3.9.1 Requirements for Off taker
The offtaker's (smaiJer ship's) standard mooring equipment is generally suitable for STS transfers.
Ships equipped with wire moorings should fit synthetic rope tails to introduce more elasticity and
electrical discontinuity, and 10 permit cutting in an emergency. [t is recommended that the fairleads
are of the enclosed type, since the relative freeboard between tbe two ~bips will change significantly
during the STS tmnsfer operation. If the lines are of wire rope. the opening of the closed chocks
musI be large enough to permit easy passage of the special shackle connecting the wil to the wire
rope.
3.9.2 Requirements for Discharge Ship
The discharge ship (larger ship) may require special mooring fittings to allow a proper mooring
patrern. Since industry practice is 10 use rhe starboard manifold of th e discharge ship, special fitLings
are generally p rovided on the starboard side only. A. can be seen in Fig. 3.12, t.he offraker's spring
lines term.inate on the discharge ship in a location not usually fitted with ch ocks. For this reason it
is recommended that tankers over 160 kDWT be fitted with cI()sed chocks with oponings of 500
)( 400 mm., about 35 metres fo~ward and aft of mid-length on the starboard side. Since the 500 )(
400 mm dimension is not a common standard size, some operators have successfully used two chocks
with 500 )( 250mJII openings arranged in pairs. in place of a single 500 )( 400mrn choek.
Similarly co requirements for the off taker, the di scharge ship's mooring fairleads should all be of
the dosed type to avoid difficulties caused by the large relative changes in frecboard. The require-
ments for closed chocks of adequate size for breast, head and stern lines may already be met by
requirements in these guidelines for mooring at piers and sea islands, and by lUg handling provisions.
But in other cases - especially on ships where closed chocks are not used for the standard mooring
lines - special STS transfer clo cd chOCks may be requjred on tbe tarboard si de. [n any event, suitable
bollards are required inboard o f the closed chocks for securing the off taker's mooring line. Some
operators aJlow only one line (0 be used in each chock to reduce rhe possibility of line cbafing with
changing ship draughts. [n litis case closed cbock. art arranged in pairs and served by a common
bollard. Further. it is recommended that means be provided for passing a messenger lin.c (allached to
the eye of the offt'aker's mooring line) tbrough the chock and onto the warping hend of a mooring
winch. For this purpose, a bitt or guide post may be used in lieu of a pedestal roUer fairlead.More details on all phases of STS transfer operations may be found in Reference 4.3.10 Mooring Augmentation in Exceptional Conditions
As menLioned in Section 2, it wouJd not be practical to design all ships for the worst. possible operating
environment. Where. the Standard Environmental Criteria are exce.eded, the ship must either leave
the bcnh, obtain continuous tug assistance or arrange for additional mooring restraint.The ship and terminal must also be prepared to ta ke appropriate actioll in other cmergc:ncies. such
as fires, and this may require additional equipment aboard the ship.3.10.1 Excessive Environmental Forces
To augment the mooring system when conditions exceed the Standard Environmental Criteria, two
ways of obtaining additional restraint capacity are feasible. One is to provide shore moorings. The
other is to provide shore puJleys around which the sbip's mooring line is led and made fast back
aboard the ship. In either case, shipside fairleads and associated bollards would be required.It is recommended to provide closed chocks, a'S~ociaLed bollards and warping ends ror a number of
additional lines equal t.O at least 50010 of rhe ship's standard mooring lines. (Nore that the ship sbown
in Fig. 3. J provides fOf 100% augmentation.) Tlle chocks will usually be located next (0 the fairleads
for the standard mooring lines.