Spare Air - Any opinions?

As i said in the first place...Twin Indies...twindies..I've been using them for 3 years now, no wastage there, both 12 litres always get used up, one at a time or I can share them out to maintain good buoyancy, bit by bit. When I go diving abroad I just require one more standard cylinder, no charge

Alex,

One thing I am most familiar with is the need for adequate bailout. Gas logistics is a matter of survival on deep dives and knowing exactly how much gas is required to get you out of dodge is fundemental.

There are a few things you should consider.

Firstly, your SAC rate has nothing to do with the amount of gas you need in a bailout situation. It doesnt matter whether you are on open circuit or on CCR, when the smelly stuff hits the fan, your breathing rate will be well elevated. On rebreathers we have a few other problems to consider in this calculation, but for the main part, assume your SAC will be double when you are in a stressful situation. there are few dives where a spare air will have sufficient capacity.

Secondly, adaptability. With any redundant air source, it should be suited to all your diving needs. We teach a simple system that should be the same for all your dives. If you have a different system for different dives, then you are reducing the possibility of reliance on muscle memory for the escape plan.

I wouldnt suggest a spare air under any circumstances. A second set of regulators connected to a second cylinder of any size would always be superior. You choose the size of cylinder dependant on your dive logistics, but the escape plan is always the same. this works for progression to twin sets and beyond.

The size, bouyancy and weight ceases to be an issue in the water if properly rigged and SpareAir units are not that different in price to a set of regs and a pony.

<edit> As for travelling, many dive centres now are beginning to become rebreather friendly so the access to 3ltr steel or alu cyls is becoming more and more easy. Taking a pony bag and second set of regs wouldnt be too hard and a little bit of pre-planning and a rew emails to dive centres would invariably get you a small pony to use I would have thought.

No one ever died from having too much bailout. Take it from someone who regularly uses a lot of secondary air sources!