There are two stances on Ponies, some say they are needless, others they are sensible.
My personal experience.
I originally learnt to dive in the Red Sea (90's).
I joined a club in the UK a few months later, after a bit of a checkout dive in the pool. I then had the opportunity to do my first open water dive.
We where at an inland quarry (in February). I was up for a 10m dive as a checkout, and to get to grips with the drysuit, I was using.
Three of the more experienced divers where doing a drop to 35m. Partly as a warm up dive for a trip they where going on, partly to checkout recently serviced kit (including regulators).
I was watching as they entered the water. 10 minutes later, two where on the surface, one was underwater, and the rescue boat was on scene.
What happened?
At around 30m, diver A had a free flow.
He went onto diver B's AAS.
As they started to ascend, his regulators started to free flow.
Diver B switched to his Pony,
Diver A switched to Diver C's AAS.
At around 20m, Diver C's regulators free flowed.
Diver A and Diver C continued to ascend on free flowing regulators.
Diver B followed them to 6m, and stopped, opting to do a few minutes at 6m on the Pony.
Diver A and C ended up on the surface, watching diver B below them.
It transpired that the first stages had all iced up.
Diver B was an ex Navy Diver, and a paraplegic, his ascent was fast at the start, then slow from 10m, with a 5 minute precautionary stop.
Diver A and C had completed 'fast ascents'.
They all went and sat in the Pub for the rest of the day!
It taught me a lesson.
- Things go wrong - even when you do everything right.
- Two divers on one first stage can easily overload it, especially in cold water.
- Cold water and well maintained regulators doesn't mean you are safe.
- A pony, when the **** hits the fan gives you time - not a lot, but possibly enough.
- A free swimming ascent from 30m+ is undesirable.
Until we switched to Twin's the majority of the divers carried a pony. The incident was a good demonstration as to why it's use is a good idea.
By the mid 90's most of us where on twins. But that also related to the depths of the dives and the amount of decompression we where doing.
Gareth