Is there a valid reason for a pony bottle

[BlueTrin]

If you're rec trained, redundancy probably isn't your main motivation for diving a twinset. After all, if a twinset is able to give you redundancy, you need to be able to shut down the manifold, and rec divers aren't trained to do that. Although the most common rec twinset in my waters is a D8.5x232, I've seen twinsets as small as D6x300, and even D4x300. Without an isolation manifold. A D6x300 doesnt carry more gas than a single 12x300, so no gain neither in gas volume nor in redundancy.

But those I know who swear to rec twins claim that they balance a lot better than a rec single. I wouldn't know, because for my diving singles are better, so I use a singles rig.

By the way I was wondering: when you dive manifold doubles, if you go on a trip and do two dives, then you have to keep your tanks for the second dive, isn’t it ? It’s not like you can swap tanks or refill when on a boat ?

So you are getting the same quantity of air than someone who swaps a single cylinder during the interval, isn’t it ? (You still have redundancy if you can use the manifold though l)

 

[grf88]

By the way I was wondering: when you dive manifold doubles, if you go on a trip and do two dives, then you have to keep your tanks for the second dive, isn’t it ? It’s not like you can swap tanks or refill when on a boat ?

So you are getting the same quantity of air than someone who swaps a single cylinder during the interval, isn’t it ? (You still have redundancy if you can use the manifold though l)

You have a little more air on the second dive if you used what you would have done on a single cylinder since you have the extra 500-1000-psi that you would normally surface with. Some take an extra HP cylinder and a transfill whip to top up between dives.

 

[Storker]

By the way I was wondering: when you dive manifold doubles, if you go on a trip and do two dives, then you have to keep your tanks for the second dive, isn’t it ? It’s not like you can swap tanks or refill when on a boat ?

So you are getting the same quantity of air than someone who swaps a single cylinder during the interval, isn’t it ? (You still have redundancy if you can use the manifold though l)

As I said: I wouldn't know, because [...] I use a singles rig.
Because that fits my diving better. Others have other priorities than I have. Like balance, or a bit more gas than can be comfortably carried in a standard single tank.

 

[Basking Ridge Diver]

when you dive manifold doubles

Some of us dive independent doubles and you can swap to your hearts content - sometimes I bring 3 tanks and only swap out the one used. For deeper and longer dives I will swap out both. YMMV

 

[barth]

By the way I was wondering: when you dive manifold doubles, if you go on a trip and do two dives, then you have to keep your tanks for the second dive, isn’t it ? It’s not like you can swap tanks or refill when on a boat ?

So you are getting the same quantity of air than someone who swaps a single cylinder during the interval, isn’t it ? (You still have redundancy if you can use the manifold though l)

I will take two sets of doubles to the boat.

(There are boats where it is possible to fill. But I will only fill on the boat if there is nitrox available. Then one set of doubles is enough for a dive trip. I will do both dives with a set of doubles with at least 200 bar.)

If I will dive to a 30 meter wreck, a single tank will give me 20 minutes of bottomtime. Doubles will give me 35 minutes bottomtime. (Doubles and oxygen stage give me 45-50 minutes of bottomtime.)

 

[Storker]

I will take two sets of doubles to the boat.

Isn't swapping tanks a bit of a chore compared to swapping a single? Or do you bring two full rigs?

That's the main reason I prefer a single tank rig. I don't have a compressor on my boat, and stowing a spare single tank is a lot easier than stowing an extra twinset.

 

[Gareth J]

If you're rec trained, redundancy probably isn't your main motivation for diving a twinset. After all, if a twinset is able to give you redundancy, you need to be able to shut down the manifold, and rec divers aren't trained to do that. Although the most common rec twinset in my waters is a D8.5x232, I've seen twinsets as small as D6x300, and even D4x300. Without an isolation manifold. A D6x300 doesnt carry more gas than a single 12x300, so no gain neither in gas volume nor in redundancy.

But those I know who swear to rec twins claim that they balance a lot better than a rec single. I wouldn't know, because for my diving singles are better, so I use a singles rig.

Nice post, I agree.

I was diving twins before I did my first tech course (recreationally trained). In those days isolated 10's (litres).
I switched to isolated manifolded 12's after I had a reg' problem and couldn't get at the much needed gas - bit of a fright really, I considered stripping the regulator and cleaning the diaphragm or swapping it over (easy on a cyklon), but discretion is the better part of valour, and aborted with a little help from my buddy.
My late partner used to dive twin 10's with the isolator closed (as if they where independent's), she was never confident she could do a shutdown in an emergency. If the shutdown had been successful, she could then open the isolator at her leisure.
I dive rebreathers these days, so shutdowns are straightforward.
Having lost a bit of mobility in my shoulder, I kind of like the idea of side mounts for OC diving, other than the fact it takes me back to isolated twins, and the fright that gave me.

I know quite a few that used small twins, either isolated manifold, or independents (normally 7's (litres), both 232's and 300 bar). A couple of the girls use them because they find it easier on their backs than their single 12's, and as you say, the balance is nicer.

Ultimately it's about comfort, and what you prefer. I don't need to dive CCR for a lot of my diving, I just enjoy it, and its lighter than twin 12's , and a lot less faf on the boat, no swapping cylinders or filling cylinders over the weekend.

Gareth

 

[Diving Dubai]

if you go on a trip and do two dives, then you have to keep your tanks for the second dive, isn’t it ? It’s not like you can swap tanks or refill when on a boat

This is where logistics etc come into play. @grf88 suggested a transfill, and that's something I do for my SM. But you get diminishing returns

With 2 x AL 80 - I have 4400 litres of gas (154cf in old money). My Steel 15 plus AL 40 gives me 4570l (161cf) Both more than enough for a single dive with some redundancy (the Al 40 can be a stage and a pony in one)

Now dive 2 if I transfill my SM from a full steel I get them back to 150 bar which is 3300 l (116cf) of gas still plenty but less than if I clipped on a new 15l

The third dive my gas volume would be lower in the SM 2640l (93cf) etc etc.

So. If I'm travelling - SM wins

If I can get new cylinders each dive them I prefer SM, but if you can get twins filled each time - no difference

If I'm multi day diving without access to full cylinders and transfilling - then Backmount and a slung (large) pony wins

If I were on a Rib then either SM or Backmount because twins would probably be a faff removing in the water and lifting them onboard.

That's not to say in any way twins are bad. What I'm trying to point out is that sometimes you need to look at the bigger picture and go with the solution that best fits with the type of diving you do and the logistics involved to achieve the required gas volume for each dive.

 

[lowviz]

That's not to say in any way twins are bad. What I'm trying to point out is that sometimes you need to look at the bigger picture and go with the solution that best fits with the type of diving you do and the logistics involved to achieve the required gas volume and comfort factor for each dive.

Bolded words are mine, not Diving Dubai's.

Still following this thread ( *sigh* ).

 

[Diving Dubai]

a lot less faf on the boat, no swapping cylinders or filling cylinders over the weekend.

Gareth

Each summer, when I'm hauling my 6 - 9 x 15l steels off the boat and it's 44C (111F) in the shade - even worse during Ramadan when you can't' drink water in public. I look with envy at the smug box divers, with ther CCR on their back and a spare dil and O2 cylinder in each hand, making the trip up the dock.. Grrr