OCIMF_Mooring_Equipment_Guidelines_(Second_Edition)

The three-Slrand rope is the most common form of twisted rope. It i.s adequate for some tasks, but
is prone 10 hock.ling (see figure 6.7). This significantly reduces strength, making it a bad choice for
use as a mooring rope.

The six-strand with core structure, used in Jetkore and Alias ropes, is a twisted rope similar to
conventional wire rope. I t is no! as prone^10 hockling as three-stTand rope and IS sometimes used
for mooring lines.

The eight-strand rope, sometimes called square braid or plaited, is constructed of braided pairs of
strands. It has cs.scntially the same strength as a three-strand rope of the same ,ize. Tt does not
hackle and is more dllIable than twisted rope. It is a good rope structure for mooring lines and for
most other purposes on ships_

Double braid rope" sometimes called braid-on-braid, is consLructed of a core braided of many :;mall
s(fands and surrounded by a cover which is also braided of many small ~rrands" It is generally
stronger than other ropes of Ihe same cliameter beca use Lhe SlructlLfC is denser. Jt is commonly us ed
for mooring hawsers at single point moorings (SPMs) and for tails on wiIe ropes.

6_3.3 Bend Radius

The strength los due to bending is apparently nO! as critical for conventional fibre lines as for wire
given their ability' [0 aJlow migration of load. Newer types of synthetic fibre such as the aramjd
Iypes are more bend radius sensitive. As for all fibres the stTength 10 5s and durability factors may
depend upon the specific material and conSlfuction. T he rope manufaclUrers guidelines should be
consulted for each speci fie applkarion.

6.3.4 Identification

If the composition of a mooring rope is not known, certain characteristics of appearance, burn

properties and density may belp to identify the material.

Fibre appearance

Polypropylene fibres are usually coarse and Ihicker than a human hair and are normally

flal instead of roulld. Polypropylene is often dyed black to provide resistance 10 sunlight.

Sometimes other dye colours, such as yellow or orange, are used.

Thus a coloured or blaCk rope with coarse flac fibres is probahly polypropylene_ The only

exceptions to thi, aft: polyei.hylene and KMat, which can have a similar appearance.

Since polyethylene ropes may not be quite as strong as polypropylene, a burn test may be

necessary to di ti nguish between the IWO for critical applications where I here is a possibility

that polyethylene ropes have been furnished.

Karat rope fibres are similar in appearance to polypropylene. They are straw coloured. as

opposed 10 the distinctive yeJlow colour of some dyed po\ypropylenc fibres.

Nylon and polyester fibres are almost always very lhin and fme, di stinguishing them from

polypropylene. However, it is virtually impo'sible to distinguLsh between nylon and polyester

by appearance. New nylon fibres have a bluish tinge, but even experts cannot always teU them

apart, especially if rhe rope has been used. The only reliable way is by a bum test.

Arami.d ro pes are normally covered by a braid strand or extruded plas! ic jacket. The aramid

fibres are very fine and straw coloured.

Density

Polypropylenc and polyethylene arc lighter Ihan waler and can readily be distinguished from

polyester and nylon by their density. Place several fibres or yarns in a glass or dish of watet

and stir, if necessary, 10 remove any air bubbles adhering to the sample ..

If the sample noats, it is polypropyleoc or polyethylene. If it sinks, it is polyester or nylon.