Pony or twin - what's safer, better...

[furmirek]

"The alternate air supply" required for some reasons/organisations seems to be a must. The question appears immediately : add 4liters pony or switch to twin (even 2x8liters) ? I am tending to ss backplate and IMHO twin would be better. What do You think ? Any ideas, pros ?

[Kestrell]

"The alternate air supply" required for some reasons/organisations seems to be a must. The question appears immediately : add 4liters pony or switch to twin (even 2x8liters) ? I am tending to ss backplate and IMHO twin would be better. What do You think ? Any ideas, pros ?

This is a question tailor made to start a flame war.

There are some strong opinions on pony bottles.

Each set up has its pro's and cons. It is more important to be familiar with the set up you dive and to use the correct set up for the dive you do, as there is no one gear configuration that is superior to all others in all situations.

[wedivebc]

"The alternate air supply" required for some reasons/organisations seems to be a must. The question appears immediately : add 4liters pony or switch to twin (even 2x8liters) ? I am tending to ss backplate and IMHO twin would be better. What do You think ? Any ideas, pros ?

I think that is a very good question. Pony bottles are good for compact travelling but my personal preference is that dual tanks are nicer to dive as far as trim and stability is concerned.
I would not be concerned about the flames. It seems the people with the least knowledge flame the loudest.

[MechDiver]

Having used both, I would also suggest twins unless this is a one shot deal. Twins are somewhat more expensive.

MD

[Kestrell]

It seems the people with the least knowledge flame the loudest.

Very true.

[ScubaDadMiami]

You will have more going for you by using double tanks with an isolator manifold than you will by adding a pony bottle to a single tank. With doubles, you can always shut down a problematic regulator and still have access to all remaining gas in your tanks. If you are having problems with just one tank, you can isolate the tank and breathe the remaining gas in the other tank, which is likely to be a larger volume than you are carrying in the pony bottle.

Once you start adding deco bottles to the scenario, an extra pony bottle will become even more of a hassle to carry around. Better to start with a diving style now and keep with it than to do something now and change later.

[Paul Evans]

With doubles, you can always shut down a problematic regulator and still have access to all remaining gas in your tanks.

Could you please explain this :06:

[John C. Ratliff]

I think this type decision is somewhat dependent upon the type of diving you are doing. If you're diving less than 33 feet, you probably do not need an alternate air supply. Simply surface. If you are diving between 33 and 66 feet sea water, it would be good to have some kind of alternate air supply to get you to the surface. A pony bottle, or even (heaven forbid, a spare air), would do the trick here without overhead hazards. I have some doubles, and really enjoy their fit and feel. I use one set with a manifold that provides for duel regulators, and sometimes mount a double hose regulator on the center mount (older, Sherwood style), and a single hose as a backup. I also dive twin 50s with a regulator with an octopus, and don't worry about the duel function. The vast majority of my dives are less than 33 feet, however.

The DIR people are very specialized, and dive deep, decompression dives in wrecks or in caves. Here, the twins with two regulators, separate SPGs, etc., are excellent choices. But do not be deceived; DIR divers who dive this way do so because they cannot simply surface! To do so risks life-threatening decompression sickness unless they complete their staged decompression. Usually, they do not dive from a boat or shore facility that has a recompression chamber (a must for decompression dives by some authorities--JY Cousteau and the US Navy, for instance). So they must, absolutely, have a dependable alternative. However, they are on the "cutting edge" of safety, and something as small as a malfunctioning mouthpiece can mean the difference between life and death. This is not "sport diving" in the sense of the word I know, and IMHO should be avoided unless you really, truly have a very, very good reason for doing this kind of diving.

SeaRat

[^*^BATMAN^*^]

Could you please explain this :06:



he means that if you are diving to the DIR type of diving(i think, im not sure if this is true) that you have a regulator on either valve, so if you have a freeflow, you can turn off one tank, but because the tanks are connected beneath the valves, you have access to both tanks through on reg.

http://www.bitz.fsnet.co.uk/images/isomanifold.jpg

as you can see here, the DIN valve is above the connection between the two tanks, if you dont quite understand, maby someone else can provide a more easily readable explination.

