No such thing as a Pony Bottle

[Colliam7]

is there a sort of rule or guide regarding, the size of the pony bottle if you stay in the recreational limits 42m and inside your NDL, for example, 35m with 3min safety stop require approximate a 19cf bottle if you are at 40m with a safety stop at 16m for 2min and another at 5m for 3 min you need a 30cf bottle aprox, in case of emergency, I know more capacity obviusly is better but as well more wait in drag and you want to keep it in proportion.

Differences in 'Drag' from a 40. Vs a 30 vs a 19 are, frankly, trivial. I wouldn't base my choice on that perception. Likewise, the regulator is often the biggest weight issue.

Perhaps, a more valid basis for selection is the relationship between what you might need it for, and the capacity it provides. For example, if you routinely dive to 60 feet, and at that depth you suffer an air supply failure, how much air (from your pony) would you need to safely surface? You would probably need a minute at depth to figure out what the problem is, and reply your pony. Then you would want enough gas to ascend at a safe controlled rate (30 ft/min), and then complete a 3 min safety stop at 15 feet. To determine how much gas you need use a reasonable SAC rate - for the circumstance. While you may have a SAC rate of ~.7 cfm under normal conditions, that rate will very likely increase with stress associated with a situation where you might need to deploy your pony. So use a SAC of at least 1 cfm, possibly higher. Figure out how much gas you would need to safely ascend.

But, if you routinely / even occasionally dive to the recreational limits of 130 feet, do the same calculation. Don't simply decide on a pony because of what we say on SB about what we use. Decide on the basis of what you might need, based on the dives that you usually do.

Personally, I sling a 30 or 40 as my pony bottle. Those fit the diving I do, and how much air I might need. Your needs may differ, or may be similar.

 

[Akimbo]

Differences in 'Drag' from a 40. Vs a 30 vs a 19 are, frankly, trivial…

Perhaps, but the physical burden can be much more for most divers. A single plus a 40 Ft³ bailout bottle is nearly as or heavier than a comparable set of independent doubles or with an isolation valve using progressive equalization.

 

[MXGratefulDiver]

I have never perceived Nitrogen Narcosis at 130' and the great majority of my dives have been in +/-50° F water. Same with most people I know. IMHO, your “red flags” are warranted.

... that's a data point of one, and insufficient to make generalized statements. My personal limit for acceptable levels of narcosis is at about 120 fsw in Puget Sound, which is cold and dark. I know some people who can go much deeper than that before claiming to be narc'ed ... and some who will show obvious signs of narcosis at much shallower depths.

The mechanism of narcosis isn't well understood ... although the symptoms certainly are. There seem to be a lot of variables ... including some that are more related to personality than to physiology.

... Bob (Grateful Diver)

---------- Post added October 6th, 2014 at 05:24 AM ----------

What this instructor is saying/ teaching is a good learning experience for you, every instructor has their way of teaching and you can now learn what not to do if and when you decide to become an instructor.

Given what the OP has described in consequence posts, I disagree. What this instructor is saying/teaching is bad scuba practices that, at best, don't make sense ... and at worst are downright dangerous.

What's the point of clipping a redundant air source at 15 feet? At that depth all it will do is provide gas for a safety stop ... assuming you make it back to the tank. What happens if you need it at 100 feet?

Forcing someone into water that cold with inadequate thermal protection isn't merely stupid, it's dangerous. I dive regularly in water that cold ... NOBODY here uses anything less than a 7 mil farmer john, and most use drysuits. They do so for a reason ... hypothermia can incapacitate you to the point that you're unable to perform the simplest skills.

When I was a DM I was asked by an instructor to come help him with his AOW deep dive. What I didn't understand ... because he never saw fit to mention it ... was that he intended to keep his students at 130 feet long enough to run out of air, and have them do an emergency ascent while sharing air with a DM (there was a DM for each student). I was furious when I realized what he was doing, and confronted him about it after the dive. He rationalized it by saying that students needed to experience how to react to OOA while narc'ed. While I agree with the principle, intentionally running someone with less than 10 dives OOA at 130 feet is a very dangerous way to do it.

