Pony rigs

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Re: Pony rigs

Postby divepirate » Mon Aug 19, 2013 11:04 am

so perhaps a comment from experienced divers in respect to a 'backup' air source would be good.
Something that can be used in the event that you are sitting at 30-40mtr's and your primary air source packs a 'snot' and your buddy is half way to the other side of the wreck or reef, finning in the opposite direction.

what is the best alternative other than to have to make an cesa (Controlled Emergency Swimming Ascent)..
(and risk DCS, Embolism, or other diving related injury).

By backup, I refer it to the IT Term Backup..
Some form or precaution taken to enable recovery in the case of catastrophic failure.
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Re: Pony rigs

Postby binklebonk » Mon Aug 19, 2013 12:54 pm

I never jump in for a <40 metre but >15 metre dive without at least a 40cuft (5.7L) BO tank. If I'm not going to be going over my NDLs then air (or whatever, that depends on what is in my tanks from previous dives) is all I take.

How much redundant gas is totally dependent on the dive, but I just don't see the point in anything smaller than a 40. You don't notice it in the water, it's a reasonable amount of gas that allows you a conservative response to a OOG situation and it's only a marginally increased cost to buy rather than a smaller tank.
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Re: Pony rigs

Postby Ulsterkiwi » Mon Aug 19, 2013 3:13 pm

no criticism taken, I enjoy the debate!

My final word. :-) And this in no way applies to you Ulsterkiwi, because you don't seem to dive this way. I think some divers might strap on a 3L pony and think "I've got redundancy" and find themselves at 35 metres inside a wreck. In this case I would suggest that the pony is not so much redundancy as a false sense of security.



I think your final word is very true. I have dived with a chap who carries a pony because he dives on his own a lot. Fair enough. His rig is set up so that he runs his BCD from a direct feed from the pony, THAT I find bizarre. His redundant air supply is getting used during the course of a normal dive..........go figure. At the back of this guys mind is "if it all goes to sh** I have another air supply" whereas in actuality what he has is something very different.
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Re: Pony rigs

Postby ChuckyBob » Mon Aug 19, 2013 10:47 pm

Ali Perkins wrote:
ChuckyBob wrote:In a wreck/cave a 3L may only give you the opportunity to run out of gas twice.


Haha you're cracking me up Greg! :-)


I can plagiarize with the best of them Ali!

I only ever dive CCR these days. I am happy to dive my rebreather with no bail out on a simple 10-15 meter dive. Below that I will always carry a separate bailout(pony) tank 5.7l in size with a minimum of 120 bar, but higher pressure depending on the depth. If its a deco dive then chances are the 5.7l tank will not be enough, and a deep bail out and a shallow bail out tank will be used. Probably a 10l and a 5.7l tank.
The key here is that if you clock up just a few minutes of deco time of CCR and then bail out to OC your deco time can increase dramatically.
But as Ali pointed out, if you are in a cave or wreck, not only do you need to get to the surface, you first need to get to the outside of the cave or wreck.

Always calculate for the worst case scenario.
Taravana cave for example. Its doable on a single tank. But what happens if that single tank bled dry due to a bust LP hose when you got to the back of the cave?

Its probably a 10 minute swim out at a minimum of 20 meters, at an elevated SAC rate due to constant swinging and a little panic. Thats 1000 litres of gas right there.And by the end of it you may even have some deco if you did it on air.

What about Canterbury wreck. Get a little disorientated. Bust LP hose, kick up some silt and cloud the exit. Panic somewhat, how many litres of gas is that?

Now how about if its not your gear that fails but your buddies?
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Re: Pony rigs

Postby ChuckyBob » Mon Aug 19, 2013 10:53 pm

Ulsterkiwi wrote:.........go figure. At the back of this guys mind is "if it all goes to sh** I have another air supply" whereas in actuality what he has is something very different.


You are right.

To me it does not make much sense.
The main issue is that most of the time his pony will not be fill as he has used it for inflation.
It may give him a few extra minutes on every dive but it does mean he has a second tank that needs refilling quite often.

