Pony Bottle Selection

[rhwestfall]

Honestly? Yes.

This is the exact question:

Hi all,

Here is a question. What size do you think is ideal for a pony bottle to be for teaching in open water (OW, AOW, Specialties), medium depth (80-120) NC Coastal diving and some self reliant quarry dives.

I will not be using this bottle for deco, just for the activities listed above.

Discuss...

So, the OP needs to determine the desired characteristics of the intended use, and "run some numbers" to select the proper tool.

 

[victorzamora]

Sorry, there was an unintended implication there. I was agreeing with you. The "honestly" was me admitting to having made a mistake, based on assuming something I probably shouldn't have assumed. I agree with you completely that some math needs to be done, if it hasn't already.

 

[Max Speed]

Screw the math. Just simulate the failure and end the dive. Breathe like you're panicked and then see how much gas volume you used. Simple. (Do not hyperventilate while simulating!)

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[Easdem]

I am sorry. I forgot that the way a question is presented on SB is almost more important than the actual content of the question. If every angle is not directly addressed in the original question, some will understand the intent of the question and answer nicely while others will nit-pick just to fuel an argument or begin an ad hominem attack without fully knowing the OP, intent or even ask questions to clarify.

I know how much gas it will take for ME to safely ascend from the recreational limits. A 19 cf. pony would be adequate for that and have enough air to be able to stop at 15 feet and complete a safety stop if I desired.

If it was just for me, on a non-teaching dive, I think I would select the 19. However, since I am an instructor, I would like to have a bit more cushion and a better all-around bottle. So I am leaning to a luxfer 30 cf bottle. I like the size better than a Catalina 30cf and the 40cf is a big too long for me to sling comfortably. I can sling it for deco gas if I have to, but I prefer the way the 30 hangs.

So I asked a question without giving all the details of my reasoning to avoid a philosophical argument.

 

[victorzamora]

Correct me if I'm wrong, but aren't Luxfer and Catalina AL30's 5.25"x20"??

Also, a vague question can lead to many different takes on it. For example, even though rhwestfall and I agreed on something....we thought we disagreed due to the fact that each of us had a different initial interpretation. The content of the question was not sufficient to get everybody on the same page. There has been no attack or "fuel" to any argument that I'm aware of. The only mildly-grumpy comments were regarding the fact that you should know how much air you would need. Hence, the clarification that I assumed you COULD figure it out and were asking for other reasons. The given data suggested to some that you could NOT figure it out yourself, which wouldn't surprise anyone considering the low level of competence many instructors show. I think you got a lot of useful information presented to you, including a calculator to help you estimate what you would need in the case of feeding two people from the same tank in the case that you had two second stages on your pony, which is uncommon. A more accurate post would have been to mention the needed ft3 for you to ascend from depths at which you would be teaching, and then asking about two second stages on the pony vs just for you and/or a student (which would lead to different sized tanks), and then mentioning your thoughts on safety stops under emergency conditions. Even if you hadn't thought that all of the way through, more responsiveness during the discussion could've curbed a lot of the ensuing confusion.

So, having said all of that: Why are you choosing the 30 instead of a 19? Instead of SM? Instead of BM doubles? Had you considered either of the double-tank configurations? Have you considered just a gigantic single for yourself?

 

[scubadada]

This has been a very frequent topic, I go with a 19, jusification listed on numerous posts, safe ascent from recreational depth at normal ascent rate and safety stop

I use my pony exclusively for a redundant gas supply while solo diving within NDL. For me, a minute at 130', 4 minute ascent to 15', a 3 minute safety stop, and ascent to the surface, at twice my usual SRMV, takes just over 17 cu ft. Of course, I'm rarely at 130 feet, would head to the surface as soon as possible if I lost or was losing my primary gas supply, could ascend faster if needed, and could skip the safety stop. I am comfortable with my 19 cu ft pony for my purpose. Clearly, many of you make your choices in a similar manner.

 

[Easdem]

Correct me if I'm wrong, but aren't Luxfer and Catalina AL30's 5.25"x20"??

