Page 142 - Practical Ship Design
P. 142
Weight-Ba sed Designs 109
io00
E
.-
s
a
0
.-
C
a
S
w io0
10
. .. . ..
10 100 1000
MCR (kW)
RPM (main engine)
Fig. 4.15. Main engine weight - slow and medium speed diesels (dry)
where MCR = maximum continuous power in kilowatts and in this case RPM is
engine RPM and not propeller RPM.
The weight given by this equation is about 5% higher than that represented by a
line through the data spots to allow for the fact that the graph really ought to be a
stepped line corresponding to cylinder numbers with approximately 10% weight
steps for the addition of each cylinder.
The constant in the formula now quoted has been modified to allow for the
power being in kilowatts and for a slight change in the line to accord with 1992 data
but the index remains unchanged.
Apart from its use when catalogues are not immediately handy it may be useful
when it is thought wise to use a “mean” weight figure in advance of taking a
decision on the make of diesel which will be fitted.
An alternative approach to dry machinery weights is provided by the use of
average weights in tonnes per kilowatt, values for each of the main types of engine
being as follows:
