Page 323 - Practical Ship Design

Machinery Selection 28 1

considered. In addition, a shaft-driven alternator may introduce problems of
frequency control necessitating the use of a controllable pitch propeller or the use
of static frequency converters, but in suitable circumstances a shaft-driven alternator
can make a useful contribution to both fuel and overall economy.
The number of generators fitted on most merchant ships is determined by the
need to have one on standby at all times. On warships and specialist merchant ships
the number should allow for one generator being under repair in addition to the one
on standby. On most merchant ships with a relatively light sea load it is usual to fit
three generators with two sharing the sea load. On ships with a higher sea load four
generators are the usual fit, but sized so that three of these share the sea load. In
some cases the economic argument between three large generators and four
smaller ones can be closely balanced.

9.6 OTHER ENGINE ROOM AUXILIARIES AND EQUIPMENT

9.6. I Items specified and arranged by the marine engineer

The engine room accommodates, and the marine engineer supervises, a wide range
of machinery and equipment. These may be conveniently be divided into six groups.

(i) Items associated with propulsion such as:
- couplings,
- gearing,
- thrust block,
- shafting,
- bearings and sterntube,
- propeller.

(ii) Items associated with auxiliary energy such as:
- main and emergency generators,
- steam generating plant,
- heat exchangers.
(iii) Other major items of machinery such as:
- pumps,
- air compressors,
- oily water separators,
- incinerators,
- water purification plant.
(iv) Piping systems in the engine room consisting of the following systems:
- fresh water,
- sea water,