Page 201 - Introduction to Marine Engineering

186 Deck machinery and hull equipment

luffing motor for raising or lowering the jib, and a slewing motor for
rotating the crane. The operator's cab is designed to provide clear views
of all the cargo working area so that the crane operator can function
alone. The crane is usually mounted on a pedestal to offer adequate
visibility to the operator. For occasional heavy loads arrangements for
two cranes to work together, i.e. twinning, can be made with a single
operator using a master and slave control system in the two cranes. A
common revolving platform will be necessary for this arrangement. The
operating medium for deck crane motors may be hydraulic or electric,
utilising circuits referred to earlier.

Maintenance

All deck machinery is exposed to the most severe aspects of the
elements. Total enclosure of all working parts is usual with splash
lubrication for gearing. The various bearings on the shafts will be
greased by pressure grease points. Open gears and clutches are
lubricated with open gear compound. Particular maintenance tasks will
be associated with the type of motor drive employed.

Hatch covers

Hatch covers are used to close off the hatch opening and make it
watertight. Wooden hatch covers, consisting of beams and boards over
the opening and covered with tarpaulins, were once used but are no
longer fitted. Steel hatch covers, comprising a number of linked steel
covers, are now fitted universally. Various designs exist for particular
applications, but most offer simple and quick opening and closing,
which speed up the cargo handling operation.
A MacGregor single-pull weather-deck hatch cover is shown in Figure
10.5. The hatch covers are arranged to move on rollers along a track on
top of the hatch coaming. The individual covers are linked together by
chains and ride up and tip onto a stowage rack at the hatch end. A
hydraulic power unit, operated from a control box at the hatch end, is
used to open and close the hatch cover. It is possible to open and close
the covers with a single wire pull from a crane or winch. Watertigtitness
of the closed covers is achieved by pulling them down on to a
compressible jointing strip. This is done by the use of cleats which may
be hand-operated or automatically engaged as the hatch closes.
Hatch covers below the weather decks are arranged flush with the
deck, as shown in Figure 10.6. In the arrangement shown a
self-contained hydraulk power pack with reservoir pump and motor is
mounted into a pair of hatch covers. This power pack serves the