Which brand of steel cylinder / tank should I buy?

[large_diver]

GM -- a question from the uninformed...

Why is an alum pony preferable -- buoyancy characteristics? I guess if you were attempting to handle/hand-off a pony underwater, a neutral tank would be easier to handle (since pony would be full, I assume an AL pony would be neutral and not positive)....

 

[Green_Manelishi]

for the purposes of discussion i am assuming the pony
will be mounted in a manner that allows access to same
at all phases of a dive. that contra-indicates carrying
your pony mounted on your back for the following reasons:

1) If you get it jammed you can't get at it
2) If you WANTED to hand it off you can't
3) IF you want to re-attach it after your buddy gets
his/her self situated you cannot
4) unless you place another long-hosed SPG on the pony
you will not be able to monitor the gas. If you DO
place another SPG you'd better be able to tell, quickly
and with no confusion *under duress* which SPG you are
examining: your BG or the pony

so we proceed:

1) steel will start more negatively bouyant and likely
FINISH more negatively bouyant. Some will use this
negative as part of their over-all weighting
arrangement. so, what happens if you 'give it to your
buddy' and are now 5 pounds lighter?

please, no-one suggest carrying extra weight just in
case you need to detach the bottle. now you are
intentionally over-weighted; DUH.

what happens if you are "staging" it and you unclip it?
you are now "lighter" and must compensate. when you
re-attach it you are heavier and must compensate.

2) aluminum will "float butt up" in your slip-stream. Steel
will NOT float and you will be dragging it through the
water column.

 

[large_diver]

Thanks GM -- helpful summary.

 

[Aegir]

Why would i be giving my pony to my buddy??

Every diver i have seen using a pony bottle (and thats alot of divers) has it back mounted via tank straps/adapter. Where else are you suggesting that i should put my pony.
I dont want it dangeling down off my thigh or under my arm for lots of reasons.

 

[large_diver]

Aegir,

Many folks advocate rigging a pony bottle like a "stage" (DIR terminology) -- i.e., setting it up with bolt snaps near the top and bottom of the tank, and then clipping these snaps to the left chest and left hip D/O rings on your BC or harness. I tried this is a pool 2 weeks ago and it was very easy -- incredibly easy to don/doff on land, in the water it sat more or less on my hip in my slipstream -- easily accessible but out of the way. By using an alum pony with neutral characteristics, this config. does not affect your trim.

Som why would someone prefer this config vs. having it attached to your tank out of the way -- easier to access if entanglement occurs, can hand it off to another diver in an emergency (and they can clip it to their harness/BC), can see SPG on pony, able to access if there is a problem with reg/valve connection, easy to reach if you forget to turn air on, etc., etc.

Here is a link from a recent discussion on this topic over on scubadiving.com if you would like to read more.

http://www.scubadiving.com/talk/read.php?f=1&i=279654&t=279654

Also -- a picture
http://www.scubadiving.com/members/photogalleries.php?s=392

 

[large_diver]

One other reason -- VERY easy to switch pony when switching tanks

 

[Green_Manelishi]

If the diver carrying will NEVER hand the bottle to
anyone and it is simply THEIR redundancy they still have to contend with HOW to read the pressure: two SPGS. Which is which? Also, if the pony is bleeding gas you might not know
and without the SPG you WON'T know how much is remaining.

I have an SPG attached to the bottle. I KNOW it is the
bottle content because I can look down at it. I do not
have to think about is it the right or the left? the metal or the plastic? black or red? Under STRESS you need to
focus on the problem not sort through multiple gauges looking for the 'correct' gauge.

If the diver intends to allow another OOA diver to use it
then again they should be able to monitor and verify the content and control the entire bottle.

If it is on your back and you are single tanking it is a
"drag": literally. An entanglement that passes within inches
of your primary supply has a better chance of snapping the
large object on your back. Now you have a problem.

Would I refuse to dive with you simply because you carry a
pony on your back? probably not. Would I refuse to carry one
on mine when I believe there is a better way? You bet.

 

[Tavi]

Hi all,

Good thread. My son and I plan on getting pony bottles before diving Grass Lake (near Alexandria Bay,upstate NY) (a freind of his has a cottage there).

I never thought of rigging them any other way than to the primary tank.Rigging them as a stage looks much simpler.

While diving in Grand Bahama one of the guys had a pony mounted to his tank. It looked like a real hassle whenever he set up on a fresh tank.

large_diver,
Thanks for the links


Tavi:tree:

 

[Atomox]

Aegir,

The point of weighting and the proper selection of equipment is to make sure that you're properly weighted for the end of the dive in a way that ensures enough of your weight is ditchable, in small enough increments, to allow you to get to the surface at a controlled and safe ascent rate even with full tank(s) and all buoyancy control devices non functional.

Proper weighting at the end of the dive is being able to hover at 10 feet with 500 psi and no inflation in wings/BC.
The reason for small incremental weight ditching is to prevent a rapid uncontrolled ascent (for deco diving this is worse than drowning).

What does this mean with respect to tanks? Are you diving dry or wet? If wet do you have a backup buoyancy device or are you able to swim up 2 steel tanks that are full and don’t forget to include the loss of buoyancy that goes with the compression of the wetsuit neoprene at depth. In all likelihood at 100 feet with the setup you described you will be 20-25 lbs. negative with no weight.

The idea of a steel tank and a steel pony is poorly thought out. In fact the idea of a pony is poorly thought out as well. The simple concept of not doing dives where you can't get out of trouble easily without the aid of a pony should be followed. If you really need the redundancy of the pony than go to doubles. If you do not need doubles than the type of diving you are doing does not require a pony. Pony bottles are from the days of single tanks and/or single outlet manifolds. There is no need for ponies with a dual outlet manifold. The concept of carrying a pony as part of the main gas supply is like carrying a can of gasoline on the frontseat of your car.

Brad

 

[nobends]

Wow Brad, I couldn't disagree with you more. Carrying a can of gasoline in the front seat of your car might save you a long walk. A pony bottle might save your life.

What would you do on deep dive if you discovered your SPG was broken (stuck at 1000psi). What if you discovered this because you are sucking on an unresponsive reg. Of course most OOA emergencies happen after you've exhaled. Are you going to perform an emergency swimming ascent? Try to get your buddies attention (who might be looking the other way several yards from you)? Or are you going to grap a couple of breaths from a pony tank while you decide what to do next?

Recreational dives typically don't require doubles. That doesn't mean they don't require redundancy in equipment. Relying on yourself for air supplies is clearly the best way to go. Pony tanks can make sense for every diver.