On the other hand, it does require him to use and as a result test it on every dive.
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Re: Pony rigs

Postby Ulsterkiwi » Tue Aug 20, 2013 11:06 am

Taravana cave for example. Its doable on a single tank. But what happens if that single tank bled dry due to a bust LP hose when you got to the back of the cave?


exactly the reason I have turned down all three opportunities I have had to dive this cave, I did not consider that my available equipment was sufficient to cover all eventualities. Did others do the dive successfully on a single tank? absolutely! Would I like to do the dive? Maybe, if I got to do it equipped the way I think I should be.

I am honestly not trying to be contentious but I am aware that some will consider this way of thinking makes me a bit of a wuss, honestly, I don't give a stuff. If I am not comfortable I wont do the dive. All you have to do to understand my thinking is read any issue of the Dive magazine and the incident/accident section. There are any number of examples where analysis of what went wrong shows someone was uncomfortable or the level of equipment was inappropriate for the dive or a dive was begun and it proceeded beyond the plan originally intended.

Plan the dive, dive the plan. If you see something which grabs your attention outside of the plan, go back another time.
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Re: Pony rigs

Postby Ulsterkiwi » Tue Aug 20, 2013 11:23 am

On the other hand, it does require him to use and as a result test it on every dive.


thats a good point.

I would say though that there must be a better way to do that. I wonder how many divers practice using an octi or buddy breathing after their open water course?
GUE diving holds no interest to me but I do have to admire the frequency with which they engage in drills and practice the skills they consider intrinsic to their diving.

We are fortunate that our equipment is so reliable, given proper care and servicing and even more fortunate that the same equipment can be so forgiving when we do not give it proper care and servicing. I do not agree when people call SCUBA gear life support equipment (a discussion for another thread) but our equipment is all that separates us from serious harm or injury, why would you not use appropriate and functional equipment you are familiar with?

Maybe its easy for me to say take some time to practice these things. I dive a fair bit and therefore have more opportunity. At the end of the day the only person who has to do what I think is right, is me, and then there are times........
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Re: Pony rigs

Postby Ali Perkins » Wed Aug 21, 2013 6:14 am

divepirate wrote:so perhaps a comment from experienced divers in respect to a 'backup' air source would be good.
Something that can be used in the event that you are sitting at 30-40mtr's and your primary air source packs a 'snot' and your buddy is half way to the other side of the wreck or reef, finning in the opposite direction.


I have a couple of approaches to this...

My first is to dive as a team. This is very different to the buddy diving approach that I generally observe. When you properly dive as a team you don't find yourself in this position: "your buddy is half way to the other side of the wreck or reef, finning in the opposite direction". When you dive as a team, the gas your team mates are carrying becomes a genuine backup for you if you have problems - by maintaining contact and awareness amongst members of the team throughout the dive, this becomes a resource you can quickly tap.

Secondly I dive with manifolded double tanks as my redundancy. I like the stability, the gas, the ability to problem solve failures without necessarily having to abort the dive, and depending on the failure type even being able to access all of your gas. This does present differences to your single tank plus a pony method though - even if in only lugging the weight of the doubles around, but it goes far beyond this. You need to be regularly practising valve drills. The benefits of manifolded doubles are only realised if you can do valve shut downs - otherwise you're just carrying a big single tank.
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Re: Pony rigs

Postby Ali Perkins » Wed Aug 21, 2013 6:46 am

I have dived with a chap who carries a pony because he dives on his own a lot. Fair enough. His rig is set up so that he runs his BCD from a direct feed from the pony...


Yes, this is very curious. I can't find the logic in doing this. I presume he also has a regulator on the pony, and as he's running his BCD inflation from it, I would assume he therefore has his pony bottle turned on all dive. So there would also be the risk of losing gas via the regulator (accidental depression of the purge) during the dive. It's an odd one to me.
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Re: Pony rigs

Postby binklebonk » Wed Aug 21, 2013 5:50 pm

For $599 you could get a .5L tyre inflator masquerading as a back up..

http://www.splash.co.nz/shop/Scuba+Products/Alternative+Air+Sources/EXTRA-AIR.html

:lol:
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Re: Pony rigs

Postby ChuckyBob » Wed Aug 21, 2013 11:40 pm

What are people thinking when they buy something like that?
What are the sellers thinking when they sell it??????
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Re: Pony rigs

Postby Ulsterkiwi » Thu Aug 22, 2013 9:59 pm

ChuckyBob wrote:What are people thinking when they buy something like that?
What are the sellers thinking when they sell it??????


probably how much they are making like most business owners.......

