Is a Pony Bottle too complicated for a beginner?

[grf88]

I should add that I will always challenge anybody who tries to discourage the use of pony tanks for recreational divers. I spell it PONEE for Piece of Necessary Emergency Equipment.

 

[Hartattack]

Let's you and I do a virtual dive to 80ft on single AL '80s, shall we? And in that dive, you have a seat failure where you start to lose your gas supply.

Dive Plan:

A critical goal in planning a dive in open water is determining how much gas is necessary for an emergency scenario, as you have listed above.
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.

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

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

Time: 11 minutes (10ft/min ascent rate plus one minute at depth to resolve the problem and initiate an ascent.

1.5 x 2.2 x 11 = 36.3 cuft of gas or (36.3 / Tank Factor 2.5 x 100 = 1,452 PSI or to make it easier on the SPG 1450 or 1500 Psi to be conservitive.

• Our plan states that if we share gas from the deepest point of the dive, we require at least 1500 psi in our AL80 to reach the surface while safely transferring from one cylinder.
So, @lexvil, at what point during the dive will we need to call it and head to the surface if all goes according to plan?

 

[grf88]

Let's you and I do a virtual dive to 80ft on single AL '80s, shall we? And in that dive, you have a seat failure where you start to lose your gas supply.

Dive Plan:

A critical goal in planning a dive in open water is determining how much gas is necessary for an emergency scenario, as you have listed above.
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.

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

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

Time: 11 minutes (10ft/min ascent rate plus one minute at depth to resolve the problem and initiate an ascent.

1.5 x 2.2 x 11 = 36.3 cuft of gas or (36.3 / Tank Factor 2.5 x 100 = 1,452 PSI or to make it easier on the SPG 1450 or 1500 Psi to be conservitive.

• Our plan states that if we share gas from the deepest point of the dive, we require at least 1500 psi in our AL80 to reach the surface while safely transferring from one cylinder.
So, @lexvil, at what point during the dive will we need to call it and head to the surface if all goes according to plan?

If each diver carries a pony sized to reach the surface from the planned depth at a safe speed including a safety stop these plans become redundant and the divers can enjoy a decent dive time. You failed to include the significantly increased SAC rate for the panicked diver, a panic that would be greatly mitigated if they knew they were self sufficient.

 

[Hartattack]

If each diver carries a pony sized to reach the surface from the planned depth at a safe speed including a safety stop these plans become redundant and the divers can enjoy a decent dive time. You failed to include the significantly increased SAC rate for the panicked diver, a panic that would be greatly mitigated if they new they were self sufficient.

Did I ask or state anything about a pony bottle or increased SCR yet? I think it would be nice to have @lexvil answer the question and we continue our virtual dive before being interrupted, no?

 

[grf88]

Nope, but you all wanted my answer and thought process, so now I am doing a virtual dive with @lexvil. What you are doing by interrupting is rude. Nevertheless, if you want to answer the question, by all means please do. I will get to your questions in a moment. But I want to keep this thread on topic for just a few minutes to give a solid and fluid explanation.

The topic is pony bottles not gas management. Please keep on topic.

 

[Hartattack]

The topic is pony bottles not gas management. Please keep on topic.

I am by showing that a new diver does not need one with an example that all of you asked me for or criticized. So with my example, what is our minimum gas for our planned dive and at what psi should we call it?

 

[Hartattack]

Great, the answer is as soon as one of us reaches 1500 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 example. To keep this dive easy and fun, this will be an all-gas usable dive in the Caribbean of the Midwest, Haigh Quarry.

Usable Gas:
1500 MG subtracted from the fill pressure of an AL 80 3000 psi


1500 psi – 3000 psi = 1500 psi usable gas


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


80 cuft tank with 1500 psi = 38cuft usable (1500 psi / 100 x 2.5 TF = 38 cuft)


0.75 cuft/ min SCR x 2.2 ATA = 1.6 cuft / min @ 80ft


38 cuft / 1.6 cuft/ min = ~ 23-minute bottom time.


Now, we are ready to dive and have fun.


But first, lets go over our pre-dive check:

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

Unified Team: Diver 1 (me) Diver 2 @lexvil

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

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


Exposure (depth and time) 80 ft for 23 minutes

Deco: Minimum Deco or MDL procedures.

Gas strategies: AL 80’s 3000 psi, MG 1500, 1500 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 would be?

 

[tursiops]

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

Silly assumption. I can only assume you have made it so your numbers work out to your advantage.
If we are out of gas we are headed for the surface as fast as is safe....which is a LOT faster than 10 ft/min, especially deep.

 

[Hartattack]

Silly assumption. I can only assume you have made it so your numbers work out to your advantage.
If we are out of gas we are headed for the surface as fast as is safe....which is a LOT faster than 10 ft/min, especially deep.

Why panic when you have the minimum gas to get both you and your buddy to the surface at that ascent rate already calculated in the dive plan? (which as you stated is a lot of time and gas)

Panic and hasty movements causes the drain of despair. No one wants that.

 

[tursiops]

Why panic when you have the minimum gas to get both you and your buddy to the surface at that ascent rate already calculated in the dive plan? (which as you stated is a lot of time)

Panic and hasty movements causes the drain of despair. No one wants that.

Do you consider an ascent rate of 10m/min a panicked ascent?