Pony Bottle Selection

[JohnN]

My thoughts... I got a 19cu just recently. Evaluated between 30 and 19 as the 2 reasonable options. My needs... Solo diving and having some redundancy available in the event of a primary failure - not as an additional gas source to extend dives.

My diving profiles do not extend beyond 100ft. So I looked at a failure at 100 feet. How much gas to ascend slowly and safely with appropriate safety stops along the way.

6cu was not feasible from a capacity perspective and 30cu was viewed as overkill but I will add that 30cu was what my local LDS was pushing me to purchase. The additional consideration was travel. 19cu is a nice size to travel with while 30cu took it over the sizing aspect for us flyers.

From a use perspective it attaches nicely to my main tank, buoyancy not a big factor, and piece of mind refreshing.

hope this helps.
tim

+1 Although I also have an AL40, I use the AL19 as my primary pony. Nice and small and my gas calculations give me enough time to hit the surface with a 3 min safety stop from 100 ft. My only complaint is that unless you get a proper fill (cold tank @ 3000 PSI), there might not be enough gas if the poo hits the fan.

 

[KD8NPB]

Which size will you actually carry?

I like a small set of doubles myself.

But if I had to choose, it would be an AL40. AL30s are a bit too niche...the AL40 can be used as a deco gas bottle if you go tech, and the resale on them is nice.

 

[tomfcrist]

A 19 will be fine for YOU to do a direct ascent from rec depths off the coast, but you say you are teaching classes, whichin my opinion requires you to plan for the event of more than one of your students going OOA(which shouldnt ever happen) and i error on the side of a 40. A 30 would work, but since my deco bottles are 40's and 80's, I use a 40. Ulimately it is up to you, but look around on your next offshore trip.....what do you see? 40's as spare/deco bottles, steel singles with H valves, and alot of doubles.....NC wreckdiving requires redundancy, as its not very forgiving to unprepared divers.

 

[Jim Lapenta]

I own a 40, two 30's, and a 19. My GF is the one who usually uses the 19. I can't remember the last time I used for something other than on my bicycle tires. I have a 6 as well for my drysuit bottle and it comes in handy as well for blowing dust out of the computer tower. Normally I sling the 40 and the 30's are for my AOW and Intro students. Standard northeast wreck diver slings on all of them except the 6. Although I am going to change the 40. I see most of my diving next year, including checkout dives for all courses, being done in Sidemount and that requires a little different set up.

 

[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

 

[dumpsterDiver]

I would select a 13, but you would think that an instructor would have a good enough handle on how to pick a bottle based on his personal assumptions for what situations the device will be used for. Does the instructor expect to immediately begin an ascent or does he assume that he will be spending 1 or 2 or 3 minutes on the bottom? What ascent rate is assumed? Is a safety stop going to be performed during the emergency? Or even what SAC rate do you have? And what rate will YOU assume YOU will have in an emergency. To try to delegate all these critical assumptions to people on the internet is .....

It is not much different than an instructor asking: What size scuba tank should I use for diving 110 ft as an instructor? It's kinda scary really..

If he had asked: what are the most popular size pony bottles for 80-120.. I would not have the same feeling.

 

[halocline]

I wouldn't use a bailout bottle while teaching, unless you're teaching solo diving. You're sending students the message that diving the way they are, with a single tank at recreational depths with a buddy but no bailout bottle, is not safe. I know you don't intend to send them that message, but what if one of them asked "why are you carrying the pony, and if it's necessary, why aren't we carrying them too?" I mean, if it's OW classes, you're teaching them specifically to share air, do CESAs, watch their gas carefully, and otherwise dive safely....yet you're demonstrating that you're not comfortable doing the same.

Bit of a snarky point, I realize.....sorry about that. It is something to think about though. I have a 13 cft pony that I've used diving exactly once in several years. But it's convenient for working on regs and filling tires.

 

[Basking Ridge Diver]

I see the OP is an instructor - what is curious to me is there is no conversation about SAC rate being used in any formulas - SAC rate x half the depth at 30 fpm ascent x ATA pressure plus a 3 min safety stop at 20 feet. Why not discuss what the OP is trying to achieve - a single person using a pony at 100+ feet with a safety stop or two the OP and a student - that to me should be driving this discussion.

I am not an instructor but I would have thought this was an easy exercise using excel and simple formulas based on worst case scenario for the OP and one of his students...

 

[rhwestfall]

hence post #4......

 

[victorzamora]

hence post #4......

Honestly? My post recommending a 40 and describing the tanks I would consider was assuming the OP calculated bare minimum for the conditions envisioned. I mentioned a 13. If the OP did math suggesting 19ft3 was minimum, I would've hoped it was obvious to disregard that option.

I thought the question implied bottle characteristics other than volume (like diameter, buoyancy, resale, etc) simply because an instructor was asking the question.

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