50% Pony Bottle

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50% Pony Bottle

Postby Jason » Mon Apr 27, 2009 11:25 pm

Just wanna know what you guys think about ...
Using a 18L tank of Air or 32% Nitrox and having a 3L or 7L Pony Bottle of 50% nitrox for Safety Stops or as a bail-out :?:
Just drifting along with whatever is current.
Currently I'm reading : The Art of Innovation by Tom Kelley.
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Re: 50% Pony Bottle

Postby binklebonk » Mon Apr 27, 2009 11:45 pm

50% wouldn't be any good for a bail out much below 20m..

Why are you thinking of this possible configuration?
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Re: 50% Pony Bottle

Postby Jason » Mon Apr 27, 2009 11:56 pm

Buddy uses 50% in his Pony and it does sound good for a safety-stop agree.
But yes I am wondering about 50% from a depth and as you say - from below 20m.
Just drifting along with whatever is current.
Currently I'm reading : The Art of Innovation by Tom Kelley.
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Re: 50% Pony Bottle

Postby Xman » Mon Apr 27, 2009 11:57 pm

There are a number of potential problems with that as a set up, and few real advantages IMO. Stick with a bail out/pony that contains the same mix as your main cylinder unless you are going to be using 100% O2 for deco purposes would be my personal opinion, but there are others that have far more knowledge and experience than I do that might be able to give further advice.
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Re: 50% Pony Bottle

Postby Andy » Tue Apr 28, 2009 12:49 pm

What are you trying to acheive, Vampy?

Redundandcy and safety are not the same thing. As has been pointed out, 50% has safe MOD of 21m...... if you run out of gas below 21m, are you self-controlled enough to not switch to the pony? You may get away with it at 30m, you may not - oxtox depends on too many factors, but it's safe to say that you wouldn't want to rely on it.

To work out the "best" configuration, you need to be quite explicit about what you want to acheive.
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Re: 50% Pony Bottle

Postby Jason » Tue Apr 28, 2009 10:39 pm

Hmm.
Ok,
I haven't actually used it myself (yet?) but a buddy of mine uses this setup and is more than happy with it.
I believe he does use the Pony Bottle (50%) for deco-stops above the 20m mark (I'm presuming this but will follow through for certain later) which he (and I do in a way) believes helps prevent 'possible' DCS/DCI. I'm under presumption that doing a 18m stop and a 5m stop upon 50% is a hell of a lot better than with air - especially if the swell is up at the 5m mark.
Maybe I have missed something or mis-explained in why such a setup but it does sound ok to have rather than with a twin-setup...anyway what do you think Andy :?:
Just drifting along with whatever is current.
Currently I'm reading : The Art of Innovation by Tom Kelley.
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Re: 50% Pony Bottle

Postby Andy » Fri May 01, 2009 6:39 am

If the intent is to provide safety by either accelerating deco, or "more conservative" safety stops then fine. To be honest, though, IMHO the best way of avoiding DCS is just dive a little more conservatively and have a nice slow ascent rate.

Assuming you are not doing deco, and want to carry a richer mix for safety you should probbly weigh up the advantages and disadvantages of several mixes - 40%, 50%, 80% and 100%.

40% - not much less nitrogen than your 32% backgas, but doesn't require O2 clean tanks/regs.

50%+ will all require O2 clean tanks and regs, to be honest this is a PITA and (for me at least) only worth the additional expense if you are doing planned deco.

50% - lets you switch to your "safety gas" deeper, but that means you need a larger tank as you will be breathing from it deeper and longer.

80% - if you breathe 80% at 6m, you've got a fairly high ppO2 but also some leeway in terms of variation of depth. If you drop a metre or two, it's not going to push your ppO2 into the risk area

100% - you can do lots of 3min stops at 6m on a small O2 tank, a 3L pony would last you all weekend for sure. High ppO2, but if you are breathing it at 6m there is very little margin for error (which applies if you are breathing 50% at 21m - more later).


So, pick your gas and pick your stop depth that allows you to keep control of your ppO2 (how good your buoyancy control is perhaps is the biggest factor here: +/- 20cm on a stop depth should be your target.


Personally, for non-deco I wouldn't bother. GUE have what they call a "minimum deco ascent", which essentially is about controlling your ascent rate. If you are on 32%, a minimum deco ascent is probably as safe as a richer mix for conservatism, and it's cheaper and easier to implement. Just my $0.02 worth.
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Re: 50% Pony Bottle

Postby Jason » Fri May 01, 2009 1:09 pm

Wow :o theres a lot more to it than just 50% (+/-)
Thanks Andy - a very valuable 0.02c worth indeed.
A lot to consider and talk about with my buddy.
I agree, a slower ascent rate is the best policy conservately.
My bouyancy is above average but not excellent - though I do wish to learn the old method (pre-BCD days) of lung manouvering a bit more so.
It would be nice to have a good volume of water just across the road where I can spend time practicing and experimenting upon a lot of things. My dive time is focused upon enjoying what I get with a buddy for the short time available. (typical inlander curse)
Interesting indeed...
Just drifting along with whatever is current.
Currently I'm reading : The Art of Innovation by Tom Kelley.
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Re: 50% Pony Bottle

Postby ScubaDog » Fri May 01, 2009 9:03 pm

Andy's reply is one to read for this, very clear and well stated.

