Caves and transmitters.

[karstdvr]

in sidemount, I'll just stay on that bottle until I can feel a buoyancy difference, switch to the other side, and when they feel unbalanced in the other direction I'll know that the "dead" side has more gas than whatever is in the "alive" side.

Not to be argumentative, but this is a okay measure if you are not stressed. Frequently, problems in cave diving multiply and snowball, and stress becomes a huge factor, and things like this aren't noticed. I have seen some crazy things in incidents and accidents, and when you detail the situation and the amount of stress, then it is understood.

If the xmitter battery fails early in the dive, and you have an spg there is no need to abort the dive

This is the assumption the transmitter fails, but the receivers are not infallible. I love my Shearwater and think they make highly reliable equipment and quality equipment. But I have mine go "tits up" a couple times in the cave, by my error with a battery that was dying, or some other unknown reason. I had a back up computer of another manufacturer, so no problem, which follows your two primary light analogy.

I am not anti-technology,but diving in the overhead, be it recreational or exploratory deserves equipment that has been well tested by a large population, and highly reliable. The analog spg has a highly reliable history in the overhead, and don't recall an accident due to a failed spg. But, wireless spgs need conservative dive profiles and X number of hours of bottom time to show a reliable history.

 

[tbone1004]

@karstdvr so kelly, assuming we aren't on a mission type dive that has to be complete and can't be turned, why not just turn the dive and come home?

on the stress thing, again. You forget to switch tanks because things went tits up, so you breathe it and it gets hard to breathe because it's empty. Switch to the other tank. How is that any different than coming home on backmounted doubles when you had to shut the left post off and have no idea what you're coming home with? You have either enough gas and you make it, or you don't have enough, and don't.

 

[karstdvr]

@karstdvr
on the stress thing, again. You forget to switch tanks because things went tits up, so you breathe it and it gets hard to breathe because it's empty. Switch to the other tank. How is that any different than coming home on backmounted doubles when you had to shut the left post off and have no idea what you're coming home with? You have either enough gas and you make it, or you don't have enough, and don't.

Just replying to the comment that was made about noticing buoyancy shift in sidemount tanks, mutually exclusive to backmount. In a CTJ moment or some other stressful moment, buoyancy shift will probably not be noticed. As Jim Wyatt eluded to this, this can increase the stress of the moment as well. Hypothetically, read Andrew Ainsle's long write up about a dive that went bad, with CO2 build up, missing his line etc, and add failed digital spg-do you think in that write up he would have said, I noticed a change in buoyancy in my sidemount tanks.

 

[tbone1004]

i'd be shocked if he did, but the point still stands that you either have enough to get out or you don't, so I think you can only argue so much on if it would create that much more of a problem. That said, I have had some interesting situations that have caused dives to get turned and on those, and even on normal dives, I don't check my SPG's on the way out. With my DPV gas planning strategy, I switch to my other stage when I take a breath and my jetstream freeflows a bit after I stop inhaling. This tells me that I'm at 200psi and it's time to switch bottles. No need to look. My buddy has a similar strategy on "normal" second stages and when he notices WoB getting different, it's time to change to the next bottle. I'd use the same in an emergency exit on backgas

 

[HDWEB]

do they make a Y or Tee that i could mount my transmitter and have a back up spg

 

[tursiops]

do they make a Y or Tee that i could mount my transmitter and have a back up spg

Your first stage undoubtedly has two HP ports. No Y/Tee needed.

 

[RyanT]

How is that any different than coming home on backmounted doubles when you had to shut the left post off and have no idea what you're coming home with? You have either enough gas and you make it, or you don't have enough, and don't.

Similarly, I use button gauges on my deco bottles (OW dives). They're great for confirming full bottles before the start of the dive. Beyond that, I rely on my gas planning, no need to monitor the pressure in those bottles during a dive.

 

[halocline]

A few of my buddies in MX are using the perdix AI in caves all the time these days. These are very experienced instructors/explorers. They feel that the new shearwater transmitters are more reliable than SPGs, and it would not surprise me if this proves to be true in time. SPGs do fail, those spool o-rings blow occasionally (although typically upon pressurization, not mid-dive).

I'm cheap and I already have an SPG and a non-ai computer, so it's not for me, but bet as time goes on more and more cave divers will be using AI.

 

[Superlyte27]

I use a Perdix AI in caves when I'm on CCR. It plugs into my oxygen and Dil. So far, I haven't had a single connection issue.

 

[Rechno]

If the xmitter battery fails early in the dive, and you have an spg there is no need to abort the dive. The same way if I carry two primary lights and one fails I do not have to abort.

But does not the same logic apply for SPG? Since it can fail as well (ok, so far my onl SPG failure was during an OW vacation dive) you would need redundancy there as well.
I´m definitely with you, in that it makes sense and if i had transmitters I would probaly also use an SPG as back-up, however I do not see this as a MUST.

I had several discussions with divers that are totally against transmitters (without back-up). They always state "if it fails you dont know how much gas you got left!" but at the same time they only dive one SPG.
Personally I say, that my "back-up" is the prio gas planning. So if transpitter or SPG fails I turn the dive and know that I got enough gas left.