Pony Bottle / Stage Bottle / Decompression Bottle. What's the difference?

[EFX]

There is one scenario that is a distinct possibility in the diving I do, where carrying the alternate second stage on the back gas, in addition to a pony tank is necessary and valuable. I solo dive with a AL80, a 19 ft3 pony strapped to the AL80, a long hose primary, the alternate main second stage clipped to my right chest D ring, and the pony second bungied on my neck. I dive where there are other rec divers of all skill levels. If another diver goes OOA and I can get to him or her before their buddy then they get my primary and I instantly go on my bungied pony. Once things have calmed down I can switch to my back gas alternate second. My pony is strictly for an emergency when my main gas has failed. For me, there is no confusion. Having the additional second stage creates a safer enviornment for me and the OOA diver in this scenario.

to what benefit? You have already been on your pony so it has to be filled at the end of the dive. If the pony is sufficiently sized, then what benefit does switching to backgas have? Why do you feel the need to have that extra complexity in your rig, yet if we were in a cave or inside of a wreck, that configuration would not be allowed?

I agree with you regarding technical dives where there are multiple gases and having non-essential regs could cause confusion that could lead to injury or death by breathing the wrong gas. The dives I do are recreational so no multiple gases. The main reason is that it is inconvenient for me to have to remove the secondary main reg for solo diving and then have to reconnect it for other diving. On a deep dive where I need to share gas with an OOA diver and having to spend some time at depth getting things calmed down it's nice not to be limited to the gas in my pony. That's the benefit in having the backup main secondary ready to go. So, for me it's not making the configuration simple (which is not a concern for me) but having options to ensure my safety and those I'm saving.

I find it kind of odd that you advocate for not having an extra main secondary reg clipped out of the way when you, as a technical diver, have multiple regs clipped or stowed. You can manage multiple cylinders and regs but you have trouble with me managing one reg on the same tank. Hmm....curious.

 

[tbone1004]

@EFX so it comes back to one of my points that most pony bottles, including your AL19 as just stated by you, are inadequately sized to make a proper ascent from depth. If it was an AL40 then you wouldn't have to worry about it.

I find it kind of odd that you advocate for not having an extra main secondary reg clipped out of the way when you, as a technical diver, have multiple regs clipped or stowed. You can manage multiple cylinders and regs but you have trouble with me managing one reg on the same tank. Hmm....curious.

You are missing the point. With technical diving, you donate out of the mouth because it is always breathable, and you go straight to your second stage on the suicide strap under your chin *which is always breathable with very rare exceptions in very deep trimix mixes at very shallow depths. Since pretty much everyone is doing that on CCR these days we will pretend that doesn't exist*. We'll say that we are doing basic technical diving with a single deco bottle and no stages, so in an OOA situation you stay on backgas. When you start an OOA event, you have done sufficient dive planning to know that you both can stay on your backgas until you get out of the water. In your situation, you are saying that you have chosen a bailout bottle of insufficient size so you have to switch back to your backgas. At that point, you are adding unnecessary complexity to your OOA procedures. What you are proposing is not something that is every done in technical diving and has nothing to do with how we deal with OOA scenarios when using multiple bottles.

so again, why don't you switch to an adequately sized pony bottle and remove the unnecessary complexity of your current configuration as well as the gas-stress that you have admitted to having by knowing your bottle is too small?

 

[Doctor Rig]

PfcAj said:

• "A pony bottle is reserve gas, used on a recreational no-deco stop dive. It’s simply there for backup. 30-40 cuft seems adequate. Opinions vary."

Yes, "opinions vary". I've been told pony bottle size is a situational decision dependent on your dive. I'm guessing a 30 or 40 cuft tank would be a safe size for most dives, as previously suggested..

I recently took a Low Visability SDI course and within their eLearning class materials they said a 13 cuft tank is optimal size for a pony bottle. I'm really confused why SDI would make that generic statement.

• "An independent back-up air supply consists of a separate smaller scuba cylinder equipped with its own regulator. The size of the cylinder is dependent on the depth to which you are diving. An optimal size cylinder for most situations is a 13 cubic foot cylinder. These small scuba cylinders are commonly referred to as “bail-out bottles” or “pony bottles” They are commonly attached to the diver’s primary cylinder by means of a small bracket."

Does anyone have any idea why SDI would make a statement like this or justify it?

 

[tbone1004]

@Doctor Rig

can't speak definitively for SDI, but here's the logic.

Likely using 100ft depth limit, so 4ata's. 3 minute ascent at 2ata average depth, 1cfm SAC rate=6cf required for the ascent
1 minute at depth to resolve everything and start the ascent=1min*4ata*1cfm=4cf required for ascent
3 min safety stop at 15ft=3min*1.5ata*1cfm=4.5cf
Total with that rough math is 14.5cf, so 13cf is "close enough".

@PfcAJ and I use a very different method of rock bottom type calculations which is why we end up with 30-40cf and I usually recommend 40cf because they're more versatile and are the same negative buoyancy despite having a third more gas.

 

[markmud]

PfcAj said:

• "A pony bottle is reserve gas, used on a recreational no-deco stop dive. It’s simply there for backup. 30-40 cuft seems adequate. Opinions vary."

Yes, "opinions vary". I've been told pony bottle size is a situational decision dependent on your dive. I'm guessing a 30 or 40 cuft tank would be a safe size for most dives, as previously suggested..

