It's embedded, and it doesn't resolve correctly for me in my phone. I meant to link this, but then I saw a butterfly and a squirrel...
Maybe a shortened link? I don't think the forum software is smart enough to get past that
Optimal Pony Bottle Size for Failure at 100ft?
- Thread starter chrisjur
- Start date
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Maybe a shortened link? I don't think the forum software is smart enough to get past that
I meant for it to be downloadable. Not sure how to do that.
Thanks!
I hope that the OP (or anyone) will find it useful.
To each his own..... For me, my 19cf back mounted pony is totally sufficient redundancy for any non overhead or penetration NDL dives to 100ft. 
The "optimal" pony bottle is to get double back tanks with an isolation manifold (plus some basic training in managing failures). This gives you a lot more options than a single tank plus pony, and is only slightly more expensive. A set of small doubles is slick and easy to dive with.
But if you really don't want doubles then the other option is to sling an 80 ft3 stage tank and breathe the stage for the entire dive. Treat your back gas as the backup. You can instantly switch to it in an emergency.
But if you really don't want doubles then the other option is to sling an 80 ft3 stage tank and breathe the stage for the entire dive. Treat your back gas as the backup. You can instantly switch to it in an emergency.
I don't speak imperial, but here is a "technical" minimum gas calculation from 30m.
• 10 minute “Normal” Ascent Time (includes a 1-2-3 minutes at 9-6-3 meter minimum deco/safety stops)
• Plus 1 minute to sort out the problem
• Ascent rate from depth to first stop: 10 meters / minute => 2 Minutes
• 11 minutes for Total Ascent (Emergency Ascent Time)
• SCR under duress is assumed to be 30L/min (= ~1cu ft. but can be more!)
• Assume 2 divers ascending on an air share (maybe not in your case)
• DCR = Takes the Average Depth (in this sample 2.5 ATA) in the Ascent
11 mins x 2.5 Ave Depth (ATA) x 30 (SCR) x 2 (Divers) = 1650 Vol Liters. I Guess this would require something around 50 cu ft cylinder
Honestly, try side-mount, you might like it and never go back to single with pony
You GUE guys need to come to terms that people are going to continue to use pony bottles for redundancy. It is a perfectly valid configuration for recreational diving. Just let it go.
1650 Liters=58 cubic feet.
But your assumptions do not match the OPs situation of no deco and solo ascent. Using your initial ascent rate and SCR I get a Total Ascent Time of 7.6 minutes at an average depth of 2.16 ATA (1 minute at 30m, 2.6 minutes to 4m for the safety stop, 3 minutes at 4 meters, 1 minute to surface).
7.6 x 2.16 x 30 = 492.5 liters or 17.4 cubic feet
johndiver999
Contributor
LOL. double tanks are declared optimal. There ain't no optimal when you consider the variability in environments and divers. The same tank(s) are best for a 90 lb woman as a 250 lb man? The same tank(s) should be used in a high energy beach dive or one that requires scrambling over rocks as a dead still quarry with a dock and a ladder?
It takes 50 cu-ft to ascend from 100 feet in an emergency? More silliness!
The OP has a good handle on it, he is specifying his assumptions and shows the math. Perhaps it is best to take pony bottle advice from people who actually use pony bottles?
As always, the discussion morphs into ridiculousness when this topic comes up.
It takes 50 cu-ft to ascend from 100 feet in an emergency? More silliness!
The OP has a good handle on it, he is specifying his assumptions and shows the math. Perhaps it is best to take pony bottle advice from people who actually use pony bottles?
As always, the discussion morphs into ridiculousness when this topic comes up.
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