In more recent years there has been growth in other man-made synthetic fibres such as polypropylene, polyethylene and polyester. All these fibres have far less stretch than that of nylon though are slightly less strong.
Nylon, polypropylene, polyethylene and polyester fibres are manufactured in long threads - the length of the rope. This produces ropes that generally have a smooth, slippery surface.

Weaker ropes are made from carded waste. This spun fibre has a vaguely fluffy surface, not unlike cotton. This type of rope is called staple spun and is not used for our type of work.

A 4.5 meter 'Dead' staple polyprop tow rope which carries an 8 tonne breaking strain

All nylon tow ropes have a shiny surface. It is amply strong enough for all towing applications, as it is rated at 12 tonne

Manufacture

From our point of view, nearly all the rope that we are likely to use with the exception of braided capstan rope and 8 strand Kinetic Energy Recovery Rope (KERR), will be 3 strand rope.

If you look at a piece of lets say 3 strand tow rope it will most probably have a right hand lay - that is, the three strands go up and around the rope clockwise just like a screw thread. This is 'hawser laid' rope that has been twisted three times in the course of the manufacture: the fibres are initially twisted to make the rope yarn, the yarn is then twisted into strands, and the strands twisted into the final rope.

Three strand ropes can either be tightly or loosely laid (twisted). The specification I ask for when having our ropes made up is between the two, giving good strength and wear characteristics.

Eight strand nylon rope is made by using four strands of left hand lay and four strands of right hand lay, which in turn is plaited in pairs to form the rope. It is this rope that we use for our 'Kinetic Energy Recovery Rope' (KERR).

In years gone by, one only referred to the ropes' size by it's circumference in inches. Nowadays, certainly in the case of synthetic rope, we quote their size in mm for their diameter.

As regards to the strength of the rope, we quote Minimum Breaking Load. We are not talking of lifting, but if we were, we would divide the above figure by six to give Safe Working Load (SWL).

 

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