Page 194 - Introduction to Marine Engineering

Chapter 10

Deck machinery and hull

equipment

The various items of machinery and equipment found outside of the
machinery space will now be described. These include deck machinery
such as mooring equipment, anchor handling equipment, cargo
handling equipment and hatch covers. Other items include lifeboats and
liferafts, emergency equipment, watertight doors, stabilisers and bow
thrusters.
The operations of mooring, cargo handling and anchor handling all
involve controlled pulls or lifts using chain cables, wire or hemp ropes.
The drive force and control arrangements adopted will influence the
operations. Several methods are currently in use, and these will be
examined before considering the associated equipment.
Three forms of power are currently in use: steam, hydraulic and electric,
Each will be described in turn, together with its advantages and
disadvantages for particular duties or locations.

Steam

With a steam powering and control system the steam pipelines are run
along the deck to the various machines. Steam is admitted first to a
directional valve and then to the steam admission valve. Double-acting
steam engines, usually with two cylinders, are used to drive the
machinery. Additional back pressure valves are used with mooring
winches to control tension when the machine is stalled or brought to a
stop by the load. Arrangements must also be made, often associated with
the back pressure valve, to counteract the fluctuations in main steam line
pressure as a result of other users of steam.
The steam-powered system was widely used on tankers since it
presented no fire or explosion risk, but the lengths of deck pipework
and the steam engines themselves presented considerable maintenance
tasks which have generally resulted in their replacement by hydraulically
powered equipment.
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