We did a re-directed belay yesterday on our hanging belay at TF. It is definitely “old school” according to this AMGA guide and this book on climbing. On the climbinglife.com website, here’s what they say about re-directing a belay.
Re-directing the belay through the anchor: Why multiply the falling force?
For some reason, this antiquated method remains a favorite among the crags that I visit regularly and likely this is a result of "old thinking" and maybe a tendency towards stubbornness in climbers as it takes a bit of tenacity to cling to a steep cliff or frozen wall of water - a trait that serves us well in many situations but can prove to be a hindrance in learning and adapting to new environments and discoveries.
The redirected belay describes the method of belaying off of the body, but rather than the rope going directly down the cliff to the second, it is "redirected" through a separate carabiner on some part of the anchor (preferably the master-point).
When we apply the same equation to the redirected belay method, we see that what seems to be a benign change of direction that reduces some of the force on the belayer (the only advantage), also adds forces to the anchor.
A falling force of "1" is the same on either side of the redirecting carabiner (minus friction) and this "pulley effect" combines to put multiply the falling forces by 1.6 to 1.8 on our anchor, not quite doubling but definitely adding substantially extra force to the anchoring system.
The re-directed belay method adds extra force to our belay in a manner that almost doubles the forces applied to each component of our anchor system. The belayer also works harder to pull rope through the friction of the carabiner.
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