Pony Bottle

[caruso]

I guess when I read:



it implied to me that you often don't have hardly any gas left (much less "at least 500 psi), and sometimes practically none, during the stop. Which implies that often you likely have inadequate air for a buddy if needed. I'm not sure how they'll get that "at least 500 psi that remains" in your main tank from you tank with 100 psi or less, but sure...

That 100 psi or less is at the END of the safety stop, on the boat as per my post. The buddy would have the same 500 psi available to them at the start of the ascent, roughly 300 psi at the start of a (questionable) safety stop, and roughly 100 psi at the conclusion of the safety stop- no different than they would have if they've been airsharing an AL80 with 1000 psi- close to zero in any case. I say "questionable safety stop" because I highly doubt any team of air sharing divers is going to do a precautionary and optional stop at 3 minutes. They probably wouldn't have the gas even if they wanted to, regardless of whether they were sharing an AL80 or one was breathing off the main and the other was breathing off a pony.

Let me phrase it a different way. Let's say you're suddenly in an airsharing situation with an AL80 that has 1000 psi at 100ft. How much gas do you think will be available to you or your buddy following the safety stop should you choose to even try to do a safety stop in an emergency OOA situation?

 

[Zef]

Let me phrase it a different way. Let's say you're suddenly in an airsharing situation with an AL80 that has 1000 psi at 100ft. How much gas do you think will be available to you or your buddy following the safety stop should you choose to even try to do a safety stop in an emergency OOA situation?

Rock Bottom would suggest that if diving a 12L tank down to @ 100 feet that you should be heading upwards to a shallower depth when your SPG reads 135bar (@ 2000psi) in consideration of the possibility of an air-sharing situation with figuring each of the 2 divers' SAC rate at 25L/min and reaching the surface with a 50bar (725psi) buffer.

If you plan to reach the surface with an empty tank in the case of an emergency air-share situation, with the same air consumption rate noted above, then from a contingency planning perspective, Rock Bottom would have you leaving 100 feet to a shallower depth when your SPG reads 85bar (@ 1233psi)....if you ascend to 20m, you can hangout at that depth until your spg reads 60bar (@870psi). This is all based on a 12L tank (@al80).

Just saying.

-Z

 

[caruso]

Rock Bottom would suggest that if diving a 12L tank down to @ 100 feet that you should be heading upwards to a shallower depth when your SPG reads 135bar (@ 2000psi) in consideration of the possibility of an air-sharing situation

All the more reason to dive solo.

 

[Zef]

All the more reason to dive solo.

If diving solo and one expected to breath the tank empty in an emergency, then one would want to start heading shallower from 100 feet when the SPG reads 45bar....if you plan to be at the surface with 50bar in the tank then you would need to head shallower when the SPG reads 95bar...

...Perhaps....

...I am not solo certified so I have no idea if there are more specific gas planning considerations that one takes into consideration.

I have attached a Rock Bottom Calculator that I and another diver came up with to help us understand Rock Bottom better when we first started reading about it.

-Z

 

[caruso]

If diving solo and one expected to breath the tank empty in an emergency, then one would want to start heading shallower from 100 feet when the SPG reads 45bar

Sure, but because I use my pony bottle in emergency gas planning considerations my "end of dive" gas limits will be less conservative from those. In other words, an emergency that results in a catastrophic loss of gas in the main tank is not going to be an issue, as at that point the main tank is no longer part of gas planning considerations, I will rely on the pony bottle for the remainder of the dive.

Edited to add: Solo diving to depths of 100' or greater on a single AL80 with no backup/redundant air source is NOT a good idea.

 

[Zef]

Sure, but because I use my pony bottle in emergency gas planning considerations my "end of dive" gas limits will of course vary from those. In other words, an emergency that results in a castrophic loss of gas in the main tank is not going to be an issue, as at that point the main tank is no longer part of gas planning considerations, I will rely on the pony bottle for the remainder of the dive.

I just recently started diving with a 3L pony bottle. I am carrying it for redundancy as I don't want to rely on my partner for an air source if things go south....as a Divemaster I find myself diving with some very experienced tried and true partners and some very inexperienced divers that don't always seems to have their head screwed on straight under water. The 3L pony gives an extra layer of security whether real or perceived and I am currently carrying it on every dive to get used to diving with it. I have fashioned something almost identical to Nomad ring bungees with a choker made from small loop of strong 6mm bungee to hold the upper bolt snap to the tank neck....so far it has been working great. I calculate that at an elevated SAC rate (20L/min for example) the bottle will give me an extra 8 minutes of air at 30meters in the case of an emergency.

My gas plan has me using my back gas based on my Rock Bottom calculations and shift to the pony in an emergency if my back gas consumption warrants it.

I have been practicing deploying, breathing off of, and restowing the 2nd stage from the pony bottle towards the end of my dives when I am shallower such as during a swimming safety stop.

-Z

 

[happy-diver]

Hey I can breathe from my pony reg clipped to my left shoulder with out unclipping

until I unclip it

that's me waving at a guy with a really big camera (looks like a spaceship) with my fingers
(probably looks more like a submersible)(or an alien)

 

[TheGraveyardDiver]

I didn't want to haul around a large bottle so I went with the 13 cuft mounted on my cylinder.

Depends on your air consumption and depth. I "practice" with mine frequently and I can come from 100 feet to the surface at a safe rate, do a short safety stop (which I'd probably skip in a real emergency) and still have a few hundred PSI left.

Anything smaller than a 20 is basically a "get you home" bottle and you won't have time to loaf around if you have to go to it for real. Nothing wrong with a 13 or smaller bottle, but you have to understand that if you have to go to it in a real situation, it's a "better than drowning" option only.

Me and my crowd generally use the "same day, same ocean" buddy system so I'm not concerning myself with having to share air with a buddy from my pony. If I have to go to my pony in a real scenario, my objective is to get to the surface safely, not share air. If my main and my buddies main both fail at the same time, I'd just write that off as a really bad day and an ungodly coincidence.

I hear all the time about peoples O-rings extruding, but I've only seen it happen once in my 20 years, and then a pony wasn't involved. We just shared air from my main cylinder to the surface.

 

[Eyegore]

I've been considering a pony rig. Alec Peirce talks about options in one of his vids and likes this one:
XS Scuba XTR Extra Air System 19 cu ft

I'll be doing solo dives in the future and will get a pony beforehand. Current set-up is a DiveRite Transpac XT with aluminum 80. Opinions/recommendations on a good pony rig would be most welcome.

 

[MaxBottomtime]