Can I use a Petzl Shunt as a back-up for rappelling?
In short, yes, the Petzl Shunt was actually designed to be a rappel back-up. The ideal setup for using the Shunt as a back-up is similar to using any other back-up system. Start by girth-hitching a nylon runner to your tie-in points and extend your belay device off this. (Learn how to properly extend a rappel here.) Then the rope below the device can be loaded into the Shunt and clipped to your belay loop. The Shunt should only be used with a single strand of 10-11mm diameter or a doubled rope (like a typical rappel) of 8-11mm for each line. Full information and technical diagrams can be found on the Petzl website (petzl.com). If the rappel calls for doing a single-strand rappel on ropes thinner than 10mm, opt to use a friction hitch (autoblock, prusik, etc.) instead, as the hitch is more adjustable and, thus, more likely to hold. As with all rappel backups, be sure to test your backup before committing to the rappel.
—Kurt Hicks is an AMGA-certified Alpine and Rock Guide. He can be reached at his website kurthicks.com.