What pony size?

[GrumpyOldGuy]

1.4 isn't all that conservative. If your "out of air" problem happens when you've been swimming into the current for a few minutes and are breathing pretty hard right before the added "excitement" of discovering you have no air, even 2.0 is not excessive.

Also, there are a number of possible first stage failures that cause an immediate and unexpected loss of all gas without warning, including a clogged dip tube, a clogged first stage inlet filter and on rare occasions, an exploding first stage (SCUBAPro Mk 10, I believe).

flots.

So are you trying to say I need 3.5X of normal SAC to deal with an OOG situation? I find that humorous, along with preparing for an exploding 1st stage. Possible, but as likely as being dinner for a roaming great white shark. Most likely when I do need it, if ever it will most likely be one of those 1:1000 things like a blown 0-Ring, failed LP hose or free flow.

What I am saying is allow for a reasonable multiplier to account for stress. 2.0 is a standard many people use, I feel for me 1.75 is enough for me. That's based on my regularly drilling with my pony and being extremely comfortable in the water. When doing these math exercises, people sometimes take the worst case scenario from every level (excess time at depth solving a problem, very high SAC) and then compound them by requiring best ascent practices (slow ascent and execution of optional safety stops). If that is the model you want to use, then slinging a 30 or larger is your tool of choice. My model is swap regs and swim up to safety stop. Then assess. When I see that I only need 1/4 of a 13cf bottle when drilling for this, then I am pretty confident a full 13cf will get the job done.

 

[flots am]

So are you trying to say I need 3.5X of normal SAC to deal with an OOG situation?

You personally? I have no idea. People in general, especially people who are buying their first pony? Probably. An RMV of 2.0 of more isn't uncommon in a really stressed diver.

I find that humorous, along with preparing for an exploding 1st stage. Possible, but as likely as being dinner for a roaming great white shark. Most likely when I do need it, if ever it will most likely be one of those 1:1000 things like a blown 0-Ring, failed LP hose or free flow.

Yeah, it's astonishingly funny and unlikely, except that I watched it happen. Happily, the gear was still above water when the first stage exploded. These aren't common occurrences, but if you're going to plan on handling "out of air" you might as well make the plan workable, no matter what caused it.

Clogged first stages are actually not all that rare with poorly maintained tanks. They happen all the time. All it takes is a tank with crap in it, a missing dip tube and the desire to flip over and see what's hiding under the ledge. In locations where VIP just means "important visitor" and a hydrostatic test is something mentioned in a book once, these events occur together routinely.

On the internet everybody has an RMV below .4, nobody panics and all the children are above average. In the real world, divers routinely come in around .7, and a stressed diver can easily triple that.

flots.

 

[rhwestfall]

In the real world, divers routinely come in around .7, and a stressed diver can easily triple that.

flots.

WOW! First time I've ever been grouped in a mass known as "normal"...... usually the prefix of "ab" is included for me...

 

[GrumpyOldGuy]

You personally? I have no idea. People in general, especially people who are buying their first pony? Probably. An RMV of 2.0 of more isn't uncommon in a really stressed diver.

Yup, everyone is different, that's why you need to do your own calculations and not use a "rule-of-thumb or one size fits all".
The thing about stressed divers is if you drill and have some significant experience, you should not be highly stressed because you o-ring blew or your 1st stage iced up and free flowed. You know you have redundant gas, you know how to use it, its a little excitement. So while I don't doubt a stressed diver without redundant gas and experience and drilling might hit 2.0 an beyond, its not the case we are speaking.

Yeah, it's astonishingly funny and unlikely, except that I watched it happen. Happily, the gear was still above water when the first stage exploded. These aren't common occurrences, but if you're going to plan on handling "out of air" you might as well make the plan workable, no matter what caused it.

Here is were we depart. You want to prepare for ALL possibilities. If you really want to do that, then doubles on an isolation manifold with 2 DIN's is the logical conclusion, anything less is leaving something on the table that might happen.

Clogged first stages are actually not all that rare with poorly maintained tanks. They happen all the time. All it takes is a tank with crap in it, a missing dip tube and the desire to flip over and see what's hiding under the ledge. In locations where VIP just means "important visitor" and a hydrostatic test is something mentioned in a book once, these events occur together routinely.

Sorry, I don't hear about it happening all the time. You have to have 3 things in your scenario, 1) missing dip tube, 2) crap in the tank, 3) flipping over. I have heard of it a couple of times. It can happen. Same poor dive op is probably giving you a little dose of CO with the gas too or may leave you stranded in the ocean. I would spend more time vetting for a good dive up than preparing for this, which at worst case is going to make me swap regs. Which takes me 5-10 seconds max. The CO thing does scare me.

