Exploring the Secrets
of Knotted Cordage to Understand How Knots Work
By Ňknot performance,Ó we mean how a knot works and how well
it works. How secure, stable, and strong is it? Where will it break? The performance of a practical knot is
determined by four factors: 1) the physical laws of mechanics, 2) the knotŐs
structure, 3) the material it is tied in, and 4) its environment and conditions
of its use.
Like all the other objects in the universe, a knot operates
according to the physical laws of mechanics. Mechanical forces that affect the
performance of a knot include friction, blockage, tension stresses, compression
stresses, and shear stresses.
The exact ways these invariable physical forces affect a knot
depend on three variable factors: its structure, the material it is tied in,
and its environment and conditions of use.
Structure is the first of the three variable determinants of
knot performance.
How well a knot performs depends largely on the way it is
configured. The most characteristic aspects of knots, the convolutions of the
segments they are made up of, include tucks, wraps, bights, hitches, parallel
strands, and curves. But as far as structure is concerned, a knotŐs performance
depends first of all on whether it is properly tied, dressed, and loaded.
A knotted rope performs more or less well depending on the
type of cordage it is tied in, whether it is twisted manila hawser, braided
cotton twine, kernmantle nylon rope, a handkerchief, leather thong, or the arms
of a sweater. Performance is also affected by the thickness of the cordage and
its physical condition. Each material has different characteristics of stretch
and elasticity, as well as different surface characteristics and coefficient of
friction, all of which affect its holding power. As experienced knot users
know, nylon rope is more likely to slip than manila or cotton rope, hollow
braid polypropylene is slick and kinky but holds well after it is set in place,
and thin ropes breaks more easily than thick ropes.
The performance of a knot is affected by way it is used in
rope systems, by variable atmospheric influences, including temperature,
humidity, and moisture, and by lubricants or foreign bodies on the surfaces
where the rope comes into contact with itself or with other objects. The
performance of a hitch is affected by the object it is tied around. The load
that falls on a knot may be applied steadily, by alternating loading and
un-loading, or from an unusual direction such as would be caused by snags or sideways
pulls on the tail of the knot.
These factors come to bear whether the knot was tied by a
jungle ape, a Boy Scout, or the President of the International Guild of Knot
Tyers. And they have always applied, from the remote time when a knot was first
tied and used to the present.
These factors come into play and interact in complex ways to
create a usable knot and make it perform the way it does. In the papers that
follow, analysis shows how mechanical forces interact with the structure of a
knot to determine how it performs.