Would YOU thumb this dive?

[jadairiii]

You have a problem, you thumb the dive, every one leaves. First year to go to Mexico cave diving, second day there, 4 of us head into the cave, within minutes one of my buddies has a gear issue, he turns and gives the thumb, I acknowledge, motion to the other 2 to continue on, I’ll exit with him. Not even a question to let him exit solo (and he could have, I guess). No big deal, there is always another dive. Funny thing, as we get to the basin I turn to see the other 2 have followed us out. HA! We get our one buddy on the surface, recalculate our gas and off we go. That is how you dive with a team.

 

[Kmart921]

Adding an SPG to the right post reg adds points of failure to the system, as well.

I've been wondering about this. How exactly does adding an SPG to the right post add a point of failure? I understand that the HP hose could fail, but couldn't you add an AI transmitter for redundancy? How is that functionally different from the HP plug with o-ring that's there regardless?

 

[rjack321]

I've been wondering about this. How exactly does adding an SPG to the right post add a point of failure? I understand that the HP hose could fail, but couldn't you add an AI transmitter for redundancy? How is that functionally different from the HP plug with o-ring that's there regardless?

Hoses are far more likely to come loose/unscrew
Hoses burst
AI transmitters snap off (or more likely to come unscrewed as well)
You don't need a right post spg so leave it off

 

[kensuf]

I've been wondering about this. How exactly does adding an SPG to the right post add a point of failure? I understand that the HP hose could fail, but couldn't you add an AI transmitter for redundancy? How is that functionally different from the HP plug with o-ring that's there regardless?

HP hose, HP spool (the little o-ring part between the pressure gauge and the hose) and the gauge itself can all potentially fail. Most likely failures would be the HP hose leaking like a champagne bottle (rare, but I've seen it a couple of times) or the HP spool failing (common, but not a real immediate concern because the volume of gas lost is mostly insignificant).

However, adding an extra hose on the right side for a backmount diver introduces a couple of potential problems. One is it's an additional entanglement hazard, the biggest concern being the possibility of hindering your ability to deploy the long hose to an out of gas diver in an emergency. And to this, I ask what would the benefit be of adding this extra pressure gauge?

 

[Kmart921]

HP hose, HP spool (the little o-ring part between the pressure gauge and the hose) and the gauge itself can all potentially fail. Most likely failures would be the HP hose leaking like a champagne bottle (rare, but I've seen it a couple of times) or the HP spool failing (common, but not a real immediate concern because the volume of gas lost is mostly insignificant).

However, adding an extra hose on the right side for a backmount diver introduces a couple of potential problems. One is it's an additional entanglement hazard, the biggest concern being the possibility of hindering your ability to deploy the long hose to an out of gas diver in an emergency. And to this, I ask what would the benefit be of adding this extra pressure gauge?

Definitely not suggesting adding a second SPG, I understand there's a myriad of issues that the extra hose presents and it's not worth the tradeoff. I suppose my question is, what would be the harm in adding an AI transmitter for backup in the event of a left post shutdown? As a novice diver (45 dives) with an interest in technical diving, who has been lurking the advanced / tech forums for a while, this is the only aspect of the tech configuration I don't understand. Why is gas monitoring the one case where there is no redundancy, while we have backups for our backups for nearly everything else?

Let me see if I can answer my own question, based off what I've read. Backup lights are carried, for example, because if the primary light were to fail in a cave or a wreck we NEED that backup light to get out. Backup mask because we NEED to read our gauges during deco if we lose a mask (however rare that is). Whereas in the case of the SPG, if we lose that, we will still have enough gas to get to the surface because we will have at least 1/3 of our back gas available for the ascent, which (presumably) we planned for. So we don't NEED to monitor the tank pressure. Am I understanding the logic correctly?

Edit: to answer your question I suppose the benefit would just be added peace of mind and to coordinate gas sharing. I can't imagine that a transmitter is any more likely to fail than the HP plug itself. I would like to know if anyone has experienced one coming undone or leaking during a dive.

 

[Jack Hammer]

this is the only aspect of the tech configuration I don't understand. Why is gas monitoring the one case where there is no redundancy, while we have backups for our backups for nearly everything else?

In tech diving you thumb the dive if there is a failure. A redundant SPG adds no benefit as you are on your way up or out.

 

[rjack321]

Edit: to answer your question I suppose the benefit would just be added peace of mind and to coordinate gas sharing. I can't imagine that a transmitter is any more likely to fail than the HP plug itself. I would like to know if anyone has experienced one coming undone or leaking during a dive.

Your answers are going to be biased by the fact that truly reliable AI sensors have only been around a few years. Many of the older ones (eg 8 yrs ago) lost signals and batteries etc rather easily. Also
1) Hitting the ceiling with one is a legit but manageable concern
2) If you did have an AI sensor fail/quit working what would you do? Do you continue without it or exit? If you continue why did you need it in the first place?

With proper gas planning (which is part of actual tech classes) you'll learn that having a right post SPG doesn't add any value even if there might be a couple of possible small benefits.

 

[JBlackman]

As a general rule of "thumb," you should thumb a dive the minute you ask yourself if you think you should thumb the dive. There is always another dive... if you follow this rule.

 

[TrimixToo]

As a general rule of "thumb," you should thumb a dive the minute you ask yourself if you think you should thumb the dive. There is always another dive... if you follow this rule.

Exactly right. If you are asking the question, then most of the time you already know the answer.

 

[divad]

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