On the internet everybody has an RMV below .4, nobody panics and all the children are above average. In the real world, divers routinely come in around .7, and a stressed diver can easily triple that.

Thanks for calling me a liar.:crying2:

 

[redacted]

You personally? I have no idea. People in general, especially people who are buying their first pony? Probably. An RMV of 2.0 of more isn't uncommon in a really stressed diver..

The way I see it, the pony should prevent most of the stress, at least until it goes LOA/OOA. I size my pony based on a fairly normal breathing rate.

 

[Panama Jones]

While probably getting away from Cocoajoe's question for while, this was a great thread for me for learning. So thanks all. As I had said in past threads, I am somewhat of an experimenter. So I made the following assumptions:

1. Cocoa is AOW so he is probably diving no-overhead in 130 feet or less (limit of his certification).
2. Wookie says you don't plan for cave ins or shrimpnets and I agree with him. You do plan for technical failures.
3. Other threads "basically' say that you can hyperventilate (TSandM says this is not possible with equipment so by hyperventilate I actuall mean panic breathing or simulated stress breathing) for a fairly long time before any blackout would occur.

So rather than try to calculate your panicked breathing rate as you don't know exactly what that is why not experiment to figure your pony needs?

1. Assume in an OOA situation due to tech failure (not stupidity) 1 minute or less to try and solve the problem and go to backup. (make it 2 minutes for conservativeness).
2. Assume the 30fpm ascent rate with SS to surface from 130 feet (60 if you are just OW)
3. Take the total time and then go down with a buddy and figure out how much air you will breathe at your max depth by simulating stressfull breathing. (also IMHO, equipment failure OOA is not a reason for high stress..most divers should take a blowout or freeflow in stride so simulated stress breathing should be way higher adding even more conservativeness).
3. See how much air you breath in the simulation and buy a pony accordingly. Also note that as you ascend, you will use less so if the test is done on the bottom, there is even more conservativeness.

Basically, if you breath half your AL80 in 9 minutes (2 minutes to try to solve, 4 minute ascent, 3 minute SS) with somewhat elevated breathing, you would buy a 40cf pony for your dive limits. Would this work or be too dangerous?

 

[GrumpyOldGuy]

So rather than try to calculate your panicked breathing rate as you don't know exactly what that is why not experiment to figure your pony needs?

I just do practice ascents from 80' (local spring) using a pony and measure how much air I use at the end of the dive. Sometimes I remove my mask and shoot my SMB then ascend (without mask) to make it more exciting. The more you drill, the less air you use due to stress.

 

[Max Speed]

On a no deco dive if my dip tube just clogged at 100+ feet there is NO chance that I am casually heading to the surface at 30 fpm. Realistically I am gonna pedal like crazy to 60 feet and then cruise a bit slower from there. When I get to 20 feet on the hang line under the boat and can see the ladder i will relax and burn whatever is left over in the bottle.

Sent from my GT-P3113 using Tapatalk 2

 

[CamG]

I have used 30 cf, sold all three went to 40's or 80's just makes more sense for my diving.
I no longer dive singles only to train OW divers and my practice is to not dive below 60' without redundant.
Just my practice and I know this is the Advanced Forum.
As far as the argument about what swims or dives easier I agree it really doesn't matter when I am diving both swim easily.

I use a Al 80 for a buddy bottle on many dives it will get me out of a pinch not to mention my buddy if he finds himself in trouble.
In the several direct ascents I have made while in training I have to agree it takes more gas in cold water than in warm.
Stress levels are a bit more intense the cold water creates a added factor but when trying to plan for a gas failure of some kind I prefer to have more than just enough gas.
Hope these thoughts help think about what your diving requires then buy it and train with it to see if it fits your dive plans.

CamG Keep Diving....Keep Training....Keep Learning!

 

[dumpsterDiver]

The problem with big pony bottles is they are heavy and cumbersome. After you have done a few (or several) hundred dives to 70 or 100 ft, all without a catastrophic failure, you begin to view that heavy pony bottle as a hindrance and a liability and a pain in the ass and soon you are leaving it on the boat for dives that are just to 70 feet or so.. And soon (once it goes out of hydro) you stop taking it...

I want the smallest pony that is "safe". Also, if I have a real emergency and have to ascend on a pony, the last thing I will do is SWIM. My air is much better used on inflating the BC slightly, and beginning a buoyant ascent and allowing myself to concentrate on slow deep breaths and total relaxation of the big leg muscles. I know this is not recommended, but that is what I would do..