I recently took a Low Visability SDI course and within their eLearning class materials they said a 13 cuft tank is optimal size for a pony bottle. I'm really confused why SDI would make that generic statement.

• "An independent back-up air supply consists of a separate smaller scuba cylinder equipped with its own regulator. The size of the cylinder is dependent on the depth to which you are diving. An optimal size cylinder for most situations is a 13 cubic foot cylinder. These small scuba cylinders are commonly referred to as “bail-out bottles” or “pony bottles” They are commonly attached to the diver’s primary cylinder by means of a small bracket."

Does anyone have any idea why SDI would make a statement like this or justify it?

Hi Doctor Rig,

I will take this question on. However, I don't know why SDI recommends 13cf, I can only speculate from my experience.

For most recreational dives in benign conditions and for divers having a good to very good SAC, a 13cf is more than enough to make a safe ascent directly to the surface! I was taught to forget the safety stop while on a "bail-out bottle" ascent. Do not under any circumstances swim u/w back to your ingress/egress point. You shoot your SMB and perform a controlled ascent directly to the surface.

During my solo training, I performed 3 simulated emergency ascents while using the same 13cf bottle, and no, it was not refilled between practice ascents. I ascended from about 65 -70 fsw. We shot our SMBs and performed manual inflation of our BC and changed our masks out while performing the simulated "bail-out-bottle" ascents.

I have done a practice pony bottle ascent using a 6cf from 90 ffw at Lake Tahoe at the Rubicon Wall. I have done a practice pony bottle ascent from 105 fsw from Scripps Canyon San Diego with the 6 cf bottle. 6 cf from those depths is not enough, although I broke the surface with hundreds of PSI left in the bottle and did a super slow, gradual ascent from 25 fsw to the surface. Way too close for comfort.

In solo diving, as I was taught, the pony does not extend your dive -- it is not part of any rule of 3rds calculation. Also, solo diving is not supposed to be technical diving. I believe SDI teaches that you perform a direct ascent to the big SCUBA cylinder in the sky. Then, resolve your other issues while breathing atmospheric air. That's what I was taught.

I would not rely on a 13cf "bail-out-bottle" for dives in restricted or no visibility conditions in the 40 to 100 foot depth range. No visibility diving below 30 feet is bordering on tech diving, IMHO. I would definitely resort to my tech training for that type of dive.

Another reason SDI may have published that recommendation is that a 40cf pony is a bigger PITA to travel with and to use. A small pony that is dived with is better than a 40cf bottle that remains in your garage. Even though the buoyancy characteristics are almost identical between a 6cf and a 40 cf! No, they really are!

Many on SB will proclaim that a 30 or 40cf pony is optimum. They usually are highly trained technical divers that resort to their technical experience and training, and seemingly reflexively think rule of thirds and think real and virtual overhead environments.

Just my 2 cents,
m²V2

 

[rjack321]

Ai Karumba, 13cf is pretty small for dives potentially in the 90-130ft recreational limits.

As weird as it sounds I brought a 13cf bottle into a sump for a cave dive as an O2 deco bottle once. I was planning on accumulating no more than about 10mins of deco given the conditions and it was 5 rope drops to get to the water. Hence the gas/volume choices

 

[RyanT]

Some folks here on SB have talked about using a 19 cf bottle or less for a pony because they you can fly with it. Outside of that reasoning, I don't understand the logic of using anything smaller than a 40 cf bottle for a pony. Perhaps clipping on that size bottle seems intimidating to those who've never used one? If so, all it takes is a dive or two with one to see that it's really quite easy. They actually aren't that heavy topside and they ride beautifully during the dive, basically like they're not there. Given the ease of it, why not take more gas?

 

[tursiops]

Depends on what they mean by "optimal." 13 is big enough to be useful, unlike a 6 or a SpareAir, but not big enough for all situations. If by "most situations" they mean 60 ft or less, then a 13 will get you to the surface at a not-fast ascent rate and allow a safety stop. From 100 ft you might not make it, even skipping a safety stop. And you can't fool around at depth before ascending with the 13.....you can easily use half the bottle in a minutes or two screwing around at 60 ft. IMHO a 19 is the minimum for 60 ft, so you've got a little slack, and a 30 for 100 ft. But since 30s are almost the same size/weight/cost as 40s, the 40s are a better solution...

 

[EFX]

@EFX so it comes back to one of my points that most pony bottles, including your AL19 as just stated by you, are inadequately sized to make a proper ascent from depth. If it was an AL40 then you wouldn't have to worry about it.

In your situation, you are saying that you have chosen a bailout bottle of insufficient size so you have to switch back to your backgas. At that point, you are adding unnecessary complexity to your OOA procedures. What you are proposing is not something that is every done in technical diving and has nothing to do with how we deal with OOA scenarios when using multiple bottles.

so again, why don't you switch to an adequately sized pony bottle and remove the unnecessary complexity of your current configuration as well as the gas-stress that you have admitted to having by knowing your bottle is too small?

@tbone1004, you are conflating two different issues. First, the AL19 pony I use is more than adequate for me to get to the surface from any recreational depth. If I'm on the pony gas I can't switch to my main back gas because it isn't available. In the scenario I cited my primary gas is available but I go on my pony while giving my primary to the OOA diver. When things settle down I can go on my primary gas using my alternate main gas reg. This is not complicated.

 

[RyanT]

When things settle down I can go on my primary gas using my alternate main gas reg. This is not complicated.

But even less complicated is having adequate gas and just staying on the pony.