a years long track record already, I might add) is not okay for less important data because it's not reliable enough. And the expensive electronics can be trusted to calculate your average depth, but not your ascent plan, and that doing it in your head is more reliable. Good luck with all that. Maybe you should take a basic Logic class, too. I won't be surprised to read that you seriously bend yourself someday operating like that.

Anyway, like I said, I've given it my best shot in explaining it to you. I can't do any better. So, I'm done responding to you.

Read & comprehend the Shearwater Perdix AI Manual again @stuartv . . .because you're still wrong:

Section 7.1 SAC Calculations. . .

• SAC vs RMV. . .
• Since SAC is based on the rate of tank pressure change, the calculations do not need to know the tank size. However, this means that the SAC is NOT transferable to tanks of a different size.
• Contrast this to Respiratory Minute Volume (RMV) which is the volume of gas in your lungs experienced per minute, in Cuft/min or Liters/min. The RMV describes your personal breathing rate, and therefore is independent of tank size. . .

Your whole original premise has just been blown-up by the above, taken verbatim from the Perdix AI Manual. . .

 

[Joneill]

Add another lazy side-mounter to the list.. I'll enjoy the digital + analog...

Scandalous . Nice job with the Lionfish, btw!

 

[scubadada]

Read & comprehend the Shearwater Perdix AI Manual again @stuartv . . .because you're still wrong:

Section 7.1 SAC Calculations. . .

• SAC vs RMV. . .
• Since SAC is based on the rate of tank pressure change, the calculations do not need to know the tank size. However, this means that the SAC is NOT transferable to tanks of a different size. . .

Your whole original premise has just been blown-up by the above, taken verbatim from the Perdix AI Manual. . .

See what happens when you never properly learn fundamentals Stuart? You get a screwed-up knowledge base to reference your post's and show how really ignorant you are. . .

The two of you are from different planets, I'm from the same planet Stuart is from, I understand everything he says . I doubt I'm the only one

 

[kelemvor]

heh.. what an entertaining thread this has become.

If you know the rate of consumption throughout the dive from the transmitter, then download it into some good software such as subsurface, you can also enter the tank volume and do additional calculations. Everybody wins!

For me, the value in the transmitter is in 1. alerts. 2. only one place to look for all data. 3. after dive analysis.

Maybe shearwater will add a datapoint for the owner to input tank volume like scubapro does. Then you could do that calculation on your wrist. I'm not saying scubapro does the calculation, I've never tried it.