Pony Bottles

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FWIW, Don't be afraid. This thread hasn't even been regulated yet.

1. Doubles have a manifold that extends across the top of the tanks. There is very little chance that something could be snagged between the tanks. If something snags on the manifold, you can reach it (reaching your valves and manifold is a drill that doubles divers practice, or at least should practice, regularly).

Tank mounted Bailouts, on the other hand, have a space between the tanks where something could get snagged. Even worse, you can't reach it.

Sling mounting the Bailout will allow you to detach it if necessary.

2. IMO, Combination Octos/Power Inflators are difficult to manage. You need to control your ascent from the same device that is supplying you with air. That means either non-horizontal positioning in the water or taking the regulator out of your mouth in order to dump. Not exactly something you want to do if your already on a backup.

Second, combining the Octo and the power inflator means that if they fail, you lose your buoyancy control AND your backup life support. Methinks that this is not the best solution.

Third, the Octo/Power Inflators that I've used breathe like Coke bottles. If I'm on a backup, I want it to breathe as well as my primary.

BTW, I started with a similar rig (Zeagle Octo+). I dumped it after trying a few ascents. Now my singles rig has a nice Apeks ATX 50 on a bungee around my neck. In fact, it is set up so that I can get the reg in my mouth without using my hands.

It didn't cost much to convert, and I am much happier and more confident that the backup will be there when I need it.
 
While Uncle Pug can be rough, and trust me, I know - I wore an Everlast punching bag sweatshirt for weeks!

Seriously, UP has been playing the diving game for a long time. Tech divers have seen it all, and that’s how GUE and DIR kinda got formed. It is the sum of many years of experience, mishaps, etc.

I too once bought into the idea that a PONY was/is the solution to many problems. Lets look at what your REALLY getting for your money:

1. Spare air
2. Annual maintenance of the tank
3. Maint of the reg
4. TASK LOADING

In the event of a serious mishap while diving, what your doing is adding 'fuel to the fire.'

Task loading (and you don't need to be a deep diver or tech diver to be subjected to task loading) is anything that you can add for a diver to do while ALREADY being stressed by a variety of factors, be they:

Cold
Fatigued
Too many items dangling off of BC
Complication of the rig
Confusion of too many regulators
Snorkels
Loss of mask

All it takes is the addition of ONE additional task to break divers back during an emergency.

This is where the beauty of DIR comes in...

I made EVERY mistake a 'newbie' can make - BC's, PONY's, etc. Believe me when I say, the latest fashion statement of your gear doesn't MAKE you a great diver. While it may LOOK COOL - it actually has nothing to do with diving.

The KEY to this PONY issue is TEAM WORK! You and your buddy need to be a unified team. Visual eye contact every couple of minutes (DIR states every 30 secs) is very necessary.

To have a PONY of any sufficient size you would need at least a 30 cu in bottle. Why not just add an AL40 to you rig and use it as stage or deco bottles?

There IS NO EXCUSE for NOT paying attention to YOUR (and YOUR PARTNERS) SPG while diving!! I can't stress this enough! Think about it - when is the last time you ran out of GAS in your car? Same thing in diving! PAY ATTENTION to your SPG and timer and you'll never have a problem.

Seems everyone missed this point!

If your worried about a LP hose failure or 1st stage failure, then switch from a K-valve to an H-valve. Redundant, and costs about $60 vs $350-400 for say an AL19 PONY with a halfway decent regulator.

Think about it...

As a GUE/DIR Instructor once told me "PONIES are for stables!"
 
Scuba446 once bubbled...

This is where the beauty of DIR comes in...


Does this mean you are back on the DIR bandwagon? Are you going to sell your BC? Can I bid on some of those d-rings separately?


To have a PONY of any sufficient size you would need at least a 30 cu in bottle. Why not just add an AL40 to you rig and use it as stage or deco bottles?


Would you please share with us the air consumption calculations you used as the basis for needing at least an AL30? Please include depth, SAC rate, etc,. etc.

Thanks,
Mike
 
Good article, but assume for a minute I’m a little slow, can you explain to me how it relates to sizing a pony (bailout bottle)?

Mike
 
Well, first, I know that a 19 cu in PONY isn't sufficient, because a very well versed GUE/DIR Instructor agreed as such, but, in all seriousness:

To calculate a SCR, start at one depth say, 33'. Note my air pressure (3000). Swim for 10 minutes. Note your air
pressure again. Say it's 2000 PSI. I have used 1000 psi in 10 minutes or 100 psi per minute at 33' ft. That would be 50 psi per minute at the surface now. So...at 66', I would use 150 psi per minute, 99' would be 200 psi per minute, and 132' would be 250 psi per minute.

