Pony vs larger tank?

[elan]

I really can't see that glancing at two SPGs and swapping regulators twice is a huge increase in the task load of a diver; and that only pertains to diving rule of thirds (for an overhead situation). If you are diving independent doubles for redundancy in a normal open-water situation those procedures are entirely unnecessary since all you are trying to assure yourself is that there is sufficient gas in each of the tanks, at all times, to get you and your buddy back to the surface in a normal ascent.

Well all tasks add up at the end. That's just another one. One more hose and one more gauge. Then sharing air with OOA buddy becomes more complicated as at each particular point you will have different regs. So you need to train for sharing 2 different regs instead of one.

 

[Thalassamania]

Well all tasks add up at the end. That's just another one. One more hose and one more gauge. Then sharing air with OOA buddy becomes more complicated as at each particular point you will have different regs. So you need to train for sharing 2 different regs instead of one.

The question is not if there is "additional" load, rather it is, "is the additional load significant?" In this case I would argue that first of all it is not significant; and second of all the removal of the isolator from the mix balances that tiny change out.

As far as air sharing is concerned ... you hand the OOA diver the regulator that is in your mouth and then start to breathe off the other one ... not exactly rocket science, especially since all you need to do is get to the surface with your buddy, remember we are not talking about overhead situations.

 

[elan]

The question is not if there is "additional" load, rather it is, "is the additional load significant?" In this case I would argue that first of all it is not significant; and second of all the removal of the isolator from the mix balances that tiny change out.

As far as air sharing is concerned ... you hand the OOA diver the regulator that is in your mouth and then start to breathe off the other one ... not exactly rocket science, especially since all you need to do is get to the surface with your buddy, remember we are not talking about overhead situations.

I will not argue, I just see that this will introduce extra activity.

As for sharing, one thing is personally I cannot stand sharing standard short hoses, it is just so uncomfortable, even in OW especially if both wear dry suits. So here is the problem - the hoses should be long. you have to keep them somewhere. Second thing is that you have to clip off your second hose somewhere otherwise it will be flying all over. In an OOa situation when you passed the reg from your mouse you need to un clip it or pull it. I donno but for me it looks so uncomfortable and cumbersome having to have two primary hoses to manage.

 

[Thalassamania]

I will not argue, I just see that this will introduce extra activity.

What's to argue about? There's some extra activity. There's some reduced activity in other areas. The only argument is does the offset balance (more or less), which I see as kind of a silly think to argue about since both the increased and decreased loads are way down in the noise.

As for sharing, one thing is personally I cannot stand sharing standard short hoses, it is just so uncomfortable, even in OW especially if both wear dry suits. So here is the problem - the hoses should be long. you have to keep them somewhere. Second thing is that you have to clip off your second hose somewhere otherwise it will be flying all over. In an OOa situation when you passed the reg from your mouse you need to un clip it or pull it. I donno but for me it looks so uncomfortable and cumbersome having to have two primary hoses to manage.

If you find that to be a problem, don't do it. I don't happen to find any difficulty.

 

[elan]

What's to argue about? There's some extra activity. There's some reduced activity in other areas. The only argument is does the offset balance (more or less), which I see as kind of a silly think to argue about since both the increased and decreased loads are way down in the noise.
If you find that to be a problem, don't do it. I don't happen to find any difficulty.

I was researching doing it in the past but those things I have found took me away from that config.

Do you use independent all the time ? or only on vacation with rental tanks ? What hoses (length) do you use and how do you route them ? What conditions do you dive in?

Thanks for the info in advance...

 

[Thalassamania]

I use them rarely, I was just answering your remarks to Dale's suggestion. I'm not a big advocate of independents or for that matter of yoked doubles. Most of the time when I've used independent doubles it is to have one tank to run an air tool and the other for air or circumstances that dictate a cylinder of backgas and a cylinder of travel mix (and usually a 40 with more back gas and a 40 with oxygen ... but that's a whole different story). A good source on independents is Bozanic's piece.

