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; most notably, it is easy to untie after being subjected to a load. The bowline is sometimes referred as King of the knots because of its importance. It is one of the four basic maritime knots (the other three are figure-eight knot, reef knot and clove hitch).
The structure of the bowline is identical to that of the sheet bend, except the bowline forms a loop in one rope and the sheet bend joins two ropes. Along with the sheet bend and the clove hitch, the bowline is often considered one of the most essential knots.
Although generally considered a reliable knot, its main deficiencies are a tendency to work loose when not under load, to slip when pulled sideways and the bight portion of the knot to capsize in certain circumstances. To address these shortcomings, a number of more secure variations of the bowline have been developed for use in safety-critical applications.
Usage: The bowline is used to make a loop at one end of a line. It is tied with the rope's working end also known as the "tail" or "end". The loop may pass around or through an object during the making of the knot. The knot tightens when loaded at pulled by the standing part of the line.
The bowline is commonly used in sailing small craft, for example to fasten a halyard to the head of a sail or to tie a jib sheet to a clew of a jib. The bowline is well known as a rescue knot for such purposes as rescuing people who might have fallen down a hole, or off a cliff onto a ledge. They would put it around themselves and sit on the loop. This makes it easy to heft them up away from danger.
A rope with a bowline retains approximately 2/3 of its strength, with variances depending upon the nature of the rope, as in practice the exact strength depends on a variety of factors.