Every instructor believes they're providing a good learning experience. Sometimes it's just not true ...

... Bob (Grateful Diver)

---------- Post added October 6th, 2014 at 05:26 AM ----------

A slung bottle is a slung bottle. It is the intended use that determines whether it is a pony, a stage, or a deco bottle. Deco bottles generally contain a higher percentage O2 mix than your primary breathing gas, and are intended to accelerate decompression from dives which have incurred mandatory deco. Stages generally contain the same gas as your primary supply, and are intended as supplemental volume to permit a longer dive. One intends to use the gas in a stage.

Pony bottles, on the other hand, are NOT intended for use. The gas they contain is not part of the gas plan for the dive. They are intended as an emergency supply only, and generally will contain the same gas as your primary supply.

Pony bottles can be mounted on the back or slung. The complications of having a pony bottle are the same as any other bottle and regulator -- the regulator can leak, resulting
in having less gas in the bottle than you expect. It can freeflow. It can come loose and get entangled in something. You can actually lose the bottle. All of these problems can be dealt with by an attentive buddy, let alone an instructor.

... it would be interesting to know whether or not these "instructors" are even bothering with a gas plan beyond "monitor your gauge and end the dive with 500 psi" ...

... Bob (Grateful Diver)

---------- Post added October 6th, 2014 at 05:28 AM ----------

You can also seek out Rob Neto, aka Dive-aholic here on ScubaBoard. Like Doppler, he's a lot of fun with little ego and very ScubaBoard friendly.

I can personally attest that Rob teaches an excellent sidemount class ...

... Bob (Grateful Diver)

 

[Akimbo]

My quoted reply was in response to this:

…I'm being told we need to meet a required 130feet in 50 degree water because they want us to be narc'd and know how it feels...

I have never perceived Nitrogen Narcosis at 130' and the great majority of my dives have been in +/-50° F water. Same with most people I know. IMHO, your “red flags” are warranted.

... that's a data point of one, and insufficient to make generalized statements. My personal limit for acceptable levels of narcosis is at about 120 fsw in Puget Sound, which is cold and dark. I know some people who can go much deeper than that before claiming to be narc'ed ... and some who will show obvious signs of narcosis at much shallower depths…

Because the statement includes “Same with most people I know”, the data point is in the hundreds. Though, to be fair, many of them have a lot of time on deep air being commercial divers.

At that depth, a student isn’t likely to learn much about Nitrogen Narcosis. Most won’t feel much of anything and those that believe they might are likely to feel the results of apprehension and elevated CO2 far more than Narcosis. Training agencies chose 130' as a recreational depth limit because Narcosis is so minimal for the great majority of people, in addition to being near the edge where staying within NDLs is reasonable.

It has been my experience that predictably experiencing Narcosis for the majority of people requires more like 160-180'. Narcosis and elevated CO2 share a lot of symptoms. Working hard a 50' can present symptoms that can be misinterpreted as Narcosis, but relaxing and deep breathing makes them go away. Anxiety compromises everyone’s judgment.

Now, if the initial statement I took exception to was something like: “I'm being told we need to meet a required 130feet in 50 degree water because they want us to know if our individual susceptibility to Narcosis was higher than average” I would have no problem at all.

My career gave me a glimpse into Nitrogen Narcosis that recreational divers rarely get an opportunity to experience. Being on deck and monitoring working divers through voice and sometimes CCTV allows uncompromised observation of impairment. It also allows divers to explain actions that are perfectly coherent but might appear suspicious when observed only.

