In reply to kwoods:
> is it not unreasonable to use one half rope for moving together and abseiling?
Abseiling on half ropes, using two strands, is perfectly normal and always has been. There is also no reason why you can't to abseil on a single strand but you would have twice the amount of rope stretch and half the amount of friction which may or may not be an issue.
Half ropes are regularly used when moving together. However, 'moving together' potentially describes a wide range of scenarios. Whilst in many, perhaps even most cases, a half rope may be suitable, it will depend on the exact situation (terrain, rock type, environmental conditions, ability of the party etc.) if that is the case.