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lots and lots of internet bollocks spouted on this subject.
would a 3L pony be my first choice for redundancy when bimbling about? not really, I'd go for indie 9's or 10's as they are more balanced and give you a lot more gas than a 12L/3L pony setup but if you already have 12L single and want to add redundancy a 3L pony is fine.
700L of gas lasts me 20 minutes at 20m, on a 6m stop I'll get 45 minutes of hanging around getting bored out of it, just how much of an independent reserve do you really need for shallow no stop or very limited deco dives?
do you really want to lug about an ali 40 on every dive you do? A 3L is small enough to just have with you without noticing it's there.
And if you do go deco diving with a twinset later on you can do a LOT of diving with a twin set and a 3L full of 80%. I used that rig to do a lot of dives that you now seem to 'need' a rebreather and two stages to do.
I just know how tightwad a northern spark will be and not wanting to spunk money ...
I made the pony mistake back in 2004. I currently use it as an O2 cylinder at home. great for when i have the flu ...
Originally Posted by Spirit of Guernsey
Fine so in your opinion it perfectly acceptable for me to calculate bailout on the following bassed on a 40 SAC & a 30% reserve:
AL80 (11 ltrs)
Buuuuuuuut not on a 3ltr?? Can you explain why the gas laws change when using a 3ltr?
Mine is used for training people to launch DSMBs with a reg up the underside (so if it all goes to the dogs, the pony gets dragged off to the surface rather than the trainee), occasionally as a suit inflation cylinder and most often of all, it is a superbly portable air source for topping up the car tyres.
Originally Posted by drysuitdiver
No, you can do 50% of the above, or at best 66.7%, unless you're diving solo.
Originally Posted by MikeF
Because as soon as you use the thing for deco, you're using it to extend the Dive and it's a team resource.
Running a 3 for deco is a totally diferent subject but for the sake of discussion (as someone who's run a 3ltr of 02 hundreds of times for deco)
Originally Posted by Ian_6301
I am struggling to understand this bit?
A 3ltr of 02 at 325 bar is 705ltrs 02
At 6m on deco for me I average about 10lpm but I gas plan on 15 so at 6m that's 24lpm and I get a smidge under 30mins at 6 on o2? SO say max 20mins with reserve but frankly my reserve is in the SAC being 15 not my usual 10.
If i have a dive with 15mins max on 02 at 6? I would use a 3 and have done many many times
My dover bailout strategy was reg on 02 supply for CCR 3ltr and a single deep bailout tin say a 7 of 18/45
Done 30-40mins deco ascent like that many times
As said you do the math on the gas requirement then you chose the tank to go round the gas.
If I find I need 200bar in a 3 yet I decide to run the equivalent 50bar in a AL80 I am a idiot
If I need 200 bar in a three and decide to take 200 bar in an AL80 frankly I am over kitting adding kit stress and making the dive more dangerous.
Wed larf at someone doing a no deco 30m dive in twin 20s and saying its required, but that's a fair comparison.
Loving the Stressed SAC rate of 40Lpm ...
try doubling that for a massive amount of people and you would be close .
move on nothing to see ,
Last edited by gobfish1; 16-04-2018 at 09:23 AM.
None diver as of 2018.
A few years ago, when I was new to diving and even newer to diving in the UK, I used to think that a PONY would be the answer to the redundant gas requirement. When thinking it through, for me it was obvious that it's a very specialist piece of kit that only works in a narrow range of scenarios. It became obvious to me that a PONY+regs would cost the same as a twin cylinders + regs but wouldn't work as well.
Moving forwards that few years, I honestly have never understood why people choose the PONY option when a twinset -- of any description: manifolded, independent (twindies), sidemount, small or large cylinders -- works so much better across a wide range of different scenarios.
Personally I think they're indicative of an old-school attitude to diving and would urge you to look at the alternatives -- even diving on singles with a better set of team-oriented buddies.
Pros of PONY:
* Provides limited emergency gas in case of a total failure of your primary gas source
* Costs and pretty much weighs the same as a twinset
* Awkward balance of your single rig
* Awkward hose routing; difficult to re-stow
* Gas and regulators aren't used except for testing prior to every dive
* Very limited gas available
* Cannot see the gauge - generally they use button gauges
* Must ensure it's turned on before every dive
* Not designed for sharing - PONY's an acronym for Piss Off Not Yours
Assume 200 bar x 3 litres = 600 litres of gas available (you breathe from it on each test)
Assume an elevated SAC of 30 bar/min
Assume a 30 metre clusterfuck....
2 mins on the bottom is 30bar x 4ATA x 2mins= 320 bar (that's over half the gas used -- you'd better get the hell out of Dodge...)
5 mins ascent - lets say average of 10 metres = 30 bar/min x 2ATA x 5 = 300 bar (oops, you've emptied the tin)
The point is that PONYs are small, somewhat too small.