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

[Wibble]

Wow this thread really went off the rails.

Been an interesting discussion though.

Sometimes there are instructors I know who want to do deep recreational dives when not teaching and we also do not gas plan the dives but do have a dive plan and no pony bottles. After all we do want to boat captions to know where we expect to be picked up and our expected dive time.

That sounds like gas planning. It doesn't take much to do, especially with MultiDeco or suchlike. After a few dives, you've got a template in your head as what the plan is.

Lets be honest here, the gas plan is very simple. You know the depth; you know the max bottom time (from the NDL tables/planning software); you know your SAC (or use a default assumption); you know the gas you'll be using; you know your ascent profile (3 mins at 5m deco safety stop); you know what reserve you need to have on the surface (50 bar); you know if there's any time constraints (boat says you be back in 1h/whatever). Then it's just arithmetic to add up how much gas you'll be needing (or let the planning software tell you).


As it's an NDL dive, it won't be that long a dive, especially if using air.

Taking a pony cylinder is simple enough to plan for: there's no adjustment to the main gas plan, all you need to do is be able to add up 3 mins at the bottom given your SAC and depth, plus the ascent including deco safety stop. Then you decide how much gas you need and which cylinder size to take.

There's not many dive profiles to remember. 20m/60', 25m/75', 30m/100', 35m/120' and 40m/132'.

Example,  for a 30m dive with air to NDL.  From PADI RDP it's 20m bottom time with 3 min 5m safety stop.  SAC assumed at 25 litres/min (that's high, but cautious)
Gas required = ∑ of:
20 x 25 x 4(ATA) = 2000 litres (bottom time)
1 x 25 x 4  (ATA) = 100 litres (ascent from 30m to 20m,  use worst case)
1 x 25 x 3 (ATA) = 75 litres (20m to 10m)
1 x 25 x 2 (ATA) = 50 litres (10m to 5m)
3 x 25 x 1.5 (ATA) = 115 litres (safety stop)
1 x 25 x 1.5 (ATA) = 40 litres (surface)
--------
total:  2380 litres.

Plus reserve (=50 bar x cylinder size)

A 12 litre tank would be 12 x 220 bar = 2640 litres.

This means that someone with that SAC would need to restruct their bottom time to their minimum gas limit:
380 litres (the amount to surface)
600 litres (the reserve of 50 bar x 12 litre tank)
approx 1000 litres required to surface

Using a 12 litre tank,  this is 1000/12 = 85 bar minimum gas

Do you need a pony? It's up to you to decide using your personal risk assessment and assessing the dive profile.

Maybe here's the difference between purely recreational trained and experienced divers and technical divers: the above is pretty trivial to calculate and risk assess.

For a benign, simple, shallow, time-limited dive in warm clear water on a reef you probably don't need a pony.

For a deeper dive to the NDL dive in a poor visibility cold water wreck dive in current, then you probably do need to take a pony named Prudence. Or not; it's your decision.

Some recreational dive operations don't have divers doing deco dives even if deco certified that is the way they run their operations as their guides are often not deco certified.

By definition a deco dive has an overhead and that's generally considered to be a technical dive (yes, some agencies such as BSAC allow for light deco within a recreational dive).

Most of the divers on this thread seem to be certified for Deco and mixed gas diving... I guess we can include Nitrox certified as mixed gas.. In my last decade of recreational diving I have yet to see anyone gas plan a recreational non deco multilevel dive.

This is because many divers get bored of being constantly limited to minuscule bottom times and shallow depths given the expense of doing the dive in the first place. This is why they move through the levels of technical training: sort your core skills (e.g. Fundies, etc), learn about decompression diving (Advanced Nitrox & Deco Procedures - ANDP, etc.); deeper diving with trimix (45m on helitrox); even deeper diving with multiple stages (normoxic trimix to 60m); even advanced trimix (100m+). But nearly all of them will move to CCR to constrain costs of 'mix diving.

NDL dives are trivial to plan, see above.

Sometimes I do gas plans before a dive on my Shearwater, but that really is for the fun of gas planning and seeing if that matches up with gas consumption for the actual dive.

AIUI, the Shearwater / Suunto planners only give you the dive profile, they don't calculate your gas requirements.

Not many of the recreational divers I meet know their SAC rates, they don't know about GF or Surf GF, CNS PPO2 etc as they just do dives and not go into deco.

Then you use a rule of thumb for your SAC: 25 litres / min (as in the example above).
Surf GF is simply the NDL limits, CNS is irrelevant, PPO2 is part of Nitrox training. NDL = No Deco Limits, therefore no deco (or in the case of BSAC, use their tables and planning you'd have been taught in your Sports Diver course)

Should dive operators be teaching recreational divers to bring a pony? I would say they would not be interested in that as then they need to provide pony bottles. I've yet to see a dive operation offer pony bottles for rent they seem to be an individual diver who brings their own.