But, I want to know how long my 19 cf pony bottle will last at a 15' safety stop?

15' divided by 33 (1 ata gauge) = .45 + 1 ata = 1.45 ata. Using my above SCR of 50 PSI per minute, I'm going to breath 72.5 PSI per minute at 15' (50 times 1.45). Therefore an Alum eighty from 3000 to 500 PSI equal 2500 PSI dived by 72.5 equals approximately 34.5 minutes at 15'

Now back to my 19 cf tank. That's one quarter of an alum 80 so divide 34.5 minutes by 4 which equals about 8.6 minutes of safety stop time. Not great - yeah, it might just get me by, but what if my breating rate IS accellerated? Stress? Task loading perhaps? Panic?

To get up from 99' to my safety stop would be 99' minus 15' equals 84 which should be 84 sec of ascent time (60' per minute). My breathing rate at 99' is 3.33 PSI per second (The above 200 psi/minute divided by 60 sec). 84 times 3.33 equals 279 psi of air to go from 99' to 15'. In reality, an SCR of 50 is a very high breathing rate. My AL19 will give me much more time at 15' because in all likelihood, I won't be performing any work.

So, in my opinion, its cutting it pretty close - by hey, thats me! When i selected the AL19, I didn't know anyhting about SCR or any formula's at all.

Not having the 'whole picture' about stuff such as this when I selected the AL19 is why I maintain its not adequate - or at least for ME!

And hey, live and learn about gear config is what this is all about. Both gear configs have their pro's and con's. But after trying both out, I found I liked the long hose better vs rec style and less bulk. What I didn't know was that zipeprs and pockets aren't always accessible just because they are ON a piece of gear! They may look useful - but I found while in a wetsuit (which I didn't have with me when I selected a BC) I can't bend my arms in a way as to GET to the zippered pockets. A glued pocket on my wetsuit would have been a better choice. Again, live and learn. There certainly isn't ANY DIR-ers or many divers I've seen locally with BP's and wings...in fact, I have only seen TWo divers toting them, and they all have been OMS IQ's and OMS wings.
 
Ponies are a vestigial left-over from the days of single outlet double manifolds, in case you hose the single reg, completely un-necessary in modern days when we have excellent isolation manifolds. It is an irrevocable separation of your gas supply, mounted on your back where it represents a huge entanglement risk. You can't reach it to ditch it, untangle it or open/close the supply valve, another huge risk. It is completely the wrong place for a back-up regulator, and since you cant reach it, you have to turn it on and leave it on during the dive where it can happily leak away unnoticed, again, a huge risk.

Pony bottles, and the invisible demons they are supposed to address, are used by the typical dive store interested only in generating sales and profits, and actually introduce bigger risks than they are alleged to address! The safety demons used
to sell these things are easily discounted and addressed by a bit of simple, logical thought.

1) If you are diving a single tank, you are, by definition, doing a no-stop dive with no overhead, which means at any
point during your dive you are free to make a direct ascent to the surface and probably not get bent. Where is the need for the additional expense and risk imposed by a pony? If you are using a pony bottle to change any part of that equation, you are a statistic looking for a place to happen. A buddy that is worth a darn removes even more of the "justification" for
a pony.

2) You have to buy a pony mount, a bottle (of limited size and actual utility, see below), additional 1st and 2nd stage and an additional SPG. In order to dive doubles you have to buy an additional bottle (of useful size and utility), a manifold,
an additional 1st and 2nd stage regulator and a set of bands. A iso manifolded set of dubs gives you *and your buddy* infinitely more rescue options. An AL40 contains a useful amount of gas, hung stage style it can be ditched or handed off,
is left turned off during the dive, thus assuring there is actually gas there "in the unlikely event" of an OOA, and can be used in infinitely more useful ways.

As the diver progresses and wished to get into staged decompression diving, the pony will end up on the floor in the garage or get Ebayed off to the next sucker anyway. A stage bottle mount consists of some cord, rubber hose and a couple hose clamps, and can be made for <$20. No-brainer.

Also, ponies seem to be the vehicle by which all kinds of baloney practices and mindsets get their foot in the door.
Most divers will begin to use their pony on every dive, and justify this use with any of a number of rediculous reasons.
This is typical of "the King and his new clothes". People who bought and use pony's defend their purchase and use with
great vigor, even in the face of overwhelming information to the contrary, another indicator to apply Rule #1 immediately.

