Deep Diving 108 feet w/ a single AL 80 (Air.) No redundancy.

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I have over a minute to get to her.
Sounds like a viable plan. /S

What about the ascent, sharing gas and being stressed? Min gas is about having enough for the whole ascent. Even when being stressed and breathing like a Hoover.
 
Sounds like a viable plan. /S

What about the ascent, sharing gas and being stressed? Min gas is about having enough for the whole ascent. Even when being stressed and breathing like a Hoover.

1000 psi gas usage is estimated based on air consumption at 5 atmospheric pressure and including the 3 minute safety stop, which can be skipped during an emergency. As we ascend, the ambient pressure will decrease and the air consumption rate would decrease.
 
As we ascend, the ambient pressure will decrease and the air consumption rate would decrease.
Interesting. Please elaborate. Preferably, with a scientific background.
 
Interesting. Please elaborate. Preferably, with a scientific background.

0.5 cfm is at the surface. 2.5 cfm is at 130 ft depth (5 atmospheres). Let’s say the average air consumption from depth to surface = 1.25 cfm. With ascent rate of 33 ft/min, it’ll take 4 minutes to get to the surface. That ascent for 2 divers would consume = 2 x 1.25 cfm x 4 min = 10 cf. Doubling the air consumption due to stress = 20 cf = 750 psi. I use 1000 psi for “hand waving” estimate.

You took the CMAS 3*. So you are the expert in this matter. I’m just a recreational diver. Please correct my calculations. Let me know what additional data you need from me. Thank you!
 
For min gas I use an RMV of 1 to account for elevated consumption and it keeps the math simple.
At 5atm, 2 divers for 1 minute to sort stuff out = 10cf
Average depth of ascent is 65ft or 3atm and the ascent takes 4.3 minutes at 30ft/min = 25.8cf

Min gas is 35.8cf

Two minute descent, nine minutes on the bottom and then back up. Maintains min gas.
 
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NDL graph is shown in red. I use GF Conservative Medium 40/85.

That red line I think is actually some relation to ongassing verses your GF. I use Dive Log 6 to log stuff but use Shearwater stuff to evaluate dives, I just looked at a deco dive and when you are on gassing, the line is close to zero, like yours shows - as you ascend, you begin to off gas and it switches over to display a GF number but I can't find anywhere that it actually explains what the number really represents........

If the red line was your NDL, it'd start high, go towards zero and then go back up as you ascended - I dunno - I wish there was a good help menu or description of it.

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0.5 cfm is at the surface. 2.5 cfm is at 130 ft depth (5 atmospheres). Let’s say the average air consumption from depth to surface = 1.25 cfm. With ascent rate of 33 ft/min, it’ll take 4 minutes to get to the surface. That ascent for 2 divers would consume = 2 x 1.25 cfm x 4 min = 10 cf. Doubling the air consumption due to stress = 20 cf = 750 psi. I use 1000 psi for “hand waving” estimate.

You took the CMAS 3*. So you are the expert in this matter. I’m just a recreational diver. Please correct my calculations. Let me know what additional data you need from me. Thank you!

Not telling you what to do, just clarifying the min gas calcs for others that may not know. This is what I was taught, what I use and how I teach it. But not the only way to do it.

Using your normal RMV doesn’t account for stress and increased breathing. Usually you see an increased rate used in calculating min gas. Probably .75 at minimum, 1 to be conservative if your normal RMV is .5.

For the ascent, you use the average depth assuming a continuous ascent rate, 65ft or 3atm. You just split the SAC in half, which gives you a lower number. Even using .5, you get 3x1x4 = 12cf. With a more typical RMV it’s 3x1.5x4 = 18cf. Or 25cf with a conservative RMV of 1.

And last, give yourself a minute on the bottom to get sorted out before ascent. You may not be at the anchor line, need a few seconds to orient yourselves for ascent, sort out an entanglement or you need to shoot a bag, stuff like that.
 
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Don't like this talk of a 45m/140' dive on a single with no redundancy. At that depth the rule of thumb is 1:1 bottom time to deco (longer deco times if on air!). Thus any dive to that depth must factor in decompression. Also, at that depth narcosis is very real and affects everyone. You train yourself to be competent(ish), but you're still affected.

Anyone can do bounce dives like that and most will live to tell the tale. However, if anything goes wrong or you're slow off the bottom, you've absolutely no contingency to handle it and worse still no redundancy should you loose gas. A bolt to the surface from there is pretty much a sure-fire guarantee of a trip to the pot (recompression chamber) -- if you're lucky. This is the classic "Divers went missing on a dive" story -- often described as "experienced" divers.

Why not dive with two cylinders? This can be either a proper manifolded twinset (DIR style), or a pair of singles clamped together (run as two singles with separate SPGs), or a couple of cylinders sidemounted, or even a single on the back with a pony-rigged ali80 as a stage on the front. This will give you the contingency and some redundancy to be able to do limited dives which is a massive weight off your shoulders -- and your buddy's.

Of course the best way to do that dive is with mixed gas and oxygen-rich decompression stage(s) -- typically a twinset with ~20% helium and one stage with 80% or two stages with 50% and 80% (other mixes are available). Then you could have over an hour on the bottom with a runtime of just over a couple of hours with stacks of contingency and redundancy. You come back relaxed and you remember the dive (helium, the gas of the gods). (Won't mention rebreathers -- they cut gas costs to a fraction of open circuit)
 
Diving within rec limits with an AL80, air or nitrox, is very common and generally quite safe. What is all this about? Thousands and thousands of dives like this all the time. Pay attention to your gas and NDL, come on now. You are responsible you your own diving.
 
Diving within rec limits with an AL80, air or nitrox, is very common and generally quite safe. What is all this about? Thousands and thousands of dives like this all the time. Pay attention to your gas and NDL, come on now. You are responsible you your own diving.
If I remember correctly, PADI's limits are 42m/132' (not sure of the feet).

Whilst it's possible to dive that deeply on a single, getting the hell out of Dodge from that depth is not easy. Maybe fine for an experienced diver who's well in control of their gas and skills, but not something for an intermediate diver to be at.

Just the risk assessment; the numbers draw in when you push the boundaries of anything in life -- driving 100mph for example.

Technical divers do way past those depths all the time. The difference is they're cautious, meticulous, have the right kit, and constantly train for adverse outcomes.
 

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