Yes, definitely. But it's up to the diver to decide.

 

[Searcaigh]

If someone could articulate exactly what combinations of conditions means a gear configuration consisting of a single tank and a pony would be optimal, I'd like to hear it. Making good decisions requires knowing what all the inputs are and what weights to give them. Obviously depth is one, but what is the threshold? Visibility and current and their effect on the likelihood of buddy separation have been mentioned, but it's hard to know what these will be like before leaving for the dive site or trip. Low-vis, high-current, 100-ft+ dives--I'm not going to do that in any gear configuration. It just seems simpler to me to have some clear thresholds and not get into the position of making these judgment calls on whether this is a dive to take the pony or a dive I can leave it at home.

From my perspective as a photographer, who dives a single AL80 with an S30 pony (stage/deco) bottle, where my local dives are generally square profile and the first dive of the morning is around 27-30m.

Sometimes I have a buddy (also a photographer) and sometimes I'm solo (so the pony makes sense). My main buddy also carries a pony. The current is slightly predictable by checking tide tables, but vis is a roll of the dice at times. All of this week it's been 2-3m vis, although occasionally we get 5m vis and once in a blue moon it's 10m+ but we always plan for poor vis.

We don't normally get separated but it happens sometimes and the pony is insurance in case SHTF..

 

[Gareth J]

It’s the rule of thirds.

You breathe from both sides, switching regs as you switch sides.

In an overhead you have a hard rule of thirds. 1/3 in, 1/3 out, 1/3 for reserve. Should one side go pop then you’ve got 1/3 left. Mostly you’d be more conservative, 1/4 or less.

In open water, it’s the same as you’ll always aim to surface with 50 bar which is the reserve you’d use. If it went pop at the very end of the bottom time, you’d still have enough to ascend to your first switch or the surface.

But as all the hardware is in front of you, you can tighten up the valve, or easily feather the broken side as it’s in front of you.

Granted you won’t do deep in sidemount unless you’re really keen.

@Wibble

I think you proved my point.

Enter with 2x220bar.
At the bottom of the shot switch from Cylinder A (190bar) to Cylinder B (220bar) - to confirm both sets are working
When cylinder B = 150bar switch to Cylinder A .

When Cylinder A reaches 140 bar you should turn for home.

When Cylinder A = 100 bar switch back to cylinder B

Now you find you have a problem with cylinder B. You only have cylinder A (with 100 bar)

You started with 4400 litres (2x10x220 = 4400 litres.)
Reserve 1500 litres

At the point of failure you should have 1500 + 1000 litres - you now have only 1000 litres. This is OK because the plan was to exit with 1500 litres. - Unless you have any additional issues!

As is the case in most diving incidents. There is seldom one single problem, they tend to come in groups and cascade.

The procedure is not that dissimilar on side mount. In theory, you only ever have about 50bar difference between cylinders.
You might do a regulator switch early, if you are expecting to be task loaded or distracted. Like going into a confined space or laying a line. But the principle remains the same, try to keep within 50bar of each cylinder.

If you are taking kit off to get through tight spaces, then side mount makes sense. I have no inclination to do that, or to dive caves. I've taken a twinset off a couple of times to get out through a tight space, but I wouldn't do it by choice. That last time I was in two minds if I was going to go back with a line to get the A**H*** out that silted out the section I was in.

 

[scubaozy]

If every single rec diver in the world carried a pony/stage, would that affect fatality or general safety stats and in what way? Think of every rec diving boat you have been on, and try to imagine if everyone used a pony..
@Lorenzoid asked a good question. What are the thresholds/borders for recommending a pony; vis, depth, temp?

I think there not too many of you disagree that solo divers will need some sort of redundant supply, so, maybe its a good idea to stop discussing that to keep the focus. In this discussion, technical divers are over-represented, how can we conclude anything reasonable for rec divers if you do not take off your tech diver or solo diver hat?

If you show up on a dive boat or a pier full of divers and half of the rec divers have pony or stage cylinders, there is a good chance conditions at that location require a pony. If you are the only one with a pony, probably you are over-equipped. It is part of your owd training to inform your self about the conditions and required equipment. You need to assess the local conditions and talk to local professionals. If you go talk to people on the tech divers corner on the pier, you will get very different answer, just like in here, they will want to talk about feathering.

 

[Blackcrusader]

Been an interesting discussion though. That sounds like gas planning. It doesn't take much to do, especially with MultiDeco or suchlike. After a few dives, you've got a template in your head as what the plan is.

