Pony Bottle Setup Question

[matt_unique]

When I dive from shore for example I will not use doubles because the slippery rock traversing with the extra weight is not a good idea. I still want redundancy so a single with a back mounted pony is my preference. I use a Highland Mills stainless steel bracket to mount my pony upside down on a single in these circumstances. When diving from my boat I always use my full doubles rig to maintain use and practice with my tech rig. Before this rig I would always dive with a pony. I would change the size based on the depth needs. I never dive with just one life support system. Even when I vacation in warm water I bring a small pony and bracket. I firmly believe in redundant systems.

You can definitely be doing dives requiring only a single tank in terms of back gas supply and want the pony as a redundant system. Many divers don't understand what a pony bottle is used for. Many think it's a way to bring extra gas to be USED during the course of a normal dive when in fact it should be used only as an emergency backup. If you are doing a dive with an 80CF primary tank and a 19CF pony you plan and end your dive with 80CF of gas.

--Matt

 

[matt_unique]

There would be no reason whatsoever to have a pony on duals (I assume you mean doubles), and in this instance, a 13 for any kind of deco bottle is way too small.

I think you need to reanalyze your needs. A pony mounted on backgas is not a good way to go BTW.

MD

To clarify for Pickens - you do take deco bottles with you when diving with doubles if your profile requires decompression with something other than your back gas. The difference between a pony bottle and a deco bottle is what you use it for. Deco bottle you plan to use for decompression, pony bottle you use only in case of emergency. If your doubles rig has a manifold with isolator or if you are using an independant singles configuration you already have your redundancy built into these systems.

--Matt

 

[MechDiver]

To clarify for Pickens - you do take deco bottles with you when diving with doubles if your profile requires decompression with something other than your back gas. The difference between a pony bottle and a deco bottle is what you use it for. Deco bottle you plan to use for decompression, pony bottle you use only in case of emergency. If your doubles rig has a manifold with isolator or if you are using an independant singles configuration you already have your redundancy built into these systems.

--Matt

And you don't mount a deco bottle on your doubles. Argon yea, deco no.

 

[matt_unique]

And you don't mount a deco bottle on your doubles. Argon yea, deco no.

With doubles you would sling the deco bottle(s).

Some people who use a pony bottle with a single like to sling it also. For this purpose I prefer to back mount.

 

[Doc Intrepid]

If you are doing a dive with an 80CF primary tank and a 19CF pony you plan and end your dive with 80CF of gas.

Matt,

Didn't you intend to say you end your dive with 19 cf in the bailout (as you've not used it) and the remainder of your Rock Bottom calc in your backgas?

(...just pickin' nits! )

 

[fldivenut]

Essentially that, if you **think** you need a pony bottle, you actually need doubles. If you don't **think** you need doubles, then you don't need a pony bottle either.

It comes down to risk management and gas management, is highly individualistic, and highly debated.

You imply that you have a pony for the extra gas. That is NOT why I have a pony, I have the pony for the redundant system (regulator) that it brings, especially when I solo dive but also when I dive with new buddies. If you need more gas get a bigger single tank or doubles.

I have also been through it (I think) and is now in more favor for H-valves than extra tanks. Why take along the tank when it is the regulator you really need.

Some said they use a 30cuft "pony", they are surely after extra gas IMHO. Although some real heavy breathers might need it to get to the surface, but they must then be diving a monster tank as their main tank anyway.
And if you leave it somewhere as someone suggested the whole purpose of the redundant equipment is lost and again they are after the extra gas which they can use when they get back to where ever they left the tank. This is IMHO not pony tanks but deco tanks or dual tanks that are hooked off. Which I think is what Matt said as well.

BTW, 40cuft is considered to be the optimal deco tank and 13cuft or 19cuft the choice for pony bottle around here now.
I have a 13cuft but see that the 19cuft could be a good choice since it is the same diameter and the 19cuft doesn't have to be completly full to give enough gas for an emergency. The 13cuft has a tendency to "leak" air and then won't have 13cuft anymore. It "leaks" air by reg freeflow at entry, accidental purging by people sitting on the reg etc.

