Learn a tip for safe and efficient multi-pitch rappells with IFMGA and AMGA certified mountain guide Adam George.
Great tips. I like how he makes use of the double length sling for both extending the rappel, thus making it smoother, and for having an anchor. Another thing to note is that he tied the prussik into the harness central loop, not the leg loop. I think this is a better option as it provides security in case one made the mistakes of (1) not threading the ropes through the belay device correctly, (2) didn't test the system before detaching from the anchor.
This method is the exact same method described in the latest Accidents in North American Mountaineering (ANAM). Typically, ANAM doesn't include any direct instructional stuff, but this year, they included a special section on rappels, since they are such a large source of accidents every year. The book has extended discussions on the reasoning behind all of the little things done in this video--recommended reading if you're looking for even deeper understanding. It also has discussions of the merits of different knots for attaching ropes, what knots to use in the ends, etc.
My favourite part about this video is the guide's warning to keep slack out of your personal attachment. I've recently read several discussions on this that included measurements of forces generated from a slip at an anchor. The bottom line was that slipping with slack in your attachment is basically like taking a factor one fall (or higher). No good.
I also like how he makes sure to use nylon for his double-length sling. Dyneema/spectra/other materials have been shown to weaken after bending and stressing, with the result being that these super-strong materials may actually become weaker than nylon after a season or two. Secondly, they have no stretch whatsoever, while nylon has a minute amount of stretch under load. Finally, knots stick better in nylon. Spectra slings are really slippery and knots can slip--you wouldn't want that happening to your overhand knot in mid-rappel.
-Matt