Optimal Pony Bottle Size for Failure at 100ft?

[lowwall]

I thought I was quite clear that you don't need precision for non-deco ascents. You don't need it for the safety stop either. I used 15' because that gives you 5' up or down of slop without causing a problem.

RE the oil rigs- We were discussing a general plan for an OW dive. If you want a plan for some specific set of conditions then you need to tell us that in advance.

 

[SpaceX Aquanaut]

I don't accept that given. The whole premise of the question doesn't make much sense. It's not a great idea to go to 130ft/39m with a single tank plus (my little) "pony" regardless of size. The NDL at that depth is only a few minutes so on a square profile it becomes a pointless bungee dive: go down, touch the bottom, and come back up.

For open circuit diving the best configuration for that depth would be to use a small set of double tanks with an isolation manifold (plus proper training in deep diving procedures and failure management). Compared to carrying a "pony" this will be hardly any different from a cost or weight perspective, and will actually be easier to handle in the water. Plus it gives you more options if something goes wrong. Alternatively, if for some reason you don't want to use doubles then the second best configuration for that depth range would be to bring an Al80 stage tank of bottom gas and use that for the entire dive while saving your back gas for emergencies. That stage will be plenty of gas to hit the NDL.

But regardless of equipment configuration, the ascent profile for a NDL dive to any depth would be the same. Assume 1 minute to deal with the problem at max depth and start moving up. Ascend directly to about 15ft/5m without stopping. If gas supply, environmental conditions, and other circumstances allow then hang there for a few minutes to complete the recommended safety stop followed by a slow ascent to the surface. Or if the team is having serious problems then skip the safety stop and go straight to the surface; maybe breathe some oxygen on the boat later if you're worried. The precise amount of gas needed for this ascent is left as an exercise to the reader, I'm sure you can do the math.

Exactly and I agree -let the above be the caveat to the OP. But the example has been given, if the OP feels "compelled" to do a multi-level Computer NDL wall dive (or an "Oil Rig Dive" like my example above), starting at 130'/39m.

It's doable with an AL40 as a "pony bottle back-up", but not advisable.

 

[SpaceX Aquanaut]

I thought I was quite clear that you don't need precision for non-deco ascents. You don't need it for the safety stop either. I used 15' because that gives you 5' up or down of slop without causing a problem.

RE the oil rigs- We were discussing a general plan for an OW dive. If you want a plan for some specific set of conditions then you need to tell us that in advance.

Alright, so how do you personally determine, measure and gauge a continuous 30fpm/9mpm ascent rate -from depth to the safety stop?

 

[lermontov]

Alright, so how do you personally determine, measure and gauge a continuous 30fpm/9mpm ascent rate -from depth to the safety stop?

constantly looking at your computer's ascent rate indicator all the way up from 130'/39m, making sure it reads no more than 30fpm

 

[SpaceX Aquanaut]

Yeah Lermie?

Staring exclusively/continuously/obliviously with no situational awareness -at your computer's ascent rate indicator in currents, poor visibility, low ambient light/night dive, and a high density kelp forest canopy (throw in some monofilament fishing line too) like we can have here at SoCal offshore divesites at Catalina/Channel Islands National Park? (Or Poor Knights Islands where you are?)

 

[lermontov]

Yeah Lermie? Staring exclusively/continuously/obliviously with no situational awareness -at your computer's ascent rate indicator in currents, poor visibility, low ambient light/night dive, and a high density kelp forest canopy like we can have here at SoCal offshore divesites at Catalina/Channel Islands National Park?

as opposed to watching your computer to monitor depth every 3m and counting 10 seconds -but now your introducing more conditions to support your argument (just like you introduced Oil rigs) when what were talking about is running OOA and switching to a pony on an NDL dive

 

[SpaceX Aquanaut]

Yeah Lermie?

as opposed to watching your computer to monitor depth every 3m and counting 10 seconds -but now your introducing more conditions to support your argument (just like you introduced Oil rigs) when what were talking about is running OOA and switching to a pony on an NDL dive

Yeah Lermie? Just like I "introduced Oil Rigs": if you don't pause at every 3m/10' from 39m/130' for at least 10 to 20sec, you will get blown up to the surface in an uncontrolled upwelling surge ascent -as you attempt to "slam the breaks" before a safety stop at 15'/5m.

