Page 313 - Practical Ship Design

Machinery Selection 27 1

The highest power currently available from a medium-speed engine is 23,450
kW from an 18 V PC 4.2 Pielstick at 428 rev/min. A twin installation can therefore
give almost 47,000 kW.
More typical, however, are powers per cylinder ranging from about 150 kW to
about 1000 kW and engine speeds ranging from 450 to 750 revdmin.
The specific fuel consumptions claimed range from about 200 down to 167
g/kWh. In general, the larger engines have the lower specific fuel consumption.
The fuel used is again a heavy marine fuel oil, but the cruder versions of this are
generally to be avoided and these engines require to be changed to diesel oil when
manoeuvring.
There is a far wider range of manufacturers than for slow-speed diesels with
Daihatsu, MAN B&W, NE1 Allen, SEMT Pielstick, Wartsila, Sulzer and Stork
being amongst the principal firms.

9.2.4 High-speed diesels
The use of high-speed diesels as main propulsion prime movers is confined, as far
as merchant ships are concerned, to small vessels and ships with diesel-electric
installations.
In warships where a high power-to-weight ratio is essential, high-speed diesels
are used either on their own or in conjunction with gas turbines.
As high-speed diesels are generally manufactured on a production line basis,
models tend to be available in a limited number of cylinder options.
The highest power currently available from a high-speed engine is 7400 kW
from a V20 M.T.U. at 1300 rev/min (370 kW per cylinder).
More typical, however, are powers per cylinder of from about 20 to 200 kW and
speeds of from 1200 to 2100 revs/min.
The specific fuel consumptions claimed range from about 250 down to 187
g/kWh. In addition to these engines having a higher specific fuel consumption than
medium-speed engines, consideration must be given in any economic comparison
of the types to the higher cost per tonne of diesel oil (about 2.0 x cost of heavy fuel,
see Fig. 9.1) and the reduced time between overhauls.
Manufacturers at the top end of the power range are M.T.U. and SEMT
Pielstick. In the middle and lower range, Caterpillar must be one of the best known
names but there are many others.

9.2.5 Gas turbines
The main advantages that gas turbines have over competing engines, which are
principally high-speed diesels, are their extremely good powedweight and power/
volume ratios. Their main disadvantage has been their much higher specific fuel