Out of air! Wireless pod

[stuartv]

You don't see any use in having an SPG? Redundancy is always nice and considered a must depending on the type of diving you are doing.

What type of diving requires redundant SPGs?

Analog SPG fails differently though.

I've never seen one give false readings, it'll just stay stuck at some pressure level, or just show zero.

What is the difference between "give false readings" and "stay stuck at some pressure level"?

In my mind "stuck at some pressure level" is EXACTLY giving a false reading. And there are plenty of stories here on SB of that happening on analog SPGs.

The debate about AI vs SPG comes down to redundancy. You have two 2nd stage regulators because one may fail, or you need to donate to a buddy. If you only have one and it free flows, loses it's mouthpiece, etc you are in big trouble. Same with a pressure gauge. You can't dive without it safely. If your AI fails or even breaks on a trip, your diving is over.

Who do you know that dives with redundant SPGs?

If your AI fails or breaks on a trip, how does that affect your diving any differently than if you only have an SPG and it breaks or fails?

I think you have the failure and its solution covered already, but I disagree on one major point with some of the other posters.
For a recreational dive I feel there is no need to have a backup pressure gauge in the water.

And there IS a need for a backup pressure gauge on some other type of dive? What type?

I'm a little confused. Is a 'pod' the same as a 'transmitter'? If yes, how can two computers be reading the same transmitter? Or did I misunderstand that?

Any radio transmitter can have any number of receivers listening to it. You could have 100 dive computers all set to the same transmitter ID and "reading" the same tank.



This thread alone provides ample evidence that SPGs most certainly can and do fail. Sometimes even during a dive. They also can give false readings (e.g. stuck at 800 psi when you're really down to 500 - would you really notice if it was only off by 300 psi?). And if they fail by having the spool blowout (a common mode of SPG failure) or a HP hose blowout (not very common, AFAIK), you actually start losing your gas. In my opinion, a wireless AI transmitter is MUCH less likely to fail in a way that gives a false (but believable) reading OR to fail in such a way as to cause you to lose any of your gas.

So, both can fail. I don't know of any evidence that modern AI transmitters that are maintained per the manufacturer's specs fail any more often than SPGs. My personal experience is that they fail less often.

If you wouldn't dive with 2 SPGs, then what is the logical argument for diving with AI and an SPG?

If I had a student come to me wanting to dive with 2 SPGs on their regulator, I would tell them to take one off. Having 2 just doubles their chance of a failure that could cause them to lose gas - and for no practical benefit. The only theoretical benefit would that if one dies, they would not have to end their dive early. Except that an SPG that dies has a good chance of dying in a way that causes gas loss, so the dive would be over anyway. The very, very slight chance of a positive benefit does not, in my opinion, outweigh the risks of diving with 2 SPGs.

I feel the same way about diving with AI and an SPG. However, the subject is controversial enough that I would not make a student remove either one.


As for the OP, setting up their own gear is always best. But, if he and his wife could not tell their gear apart, then obviously the boat crew wouldn't be able to, and that just seems like a bad idea, no matter what. In the end, the real problem was not the boat crew, or the gear markings (or lack thereof).

It was that they did not trust their AI.

If they had trusted their AI, then when his wife's computer wouldn't read her tank (or so they thought), they would not have re-paired her computer. They would have gone looking for some other reason for why it wasn't reading and (presumably) figured out that it was because the reg sets had been swapped.

 

[tursiops]

And if they fail by having the spool blowout (a common mode of SPG failure) or a HP hose blowout (not very common, AFAIK), you actually start losing your gas.

Although I've seen a lot of spools bubble, my wife's HP hose blew out on a dive in the Maldives. We both knew it would be a slow air loss, even though there were a LOT of bubbles. We got the DM's attention and signaled we were surfacing. He rushed over and tried to get her to take his alternate. We waved him off, signaled him to stay with the group, and up we went, nice and slow, safety stop and all. Lots of air still left when we got to the surface. I always carry spare hoses, and had it replaced before the DM and group surfaced. He came over and tried to take her rig away and give her a rental. We finally got him to understand it was an annoyance, not an emergency, and all was now OK.

 

[WinfieldNC]

What type of diving requires redundant SPGs?



What is the difference between "give false readings" and "stay stuck at some pressure level"?

In my mind "stuck at some pressure level" is EXACTLY giving a false reading. And there are plenty of stories here on SB of that happening on analog SPGs.



Who do you know that dives with redundant SPGs?

If your AI fails or breaks on a trip, how does that affect your diving any differently than if you only have an SPG and it breaks or fails?



And there IS a need for a backup pressure gauge on some other type of dive? What type?



Any radio transmitter can have any number of receivers listening to it. You could have 100 dive computers all set to the same transmitter ID and "reading" the same tank.



This thread alone provides ample evidence that SPGs most certainly can and do fail. Sometimes even during a dive. They also can give false readings (e.g. stuck at 800 psi when you're really down to 500 - would you really notice if it was only off by 300 psi?). And if they fail by having the spool blowout (a common mode of SPG failure) or a HP hose blowout (not very common, AFAIK), you actually start losing your gas. In my opinion, a wireless AI transmitter is MUCH less likely to fail in a way that gives a false (but believable) reading OR to fail in such a way as to cause you to lose any of your gas.

