Optimal Pony Bottle Size for Failure at 100ft?

[Celt]

It seems it depends on how much air you need to get to the surface and whether you plan to take a detour rather than going straight up. And do you plan to hang around for a few minutes making up your mind.

 

[johndiver999]

It seems it depends on how much air you need to get to the surface and whether you plan to take a detour rather than going straight up. And do you plan to hang around for a few minutes making up your mind.

No it is much more complicated than that... You need to consider options......LOL

 

[SpaceX Aquanaut]

FWIW, a quick estimate on a direct surfacing return with an AL40 from the "recreational limit" of 130fsw/39msw:

28 litres/min SCR (roughly same as 1cuft/min stressed volume SAC rate in US Imperial units), with 39meters ( 4.9ATA) depth NDL with one minute stops every 3 meters to surface:

4.9 x 28 x 1 = 137.2
4.6 x 28 x 1 = 128.8
4.3 x 28 x 1 = 120.4
4.0 x 28 x 1 = 112
3.7 x 28 x 1 = 103.6
3.4 x 28 x 1 = 95.2
3.1 x 28 x 1 = 86.8
2.8 x 28 x 1 = 78.4
2.5 x 28 x 1 = 70
2.2 x 28 x 1 = 61.6
1.9 x 28 x 1 = 53.2
1.6 x 28 x 1 = 44.8
1.3 x 28 x 1 = 36.4
1.0 x 28 x 1 = 28


Sum Total: 1156.4 litres gas needed for one person to ascend to surface from 39m depth for an emergency contingency with a fairly reasonable & controlled ascent rate.

A 5.5L cylinder (AL40 "pony bottle") filled to 200 bar pressure supplies 1100 litres.

(Note: this is for worst case contingency option only, with no decompression obligation or barely any remaining air left for a "Safety Stop")

 

[-JD-]

FWIW, a quick estimate on a direct surfacing return with an AL40 from the "recreational limit" of 130fsw/39msw:

28 litres/min SCR (roughly same as 1cuft/min stressed volume SAC rate in US Imperial units), with 39meters ( 4.9ATA) depth NDL with one minute stops every 3 meters to surface:

4.9 x 28 x 1 = 137.2
4.6 x 28 x 1 = 128.8
4.3 x 28 x 1 = 120.4
4.0 x 28 x 1 = 112
3.7 x 28 x 1 = 103.6
3.4 x 28 x 1 = 95.2
3.1 x 28 x 1 = 86.8
2.8 x 28 x 1 = 78.4
2.5 x 28 x 1 = 70
2.2 x 28 x 1 = 61.6
1.9 x 28 x 1 = 53.2
1.6 x 28 x 1 = 44.8
1.3 x 28 x 1 = 36.4
1.0 x 28 x 1 = 28


Sum Total: 1156.4 litres gas needed for one person to ascend to surface from 39m depth for an emergency contingency with a fairly reasonable & controlled ascent rate.

A 5.5L cylinder (AL40 "pony bottle") filled to 200 bar pressure supplies 1100 litres.

(Note: this is for worst case contingency option only, with no decompression obligation or barely any remaining air left for a "Safety Stop")

Am I correct that you are basing that on a 3 meters/minute (10 feet/minute) ascent rate?

Nominal "direct" safe ascent rate is generally considered as 3x that: 9 meters/minute (30 feet/minute). That would require significantly less gas.

 

[SpaceX Aquanaut]

Am I correct that you are basing that on a 3 meters/minute (10 feet/minute) ascent rate?

Nominal "direct" safe ascent rate is generally considered as 3x that: 9 meters/minute (30 feet/minute). That would require significantly less gas.

In actual practice, it's an "ascent hold" at depth for 30sec -at each "triad" cardinal number depth by-threes in meters, or "decade" by-tens in US Imperial), and then "move up" to the next cardinal depth in 30sec.

So for example, stop at 36m/120' for 30 seconds, then move up to next depth of 33m/110' in 30 seconds; do a hold at 33m/110' for 30 seconds, then move to 30m/100' in 30 seconds; and so on etc.

 

[scubadada]

In actual practice, it's an "ascent hold" at depth for 30sec -at each "triad" cardinal number depth by-threes in meters, or "decade" by-tens in US Imperial), and then "move up" to the next cardinal depth in 30sec.

