Is there a valid reason for a pony bottle

[MichaelMc]

Some have mentioned they don't dive a pony with single tank. I'd point out that many went on to say it's because if they want redundancy they use doubles or sidemount. That if they are using a single tank it really is a very benign environment FOR THEM, say above X feet in clear warmish water. But for their other dives, they have redundancy.

I'm amazed at the volume of posts that don't really answer the OP's question.

Yes, there are situations where there are good and valid reasons to dive with a pony bottle. There are three parts to the decision:

1. Whether a redundant air supply is necessary for a safedive
2. Whether a pony bottle is the best redundant air supply under the circumstances
3. What sizes pony bottle would be appropriate

There are many dives where some sort of redundant air supply is widely considered necessary to complete the dive safely. While some of these dives are outside the scope of the Basic forum, they are nonetheless worth brief mentions as part of a complete answer. The dives where redundant air is widely considered necessary include:

1. Cave dives
2. Wreck penetration dives
3. Decompression dives
4. Solo dives to depths beyond around 30-60 feet
5. Coldwater dives where regulator freezeup is a major concern
6. Buddy dives to depths beyond around 30-60 feet where visibility, the buddy's inexperience, other factors that could lead to buddy separation are present.
7. Dives with other risk factors, such as entanglement, or lack of reliable surface support,

Now, there are a variety of redundant air supply alternatives that have various pros and cons. The choices as I see them are:

1. Manifolded backmount doubles.
2. Independent backmount doubles.
3. Sidemount.
4. Use of an H-valve.
5. Pony bottle, either alone or in combination with any of the above systems.
6. Larger single cylinder.

I have used all of these except sidemount. They all have pros and cons. I find that I use manifolded doubles on most dives where I want redundant air, but that isn't a suitable strategy in all cases. Here's a rundown of the pros and cons.

Manifolded doubles (backmount). With proper training, these are widely considered the gold standard for redundancy, because they provide access to the full gas supply in the event of most equipment failures. They do require skill to use, and are heavy, and require equipment that is difficult to find on a rental basis, and are not permitted on many boats. Progressive equalization can be used in situations where the main concern is SPG monitoring or failure.

Independent backmount doubles. An alternative to manifolded doubles that provides a similar level of redundancy. No manifold is used, and a second SPG is required to monitor the second cylinder. The main advantage over manifolded doubles is that there is no need to source twinsets; ordinary AL80s can be used. Heavy, requires a suitable BC and a special regulator setup, and skills.

Sidemount. Similar to independent backmount doubles but lighter to handle since there is never a need to lift both cylinders at once while topside. I haven't used sidemount and will leave a more thorough treatment to people who have.

H-valve (or y-valve) For those not familiar, this is a setup where there are two valves and two 1st stages attached to a single cylinder. Usually a large cylinder, 117-149 cf, is used. Useful for dives where the main redundancy concern is equipment failure. Requires skill to use. The valves are harder to reach than for manifolded doubles. Lighter than manifolded doubles of the same capacity, compatible with any BC.

Pony bottle. What we're here to discuss, with various size and rigging options. When I use one, I sling it, because I believe that's safer and more flexible than backmounting it.

Larger single cylinder. Typically not considered "redundant air," but where the main concern is simply exhaustion of the primary air supply due to an SPG failure, or failure to monitor the SPG, or whatever (rather than some sort of equipment failure) it is an alternative to consider.

Now, considering all that, sure, there are situations where a pony bottle is the best answer. I do find that I prefer manifolded doubles, but it isn't always feasible to use them. A pony bottle is relatively portable and, unless deployed, can be used for multiple dives between fills. So you can use an AL80 or whatever that you've rented locally or that is provided by the boat, and augment it with a pony for redundancy. That's the most common use case.

Some divers use a pony bottle in addition to some other form of redundancy (such as manifolded doubles) for safety in the event of entrapment or entanglement. Doing so allows the alternative of abandoning the entire scuba kit and completing the dive with the pony alone. Careful attention to weight placement is vital, and overall, this is an advanced technique.

