Ropes classification | blog

luka turmanidze
Rope has been used on board vessels since man first went to sea. It can be made from many different materials, such as natural fibre, synthetic fibre, metal wire, or any combination. It can be classified as fibre rope and wire rope. Fibre rope is further divided into natural and synthetic.

Natural fibre rope is made from fibres such as abaca, hemp, sisal, coconut and cotton, hemp being the most common.

Manila is made from the fibre of abaca, a wild banana plant grown largely in the Philippines. It took its name from the Port of Manila, from which it is exported. Manila rope is soft, glossy, smooth, pliable and has good stretch. It has the greatest tensile strength of all natural fibre rope, but when wet loses half its tensile strength and has only about half the strength of a similar sized synthetic line.

Hemp is made from the stem of the plant cannabis sativa. It has the same tensile strength as manila, and is primarily used for making small cordage. Its main advantage is that it doesn’t shrink or swell when wet.

Sisal is a hard, hairy fibre with three quarters the tensile strength of manila; it is made from the leaves of the tropical plant Agave Sisalana, of the cactus family. It is a cheaper grade of rope, often used when other types are not available and mostly for mooring lines.
Coir is derived from the Malayalam Kayar. It is made from coconut shell fibre, and hence very rough and hairy but also light and elastic. It has only one-half the tensile strength of manila.

Cotton is soft and pliable. Its tensile strength is slightly less that sisal’s and a lot less than manila’s; many cotton ropes have a synthetic core to increase their strength. Cotton has low resistance to rot, oils, gasoline, grease, and most chemicals.

Synthetic fibre ropes are made from nylon, polyester, polypropylene, polyethylene and aramid. Synthetic fibre rope is stronger and lasts longer than natural rope. It is also more flexible and easier to handle, and take less space for storage. It is therefore more popular than natural rope.

Nylon is a man-made fibre with a complex form structure of carbon, nitrogen, oxygen and hydrogen. It has higher resistance to abrasion, higher tensile strength (3 or 4 times that of manila), more elasticity (up to 40%) and more durability than natural rope, and will not rot or mildew. It resists moisture and most chemicals such as mineral oils and greases, but is affected by paint, linseed oil or acids. When wet, nylon becomes slippery and loses about 10% to 20 % of its strength. When under excessive load, nylon will break without warning. Hence it is good for mooring line, but should not be used as tow line.

Polypropylene is lightweight, water resistant and floats. It has good resistance to rotting, mildew, and abrasion and moderate elasticity; is easily affected by heat; is difficult for forming knots or hitches; and is excellent for use as tow line.

Polyethylene has similar characteristics to polypropylene. It is lightweight, water resistant and floats; resists chemicals and abrasion; has moderate elasticity; is difficult for forming knots or hitches; and is excellent for tow line.

Polyester was formerly known as Dacron and Terylene. It has high strength (but less than nylon), but low elasticity. It has high resistance to abrasion and temperature; similarly to nylon, and is not easily damaged by water, sunlight, or most chemicals such as acids, oils and organic solvents, etc. Also similarly to nylon, polyester will not float and should not be used for tow line.

Aramid fibre has high tensile strength and heat resistance; low shockabsorbing ability; is easily damaged by abrasion; and is difficult forforming knots or hitches.

Wire rope is made of steel or other metal, except for its core, whichis likely to be fibre or metal wire. Wire rope consists of three components: core, wire and strand.

The core acts as the foundation to keep the wire rope round, as a shock absorber when the wire rope is under strain, and as a reservoir for lubricant. Cores can be natural fibre, synthetic fibre, strand wire or independent wire rope core (IWRC). The wire core is stronger than fibre core, and is used where conditions such as high temperatures would damage the fibre.. 

The wires are laid around an axis consisting of a wire or fibre at the centre to form strands. Strands are laid around a core to form the wire rope. The number of wires in a strand varies according to the intended purpose of the rope.

source: The ships' officers handbook by captain Khan