So, both can fail. I don't know of any evidence that modern AI transmitters that are maintained per the manufacturer's specs fail any more often than SPGs. My personal experience is that they fail less often.

If you wouldn't dive with 2 SPGs, then what is the logical argument for diving with AI and an SPG?

If I had a student come to me wanting to dive with 2 SPGs on their regulator, I would tell them to take one off. Having 2 just doubles their chance of a failure that could cause them to lose gas - and for no practical benefit. The only theoretical benefit would that if one dies, they would not have to end their dive early. Except that an SPG that dies has a good chance of dying in a way that causes gas loss, so the dive would be over anyway. The very, very slight chance of a positive benefit does not, in my opinion, outweigh the risks of diving with 2 SPGs.

I feel the same way about diving with AI and an SPG. However, the subject is controversial enough that I would not make a student remove either one.


As for the OP, setting up their own gear is always best. But, if he and his wife could not tell their gear apart, then obviously the boat crew wouldn't be able to, and that just seems like a bad idea, no matter what. In the end, the real problem was not the boat crew, or the gear markings (or lack thereof).

It was that they did not trust their AI.

If they had trusted their AI, then when his wife's computer wouldn't read her tank (or so they thought), they would not have re-paired her computer. They would have gone looking for some other reason for why it wasn't reading and (presumably) figured out that it was because the reg sets had been swapped.

I wasn't saying that two SPGs are required. It does kind of look like I was saying that though. My comment was in response to someone who said that SPGs were old technology and had no place (I now know he was joking). Redundancy is stressed in tech and solo when it comes to just about everything else as you know (gas supply, buoyancy, cutting tool, reel, light). I like the features provided by an AI computer (right post) and the lack of batteries in an SPG (left post).

 

[foob]

Redundant spg just allows one to continue the dive vs calling it.

It's definitely not mandatory compared to a redundant second stage.

 

[stuartv]

Redundant spg just allows one to continue the dive vs calling it.

It's definitely not mandatory compared to a redundant second stage.

I agree with all of that. But, I have never seen anyone dive with 2 SPGs (on the same gas supply). Not in tech diving or recreational diving.

 

[foob]

I agree with all of that. But, I have never seen anyone dive with 2 SPGs (on the same gas supply). Not in tech diving or recreational diving.

Fair enough. The only reason I keep my SPG is because I like to make sure tank is open just before I drop. If I switch to sidemount I might not bother with that with AI then

 

[stuartv]

Fair enough. The only reason I keep my SPG is because I like to make sure tank is open just before I drop. If I switch to sidemount I might not bother with that with AI then

I like to make sure mine is open, too. I take 3 good, deep breaths off my regulator to make sure....

I had a button gauge on my first stage for a while. My thought was that it let me assemble my rig, turn on the gas, and verify that the tank is least approximately full without having to dig out my computer.

Then I realized that by taking the button gauge off, it forced me to dig out my computer and check the tank pressure that way. That has several benefits to me. It makes sure that I have my computer. I didn't leave it in my truck or something dumb like that. And it makes sure my computer is charged up and the AI is working (AI battery is not dead). If it's not, I'd rather find that out when I assemble my rig and I'm still at the dock than when I'm gearing up just before I splash. And it eliminates the (small) snag hazard that having that button gauge was.

I do have to remember to depressurize my reg after assembling and checking. Otherwise, if the reg stayed pressurized, that would keep the AI transmitter turned on the whole time (i.e. for the whole boat ride to the dive site) and run the battery down prematurely.

Once it's assembled and I've checked everything, I'll just buckle the strap of my wrist computer through a D-ring on my harness, so it can't go anywhere and it's right there ready to go when it is time to gear up just before splashing. I have forgotten to put my computer on my wrist before splashing before. Having it right there on my harness means if I do forget, I can take it off my harness and put it on my wrist (carefully!) after I splash. Or I guess I could just leave it there on my harness, too, if I wanted.

 

[chillyinCanada]

What a great community! Here is what we have done in light of the experience itself and what we have deduced is a better way to do this, and with the help of all of the excellent advice presented on this board:

• All of our gear is now tagged with our IDs with tags from yourbagtag.com. Mine are yellow and my wife's are bright pink. The tags are attached with crimped stainless leaders so they are as permanent as a tag can get.
• We personally rig our own tanks and politely decline the offers to do so by the dive crews.
• I have memorized the last four digits of the serial number of my pod and check both of our computers to verify that we are both sync'd to the correct pod.
• As a double check, we now open the tank valves one at a time exclusively, to verify the tank pressure on our respective computers.
• Our faith in the buddy system is reaffirmed. We are each now aware of how many kicks we are from our respective backup air sources, keeping in mind that we may have to do it AFTER exhaling our last breath. I recommend that instructors enhance the drill by making the students exhale before taking their second stage out of their mouth.

Just curious, has your buddy also memorized the last 4 digits and also does the check that you do now?

 

[martincohn]

I like the features provided by an AI computer (right post) and the lack of batteries in an SPG (left post).

Back mount doubles I'm guessing?

 

[DrMack]

It was that they did not trust their AI.

If they had trusted their AI, then when his wife's computer wouldn't read her tank (or so they thought), they would not have re-paired her computer. They would have gone looking for some other reason for why it wasn't reading and (presumably) figured out that it was because the reg sets had been swapped.

Yup, this is one of our biggest take-aways from the experience.