Is there a valid reason for a pony bottle

[Diving Dubai]

2.5 minutes to surface from 90 ft. with a 13 cf pony used.

A 13cf pony is all you need if you are solo diving in the normal recreational range

Okay, lets discuss. I can plug those numbers into my spreadsheet and make them work - at 0.8cf/min you use 6cf - in metric thats 22/m Sac using a total of 161 litres or 88 bar (assuming 200 bar fill) on a 13Cf (1.8l) cylinder.

I would say however that's not realistic. 2.5 mins from 30m /98ft assumes no reaction time and a continuous 10m/min or greater ascent rate.

At the very least while its do-able (on paper) it's pretty aggressive with no room for error

I would propose a different way more conservative way of looking at it would be as follows.

Firstly you really should allow for some reaction time to the incident. 1 min is a safe number on paper to react and solve the problem before starting your ascent

Secondly once you're on your pony, the emergency is over. You've got (or should have) enough gas to make a safe calm ascent to the surface.

Thirdly I'd plan a safety stop. Now I know some training states that in an emergency you can miss this, but remember the emergency is (or should be over)

Further more the incident may be on one of the last dives of say a weeks diving, so you have a higher residual N2, with the addition of a the fast ascent greatly increases the risk of a DCS

So I would suggest a more realistic time is 4 min ascent plus 3 min SS which also allows you to launch your dsmb. But using a 13cf that puts you on the surface with a near empty cylinder - if the surface is choppy you would want to keep your reg in for instance.

If it were calculations for myself I'd be using a max of 8m/min ascent and 1min time from the safety stop to surface which then gives an ascent time of 8 mins using 14cf of gas (or 175bar) on a AL 19


Still not enough reserve for my personal tastes but possible at a push depending of an individual's elevated SAC rate

 

[markmud]

Okay, lets discuss. I can plug those numbers into my spreadsheet and make them work - at 0.8cf/min you use 6cf - in metric thats 22/m Sac using a total of 161 litres or 88 bar (assuming 200 bar fill) on a 13Cf (1.8l) cylinder.

I would say however that's not realistic. 2.5 mins from 30m /98ft assumes no reaction time and a continuous 10m/min or greater ascent rate.

At the very least while its do-able (on paper) it's pretty aggressive with no room for error

I would propose a different way more conservative way of looking at it would be as follows.

Firstly you really should allow for some reaction time to the incident. 1 min is a safe number on paper to react and solve the problem before starting your ascent

Secondly once you're on your pony, the emergency is over. You've got (or should have) enough gas to make a safe calm ascent to the surface.

Thirdly I'd plan a safety stop. Now I know some training states that in an emergency you can miss this, but remember the emergency is (or should be over)

Hi Diving Dubai,

I like your rationale and I can't fault it...at all. I should follow it.

However, on a philosophical plane-of-thought, I don't even need a pony because my gear is serviced by trained techs and replaced based on age and abuse. I have a new primary first stage and second stage because of external abuse and overhaul cycles on the old system.

The catastrophic and instantaneous failure rate for diving systems is so low that a pony is really not necessary. So, if you must carry a redundant system, why not go with a redundant system that is the smallest required? A system that travels easily? After all, you will never need it, statistically speaking of course.

Devils advocate, yeah maybe.

markm​

 

[Diving Dubai]

Hi Diving Dubai,

I like your rationale and I can't fault it...at all. I should follow it.

However, on a philosophical plane-of-thought, I don't even need a pony because my gear is serviced by trained techs and replaced based on age and abuse. I have a new primary first stage and second stage because of external abuse and overhaul cycles on the old system.

The catastrophic and instantaneous failure rate for diving systems is so low that a pony is really not necessary. So, if you must carry a redundant system, why not go with a redundant system that is the smallest required? A system that travels easily? After all, you will never need it, statistically speaking of course.

Devils advocate, yeah maybe.

markm​

On the your point of equipment failure likely hood - I can't argue with it. I run monthly weekend dives for a group of friends and have for 5 years. We keep records or dive stats and "incidents", so looking back I can tell you that with a combined total of 5342 individual dives teh failures have been as follows

1 x LPI inflator runaway (mine)
4 x hose bursts on the surface while turning tanks on
6 x O-ring failures on the surface - again found when turning tanks on.

So yeah nothing of consequence. And 1000's of rec dives are made daily with basic rental gear without incident.

But if you do have a redundant system - my view that it shoudl be big enough to handle your worst case (being sensible). My figures for instance assumed that a 13cf held 13cf - but as you pointed out an 80 only holds 77cf. I want to not have to worry that my redundancy is just enough.

