Testing a Spare Air

[2airishuman]

Where do you get that idea from? Don't know about you but you but I can swim the length of a 40' I ground pool and back on one breath. Add a half dozen breaths provided by a 3ff cylinder and that's another 40-50' easy.

Part of my workout routine is 8 laps in a 25 meter pool. I'm not really a freediver but go deeper with a snorkel than, well, most people who snorkel. People vary in their ability to do a breath hold based on physiology, condition, and experience. You could probably do a CESA from 100'. I could probably do a CESA from 100'.

That isn't what this thread is about.

Let's look at the example of a typical diver who runs out of air at 90' on a dive that is going badly. With a direct ascent to the surface and a SAC rate of 0.8 under the circumstances, which is not especially conservative, and a 60 fpm ascent with no safety stop, they'll use exactly 3 cf of gas. I'm doing the math in my head, so correct me if I'm wrong. (Average depth of 45 ft = 2.5 atm; actual air consumption 0.8 x 2.5 = 2.0 cfm; x1.5 minute ascent gives 3.0 cf used).

So, on a deep dive to 100', a typical diver isn't going to make it to the surface on a 3.0 cf air supply, even if they do everything right, and even if we make favorable assumptions like an immediate 60 fpm ascent and no safety stop and the bottle is actually full and zero time spent at depth deciding what to do.

If the whole point of a Spare Air is that you can do a CESA from a shallower depth, well, great, they meet that goal. That isn't how I plan for contingencies on my dives.

I personally have settled on a 19 cf cylinder as being suitable redundancy for the dives I make. It is sufficient for a prompt, direct ascent to the surface, at a 30 fpm ascent rate, under balanced assumptions regarding bottle fill, SAC rate, time at depth before beginning ascent, etc. Other people make different assumptions and end up with 13 or 30 with some people going with 40 rather than 30 because they like how the 40 cf bottle trims out better than the 30cf or need one for a stage for tech dives or whatever. I think those are all reasonable choices.

 

[Bob DBF]

Let's look at the example of a typical diver who runs out of air at 90' on a dive that is going badly.

The typical diver dosen't even have a Spare Air, so it's going worse than you think.

How the scenario goes would depend on whether the Spare Air owner ever actually trained for the casulty. If they just bought it to make themselves safe without any thought or practice it will be as big a fuster-cluck as if they never bought the unit, may be worse.

I agree with your approach to determining your pony size and how it would be used. It may not slow Spare Air sales, but following your example would give those that buy them something to think about.


Bob

 

[markmud]

The typical diver dosen't even have a Spare Air, so it's going worse than you think.

How the scenario goes would depend on whether the Spare Air owner ever actually trained for the casulty. If they just bought it to make themselves safe without any thought or practice it will be as big a fuster-cluck as if they never bought the unit, may be worse.

I agree with your approach to determining your pony size and how it would be used. It may not slow Spare Air sales, but following your example would give those that buy them something to think about.


Bob

Hi Bob,

I remember the J-valve from when my dad was diving. And when he would make me strap on his gear and clean the barnacles and dickfish of the hull in the middle of winter. He did not mind doing it in the summer.

Back on topic: What frequency do you carry your pony and what are the odds that you will ever need one?

I would like to throw in another factor point that most anti-pony bottle posters (mostly on other threads) use to justify their position. They contend that the odds of your primary system completely failing are pretty close to zero. They then contend that most divers who use a large pony are also using it as a contingency in case of entanglement. Then they add that that diver is better off diving with a larger primary cylinder that has enough reserve capacity to cover an entanglement situation. Logical thinking? Yes it is.

I do subscribe to both of those theories. In entanglement areas (where commercial fishing and kelp are common) I use a 100cf tank. I rarely come aboard with less than 40 cf remaining in the tank and usually more. My SAC rate is .5.

I have suffered 3 primary system failures while u/w. All three ended solo--two started solo and the other ended solo when my instabuddy ditched me u/w.

I did not need my pony, or have to switch to my pony (if I had one in one case). I breathed off free flow or remaining back gas.

The odds of a person needing a pony for real are slim to none. The odds of someone needing a pony on the deepest part of their dive are even slimmer and none-r.

I am full circle, I am finally landing the plane, here is my point:

If the odds are so slim that you would ever need one, why pack around a 19cf, a 30cf or even a 13cf pony? You won't sling it because it is a PITA. For everyone that uses a pony, do you use it on every dive?

I use one on every dive. Sometimes it is my tank mounted 6cf. Lately, I have used my 13 cf in conjunction with my 6cf because I am to lazy to derig the 6cf for the one dive where I need a bigger pony (appreciably below 100 fsw). My 13cf is a sling bottle unit.

