Stage bottles transmitter plus SPG setup...

[Wstern5]

Two divers go into a cave, they drop their stages at the agreed upon drop pressure and continue on using back gas. One diver has a massive failure just as his buddy calls the dive on gas, and they go into a gas share and start heading out, they get to their stages and one is empty/gone/malfunction- between the back gas and single stage they have enough to get out but not a lot extra, and the gas share is going a bit slower than they would like so they decide for the OOA diver to take the stage to facilitate a speedy exit but the stage has a transmitter…well he will just assume it’s half full. As the diver is entering the last restriction 30’ before the cave entrance he runs out of gas and unable to turn around to signal his buddy he dies. Had he known the amount in the stage they could have gone back into a gas share and exited safely.

 

[rddvet]

I normally like to leave things to flow except to answer direct questions, but I am slightly confused.

The way I was taught stage planning for the 1/2+2. Is to take how much gas that would be, so assuming full,
1300 psi
Which is 13* 2.5 = 33cuft
33cuft / 6.4 = 5.1
Round that up to 600 psi.

So if you are starting with 3,600psi, you have 3,000psi to work, or 1,000psi if you are diving hard thirds.

What he’s talking about is if you dive half + 200, some divers don’t adjust their backgas usage.

They should.

If you dive 1/2+200 (which I do believe to be the best stage technique), you need to reduce penetration gas on your back so you don’t exceed thirds of your total starting volume.

What AJ saiid. I generally don't go into great detail about it online since it's something everyone should have been taught, but apparently have been. I know I wasn't. I was taught by mentors and quickly understood what was wrong with the way I was taught

 

[beldridg]

You've planned out all your gas consumption and contingencies ahead of time. What scenario might occur where being able to see an SPG on your deco/stage/BO cylinder might change what you are doing? I.e. something goes wrong. You're now into a contingency plan. You can see an SPG on the cylinder you're now using. What do you do? Same scenario except you can't see an SPG on that cylinder. What are you doing differently?

I'm not trying to be contentious. I'm trying to understand what scenarios might occur where having an SPG (versus AI or a button gauge or AI and a button gauge) would make a difference regarding how the scenario plays out.

Personally, I don't use AI on my BO or deco bottles. I just don't feel any need. If I wanted to know my exact consumption of my deco or BO gas, I would note the cylinder pressures before and after the dive and then use my dive profile data - including the data on when I did my gas switches - to calculate it (or, really, plug the numbers into Subsurface and let it tell me). Otherwise, I planned it out ahead of time, I start with full cylinders, and I either have enough gas or I don't.

My thinking is that being able to look at an SPG during the dive is not going to change anything if I screwed up and didn't bring enough gas. If I run out in one cylinder, I'll switch to some other cylinder. If I have to switch to a way-too-hot mix and make a very rapid ascent to get to the MOD of that gas, I'll do that before I try to breathe water. If I run out of all my gas in all my cylinders, well, by the time I'm breathing on my last cylinder that has any gas in it, I'm going to have gotten shallow enough that, if it runs out too, I can get to the surface and deal with possibly being bent there.

In short, I think having an SPG on a cylinder on a tech dive seems far less important that having an SPG on a cylinder being used on a recreational dive. If I planned my tech dive correctly, and dive my plan, why do I even need ANY SPGs (beyond one on my bottom gas, to know if I'm at my turn pressure)? I'm not saying to dive without SPGs. I'm just saying that the importance some people place on a full-sized SPG and also the importance some people place on having a redundant SPG (if using AI) seems out of proportion. A good quality button gauge on deco/BO cylinders seems adequate for most all scenarios.

However, I am VERY open to explanation of why an SPG is needed. An actual example, with details, would be very helpful, in that case.

Assume you are diving on a rebreather with a buddy also on a rebreather and you each have bailout bottles. Your bottle has only AI and no SPG.

The buddy's rebreather completely fails and they bailout on their deep cylinder. In many cases, instead of breathing it down to almost nothing (assuming the situation requires more than 50% of the bailout -- which is another whole topic), they would breath it down to about 50% and then take your full bottle in order to have more gas reserve and you would take the half-empty bottle.

If your bottle only has AI, they won't be able to tell when that bottle gets to 50% and to switch back.

It is obviously a different situation than open circuit diving where each diver needs to use each of their cylinders to complete their deco obligation.


Regards,

- brett

 

[rjack321]

Yeah if I have an OOA or Bailed buddy I am going to be encouraging them to use some of my extra resources (gas) when its easy to do so. Like after we come up from depth on a deco dive and are doing the stops required before the gas switch. Or when the cave is wide open and we know there's a restriction later closer to the exit.

Then they are less likely to be on fumes before the switch or in a restriction. When they give the bottle (or 2nd stage) back to me and go back to their own gas, I can check the consumption and have a good idea how stressed they've been and if I need to be stepping in and recommending we shave stops or otherwise move faster or share something else before they go OOA on me.

Calculating your SAC rate with AI on your stage is really really low priority compared to having sharable resources.

 

[Wibble]

All team members need to know what resources are available so the best decisions can be made.

If you are by yourself just trying to get to the surface by any means necessary then you’re right, it doesn’t really matter.