We also could observe divers deep on air through viewports on chambers, though much less frequently. I have known some people with repeatedly unusually high Narcosis tolerance. The one data point I have is 285' on air… everyone is consistently compromised. How do I know? That is the depth that all Navy First Class Diver students were (are?) were pressurized to in a chamber. I have never even heard of a boast about being in control on those dives.

Why did the Navy choose 285'? Because the PPO2 on air is 2.0, the safe limit at the time and absolutely everyone gets so screwed up from Narcosis they can’t deny it even to themselves.

IMHO, there is entirely too much hysteria over Nitrogen Narcosis in recreational diving.

 

[MXGratefulDiver]

Because the statement includes “Same with most people I know”, the data point is in the hundreds. Though, to be fair, many of them have a lot of time on deep air being commercial divers.

That was kinda my point ... there's a massive gulf of difference between a relatively new recreational diver and a commercial diver with extensive training and experience working under high narcotic conditions. It goes way beyond comparing apples and oranges.

That said, it's more likely that you didn't notice your narcosis not because you weren't narced, but because you were so used to it that you'd mentally adapted to the condition ...

IMHO, there is entirely too much hysteria over Nitrogen Narcosis in recreational diving.

I'm not sure I'd agree. The thing about narcosis is that it impairs your ability to think through problems. People who have been trained and conditioned to deal with those problems on "auto-pilot" ... such as those who've gone through commercial training ... have much less difficulty thinking through problems because they've already been there and done that, and so they can operate with a reasonable effectiveness while impaired. A typical recreational diver doesn't have that ability, and therefore must rely more on having the bandwidth to think their way through a problem.

I will, however, say that I think the current method of having someone solve puzzles or write their name backward or some of the other acts of stupidity that dive instructors call "tests" on the deep dive serve no useful purpose. They're artificial data points, since no one's ever going to do those things on a real dive ...

... Bob (Grateful Diver)

 

[PfcAJ]

"I feel fine!"

Says every drunk driver ever.

 

[mruseless]

I agree with what you said about gas management. I was on an Aggressor boat last year with a guy who used a 13cu ft pony. Good for him, I thought. Until he went OOG and had to surface on his pony (far from the boat, I might add). TWICE. He had incredibly poor gas management skills. Blamed it on his photography, went chasing an eel or something until he ran out of air. How does that happen? Easy, he was using the pony as a crutch so he didn't have to care about his gas supply.

So I think a pony is a fine idea, IF you have good gas management/planning skills.

Admittedly, I have not read all the posts so I apologize if this has been said. A similar situation happened to me a few years back. I thought I might be able to give some insight into the shop owners thinking. After an uncomfortable dive with a poorly trained diver, it became clear to me that not all buddy's are equal. Some buddy's simply do not provide the safety and redundancy you need underwater. I decided to dive completely redundant. I began using a 40 cf on my dives, especially those deeper than 60 feet. A very good and capable instructor looked disapprovingly upon my new set up. He suggested that pony bottles encouraged divers to dive longer and deeper and to subsequently use more air. He suggested that pony bottles were the first step to poor gas management. I respect his concern about air management. He was genuinely concerned that divers would develop bad air management. The problem lies with the diver not the pony. I carry a RAS on all dives. It's just good dive practice.

 

[Akimbo]

That was kinda my point ... there's a massive gulf of difference between a relatively new recreational diver and a commercial diver with extensive training and experience working under high narcotic conditions. It goes way beyond comparing apples and oranges…

I considered that, but it doesn’t explain how these factors fit into my observations:

• I started recreational diving 8 years before Navy Training and had the same experience. We would frequently dive to 120-160' in Carmel Bay.
• I was the rare exception among Navy diver trainees that had any diving experience before starting class. Therefore, there was no extensive training or experience to draw on. Until First Class Diving School, most trainees hadn’t been below 60' since Second Class School — where we only made one dive deeper than 100'. However, most did have lots of time underwater and in zero visibility which was no doubt helpful in managing any Narcosis.
• I have made a hundreds of dives in cold water to the 120-150' range on private and charter boats off Norway, the UK, and the Northern California coast with recreational divers.

