The bowline appears on the 26th century BC solar ship of the pharaoh Khufu, and more than 4,500 years later the Federal Aviation Administration recommends it for tying down light aircraft while UK firefighters must pass a test tying it. Its job is to make a fixed loop that will not shrink, and the rabbit out of the hole mnemonic describes a structure identical to the sheet bend. Under load the knot pinches its own tail, yet it unties easily afterward, a trade for which it gives up about a third of the rope’s breaking strength. The name comes from the bowline, a line on square rigged ships that held the edge of a sail toward the bow to keep the ship from being taken aback, and John Smith first named the knot in his 1627 book A Sea Grammar, claiming the sail would split before it slipped.

Smith was right for his era, because hairy hemp and manila gripped like Velcro. Slick modern nylon and Dyneema expose a flaw: with no load there is no pinch, so cyclic loading from a bouncing climber or a boat on waves lets the tail creep out millimeter by millimeter, and pulling the loop sideways can capsize the knot. Climbers now back it up with a stopper knot or switch to variations such as the Yosemite bowline, while rescuers still value that the basic knot can be tied around your own waist with one hand.

• Saying a ship sailed on a taut bowline meant it was sailing close hauled to the wind.
• The one-handed lightning method uses the rope’s tension against your body to snap the knot into place.
• The Yosemite bowline threads the tail back through the round turn to lock it against the standing line.
• The water bowline adds a clove hitch so wet, swollen rope does not weld the knot shut.
• Joining a bowline’s two free ends produces a 6-2 knot in mathematical knot theory, with six crossings.