13 cubic foot bottle

[AndyNZ]

So I don't know why anyone would want a 13, except maybe that it's shorter...?

Oh, I dunno..... it's a pretty good size for drysuit inflation....

 

[DandyDon]

+4.9 cubic feet
+4.5 cubic feet
+3.6 cubic feet
+2.8 cubic feet
+2.5 cubic feet
+2.2 cubic feet
+1.9 cubic feet
+1.5 cubic feet
22.4 cubic feet skipping the 3 minutes @ 20 ft, or was there something else I was supposed to know about this?

Because you should plan too have too much gas in a worse-case scenario, not the opposite.

Which is why I spent $10 more to carry 2# heavier tank and 50% more air.

Another way to view a 19 cf is that it's 1/4 of a 80 cf since they are really not 80s, or equivalent to to 750# of 3000# of a 80 vs a 13 cf equivalent to to 500# of a 80. The 19 seemed call for 130 ft diving and sometimes I wish I'd got the 30.

 

[Doc Harry]

+4.9 cubic feet
+4.5 cubic feet
+3.6 cubic feet
+2.8 cubic feet
+2.5 cubic feet
+2.2 cubic feet
+1.9 cubic feet
+1.5 cubic feet
22.4 cubic feet skipping the 3 minutes @ 20 ft, or was there something else I was supposed to know about this?


Which is why I spent $10 more to carry 2# heavier tank and 50% more air.

Another way to view a 19 cf is that it's 1/4 of a 80 cf since they are really not 80s, or equivalent to to 750# of 3000# of a 80 vs a 13 cf equivalent to to 500# of a 80. The 19 seemed call for 130 ft diving and sometimes I wish I'd got the 30.

Oops, was my math off? Thanks for the correction. I made the adjustment above.

 

[DandyDon]

Oops, was my math off? Thanks for the correction. I made the adjustment above.

I hope your math on the steps was correct. I just added the lines out of curiosity. So it's 22.4 cf without the 20 ft stop...?

I looked at some on ebay. This one was cheaper when I asked him what size it was...
U S Divers Aqua Lung Aluminum Scuba Tank Professional
His reply was "Standard Size." :silly: Now it's higher than I would pay for a used tank anyway, presuming it's an 80 maybe, without hydro or viz info.

 

[dumpsterDiver]

Would any of us actually stick to 30ft/min ascent rate if we were OOA and breathing on a pony??? Just posing a question. I know I would have a hard time with that. I would get to 60ft. really quick then start a slower ascent.

I use a small pony bottle and would need to do a fast ascent rate for the deeper portion of the ascent, but if someone is willing to drag around a 30 cu-ft tank, then I see no reason why they would rush their ascent.

There is no correct answer, it is just a matter of risk assesment and how much extra weight a diver is willing to carry.

 

[Reg Braithwaite]

Would there be enough air in a thirteen cubic foot bottle to make an ascent from 130 feet, which would include a one minute stop at 30 and 50 feet and a three minute at 20, for a person like myself who is pretty easy on air most of the time?

I don't know about you, but I can say with certainty that my own SAC doubles under stress. How do I know this? Because when I took the AOW, one of the exercises I had to complete as part of the deep dive was SAC calculation, and my instructor specifically stressed me in order to demonstrate what happens to SAC under stress.

My bailout ascent plan is to slowly head up to a 15' safety stop and hang around for 3 minutes, or until the 19 cuft pony is out of air (whichever is shorter) and then surface.

I'm a little curious about this. So do you breathe the pony down until it is OOG and then surface from 15'? I ask because this seems counter to the advice that surfacing slowly is most important during the shallowest portion of the dive. If that was a consideration, I would assume that it's better to cut the deco time at 15' and surface slowly than to stay a little longer and then surface immediately because you can't breathe.

What do you think?

 

[Colliam7]

Would there be enough air in a thirteen cubic foot bottle to make an ascent from 130 feet, which would include a one minute stop at 30 and 50 feet and a three minute at 20, for a person like myself who is pretty easy on air most of the time?

Assume SAC = 1.0 if you're bailing out ... Assume ascent rate 30 feet/min with average depth halfway between

TOTAL REQUIRED = 24 cubic feet to get you back on the boat with 0 p.s.i. remaining

So, the answer is 'No'. Even if I use a slightly less conservative calcuation (0.75 CFM SAC, and no diddling around at 130), I come up with the same answer - 'No'.

