knot (ornithology) - Usage, Properties, Categories

Either of two species of sandpiper; the widespread knot or red knot (Calidris canutus); and the eastern knot or great knot (Calidris tenuirostris) from E regions of the Old World.

Usage

There is a large variety of knots and each knot has specific properties and suitability for a range of tasks. Some knots are well-adapted to attach to particular objects such as another rope, cleat, ring, or stake. Choosing the correct knot for the job at hand is one of the most fundamental aspects of using knots well.

Learning

The number of books, websites, videos, and other resources available to those interested in learning about knots is a testament to the value they hold for humankind. While some people possess an innate ability to look at a diagram or photo and tie the illustrated knot, for others the initial stages of learning are best accomplished by being shown knot tying methods by a person who already knows them. As more knots are learned, patterns begin to become evident in their structure and methods of tying.

Applications

Knots are essential in many industrial, occupational, recreational, and domestic settings. In addition to safety, appropriate knots can prevent the necessity of cutting lines.

Knots can be applied in combination to produce complex objects such as lanyards and netting. In ropework, the frayed end of a rope is held together by a type of knot called a whipping knot.

Properties

Strength

Knots invariably weaken the rope they are made in. When knotted rope is strained to its breaking point, barring any flaws or damage in the rope itself, the rope almost always fails in or near the knot. The same bending, crushing, and chafing forces that produce the friction which holds a knot in place are also responsible for unevenly stressing the rope fibers and ultimately lead to the reduction of strength.

The relative knot strength, also called knot efficiency, is the breaking strength of a knotted rope expressed as a percentage of the breaking strength of the rope without the knot. There are many difficulties in determining an overall numeric knot efficiency for a given knot. This is due to the many factors that can affect the results of a knot efficiency test: the type of fiber, the style of rope, the size of rope, whether it is wet or dry, how the knot is dressed before loading, how rapidly the knot is loaded, whether the knot is repeatedly loaded, and so on. With those limitations noted, and in order to give a sense of how much loss of strength knots cause, most knots in common usage have an efficiency between 40% and 80%.

While some rope splices can retain nearly the full strength of the rope when forming loops and bends, conventional knots are much more practical in most situations. Thus the prudent knot user will always allow for a large safety margin in the strength of rope chosen for a task due to the weakening effects of knots, aging, damage, shock loading, etc. Always consult experienced practitioners before using ropes and knots in situations where safety of life, limb, or property is involved.

Security

Even if the rope does not break, a knot may still fail to hold. The main ways knots fail to hold are:

Slipping — The tension from the load causes the rope to work back through the knot in the direction of the load. If this continues far enough the working end will pass into the knot and the knot will unravel and fail. This behavior in knots can be worsened when the knot is repeatedly strained and let slack, dragged over rough terrain, or subject to repeated impacts such as against a mast or flagpole. Even with secure knots some slippage may occur as the knot is first put under real tension. This can be dealt with by leaving plenty of rope at the working end outside of the knot and by dressing the knot cleanly and tightening it as fully as possible before loading. In some cases the use of a stopper knot or, even better, a backup knot can prevent the end from passing through the knot, but it is generally better to use a more secure knot if one is observed to slip. In life critical uses backup knots are often added to already secure knots in order to maximize safety. Capsizing (or Spilling) — Capsizing a knot is changing its form, rearranging its parts, usually by pulling on specific ends in specific ways. For an excellent example of a knot that capsizes dangerously, see the discussion of the reef knot used as a bend. Sometimes a knot is intentionally capsized as a method of tying another knot, such as the "lightning method" of tying a Bowline. Some knots, such as the Carrick Bend, are generally tied in one form and then capsized to attain a stronger or more stable form. Sliding — In knots that are meant to grip another object, failure can be defined as the knot moving relative to the object being gripped. Sometimes this can be corrected by working-up the knot tighter before subjecting it to load but usually a knot with more wraps, or a different size or type of rope will need to be employed. Many knots, such as the bowline can be tied in either the end or the bight. Bitter end More a ropeworker's term than a knot term, the reference is to the end of a rope that is tied off, hence the expression "to the bitter end". Note that the term 'loop' is also used to refer to a category of knots (see 'Categories' below). Standing end The end of the rope not involved in making the knot, often shown as unfinished. Standing part Section of line between knot and the standing end. Working end The active end of a line used in making the knot. Working part Section of line between knot and the working end.

Categories

The list of knots is extensive, but common properties allow for a useful system of categorization. For example, loop knots share the attribute of having some kind of an anchor point constructed on the standing end (such as a loop or overhand knot) into which the working end is easily hitched to using a round turn. An anti-knot is a hypothetical knot on a rope that cancels out the corresponding knot when the two are made to meet along the rope. A knot uniting two lines (for knots joining two ends of the same line, see binding knots or loops). Knots used to tie up lines for storage. A knot used to hold (usually) poles together. A knot used to create a closed circle in a line. A knot used to hold two lines or two parts of the same line together. A knot formed by interweaving strands of rope rather than whole lines. A knot tied to hold a line through a hole. A binding knot used to prevent another line from fraying.