Also, a vague question can lead to many different takes on it. For example, even though rhwestfall and I agreed on something....we thought we disagreed due to the fact that each of us had a different initial interpretation. The content of the question was not sufficient to get everybody on the same page. There has been no attack or "fuel" to any argument that I'm aware of. The only mildly-grumpy comments were regarding the fact that you should know how much air you would need. Hence, the clarification that I assumed you COULD figure it out and were asking for other reasons. The given data suggested to some that you could NOT figure it out yourself, which wouldn't surprise anyone considering the low level of competence many instructors show. I think you got a lot of useful information presented to you, including a calculator to help you estimate what you would need in the case of feeding two people from the same tank in the case that you had two second stages on your pony, which is uncommon. A more accurate post would have been to mention the needed ft3 for you to ascend from depths at which you would be teaching, and then asking about two second stages on the pony vs just for you and/or a student (which would lead to different sized tanks), and then mentioning your thoughts on safety stops under emergency conditions. Even if you hadn't thought that all of the way through, more responsiveness during the discussion could've curbed a lot of the ensuing confusion.

So, having said all of that: Why are you choosing the 30 instead of a 19? Instead of SM? Instead of BM doubles? Had you considered either of the double-tank configurations? Have you considered just a gigantic single for yourself?

The shop manager and I were discussing this recently, and he pulled out (not sure how old) an AL Catalina 30cf pony which we compared with the Luxfer. The Catalina has less diameter and was a bit longer. I thought they would have been the same size like you said, but not in this case, I took it at face value. I'll have to make sure something wasn't overlooked.

When I teach in OW for OW class sometimes I use an HP120 sometimes an AL80. It depends on the class size. The 120 is is a huge amount of gas for those dives. I can go all day without having to change cylinders and have plenty of gas for contingencies. We don't go any deeper than 35. In that scenario a 19 is plenty, probably not even needed.

For the AOW deep adventure dive, you don't need to have back-up air supply, but I think its a good idea to. A 19 would probably be OK in this case. The deep specialty PADI requires that there be back-up air supply, I know 19cf is enough for me to ascend, but is it enough for a panicky student? Maybe...I'd feel more comfortable with a bit more air to give away.

On the coast here in NC most people opt for big steel tanks and some slung pony for the deeper wrecks. I use my HP120's, if I had doubles, I would wear them. Again, a 19 is definitely enough to reach the surface safely, I could probably reach the anchor line if there wasn't a strong current or shoot a bag and ascend. However, I would feel more comfortable with a 30, knowing that I have more gas if I need it. (this is assuming worst case scenarios).

So for the marginal cost difference and the slight size difference I prefer the 30cf.

 

[victorzamora]

The shop manager and I were discussing this recently, and he pulled out (not sure how old) an AL Catalina 30cf pony which we compared with the Luxfer. The Catalina has less diameter and was a bit longer. I thought they would have been the same size like you said, but not in this case, I took it at face value. I'll have to make sure something wasn't overlooked.

When I teach in OW for OW class sometimes I use an HP120 sometimes an AL80. It depends on the class size. The 120 is is a huge amount of gas for those dives. I can go all day without having to change cylinders and have plenty of gas for contingencies. We don't go any deeper than 35. In that scenario a 19 is plenty, probably not even needed.

For the AOW deep adventure dive, you don't need to have back-up air supply, but I think its a good idea to. A 19 would probably be OK in this case. The deep specialty PADI requires that there be back-up air supply, I know 19cf is enough for me to ascend, but is it enough for a panicky student? Maybe...I'd feel more comfortable with a bit more air to give away.

On the coast here in NC most people opt for big steel tanks and some slung pony for the deeper wrecks. I use my HP120's, if I had doubles, I would wear them. Again, a 19 is definitely enough to reach the surface safely, I could probably reach the anchor line if there wasn't a strong current or shoot a bag and ascend. However, I would feel more comfortable with a 30, knowing that I have more gas if I need it. (this is assuming worst case scenarios).

So for the marginal cost difference and the slight size difference I prefer the 30cf.

if there is a difference, I'll be surprised as I checked mfg specs... but I could've misread.

Having said that, a 30 is over 11ft3 and >50% bigger than an al19. An al40 is 10ft3 and 33%bigger than an al40. The size difference is greater between the ones you claim has a slight size difference. However, your mind had clearly been made up on an al30 since the get go. Get the 30. You'll be happier in the long run, unless you resell it or go tech.

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[Crass3000]

I use an AL40. It seems to sling easy enough with no trouble. Why not have a little more gas. For the person saying you wouldn't teach with a pony bottle, one LDS around here will not do the deep dive specialty without all students having a pony. Granted they are the odd ones in requiring it most don't. I have to say that it is a good habit to get into though.