Bowline on a bight advocate the use of a figure eight twisted version of the Bowline on a bight. This knot can be used to provide a toe hold in the middle of a rope; to make an emergency bosun's chair; and to create an upper rope "block" to make a crude purchase by threading the rope round an anchor point and then back up through the loop. It is sometimes used in sport climbing to tie into two anchor bolts independently. This knot is convenient when a dependable loop is required but neither end of the line is available. It's also commonly used
Double bowline is easier to untie after being weighted in a fall, and so is used by sport climbers who take multiple lead falls and then have trouble untying their figure eights. The disadvantages of the double bowline are that it is less secure than a figure eight knot, takes longer to tie, and is not as easy to check. Unlike the figure eight, there are many variations of the bowline, with ambiguous names, and some are not safe for climbing. The Bowline on a bight, when re-threaded instead of being tied on a bight, can also be used for tying into