Pony vs. Doubles -- Philosophical Difference?

[Doc Intrepid]

When I dive in locations where I control which tanks I use, I tend to use doubles.

When I dive in locations where I have no control over which tanks I am assigned (rental singles), I tend to bring along a small sling tank.

Often the environment you find yourself in influences your choices...

 

[evil_xander]

I dive dry from October until late April/early May, drysuit weighting is a PITA with a single steel tank, hence 2x12 manifolded steel tanks. I doubt I'll be using them with the wetsuit, they are too negative to start with.

I don't usually spend too much air so I can do without problems two dives with that setup, ideal for private diving trips my buddies and I frequently organize, no need to get/find fills in between.

Otherwise, when not needed not in use, the right tool for the job and stuff philosophy, I most definitely don't plan on hauling them along for very shallow dives (besides practise).

OTOH, I never considered/needed a pony. For that kind of redundancy I have my buddy nearby.

Isn't that just plain weird.

 

[pengwe]

Ponies are "easy" and doubles are "hassle".

 

[DaleC]

At the end of the dive, the singles diver will have 500psi or 13 1/3 cuft of gas left in his tank.* He then leaves that gas on the boat for dive number two and starts with a fresh 80 at 3000 psi.* At the end of dive 2, he has another 500psi in the tank as his safety margin.On the other hand, the doubles diver uses the same 66 2/3 cuft of gas on his first dive and surfaces with 93 1/3 cu ft or 1750 psi.* at the end of dive 2, he surfaces with 26 2/3 cu ft of gas in his tanks at approximately 500 psi.Bottom line: without getting into complicated gas management issues that I have no clue about (especially when talking about two buddies with different tanks and different SACs) the diver using doubles ends the second dive with more gas in reserve that the singles diver (ALL ELSE BEING EQUAL)

The doubles diver has 26 2/3 cuft and the singles diver has 13 1/3 + 30 cuft (43 1/3cuft). You forgot the pony.

 

[gcbryan]

I think the philosophical difference is in trying to include either in a philosophy. What are the philosophical differences between a 120 cu ft tank and a 100 cu ft tank or a black mask and blue one...there aren't any!

Doubles are for whatever you want them for of course but mainly they are for redundancy and for additional gas. Ponies are for redundancy where you don't need "additional gas". If most of your diving is one dive a day then why carry around 2 tanks when a much smaller/lighter slung pony would do. If you are shore diving why carry around two bulky tanks when you don't need to? If you dive from a small car why try to put attached/manifolded doubles in the trunk when one or two single tanks is much easier to put in and to pull out?

On the other hand, if you mainly dive deep, square profiles then doubles are your choice and ponies probably don't make sense.

You can still dive as a "team" and go to your buddy for help should you need it. You don't have to go to the pony first unless you choose to under the circumstances. You can bring philosophy into this but it isn't there inherently.

 

[OH-JJ]

I personally think Doubles are more comfortable under water, (of course they are a pain out of the water.)

and I will take my AL40 when diving Doubles and when diving singles.

Spare Air Scuba Safety Tank: Underwater Test Dive

Interesting

I know I Shouldn't, but I'll feed the troll...

That guy, in the video, is an obvious tool.

#1 You never will be going straight to the spare-air nor a pony, after taking a breath of a working reg. you will be out of air hence out of breath.

#2 That has to be to worst placement for the spare air, look how long it took from reaching for it to his first breath. with my slung pony, I can reach, put it in my mouth, exhale/purge to clear, take my first breath, and have it turned on, in less than 20 seconds.

#3 Of course he now dives with it... he got one free for doing the review. The question is would he buy one.

 

[mwilding]

The doubles diver has 26 2/3 cuft and the singles diver has 13 1/3 + 30 cuft (43 1/3cuft). You forgot the pony.

no i didn't - hence the "ALL ELSE BEING EQUAL" comment. In your scenario, the singles diver has 30cuft of extra gas. Would it be fair then to give the doubles diver twin LP 108's to even up the gas amounts? If so, the doubles diver finishes the second dive with more air that the singles diver started with in his AL80. Or he could sling a pony too, in which case he still has far more reserve for both dives.

A doubles configuration is a more efficient way to manage your gas supply that singles when making two dives. That is really my point. It comes at the expense of carrying a crapload of weight around on your back though...

 

[DaleC]

no i didn't

Yes you did. I'm using your numbers. You are quoting for twinned 80's vs a single 80. The singles diver came out with 13 1/3cuft left but that doesn't take into account the pony.

In your scenario, the singles diver has 30cuft of extra gas. Would it be fair then to give the doubles diver twin LP 108's to even up the gas amounts?

No, because then you would have to give the singles diver a HP 130 etc... I think doubled 80's vs a single 80 is a fair comparison. I used a 30cuft pony because that is an often recommended size for a viable pony. In the end (as my therapist always says) It's not the size that matters but what you do with it that counts.

Or he could sling a pony too, in which case he still has far more reserve for both dives.

but wouldn't that concede the point that doubles fall short and a pony is the better option?

All in good fun and discussion sake only. I am just playing devils advocate here and have no ingrained preference. In reality I agree with others that say the proper tool for the job. I also believe there is more than one right way to do something.

 

[DA Aquamaster]

Being the devil's advocate can be hard.

Personally, pound for pound I think HP 100's are a better choice for doubles than double AL 80's and would be more likely to be encountered as the HP 100 and AL 80 tanks weigh the same.

That leaves you with 200 cu ft versus 154 plus 30 for the two single AL 80's (that only hold 77 cu ft each) plus 30 cu ft pony diver.

So...

..........................Doubles diver...................Single + pony diver
First dive..............100 + 100 (200)cu.ft. ..........77 + 30 (107)cu.ft.
Second dive..........50 + 50 (100)cu.ft. .............77 + 30 (107)cu.ft.