But I understand that you have limitations on travel and you could argue that some is better than none. Again fair point as long as when people do the maths they understand the limitations of any compromise they've made and act accordingly.

This is why I travel with Sidemount. I always have way more gas than I need on each dive, and without the hassle of lugging a pony cylinder on an aircraft. I've never had issues with my SM at the destination but we're able to choose "grown up operators"

 

[tursiops]

Hi Diving Dubai,

I like your rationale and I can't fault it...at all. I should follow it.

However, on a philosophical plane-of-thought, I don't even need a pony because my gear is serviced by trained techs and replaced based on age and abuse. I have a new primary first stage and second stage because of external abuse and overhaul cycles on the old system.

The catastrophic and instantaneous failure rate for diving systems is so low that a pony is really not necessary. So, if you must carry a redundant system, why not go with a redundant system that is the smallest required? A system that travels easily? After all, you will never need it, statistically speaking of course.

Devils advocate, yeah maybe.

markm​

LOL. Not even a good Devil's Advocate argument. To follow your logic, a SpareAir is plenty, because you will never need it anyway.

Added: in fact, a picture of a pony bottle will be just fine.

 

[barth]

When would you say single tank and buddy is not enough for you?

Edit: noting that this is a a DIR diver with 1000-2500 dives.

For me there are 2 reasons for using doubles instead of single tank.

- If I want extra redundancy (dpv, deeper than 30 meter/100 feet, overhead and low water temperature.are good reasons for me for using doubles).

- If a single tank doesn't contain enough gas for the dive/ if I want more bottom time.

When I don't need extra redundancy and there fits enough gas in a single tank I will use a single tank.

 

[markmud]

LOL. Not even a good Devil's Advocate argument. To follow your logic, a SpareAir is plenty, because you will never need it anyway.

Added: in fact, a picture of a pony bottle will be just fine.

Hi tursiops,

I never thought of a spare air as a viable option. I can't do sheet on 1.5 or 3cf.

Is your spare air still in hydro and vis? Why would you assume spare air, was it a statement against self-interest?

Spare air is death-in-a-can, that we can agree on.

thanks,
markm

 

[markmud]

On the your point of equipment failure likely hood - I can't argue with it. I run monthly weekend dives for a group of friends and have for 5 years. We keep records or dive stats and "incidents", so looking back I can tell you that with a combined total of 5342 individual dives teh failures have been as follows

1 x LPI inflator runaway (mine)
4 x hose bursts on the surface while turning tanks on
6 x O-ring failures on the surface - again found when turning tanks on.

So yeah nothing of consequence. And 1000's of rec dives are made daily with basic rental gear without incident.

But if you do have a redundant system - my view that it shoudl be big enough to handle your worst case (being sensible). My figures for instance assumed that a 13cf held 13cf - but as you pointed out an 80 only holds 77cf. I want to not have to worry that my redundancy is just enough.

But I understand that you have limitations on travel and you could argue that some is better than none. Again fair point as long as when people do the maths they understand the limitations of any compromise they've made and act accordingly.

This is why I travel with Sidemount. I always have way more gas than I need on each dive, and without the hassle of lugging a pony cylinder on an aircraft. I've never had issues with my SM at the destination but we're able to choose "grown up operators"

Hey DD,

Sidemount seems so sensible. One of these days.

Your points are well taken.

Thanks.

markm

 

[TMHeimer]

I haven't used my pony in over a year, so it hasn't been Visualed. Still is full, think it should be visualized before use?

 

[grf88]

If I had no reason to be concerned such as a questionable source of air I wouldn't bother. If it was steel I would probably check O2 percentage just in case you had a wet fill. YMMV

 

[Storker]

For me there are 2 reasons for using doubles instead of single tank.

- If I want extra redundancy (dpv, deeper than 30 meter/100 feet, overhead and low water temperature.are good reasons for me for using doubles).

- If a single tank doesn't contain enough gas for the dive/ if I want more bottom time.

When I don't need extra redundancy and there fits enough gas in a single tank I will use a single tank.

If you're rec trained, redundancy probably isn't your main motivation for diving a twinset. After all, if a twinset is able to give you redundancy, you need to be able to shut down the manifold, and rec divers aren't trained to do that. Although the most common rec twinset in my waters is a D8.5x232, I've seen twinsets as small as D6x300, and even D4x300. Without an isolation manifold. A D6x300 doesnt carry more gas than a single 12x300, so no gain neither in gas volume nor in redundancy.

But those I know who swear to rec twins claim that they balance a lot better than a rec single. I wouldn't know, because for my diving singles are better, so I use a singles rig.