Defective pony, what would you do?

[Packhorse]

On another note...What is a 13cf pony good for anyway?

According to my calculations it will get you back from 50m to the surface at 10m per minute or from 40m to the surface with a 5m saftey stop for 3 minutes. based on a SAC of 25lpm.

So in answer to your question a 13 cf pony is good for no deco dives down to 50 meters. Please correct me if I am wrong.

 

[Ob1Stogie]

As a side note, I got the new tank today and put a Diverite stage bottle rig on it. I then let my two girls swim around in the bottom of our pool (with me supervising) with the tank and a reg (they are both very good snorkelers and excellent swimmers). They had a blast and it lasted about a half hour. I see two diving buddies in my near future (they are 8 and 9).

 

[rainman_02]

According to my calculations it will get you back from 50m to the surface at 10m per minute or from 40m to the surface with a 5m saftey stop for 3 minutes. based on a SAC of 25lpm.

So in answer to your question a 13 cf pony is good for no deco dives down to 50 meters. Please correct me if I am wrong.

Let's see...

I ran some calculations on my own when a friend asked me about a 13cf bail out bottle.


Let's say you're diving at 100fsw. You run out of air or lose your primary regulator, forcing the change to the bail out bottle. You're probably a bit nervous, figure a 1cfm surface breathing rate, and it takes you a minute to get sorted out on the pony. You ascend at 30fpm to 15fsw. That takes 2.5 minutes. 3 minutes at 15fsw. 30 seconds to the surface. A total of 7 minutes.

Ok, so how to calculate your gas requirement? The average depth winds up 15fsw thanks to the nice ascent rate. That is 1.45ata. So, you're breathing 1.45cfm average over the 7 minutes of ascent. Therefore, you use 10.15 cuft of your bail out bottle.


Your numbers sound pretty good to me. Again, someone correct us if we're wrong (and I'm not meaning debate the merits of bail out / pony / stage / etc, just the raw numbers for scenarios...the bail out / pony is not my choice, just helping educate).

 

[Packhorse]

I use this spread sheet that I made to calculate consumed air. Its in metric so will not suit everyone.
If anyone questions any of the logic involved please let me know as there maybe somethings I have left out or miscalculated.
The numbers in green can be changed to suit.
By the way
13cf = 1.6L @ 232 bar
24.5cf=3L @ 232 bar
90CF=11l@ 232 bar
123cf= 15l@ 232 Bar

I dive with a 3L pony.

 

[Scared Silly]

Let's say you're diving at 100fsw. You run out of air or lose your primary regulator, forcing the change to the bail out bottle. You're probably a bit nervous, figure a 1cfm surface breathing rate, and it takes you a minute to get sorted out on the pony. You ascend at 30fpm to 15fsw. That takes 2.5 minutes. 3 minutes at 15fsw. 30 seconds to the surface. A total of 7 minutes.

Ok, so how to calculate your gas requirement? The average depth winds up 15fsw thanks to the nice ascent rate. That is 1.45ata. So, you're breathing 1.45cfm average over the 7 minutes of ascent. Therefore, you use 10.15 cuft of your bail out bottle.

Your average depth is not correct. You want to break it up into stages. For example:

Assume a SAC of 1 CF/M

1' 100' = ~4 ATM = 4 cf
1' 100'->66' = ~3.5 ATM = 3.5cf
1' 66'->33' = ~2.5 ATM = 2.5cf
0.5' 33'->15' = ~1.75 ATM = 0.875cf
3' 15' = ~1.5 atm = 4.5 cf
0.5 15'->0' = ~ 1.25 atm = 0.625 cf

I get 16 cf of gas is needed. Better off with a 19cf bottle.

 

[cerich]

As a side note, I got the new tank today and put a Diverite stage bottle rig on it. I then let my two girls swim around in the bottom of our pool (with me supervising) with the tank and a reg (they are both very good snorkelers and excellent swimmers). They had a blast and it lasted about a half hour. I see two diving buddies in my near future (they are 8 and 9).

Just remember the most likely place to have an over expansion injury (esp with young, still growing lungs!) is shallow.

Not trying to be a preacher.

 

[Mambo Dave]

Just remember the most likely place to have an over expansion injury (esp with young, still growing lungs!) is shallow.

Shallow as in one ATM (33'), a 14' to 17' shore dive, or shallow as in a 6 foot pool?

Not tryin' to be a trouble-maker (I do that enough off of SB), but I think this needs clarified.

 

[SparticleBrane]

"Defective pony, what would you do?"






Shoot it.

 

[cerich]

Shallow as in one ATM (33'), a 14' to 17' shore dive, or shallow as in a 6 foot pool?

Not tryin' to be a trouble-maker (I do that enough off of SB), but I think this needs clarified.

you have bigger expansion from 6 feet to surface (by volume) than say 16 feet to 11.

Just drill rule one, never hold your breath. Of course I recommend instructors teach people to dive.