6.2.6 Standard Specifications
Wire ropes are covered by many national standards. The following standard specifications concern
wire ropes that comply with tbe material and construction recommended in paragrapbs 6.2.1 and
6.2.2- American Federal Specification (FS) RR-W-410-A: 6>< 37 with IWRC special improved plow
steel. - DlN 3066-SE-I770; equal lay, right hand, with heavy galvani ing per DIN E 1548.
- BS 3021 987
- ISO 4344.
6.2.7 Use of Synthetic Tails
In order to provide additional elasl.icity. the wire mooring lines of some large tankers are fined al
the shore end with'a length of synthetic rope, or tail. This additional elasticity reduces the dynamic
loads induced in the wire mooring lines by allowing the ship tQ respond more closely to various
combinalions of wind, wave and current, as well as to ships passing nearby at low speeds. Tails also
tend to distribute the loadings more evc.nly amoug mooring lines in the same service. Finally. the
elongation of the mooring line system furnished by the tail serves to reduce the risk potential asso-
ciated with poor line tending by lessening tbe frequency aod precision of line rcnding requirements,
particularly in benhs with large tidal variations andlor high cargo handling rales.The main disadvantage of Lails is that they may introduce a weak link inlo the moorings which is
not readily apparent to the ship operator. Tests conducted on fa.ilures bave revealed that tails can
undergo a subslanljal reduction in breaking slTcnglh in a relatively sbort period of time. Additionally,
if tbe tail is too elastic the ship movement may be in excess or that which ca.n be tolerated by the
terminal's cargo transfer system.If used. tails should be made of a material with high breaking strength such as braided or plaited
nylon. The size of rope selected should be capable of easy handling, while lit the same time being of
sufficient quality 10 ensure that the tail has a dry breaking strengt11 al least 25070 greater than that
of the wire line to which it is attached. Lncreasing the MBL of the synthetic taU above that of
the wire will ensure that the 10adings, as a percentage of the breaking st.rength of the tail, wiU be
lower than that in the wire moorillg line. For example, if the load is 55070 of the MBl of the wire.
it will correspond to approximately 45% of the MBl of a synthetk tail baving a 25070 higher MBL.
Reducing (he maximum per cent loading will increase the useful life of the tail, as experience
indicates that the cyclic loadings degrade synthetic lines more quidly than wire under similar load
conditions.Another factor to consider when specifying a nylon material for the tails is the melting point of the
grade. The higher the melting point, the less possibility of damage rhere will be from internal heat
generated at h.igh cyclic loadings.Nylon tails have ofle n I cen observed to be c.onnl:cted t(l the wire mooring lines with a cow hitch
or otber type of knot. This practise results in severe abrasion to lhe synthetic line. and should be
actively discouraged. To guard against cbafing. a wire line syntheric tail shackle such as the Mandel
or Tonsberg shackle should be used and the eyes of tbe tail served with leather or plastic sheathing.
(Fig. 6.3)In summary, tails. if used, should preferably be made of nylon line (not three strand consrruction).
be about 1 I metres long overal.] and have a dry breakil lg strength at least 25°io greater than the
MBL of (he wire to which they are attached. Tails should be replaced at least every 18 months
unless experience and/or inspection indicates a longer or shorter period is warranted.