The Bowline on a bight
is a knot
A knot is a method of fastening or securing linear material such as rope by tying or interweaving. It may consist of a length of one or several segments of rope, string, webbing, twine, strap, or even chain interwoven such that the line can bind to itself or to some other object—the "load"...
which makes a pair of fixed-size loops in the middle of a rope. Its advantages are that its loops do not slip and it is reasonably easy to untie after being exposed to a strain. This knot can replace the figure-eight knot when tying into a climbing harness. However, it is critical to use a strong backup knot with plenty of tail beyond the knot.
This knot can be used to provide a toe hold in the middle of a rope; to make an emergency bosun's chair
A bosun's chair or boatswain's chair is a device used to suspend a person from a rope to perform work aloft. It is distinguished from a climbing harness by the inclusion of a more or less rigid seat, providing more comfort than even the best-padded straps for long-term use...
; 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
Sport climbing is a form of rock climbing that relies on permanent anchors fixed to the rock, and possibly bolts, for protection,...
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 as a seat while being hoisted as there are two secure loops as opposed to the traditional one loop bowline. In theory, this knot would make hoisting many people with one line possible. This knot is very popular in potholing as it allows the load to be spread between two anchor points, reducing the stress placed on them and providing a backup should one fail. Commonly known as the Y-hang it allows for a free-hang descent and can be easily adjusted to avoid waterfalls or rub points.
As mentioned earlier, this knot can replace the figure-eight knot when tying into a climbing harness by tying a regular bowline knot and then re-threading it, such as is done with a figure eight knot. However, it is critical
to use a strong backup knot with plenty of tail beyond the knot, as the knot may untie during long climbs. The advantage of using this knot instead of the figure eight knot is that it can be easily untied after a severe fall. Another advantage, is that the rope ends up threading through the harness twice, and therefore may spread out wear and load over a wider region of the tie-in locations on a harness. While no direct evidence can be provided as proof, this could extend the life of the harness and may be stronger than having just one section of rope tied through the harness.
In knot tying, a bight is a curved section, slack part, or loop between the two ends of a rope, string, or yarn. The term is also used in a more specific way when describing Turk's head knots, indicating how many repetitions of braiding are made in the circuit of a given knot.-Slipped knot:In order...
of rope is initially used to make a bowline
The bowline is an ancient and simple knot used to form a fixed loop at the end of a rope. It has the virtues of being both easy to tie and untie. The bowline is sometimes referred as King of the knots because of its importance...
in the usual way (picture on right). However, the bowline is not
completed by going on round the standing end(s) and tucking the bight back down beside itself. Instead, the bight is opened up to allow the whole knot to pass through it (see picture on right). When tightened, the bight now embraces the pair of standing ends (see top picture)