We've had endless discussions on the best size pony bottle to use. There is no single correct answer as it depends on the circumstances of the dive and the goals of carrying a pony bottle. I most often use an AL19, but not always.

I'm also going to quote part of Stoo's post which is insightful and worth reading in full.



If you've never been in water colder than 40 degrees, you probably don't realize what it's like.

This is a great post. There are several forms of individual gas redundancy. Pony is one of the simpler to add.

 

[barth]

1- My girlfriend doesn't always dive with me. On that trip I did every available dive (about 27) she did about 2/3 that amount. When not diving with her (or my siblings on other dive vacations) I prefer to dive alone rather than take my chances with an instabuddy. Even if the unknown buddy is a good diver, it's still inconvenient to have to keep track of where they are, let them know I want to go this way or that way to see something interesting, etc. It is without question that solo divers must have the redundancy in the form of an independent bottle. It's mandated by the solo diver certification and most dive ops will enforce if it they allow solo diving at all- which the Belize Aggressor 1V does.

Your awareness should be good. You should know where your buddy is. If you don’t know where your buddy is and you don’t communicate what you want to do the system don’t work. If your girlfriend is diving with you, you should also behave as a good buddy ;-).

2- Piece of mind. On a Cozumel trip a year or two back I didn't bring the pony bottle which is not typical for me. As I type this I forget why, perhaps I didn't expect to be doing much in the way of deeper dives, or there wasn't that much diving planned for that particular trip and I didn't want to bother lugging it around. Anyway I didn't have it. On one dive -think it was Palancar Deep-, I swam away from the group as I often do and was perhaps 30 years into a swimthrough and it suddenly occurred to me that if I had a catastropic failure of my regulator, or burst a hose I'd never make it back out and to the surface or to the group in time and it made me feel rather tense. Having that pony bottle allows me to enjoy my diving more because just knowing it's there allows me to relax when I'm off on my own.

If you are diving with a buddy you shouldn’t swim (to far) away of him. And your buddy should not let this happen. If something goes wrong with your buddy and he is out of gas that’s a big problem for him. The same for you, if you swim away from your buddy. It is a dangerous situation which you are creating by your own and your buddy accept this situation. Otherwise he was close to you.

3- I mentioned it earlier but just to round out this post and make it complete for those who didn't read the entire thread and to clarify what seems to be a confusing point- I typically "use" the pony bottle (without EVER taking a breath from it) as a reserve to my main tank gas which allows me to draw more gas from the main tank and surface with perhaps 200 psi or even less. That amounts to many hours of extra diving time over the years. Again I am not "extending the dive by using the pony", I am extending the dive because I am not surfacing with 700 psi in my main tank that will never be used.

I use my pony bottle for both. During most of the dive, its an emergency supply of gas. Towards the end of the dive, it becomes my primary reserve so I can draw the main tank lower. I've been told by others that my strategy is going to kill me some day because that's not how you're supposed to do it. The fact that I've got 2 completely separate supplies of gas and I almost always surface with more gas than any other diver on the boat doesn't seem to matter.

This can be a problem. For a 30 meter/ 100 feet dive I want 1200 liter of minimum gas.

If my buddy is out of gas I have 600 liter for myself and 600 liter for my buddy. If you have 400 liter in a pony and 800 in a single tank and both breathing from the single tank then it can be a problem. Before you are at the surface the single tank is empty if you both need 600 liter. Then you start buddy breathing from you pony or something like that.


If your buddy is using your single tank for breathing and you are breathing from your pony than your pony will be empty before you’re at the surface. If your single tank has 2 second stages you can switch to your single tank.


But actually, you don’t know how much each person will use. If I use doubles (with an open isolator), it is possible to share the gas between 2 divers until both tanks are empty. That is also possible when you’re using a single tank with 2 second stages. But when you’re using sidemount, independent doubles or a pony it is not possible share gas between divers and have the tanks empty at the time.