Unless you have a multi-gas computer, a pony with anything richer than the back tank is wasted for getting out of the water quicker. And the risk of something going wrong (although slim) with the mix is increased. Higher risk, for no real benefit.

A pony bottle is a get to the surface safely system (virtual buddy). Either a 2 - 3L cylinder, just filled it with Air, it does not take much to drop the pressure in the bottle over progressive dives, if there is anything else in it you will prob be reluctant to top up - cost or difficulty to fill). Air is the easiest to top up, anything else is tricky.

If you wanted to pad the safety stop use 32-40% Nitrox and breath the whole thing down. At least with 32% it can be breathed from recreation depths to the surface.

KISS - Air

Pony facing up - turned on all the time - less task loading
Pony facing down - turn on for the entry and turn off for the dive - turn on if you need it - minimal gas loss (but more task loading)

As a side line, very short emergency exposures to high ppO2 generally will not cause an instant hit. A LAR V oxygen rebreather rated for 6m, the table used to allow for a 5min (ish) exposure to 30m (ish). An assault swimmer at 6m with the choice of going through the screws of a tanker, or going deep. Most of the time he will come up.

KISS - Air
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Re: 50% Pony Bottle

Postby Xman » Fri May 01, 2009 11:51 pm

ScubaDog wrote:As a side line, very short emergency exposures to high ppO2 generally will not cause an instant hit. A LAR V oxygen rebreather rated for 6m, the table used to allow for a 5min (ish) exposure to 30m (ish). An assault swimmer at 6m with the choice of going through the screws of a tanker, or going deep. Most of the time he will come up.


But an assault swimmer is hardly representative of the physical condition of divers as a whole.
It is not worth risking an oxtox for no significant benefit IMO (in reference to this thread rather than the military diver).
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Re: 50% Pony Bottle

Postby binklebonk » Sat May 02, 2009 12:40 am

Xman wrote:But an assault swimmer is hardly representative of the physical condition of divers as a whole.


Or mindset... :shock:
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Re: 50% Pony Bottle

Postby justsimon » Sat May 02, 2009 11:50 am

Pony facing down - turn on for the entry and turn off for the dive - turn on if you need it - minimal gas loss (but more task loading)


Why would you turn it on for the entry only to turn it off again for the dive?
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Re: 50% Pony Bottle

Postby Andy » Sat May 02, 2009 11:58 am

justsimon wrote:
Pony facing down - turn on for the entry and turn off for the dive - turn on if you need it - minimal gas loss (but more task loading)


Why would you turn it on for the entry only to turn it off again for the dive?


I carry my pony on a sling, and generally it can free flow on entry - if it's pressurised but turned off, you can quickly lose all the gas in line and some regulators may then get water in the first stage. If it's on, this can't happen.

In the water, if it's on you can quickly lose all the gas from a minor leak somewhere. Generally,I keep mine off and feather the valve open every 5-10 minutes or so to maintain pressure.

Some regs work perfectly fine when flooded, others don't. I prefer the former on my pony bottle!
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Re: 50% Pony Bottle

Postby ScubaDog » Sat May 02, 2009 5:33 pm

Xman wrote:
ScubaDog wrote:As a side line, very short emergency exposures to high ppO2 generally will not cause an instant hit. A LAR V oxygen rebreather rated for 6m, the table used to allow for a 5min (ish) exposure to 30m (ish). An assault swimmer at 6m with the choice of going through the screws of a tanker, or going deep. Most of the time he will come up.


But an assault swimmer is hardly representative of the physical condition of divers as a whole.
It is not worth risking an oxtox for no significant benefit IMO (in reference to this thread rather than the military diver).


It was not a recommendation or a procedure to adopt, simply a little bit of interest on the side
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Re: 50% Pony Bottle

Postby justsimon » Sat May 02, 2009 6:53 pm

justsimon wrote:
Pony facing down - turn on for the entry and turn off for the dive - turn on if you need it - minimal gas loss (but more task loading)


Why would you turn it on for the entry only to turn it off again for the dive?

I carry my pony on a sling, and generally it can free flow on entry - if it's pressurised but turned off, you can quickly lose all the gas in line and some regulators may then get water in the first stage. If it's on, this can't happen.


Ah, I misunderstood. I couldn't understand why one would turn it on for the moment when it's likely to freeflow.
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