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Very Good Chuck but I think I have some valid points as well. I'm not a
tech diver. I am a very experienced diver on the verge of training to a
higher level of scuba.
1.. The type of dry suit that wear does not allow you to shut down tank
valves. I am a commercial diver first and have to wear a Viking because you
can fix it fast and will hold up to extreme diving conditions. In all my
years of running a charter operation, I saw VERY few diver could shut the
isolator down because of the thickness of the underwear needed to dive cold
water.
2.. I use the pony worn like a side mount rigged WKPP style and can be
give to another dive in trouble.
3.. The 30cuft pony is back to the surface gas in case of main stage
failure. (The pony is NEVER part of the projected amount of gas needed for
the dive.) I don't dive inexcess of being able to return to the 20' O2
surface supply or doing all deco on the 30. I don't do deco over 20
minutes, which is my personal level of boredom.
4.. To exceed the pony's capabilities of getting you back to the surface
would mean the use of doubles rigged properly.
5.. The dive skill level in the area is low (rec. level)and the water is
40* F on average year around. These 2 factors make it necessary for a
detachable system because of more diver and equipment failure. ( for the
record I've never used the pony but like I read here it gives me that warm
fuzzy feeling knowing it is there).
6.. I solo dive even when in a buddy team. I got myself into trouble I
will get out myself. I do a lot of high current(10+knots) & low vis (-10')
diving. Neither of these types of diving all be it not technical do require
a a lot of skill and diver independence.
7.. When I do get to the point in diving that a pony won't get me back
the surface after the catastrophic failure then I have to buy a suit that
will allow me shut down the isolator valve. I thought the OMS remote valve
was a good idea but the list cured me of that. If the opinion has changed
let me know.
8.. The way I rig to dive deep (140' deepest dive to date) is with a 125
and a 30. This is over kill for a 20 minute bottom time. The last time a
actually logged a dive like this I used an 80 for the main tank, used it for
deco, held on to a diving fatality and still had 1600 psi left in the 80.
9.. The use of doubles for my kind of diving would be extreme over kill.
I believe in the Hogarth religion if you don't need it don't bring it
Randy Sullivan
Sault Ste. Marie, Ont
sulteck@ic*.ne*
-----Original Message-----
From: CHK BOONE <CHKBOONE@ao*.co*>
To: techdiver@aquanaut.com <techdiver@aquanaut.com>
Date: Friday, January 23, 1998 2:25 PM
Subject: Pony Bottles
>
>Part of this is excerpted from some info I made up for someone off this
>list asking about solo diving. Thought it might be of interest in this
>thread .
>
>
>Pony bottles :
>
> For the solo diver the pony bottle really only serves as the wrong
>place to put a back-up regulator and imposes an irrevocable
>partitioning of your gas supply. A case of attempted back-up by
>simple redundancy that actually amounts to a system of independent
>singles too grossly mismatched to be managed as back-ups for each
>other. A poor back-up system in the final analysis compared to what
>else is available that provides for less drag, better reliability, and,
>usually, access to a greater supply of gas.
> The pony tank was more easily justified in the old days before SPG's
>to reduce the risks of running out of gas and has stayed with us as a
>cool looking option often used by guys who can't keep track of their
>status. How disappointing it is for the cool diver to find that those he
>intends to attract and impress see this thing as a "cute little tank"
>instead of the neat-o technical device he thinks of it as being.
>Actually I think women do this just to hurt our feeling. We only have
>one feeling, right ?
>
> The only situation where a pony bottle (completely independent gas
>supply system) is a better option over the Y valve on a bigger single
>tank for the solo diver is if you blow the tank to valve O'ring or a burst
>disc so that you loose everything in your primary supply - not
>impossible, but with decent maintenance, highly unlikely, and any time
>you are in a situation where you would not still be able to make a
>safely controlled ascent in such a case (a couple of final breaths as
>the tank drains during ascent and no need for decompression - or
>have a partner) should find you with isolatable manifolded doubles on
>your back.
> One reason the Y valve is more reliable from the standpoint of the
>system as a whole is that the pressure on the only two failure points
>that the Y valve does not cover (Oring & burst disk) is dropping as the
>dive progresses so that the odds of them blowing is much lower by the
>time you reach the point in the dive where a fast ascent becomes
>appreciably dangerous. The odds, small as they are, of these blowing
>in the pony tank will be higher till it is breathed down and, ironically,
>this potential failure is the only reasonable one that can justify
>partitioning of your gas into two totally independent supplies. Diving
>with a fear of running out of gas is not reasonable.
>
> I've never seen it happen but I'm sure loss of gas through a bad or
>extruded O'ring is not fast enough to prevent a reasonably safe ascent
>from recreational exposures and might even allow a safety stop. The
>burst disk on the Y valve can be modified in two ways to reduce the
>risk if its blowing - higher rating or plugging. I cant suggest
plugging
>because it may be against the law even for a private owner but a
>higher rating should still provide the intended protection in fires since
>the disk will melt and weaken no matter what the rating.
>
> If you need a back up regulator get an H or Y valve. If you need
>more gas get a bigger tank. If you need both, or more gas than a
>single can hold, plus more versatile emergency management because
>of dependency on functioning equipment for escape then get a set of
>doubles with an isolation manifold and learn how to use them.
