OCIMF_Mooring_Equipment_Guidelines_(Second_Edition)

6.3.1.5 Ararnid and Other Materials

A number of t.he newer synthetic materials for ropes, such as aramid fibre offers high strength, low
weight, low stretch, flexibility and corrosion resistance. Weight for weight aramid fibres are about
five times as strong as steel, wrule elaSticity is only about 3OJo at 50070 breaking load.

Despite tJ)e relative cost o f aramid fibres tbeir u se as ,ub tilUte fOT other sYllIbetics has alre.ady been
eSlablished, a nd high modulus polyet.hy1ene su ch as Dynecma bas also been installed as replacement
for mooring wires.

With regard to aramid fibres t.he main benefits are in reduction of diameter and tberefore weight
of line requir'ed. The reduction in line size is advantageous if winch drum size is limited, whereas
the reduct io n in weight makes handling substantially c-<lsicr.

Besides tlle cost, there llre other drawbacks to the use of synthetic fibres. In the case of aramid
fibres tbere are restrictions with regard to bend radius and in the majority of cases there is a need
to sheath the fibres to guard against ultTaviolet rays and m ecbank a I wear. Damage to the oUler
sheath can re ult in rapid degradation of the core fibres, and may result in difficulty to relrofit using
existing fittings.

6.3.1.6 Combinations oJ Materials

The following are examples of proprietary ropes manufactured by combining different materials:

Jelkore rope is a six-strand construction comprised of nylon, polyester and polypropylene.

Since nylon is the principal strength-carrying element in Jetkore Tope, it has essentially tbe

same strength and elasticity characteristics as conventional nylon rope. The unique combination

of polyester and polypropyleoe on t.he strand surface provides very good resistance t.o abrasion.

Jelkorc rope does n(lI suffer sigllifjcanr strength reduction from cyclic loading. It is therefore

a suitable alternat ivc for tails on wires where high elasticity is required. It is also used

succes, fully for winch-mounted lines on some sbjps where motio ns l~an be tol,eratcd.

Atlas Per/on rope is a six-strand construction made of both monofi.1ament and multifilament

nylo n yarns. The monofilaments are almost as lar e in diameter as a pencil an d alternate

with muItifilament yarns as the outer yarns on the strands. Abrasion resistance is good, but

cyclic load performance may be poor. It is used for wi nch-mounted lines on so me smaller

sh.ips,

Po{yeslerlPolypropylene Several manufacturers make rope comprised of mixtuJ"es of poly-

ester and polypropylcne fibres. T hese ropes arc les s expensive t han pure p ol yester ropes.

Their strength lies somewhere between corresponding ropes made of only polyester and only

polypropylene. Depending 00 how the fibres are arranged in t.he yarns, abrasion resistance

and cyclk load performance can be almost as good as for pure polyester. Tbe better qualjty

polyester /polypropylene mixed fibre ropes are a possible lower cost alternative to polyester

ropes where slightly lower strength for a given size rope is acceptable.

Karal rope is made of fibres whi ch are a meJt mixrore of polyester and polypropyIe.ne. It

will noat on salt waler. Karat rope is significantly stronger than polypropy1ene rope, though

some of this extra strength is achieved because the strands are not as tightly twisted. For

this reason, Karat rope may not be as resistant to some forms of abrasion and o t her haodEng

abuses.

6.3.2 Construction

Figure 6. S shows the common st ructures used in synthetic ropes; three-strand. six-strand, eight-strand

and double braid.