Its like anything, if you have realistic expectations its one thing, trouble is many people will have unrealistic expectations for something like that bit of kit.
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Re: Pony rigs

Postby AndrewRawlingson » Tue Aug 27, 2013 3:34 pm

Ali Perkins wrote:
Ulsterkiwi wrote:I enjoy the added security of a redundant system with a meaningful amount of air for the depths I go to. I am also a more useful buddy with the ability to hand off the pony rig to others so thank you for pointing out that benefit!


I hope I'm not being too provocative by posting here (not my intention) but I was pondering the utility of a 3 litre pony bottle... instinctively it doesn't seem like much gas to me.

So I thought I'd do the maths:

Assuming a 3L bottle filled to 210 bar, you have 630L of gas.
Assuming a surface air consumption (SAC) rate of 20L/minute (a fairly normal diving breathing rate).
At 20 metres you will consume 60L/min which means your pony bottle will last 10.5 minutes.
At 30 metres you will consume 80L/min which means your pony bottle will last ~8 minutes.

Now assuming that if you're switching onto your pony bottle something is probably going wrong, so it is highly likely your SAC will be elevated, let's say 30L/min.
At 20 metres you will consume 90L/min which means your pony bottle will last 7 minutes.
At 30 metres you will consume 120L/min which means your pony bottle will last ~5 minutes.

It is my understanding that many people under stress will have a SAC in excess of 30L/min.

I guess I would conclude from all of the above that a 3L pony bottle has fairly limited utility. And if you were in a situation that someone required you to hand that over to them, well I'd hope they were making their way to the surface pretty promptly!

Anyone else care to weigh in with their thoughts - maybe I'm being too conservative?



The most important point is that a pony is bailout and it needs to suit you and the kind of diving you're are doing.

My SAC is around 10 L/min. In an out of gas situation, I would expect this to increase 2 - 3 fold, maybe more, maybe less. Switching to a pony should be a calm, controlled and well practiced procedure, like a twinset diver doing a shutdown. If you don't have these basic skills, then maybe you shouldn't be diving at all.

Even in your worst case calculation, 5 minutes is time to get to the surface from 30 meters in a safe manner and even if it isn't, I'd rather be bent than drowned.

A full 3 L pony carries the same amount of gas as a 12 L cylinder with 50 bar in it. I don't know what's so magical about 50 bar, but it puts things in perspective. I would say that a 3 L pony has plenty of utility for recreational dives (i.e. non-deco, non-overhead environment) to 30 metres and I would applaud anyone for carrying redundancy. What it doesn't do is make you invincible or allow you to defy the laws of physics.

As I said in a previous post, I carry a 6 L pony because it suits the kind of diving I do. Actually, it's a little excessive, but I'm sure you wouldn't be critical of that :)
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Re: Pony rigs

Postby binklebonk » Tue Aug 27, 2013 7:15 pm

Fair enough Andrew, but your calcs assume that you are the one needing the gas. Not everyone will have their shit together in a tense situation and be breathing at a moderate rate.

I have heard (possibly apocryphal) that many OOG situations arise from divers other than those you enter the water with. For a newbie in a freak out, a SAC rate of 75 isn't unreasonable to consider for calcs. IMHO.
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Re: Pony rigs

Postby divepirate » Tue Aug 27, 2013 7:29 pm

An example of this is something that crossed my desk the other day.

OOG diver inside a wreck gets 7ft reg hose from diver outside wreck.

Neither have any redundant air source, diver inside consuming Air at higher rate.
Both divers become in OOG situation.

You can't plan for the stupidity of others.
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