>
> The real beauty of the isolation manifolded doubles is not the
>volume of gas available for the dive but the ability to easily manage
>what you have for a true and reliable back up system in any
>reasonable scenario (you are usually diving only to 3rds anyway).
>You don't have to use big heavy tanks for this, a pair of 50's or 63's
>would provide a lot more gas than a single 80 along with the best
>back-up capability presently available for open circuit (if you know how
>to use it).
> This small set of twins is a reasonable option for dives to the limit
of
>the accepted recreational range - but remember that a set of doubles
>does not qualify you for technical exposures.
>
> The one place the pony tank shines is when diving with a partner or
>group where the ability to hand it off is a useful advantage. This is a
>good option for a divemaster leading a group to have since he would
>not be tied up buddy breathing with a single diver when he needs to
>remain in a position to lead or manage the rest of the group at all
>times.
> Yes, this diver should have a partner to buddy breath with anyway
>but why not reduce the potential for problems it presents by preserving
>this divers independence long enough to get the group organized for
>an ascent (or whatever you decide to do). You don't want two divers
>preoccupied with sharing gas or pressured to get to the surface quickly
>when you are trying to communicate with everyone and stay organized
>as a group.
> This pony tank should have a clip that allows it to be easily attached
>to AND REMOVED FROM the receiver without having to hold it. The
>hose should be long enough to allow comfortable head movement and
>I like the idea of being able to wrap it around the neck.
> This is a scenario that would normally be played out among
>recreational divers and once implemented the dive is over anyway so
>that there is no need to try to rig this pony as a typical stage would be
>for a tech diver.
>Keep it simple, easily manageable by the unfamiliar, and comfortable.
>
>- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>Review
>
>A pony bottle does not allow you to get into that part of your supply
>unwittingly so that it actually functions much like the old J valve by
>warning you of low gas supplies. Useful if you tend to run out of gas
>by surprise, in which case you should certainly not be diving solo or
>deep. If you have a partner and are following Rule #1 why do you
>need a pony bottle when he is functioning as your spare air bearer ?
>
>The H or Y valve and the manifolded twins allow you to breath all your
>gas out with no warning so that if you are not monitoring your status
>(supply) you are no better off than with a single 80 with a K valve.
>Much worse if you stayed long and deep enough to need
>decompression stops.
>
>The pony bottle and the isolation manifolded twins cover the
>catastrophic loss of gas by burst disc or O'ring failure where the Y or H
>valve does not. But the odds of this failure become greater in the pony
>than the primary tank by the time one would need it for a safe ascent.
>
>A pony bottle can be handed off to another diver in an emergency
>making management of the situation easier and safer in many cases.
>It also allows a diver responsible for a group to provide gas to an out
>of air diver and still retain the ability to manage the group.
>
>A pony bottle is easy to take on a trip, but a Y valve is even easier -
>just put it on the tank you'll be using for the week. (I bought a
>complete isolated manifold and bands to make twins out of 80's or
>63's wherever I go).
>
> As a back-up for a failed primary regulator a pony actually forces you
>to shift to a lesser supply. So what you actually have done is turned
>what would have only been a failed regulator into a reduced gas
>supply as well, and paid for the privilege by dragging the weight and
>resistance of the pony tank around to boot. If you use a pony tank
>large enough to negate this factor you may as well make it doubles !
> The H or Y valves provide access to the complete supply of primary
>gas in the case of regulator failure. (one of the primary reasons not
>to dive independent twins)
>
> A Y valve is a little lighter weight and has fewer failure points than
>an H valve but faith in the H valve system at this additional potential
>failure point is high enough that the manifolds used by the best of the
>caving community use it with no qualms expressed. I believe the H
>valve is worth the versatility it allows if there is a chance you will use
it
>to make doubles - otherwise go with the Y valve.
>
> So! WITHIN RECREATIONAL LIMITS, if you feel the need to
>compensate for your inability or failure to keep track of your status, a
>total loss of primary gas (Oring / burst disk), or to make sharing gas
>easier and less restricting in a group situation the pony bottle may be
>the best bet. If you only need to back up failed regulators the H or Y
>valve is better and I see no logical reason to partition your gas supply.
>
> The only system you should use in any overhead or for
>decompression dives is isolation manifolded doubles.
>
>
>A little philosisifulsizing :
>
> The point of a pony bottle, "Y" valve, or any other such back up
>system should not be to "get you to the surface" AND the surface
>should not be treated as a place of refuge as far as dive planning
>goes. The point of these back up systems is to prevent being "forced"
>to the surface by providing a point or situation of refuge below a safe
>ceiling - to provide or maintain options that allow you to retain control
>of your status - to buy time.
> The reason the "spare air" is scoffed at is because it fails to do
this -
>you are still having to run for the surface though you have a better
>chance of making it if you happened to exhale just before you lost
>your gas or are choking / coughing due to aspired water.
> Often, how you configure, manage, and use a back-up system will
>determine whether it is just a bunch of gear that you use to keep you
>alive while you run for safety or an efficient system that guards against
>loss of control of your status by maintaining or providing options in the
>event of foreseeable failures or problems.
>
>
>Chuck Boone
>
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