--A

 

[Doc Intrepid]

I have the pony for the redundant system (regulator) that it brings, especially when I solo dive but also when I dive with new buddies. If you need more gas get a bigger single tank or doubles.

Some said they use a 30cuft "pony", they are surely after extra gas IMHO. Although some real heavy breathers might need it to get to the surface, but they must then be diving a monster tank as their main tank anyway.

BTW, ...13cuft or 19cuft the choice for pony bottle around here now. I have a 13cuft but see that the 19cuft could be a good choice since it is the same diameter and the 19cuft doesn't have to be completly full to give enough gas for an emergency. The 13cuft has a tendency to "leak" air and then won't have 13cuft anymore. It "leaks" air by reg freeflow at entry, accidental purging by people sitting on the reg etc.

fldivenut,

Couple points –

1. You don’t pick a bailout bottle and then configure your dives around your equipment. You plan for your dives, and calculate the amount of gas you need first. Then you select which container to put it in. For example:

Suppose you habitually dive in your local area to depths somewhere between 90 and 120 fsw. You choose to carry a redundant regulator and gas supply in the event of unforeseen circumstances that cause a need to get yourself back to the surface in the absence of a buddy. This indicates some sort of situation occurring that you need to react to…for example, you’re spearfishing quasi-solo and you become entangled in a monofilament fishnet hanging off a wreck. Narcosis at these depths can creep up on a diver in distress in ways that might not be experienced otherwise.

Many divers plan that under duress their respiration rate/gas consumption goes up. A figure used on this board in the past was an estimated Respiratory Minute Volume (RMV) of 1.3 cu ft per minute. You plan to do a normal 30 fpm ascent up the line, with a minimum 3 minute safety stop at 15’ or 10’.

So… a worst case scenario puts you at 120’ unexpectedly with “issues”. You plan for:

• 3-5 minutes to deal with the entanglement;
• 3 minutes to return to the downline or mooring line;
• 4 minutes to ascend 120’ at a rate of 30 feet per minute;
• 3 minutes of safety stop at say 10’;
• For a total of 15 minutes maximum on the bail-out gas.

15 minutes on bail-out gas at a respiration rate of 1.3 cu ft per minute = a planned requirement capacity of 19.5 cubic feet of gas. Remember that things don’t always go as you plan. Adding a 3% margin of error puts you over 20 cu ft.

Depending on your personal dive profiles, etc., you may need more or less gas. But the idea is the same. Calculate estimated gas requirement first. Select the tank needed to contain it second. It might be a 19, it might be a 30, but the circumstances determine the tank – not the other way around.

2. For precisely the “leakage” reasons you describe, deco, stage, and bailout tanks are carried with the regulator charged and then the valve turned off. It’s important to know that the planned capacity of gas required is actually in the cylinder. It’s equally important to be able to turn the valve on if/when you need the gas. That’s why deco, stage, and bailout tanks are carried so the diver can access the valve.

 

[fldivenut]

1. You don’t pick a bailout bottle and then configure your dives around your equipment. You plan for your dives, and calculate the amount of gas you need first. Then you select which container to put it in. For example:

That is all good if you have a lot of different tanks to chose from in your garage. The average diver does not though. Now this thread started with how to configure the pony and not what tanks to chose. I would hate if we jointly would recommend someone to get a 30cuft pony for going to Cozumel.
The redundant regulator setup is the most important addition to your safety with the pony. Then the size of it seem to vary from region to region, we warm water divers like to carry as little as possible and thus go for the smaller tank.

So… a worst case scenario puts you at 120’ unexpectedly with “issues”. You plan for:

• 3-5 minutes to deal with the entanglement;
• 3 minutes to return to the downline or mooring line;
• 4 minutes to ascend 120’ at a rate of 30 feet per minute;
• 3 minutes of safety stop at say 10’;
• For a total of 15 minutes maximum on the bail-out gas.

15 minutes on bail-out gas at a respiration rate of 1.3 cu ft per minute = a planned requirement capacity of 19.5 cubic feet of gas. Remember that things don’t always go as you plan. Adding a 3% margin of error puts you over 20 cu ft.

