Page 373 - Bob Holtzman "The Field Guide to Knots How to Identify.."

43. Alpine Butterfly

Also known as: Alpine Butterfly Loop, Lineman’s Loop

This is a quick, easy loop to tie on a bight. It’s used by mountaineers to
create a tie-in point for a third climber between two others climbers. It
serves well as a purchase for lashing boats or cargo to a car’s roof rack and
for making a line tight between two trees, to serve as a clothesline or a tarp
ridgeline.

Uses: mid-rope tie-off point, purchase for tightening a line
Pros: easy and quick to tie, suitable for loads in either direction

Cons: only useful on a bight, awkward to tie for large loops

Instructions

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