Page 199 - Introduction to Marine Engineering

184 Deck machinery and hull equipment

particularly on larger vessels, is the split windlass where one machine is
used for each anchor.
One unit of a split windlass is shown in Figure 10.2. The rotating units
consist of a cable lifter with shaped snugs to grip the anchor cable, a
mooring drum for paying out or letting go of mooring wires and a warp
end for warping duties. Each of these units may be separately engaged
or disengaged by means of a dog clutch, although the warp end is often
driven in association with the mooring drum. A spur gear assembly
transmits the motor drive to the shaft where the various dog clutches
enable the power take-off. Separate band brakes are fitted to hold the
cable lifter and the mooring drum when the power is switched off.
The cable lifter unit, shown in Figure 10.2, is mounted so as to raise
and lower the cable from the spurling pipe, which is at the top and
centre of the chain or cable locker. Details of the snugs used to grip the
cable and of the band brake can be seen.
Anchor capstans are used in some installations where the cable lifter
rotates about a vertical axis. Only the cable lifter unit is located on deck,
the driving machinery being on the deck below. A warping end or barrel
may be driven by the same unit and is positioned near the cable lifter.

Cargo handling equipment

Cargo winches are used with the various derrick systems arranged for
cargo handling. The unit is rated according to the safe working load to
be lifted and usually has a double-speed provision when working at half
load.
In the cargo winch, spur reduction gearing transfers the motor drive
to the barrel shaft. A warp end may be Fitted for operating the derrick
topping lift (the wire which adjusts the derrick height). Manually
operated band brakes may be fitted and the drive motor will have a
brake arranged to fail-safe, i.e. it will hold the load if power fails or the
machine is stopped.
A derrick rig, known as 'union purchase', is shown in Figure 10.3. One
derrick is positioned over the quayside and the other almost vertically
over the hold. Topping wires fix the height of the derricks and stays to
the deck may be used to prevent fore and aft movement. Cargo handling
wires run from two winches and join at the hook. A combination of
movements from the two winches enables lifting, transfer and lowering
of the cargo. This is only one of several possible derrick arrangements or
rigs. Although being very popular for many years, it requires
considerable crew time to set up and considerable manpower for
operation.