TOTAL REQUIRED GAS:
3 min ascent x 85 feet (3.57 ATA) x 0.75 CFM = 8.4 cCF (130' to 50')
1 min at 50 feet (2.5 ATA) x 0.75 CFM = 1.9 CF
1 min ascent at 40 feet (2.2 ATA) x 0.75 CFM = 1.7 CF
1 min at 30 feet (1.9 ATA) x 0.75 CFM = 1.9 CF
3 min at 20 feet (1.6 ATA) x 0.75 CFM = 1.9 CF
1 min ascent x 15 feet (1.45 ATA) x 0.75 CFM = 1.5 CF

TOTAL REQUIRED = 17.7 CF

However, if you used this schedule, AND assumed a SAC of 0.5 CFM - which a lot of people use as their 'resting' SAC or deco SAC, you end up estimating a need for 11.8 CF, which would theoretically work. It might be fun to try it, to see for yourself. Take a 13 CF bottle with you to 130. Switch to the bottle and do a controlled, comfortable ascent. See if it lasts until you surface. You still have plenty of air in your backgas tanks, so it is not a safety issue if you run out and need to switch back. But, you can empirically answer the question that way.

 

[halocline]

I agree that the deeper portion of the ascent, at least to 60 ft, could easily go at 60 ft/min, and if I were within NDL, I'd almost certainly head straight for a safety stop. So I would plan on 2 minutes total to get started and get from 130 ft to 60, roughly from 5 to 3 ATM, so at an elevated SAC of 1, I guess that's about 8cft, correct? Then another 2 minutes to get to the safety stop (a little slower than 30ft/min) that's roughly from 3 ATM to 1.5, or somewhere around 4.5cft, that leaves you with no safety stop and only a .5cft reserve at that. Pretty tight......I guess if you were reasonably calm and had an average SAC of .6 throughout the whole affair you'd use 7.5cft on the same schedule, leaving you with theoretically enough gas for a 5 minute stop and plenty to get to the surface. One problem is the near certainty that your anxiety (and breathing rate) would be higher at the onset of the emergency, when you're deepest. If you began your ascent immediately and got to 60ft in one minute, you'd have an extra 3-4cft to work with. So, it's not impossible to safely get to the surface with a 13ft bottle, but there's very little margin for error or even normal variation in the situation. Feel free to correct/comment on whether or not my calcs are even close!

Of course the biggest issue is what Wookie brought up, 130ft and OOA is probably going to mean a deco obligation, unless A) you had a tank/reg failure, B) you began the dive with very little gas, or C) you dove a reverse profile and took forever to get down there.

If you start thinking about possibly being at 130 ft with no buddy in the immediate vicinity, doubles start looking pretty good, as does some deco procedures training.

 

[AndyNZ]

Which is why I spent $10 more to carry 2# heavier tank and 50% more air.

Which is pretty much the same logic I applied to getting a 30 cu ft rather than a 19 cu ft.

 

[DandyDon]

I'm a little curious about this. So do you breathe the pony down until it is OOG and then surface from 15'? I ask because this seems counter to the advice that surfacing slowly is most important during the shallowest portion of the dive. If that was a consideration, I would assume that it's better to cut the deco time at 15' and surface slowly than to stay a little longer and then surface immediately because you can't breathe.

What do you think?

Good point. I think you're right. You can do a pretty slow OOA ascent from 15 ft, but easier to control with 100# to work with.

If you were in deco at 130 ft, I think doing the best you can to get out of it on the ascent is good, but making the ascent without drowning is your first priority - then hope the boat's O2 bottle is ready. Seen a couple of failures on the latter but at least they were alive to deal with that.

Which is pretty much the same logic I applied to getting a 30 cu ft rather than a 19 cu ft.

Yep, could call it that way too. More air is always better for me.

This chart Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan shows for Catalina tanks...
13: 4.38" OD 12.8" long plus valve 5.7# -0.8# buoyancy empty
19: 4.38" OD 17.4" long plus valve 7.8# 0# buoyancy empty
30: 5.25" OD 20" long plus valve 13.7# -0.2# buoyancy empty
As heavy as my 19 is to walk around with in the Santa Rosa NM parking lot with 7 mil suit & lead, or climb out of the water with, the 6# difference is small in comparison to the total load, but it all adds up. How much do you want to carry?

Most divers I know don't carry any pony bottle weight tho, so at least I got what I got with me. Have been glad a couple of times.