“STAGE versus PONY'': HOW TO MOUNT THEM PROPERLY and WHERE

posted by siteadmin on 12 december, 2007 - 00:00
Hogarthian Diving

Many people start off with a 15L or 12L cylinder and then, as they venture deeper/longer, they realise the need for either more gas or a back-up gas supply.  Most therefore opt for a “pony”.  A “pony” is a small (usually 3L) cylinder that one fits a second regulator and contents gauge to.  I have nothing against “ponies” per se but I do have some comments on how they are set-up and where they are put.


Short definition:
"Stage" - aluminium cylinder use as deco bottle or stage usually Luxfer  size S40 (5,6L) , S80 (11,1L) or 7L . 

 

"Pony" - is a small (usually 3L) steel cylinder that one fits a second regulator and contents gauge to.Firstly, my comments above regarding steel verses aluminium cylinders apply.  Most “ponies” that are sold are made of steel.  Aluminium “stages” are slightly heavier than steel ones because the wall thickness has to be thicker for aluminium tanks because of the lower tensile strength of aluminium.  But the aluminium cylinder is less dense and therefore less negatively buoyant.  Steel “pony” is about 2-3KG negative once fitted with regulator. 

 

This will roll you if you mount it on your cylinder (as is the norm – but see later comments).  An aluminium “stage” is only slightly negatively buoyant when full and neutrally buoyant once you have breathed it down a bit.  It therefore doesn’t have a tendency to roll you. 


Secondly, most divers mount their “pony” by strapping it to the side of their tank.  This has many pitfalls:

  1. Because the “pony” is strapped to their tank it is out of reach.  You must therefore dive with the valve open and the regulator pressurised.  This means that if the regulator free-flows you can’t turn it off yourself.  Your buddy may be able to help but by then a significant amount of your valuable reserve/deco gas has gone.  It also means that you are RELYING on your buddy.
  2. Because the “pony” cylinder has to be turned on throughout the dive, it means that your buddy (anybody else) could breathe it by mistake if they had an emergency.  This is a serious problem if your “pony” deco bottle has an enriched Nitrox mix and you happen to be deeper than the safe Maximum Operating Depth (MOD) of that gas.  A buddy check before the dive may be one thing but in a panic situation things may get desperate and it may not even be your buddy (won’t have been briefed therefore).
  3. Whilst strapped to the outside of you main tank it poses a significant entanglement threat and the worst place to get entangled is behind you where you can’t reach.
  4. It creates more drag and increases your profile.
  5. They usually “slop” around.

The way to get around these serious drawbacks is to mount the aluminium “stage” on your left hand side by attaching it to a D-ring at the collarbone and another at your hip. Because the pillar valve of the “stage” is about where your left nipple is, you can turn it on and off easily.  You dive with the regulator pressurised but the pillar valve OFF.  This means that points 1) and 2) above no longer apply.  Because the tank is off you cannot get more than a single breath of the gas.  This is not enough to cause an O2 hit. When it comes to use the “stage” you simply turn the “stage “pillar valve on.

Alluminium S80 (11,1L) Stage cylinder

In this position, the “stage” sits under your left armpit and thus introduces very little drag.  It is also unlikely to get entangled but if it did, you would easily be able to deal with it, as it is visible and accessible in front of you.  The best way to for someone unfamiliar with this arrangement to understand is by demonstration. 

Below is a picture of a deco bottle correctly set up.  Note the use of stainless steel piston clips (not snap hooks) and the use of only 1 jubilee clip which is under a piece of bicycle inner tube at the bottom.  This cylinder is 11,1L but the same set-up is used for a 5,6L or 7L Stage.  The rope, piston clips and jubilee clip together costs about 20 Euro.  You can get the length of garden hose (shown in red) and the bicycle inner tube for free.

At the beginning of this section I described how many people move on from using just a single tank to using a single tank and a “pony”.  Consider that a 15L steel cylinder plus a 3l “pony” weighs (16.6KG +3.3KG = 19.9KG) MORE than Faber 232 Bar twin 7L’s (8KG + 8KG plus say 1KG for manifold).  The advantage of a twin-set over a pony set-up is that the set is more balanced and the weight closer in to your back.  You also have access to more air/gas if you have to shut down one side than if you switched to a 3L pony. 

Unfortunately a lot of recreational divers regard a twin-set as “Tekkie” and suited only to macho-types and those people doing deep dives.  Yes, there are lots of macho-types who use twin-sets and all sorts of other ridiculous gear (a trip to Stoney Cove on a winter weekend will confirm that), but just because you use a twin-set doesn’t necessarily mean that you are in this camp.  It may simply mean that you have given the subject some thought.

For all of my diving I use a twin-set because of the added safety and the comfort factor.  If I intend to use enriched Nitrox mixes or pure O2 for deco I will carry that side-mounted as described above.

Some divers use D-rings mounted on the bottom of the cylinders for hanging torches and reels etc.  These are, in reality, mounted in a terrible place.  The D-rings are an entrapment point for any line or monofilament that the diver brushes against.