One SPG only..?

[Uncle Pug]

VeniVidi, a couple of questions for you:
1. You are diving with two SPGs and they begin to show a discrepancy. Which one is right and which one is wrong?
2. You have realized that one or both of your SPGs is failing and have turned your dive. Will you pay attention to one (which one?), both (confusion is certain) or neither (paying attention only to your egress) on your way out/back/up?

 

[VeniVidi]

I would like to address your questions in two different ways.

First, you are over-estimating the ability of DIR divers to employ the Force. DIR divers aim to minimize the need to make up a plan on the fly during an emergency. The idea is actually to try and avoid having to make too many important decisions during a stressful situation underwater by planning out the dive with the team before it starts. This includes planning gas management. The team plans for a complete gas failure by at least one team member at the point where it is the hardest and longest to get back to safety, taking into account an allowance to deal with the emergency, and also taking into account the likelihood of higher gas consumption during an emergency. How much gas should the remaining team members have in that scenario for everyone to get back safely and make all required stops on the way? This is decided before the dive starts. The dive ends for the whole team when the pre-planned limit is reached. So even if there is an equipment failure at that point, such as loss of an SPG, or even total loss of a team member's gas, the team already knows it has enough gas to get everyone back safely. If the failure happens before that, the dive is terminated, and there is by defintion more than enough gas to get back. So having an extra SPG for one diver adds nothing to the safety of the team. Note that this type of planning depends on the unity of the team and excludes solo diving.

Thanks a lot for this reconaissance. This makes perfect sense. And if any problem emerges, there are team members around to solve it as a team. Point taken.

Second, what are you gaining by having two SPGs? (I am assuming that you are diving with essentially one air source, such as manifolded doubles or a single tank, and not independent doubles - which would not be DIR anyways.) With two SPGs, you need to look at both of them. If they read the same, you simply have a good idea of how much gas you have. If one fails, or has a reading different than the other one, aren't you going to terminate the dive immediately? It would seem that a second SPG adds another item of equipment that like all equipment sooner or later will fail, but the addtional item does not help you in any appreciable way.

Your assumption in this case is incorrect. I am referring to doubles. In terms of a failing SPG - yes, dive aborted. But if I had to shut off the left post, it is a good thing to terminate the dive with readable figures on a gauge. But as I said, I agree on you with the (gas) planning. One really knows how much is left in the tank if you do some routine dives. But how many times does one get entangled in a fisher's net on a zero vis and temperatures around 4 centigrades?

 

[JeffG]

Your assumption in this case is incorrect. I am referring to doubles.

He said mainfolded doubles...So he assumed correctly (Hence..the rest of his post was valid)

But how many times does one get entangled in a fisher's net on a zero vis and temperatures around 4 centigrades?

How does two SPG's help in this situation?

 

[MSilvia]

He said mainfolded doubles...So he assumed correctly

...unless VeniVidi's doubles aren't manifolded, which of course isn't DIR.

 

[JeffG]

...unless VeniVidi's doubles aren't manifolded, which of course isn't DIR.

True...But then he would need two SPG's and asking if needed two (spg's) for an independent system would....ummmmm...be a little silly.

 

[VeniVidi]

VeniVidi, a couple of questions for you:
1. You are diving with two SPGs and they begin to show a discrepancy. Which one is right and which one is wrong?
2. You have realized that one or both of your SPGs is failing and have turned your dive. Will you pay attention to one (which one?), both (confusion is certain) or neither (paying attention only to your egress) on your way out/back/up?

Hi Uncle Pug

1. This is where the (gas) planning comes in, by which one "knows" how much is left. I agree so far with all the responses that nothing can be replaced by experience and that it is sometimes advisable to be approximately right than precisely wrong. For safety's sake I would abort the dive.

2. in this situation I think neither the "two-gauged" nor the DIR diver is better off. Both have to rely on what they know about their experience.

Yet my point goes rather to the coverage of unexpected and streneous situations when one is distracted from glancing at the SPG due to problem solving for some time. If you carry one SPG you have to check it prior to valve closing and also when you have closed it. Only then you have a good guess about what is left. So much about task loads....

 

[JeffG]

Yet my point goes rather to the coverage of unexpected and streneous situations when one is distracted from glancing at the SPG due to problem solving for some time. If you carry one SPG you have to check it prior to valve closing and also when you have closed it. Only then you have a good guess about what is left. So much about task loads....

So...You have had an equipment malfucntion..Your left post is off...you have aborted the dive...and then you get "trapped" (or some other issue)

You either have enough gas or not...having a second SPG doesn't help you in anyway.

 

[VeniVidi]

He said mainfolded doubles...So he assumed correctly (Hence..the rest of his post was valid)

OOPS. My apologies. Mea culpa maxima. Your assumption is correct it is a dual-orifice, isolation manifold.

How does two SPG's help in this situation?

This refers to when one has successfully tackled the problem (including valve shutting), used up a lot of air and needs to regain information about the current situation. One needs unexpected (not unanticipated) resources when all senses are distracted.

 

[WJL]

Hi Uncle Pug

1. This is where the (gas) planning comes in, by which one "knows" how much is left. I agree so far with all the responses that nothing can be replaced by experience and that it is sometimes advisable to be approximately right than precisely wrong. For safety's sake I would abort the dive.

2. in this situation I think neither the "two-gauged" nor the DIR diver is better off. Both have to rely on what they know about their experience.

Yet my point goes rather to the coverage of unexpected and streneous situations when one is distracted from glancing at the SPG due to problem solving for some time. If you carry one SPG you have to check it prior to valve closing and also when you have closed it. Only then you have a good guess about what is left. So much about task loads....

At this point you have the DIR reasoning on why you don't need two SPGs. Your comments and responses haven't done anything to cause that thinking to be revised. "Unexpected and strenuous" situations are at the foundation of the planning process for DIR, but do not require the need for one diver to carry two SPGs.

If you want to use two SPGs on your rig, go ahead. Veni. Vidi. Vici.

 

[JeffG]

This refers to when one has successfully tackled the problem (including valve shutting), used up a lot of air and needs to regain information about the current situation. One needs unexpected (not unanticipated) resources when all senses are distracted.

Still doesn't help...You either have enough gas or you don't. Either way the dive is done and you head back.