Pony Bottle Comments

[Brent Bowman]

Hi All,

I have been interested in pony bottles for awhile because I like to solo dive and thought I would share some experience that I have gained. When I was initially trying to research pony bottles online I noticed that there is quite a bit of discussion and back and forth about what size pony bottle you need. I mostly just shore dive here on the Big Island which usually involves some kind of hike across the lava and climbing up and down lava rock to get in and out of the water so I try to pack as little weight as possible.

I will start with the disclaimers hoping to ward off the inevitable criticisms that occur when you post online. First disclaimer is that I am claiming very little other than practical knowledge on the topic of air consumption and the methodology used to test my gear wasn't that precise. I just wanted to see what my pony bottle setup would do in real life so I would know if it was adequate for my application and be comfortable using it if the need arises. The pony bottle setup I tested today was a Catalina aluminum 13 cf bottle with a Sherwood pro valve and my pony bottle regulator is an Aqualung Titan LX first stage in DIN and the second stage is an Aqualung ABS octo. I mount the pony bottle on the back of my main tank and I have a pressure gauge on a hose so I can monitor the pony bottle pressure.

I tested the pony bottle from the max depth that I usually go to at my favorite dive site which is 92' at the green can in the Honokohau Harbor. I started at 92' with a good fill of 3200 psi, did a nice slow ascent over about 2.5 minutes to a depth of about 15', did a nice casual 3 minute safety stop and then ascended to the surface by the green can. At the surface I had a little over 1900 psi left in the 13 cf pony bottle.

Conclusions, starting with more disclaimers: I dive a lot so I'm pretty good on air, and there was no panic or time wasted before I started the ascent, but it appears that I can easily and safely ascend to the surface from 92' with the 13 cf pony bottle so it is going to be my choice when solo diving in shallower water. I felt good about trying out my pony bottle setup today and would encourage everyone to go test your pony bottle equipment so you have some idea regarding how it will work for you in real life.

Thanks for reading this,
Brent Bowman

 

[stepfen]

Congratulations to actively trying this.
Some things to consider:
- You seem to have consumed about 1300 psi (3200-1900) in your planned trial under minimal stress conditions. In reality if something goes wrong your consumption can easily double (or more). Hence you should expect to need about 2600psi for such an ascent, leaving you with a 600psi margin.
- You also started with a good fill (3200psi). In practice that will be lower. Especially since you mentioned that you dive often and with such a small cylinder, your pony's pressure drops with every use (just to charge it to check its' pressure is enough). Hence at a random dive you should expect lower starting psi, unless you DO top up your pony very often. Do you?
- Finally you haven't counted any time for problem solving at depth (which is the most gas demanding phase). Are you sure that your issue at depth with will be as simple as a "gas switch and go" type of issue?

Based on these, you might need to reconsider if this is the optimal size for your needs.

 

[MB NZ]

Congratulations on working out that you need the gas supply that you need, not what someone on the internet says you need. Also consider a typical recreational buddy team where one diver has OOA event and the other diver has half the gas that they started with in their cylinder (e.g. 12L). The amount of gas available to each diver is the same as that contained within a small pony cylinder (e.g. 3L). All other things being equal, in an OOA situation, I'd put money on a solo diver with a pony making it to the surface in a more orderly, safer fashion than a buddy team breathing off one SCUBA unit.

 

[Divin'Papaw]

Good on you for both doing your calculations and running a test. For anyone who does regular solo diving, it is very important to be very comfortable with your gear in the event of an emergency. Switching to your alternate air source needs to be second nature. Same thing with accessing your line cutter(s).

I regularly see divers in South Florida, primarily photographers, who are essentially solo divers but have zero redundancy. Nowhere near any sort of buddy but yet with no alternate air source. It always puzzles me. I'm never without my pony except on very shallow dives that are essentially just long safety stops.

Something to consider with a smaller bottle like your 13 cf is that you really need it full or nearly full for just about every dive. This is one reason I prefer a larger bottle. I also use by pony bottles (I own two AL40s) for occasionally adding car air to tires and for deploying my DSMB on most dives. While I've never had to use it as an alternate air source so far, it is slowly depleted from use dive after dive after dive. With an AL40, I am perfectly fine down do about half full or a bit less and I still have plenty of gas for an emergency.

