Is a Pony Bottle too complicated for a beginner?

[KenGordon]

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?

You have a bogus ascent rate here leading to excessive min gas and so a pointlessly short planned bottom time. Who wants to do a 23 minute dive? You also make the classic mistake of adding conservativism in multiple places. Use realistic numbers of you’ll be getting out with 150 bar thinking why did I bother.

 

[Hartattack]

You have a bogus ascent rate here leading to excessive min gas and so a pointlessly short planned bottom time. Who wants to do a 23 minute dive? You also make the classic mistake of adding conservativism in multiple places. Use realistic numbers of you’ll be getting out with 150 bar thinking why did I bother.

Fair enough, how would you plan this recreational dive as a new diver with enough minimum gas to get you and your buddy to safety while sharing Gas from a single AL 80?

You plan it, I’ll follow along.

 

[barth]

It’s all about risk. How much redundancy do you need? How important is it to get good training and have a good buddy? Should you do the dive or not? When is adding more equipment necessary and when is it nonsense?

With a oc tech dive I would plan a dive and if my buddy has a failure we can share backgas/decogas. I do plan for that scenario. But I don’t bring two extra stages (backgas and decogas) for myself to be a independent /self reliant diver if I do have a failure.

I won’t bring a stage/ponybottle for a rec dive when I dive with a buddy to be a independent/self reliant diver. But I think it’s a grey area… I know a lot of people who are doing rec dives with doubles (cold water and poor visibility.)

It would be better if I won’t tell other people what to do. But it wouldn’t make sense if other people are telling (me) that bringing more gas/tanks would make (my) diving safer.

At some point bringing more (gas /)tanks is introducing new problems.

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 the dive is at 80 ft max depth and you reserve 1 minute to solve problems it will take 9 minutes to get to the surface (8+1). I think your calculation is for 30 meter / 100 ft.

But I don’t like the cat calculation. I prefer the old style calculation.

For rec diving I use a minimum gas of 1100 liter between 18 and 30 meter and 550 liter between 10 and 18 meter and 40 bar between 10 meter and surface.

 

[scubaozy]

Use of pony is a cultural matter. How much risk is considered socially acceptable? How many of you drive with an extra canister or petrol in your trunks? Shouldn’t we all wear helmets when driving a car? Why don’t we do it when we have considerably higher probability of serious injury? My car came with a spare tire, never used it. I have been lagging around extra weight for years. Should I insist for a spare tire for my next car?
One function of SB is to make things socially acceptable as there is a community. But irrational is still irrational even it is socially acceptable.

 

[chillyinCanada]

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