All About Pony Bottles

[M_Bipartitus]

Thanks everyone. I was thinking of just mounting it to the tank, but it sounds like most people prefer slinging it. I figured that slinging say a 30 cf bottle would get in your way when diving, but no one has issues with it? And I just want to make sure I understand what slinging it means, the pictures I've seen have two clips, and I guess does one go on a ring at the front and one on a ring at the back of your BCD and it just stays attached beside you, or how does this work?

It is the same as tech divers configure a stage or decompression bottle, in may cases (including my own) See this site for some ideas on how the clips are attached to the tank.

TechnicalDiver.Com - Stage Bottle Rigging

The clip near the first stage is then clipped to a on a d-ring near the chest and the other is clipped to BC on your side.

Also, I'm sure someone will know, those little pressure gauges without a hose, do those just hookup to your first stage or what?

They screw into a high pressure port on the first stage.

...
But that does make me think, do you need more or less weight with a pony bottle on? I'm not sure, but I think a steel tank full of air on its sinks, which would mean less weight, but I'm not sure about this.

It depends on the tank, but you generally need a few pounds less. If you search for tank specs, you should be able to find buoyancy characteristics for all different size tanks. For example the last column on this site.

Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan

 

[Coldwater_Canuck]

It is the same as tech divers configure a stage or decompression bottle, in may cases (including my own) See this site for some ideas on how the clips are attached to the tank.

TechnicalDiver.Com - Stage Bottle Rigging

The clip near the first stage is then clipped to a on a d-ring near the chest and the other is clipped to BC on your side.





They screw into a high pressure port on the first stage.



It depends on the tank, but you generally need a few pounds less. If you search for tank specs, you should be able to find buoyancy characteristics for all different size tanks. For example the last column on this site.

Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan

Thanks. Sounds like slinging may be the best route here.

Now I'm trying to figure out the size. I know that a dive almost at the surface I can last about 60 minutes, and 130 feet is 1/5 the volume, so it equals 12 minutes at 130 feet. I'd like 3 minutes to safely ascend, so being very conservative (ignoring the fact I'll use progressively less air while I ascend), I'll need a tank 1/4 the size of my main tank. If my main tank was 120cf, then I should probably get a 30. If my main tank was 80cf, then 20 may suffice.

Does anyone know what a standard tank size is that you'd be likely to get for open water training?

 

[Hank658]

Just to throw into the mix: a pony bottle is not all that expensive so if you are like many divers you will end up with a couple. Maybe a 19 for shallower dives, a 30 for deeper dives and a 40 if you get into more complicated dives (wreck penetration where a direct 3 minute ascent might not be possible).

The comments about using doubles is taking the idea a pony to the next level to where you have two tanks of equal size with a regulator on each. This leads to the concept of redundancy, where you have the tools, and the training, to manage more chalenging situations. Doubles, as well as a pony, do add tasks and more complexity to a dive. When adding another tool or system to your normal diving kit it is a good idea to work out the routines and methods in a controlled setting such as a pool or quarry first before going out into more unpredictable situations. Classes such as AOW and a Deep specialty are good places to get introduced to the equipment and techniques for this kind of diving.

Kudos on asking your questions as well as furthering your diving education!! Enjoy the classes and safe diving.

H.

 

[Coldwater_Canuck]

Just to throw into the mix: a pony bottle is not all that expensive so if you are like many divers you will end up with a couple. Maybe a 19 for shallower dives, a 30 for deeper dives and a 40 if you get into more complicated dives (wreck penetration where a direct 3 minute ascent might not be possible).

That's a good idea, and eventually that's probably what I'll do. Although in my situation right now it's not really realistic (even though the bottles are onlyu a little over $100 a piece, it does start to add up) but also I'm travelling between Seattle and Ontario every 4 months, so the less I have to take with me, the better. But once I graduate and have some more money, I'll probably get a few. For now I could use pro

But would 40 even be necessary for (non-technical) wreck dives? In my calculations, I was being very conservative in almost every calculation and gave myself a whole extra minute while ascending. And I know the PADI wreck limits are 100 feet depth + penetration or only penetrating in the light zone. The PADI wreck diving course really interests me, although I'm still a ways away from being ready to take it (I don't even have my advanced yet - although it's the first thing I'm taking when I get back to Seattle).

Kudos on asking your questions as well as furthering your diving education!! Enjoy the classes and safe diving.
H.

And thanks to all the instructors and veteran divers on here to help us new divers out

Taking courses is something I plan to do a lot of. I figure it's crazy to limit myself to the type of diving OW teaches, plus following an instructor is nice in that they know where they're going and can show you the good dive spots. The courses I want to take immediately are AOW, Nitrox, and Peak Performance Buoyancy, and after that I'll see (deep and night are in my plans).

 

[David_57]

I use a 40 cuft bottle as you can use it for a deco bottle if you decide to get into more technical dives besides you can never have to much air ;-}. I attach it to my D rings on my shoulder and waist, as for gas it should be the same as your back gas. As for the gauge you can buy the ones that screw directly into the first stage with no hose.