P.S- about isolating the tanks, i dont know what could happen to the tank, but hte valve in the center of the manifold is so you can isolate the tanks so they are seperate

[tamorgen]

Not to contribute to the flame, but I think what is better really depends on your situation. I think the arguement for twin tanks is very strong, in fact, I dive twin tanks myself sometimes. However, twins are not suited for all types of diving, or all dive centers to be more precise. My dive shop in Columbia, MD is very conservative for the most part. There are a few rebreather divers, but almost no one who shows much interest in any sort of tech diving. When I dive with them, I tend to dive with a pony, because that's what is accepted. Some of the instructors and trip leaders frown upon twins simply because they believe its "tech".

Of course the other disadvantage to doubles is cost. To begin with, if you dive twin, you are most likely going to have steel cylinders, which are much more expensive than AL anyway. Then you have to buy the manifold and bands to connect the tanks. You also need two first stage regs and at least one second stage for each. You can easily spend $2000 + on a twin cylinder setup at $400 a tank, plus the regs & manifold.

Pony bottles are significantly cheaper. Even a steel 20 l tank is less than $200. AL are usually less than $100. You can also through on a cheap reg on a pony and not be too worried, unless you are careless and start using your pony bottle as your reserve supply. You don't need a high performance regulator to simply accend out of an out of air/equipment malfunction. A simple sherwood piston reg is fine for this application. All told, I can't see why anyone would spend more than $500 on a pony setup, unless they are a tech diver and insist only on the $1000 titanium regs for all of their cylinders.

Just my $0.02. Feel free to correct me if any one feels my comments are wrong.

[MechDiver]

When I dive with them, I tend to dive with a pony, because that's what is accepted. Some of the instructors and trip leaders frown upon twins simply because they believe its "tech".


It sounds like you need to find a shop that knows its the 21st century, and a new bunch of dive buddies.

Doubles may indeed imply tec, but they are not tec by themselves, that takes much more. Tell your buddies safety and common sense should overrule ignorance.

MD

[tamorgen]

MechDiver, I agree almost entirely. They are behind the times a bit, and there are other scuba shops in my area who criticize them for being that way. They just don't like to take risks. The dive shop owner from what I'm hearing is finally trying to get certified as a "Advanced Nitrox" instructor by TDI, but that is as far as he wants to go. Unfortunatley, to do any sort of tec diving in my area, I have to travel about an hour and a half to the one store in my area that even participates in PADI's new tech program. I wish I had another option, but there's little I can do to change my stores mind aside from becoming a tec instructor myself and getting the owner to recognize the rewards of more technical diving.

[idratherbediving]

i dive doubles and dont consider myself a tech diver , yet. i am fascinated by "tech" diving and when i feel i am ready to spend the money on the gear and training, i will pursue it. right now, however, i still see the benefit of diving doubles. i dont have to change tanks after a nice long dive and should i have an equipment malfunction, i dont have to stress and immediatly abort a dive.
just my 2cents.

[MyDiveLog]

It's more a question of the right tool for the job. I don't do decompression diving or especially deep diving, so don't find the need for doubles. I use a 19 cubic foot pony bottle when solo diving or doing any diving below 100'...just thinking of lugging doubles on a beach dive makes my back hurt.

If you are doing mostly boat diving, deep diving, decompression diving, etc. then doubles probably make sense.

BTW, the issue for me isn't the one-time cost, but rather the hassle of lugging the darn things around! ... My $0.02 worth.

[MechDiver]

Unfortunatley, to do any sort of tec diving in my area, I have to travel about an hour and a half to the one store in my area that even participates in PADI's new tech program. I wish I had another option, but there's little I can do to change my stores mind aside from becoming a tec instructor myself and getting the owner to recognize the rewards of more technical diving.

Tech PADI is an oxymoron.

I had to drive 5 hours each way to take my tech training so I'm afraid I don't have any sympathy for only 1 1/2 hours. There are far better choices, IMO, for tech training. Have you checked the IANTD or TDI websites for instructors in your area?

