This is a technique that's best avoided if you can get hold of a longer rope: I keep a 90 metre static rope stuffed in a caver's rope bag for bigger approach abseils. I hang the bag off my harness and just pull out a metre or two of rope at a time; thus protecting the rope if I knock off any blocks on the way down. If you find yourself having to abseil past a knot you will need to use skills that are best practiced a few inches above the ground rather than trying out for the first time above a yawning void.
Join the ropes with a knot that includes a fixed loop, allowing you to clip into the loop as a back up while you change over. Place the back-up prusik above the belay device and connected to the harness by a sling. The length is fairly critical because if the sling is too long, it's the devil's job to unfasten the prusik (because you can't reach it) once you've transferred from one rope to the next.
The routine is as follows; abseil to within half a metre of the joining knot, lock off the prusik and transfer your device to the other rope. Once transferred, lock off the abseil device and release the prusik. This may be quite difficult; if it's stubborn, use a second prusik to make a foot-loop. Step up using this to un-weight the jammed prusik and unclip/release it. The foot-loop prusik can then be attached to your harness leg loop as the new autobloc.
Self Rescue for Climbers DVD
Aimed at recreational climbers, Self Rescue for Climbers is a comprehensive guide to solving problems encountered in such situations as multi pitching in the mountains, sea cliffs or roadside crags. The DVD's format enables the viewer to access relevant information quickly, providing a basic toolbox of techniques which can be applied in any situation.
With scenarios filmed on famous climbs in locations including Malham, Gogarth, the Llanberris Pass and Tremadog, Self Rescue for Climbers is not only 90 minutes of expert instruction, but also a stunning tribute to the possibilities available to the recreational climber in North Wales.