(The amount of gas is not the only important thing. If I do a cave dive in a team of 3 divers I use doubles and a bottom stage. The bottomstage is almost empty when the dive is finished. The doubles are 50% empty when the dive is finished. The reason for that is that it’s possible to share my gas in my doubles with another diver. It is not possible to share the gas in my bottomstage. )

 

[txgoose]

The same thing happened to Henry Cook, an experienced diver at the oil rigs last year.
Accident on Southern Cal Oil Rigs Dive

Care should definitely be taken so that we don’t repeat the mistakes of the many that have passed before us. A very sad story.

 

[lowviz]

Just a note on elevated breathing rates.
The RN did 'tests' on clearance divers, They compromised the equipment without warning and then measured the elevated breathing rates. Initially, divers where breathing something like 5 to 6 times their normal rate. This did drop in stages. The biggest drop was when the diver reached their first perceived point of safety, for some this was the first stop, for others it was the second, or the first gas switch.

Nice factoid. Do you possibly have a reference to this? I can't find anything.

I'm not calling you on it, totally believable to me. I would like the ref for gas planning purposes...

 

[grf88]

If you have practiced deploying your pony I see no reason that your breathing rate would significantly increase when you required it. It may go up some depending on the emergency that required it but not by a factor of 4 or 6.

 

[caruso]

If you don’t know where your buddy is and you don’t communicate what you want to do the system don’t work. If your girlfriend is diving with you, you should also behave as a good buddy ;-).

That's true, but I wouldn't leave her alone, this would only be during a group dive situation. I like to explore stuff, she doesn't. I get my little excursion, she's got the safety of the group nearby. It's not a best case scenario but it's the only way I'm going to get the opportunity to stick my head inside a few swim throughs or drop a bit deeper or whatever. Yes I will admit my need to explore will sometimes work contrary to being a good buddy and it's not a defensible position but that's probably a topic for another thread.

If my buddy is out of gas I have 600 liter for myself and 600 liter for my buddy. If you have 400 liter in a pony and 800 in a single tank and both breathing from the single tank then it can be a problem. Before you are at the surface the single tank is empty if you both need 600 liter. Then you start buddy breathing from you pony or something like that.

Yes that is one drawback to using a pony in this way. Since the remaining backup gas is split between two tanks it's conceivable the main tank would drain before the pony requiring buddy breathing off the single pony regulator for the duration of the ascent. If the pony empties first then it's no different as far as sharing gas from the main tank with an octopus.[/QUOTE]

 

[2airishuman]

Excellent writeup, one minor quibble. Larger cylinder isn't redundancy in any way, and I wouldn't consider it a way of addressing those problems you listed. If you aren't monitoring your SPG, a larger tank isn't a solution. The reason to use a larger single tank is if your SAC rate is so low that you are limiting your buddy's dive, or if your dives are gas limited when they could be NDL limited.

::shrug:: Maybe it isn't really redundancy. I guess it's a question of definitions.

One of the implicit "elephant in the room" thoughts during most discussions of pony bottles is that the pony bottle is there to deal with the diver who "doesn't monitor their SPG."

It is my observation that relatively few divers monitor their SPG. Those divers who have a relatively low SAC rate get away with it because their dives conclude for other reasons before they run out of air. Either their hour's up, their buddy or DM wants to ascend, or they reach their NDL. Divers who through a combination of inexperience and physiology have high SAC rates are the ones who run out of air.

A pony bottle fixes that, not because it's redundant equipment, but because it is a source of redundant air. You can put that same redundant air in the primary dive cylinder, and fix the problem with a lot less gear.

Now, it isn't always possible to get a cylinder of suitable size, because the industry has standardized on AL80s, and some places don't have any alternatives or can only offer you a short-filled AL100 that actually has 90 cf of gas in it, and so for people in this situation, having a pony bottle makes sense.

 

[Gareth J]

Nice factoid. Do you possibly have a reference to this? I can't find anything.

I'm not calling you on it, totally believable to me. I would like the ref for gas planning purposes...

I remember it from a presentation or after presentation discussion by Gavin Anthony Technical Manager for Maritime Life Support at QinetiQ Haslar. I don't think it was a surprise that an unexpected equipment failure escalated breathing rates. The thing I found interesting was the issue of differing individual perceived point of control. Once this point was reached, breathing rates dropped back to a normalised rate.