I don't know how many times I have heard people tell the "I beat death again!" type stories because they went for their pony reg and it was either turned off or empty (used it on the last dive).

"When you least expect it, you're selected!"

Back mounted pony's should be going the way of the Dodo, as should those who advocate them. Instructors who use, sell and recommend them should be avoided like the clap. There is a much better, safer way. Back mounted pony bottles are a bad answer to a stupid question. If one must insist on carrying a pony it should, at very least, be carried stage style.

Use a set of iso manifolded doubles and/or a front mounted stage bottle. Anything else is simply mental masturbation.

A back mounted pony indicates, in no uncertain terms, possession of an entirely wrong mindset, and gives every reason to thumb the dive in the parking lot. When you hear some yak quoting the TDI manual where they advise filling the pony with 40% OEA "in case an un-planned decompression profile develops" run like a scalded dog. There are more smoking holes in that single statement than an Afghani outhouse.

More than you ever wanted to know about gas consumption:

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From the US Navy Diving Manual, Revision 4, Volume One, Chapter Three:

3-4.5.2 Respiratory Rate. The number of complete respiratory cycles that take place in 1
minute is the respiratory rate. An adult at rest normally has a respiratory rate of
approximately 12 to 16 breaths per minute.

3-4.5.3 Total Lung Capacity. The total lung capacity (TLC) is the total volume of air that
the lungs can hold when filled to capacity. TLC is normally between five and six liters.

3-4.5.4 Vital Capacity. Vital capacity is the volume of air that can be expelled from the
lungs after a full inspiration. The average vital capacity is between four and five
liters.

3-4.5.5 Tidal Volume. Tidal volume is the volume of air moved in or out of the lungs
during a single normal respiratory cycle. The tidal volume generally averages
about one-half liter for an adult at rest. Tidal volume increases considerably during
physical exertion, and cannot exceed the vital capacity.

3-4.5.6 Respiratory Minute Volume. The respiratory minute volume (RMV) is the total
amount of air moved in or out of the lungs in a minute. The respiratory minute
volume is calculated by multiplying the tidal volume by the rate. RMV varies
greatly with the body's activity. It is about 6 to 10 liters per minute at
complete rest and may be over 100 liters per minute during severe work.

3-4.5.7 Maximal Breathing Capacity and Maximum Ventilatory Volume. The maximal
breathing capacity (MBC) and maximum ventilatory volume (MVV) are the greatest
respiratory minute volumes that a person can produce during a short
period of extremely forceful breathing. In a healthy young man, they may
average as much as 180 liters per minute (the range is 140 to 240 liters per
minute).

3-4.5.8 Maximum Inspiratory Flow Rate and Maximum Expiratory Flow Rate. The
maximum inspiratory flow rate (MIFR) and maximum expiratory flow rate (MEFR)
are the fastest rates at which the body can move gases in and out of the
lungs. These rates are important in designing breathing equipment and computing gas
use under various workloads. Flow rates are usually expressed in liters per
second.

3-4.5.9 Respiratory Quotient. Respiratory quotient (RQ) is the ratio of the
amount of carbon dioxide produced to the amount of oxygen consumed during cellular
processes per unit time. This value ranges from 0.7 to 1.0 depending on diet
and physical exertion and is usually assumed to be 0.9 for calculations. This
ratio is significant when calculating the amount of carbon dioxide produced as oxygen
is used at various workloads while using a closed-circuit breathing apparatus.
The duration of the carbon dioxide absorbent canister can then be compared to
the duration of the oxygen supply.

3-4.5.10 Respiratory Dead Space. Respiratory dead space refers to the part
of the respiratory system that has no alveoli, and in which little or no exchange of gas
between air and blood takes place. It normally amounts to less than 0.2 liter. Air
occupying the dead space at the end of expiration is rebreathed in the following
inspiration. Parts of a diver's breathing apparatus can add to the volume of the dead
space and thus reduce the proportion of the tidal volume that serves the purpose of
respiration. To compensate, the diver must increase his tidal volume. The problem can
best be visualized by using a breathing tube as an example. If the tube
contains one liter of air, a normal exhalation of about one liter will leave the tube
filled with used air from the lungs. At inhalation, the used air will be drawn right
back into the lungs. The tidal volume must be increased by more than a liter to draw
in the needed fresh supply, because any fresh air is diluted by the air in the dead
space. Thus, the air that is taken into the lungs (inspired air) is a mixture of
fresh and dead space gases.