If you plan to return to the exit point as your example is you really need to dive doubles or a large tank with H-valve and use the rule of 1/3 for your gas management. IMHO I don't think that is necessary diving in openwater NoDeco. In case of an emergency I would surface right there, do my safety stop for as long as I have air (if less than 3-5). The decribed scenario is also a two "failure" scenario, that you would get entangled and have a catastrofic regulator failure at the same time is like having both your regulators fail on you. Not even overhead divers carry more than one failure redundant equipment.
Your gas calculation is of, you have to take the depth into account and not use an average rate. We don't have to discuss that here though since I'm sure there are other threads that does that in detail.

2. For precisely the “leakage” reasons you describe, deco, stage, and bailout tanks are carried with the regulator charged and then the valve turned off. It’s important to know that the planned capacity of gas required is actually in the cylinder. It’s equally important to be able to turn the valve on if/when you need the gas. That’s why deco, stage, and bailout tanks are carried so the diver can access the valve.

That is correct, good point, and that is also why I recommend that 13 and 19 cuft back mount bottles are mounted up side down so you can get to the valve down at you hip.

--A

 

[matt_unique]

That is all good if you have a lot of different tanks to chose from in your garage. The average diver does not though. Now this thread started with how to configure the pony and not what tanks to chose. I would hate if we jointly would recommend someone to get a 30cuft pony for going to Cozumel.
The redundant regulator setup is the most important addition to your safety with the pony. Then the size of it seem to vary from region to region, we warm water divers like to carry as little as possible and thus go for the smaller tank.



If you plan to return to the exit point as your example is you really need to dive doubles or a large tank with H-valve and use the rule of 1/3 for your gas management. IMHO I don't think that is necessary diving in openwater NoDeco. In case of an emergency I would surface right there, do my safety stop for as long as I have air (if less than 3-5). The decribed scenario is also a two "failure" scenario, that you would get entangled and have a catastrofic regulator failure at the same time is like having both your regulators fail on you. Not even overhead divers carry more than one failure redundant equipment.
Your gas calculation is of, you have to take the depth into account and not use an average rate. We don't have to discuss that here though since I'm sure there are other threads that does that in detail.



That is correct, good point, and that is also why I recommend that 13 and 19 cuft back mount bottles are mounted up side down so you can get to the valve down at you hip.

--A

The purpose of the pony is not just the extra regulator as resolved with the use of an H-valve. The purpose is to have a TOTALLY redundant system in case of primary system failure. For example, blown tank o-ring. The best singles configuration in terms of redundancy is a single with an H-valve AND a pony bottle. The first step to increase redundancy would be to add a pony bottle.

--Matt

 

[Doc Intrepid]

Sorry, I wasn't clear enough. I didn't mean you selected a bailout from 2 or 3 tanks available in your garage. I meant you took a look at the dives you most frequently found yourself doing - your own personal dive profiles, and selected one tank based on the gas management planning most appropriate for your own circumstances. One tank. Not many. But one tank based on a gas consumption analysis taking into consideration your own RMV and most plausible worst-case scenarios.

In terms of scenarios, the scenario in my post above was intended to illustrate my point, not be considered on its own terms. (Although, divers have indeed had issues at depth, become narked to a point that they focused on resolving the issues, and consequently sucked a tank dry. It isn't impossible.) (Also, if you intended to hang for 3 minutes in any current, and you wanted to surface near the boat, getting back to the upline might be prudent.)

Perhaps a more plausible scenario might be one discussed in a recent DAN Alert Diver magazine article, where oxide particulate from inside an improperly cared for resort scuba tank clogged up a first stage intake to a point that while the SPG continued to indicate pressure in the tank, no gas could get through the intake.

I'm curious, however, as to what you consider the most likely scenario to be where your bailout would be the optimal solution.

FWIW, I agree with Matt - the value of a bailout in single tank diving (assuming a less than predictably reliable buddy) is a completely redundant gas source. If I only cared about a redundant regulator, an H-valve would be adequate.

Sorry if I wasn't clear previously.