Page 9 - Alpheus Hyatt Verrill "Knots, Splices and Rope-Work"

Rope is usually three-stranded and the strands turn from left to right or "with the sun,"
while cable is left-handed or twisted "against the sun" (E, Fig. 1). Certain ropes, such as
"bolt-rope" and most cables, are laid around a "core" (F, Fig. 2) or central strand and in
many cases are four-stranded (Fig. 2).

The strength of a rope depends largely upon the strength and length of the fibres from
which it is made, but the amount each yarn and strand is twisted, as well as the method
used in bleaching or preparing the fibres, has much to do with the strength of the finished
line.

Roughly, the strength of ropes may be calculated by multiplying the circumference of the
rope in inches by itself and the fifth part of the product will be the number of tons the
rope will sustain. For example, if the rope is 5 inches in circumference, 5 X 5 = 25, one-
fifth of which is 5, the number of tons that can safely be carried on a 5-inch rope. To
ascertain the weight of ordinary "right hand" rope, multiply the circumference in inches
by itself and multiply, the result by the length of rope in fathoms and divide the product
by 3.75. For example, to find the weight of a 5-inch rope, 50 fathoms in length: 5 X 5 =
25; 25 x 50 = 1,250; 1,250 ÷ 3.75 = 333-1/3 lbs. These figures apply to Manila or hemp
rope, which is the kind commonly used, but jute, sisal-flax, grass, and silk are also used
considerably. Cotton rope is seldom used save for small hand-lines, clothes-lines, twine,
etc., while wire rope is largely used nowadays for rigging vessels, derricks, winches, etc.,
but as splicing wire rope is different from the method employed in fibre rope, and as
knots have no place in wire rigging, we will not consider it.