Just want to pick up one thing…

All dives should assume a solo ascent even if you’re diving with a team/buddy. It’s very easy to loose a buddy and if you’re doing serious dives, you must take what you need (not talking extreme diving here) — diving with insufficient gas is a mugs game. Minimum gas is whatever you need to get to the second deco stage switch if on OC. If CCR max bottom time is whatever you’ve calculated your max bailout plan is.

The stage reserve is for your buddy should you need to ascend together and they’ve lost their deco gas. Obviously if sharing then you’ll be staying down longer as you switch gasses during the ascent. 50% may not be enough.

 

[Wibble]

Hmm, seems the more experienced divers seem to have a consensus on AI on stages (bailout, deco and drop tanks)

 

[kensuf]

I'm just curious what are the problems people are trying to solve by going with AI on stage/deco bottles?

 

[Wibble]

So far, nobody has given a specific, detailed example, of how having a full-sized SPG on their deco or BO would matter. Let me give one to show what I mean:

I'm doing a dive to 200', carrying a cylinder of 50% and a cylinder of 100% for deco.

Just when it's time for me to start my ascent, the tank valve O-ring on my O2 blow out and I lose all my O2.

I ascend to 70' and switch to my 50%, per my plan.

I do my deco stops up to where I am at 20'. I don't have O2 to switch to, so I keep breathing my 50%. My buddy switches to his O2.

Depending on how I planned my dive, I might have planned Lost Gas so that I can finish all my deco on 50%, or I might have planned it knowing that I would have to get gas from my buddy in this scenario.

In the former case, I deco out on 50%. In the latter case, I keep breathing my 50%. If it runs out, I switch to back gas briefly and then swap 50% bottles with my buddy and then switch to breathing that. When my buddy is clear on deco, he gives me his O2 and I finish my deco and we get out.

Nowhere in there does having an SPG or not on my deco bottles make any difference.

Realistically, I wouldn't plan the dive this way (as it's less conservative with respect to deco), but if it actually happened, I would probably immediately go to riding my GF99 at somewhere between 85 and 95 to get as shallow as possible as quickly as possible - to maximize how long my gas will last - and then stay at my last stop as long as possible (or until my SurfGF came down to the low side of what I normally look for before getting out).

What's an example, with details, where having an SPG would (or could) make a difference to how you finish your dive? What scenario could happen where you would look at a deco/BO SPG and say "if it's above X, we'll do this but if it's X or less, we'll do this other thing instead"?

Would you really be comfortable undertaking a 60m/200' dive without SPGs on your deco cylinders?

 

[Wibble]

I'm just curious what are the problems people are trying to solve by going with AI on stage/deco bottles?

The usual argument for AI is "I can see everything in one place", closely linked with I don't want to use a separate SPG on a hose. Most of this is due to the way recreational BCDs work (DIR people have the SPG clipped off to the hip D-ring).

My personal argument for AI on my rebreather is to clean up the front (the two long HP hoses both broke as the rebreather was stood on the SPGs as they're very awkward) and as I have a Nerd which is always in front of my eye, the info is definitely close to hand. It works well.

When it comes to stages (drop tanks, bottom stages, bailout and deco) it's a completely different requirement. Those tanks need to be interchangeable with different people and they're clipped off to your front, so you can easily see the SPGs and you must be able to monitor your gas.

Aside from one use case, accurately auditing the diver's SAC/RMV/gas consumption, there's no real benefit and many many drawbacks especially if other divers are involved.

 

[stuartv]

I'm just curious what are the problems people are trying to solve by going with AI on stage/deco bottles?

IIRC, the OP wanted to have AI on his stage/deco cylinders in order to capture his personal consumption data in detail, for post-dive review.

Would you really be comfortable undertaking a 60m/200' dive without SPGs on your deco cylinders?

In case I have not been clear, I do not and have never used AI on anything except my back gas (OC) or Dil/O2 (CCR).

Almost all my diving past 150' (to a max of 305', so far) has been with button gauges only on my deco/BO regs. So, yes, I am comfortable with 200' dives with no "traditional" SPG on my deco cylinders.

I orient my button gauges so they are pointing up/forward. I'm not going to say it's super easy, but it's also not super hard for me to read them in the water. I grab the tank valve and pull it out some and I can see the gauge well enough to read. I don't think that part is really any different than if I were trying to read an actual SPG that was on a hose extending down the side of the cylinder (versus a SM style SPG sticking out in front, like some people do). It probably is a little harder than reading an SPG that is wrapped around and held up by the 1st stage, like some people do.

All that said, I will be the first to say that I do not feel like I am super experienced at deep diving. I have a handful (okay, double handful) of dives past 200'. I am definitely still learning. Learning by doing and also trying to learn from the people around me (including here on SB) who ARE very experienced.

I have been considering changing all my deco/BO regs from button gauges to actual SPGs. There are a few reasons for that:

- the people here whose opinion I really respect and who recommend it.
- an actual SPG does not make it any harder to manage the cylinder in the water.
- the button gauge sticking up from the 1st stage is sometimes a snag point for the bungee loops I use to hold the tops of the cylinders (SM-style slinging).
- more precise knowledge of cylinder pressure (than you get from even a good button gauge) is never a bad thing.

So, it seems like there is potential benefit and no real downside (beyond cost).

Still thinking about it...