Pony Bottle Size

[ththooft]

Hello-

I'm curious which size pony bottle people are using for a redundant air supply. I'm not doing any tech diving so it would be a purely extra air source to come along for the ride. I want something that's a decent size but not way larger than I would need.

Thanks!

 

[dkktsunami]

Hello-

I'm curious which size pony bottle people are using for a redundant air supply. I'm not doing any tech diving so it would be a purely extra air source to come along for the ride. I want something that's a decent size but not way larger than I would need.

Thanks!

Answer totally depends on type of diving you are doing, the depth of the dives, and your surface consumption rate. First determine your SCR, and then use this information to determine how much air you would need to surface from one of your typical dives.Your ascent should be at 30'/min. and include a 3 min. stop. If you are diving deep, cold, and dark your needs will be greater than for shallow warm water dives.

 

[redacted]

I use a 13 which is minimally adequate for me. In the water, a 19 is no more of a burden than a 13 but has almost 50% more gas. In the suitcase, the 13 is a bit easier. How much gas have you calculated you would like/need? Then start trading off the alternatives.

 

[spectrum]

Hello-

I'm curious which size pony bottle people are using for a redundant air supply. I'm not doing any tech diving so it would be a purely extra air source to come along for the ride. I want something that's a decent size but not way larger than I would need.

Thanks!

Let me take a stab at this, I'll make some assumptions and you can do you own math based on you and your diving.
*You want redundancy to 99 feet
*You want 2 minutes of air on the bottom to collect yourself, solve a problem or move to an ascent location which may or may not be a wise thing to do.
*I'll assume a SAC of 1 which is common for a stressed diver. Your actual may easilly be 1/2 of this but the situation may change that.
*An ascent rate of 30 FPM
*3 minutes at 15 Feet for a safety stop

So.....
2 minutes on the bottom X (3+1) Atmospheres X SAC of 1 = 8 cubic feet will be consumed on the bottom

During ascent to 15 feet your average depth is 2.75 ATM X ~3 minutes X SAC of 1 = 8.25 cubic Feet

At your safety stop your depth is 1.5 ATM X 3 minutes X SAC of 1 = 4.5 cubic feet

A leusurely minute to surface in a minute 1.25 ATM X 1 minute x SAC of 1= 1.25 cubic feet

All told the 4 increments add up to 22 cubic feet of air. The SAC of 1 is agressive but you need to bounce that against how perfect the fill was, how accurate your gauge is, you don't want to be sucking the cylinder dead empty and a host of other safety factors. You may choose to consider the safety stop as expendable, you may prefer to add a deep stop 1/2 way up.

As Awap stated 19 can be nice and many diver go for more than that. Don't guess, consider your needs and decide what is appropriate for you. Knowing the math behind it can make a big difference in your comfort and safety if the day comes when you are relying on this as your air source.

Pete

PS Almost everyting I know about this I learned here so if I messed up correct me.

 

[M_Bipartitus]

nice calculation. I use a 19cf for a much simpler reason... someone was selling one used when I was looking for a pony... bottle+reg+guage <$200

 

[Mark Vlahos]

Let me take a stab at this, I'll make some assumptions and you can do you own math based on you and your diving.
*You want redundancy to 99 feet
*You want 2 minutes of air on the bottom to collect yourself, solve a problem or move to an ascent location which may or may not be a wise thing to do.
*I'll assume a SAC of 1 which is common for a stressed diver. Your actual may easilly be 1/2 of this but the situation may change that.
*An ascent rate of 30 FPM
*3 minutes at 15 Feet for a safety stop

So.....
2 minutes on the bottom X (3+1) Atmospheres X SAC of 1 = 8 cubic feet will be consumed on the bottom

During ascent to 15 feet your average depth is 2.75 ATM X ~3 minutes X SAC of 1 = 8.25 cubic Feet

At your safety stop your depth is 1.5 ATM X 3 minutes X SAC of 1 = 4.5 cubic feet

A leusurely minute to surface in a minute 1.25 ATM X 1 minute x SAC of 1= 1.25 cubic feet

All told the 4 increments add up to 22 cubic feet of air. The SAC of 1 is agressive but you need to bounce that against how perfect the fill was, how accurate your gauge is, you don't want to be sucking the cylinder dead empty and a host of other safety factors. You may choose to consider the safety stop as expendable, you may prefer to add a deep stop 1/2 way up.

As Awap stated 19 can be nice and many diver go for more than that. Don't guess, consider your needs and decide what is appropriate for you. Knowing the math behind it can make a big difference in your comfort and safety if the day comes when you are relying on this as your air source.

Pete

PS Almost everyting I know about this I learned here so if I messed up correct me.

Pete,

Good post!

If a diver is going to use a pony, then they would be well advised to use one that is large enough. I would say that a 30cf is a nice size. If you have aspirations of technical diving in your future get a 40cf for eventual use as a decompression bottle. I also like rigging them as stage bottles keeping the entire thing in front of you within easy reach. In the event that you need to give it to a buddy you can give them the entire rig.

Mark Vlahos

 

[SteveAD]

another rule of thumb is there is no such thing as too much air. go ahead and use petes calculations to figure out how much is your bare bones requirement, and then get the biggest one you're willing to carry, I use a 40 cf but I'm a BIG guy

 

[PaulChristenson]

http://www.scubadiscount.com/page36.html

 

[coachrenz]

I use a 40cf. I like it because it is the same height as my al80. I have a custom made mount that works like a charm made by John here in the Seattle area. I don't do any tech diving, just like to know that I have a lot of extra air on me. Redundacy is the key for me.

 

[Aquanautchuck]

When I am diving for fun I always have my 19 pony. If I am doing any dive that may be deeper than 100' or there is other factors I take me 30 sling.

By the way, not to long after getting my 19 it saved my butt. Had a 2nd stage go into free flow [ got kicked in the face by a diver and reg was knocked out of my mouth] it would not shut down. Got my 2nd stage from my pony and headed up. By the time I got to my safety stop my main tank was empty. I feel naked without my pony now.