All About Pony Bottles

[mwm]

OK. You go OOA for what ever reason. You switch to your pony.

Now, what is your next move?

 

[Doc Intrepid]

Thumb the dive.

Ascend.





Of course, occasionally it doesn't go quite that smoothly.)

 

[mwm]

Yes, but give me a little more detail.

 

[Doc Intrepid]

Yes, but give me a little more detail.

Sorry, about what?

A huge number of factors or variables might cause a problem.

Some may not be your issues - another diver may be having issues.

You could hand off the sling bottle to them, or donate to them and use it yourself...

"Response techniques" will vary depending on the circumstances.

Do you have anything specific in mind?

 

[mwm]

Sorry for being so vague. I am trying to get the OP with <25 dives to think through the situation.

I guess a better question would be if YOU went OOA and switched to your pony, would you ascend on your pony gas or are there better options?

 

[Doc Intrepid]

oh that

as we are not in the solo divers forum, I will recuse myself from further comment and will let you pursue your point with the OP.

Regards,

Doc

 

[charlesml3]

Graeme,

Nobody has asked this yet : Where do you plan to do most of your diving?

If you're staying local, then these larger 20 and 40 foot tanks are fine for a pony. If you're taking it on the airplane down to the Carribbean then that's completely different.

I suppose you COULD take a 40 down but it would be a pretty miserable experience.

I carry a 13 cubic foot. It's band mounted to my tank with the Zeagle pony straps. Works like a champ.

I prefer to charge the pony bottles line prior to entering the water and having it shut off during the dive...on occasion feathering it on the ensure it stays charged.

I have never understood this practice. I did a week aboard the Palau Aggressor about a year ago and left the valve on my pony turned on the whole time.

-Charles

 

[drdaddy]

Graeme, I've marked my responses with "-w-".

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

-w- No. Keep the octopus.

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. I always thought that a pony bottle was attached to a tank and turned on for the entire dive? Are they just different options, or how do people usually use them?

-w- I have both a sling and a tank attachment. I have come to use the tank attachment almost exclusively. This is because I do a lot of jetty/rock/hunting/crabbing diving in current and find that the sling has more of a tendency to get in the way and sometimes drag on bottom - especially when picking up our delicious dungeness crabs. Also, I have found the tank attached system altogether less awkward.

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)?

-w- I have two tank sizes which I put together myself. 13 cu feet when diving 50 ft and less and 19 cu feet for 100 feet. At 130 feet, you'd better be ready to come right up - "spare air packages" are pretty inadequate at that depth. If only occasionally diving at depth, a sling with an extra 80 would be sufficient. Going to doubles is expensive and necessary if you plan to regularly dive deeper (or really want to stay down longer), but I find that most of my diving is done at 50 ft or less - whether in the Pacific NW or in coral seas.

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?

-w- Air - you'll understand better after you take your Nitrox Class. Ponies don't need a PSI gauge if you just use them to come right up, but I added one because it is nice, in an emergency, to see when you are going to be really out of air - especially if you are trying for a safety stop.

5.) Any recommendations or at least give a rough idea of how much I should be planning to spend?

-w- Cost of A 13 or 19 and a reg set. You can buy or rig up sling or tank attachment. I rigged up my own sling and bought the tank attachment. $300 is a fast/rough guess. If you go buying use equipment (checked out by LDS, of course) - it can be a lot less.

-w- Oh, on the sling a backup reg can be easily turned on, but when I use mine on my tank, I have come to turning and leaving it on. I can reach it and turn it on, but it is difficult - and I don't want difficult when I am having a primary air source failure.

-w- My backup tank attached system easily attaches to my tank by a tank belt and is easily transfered when I switch out tanks. Obviously a sling system can just be slung on and off. The nice thing about a sling is that it can be handed off to a buddy who has an out of air situation - advantages are obvious.

-w- I hope all this helps. I had to figure this out myself with some assistance from my LDS tech/instructor Ed. Support your local dive shop or they and their priceless expertise and support (I'm known as a real "pest" at my LDS - Eugene Skin Divers Supply) will be gone.

William

 

[Coldwater_Canuck]

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

Thanks, that was quite informative. I guess it's tough because you can always think of "just one more thing" to go wrong.

Sorry for being so vague. I am trying to get the OP with <25 dives to think through the situation.

I guess a better question would be if YOU went OOA and switched to your pony, would you ascend on your pony gas or are there better options?

Are you getting at that it may be best to use your buddies air because then if his runs out, reg breaks, etc. you still have the pony for the two of you? That's about all I can come up with.

 

[Coldwater_Canuck]

Graeme, I've marked my responses with "-w-".

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

-w- No. Keep the octopus.

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. I always thought that a pony bottle was attached to a tank and turned on for the entire dive? Are they just different options, or how do people usually use them?

-w- I have both a sling and a tank attachment. I have come to use the tank attachment almost exclusively. This is because I do a lot of jetty/rock/hunting/crabbing diving in current and find that the sling has more of a tendency to get in the way and sometimes drag on bottom - especially when picking up our delicious dungeness crabs. Also, I have found the tank attached system altogether less awkward.

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)?

-w- I have two tank sizes which I put together myself. 13 cu feet when diving 50 ft and less and 19 cu feet for 100 feet. At 130 feet, you'd better be ready to come right up - "spare air packages" are pretty inadequate at that depth. If only occasionally diving at depth, a sling with an extra 80 would be sufficient. Going to doubles is expensive and necessary if you plan to regularly dive deeper (or really want to stay down longer), but I find that most of my diving is done at 50 ft or less - whether in the Pacific NW or in coral seas.

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?

-w- Air - you'll understand better after you take your Nitrox Class. Ponies don't need a PSI gauge if you just use them to come right up, but I added one because it is nice, in an emergency, to see when you are going to be really out of air - especially if you are trying for a safety stop.

5.) Any recommendations or at least give a rough idea of how much I should be planning to spend?

-w- Cost of A 13 or 19 and a reg set. You can buy or rig up sling or tank attachment. I rigged up my own sling and bought the tank attachment. $300 is a fast/rough guess. If you go buying use equipment (checked out by LDS, of course) - it can be a lot less.

-w- Oh, on the sling a backup reg can be easily turned on, but when I use mine on my tank, I have come to turning and leaving it on. I can reach it and turn it on, but it is difficult - and I don't want difficult when I am having a primary air source failure.

-w- My backup tank attached system easily attaches to my tank by a tank belt and is easily transfered when I switch out tanks. Obviously a sling system can just be slung on and off. The nice thing about a sling is that it can be handed off to a buddy who has an out of air situation - advantages are obvious.

-w- I hope all this helps. I had to figure this out myself with some assistance from my LDS tech/instructor Ed. Support your local dive shop or they and their priceless expertise and support (I'm known as a real "pest" at my LDS - Eugene Skin Divers Supply) will be gone.

William

Now you've got me second guessing the sling What you said were my original instincts, that slinging a larger pony would be an annoyance. I know in my OW class my instructor had his pony attached to the main tank, it looked like a 30 or 40 (he said he was a fan of deep diving). Thanks for your help.