 

[Spimon]

But would 40 even be necessary for (non-technical) wreck dives?

Time for a little shameless self advertising!

If you head to my website and hit up the 'tools' section, I've created a spreadsheet that will calculate the dive time from a given tank, based on size, start pressure, depth and SAC rate. It can also help calculate your SAC rate from your previous dive history).

In a stressful situation (unusually high SAC rate), I'd expect a 40cuft tank would last me about 15 minutes at 30m (100').
Up to you to work out how long you'd like to give yourself to get out of any tangle you get yourself into.

Apologies to the Americans, all my calculators are in metric. My website is HERE

But that does make me think, do you need more or less weight with a pony bottle on? I'm not sure, but I think a steel tank full of air on its sinks, which would mean less weight, but I'm not sure about this.

Also in the tools section of my website is a buoyancy characterisitics calculator. Input the capacity of your tank, weight when empty and starting pressure and it will approximate the buoyancy when full and empty, in salt or fresh water and for steel or aluminium tanks.

 

[Coldwater_Canuck]

I use a 40 cuft bottle as you can use it for a deco bottle if you decide to get into more technical dives besides you can never have to much air ;-}. I attach it to my D rings on my shoulder and waist, as for gas it should be the same as your back gas. As for the gauge you can buy the ones that screw directly into the first stage with no hose.

If I ever want to go into tek I won't mind spending the extra $100 if I need a new bottle. I guess my question is, would a 40 be required for a semi-technical recreational dive (like PADI wreck course)? It will be years before I do any true technical diving, but I could see myself taking some things like the wreck course or ice diving after I get some more dives and courses under my belt.

Granted, you can never have too much air, and the 40 is only like $10 more, but I guess I'm just wondering how much the tank would get in your way when you're diving. If you don't even notice it, then you may as well get a 40, but if a 30 is more than enough, then I may as well just get that.

 

[Coldwater_Canuck]

Time for a little shameless self advertising!

If you head to my website and hit up the 'tools' section, I've created a spreadsheet that will calculate the dive time from a given tank, based on size, start pressure, depth and SAC rate. It can also help calculate your SAC rate from your previous dive history).

In a stressful situation (unusually high SAC rate), I'd expect a 40cuft tank would last me about 15 minutes at 30m (100').
Up to you to work out how long you'd like to give yourself to get out of any tangle you get yourself into.

Apologies to the Americans, all my calculators are in metric. My website is HERE




Also in the tools section of my website is a buoyancy characterisitics calculator. Input the capacity of your tank, weight when empty and starting pressure and it will approximate the buoyancy when full and empty, in salt or fresh water and for steel or aluminium tanks.

Neat spreadsheet you designed. Using very rough numbers, I figure a 30 would give me about 4 minutes, but I really need to do some dives where I keep a closer eye on my exact time and PSI measurements (and figure out what size tank I've been using

 

[Colliam7]

I will echo some of the sentiments already expressed.

1.) Does a pony bottle replace the need for a backup second stage from your main tank?

No.

2.) I see a lot of stuff about pony bottles being attached to a BCD, or turning them on only when needed, and all this stuff.

Smaller pony bottles (6-19cf) are not infrequently attached to the (backgas) tank. In those cases, it is easiest to turn them on before entering the water, since the valve may not be particularly accessible once you are in your BCD (there are exceptions, some find it practical to mount a pony, inverted, to their tank and turn it on while in the water). If you sling the bottle in front, from a chest D-ring and a hip / waist D-ring, a common practice is to turn it on before entering the water, to pressurize the regulator, then turn it off until it is needed. Not a requirement, only a habit that many adopt.

3.) When purchasing, what size would be preferable (assuming the possibility of deep diving in the future - up to 130 feet)? Also, is it generally best to buy a pre-configured system or just buy a tank and regulator yourself? Are they generally easy to switch between tanks (I plan to continue renting my main tanks)?

A 'stand alone' system, with a tank and a regulator, that you can sling from D-rings on your BCD, is probably the easiest to use. A smaller pony attached to your tank requires a bit more manipulation when you change tanks, although it is not problematic. Some mount smaller bottles on their jacket BCD or backplate, and that works as well. Size is a matter of preference and convenience. I started with a 40cf because I planned to ultimately use it as a deco bottle as well (which I did, but not until 4 years later, so I used the 40 as a pony for quite a while). I subsequently bought a couple of 30cf bottles for deco use, which also function as pony bottles. I did not find a slung 40cf bottle to be particularly challenging to dive with, although I made a point to practice with it in the quarry, and on several shallow (reef) boat dives in FL, before taking it deeper (e.g. to the Spiegel Grove). After several dives I found I didn't even notice it was there, and it had no effect on my trim.

4.) Would you generally fill a pony bottle with air or nitrox? Do pony bottles need a PSI gage to tell how much air is remaining?

Air. I recommend a pressure gauge. I don't use one of the small ones that screw into a HP port (because I find them awkward to see), rather I use a small SPG mounted on a short piece of hose.