 

[elan]

I use them rarely, I was just answering your remarks to Dale's suggestion. I'm not a big advocate of independents or for that matter of yoked doubles. Most of the time when I've used independent doubles it is to have one tank to run an air tool and the other for air or circumstances that dictate a cylinder of backgas and a cylinder of travel mix (and usually a 40 with more back gas and a 40 with oxygen ... but that's a whole different story). A good source on independents is Bozanic's piece.

Yeap that's a nice article. I have read it.

 

[diverdowndude]

I go with the idea that a pony is an emergency item and is not included in your dive plan gas calculations. It is there to give you a second chance if you have failures or if you simply make a mistake and need air.

a larger pony bottle would probably be included in gas calculations and planning in a overhead environment by most teams.

If you buy a bigger tank, you've extended your dive time, but you haven't accounted for emergencies.

I think you meant redundancy instead of emergencies- A single tank regardless of size with multiple regulators is not redundant in the event of a burst disc / neck seal failure. The odds of a burst disc or neck seal failure in a properly maintained tank is almost nil.

 

[DaleC]

Sorry for not replying sooner, I seem to have lost track of the thread.

Increased task loading as you need to monitor 2 gauges and switch the regs every now and then to keep them balanced.

Whether one dives manifolded doubles (MD) or independant twins (IT) there is some "tasking" involved.
With IT's the task is monitoring your SPG and making one (or two) reg switches when required. I derive my rockbottom gas pressure for max depth and that is my switch pressure.
With MD's the task is being able to perform a set of valve shutdowns should a gas loss occur. You don't need to make a reg switch but you do still need to derive rockbottom turn pressures and monitor a SPG.

Well all tasks add up at the end. That's just another one. One more hose and one more gauge. Then sharing air with OOA buddy becomes more complicated as at each particular point you will have different regs. So you need to train for sharing 2 different regs instead of one.

Sharing air is the same as a MD diver. The IT diver donates the long hose and breathes off the short one. A single tank PADI rigged diver donates the longer hosed octo as well (if they can find it).

One difference is that for half the dive the IT diver will be breathing off the shorthose when an OOA diver needs a reg (and the longhose is clipped off). For this reason the IT longhose should be secured to the boltsnap with a tearaway like an O ring because you still want to donate the longhose.

One advantage the IT diver has is that he/she routinely breathes the B/U reg and so knows it is in working order. Many PADI rigged divers never really breath their octo's and are just "hopin" they will work on the rare occation they are needed.

I will not argue, I just see that this will introduce extra activity.

Compared to a single tank diver yes. That extra activity is the price of more useable gas and redundancy. Compared to a MD diver who needs to contend with valve shutdowns, no.

As for sharing, one thing is personally I cannot stand sharing standard short hoses, it is just so uncomfortable, even in OW especially if both wear dry suits. So here is the problem - the hoses should be long. you have to keep them somewhere. Second thing is that you have to clip off your second hose somewhere otherwise it will be flying all over. In an OOa situation when you passed the reg from your mouse you need to un clip it or pull it. I donno but for me it looks so uncomfortable and cumbersome having to have two primary hoses to manage.

The IT diver can (should IMO) have the same hose configuration as a MD diver. Longhose primary and short hose bungied. The only differences are one more hose/SPG and one less isolator valve. The one time a IT diver could have two shorthoses would be soloing in a non overhead environment.


There is no right or wrong way to acheive redundancy so don't feel that it is an "arguement" to hold a different viewpoint. The main thing is to understand that each method has it's advantages and disadvantages. Often times by discussing in point - counterpoint fashion we (and the others reading) can see those advantages/disadvantages.
For recreational depths a single tank/pony combo will get one by.
For more demanding dives that require access to all available gas MD's are best.
For more demanding dives that do not require access to all gas but do require full redundancy IT's will work just fine.