MD

[6474286]

"The alternate air supply" required for some reasons/organisations seems to be a must. The question appears immediately : add 4liters pony or switch to twin (even 2x8liters) ? I am tending to ss backplate and IMHO twin would be better. What do You think ? Any ideas, pros ?

Personally, I would recommend the twin set over the Pony bottle. I very rarely use anything less than a double 12 when Diving, and I have two underlyin reasons for this:

The first is the obvious safety factor, basically the more segregated air you have the better; the one thing you can never have too much of is air!

Secondly; I find diving with a double set more comfortable underwater; you are nicely balanced!

Hope this helps!

Paul

[6474286]

P.S- about isolating the tanks, i dont know what could happen to the tank, but hte valve in the center of the manifold is so you can isolate the tanks so they are seperate

With regards to Isolating the Tanks; it is possible for teh O ring in a tank to rupture or burst, thus causing a very quick loss of air. By being able to isolate the tanks, you can keep 1/2 of your air in such a circumstance!

Paul

[DA Aquamaster]

Another alternative to a pony or manifolded doubles would be independent doubles secured with a set of "travel" bands.

You have the same basic set up as a pony except you add an SPG to your "pony" reg. Independent dobles give you the option of using both tanks and managing the air in thirds (with 2 reg switches during the dive) or on shorter rec dives of using one tank with the other along as sort of a "super pony".

It actually works better than a pony for dive travel as you don't need to carry the pony with you. At the destination just strap on both your tanks for the two tank trip and go to it. In a rec situation, the 500 psi or so left in one tank after the first dive becomes the "pony" for the second dive.

In cold water they also offer some advantage as well as they are isolated and with proper gas management you do not need to take any action to preserve enough air to safely end the dive at any point if one of the regs freeflows. It's a good idea to shut the frozen reg off, but your life does not depend on having to do it.

[Northeastwrecks]

Could you please explain this :06:

Divers using twin tanks commonly use a system in which the tanks are joined by a manifold. Essentially, the manifold is a pipe threaded into the left and right tank valves that connects the two tanks and allows gas to pass between them when the isolator valve is open.

Manifolded twins have three valves. The first is on the right tank and is called the right post. The second is on the left tank and is called the left post. The third is the isolator described above. It is disposed in the middle of the manifold.

Each post has a first stage that is connected to a single second stage. There are other things attached to the first stages, but they are irrelevant for the purpose of this discussion.

The valve on each post turns off the gas flowing to the first stage to which it is connected. However, turning off a tank valve does not turn off the manifold. In other words, if I turn off my right post, I will lose the ability to breathe from my primary regulator because the primary is connected to the right post. However, I can still breathe the gas in the right tank because the gas will flow across the manifold to the first stage connected to my left post, which is connected to my backup regulator.

Turning off the isolator shuts down the manifold. When the isolator is closed, I can only breathe from the tank to which the regulator I'm breathing from is connected.

Accordingly, if I have a problem with a first or second stage regulator, I can shut down the reg and still access all of my gas. If I have a problem with the tank itself, such has an extruded tank o-ring or some other major disaster, shutting down the post will not solve the problem. At that point, I need to isolate. If I don't, I'll lose all of my gas.

Hope that this helps.

With regard to the original question, imho, if you need a redundant air source, go for doubles. The reason I believe this is that the pony is, by definition, a more limited system. I'd rather have my full supply of gas available in as many failure modes as possible instead of relying upon a smaller supply at a time when I'm facing some type of crisis.

Unless I'm forced to isolate, thereby cutting my gas by half, I know that I'll have enough gas to get back to the exit point of the dive without a problem. In addition, unless I've isolated, I'll have enough gas to share if I need to, although I'll freely admit that air sharing with a right post failure is not fun. However, since all of my buddies are also in doubles, the chance that this will happen is relatively small.

Twins are certainly not necessary for every type of diving. Proper gas management will make sure that you and your buddy always have enough gas ascend safely to the surface while sharing gas. Whether this means returning to the point where you started or whether it means an immediate surface depends on the conditions of the dive.

[Paul Evans]

Cheers Batman and Northeastwrecks ;)

I didn't realise the manifold is connected under the main tank valves :blush: How stupid do I feel right now?????