Section 6.0
Mooring Lines
6.1 DESIGN STAGE DECISIONS
A major decision must be made at the ship design stage as to whether wire or synthetic fibre
mooring tines are to be used. The type of line used wiU influence such items as winch drum size,
types of fairleads, bend radius of fairleads and required deck space.The principal considerations in selecting a line type are discussed in Section I. Wire is advantageous
where limited movement is required. such as at benhs with bard ann equipment and wbere low
dynamic loads are expected. For t.hese reasons wires are recommended on large ships.
Synthetic lines are often. favoured for small ships where ease of handling, flexibility of moorings and
lower line temion are important crite.ria. Other factors which may inl1uence the choice of material
include cost and the type of out fitting customarily used within a particular rrade.A system utilising wire spring lines and synthetic breast lines, as found on some s hips. has certajn
theoretical advantages. It reduces tbe fore and aft excursion of tbe ship while moored which in furn
reduces shifting of loads from one breast line to another and limits the motion of loading arms or
hoses. Nonetheless. for simplicity and operational flex ibility, it is recommended that all lines be of
the &ame material.Some newer 'high modulus polyethylene' (HMPE) and synthetic aramid fibre ropes with high strength
and low stretch characteristics. may be suitable alternatives to steel lines. But they arc expensive and
have some disadvantages such as low abrasion resistance and being difficult t'O splice. Retrofitting can
also prove problematical as wire li.ne induced mechanical wear on fairleads can resuJt in exccssrve
abrasion of fibre tines.6.2 WIRE MOORING LINES
6.2.1 MaterialTo meet the requirements of in creased strength for wire mooring lines, manufacturers bave developed
preformed, drawo galvanized wire wilh. high tensile strengths. The drawn galvanized wire provides
strengths of tbe same magnitude as bright wire and an improvement in wire Line quality. To save
weight, pedormed drawn galvanised wire strands 'Of a minimum tensile strength of 180kg/ rrun^1 are
recommended.6.2.2 ConstructionA line should be selected which combines tbe proper attributes for mooring when reasonable flexibility
and high MBL are top priority requi remenrs. The recommended construction is 6 x 36 or 6 x 41 (6 )(
37 class) with the wires in each strand of equal lay and the strands 'Of regular (ordi.oary) fight hand
lay.Figure 6.1 illustrates these constructions. Equal lay for lines in each strand is recommended when
available because of its bigher MBL than cross lay. While Lang lines have a slightly greater MBl
than regular lay lines, they have a greater tendency to kink and unlay (or open up the lays of lhe
strands) which is undesirable where grit, dust and moisture are present.