So for example, stop at 36m/120' for 30 seconds, then move up to next depth of 33m/110' in 30 seconds; do a hold at 33m/110' for 30 seconds, then move to 30m/100' in 30 seconds; and so on etc.

Where does this ascent strategy come from?

Thanks

 

[lowwall]

In actual practice, it's an "ascent hold" at depth for 30sec -at each "triad" cardinal number depth by-threes in meters, or "decade" by-tens in US Imperial), and then "move up" to the next cardinal depth in 30sec.

So for example, stop at 36m/120' for 30 seconds, then move up to next depth of 33m/110' in 30 seconds; do a hold at 33m/110' for 30 seconds, then move to 30m/100' in 30 seconds; and so on etc.

Why on earth would you do that? This is a NDL dive. For a realistic scenario, run your numbers with a 60f/m (18m/m) ascent rate and a 3 min safety stop at 3.5m/12’.

You can do a 30f/m ascent rate if you insist.

 

[SpaceX Aquanaut]

FWIW, a quick estimate on a direct surfacing return with an AL40 from the "recreational limit" of 130fsw/39msw:

28 litres/min SCR (roughly same as 1cuft/min stressed volume SAC rate in US Imperial units), with 39meters ( 4.9ATA) depth NDL with one minute stops every 3 meters to surface:

4.9 x 28 x 1 = 137.2
4.6 x 28 x 1 = 128.8
4.3 x 28 x 1 = 120.4
4.0 x 28 x 1 = 112
3.7 x 28 x 1 = 103.6
3.4 x 28 x 1 = 95.2
3.1 x 28 x 1 = 86.8
2.8 x 28 x 1 = 78.4
2.5 x 28 x 1 = 70
2.2 x 28 x 1 = 61.6
1.9 x 28 x 1 = 53.2
1.6 x 28 x 1 = 44.8
1.3 x 28 x 1 = 36.4
1.0 x 28 x 1 = 28


Sum Total: 1156.4 litres gas needed for one person to ascend to surface from 39m depth for an emergency contingency with a fairly reasonable & controlled ascent rate.

A 5.5L cylinder (AL40 "pony bottle") filled to 200 bar pressure supplies 1100 litres.

(Note: this is for worst case contingency option only, with no decompression obligation or barely any remaining air left for a "Safety Stop")

Where does this ascent strategy come from?

Thanks

Post in thread 'Optimal Pony Bottle Size for Failure at 100ft?'

Wednesday at 7:51 PM

In actual practice, it's an "ascent hold" at depth for 30sec -at each "triad" cardinal number depth by-threes in meters, or "decade" by-tens in US Imperial), and then "move up" to the next cardinal depth in 30sec.

So for example, stop at 36m/120' for 30 seconds, then move up to next depth of 33m/110' in 30 seconds; do a hold at 33m/110' for 30 seconds, then move to 30m/100' in 30 seconds; and so on etc.

Why on earth would you do that? This is a NDL dive. For a realistic scenario, run your numbers with a 60f/m (18m/m) ascent rate and a 3 min safety stop at 3.5m/12’.

You can do a...

• lowwall

• 
• 

Just a "very conservative & controlled" ascent strategy in an emergency loss of backgas from the recreational limit of 39m/130', given the OP parameters of already choosing an AL40 Pony for 100fsw in Post #1.

 

[rsingler]

It's a little hard to believe this thread has lasted for 20 pages.
Kudos to those that know its gonna take a moment before you're aware enough, have switched to your pony and have gotten on your way.
I have no idea where the above ascent strategy with a known limited gas supply came from. "Ascent/Hold" sounds like a variant on Deep Stops. Bizarre, IMO. I would not follow that recommendation.

But if you want to play with the numbers...
How long at 100' with elevated consumption before you start up?
How much has your SAC/RMC jumped?
Will you start with an accelerated ascent rate from 100'?...

Here's a little spreadsheet for you to play with.
With wildly exaggerated numbers, you can still make it with an AL40 if you skip your safety stop.

With anything approaching real world numbers, assuming you are stressed but don't panic, it's a piece of cake for TWO of you, even with a 5 minute safety stop:

The tool is attached below...

 

[SpaceX Aquanaut]

. . <snip>
I have no idea where the above ascent strategy with a known limited gas supply came from. "Ascent/Hold" sounds like a variant on Deep Stops. Bizarre, IMO. I would not follow that recommendation.

. . . <snip>

What would your recommendation be then, given an AL40 with ascent from 39m/130'?