A lot of inexperienced divers have the strange impression that Nitrogen Narcosis is some kind “reefer madness” that overtakes all reason and starts like a light switch. I have never observed that even on those 285' chamber dives.

In the vast majority of recreational cases of Narcosis I have seen and experienced, the diver recognizes their impairment. Their sensory abilities and hand-eye coordination are usually far more compromised than their judgment. Of course, limited “inputs” can cause suboptimal and sometimes incorrect judgments. In fact, most divers tend to become overcautious as a coping method — not a bad thing at all.

The real point I am trying to make is you aren’t likely to experience Narcosis at 130', even on your first dive. You are likely to be apprehensive and have elevated CO2 due rapid shallow breathing, which mimics a lot of Narcosis symptoms. I believe that divers would be better served with a more realistic representation of Narcosis rather than what amounts to scary sea stories.

"I feel fine!"

Says every drunk driver ever.

How is a diving supervisor on deck monitoring working divers and chamber occupants going to be impaired by Narcosis? Those are the observations that have the most validity, in addition to getting complex work accomplished.

 

[PfcAJ]

I considered that, but it doesn’t explain how these factors fit into my observations:

• I started recreational diving 8 years before Navy Training and had the same experience. We would frequently dive to 120-160' in Carmel Bay.
• I was the rare exception among Navy diver trainees that had any diving experience before starting class. Therefore, there was no extensive training or experience to draw on. Until First Class Diving School, most trainees hadn’t been below 60' since Second Class School — where we only made one dive deeper than 100'. However, most did have lots of time underwater and in zero visibility which was no doubt helpful in managing any Narcosis.
• I have made a hundreds of dives in cold water to the 120-150' range on private and charter boats off Norway, the UK, and the Northern California coast with recreational divers.

A lot of inexperienced divers have the strange impression that Nitrogen Narcosis is some kind “reefer madness” that overtakes all reason and starts like a light switch. I have never observed that even on those 285' chamber dives.

In the vast majority of recreational cases of Narcosis I have seen and experienced, the diver recognizes their impairment. Their sensory abilities and hand-eye coordination are usually far more compromised more than their judgment. Of course, limited “inputs” can cause suboptimal and sometimes incorrect judgments. In fact, most divers tend to become overcautious as a coping method — not a bad thing at all.

The real point I am trying to make is you aren’t likely to experience Narcosis at 130', even on your first dive. You are likely to be apprehensive and have elevated CO2 due rapid shallow breathing, which mimics a lot of Narcosis symptoms. I believe that divers would be better served with a more realistic representation of Narcosis rather than what amounts to scary sea stories.



How is a diving supervisor on deck monitoring working divers and chamber occupants going to be impaired by Narcosis? Those are the observations that have the most validity, in addition to getting complex work accomplished.

You seem to be confusing commercial diving with rec diving again.

With rec diving you're on your own, there's no topside support, no comms, and limited gas.

There are PLENTY of reports of folks experiencing narcosis symptoms in the 80ft range. I've been there myself. To say otherwise is just ridiculous, and to pretned that commercial diving and all the support measures that are in place are even slightly similar to rec diving is beyond the pale. Just having the ability to talk through issues might be the edge that allows commercial guys the ability to deal with increased narcosis.

 

[Akimbo]

You seem to be confusing commercial diving with rec diving again.

With rec diving you're on your own, there's no topside support, no comms, and limited gas...

Not really, I gave plenty of examples of recreational experiences. Besides, topside support, communications, and unlimited air supplies doesn’t change human physiology. However, the commercial diving setting provides far greater opportunities to reliably assess diver performance.

What makes you believe you were narked at 80' rather than apprehensive and/or influenced by elevated CO2? Nitrogen Narcosis unjustifiably gets blamed for many perceived aberrations, most of which aren’t relevant to diver performance.