OCIMF_Mooring_Equipment_Guidelines_(Second_Edition)

The transfer of the wire from the storage section to the tension section is clifficult to judge particu-
larly when long drifts of wire are used such as at multi-buoy moorings. Care must also be exercised
to prevent tension coming on the wire during the transfer at the time when it passes through tbe
slot. If this is nOI done such tension could cause damage to the wire or to personnel involved in
tbe transfer. There is also concern that the mooring operations could take longer especially when
excessive layers develop on tbe tension section. The delay occurs because steps must be taken prior
to mooring completion to correct the number of turns on the tension balr.

Figure 7.2 is a graph which one operator has distributed to its ships to provide a better understand-
ing of tbe forces in the line and to show the effect of relative heigbt cbanges between vessel and
pier due (0 tidal changes and changes in vessel draft. The graph shows (for a 2 ft diameter drum),
the number of !Urns that are required 00 the tension section at the time of mooring to allow line
tending adjustments (0 be made from the tension drum only. The use of this guide will also ensure
tbat there will always be sufficient turns of wire left on the drum to minimise the force at the
transfer point between tension and storage sections. For instance, when seven turns are on the tension
section, the load at the transfer point is only I % of the line pull. A calculation made for an extreme
tidal range location indicates a maximum adjustment of approximately two turns. It should be noted
that the curve for the required turns 00 the drum (shown on the right side) was developed for the
particular drum size as shown. The curve for tbe force at the transfer poim (shown on the \eft side)
is a function of tbe coefficient of friction and number of rums and is, therefore, applicable to any
size drum.

7.3.2 Undivided Dmms

Tbe undivided drum winch is commonly fouod on smaller ships and is preferred by some operators
for VLCCs. These operators prefer tbe undivided drum to avoid the need to transfer the wire from
section to section as is required for a split-drum winch when a poor estimate has been made of the
spoojing requirements. The undivided drum eliminates the potential for wire damage and personnel
injury tbat exjsts at the time of transfer on a split drum.

However, if this type of drum is selected, tbe operator should be aware that it is ofcen difficult to

spool and stow the wire on the drum satisfactorily. If the wire is not spooled properly, the wire can

be damaged when tension is applied to the system. To reduce this problem, care should be exercised

in the location of the winch. It shouJd be placed a sufficient distance from the fairlead to ensure

that the wire can be properly spooled.

7.3.3 Handling oj SPM Pick-up Ropes

Most, if not all, storage drums, regardless of whether split or undivided, are designed [0 meet the

required capacity for storage of steel wire ropes to suit normal moorings at piers, and it is a fact

thac the designs of conventional wind.lasses or mooring winches have no consideration for handling

buJky pick-up ropes at SPM terminals.

Section 6.3 of Reference I recommends a direct lead between bow fairleads and bow stoppers. The

publication also states that if a winch storage drum is lIsed to stow the pick-up rope, it shouJd be

of sufficient size [0 accommodate 150 metres of 80mm diameter rope.

Whilst it is recognised that. either a warping eod or a wire drum may be used to heave in the SPM

pick-up rope prior LO connection of the chafing chain to the stopper, opinions as to which should be

used are equally divided.

Following reports of accidents and "near misses" during unmooring at SPMs when the pick-up rope

has been released and allowed to fall un-controlled from the ship, it is recommended tbat each

windlass be provided with a special drum of sufficient capacity lO accommodate 150 metres of 80mrn

diameter rope. If fitted at the inboard end of windlasses they will minimise rope turns and angles.

These drums may also be used for nonnal wire moorings.