Pony tank
- Thread starter k954triniz
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
Sure, let's play that out.
Here is what the original post said about eating into the reserve on the primary gas supply:
In this case, you are at the bottom of the dive starting your ascent with 500psi (your number of 1/2 the reserve of 1000psi) or 600psi (his number) and a full pony tank.
You buddy has a single failure and his/her back gas is completely wiped out.
You, being the good buddy, give them the pony tank. I'm assuming that it would take a minute or so to sort that out so you are already eating into your 500psi of gas.
As the poster said, he generally doesn't take a pony on shallow dives so I'm assuming that this is a deeper dive and he is close to NDL.
Let me ask you: Would you really want to be on the deepest portion of your dive with only 500psi (or less) in your tank? Remember that you no longer have access to the gas in the pony.
Let's not forget that most regs have an IP of about 140psi to work.
So you have, what, 300 "usable" psi in a AL80 to get from the bottom of your dive, complete a safety stop, maybe have to inflate a SMB because if things have gone pear-shaped you are separated from other divers, ...
Just doesn't seem like a good idea to me.
- brett
Getting back to the original question, you’re talking about spare air not a “pony”, I wouldn’t ditch the octo for either a real pony or a spare air.
johndiver999
Contributor
I made the post because I think it is useful for people to think through these scenarios for themselves.
My risk tolerance might be different than other people, and I understand and accept that. To ask me what I personally feel comfortable with, is somewhat outside of my original intended discussion. I pretty much always dive with a pony, so I don't really have to consider the scenario where I plan on being deep, with a buddy who has no air and me having no pony. I just don't do that, it is too aggressive and makes me uncomfortable.
I have clearly stated that a reasonable assumption is that the dive should be terminated when the main tank is down to enough gas to get a person to the surface. In my case, I would donate the primary tank and then probably switch to the pony if I was concerned there was not enough air left in the main tank for both me and the victim.
Your assumption about 140 psi Intermediate pressure being unavailable is inconsistent with my personal experience. On the other had, assuming your spg is exactly correct is not so smart.
You are correct.
The travel gas is a transitioning gas, to / from the hypoxic bottom gas. Some divers are happy to descend on a hypoxic mix. However, as a general rule (I think) we are taught to use a travel gas initially to avoid the risk of blacking out initially when the PO2 is low and potentially the work load is high at the surface.
Irrespective of you descend or don't on the travel gas. The travel gas is part of the decompression profile.
I was trying to keep my explanation as simple as possible. Sorry if it was misleading.
As has been said, it is about peoples acceptance of risk. However, it isn't just about acceptance of risk it is also about the understanding of risk. An OW divers understanding is not as comprehensive as a diver who has completed an ADP course. Look at the fatalities that occur in caves, when experienced open water divers venture into cave systems!
Best practice is there, more often than not because of historical failures, and modifications of training and practice as a direct consequence. Often because people have died. Many of the things we teach are because of previous fatalities. Once upon a time we used to rely on buddy breathing! Now everyone carries an Octopus (or equivalent). Because it is safer and easier to effect a rescue using a second regulator than attempting buddy breathing.
If you want to extend the dive, then either switch to a twinset, and / or carry a stage cylinder. DO NOT misuse a Pony cylinder.
In my experience, single failures are seldom a problem for most divers to manage.
It is the incident pit that it is the issue, when problems cascade. The severity increases and the speed of the next issue increase. All of my scary moments diving have been when more than one 'failure' has occurred. Assuming you will have a single failure is a darwinian approach.
A pony bottle is there precisely to manage two failures, a gas issue and a buddy who is not close enough (or able) to render immediate aid.
Best practice is there, more often than not because of historical failures, and modifications of training and practice as a direct consequence. Often because people have died. Many of the things we teach are because of previous fatalities. Once upon a time we used to rely on buddy breathing! Now everyone carries an Octopus (or equivalent). Because it is safer and easier to effect a rescue using a second regulator than attempting buddy breathing.
If you want to extend the dive, then either switch to a twinset, and / or carry a stage cylinder. DO NOT misuse a Pony cylinder.
In my experience, single failures are seldom a problem for most divers to manage.
It is the incident pit that it is the issue, when problems cascade. The severity increases and the speed of the next issue increase. All of my scary moments diving have been when more than one 'failure' has occurred. Assuming you will have a single failure is a darwinian approach.
A pony bottle is there precisely to manage two failures, a gas issue and a buddy who is not close enough (or able) to render immediate aid.
Sorry if my reply sounded critical, it wasn't meant to be. I like your definitions. They are concise and make sense. I was just pointing out that a travel gas is also sometimes used during the surface -> descent portion of the dive.
Back to the original topic and OP, I think what many of us are trying to point out is that you should get proper training if you are going to add a bottle to your normal dive setup.
The type of training will depend somewhat on the way you plan on using that bottle (stage, pony, deco, etc) and what gas you plan to put in it, and the size.
I would try to take that class and understand proper gas planning for your intended use before you figure out what size tank to buy. It will greatly inform your decision. If you take a class, they will probably have tanks for you to rent before you go buy one.
Just one other note: generally, as the number and size of tanks and different gasses increase, the complexity of the gas planning is increased non-linearly.
- brett
Thats a good idea. On deeper dives going forward when I'm diving with any buddy I won't consider using the pony bottle to extend my dive. In fact that's usually what I do anyway because my buddies gas supply remaining will limit the dive to the supply of gas in their main tank using the typical reserve amount.
But again- I rarely if ever will accept a dive with an instabuddy- usually for the other common reasons (legal liability, an inexperienced instabuddy can totally screw up a dive, more likely to have different dive styles and I like to do my own thing and take videos without having to keep an eye out for a buddy, etc)
This is where my application of a "pony" gets vague.
I consider it my left cylinder while diving a single 80s on recreational, tropical dives.
I don't see the need for 2 80s but I'm not willing to give up redundancy.
The smaller cylinder is my designated emergency gas and yours is maintained in the larger cylinder with the long hose.
Without an emergency, it is never consumed.
I do use it to ascend on the last dive of trips and haven't needed half of its capacity.
FWIW I have surfaced with plenty who have nearly drained their only cylinder...
Sorry for not being clear. A pony is a small cylinder (in the UK generally 3 litres), an addition to the primary cylinder. The primary cylinder carries the "dive" gas. The pony carries emergency gas, which is not, under normal circumstances used during the dive.
How the pony cylinder is carried varies, from side slung, too secured to the back mounted primary gas cylinder.
Personally, when diving single cylinder rigs, I always preferred my pony inverted and mounted to the side of my primary cylinder. I know many prefer to carry it as a side slung cylinder. Generally, pony cylinders are only carried by those diving single cylinder rigs. Ultimately it's about convenience and personal preference.
I hate carrying a side slung if I can avoid it. That said, I almost always have a Ali'80 side slung on my left side because I predominantly dive CCR. So, even if I am shallow enough not to require the side slung, I am carrying it for an OC buddy.
Similar threads