And surely you can "count 10 to 20 seconds" at every 3meters hold -without looking at your computer and being situationally aware of your surroundings- can you not do so Lermie ?

 

[johndiver999]

Ok, you could do that profile. But why on Earth would you do?

You claim it's easier to do these ascend and holds rather than a continuous moderate ascent. I'm not sure that is true, especially since there is no need to maintain a precise ascent rate. Anything between 30 and 60 feet per minute is fine.

But much more important is risk mitigation. You want to quickly get your butt out of the deep water with its narcosis fog, fast Nitrogen uptake, and high gas usage. Save the gas for a safety stop or rough surface conditions or other unforeseen conditions.

Yes! For me and if I was using a small pony from 130, I would most likely do a 60 fpm ascent from 130 to around 60 feet and really try to keep my air consumption limited for that 60 second period. Once I reach 60-70 feet, I am much safer and air consumption is a lot less, so I would try to slow the ascent to maybe 30 fpm. I am not going to blow up, since the expansion rate is still slow at this depth.

In this scenario, I am at 40 feet in 2 minutes and have been riding the BC up and not kicking. From there, I know I can make the final ascent with zero air, so I should be relaxed and calm and can take a minute or so to go from 40-20 feet (3 minutes elapsed time) and then decide if I want to hang a little at 15.

The whole idea that somebody has to completely stop every 10 feet simply to be able to control their ascent rate is silly- especially when they are well below 100 ft depth!

I use old crappy computers and if I stare at them, they will flash and give warnings when the ascent rate is too fast- it is quite obvious. I remember reading another suggestion a long time ago - "on your ascent go slow enough that it reads out every foot depth, don't go so fast that you skip a number or they are flying by". Something as simple as that, should help people to maintain a reasonable ascent in an emergency, even if they are not that familiar with their dive computer.

 

[scubadada]

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...

...But regardless of equipment configuration, the ascent profile for a NDL dive to any depth would be the same. Assume 1 minute to deal with the problem at max depth and start moving up. Ascend directly to about 15ft/5m without stopping. If gas supply, environmental conditions, and other circumstances allow then hang there for a few minutes to complete the recommended safety stop followed by a slow ascent to the surface. Or if the team is having serious problems then skip the safety stop and go straight to the surface; maybe breathe some oxygen on the boat later if you're worried. The precise amount of gas needed for this ascent is left as an exercise to the reader, I'm sure you can do the math.

A month and a half ago

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

Dec 4, 2023

Many of the contentious issues regarding the use of a pony for redundant gas supply have been discussed many times before. It comes down to personal preferences.

I dive a slung pony with a SPG on a short hose and the valve on. The pony is always right in front of me, I could easily see any leak, I know exactly how much gas is in it, and it is immediately ready for use.

I chose to use a 19 cu ft pony. The deepest I would dive solo is around 130 feet, nearly all my dives are shallower than that but are not uncommonly around 100 ft. My conservative calculation for gas requirement is a...

• scubadada

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[inquis]

Alright, so how do you personally determine, measure and gauge a continuous 30fpm/9mpm ascent rate -from depth to the safety stop?

Bubbles are visible in your peripheral vision. If I'm outpacing them, I'm going "fast". In an emergency, I go "fast" to 60ish, then slow down to not outpace the bubbles, especially the tiny ones as I get to 30ish ft. Basically a normal ascent from there. No need to stare at a computer.

The fact I planned to have enough gas for a mere 30 fpm ascent adds additional conservatism compared to my actual ascent.