Section 7.0
Winch Performance, Brake Holding
Capacity and Strength Requirements
7.1 FUNCTION AND TYPE OF MOORING WINCHES
Mooring winches perform a Illuhitude of functions. They secure tbe shjpboard end of mooring
lines. provide for adjustment of the mooring line length to suit the mooring pattern in each port
and compensate for changes in draCt and tide. They serve to store the mooring line when not in
use and to haul the ship into position against environmental or inertia forces. They also act as a
safety device that releases the line load in 3. controUed manner once the force in the Ijne increases
to the point of o ear-breakage. General requirements for shipboard mooring winches arc dealt with in
lSO Standards 3730 and 7825.
Wincbes can be categorised by their control type (automatic or manual tensiorung), drive type (steam.
bydraulic or electric), by the number of drums associated with each drive (single drum, double drum,
triple drum). by the type of drums (split, undivided) and by t.heir brake type and brake application
(band. disc. mechanical screw, spring applied). Eacb of these featu:res innuences the mooring winch
function and will be brieny discussed below.
7.2 AUTOMATIC TENSION WINCHES VERSUS MANUAL
WINCHES
Automatic tension winches are designed to automatically hea"'e-in whenever the line tension falls
below a certain prc-set value. Likewise, they will payout if the line tension exceeds a pre-set value.
Manual winches always require a person to handJc. the controls for hea.ving or rendering.
In practice, tIle use of the self-tension winch is not recommended except for moorings deployed at
90° to lbe sbip's a'(is. Automatic tension winches should not be used for spring lines, for example,
since it has been known for the winches to cause the sbi·p to 'walk' along the pier. This is because
spring line forces oppose each. other, leaving only the difference betwe.en the heaving and rendering
values of tbe winches available to resist longitudina.l environmental forces.
In theory, automatic tension winches would be ideal for breast lines forming a 90° angle to the
ship axis. If t.he breast lines cannot be· arranged at the optimum 90° angle due to the locarion of
mooring fi1tings at the pier and 011 the ship, the mooring restraint capability may be reduced because
the lines' fore-and-aft components oppose each other. For this reason, most termi:nals do not alJow
the use of tbe automatic feature and require that the winch be placed on the manual brake while
the ship is moored. See also Reft:rence 6. Section 3.5.4.7.3 WINCH DRUMS
Winch drums may be either split or undivided. The split drum is composed of a tension section and
a line storage section. Tt has the advantage that it c·an maintain a constant brake holding capacity
and heaving force, due to the fact that the mooring line is always rUIl off the first layer of tbe
tension drum. For this reason, split drum winches are preferred by ~ome operators, especially for