I never need to have my pony bottles filled. I use one for about 6-7 months and then switch over to my other AL40 when the prior is ready for VIP. Then have the prior VIPed and filled and set it aside while I used my other AL40. I just rotate through them like that throughout the year.

Just something else to consider. It works well for me but YMMV.

 

[bradlw]

Congratulations to actively trying this.
Some things to consider:
- You seem to have consumed about 1300 psi (3200-1900) in your planned trial under minimal stress conditions. In reality if something goes wrong your consumption can easily double (or more). Hence you should expect to need about 2600psi for such an ascent, leaving you with a 600psi margin.
- You also started with a good fill (3200psi). In practice that will be lower. Especially since you mentioned that you dive often and with such a small cylinder, your pony's pressure drops with every use (just to charge it to check its' pressure is enough). Hence at a random dive you should expect lower starting psi, unless you DO top up your pony very often. Do you?
- Finally you haven't counted any time for problem solving at depth (which is the most gas demanding phase). Are you sure that your issue at depth with will be as simple as a "gas switch and go" type of issue?

Based on these, you might need to reconsider if this is the optimal size for your needs.

this is why when I retired by 13 pony for pitting, I switched to a 30 Cuft pony. I was constantly concerned about the short fills (<3,000psi after it cooled) and also with the pressure loss from just routine charging and test breathing before the dive, etc... Also the occasional free flow event during entry wasting a little bit of gas. It was often <3,000psi before a dive.
All of this is less of a concern if you have a fill whip and can top it off from a full fresh tank, of course, but that's a whole other thing to keep up with.

Considering though, that @Brent Bowman dives a lot and is diligent about knowing his kit, I wonder if the x2 safety factor is necessary. In my case, at that sort of depth, I would be heading up as a switch to the pony, knowing that my margin is tight. I'm guessing that he's thinking the same way. Still, I agree with you that it's a good gut check to consider that if you need the pony for real, you'll be panicked, maybe injured, etc.. and your gas demand will almost certainly be higher.

Anyway, while a x2 factor of safety is probably a great rule of thumb, maybe for an experienced diver going into this with eyes open and things well thought through, would a slightly smaller factor of safety be ok? (as a compromise) Maybe something like x1.5 or x1.7?

 

[davehicks]

I suggest a 40cf bottle that you sling from your BC. Since you are concerned about weight, this may work better. Before entering the water with all of your gear, just carry your pony, fins, camera to the waterline. Go back , gear, up, return with you full rig. Clip on the pony and go dive.

A 40 is also better because it is neutral in the water. It will actually weigh less than the 13 in the water. You won't even feel it in slung position and it won't impact your weighting.

 

[inquis]

Maybe something like x1.5 or x1.7?

I plan for 1.5x, but also 2 mins at depth.

 

[happy-diver]

Yeah a standard tank a Faber 100 and look at that massive 40 that you want to strap to yourselves

But I don't even know it's there???????

So the tank strapped to the back, and another on the front


Yeah from the stealth of a seal to the wallowing of a walrus


Without understanding the concept, destroying the freedom of recreational diving

 

[Brent Bowman]

Thanks everyone, I appreciate all of the great responses. Looks like I started a good discussion and elicited a lot of good info and opinions on pony bottles.

I did two dives this weekend with my 19 cf pony bottle while the 13 cf was getting filled and I felt that the few extra pounds difference in weight attached to the back of my HP100 tank made me more off balance when walking on loose lava and climbing down the rocks to get in the water so it made me appreciate the smaller 13 cf bottle more. Attaching the pony bottle to the back of my main tank is a convenient way to carry it but I want to try slinging it in front some time.

Check out the cool shark video I got with the 13 cf pony bottle last weekend, it was an exciting dive. You might have to cut and paste the YouTube link?

 

[Still Kicking]

Thanks everyone, I appreciate all of the great responses. Looks like I started a good discussion and elicited a lot of good info and opinions on pony bottles.

I did two dives this weekend with my 19 cf pony bottle while the 13 cf was getting filled and I felt that the few extra pounds difference in weight attached to the back of my HP100 tank made me more off balance when walking on loose lava and climbing down the rocks to get in the water so it made me appreciate the smaller 13 cf bottle more. Attaching the pony bottle to the back of my main tank is a convenient way to carry it but I want to try slinging it in front some time.

Check out the cool shark video I got with the 13 cf pony bottle last weekend, it was an exciting dive. You might have to cut and paste the YouTube link?

Excellent video - congratulations!