Page 310 - Practical Ship Design

268 Chapter 9

At a Power of about 7000 kW

Slow speed diesel:
7000 kW Q 100 rpm
31 7 tonnes
1.1 1 tonnes/m3 or 0.90 m3/tonne
0.044 tonnes/kW or 23 kW/tonne

Medium speed diesel:
7650 kW Q 520 rpm
153 tonnes
0.80 tonnes/m3 or 1.25 m3/tonne
0.02 tonnes/kW or 50 kW/tonne

High speed diesel:
7000 kW Q 1300 rpm
21 tonnes
0.84 tonnes/m3 or 1.9 m3/tonne
0.003 tonneslkw or 330 kW/tonne

Fig. 9.2. A comparison of the size, density and weight per kW of various types of main engines.

(ii) medium-speed diesels with a speed of rotation mainly in the range 450 to
800 revdmin;
(iii) high-speed diesels with a speed of rotation mainly in the range 1000 to
3000 revs/min
There are of course some diesel engines with revs/min in the gaps between the
above ranges, but these are the generally accepted bands.
A comparison of the size, the density and the weight per kW of each of these
machinery types is given in Fig. 9.2, all of the examples chosen being of about 7000
kW - this power being chosen as one at which all three engines compete. A similar
comparison between a slow-speed diesel and a marine gas turbine is given in Fig 9.3.
In this case the power is 22000 kW representing the top end of the gas turbine range.