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Bored at work so couldn't resist adding something to the debate. IMO pony bottles used as an emergency reserve bottom gas have no place in 'technical' diving - as has been said, if you're in the relms of deco then you're likely to be in depths of excess of 30m & it's twins you need on your back. However, I don't right off ponies full stop. I dive a mix of 'tech' and club diving. We are a BSAC club & as such train our members internally from complete beginner to competent open water divers and beyond. There are no 'schools' employed and all work by the instructors in a BSAC club enviroment is done voluntarily and their palms DO NOT get crossed with silver. Instead the instructors are investing in their club by introducing and training new members up to be competent divers who themselves will later dive with on club dives. While under tuition the dives progress towards and upto 30m. Once they have proven their ability to dive safely they are then 'qualified' to dive together without the guiding hand of the instructor. Now UK diving down to 30m can be fairly arduous with cold (dry suit) & at best average viz (~5m). Many quickly realise that this is a hostile enviroment which is just waiting to bite them on the arse! All the instructors in our club dive twins & the trainees are educated in the merits of a redundant system from day one. At this stage most of their diving will be in the 20-30m range. Here singles are IMO out of the question and are a thing of the past. However twins may be too much of a large jump for these relatively inexperienced divers. The club provides a number of pony cylinders to meet them half way. However, configuration is something that is thought about quite extensively. For some this is merely a transition from the single to twins, for others where they have decided not to venture into serious deco diving, it may be their 'limited' redundancy, because the idea of a 'single' supply of gas scare the hell out of them! Starting on a pony installs a certain ammount of skills which they can apply throughout their diving progression. Although, some do just bypass this stage a go straight for twins, especially when they venture out & buy their own kit (the club has a number of 12l's & ponies for members use) as the cost difference between buying a single & pony compared to twins is negligible! So.. Configuration - We prefer they set them up as twin independants on their back, but understand that the pony is never to be breathed off unless in an emergency. Extensive practice is done on reg switching, so that if the need arises it is second nature. A long hose can be used on the main (single cyl) - as this will be donated in an OOA and the pony reg can be hung round neck turned on & ready to go. Hoses do not need to stick out at right angles with immense snagability & can be routed running straight down & under the arm as for any reg on a cyl! The pony feeds the BC, while the Single - the dry suit. This gives two forms of independant buoyancy. If catastrophic failure of Single cyl, the diver can assist himself both with air & buoyancy. As for a PG, IMO if it's an isolated cyl then I'd prefer a guage - especially when you look at the experience of the diver that may utilise such a system. All in all the only main config difference between twins & a single & pony setup is the size of one tank, they're independants & the pony is only ever used in an emergency - so will start & finish every dive with almost as much air, save the gas used in BC. To make the transistion to twins - change one tank, add a isolated manifold & start using rule of thirds! For UK diving - IMO - a single cylinder in all but a splash in the bath is - how do you say it - a 'foxtrot' waiting to happen. You can't just dash for the surface in 20-30m that's VERY BAD practice. If you're in that 'mentality', it will continue with you into the depths! All potential situations should be thought about so that they can be sorted at the time & place of occurance. A single leaves little room for error. Although a pony does in no way replace twins, they have a place for those club divers who are still learning about this enviroment and is a logical step, for most gaining experience, before the diving they pursue requires the use of twins. Singles, for UK diving, need to remain in the pool! Back to work for me then - you'll be pleased to know! Alex -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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