How deep until you need to bring along a pony bottle?

[neil]

Does anyone here use a small set of doubles, like twin 50's or even 40's for shallowish OW diving. It seem that might be an answer for those who don't need all the gas of 80's or 100's. And it would be more balanced and out of the way than a pony. I have an OMS catalog that shows twin 46's. Looks like a sweet little setup.

When a reg on a set of doubles fails, or an o-ring goes, how long does it really take to shut it down and switch to the other?
Neil

 

[Diver0001]

MHK once bubbled...

<snip>
Doubles are the recomended option in diving to those depths, <snip>

Lets try thinking a little out-of-the box, shall we? From the perspective of the recreational diver we have free access to the surface and all we really need is to bridge maybe 60 seconds in the extremely unlikely event that you have some kind of equipment problem that leaves you OOA at a depth deeper than you can execute a CESA.

To manage this extremely remote risk you could:

(a) Spend a lot of time, effort and money reconfiguring for twins and learning how to handle the equipment. You can carry an extra 15-20kg of gear everywhere you go for the rest of your life and so forth. This may be a general purpose solution for a wide variety of contingencies when bailing out to the surface is not an option but it's killing a mouse with a canon for the unlikely event that you may, perhaps, once in your life, maybe need to bridge those 60 seconds.

or

(b) you could carry a pony and have essentially an independent twin large enough to bridge the 60 second gap at a cost of about 3kg.

There are a other possibilities too but since this thread isn't about those, I'll leave it at that.

The DIR upper echelon calls a pony "a solution to a problem that doesn't exist" but I would submit that the problem does exist and that the DIR top are out of touch and are acting like the manager who doesn't have a clue what's going on two levels below him.

R..

 

[MikeFerrara]

I'm not going argue about whether or not a pony ever makes sense (again), but I am a little concerned about some suggesting they are appropriate in an overhead. What kind of overhead dives are you doing where you would use a pony instead of doubles?

 

[LUBOLD8431]

neil once bubbled...
I have an OMS catalog that shows twin 46's. Looks like a sweet little setup.

Yeah, they are cool, however, NO ISOLATION VALVE IN THE MANIFOLD!!! Meaning, all you really have is two tanks connected by a crossbar. Not good for redundancy, because you cant isolate the two tanks...

 

[Genesis]

I don't believe that a pony is adequate in an overhead environment.

I also believe that in an overhead environment, a twinset is probably not enough all on its own, especially if there is a deco obligation involved (that is, the overhead is either entirely or partially "synthetic")

A blown tank O-ring or other catastrophic failure in the gas delivery system (e.g. crossbar seal failure, etc) that requires you to isolate could cost you enough gas to hose you even if you get to the offending valve, and its the right one, immediately, as it costs you at least one-half of your remaining gas supply.

If you dive the "rule of thirds", and the "oh s@#@" happens at the turn point, you could still be hosed, because (1) the valve shutdown is NOT instantaneous, and (2) losing half plus any, which is a given, of the REMAINING gas supply puts you below minimums at that point.

Never mind that "thirds" is computed at your "usual" SAC, and the "brown water" syndrome is going to boost that significantly, so suddenly you're not where you think you are.

With that said, its infinitely preferrable to the alternative, which is suddenly having no gas, which is what happens with a single!

More "stuff" to think about.... but IMHO the argument for doubles has to do with the required amount of backgas more than anything else. The rest of the hardware (and configuration) is just a balancing act in an attempt to insure that you get to use as much of that backgas as possible in all potential circumstances.

 

[Rob Meddes]

neil once bubbled...

When a reg on a set of doubles fails, or an o-ring goes, how long does it really take to shut it down and switch to the other?
Neil

Should take seconds. I take about 3 secs to isolate (which stops gas loss from both tanks) & about another 3-7 to shut down the offending valve depending on what i'm doing at the time.
Good diving
Rob

 

[neil]

LUBOLD8431 once bubbled...

Yeah, they are cool, however, NO ISOLATION VALVE IN THE MANIFOLD!!! Meaning, all you really have is two tanks connected by a crossbar. Not good for redundancy, because you cant isolate the two tanks...

Yeah, I noticed that, but assumed the isolator would be an option you can get. Don't know enough about the product line, but I bet it can be ordered with the isolator installed.
Neil

 

[nickjb]

neil once bubbled...

When a reg on a set of doubles fails, or an o-ring goes, how long does it really take to shut it down and switch to the other?
Neil

'Diver' did an article on this a while ago

http://www.divernet.com/technique/0102twins.htm

 

[MHK]

Diver0001 once bubbled...


Lets try thinking a little out-of-the box, shall we? From the perspective of the recreational diver we have free access to the surface and all we really need is to bridge maybe 60 seconds in the extremely unlikely event that you have some kind of equipment problem that leaves you OOA at a depth deeper than you can execute a CESA.
R..

Let's really try to think outside the box, but let's do it this time thinking the problem through to it's next logical conclusion..

CESA's aren't the issue, what a diver should be looking to when considering diving in the deeper ranges of recreational limits, ie; 100'-130' range.. A very real consideration is gas management and available BT's.. If you approach gas management with a view's towards reserving sufficent gas to provide for both you and your buddy to surface in the event of a failure at depth, and also provide for gas management protocols that allow for slow, safe ascent rates even during an emergency, then you'll see that pony's and CESA's are the wrong approach to solving a potential problem..

When you dive in the 100'+ range gas management and contingency reserve are very real considerations that should be planned for in advance.. Approaching these types of dives, and acknowledging that if you use the proper gas, the proper volume and do the proper planning you can do nearly 40 minutes at 100' and if you have a failure at that point you can safely ascend [ ie; NOT a CESA]..

That is how we think outside the box, we try to think the whole problem through and consider that using a pony to do a CESA is only looking at part of the problem, not really looking at how to approach a dive of that magnitude..

Later

 

[Genesis]

MHK continues to pontificate in ways that, at the final analysis, make no sense.

We carry safety equipment for contingencies.

That's WHY you have a "safe second", WHY you have extra gas, WHY you turn on thirds in an overhead, WHY you have manifolded doubles.

Now this very same person who advocates all of these things - extra gas, thirds, a second backup regulator, doubles - suddenly refuses to accept that when it comes to a buddy, that things may "break" there as well.

Given Kane's obsession with "perfection", it is reasonable under his rubric to not have a backup regulator, a manifold, or even a buddy. Why take them? Since he assumes that a buddy will never "break", he can easily assume the same thing about the rest of the dive. Just make sure your regulator is in good condition, overhauled regularly, that your hoses are new, and that your O-rings are replaced long before they could fail. Nothing will break under the GUE rubric, you see, because perfectlion is the order of the day, so we do not need to worry about it.

Of course that's a stupid point of view, because things do break.

But then again, we're back to the irrationality of the GUE argument - "everything may turn brown on you, EXCEPT that your buddy never will and never may, and as such it is perfectly reasonable to DEMAND perfection from your dive team, while expecting (and providing for) a major C.F. from everything else when you select your gear configuration."

Yep. There you have it - the double standard of GUE/DIR, in scaldingly-bright relief for 'ya.

Oh yeah, and if you are less than perfect, you get compared to farm animals by GI3, while a gear failure or environmental problem is just "part of the deal."

The arrogance of this point of view goes beyond self-serving to the point that one has to wonder if they WANT to see people die due to problems underwater that are ultimately "human."