The rope is strongest when the fibres are at an angle of 45 degrees to the run of the rope. When at a greater angle than this, the fibres are apt to break, and when at a less angle, the friction between the parts—upon which the strength of a rope greatly depends—is lessened.
The durability of tarred ropes is greater than when untarred, but not to such an extent if kept dry.
A splice weakens a rope about one eighth.
Ropes are adulterated by the admixture of rubbish fibre termed ‘batch.’ To test a rope as to condition, untwist it and notice whether any short ends break upwards. If so, or if the tarring has decayed internally, the rope must be viewed with suspicion.
Hemp ropes, after four to six months’ wear, are often one fourth weaker than new ones.
Scaffold cords are from 15 to 18 feet in length.
Moisture will cause a shrinkage of 6 inches in an 18-foot cord.
A good hemp rope is more reliable than an iron chain, as the latter sometimes snaps on surgeing.
The following diagrams show the various knots used in scaffolding, both in the erection of the scaffold and for attaching materials to a hoist. They are shown in a loose condition as being more useful for study by a pupil. Several knots are, however, too intricate to explain by diagram, and in these cases an attempt has been made, with but scant success, to instruct as to their method of creation in the notes. It will, however, be found by the student that half an hour with an expert scaffolder, preferably an old sailor, will afford more instruction than hours spent in studying diagrams.
The art of knot making is governed by three principles. First, a knot must be made quickly. Secondly, it must not jam, as this prevents it being undone easily. Lastly, under strain, it should break before slipping.