Optimal Pony Bottle Size for Failure at 100ft?

[MB NZ]

Consider this... buddy pair doing a recreational dive with typical recreational gear. Buddy one has a catastrophic loss of gas at depth. Buddy two has half a tank of gas left which they share for their ascent. Run some numbers. How do they do?

 

[lowwall]

Consider this... buddy pair doing a recreational dive with typical recreational gear. Buddy one has a catastrophic loss of gas at depth. Buddy two has half a tank of gas left which they share for their ascent. Run some numbers. How do they do?

Maybe this is your point, but screw the numbers. Up you go at 60fpm until safety stop depth. This is what they teach in OW and there is no reason to complicate it.

 

[rsingler]

Consider this... INSTAbuddy pair doing a recreational dive with typical recreational gear... How do they do?

FTFY.

But seriously, for 90% of urgent situations, of course you're right. Then again, redundant gas is redundant gas. I don't think we should argue over the basic premise of redundant gas.

 

[scubadada]

Consider this... buddy pair doing a recreational dive with typical recreational gear. Buddy one has a catastrophic loss of gas at depth. Buddy two has half a tank of gas left which they share for their ascent. Run some numbers. How do they do?

Fine.

It's a little hard to believe this thread has lasted for 20 pages.

28 pages

 

[lowwall]

FTFY.

But seriously, for 90% of urgent situations, of course you're right. Then again, redundant gas is redundant gas. I don't think we should argue over the basic premise of redundant gas.

What makes you such an expert on gas?

 

[SpaceX Aquanaut]

Consider this... buddy pair doing a recreational dive with typical recreational gear. Buddy one has a catastrophic loss of gas at depth. Buddy two has half a tank of gas left which they share for their ascent. Run some numbers. How do they do?

18m Beginner/Novice OW Limit

A Quick Contingency "Rock Bottom" Calculation and Gas Plan Estimate for Open Water. . .

Given a single 11 litre tank (AL80), with a standard spec of 11 litres/bar metric tank rating, and a diver's gas volume Surface Consumption Rate (SCR) of 22 litres/min -same as a pressure SCR of 2 bar/min*ATA (divide 22 litres/min by 11 litres/bar equals 2 bar/min*ATA)- using an example NDL air dive to 30m (4 ATA) depth in Open Water.

Emergency Reserve/Rock Bottom pressure calculation, from 30 meters with one minute stops every 3 meters to the surface,
-->Just "tally the ATA's":
4.0
3.7
3.4
3.1
2.8
2.5
2.2
1.9
1.6
1.3

Sum Total: 26.5

Multiplied by 2 bar/min*ATA equals 53 bar Rock Bottom absolute reading remaining on your SPG. --this also happens to be the pressure in bar needed for one person (Solo Diver) in an emergency contingency to reach the surface with the above minimum decompression ascent profile.

So ideally for a two person buddy team, multiply 53 by 2 which is 106 bar for both to reach the surface (sharing in a buddy Out-ot-Gas contingency).

But realistically, for two experienced divers stressed: 106 bar plus 30% of 106 bar equals 138 bar Rock Bottom SPG reading. (For an experienced Solo Diver, the SPG reading of the primary AL80/11L Tank would be half of 138 or 69 bar. A full auxiliary/redundant pony bottle equivalent to this amount to have along as a contingency, independent or emergency back-up would be an AL30/4.2L tank)

For two novice divers stressed: 106 bar plus 100% of 106 bar equals 212 bar (!!!) A full 11L (AL80) cylinder is 200 bar. . .
--->obviously then, two novice divers on single 11L tanks should not be diving to 30m for any significant length of time, hence the basic open water limit depth of 18m. . .


(For a novice certified Solo Diver going this deep to 30m, the SPG reading would just be 106 bar; a full auxiliary/ redundant/independent pony bottle nearly equivalent to this amount to attach along the main AL80/11L tank -or slung like a stage tank- would be an AL40/5.5L cylinder).

 

[MarkA]

Maybe this is your point, but screw the numbers. Up you go at 60fpm until safety stop depth. This is what they teach in OW and there is no reason to complicate it.

Sounds like it’s better to be on the surface with a squawking computer than not make it up.

 

[-JD-]

Dude, just STOP with the 1 minute stops thing already.

Novice divers are not taught to dive that way, so it is objectvely irrelevant to gas calculations for them.

I'll admit it is an "interesting" ascent methodology. But other than ensuring that you can't be ascending too fast, it seems worse than any normal strategy in: deep nitrogen loading, air consumption (just plain getting to the surface), SS & shallow SLOW ascent "reserve", and consequence of secondary failure.

If you feel that you have to stop every 3m/10' , just a 10 second pause absolutely ensures that you can't be exceeding 60' per minute even if you are teleporting between stops.

 

[Celt]

The reality of an emergency ascent is totally different than what people are thinking, when you make a 100 foot emergency ascent ( I made one from 140 feet in 2 minutes and was able to get a breath at 60 feet from a tank that was empty at 140) gas is expanding if you’re going fast enough and you couldn’t inhale even if you wanted to till you stop.

 

[lowwall]

The reality of an emergency ascent is totally different than what people are thinking, when you make a 100 foot emergency ascent ( I made one from 140 feet in 2 minutes and was able to get a breath at 60 feet from a tank that was empty at 140) gas is expanding if you’re going fast enough and you couldn’t inhale even if you wanted to till you stop.

FWIW, we are talking about an ascent on a pony after a failure or out of gas on a single tank rig. Not a CESA.

At least that's what we started with. At this point?
¯\_(ツ)_/¯