Is a 6cf pony bottle good enough as a back up?

[bigrich954rr]

If so whats a good one to buy ?

 

[Rainer]

It's fine for inflating a drysuit; that's about all.

 

[Tanked]

Short answer? No.
I wouldn't use a 6cf pony as backup to dive in a pool.

 

[dumpsterDiver]

I use one for solo diving to around 100 feet..

 

[PSFlyer]

Depends on the depth of your dives and the speed of your ascent to the surface. A 6cuft bottle can get you to the surface from about 100 ft but I would not call it adequate. It is cutting too close in my opinion. I hope some experts chime in to validate or counter my opinion. I do not use a pony so I am going strictly by the numbers here, as follows:

1. SAC of a stressed diver hovers around 1cu/ft
2. Let's assume 100 ft depth
3. Average Pressure for your ascent would be (50/33)+1 = 2.5, so you are looking at using 2.5cuft per minute.
4. Assuming a 45ft/min ascent it would take you roughly 2.25 minutes to reach the surface - that means you would need 5.6 cu ft of air.

So using a 6 pony, I guess you make it to the surface if you do not spent any time on the bottom trying to sort out your or your buddy's problem as the case may be, there are no other issues, etc. Again, cutting it very close. Getting back from deeper than a 100ft on a 6 pony - hardly possible. Happy diving!

 

[diver 85]

Short answer? No.
I wouldn't use a 6cf pony as backup to dive in a pool.

boy, I want to see that pool you're diving------

 

[Spg01]

If you want safety stops included you will need about 20 cuft from 100 ft. I am sure people use less, but that is what I have heard.

 

[PSFlyer]

If you want safety stops included you will need about 20 cuft from 100 ft. I am sure people use less, but that is what I have heard.

I am sorry I forgot to mention in my calculations that I assumed skipping the safety stop. Not advisable but I guess in a real emergency, assuming a safe ascent rate ( I quoted 45ft/min) not likely to cause harm.

Revising the numbers to include safety stop, (but not the deep stop) here is what I come up with:

1. Ascent from 100 to 15 feet: Avg Pressure 2.75 * SAC 1.0 * Ascent time 1.9 min = approx 5.25 cu ft

2. Safety stop at 15 ft: Pressure 1.5 * SAC 1.0 * 3 min = 4.5 cu ft

3. Reaching the surface: Avg press 1.25 * SAC 1.0 * 0.5 min = 0.6 cu ft

4. All of that totals: 10.35 cu ft.

Conclusion: Most likely a 13 cu ft would be adequate from 100 ft. As far as I now the difference in size between a 13 and 19 (or20) is not that great, so If I were to get one myself, I would choose to go with 19.

Experts, please chime in - are we good with those numbers? or is my logic flawed in some way? Once again, I m going by the numbers as I have never practiced using a pony.

Happy Diving

 

[adelman]

There is enough gas in a 6cuft cylinder to allow you to safely ascend to the place where you are going to drown...

 

[Crush]

You will have to answer a few questions:

1. At what maximum depth do you plan on using your pony?
2. Do you want a minute at max depth to resolve your problem, or are you assuming that you can immediately begin a direct ascent?
3. What is your maximum desired ascent rate between depth and 30 feet? What is your maximum desired ascent rate between 30 feet and the surface?
4. Do you want to be able to carry out a three-minute safety stop at 20 feet?

A faster-than-recommended ascent rate may or may not lead to DCI, but you would certainly be advised to stop diving for that day and perhaps for a few subsequent days.

Finally, a pony is useless unless you practice with it regularly. You will be able to fill it from your main tank between dives with one of these: Tank to Tank Equalizer discounts on sale IST

I made a lengthier post on pony bottles here: http://www.scubaboard.com/forums/tanks-valves-bands/372271-pony-redundant-set-up-2.html#post5761909