If you have practiced deploying your pony I see no reason that your breathing rate would significantly increase when you required it. It may go up some depending on the emergency that required it but not by a factor of 4 or 6.

From my understanding it was sudden equipment failure caused the candidate to escalate their breathing rate. The most interesting thing was the fact that differing individual had different points of perceived control. For some it was the first decompression stop, for others it was reaching the first bailout gas switch.

I don't know how they simulated this.

 

[BRT]

As both of you guys are based in areas where the water is cool, not cold, I'll cut you some slack....

In these parts, a catastrophic reg freeze-up is a distinct possibility for about 1/2 of the dive season, and a reasonable possibility for the rest of it. And before you dismiss this with a comment about "proper cold water regs" etc, bear in mind that I see this most often in relatively newer divers. Most of us that dive in Tobermory regularly and for an "extended season" wear doubles, or dive SM. It's not because we need the extra gas, it's because we want the redundancy of a completely separate reg and gas supply.

A pony is a simple "entry level" redundant system. When I was actively teaching, I encouraged students to include a pony and cheap, cold water reg as a "required" bit of kit.

To give you a specific example, last spring I was at one of our wreck sites, mid May. The wreck lies in 105' of water, but most of the dive would typically be conducted in 90' or so. Very much an advanced recreational dive. Water temp at the surface at the time of year is typically about 40°/4° and about the same at the bottom, although it can be as low as 37°/3° and it will never be above 42°/5° all year, other then when there's some weird current blowing through.

The morning we were there, there was a charter with I would say 8 divers on it. I didn't know them, but they were all in dry suits, so presumably "advanced" divers. Every single one of them froze up within 10 minutes of heading down. Thankfully, many freeze-ups happen on descent, when a diver makes the mistake of laying on their inflator and inhales at the same time. In those cases, typically, it's pretty simple to beat a hasty retreat to the surface. If you're watching from another boat, you can see the geyser of bubbles long before the diver rockets out of the middle of them. The odd person is completely freaked by the experience. Most are shaken. A few laugh it off, and once in a while, someone embolizes and dies. There was a 31 year old woman that embolized this spring after a freeze-up in 100'. She's been in a vegetative state ever since.

If the freeze-up occurs later in the dive, when the diver is say at 1000 psi and heading back to the upline, he's got a real problem, because that 1000 psi will blow through his regulator very quickly. Plus, he now has the added worry of a potential decompression obligation or close to it. Guaranteed their ascent rate is going to exceed 30 fpm and a safety stop isn't happening. Best case is that they have a near miss. Next best is a bend, and last, is they run out of gas in 60', panic and die. To quote our local Hyperbaric Physician, "We can fix bent. We can't fix dead."

Incidentally, when I worked in Tobermory, and before true cold water regs were really a thing (Other than the Blizzard) double fatalities were common and outnumbered singles. That was because of the proverbial "cascading events"... a freeze-up led to air-sharing which led to double freeze-ups and double embolisms. We lost 12 people in two years here. That was a long time ago, but my recollection is that ever one of them involved a freeze-up and most began with one.

Sorry for the long reply, but a pony and a second reg has the potential to end a serious event. It's not perfect, but it's a great help.

And no matter how well someone maintains their gear, a freeze-up is always possible. I had one at 170' a few years ago, and even with full redundancy in my doubles, AND a slung bottle of 50%, it's a puckering moment. It's great you can shut down one post, but if one reg freezes, the other one likely isn't too far behind, but it sure beats nothing!

I have been watching in warm water when a lady went head down into a hole and her air shut off. I see another guy around the dock who can kind of walk now. Same thing happened to him. I read recently on this board of a first stage failing off. Doesn't have to be cold water.

 

[NAUI Wowie]

I really can't see why cave diving has anything to do with "Basic Diving Discussion".

Back to the question:
There is NO right or wrong to bring a pony to a recreational dive. This is entirely a personal decision.
Nobody dies from having too much breathing gas in scuba diving.

Centrals are you currently in HK or are you in PI? Not trying to hunt you down or anything just curious if you are near Cebu or Palawan Coron