Recreational Pony Bottles, completely unnecessary? Why or why not?

[tursiops]

if you have to be in a single AL80, just plan it with MG in mind.

Nobody disagrees.
The disagreement comes in (a) how to calculate MG (10ft/min is an absurd ascent rate), and (b) what do you do if there is no buddy to hand you an AAS?

 

[Gone for diving]

I'd say that most dive ops out my way do not have sets of doubles unless they are teaching tech as well as recreational diving.

When I travel on dive trips which is mainly to photograph pretty slugs and weird critters, I've not seen one set of doubles for hire apart from one dive op in Bali that also has a tech side, and they are solely used for tech diving.

I don't know... but do you see alot of sidemount????
Seems to me sidemount is the new travel friendly doubles....
2 aluminum tanks rented anywhere is a set of doubles with less hassle than backmount ....

 

[Hartattack]

I think my philosophy on recreational pony bottles gets lost in the sauce or misconstrued when I discuss dive planning and the term minimum gas. So with that said, it might be easier to show that in a virtual dive here, both in a single AL 80 and for easy of understanding double AL80's. @tursiops makes a good point about ascent rate and that was my mistake in the other thread, I calculated for 100ft and not 80 so apologies on that. Nevertheless, please see below.


Dive Plan:

A critical goal in planning a dive in open water is determining how much gas is necessary for an emergency scenario; With that in mind, we want to plan for one diver to suffer an out-of-gas emergency during the deepest part of the dive, which provides sufficient reserves for any range of potential problems within the buddy group.


Let's make a few educated assumptions that leave us all with a bit of room for conservatism.

1. Let's assume that our average surface consumption rate is ~ 20 L/ 0.75 cuft per minute.

2. The assumed ascent speed will be on average 3m/10 ft per minute.

3. The average depth of the ascent is used for all calculations. Divers should attempt to maintain a controlled ascent of between 20 to 30 feet per minute and follow minimum deco (MDL/NDL) profiles. This is based on a slow but foreseeable ascent rate that provides some wiggle room for safety. Also, the 20 L/ 0.75 cuft per minute SCR is approximate based on the outcome of an average diver in most situations.

• MG should never be less than 40 bar/600psi to account for inaccuracy and/or readability in SPG's.

Let's determine our minimum gas for the dive.


Minimum Gas:

Consumption= 0.75 SCR x 2 divers= 1.5 cuft /min

ATA: (80ft / 2 = 40ft); (40 ft / 33 +1 = 2.2 ATA

Time: 9 minutes (10ft/min ascent rate plus one minute at depth to resolve the problem and initiate an ascent (8 + 1= 9).

1.5 x 2.2 x 9 = 29.7 cuft of gas or (29.7 / Tank Factor 2.5 ) x 100 = 1,188PSI or to make it easier on the SPG 1200 Psi Minimum Gas to be conservitive.


To keep this dive easy and fun, this will be an all-gas usable dive in the Caribbean of the Midwest, Haigh Quarry. Our plan states that if we share gas from the deepest point of the dive, we require at least 1200 psi in our AL80 to reach the surface while safely transferring from one cylinder. As soon as we get 1200 psi, we would have to call the dive and begin our ascent. With that said, let's determine our usable gas with our MG and SCR examples.


Usable Gas:

1200 MG subtracted from the fill pressure of an AL 80 3000 psi

1200 psi – 3000 psi = 1800 psi usable gas


Now, with that information, let's determine our bottom time:


Bottom Time:

80 cuft tank with 1800 psi = 45 cuft usable (1800 psi / 100) x 2.5 TF = 45 cuft

0.75 cuft/ min SCR x 2.2 ATA = 1.65 cuft / min @ 80ft

45 cuft / 1.65 cuft/ min = ~ 27-minute bottom time.


Now, we are ready to dive and have fun on a single tank without a need for a pony bottle.


However, this does give us some wiggle room if we want to go for a more extended dive, right? According to the MDL for Standard Gas 32% (My agency), we have up to 50 minutes at 80ft. So let's do this dive in the AL 80s.


Minimum Gas:

Consumption= 0.75 SCR x 2 divers= 1.5 cuft /min


ATA: (80ft / 2 = 40ft); (40 ft / 33 +1 = 2.2 ATA


Time: 9 minutes (10ft/min ascent rate plus one minute at depth to resolve the problem and initiate an ascent. 8 + 1= 9)


1.5 x 2.2 x 9 = 29.7 cuft of gas or (29.7 / Tank Factor 5 ) x 100 = 594 PSI or make it easier on the SPG 600 PSI Minimum Gas to be conservative.


Usable Gas:

600 MG subtracted from the fill pressure of an AL 80 3000 psi

600 psi – 3000 psi = 2400 psi usable gas


Bottom Time:

Double 80 cuft tank with 2400 psi = 120 cuft usable (2400 psi / 100) x 5 TF = 120 cuft


0.75 cuft/ min SCR x 2.2 ATA = 1.65 cuft / min @ 80ft


120 cuft / 1.65 cuft/ min = ~ 72-minute bottom time which goes over our 50 minute MDL time. So, as a buddy team, you would have to be watching your depth and time throughout the dive if you decided to use doubles.


let's go over our pre-dive check:


Goal: Have fun at Haigh Quarry and see some catfish.