I guess my question is, would a 40 be required for a semi-technical recreational dive (like PADI wreck course)?

Required? No. Acceptable, and functional? Yes.

I'm just wondering how much the tank would get in your way when you're diving. If you don't even notice it, then you may as well get a 40, but if a 30 is more than enough, then I may as well just get that.

Either one would be fine. I bought my 40 new. I have the two 30s because I bought them used, along with two sets of doubles. At the time, I would have preferred 40s. After I started using the 30s, I found I like them. I don't notice either bottle during a dive when it is not in use. One other comment. When I started diving trimix, I began using a separate bottle for drysuit inflation, a 6 cf bottle, mounted inverted on the lower left side of my backplate. I thought it would be inconvenient, but it is not. Presumably, such an approach could also be used as a pony system, although with only 6 cf. of gas.

 

[Doc Intrepid]

Thanks. Sounds like slinging may be the best route here.

Now I'm trying to figure out the size. I know that a dive almost at the surface I can last about 60 minutes, and 130 feet is 1/5 the volume, so it equals 12 minutes at 130 feet. I'd like 3 minutes to safely ascend, so being very conservative (ignoring the fact I'll use progressively less air while I ascend), I'll need a tank 1/4 the size of my main tank. If my main tank was 120cf, then I should probably get a 30. If my main tank was 80cf, then 20 may suffice.

Does anyone know what a standard tank size is that you'd be likely to get for open water training?

CC,

There really is no 'standard tank' for bailout bottles - as each diver needs to calculate their own needs based on their own individual circumstances (anticipated depths, purposes, potential for entanglement, etc.)

You are likely looking for a Luxfer 19 or 30.

Regardless, the above quote is close-but-no-cigar...you've got the idea, but you've left out a few steps in the calculations.

First you're looking for your Surface Air Consumption (SAC) rate. (Keep in mind, you're not measuring it in an emergency...)

SAC = Total Gas Consumed (psig) -:- [Depth (ATA) x Time (minutes)]

You next convert SAC to Respiratory Minute Volume (RMV) to quantify a "cubic feet of gas consumed per minute at X depth" measurement. You're looking for your personal rate of gas consumption. (Obviously the calc includes depth; not so obviously it also includes which tanks you're using)

RMV = SAC -:- [rated cylinder working pressure -:- rated cylinder volume]

To find RMV:
1. Divide the rated cylinder working pressure by the rated volume;
2. Divide your SAC by this value (from step 1) to find your RMV.

Those are the formal steps, however, none of it accounts for the extremely elevated respiratory rates that are experienced by divers in a state of high anxiety. As this is difficult to quantify, most guys estimate.

An estimate of approximately 1.3 cfm is a conservative figure, but OTOH, those of us who have screwed the pooch a few times can vouch for the fact that divers can go through gas real quick under certain circumstances.....

So, using an estimate of 1.3 cfm at say ~99' (4 ATA), you then count the estimated number of minutes.

You may want to allow, say, 4 minutes to deal with whatever issues you may have (entanglement, panicked OOA diver, clusterpuckery, whatever) at depth. You may be assisting someone with a large camera, a heart attack, a lost mask, its tough to predict.

At a relatively composed rate of ascent of 30 fpm you have 3 min from 4 ATA to 10', then a 3 minute safety stop, say 6 minutes of total ascent. That's 10 minutes total.

At an average consumption of approximately 1.3 cubic feet per minute, over a 10 minute period, you'll be needing a minimum of 13 cubic feet of gas.

But you could easily add environmental or situational parameters such as you are inside a wreck, and must swim horizontally out of the wreck (back to the upline, against potential current, with an OOA diver or large camera, etc. - whatever your personal potential characteristics might entail). If you are going to traverse any distance underwater at depth before ascending, then add the approximate number of minutes it might require you to traverse a distance horizontally at depth.

If you add another 5 minutes for dealing with environmental or situational parameters, whatever these may be in your case, extending your time on bailout to 15 minutes total, then your max cubic feet of gas needs may approach 19.5 cubic feet (at 1.3 cfm).

Add other issues? Your max gas needs may increase accordingly...

(Depth is huge. At 5 ATA (~130') and 1.3 cfm, a 40 will go pretty fast given any sort of issues. Give it a try, like I did, and you'll notice this even without a elevated rate of respiration.....)

Hopefully you can see that "what you need" is not a standard answer. "What you need" depends on you, what you're doing at depth (wrecks?), where you're diving - under what conditions (currents?), with whom (solo or around other divers), etc.

No one can answer these questions but you. So you sort of need to sit down and from a conservative perspective describe what you think you need a bail-out FOR, under what conceivable conditions would you deploy one? Then, based on that personal review, you can calculate out the conditions under which you'd use it, and how much gas you'd potentially need.

There are many threads on this topic, some of which you might find useful. You may want to do a search. Here is an older thread, one example among many in the archives:

http://www.scubaboard.com/forums/ne...g-diving/216419-pony-bottle-vs-spare-air.html

Best,

Doc