It looks like the advantage is still with the two single 80's plus pony, but it is not.

Practically speaking on dive one I enter the water with 3400 psi (rounded down from 3442 psi) and plan to be back on the boat with no less than 1700 psi. If I have a problem on dive one, I have lots of gas in reserve over 100 cu ft, a clear advantage on dive one. But it gets even better than that.

Assuming the buddy has an AL 80 and a 500 psi reserve, he or she has 64 cu ft available for the dive. That 64 cu ft equates to only 1100 psi used in the double 100's. So assuming an equal SAC I am getting out of the water after dive one with 2300 psi. (The irony here is that 2266 psi would in fact be the way too conservative thirds everyone is talking about - so diving thirds with doubles actually works on pretty fish dives with no loss of bottom time.)

On dive two, I start with 2300 psi (133 cu ft or 26 cu ft more than the AL 80 plus 30 buddy has total) and plan to end the dive with a reasonable reserve of 500 psi, which coincidentally happens to be 29 cu ft. (very close to the 30 cu ft pony). So 133-29 = 104 cu ft left for the dive, with a 29 cu ft reserve. Potentially lots more bottom time on dive 2 with a liberal reserve.

But again the AL 80 buddy has only 64 cu ft available so I am again ending the dive with a lot of reserve gas - about 69 cu ft total or 1187 psi. (and again 1133 would be 1/3rd of the original 3400 psi and 1150 psi would be half the 2300 psi I started dive 2 with, so on dive 2 I am actually diving halves - extremely conservative gas planning.)

Now, if we assume I really only did have AL 80 doubles - I start with 154 cu ft, use 64 cu ft on each dive and still have a large 26 cu ft left in reserve at the end of dive 2 - with no need to haul along a pony.

The major efficiency with single AL 80's versus AL 80 doubles in that case is that the 13 cu ft left in my buddy's first AL80 with 500 psi remaining is on the boat for dive two while the 13 cu ft reserve I had after dive one is still in my tanks and is available to me.

---------

When I used to do a lot of very cold water diving with a dry suit, very heavy underwear and dry gloves with thick liners, I preferred either independent doubles or manifolded doubles with the isolator closed as it eliminated the need for me to rely on being able to close the isolator to preserve the other half of my remaining gas. The same argument works in a restriction while cave diving or anywhere else where closing the isolator may not be feasible.

Gas management is not overly hard with independent doubles - use 1/3 from the left tank, switch to the right tank and use 1/3rd, turn the dive, use another third of the right tank and then switch back to the left tank to use the 2nd third from it - at which point you should be back on
the surface.

---------

Given that I also do overhead diving in caves wrecks etc, diving doubles all the time has the advantage of keeping me in a familiar configuration all the time.

Larry

 

[DaleC]

Personally, pound for pound I think HP 100's are a better choice for doubles than double AL 80's and would be more likely to be encountered as the HP 100 and AL 80 tanks weigh the same.

That leaves you with 200 cu ft versus 154 plus 30 for the two single AL 80's (that only hold 77 cu ft each) plus 30 cu ft pony diver.

So...

..........................Doubles diver...................Single + pony diver
First dive..............100 + 100 (200)cu.ft. ..........77 + 30 (107)cu.ft.
Second dive..........50 + 50 (100)cu.ft. .............77 + 30 (107)cu.ft.

It looks like the advantage is still with the two single 80's plus pony, but it is not.

Practically speaking on dive one I enter the water with 3400 psi (rounded down from 3442 psi) and plan to be back on the boat with no less than 1700 psi. If I have a problem on dive one, I have lots of gas in reserve over 100 cu ft, a clear advantage on dive one. But it gets even better than that.

Assuming the buddy has an AL 80 and a 500 psi reserve, he or she has 64 cu ft available for the dive. That 64 cu ft equates to only 1100 psi used in the double 100's. So assuming an equal SAC I am getting out of the water after dive one with 2300 psi. (The irony here is that 2266 psi would in fact be the way too conservative thirds everyone is talking about - so diving thirds with doubles actually works on pretty fish dives with no loss of bottom time.)

On dive two, I start with 2300 psi (133 cu ft or 26 cu ft more than the AL 80 plus 30 buddy has total) and plan to end the dive with a reasonable reserve of 500 psi, which coincidentally happens to be 29 cu ft. (very close to the 30 cu ft pony). So 133-29 = 104 cu ft left for the dive, with a 29 cu ft reserve. Potentially lots more bottom time on dive 2 with a liberal reserve.

But again the AL 80 buddy has only 64 cu ft available so I am again ending the dive with a lot of reserve gas - about 69 cu ft total or 1187 psi. (and again 1133 would be 1/3rd of the original 3400 psi and 1150 psi would be half the 2300 psi I started dive 2 with, so on dive 2 I am actually diving halves - extremely conservative gas planning.)

??? Why do the doubles proponents always want to skew the playing field in their favor? If you are going to use double HP 100's then give the singles diver one too. Otherwise you are comparing apples and oranges.

Now, if we assume I really only did have AL 80 doubles - I start with 154 cu ft, use 64 cu ft on each dive and still have a large 26 cu ft left in reserve at the end of dive 2 - with no need to haul along a pony.

but you do haul along an extra 80 and my point was that the single/pony diver has (roughly) 43cuft after dive two.

The major efficiency with single AL 80's versus AL 80 doubles in that case is that the 13 cu ft left in my buddy's first AL80 with 500 psi remaining is on the boat for dive two while the 13 cu ft reserve I had after dive one is still in my tanks and is available to me.

or you could look at it that you are lugging that extra 80 just to have access to that 13cuft. The doubles user hauls 2 80's and the pony diver hauls an 80 and a 30.