Unified Team: Diver 1, Diver 2, etc.


Equipment Check: Does all of our equipment work properly, valves, regs, inflators, valve dumps, primary light, backup light, what's in our pockets? Computers on and working? Do we have a cutting device?

Modified S-drill to make sure the primary hose is free from obstructions.

Exposure: (depth and time) 80 ft for 27 minutes (Single Tank) 50 (Doubles)

Deco: Minimum Deco or MDL procedures. 50 Minutes on 32% EANX @ 80 ft.

Gas strategies:

AL 80: 3000 psi, MG 1200, 1800 UG.

AL 80 x 2 3000 PSI, 600 MG, 2400 UG.

Environment: Haigh Quarry, viz is about 30 ft, water temp 55 at depth.


So, before we "ok" each other as a buddy team to descend, after planning the dive and checking all of our gear, what do you think the likelihood of a catastrophic failure or the need for a pony bottle would be?

 

[grf88]

I think my philosophy on recreational pony bottles gets lost in the sauce or misconstrued when I discuss dive planning and the term minimum gas. So with that said, it might be easier to show that in a virtual dive here, both in a single AL 80 and for easy of understanding double AL80's. @tursiops makes a good point about ascent rate and that was my mistake in the other thread, I calculated for 100ft and not 80 so apologies on that. Nevertheless, please see below.


Dive Plan:

A critical goal in planning a dive in open water is determining how much gas is necessary for an emergency scenario; With that in mind, we want to plan for one diver to suffer an out-of-gas emergency during the deepest part of the dive, which provides sufficient reserves for any range of potential problems within the buddy group.


Let's make a few educated assumptions that leave us all with a bit of room for conservatism.

1. Let's assume that our average surface consumption rate is ~ 20 L/ 0.75 cuft per minute.

2. The assumed ascent speed will be on average 3m/10 ft per minute.

3. The average depth of the ascent is used for all calculations. Divers should attempt to maintain a controlled ascent of between 20 to 30 feet per minute and follow minimum deco (MDL/NDL) profiles. This is based on a slow but foreseeable ascent rate that provides some wiggle room for safety. Also, the 20 L/ 0.75 cuft per minute SCR is approximate based on the outcome of an average diver in most situations.

• MG should never be less than 40 bar/600psi to account for inaccuracy and/or readability in SPG's.

Let's determine our minimum gas for the dive.


Minimum Gas:

Consumption= 0.75 SCR x 2 divers= 1.5 cuft /min

ATA: (80ft / 2 = 40ft); (40 ft / 33 +1 = 2.2 ATA

Time: 9 minutes (10ft/min ascent rate plus one minute at depth to resolve the problem and initiate an ascent (8 + 1= 9).

1.5 x 2.2 x 9 = 29.7 cuft of gas or (29.7 / Tank Factor 2.5 ) x 100 = 1,188PSI or to make it easier on the SPG 1200 Psi Minimum Gas to be conservitive.


To keep this dive easy and fun, this will be an all-gas usable dive in the Caribbean of the Midwest, Haigh Quarry. Our plan states that if we share gas from the deepest point of the dive, we require at least 1200 psi in our AL80 to reach the surface while safely transferring from one cylinder. As soon as we get 1200 psi, we would have to call the dive and begin our ascent. With that said, let's determine our usable gas with our MG and SCR examples.


Usable Gas:

1200 MG subtracted from the fill pressure of an AL 80 3000 psi

1200 psi – 3000 psi = 1800 psi usable gas


Now, with that information, let's determine our bottom time:


Bottom Time:

80 cuft tank with 1800 psi = 45 cuft usable (1800 psi / 100) x 2.5 TF = 45 cuft

0.75 cuft/ min SCR x 2.2 ATA = 1.65 cuft / min @ 80ft

45 cuft / 1.65 cuft/ min = ~ 27-minute bottom time.


Now, we are ready to dive and have fun on a single tank without a need for a pony bottle.


However, this does give us some wiggle room if we want to go for a more extended dive, right? According to the MDL for Standard Gas 32% (My agency), we have up to 50 minutes at 80ft. So let's do this dive in the AL 80s.


Minimum Gas:

Consumption= 0.75 SCR x 2 divers= 1.5 cuft /min


ATA: (80ft / 2 = 40ft); (40 ft / 33 +1 = 2.2 ATA


Time: 9 minutes (10ft/min ascent rate plus one minute at depth to resolve the problem and initiate an ascent. 8 + 1= 9)


1.5 x 2.2 x 9 = 29.7 cuft of gas or (29.7 / Tank Factor 5 ) x 100 = 594 PSI or make it easier on the SPG 600 PSI Minimum Gas to be conservative.


