Elasticity of a given Iype of line also varies with its diameter and conlIuction. Usually tbis factor
IS not an important. consideration since the load relative to a line's strength is the governing factor
rather than the absolute load.
1.5 GENERAL MOORING GUIDELINES
Consideration of the principles of load distribution in 1.4 lead to the following mooring guidelines.
rhese assume Ihat lhe moored ship may be exposed to strong winds or current from any djrection.
- Mooring lines sbould be arranged as symmetrically as possible about the midship point of the
sbjp. (A symme(,rical arrangement is more likely to ensure a good load distribution than an
asymmetrical arrangement.) - Breast lines should be oriented as perpendicular as possible 10 the longitudinal centre line of
the ship and as fa[ aft and forward as possible. - Spring lines should be oriented as parallel as possible to the longitudinal centre line of the
ship.
Head and stern lines are normally not efficient in restramlng a ship in its berth. Mooring facilities
with good breast :ltld spring lines allow a ship to be moored most efficiently, virtually 'within its own
length'. The use of head and stern lines requires two additional mooring dolphins and decreases the
overall restraining efficiency of a mooring pallcrn when the number of available lines is limited. This
is due to their long length and consequently higher elasticity and poor orientation. They should only
be used where required for manoeuvring purposes or where necessitated by local pier geometry, surge
forces or weather conditions. Obviously, small ships berthcd in facilities desigoed properly for larger
stUps may have head and stern lines because of the berth geometry.
- The vertical angle of the mooring lines should be kept to a minimum.
The' flatter' t be mooring angle, t.he more efficient the line will be in resisting horizontally-applied
loads on the s hip.
A comparison of Cases I and 3 in Fig. 1.4 demonstrat.es that a ship can usually be moored more
efficiently within its o\vn Iengtb. Although lhl: ~al11e nllmber of lines ale 11 cd in each situation, Case I
results in a better load distribution, minjmising the load in any single line.
- Generally, mooring lines of the same size and type (material) should be used for all leads. If
Ihis is not possible due to the a,'ailable equipment, aB lines in the same service, i.e. breast lines,
spring Lines, head lines, etc. should be t.he same size and type. For example, a.ll spring lines could
be wire and aU breast lines synthetic.
Fir t lines ashore can be synthetic lines, even though the main mooring Ii'nt\ are wire. This is accept-
able as long as it is realized that lhe fibre lines will not add lo the final re-slraining capacity of the
s'yslem unless all lines in that group are of the same material.
- .If tails are used on the wires, the same size and type of tail should be used 011 all lines run
out in the same service.
Synthetic taiL are often used on the ends of wire lines to permit e.as ier handling and to increase line
elasticity. The addition of an 11 m nylon tail would increase line elas1iciry of a 45m long wire line by
five [Q sixfold ( e.c aLo Section 6.2.7).
- Mooring lines should be arranged sa that aH lines in the same service are about the same length
between the ship's wincb and the shore bollard. Line elasticity varies direclly with (jne length
and shorter lilies will assume more load.