Marlinespike – Rope Materials
There are many materials used today to make rope; synthetic fiber, natural fiber and wire. The most popular is nylon, a synthetic. It is strong, holds up well to the weather and stress, and coils without kinking. Line is also made from natural fibers like cotton and hemp (manila), and other synthetic fibers such as dacron, kevlar, and polypropylene.
Polypropylene line is the least expensive of the synthetic lines, however, it deteriorates quickly from ultra-violet rays and wear. It is not a good line for dock line because its hard surface tends to slip from cleats and can cause cuts if it runs free through your hands. It floats, so it is good for rescue lines. It is also appropriate for ski lines, dinghy painters, short mooring pendants or other applications where you want to be able to see the line on top of the water. Not for use as dock, anchor or towing lines.
Nylon rope has a lot of stretch (up to 40%) and is very strong for its size, allowing it to absorb shock loads well. However, when it is wet it can lose up to 25% of its strength. It wears well, resists mildew and rot, and does not float. Nylon three-strand is the preferred line for dock lines since it stretches sufficiently to dampen the shock of wave action and wind against your cleats. Just make sure it does not stretch too much for the situation in which you use it.
Polyester rope wears better than polypropylene, is almost as strong as Nylon, and retains its strength when wet. It does not stretch as much as Nylon and does not float. Polyester (such as Dacron) is used for sailboat running rigging, anchor rode, towing lines and other applications where you don’t want line stretch to interfere. It will, however, chafe easily so check it often and protect as necessary.
When cutting synthetic rope, prevent the ends from fraying with a temporary binding or whipping. Synthetic rope ends can be sealed by melting, either with a special heat tool for the purpose of cutting and sealing (as shown in photo), or by melting over a flame to fuse the fibers. Adhesive tape wound around the ends can be a temporary binding. Small line ends can be dipped into acetate glue or a commercial “liquid whipping” material. Plastic heat-shrink tubing is also available.
Synthetic lines are lighter and stronger and more rot-resistant, generally, than natural fiber ropes. Synthetic lines are slipperier than natural fiber ropes so be sure to check your knots to make sure they are secure. Synthetic lines should be cleaned with fresh water and detergent, kept out of sunlight, inspected frequently for chafe, and stored dry.
Natural fibers such as manila, sisal, hemp and cotton will shrink when they get wet and also tend to rot or become brittle. Manila is still used today on large ships and is the best natural fiber for mooring lines, anchor lines and as running rigging. Manila has a minimum of stretch and is very strong. However, it has only about one-half the strength of a comparable-sized synthetic line.
Natural fiber line should be uncoiled from the inside of a new coil in order to prevent kinks. Always whip or tape the ends of natural fibers to keep them from unraveling. When natural fiber lines have been in salt water you should rinse them in fresh water and allow to dry thoroughly. They should then be properly coiled and stored on grates above deck in a dry, well-ventilated place to help prevent mildew and rot.