Usable Gas:

600 MG subtracted from the fill pressure of an AL 80 3000 psi

600 psi – 3000 psi = 2400 psi usable gas


Bottom Time:

Double 80 cuft tank with 2400 psi = 120 cuft usable (2400 psi / 100) x 5 TF = 120 cuft


0.75 cuft/ min SCR x 2.2 ATA = 1.65 cuft / min @ 80ft


120 cuft / 1.65 cuft/ min = ~ 72-minute bottom time which goes over our 50 minute MDL time. So, as a buddy team, you would have to be watching your depth and time throughout the dive if you decided to use doubles.


let's go over our pre-dive check:


Goal: Have fun at Haigh Quarry and see some catfish.


Unified Team: Diver 1, Diver 2, etc.


Equipment Check: Does all of our equipment work properly, valves, regs, inflators, valve dumps, primary light, backup light, what's in our pockets? Computers on and working? Do we have a cutting device?

Modified S-drill to make sure the primary hose is free from obstructions.

Exposure: (depth and time) 80 ft for 27 minutes (Single Tank) 50 (Doubles)

Deco: Minimum Deco or MDL procedures. 50 Minutes on 32% EANX @ 80 ft.

Gas strategies:

AL 80: 3000 psi, MG 1200, 1800 UG.

AL 80 x 2 3000 PSI, 600 MG, 2400 UG.

Environment: Haigh Quarry, viz is about 30 ft, water temp 55 at depth.


So, before we "ok" each other as a buddy team to descend, after planning the dive and checking all of our gear, what do you think the likelihood of a catastrophic failure or the need for a pony bottle would be?

For crying out loud what part of "a pony bottle does not form part of any gas plan" don't you understand. It plays no part in gas planning any more than a DSMB plays in buoyancy calculations. Yes! a DSMB can be used in a emergency when your other buoyancy devices fail and that is the purpose of a pony bottle, to bail you out when your primary gas supply system fails.

 

[Hartattack]

For crying out loud what part of "a pony bottle does not form part of any gas plan" don't you understand. It plays no part in gas planning any more than a DSMB plays in buoyancy calculations. Yes! a DSMB can be used in a emergency when your other buoyancy devices fail and that is the purpose of a pony bottle, to bail you out when your primary gas supply system fails.

You're right. Pony bottles are worthless. Especially if you have no idea how much gas is in one, lol. Why would you not add that amount of gas to your plan? You would need to calculate the amount of gas in the bottle required to mitigate the problem and return to the surface the same way minimum gas would get you there if you brought it along, wouldn't you? Also, this adds to @tursiops 2nd question, if your buddy is not near you in an OOG situation—you know you haven't reached minimum gas yet (you haven't called the dive), how long would it take you from max depth (80ft) to do a direct ascent to the surface? We are in recreational levels, so technically no need for a safety stop (CESA) if you would like to bring PADI into this.
.

 

[boulderjohn]

We are in recreational levels, so technically no need for a safety stop (CESA) if you would like to bring PADI into this.

There is nothing in the PADI literature calling for divers to do a safety stop during an OOA event on an NDL dive. They could do one of they had the gas, of course, but the agency does not call for it. For the 80 foot dive mentioned above, I assume your average pair of divers doing an OOA ascent from that depth would arrive at the surface in 3 minutes, maybe less. A 60 FPM ascent rate was considered safe for decades before people decided 30 FPM was better, so an ascent from 80 feet would likely take no more than about 2 minutes.

Of course, Hartattack above says it will take 9 minutes. That would not be my expectation.

 

[tursiops]

We are in recreational levels, so technically no need for a safety stop (CESA) if you would like to bring PADI into this.

You continue to obfuscate, and you are wrong. A safety stop is not a CESA, nor is it solely a PADI recommendation.
I'm sorry you don't know how to use a pony bottle, but it does show.in your responses, like trying desperately to get the gas in the pony to be part of the dive plan.

 

[Hartattack]

There is nothing in the PADI literature calling for divers to do a safety stop during an OOA event on an NDL dive. They could do one of they had the gas, of course, but the agency does not call for it. For the 80 foot dive mentioned above, I assume your average pair of divers doing an OOA ascent from that depth would arrive at the surface in 3 minutes, maybe less. A 60 FPM ascent rate was considered safe for decades before people decided 30 FPM was better, so an ascent from 80 feet would likely take no more than about 2 minutes.

Of course, Hartattack above says it will take 9 minutes. That would not be my expectation.

Thanks John, it would take 9 minutes once the OOG situation was mitigated and both divers were on their way up sharing gas. E.g. I let my buddy know I was OOG, we do an s-drill, stop, stabilize and then head up. A direct ascent would take ~ 3 minutes and I would only recommend this if you could not reach you buddy. or the buddy had no idea.

 

[Hartattack]

You continue to obfuscate, and you are wrong. A safety stop is not a CESA, nor is it solely a PADI recommendation.
I'm sorry you don't know how to use a pony bottle, but it does show.in your responses, like trying desperately to get the gas in the pony to be part of the dive plan.

How much gas is in that pony you keep talking about if you don't add it to the dive plan?

 

[tursiops]

Of course, Hartattack above says it will take 9 minutes. That would not be my expectation.

Nor mine.
He use an extremely slow ascent rate so that his min-gas calculation meet his personal desires, not what would be a reasonable ascent rate nor a reasonable min-gas calculation.