To iterate, my 6cf is easy to fly with, it is easy to rig, it is completely secure and totally out of my way while diving; therefore, I don't mind diving with it on every dive. It is benign, it is painless, it is forgettable, it is not noticed, it is weightless, it may as well not be there in my mind unless I want to practice with it or use it for real.

Can any of you say that about your 19cf, your 30cf, or your 40cf pony bottles? Are your ponies in hydro and do they have a current vis sticker?

If the OP has chosen a Spare Air and will carry it on every dive, he is better off than choosing a 19cf that sits in his garage collecting dust.

Dang it, why do I have to be so long-winded?
markm

 

[Johnoly]

If the odds are so slim that you would ever need one, why pack around a 19cf, a 30cf or even a 13cf pony?

People ask me all the time on boats why I have a pony.

I just ask them why they wear seatbelts if they haven't been in an accident?

 

[Marie13]

Your diving experience places you well past the target demographic, you have to look back when you started your interest in advanced diving and wanted redundancy, and have no contact with ScubaBoard. Or be a diver that has lost a buddy or two and wants some backup. That is the target demographic.
Bob

I was certified in Oct 2016 and bought a pony that winter. I was influenced by a friend who carried a 30cft. She had an instructor that advocated redundancy, at least 30cft. So SB didn’t even come into the equation for me.

 

[dhaines429]

Before I went sidemount I carried a pony. I had a 30cf pony and then a 40. I never had to use it but I dive solo so I consider redundant gas my buddy. In terms of size I settled on 30 becase it would be enough gas to get me safely back to surface with gas to spare. I carried it buddy diving as well because we all know that buddy separation happens and I also like the idea of having them on pony in a situation rather that attached to me by hose to my tank. There are a lot of people that hate on the spare air and criticise it's use but I do commend the OP for actually testing it. So while I wouldn't use it even if I was doing single tank again if someone has tested it and found it to be enough I say go ahead.

 

[vjongene]

I certainly agree with you about running out of gas but the OP does mention OOA twice and the DAN reports are full of people OOA. Behind medical issues its the number 2 cause of scuba accidents. I hope he is disciplined and manages his air well and always surfaces with some in reserve. But I dont know that he is disciplined all I know is he is human and can have a bad day and screw up.

The really interesting thing is this conversation is not really about spare air its about mitigating risk. OP is diving alone photographing and recognizes he is taking additional risk.

Spare air is a way to mitigate that risk but is it a good way?

Are there better ways for this diver to mitigate the risk of diving alone and being distracted? Yes i think so

I mentioned OOA, but in fact this is something that has never happened to me. At any point in a dive, even while distracted by taking pictures or doing coral gardening (my other hobby), I can tell within 10-20 bar how much air I have left. I am more concerned about equipment failure, although this has not happened so far either. In either case, not having a buddy nearby, I wanted to make sure that I could surface from any depth I would be comfortable to dive alone. My other risk mitigation device is a rescue GPS, so I can alert the Coast Guard if something should go pear shaped at the surface. And finally yes, someone always knows that I am out there alone, and would sound the alarm if I didn't come back within a reasonable time.

 

[Johnoly]

.. device is a rescue GPS, so I can alert the Coast Guard...

The power of Scubaboard......Just learned something new, THANK YOU !!

The Curacao Dutch Caribbean Coast Guard

Dutch Caribbean Coast Guard - Wikipedia

 

[johndiver999]

I have never used a spare air. The new 6 cuft model seems to be approaching a capacity that may handle an ascent for 100 ft (again depending on assumptions).

Excuse my ignorance, but I always thought the idea was that you could stick the spare air in your mouth and hold it with your teeth and free up your hands? Is that correct?

If so, I would be interested to see how a 6-cu-ft bottle feels while being retained only by my teeth and a zip tie on a mouth piece?

A whole bottle hanging from your teeth is a lot different than a regulator attached to a hose.

 

[markmud]

I have never used a spare air. The new 6 cuft model seems to be approaching a capacity that may handle an ascent for 100 ft (again depending on assumptions).

Excuse my ignorance, but I always thought the idea was that you could stick the spare air in your mouth and hold it with your teeth and free up your hands? Is that correct?

If so, I would be interested to see how a 6-cu-ft bottle feels while being retained only by my teeth and a zip tie on a mouth piece?

A whole bottle hanging from your teeth is a lot different than a regulator attached to a hose.

Hey Johndiver999,

Good point. Although, a trip to the orthodontist is probably better than a chamber ride, or being in intensive care suffering with an AGE. And then there is that morgue thing.

Several of us had a discussion regarding the price of alternatives. The link below takes you back to it. I found a button gauge for $30.00 less on EBAY from a dive shop. So the pony set-up I listed can be had for $300.
Testing a Spare Air

I would buy the 6cf pony.

Cheers
m