As it's an NDL dive, it won't be that long a dive, especially if using air.

Depends on what you call long? I have done some 2 hour dives by staying shallow ( less than 20m max depth ) on air. On this dive all we did is to decide to end the dive at 50 bar and not worry about a time limit. Great dive got some photos and video of some sea horses and other critters that are seen so often. Actually one of the dives I have with really good memories from this dive. For many recreational divers a 93 minute dive they find to be a long dive. Yes been a fun discussion. Some divers feel cold after an hour some get bored. What is your definition of a long dive time? I will do 3 or 4 dives a day for 10 - 14 days straight a day on my vacations.

 

[Wibble]

I think you proved my point.

Enter with 2x220bar.
At the bottom of the shot switch from Cylinder A (190bar) to Cylinder B (220bar) - to confirm both sets are working
When cylinder B = 150bar switch to Cylinder A .

When Cylinder A reaches 140 bar you should turn for home.

When Cylinder A = 100 bar switch back to cylinder B

Now you find you have a problem with cylinder B. You only have cylinder A (with 100 bar)

You started with 4400 litres (2x10x220 = 4400 litres.)
Reserve 1500 litres

At the point of failure you should have 1500 + 1000 litres - you now have only 1000 litres. This is OK because the plan was to exit with 1500 litres. - Unless you have any additional issues!

As is the case in most diving incidents. There is seldom one single problem, they tend to come in groups and cascade.

The procedure is not that dissimilar on side mount. In theory, you only ever have about 50bar difference between cylinders.
You might do a regulator switch early, if you are expecting to be task loaded or distracted. Like going into a confined space or laying a line. But the principle remains the same, try to keep within 50bar of each cylinder.

If you are taking kit off to get through tight spaces, then side mount makes sense. I have no inclination to do that, or to dive caves. I've taken a twinset off a couple of times to get out through a tight space, but I wouldn't do it by choice. That last time I was in two minds if I was going to go back with a line to get the A**H*** out that silted out the section I was in.

With overheads you decide on your turn pressure based upon various factors. The rule of thirds is generally considered as the absolute maximum amount. Typically it would be less, quarters or sixths.

Factors would include gas planning, solo or team, flow/current, restrictions, depth, kit, temperature, mitigating factors, etc.

For sidemount it's sort of 1/3ds. This should leave you with 2/3ds spread across the cylinders, i.e. 1/3 each side left at the turn point. In the event of a failure, you should be heading out without hanging around, thus leave faster than you entered. Again, this would be planned according to the conditions, so you may need to allow more contingency for adverse flows (swimming up-current on the way out needs more gas than swimming in). Even dropping off stage cylinders on the way in would help.

Obviously this is way way outside of recreational diving!

 

[Lorenzoid]

In my last decade of recreational diving I have yet to see anyone gas plan a recreational non deco multilevel dive.

I can't match Wibble's thorough reply to your well-thought-out post, but for me, gas planning a multilevel rec/sport dive can be as simple as memorizing a few pairs of numbers. If my buddy and I are at X depth, I had better see at least Y on my SPG or else I need to ascend a bit. We know we would always have enough gas to surface while sharing gas in an out-of-gas emergency.

If you show up on a dive boat or a pier full of divers and half of the rec divers have pony or stage cylinders, there is a good chance conditions at that location require a pony. If you are the only one with a pony, probably you are over-equipped. It is part of your owd training to inform your self about the conditions and required equipment.

What comes to mind is the time I showed up at a dive boat for some recreational dives to depths just over 100 ft and noticed all or almost all of the divers had one of three configurations: single tank and pony, double tanks, or rebreather. It was evident that most or all divers believed there would be too much risk without a redundant air source, but it wasn't evident what their collective wisdom believed was the optimal configuration.

 

[Wibble]

What comes to mind is the time I showed up at a dive boat for some recreational dives to depths just over 100 ft and noticed all or almost all of the divers had one of three configurations: single tank and pony, double tanks, or rebreather. It was evident that most or all divers believed there would be too much risk without a redundant air source, but it wasn't evident what their collective wisdom believed was the optimal configuration.

That’s very common in the UK where the perceived risk is greater. Divers vote with their actions.

 

[grf88]

That’s very common in the UK where the perceived risk is greater. Divers vote with their actions.

The same in my area of the Great Lakes.

 

[grf88]

A vehicle analogy was made earlier and I would like to add one. When I talk to certain divers who keep pushing their advanced training I frequently ask what advanced driver training they have taken such as skid-pan, crash avoidance etc. Invariably then answer is none but all of them spend more time driving than diving and the death statistics can be scary.