3-4.6 Alveolar/Capillary Gas Exchange. Within the alveolar air spaces, the
composition of the air (alveolar air) is changed by the elimination of carbon dioxide
from the blood, the absorption of oxygen by the blood, and the addition of water
vapor. The air that is exhaled is a mixture of alveolar air and the inspired air that
remained in the dead space. The blood in the capillary bed of the lungs is exposed to
the gas pressures of alveolar air through the thin membranes of the air sacs and the capillary
walls. With this exposure taking place over a vast surface area, the gas pressure of the
blood leaving the lungs is approximately equal to that present in alveolar air.
When arterial blood passes through the capillary network surrounding the
cells in the body tissues it is exposed to and equalizes with the gas pressure of the
tissues. Some of the blood's oxygen is absorbed by the cells and carbon dioxide is
picked up from these cells. When the blood returns to the pulmonary capillaries and
is exposed to the alveolar air, the partial pressures of gases between the
blood and the alveolar air is again equalized. Carbon dioxide diffuses from the blood
into the alveolar air, lowering its pressure, and oxygen is absorbed by the blood
from the alveolar air, increasing its pressure. With each complete round of
circulation, the blood is the medium through which this process of gas exchange occurs. Each
cycle normally requires approximately 20 seconds.

3-4.7 Breathing Control. The amount of oxygen consumed and carbon dioxide
produced increases markedly when a diver is working. The amount of blood
pumped through the tissues and the lungs per minute increases in proportion
to the rate at which these gases must be transported. As a result, more oxygen is
taken up from the alveolar air and more carbon dioxide is delivered to the lungs for
disposal. To maintain proper blood levels, the respiratory minute volume
must also change in proportion to oxygen consumption and carbon dioxide output.

Changes in the partial pressure (concentration) of oxygen and carbon dioxide
(ppO 2 and ppCO 2 ) in the arterial circulation activate central and
peripheral chemoreceptors. These chemoreceptors are attached to important arteries. The
most important are the carotid bodies in the neck and aortic bodies near the
heart. The chemoreceptor in the carotid artery is activated by the ppCO 2 in the
blood and signals the respiratory center in the brain stem to increase or decrease
respiration. The chemoreceptor in the aorta causes the aortic body reflex. This is a
normal chemical reflex initiated by decreased oxygen concentration and increased
carbon dioxide concentration in the blood. These changes result in nerve impulses
that increase respiratory activity. Low oxygen tension alone does not increase
breathing markedly until dangerous levels are reached. The part played by
chemoreceptors is evident in normal processes such as breathholding.

As a result of the regulatory process and the adjustments they cause, the
blood leaving the lungs usually has about the same oxygen and carbon dioxide
levels during work that it did at rest. The maximum pumping capacity of the heart
(blood circulation) and respiratory system (ventilation) largely determines the
amount of work a person can do.

3-4.8 Oxygen Consumption. A diver's oxygen consumption is an important
factor when determining how long breathing gas will last, the ventilation rates
required to maintain proper helmet oxygen level, and the length of time a canister
will absorb carbon dioxide. Oxygen consumption is a measure of energy expenditure
and is closely linked to the respiratory processes of ventilation and carbon
dioxide production. Oxygen consumption is measured in liters per minute (l/min) at
Standard Temperature (0°C, 32°F) and Pressure (14.7 psia, 1 ata), Dry Gas (STPD). These rates of
oxygen consumption are not depth dependent. This means that a fully charged MK16 oxygen bottle
containing 360 standard liters (3.96 scf) of usable gas will last 225 minutes at an oxygen
consumption rate of 1.6 liters per minute at any depth, provided no gas leaks from the rig.

Minute ventilation, or respiratory minute volume (RMV), is measured at BTPS
(body temperature 37°C/98.6°F, ambient barometric pressure, saturated with
water vapor at body temperature) and varies depending on a person's activity
level, as shown in Figure 3-6. Surface RMV can be approximated by multiplying the
oxygen consumption rate by 25. Although this 25:1 ratio decreases with
increasing gas density and high inhaled oxygen concentrations, it is a good
rule-of-thumb approximation for computing how long the breathing gas will last.

