Page 307 - Practical Ship Design

Machinery Selection 265

the cost of gearing andor the need for separate pumps for one alternative whereas
another may use direct drive and have engine driven pumps included in the main
engine price.

9.1.6 Running costs
Usually, the most important item of running costs is the annual fuel bill. In recent
years fuel prices have been very volatile, as Fig 9.1 shows. Whilst at the time of
writing (1995) fuel prices are well down from their peak in the period 1979-1985,
the lessons learnt then ensure that these costs remain a very major factor in
machinery selection.
For a required horsepower there are, in principle, two fundamentally different
ways of minimising expenditure on fuel:
(i) by fitting as fuel efficient an engine as possible even if this requires a
relatively expensive fuel; or
(ii) by the use of machinery which can bum a cheap fuel even if its specific
consumption is comparatively high;
and, of course a compromise between these extremes, with the ideal being an engine
capable of achieving a low specific consumption whilst burning a cheap fuel.
Whilst seeking minimum fuel costs, however, it is important not to overlook
other running costs, such as lubricating oil, spare gear, annual maintenance and -
not least - the cost of manning. A reduction of one in the number of engine room
staff may reduce running costs by as much as, or more than, can be achieved by
expensive improvements in engine efficiency.

m , __ Calorific value kJh A

3 COAL 15to33(mean24) I \ Wine diad oil
..-

I , , . , , . , , , . , , , .
1910 1915 1980 198s 1990 1995

Fig. 9.1. Fuel prices through the years. For recent years the oil prices are those recorded in M.E.R. for
January at Las Palmas which is a reasonable mean between the cheapest prices (generally at
Rotterdam) and the most expensive (generally in the Far East). The MFO prices relate to IF0 180.