Knots by Support, Bend and Binding | Sailmaker's Fieldbook

Three checks before you act

1. 01
   Every knot weakens the rope at the knot, because the fibres are bent and the load is carried unevenly.
2. 02
   The practical sequence is to identify the family, choose the knot, dress it, set it by loading it, and inspect it.
3. 03
   A knot that cannot be identified at a glance is a knot that will be mistied under pressure.

Attachments to a support: hitches

A hitch holds because the rope wraps a support and the load pulls the turns tight against it. The clove hitch is the standard quick attachment around a post or rail. Two crossing turns trap the standing part, and the knot grips in proportion to the load. It is fast to tie and fast to adjust, which is also its weakness: on a smooth or tapered post, or under a load that swings, the turns can walk and the hitch can spill. On a piling or a rail where the line leads fair and the load is steady, it holds well. Where the load alternates, add a half hitch or two on the standing part, or use a different family.

The prusik is the attachment that grips a loaded rope and slides when unloaded. Tied from a cordelette of smaller diameter than the host rope, two or three wraps around the host, finished through the loop, it holds under load and releases when the load comes off. The grip depends on the diameter ratio: a cordelette around sixty to eighty percent of the host diameter bites reliably, while a cordelette close to the host diameter may slip. On wet or icy rope, add a wrap. The prusik is not a hitch to a post; it is a hitch to a rope, and it is used for ascending, for backup, and for progress capture.

How does a sheet bend join two ropes of different diameters?

The sheet bend joins two ropes of unequal diameter. The larger rope forms the bight, the smaller rope passes up through the bight, around behind both parts of the bight, and tucks under itself. The tail of the smaller rope must finish on the same side as the standing part, otherwise the knot capsizes under load. When the two ropes differ a great deal, double the smaller rope around the bight before tucking, which is the double sheet bend. The knot holds under steady tension and unties after heavy loading, which is why it is used for bending a heaving line to a hawser or joining lines of different sizes. It is not a knot for cyclic loading: the tails can work loose, so leave long tails and check them.

Fixed loops: bowline and figure eight

The bowline makes a fixed eye that does not slip under load and unties after being loaded hard. The standing part forms a small loop, the working end comes up through it, around behind the standing part, and back down through the loop. The result is an eye that holds its size. The bowline is used for a line around a cleat, for a rescue line around a person, and for any eye that must stay open. It can shake loose when slack and repeatedly worked, so it is often backed with a stopper knot or a second turn. It is not suitable for a load that alternates direction, where a figure eight loop is more stable.

The figure eight loop, also called a figure eight on a bight, makes a fixed eye that is easy to inspect and does not shake loose. The rope is doubled, an eight is formed, and the bight is passed back through the eight. The knot is bulkier than a bowline and harder to untie after heavy loading, but it holds under cyclic load and is the standard tie-in for climbing harnesses. For a fixed eye that must never slip, the figure eight loop is the safer choice; for an eye that must untie easily after a hard pull, the bowline is the better one.

What is a constrictor knot used for?

The constrictor knot is a binding knot that squeezes a bundle and locks itself. It is tied like a clove hitch with the working end tucked under the crossing turn, so the knot grips its own standing part. Once loaded, it will not loosen, and it often must be cut off. It is used to bind the end of a rope to stop it unlaying, to clamp a hose onto a fitting, to hold a bundle of sticks or tubing, and to seize a rope. On a rope end, it replaces a whipping when a temporary or very tight binding is needed. Because it jams, it is not used where the knot must be undone later.

Marking and identification

A knot that cannot be identified at a glance is a knot that will be mistied under pressure. The working habit is to sort knots by family, hitches, bends, loops, bindings, and to keep an alphabetical index so a specific knot can be found by name. A three-level difficulty scale helps a beginner choose a knot that can be tied and checked reliably in the conditions at hand. On deck, the same discipline applies: the knot is dressed, the tail length is set, and the knot is inspected before load. A knot that is not dressed, with crossed parts and uneven turns, is weaker and harder to inspect than the same knot dressed fair.

Load paths and the point of failure

Every knot weakens the rope at the knot, because the fibres are bent and the load is carried unevenly. A bowline typically retains around sixty to seventy percent of the rope's strength, a figure eight loop somewhat less, and a well-dressed hitch depends on the support and the number of turns. The point of failure is usually at the entry of the rope into the knot, where the bend is sharpest. This is why the knot is not the only consideration: the rope, the support, and the load path all matter. A hitch on a smooth post with a fair lead and a steady load holds; the same hitch on a tapered post with a swinging load can spill. A bend between two ropes of very different diameters holds better when the smaller rope is doubled. A binding holds when the turns are tight and even, and fails when they are crossed.