Unlike oxygen consumption, the amount of gas exhaled by the lungs is depth
dependent. At the surface, a diver swimming at 0.5 knot exhales 20 l/min of
gas. A scuba cylinder containing 71.2 standard cubic feet (scf) of air
(approximately 2,000 standard liters) lasts approximately 100 minutes. At 33 fsw, the diver
still exhales 20 l/min at BTPS, but the gas is twice as dense; thus, the
exhalation would be approximately 40 standard l/min and the cylinder would last only half as
long, or 50 minutes. At three atmospheres, the same cylinder would last only
one-third as long as at the surface.

Carbon dioxide production depends only on the level of exertion and can be
assumed to be independent of depth. Carbon dioxide production and RQ are
used to compute ventilation rates for chambers and free-flow diving helmets.
These factors may also be used to determine whether the oxygen supply or the
duration of the CO 2 absorbent will limit a diver's time in a closed or semi-closed
system.

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Boiled down to gravy for SCUBA divers:

1 Liter = 0.03531467 cuft
1 cuft = 28.31685 liter

Go to 33 feet, mark your time and pressure on a slate. Stay still for ten minutes at the same depth.
Record how much pressure you used.

Now, mark the time and the pressure again, and swim normally for ten minutes at 33 feet.
Record how much pressure you used.

Let's say:

95 cu ft bottle @ 2400 PSI

95/2400 = .0395 cuft per PSI

Let's again assume you dropped 200 psi in ten minutes at rest .0395 X 200 =
7.9 cuft used at 2 atm.

7.9/2 = 3.95 cuft used at 1 atm

3.95/10 = .395 cuft per minute SAC at rest, at 1 atm.

Say you used 400 psi during the swim.

400 X .0395 = 15.8/2 = 7.9/10 = .79 cuft per minute working SAC at 1 atm. Now, remember this number can change drastically
in the "bad" direction as temperature goes down and work load/panic/stress/hangover factor goes up.

Take your working SAC, multiply by the depth in ATM, and you get the amount of gas you *probably* need for that portion of the dive. Double or triple it for safety and for your buddy in case of a complete gas supply loss.

You would use the at rest SAC to determine deco gas requirements.

And, of course, all this changes from day to day, dive to dive.

The Navy notes 2.5 cuft per minute, swimming against a 1.2 knot current, and this was calculated using a very fit young diver:

99 fsw = 4 ATM

2.5 x 4 = 10 cuft per minute, which makes a 13 or 19 cuft pony a joke that's not funny if things go seriously wrong.

I have seen a new diver (father and daughter, dad was freaking) go through an AL80 in 9 minutes, and our deepest depth
was 60 feet.

Best is to do this several times, over several dives, and for different (longer) lengths of time. After a while, you will
get a realistic window of your average SAC rate.

Scott
 
As someone who recently switched over to using a slung 40 cu ft bail out from a back mounted 20 cu ft "pony", I think most would be surprised how little you notice the 40 when you have it slung right. Just my O2.
 
Birdman once bubbled...
As someone who recently switched over to using a slung 40 cu ft bail out from a back mounted 20 cu ft "pony", I think most would be surprised how little you notice the 40 when you have it slung right. Just my O2.

Yep.

When you get it sorted out, they follow you around like a little puppy.

Scott
 
I dive with a pony and love it. Its back mounted and I think that works just fine for me.

I dive mostly solo sometimes on a 123cuft single with a 20cuft Pony and I find it works very good for me. I consider it to be my buddy, its always there and is throughly depenable.

To answer a couple of questions that I have read here concerning pony's - there are centainly alot of debate - mostly against. I respect your point of view, but and this is a big BUT, what works for you and your type of diving ... does not work for everybody, otherwise we would all be (dressed in black) DIR drones - if you believe what the DIR gurus have to say (not a big fan of DIR).

I don't find I have any bigger danger of entaglement with a pony than I do with doubles - here our bigest entanglement danger is fishing line which has an amasing habit of sliding down between the tank and the BC.

On the dive I don't have my Pony turned off, it is on all the time - a simple leak check at 5m on decent will identify an leak issues (pause at 5m lean back look up pause the breathing cycle after exhaling and look for a stream of airbubbles). if found either return to the surface to sort it out or turn off the pony until, if and when it is required (I have my pony mounted unside down, so I can reach the knob). It also pays to leak check several times during the dive.

The old saying of plan your dive and dive your plan, works very well here, with a single tank, solo dive if the crap hits the fan and for what ever unlikly reason I have an OAE all I require my pony to do is get me to the surface.
 
https://www.shearwater.com/products/peregrine/

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