FIGURE 6.3: STAINLESS STEEL SHACKLE FOR LINES WITH TAILS6.3 FIBRE MOORING LINES
6.3.1 Material
Today practically all fibre mooring lines are made from synthetics. the most common materials being
polyester, nylon, polypropylene and polyethylene. Some ropes are made of comhi.oations of tbese
materials. Table 6.1 details materials used in making synthetic ropes, giving the construction in
which these materials are normally used and the general characteristics of each. Table 6.2 states
typical strengths for ropes of different materials. Table 6.3 summarises the recommended application
for various ropes. Figure 6.4 shows typical elongation values for various rope materials.
6.3.1.1 Po/yes/er
Polyester is the most durable of the common materials. It has high strength, bot.h wet and dry.
It has good resistance against external abra.~ion aod does not lose strength rapidly due lO cyclic
loading. Recent Tests under OCIM F sponsorsrup indicated that polyester lasts 190 times longer
than nylon and 570 times longer than polypropylene when subje.cted to cyclic loads. Although
polyester ropes are the most expensive (about three times that of po[ypropyleoe and about 1.2 times
that of nyloo on an f4ual strength basis), tbe initial outlay is more than compensated by their much
longer service I.i re.Broken-in polyester rope will stretch about 9070 when loaded to half its new brea king strength. In
comparison. wire rope stretches about l!tJo at half its breaking strength.Polyester's low coefficienr of friction allows it to slide easily around bitts. Its relatively high melting
point (230°C/450°F as against 165°C1330op for polypropylene) reduces the chances of fusion.
Polyester is therefore preferred for large and small rope ma teTial where strength and durabili ty are
important and where high elasticity is not required.