Here's a trick that can reduce the amount of time spent coiling ropes, and avoids the problem of not knowing where the centre is.
Simply coil the rope in two halves after an abseil. To do this for the first time you will need to know how many loops of your arms it takes (for me it takes 17 loops for each half of my 57m "60"). Once you know this, it shouldn't change. When you reach the next abseil:
- feed one half through the anchor
- unsecure each half
- tie a knot in each end, and
- throw the coils off one by one.
No need to recoil. You can be set up in 20-30 seconds.
If the next abseil is only short, say 10m, don't even bother unsecuring one of the halves. Uncoil the other half and effectively you've got a 30m rope. Just make sure you pull down the right end. Shouldn't be hard, as the end to pull has a 30m coil on it!
You might argue that you have to coil both halves, so it takes longer. But in fact you can have two people coiling the same rope at once - one coiling each end.
The one disadvantage of this method is when the abseil is off ring bolts, or off a sling with a very small hole. Then it is impossible for one half to be passed through. However, there are very few canyons where this is the case (Empress, Mt Hay, Fortress are a few exceptions).
See the picture at right for what a coiled rope looks like.