Page 270 - Practical Ship Design
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228 Chapter 7
Fig. 7.19. Grim vane wheel.
7.8.3 Efficiency claims
Major claims have been made for each of the devices mentioned, but none of them
appear, so far, to have won general acceptance. A question which must be asked in
relation to each claim is the extent to which the device in question can improve a
good conventional design - or is its best use in rectifying a poor design?
Another interesting question is the extent to which the savings claimed can be
additive, where the devices themselves are physically compatible.
7.9 DESIGN OPTIMISATION FOR POWERING
Having dealt with powering methods in this and the previous chapter, it now seems
appropriate to consider some of the principal features which determine whether a
ship will be power efficient or not.
7.9.1 Block coefficient
The Froude number-block coefficient relationship which is probably the most
important factor in optimising a design from the powering point of view has
already been discussed in 53.4 and the derivation of the WatsodGilfillan line has
been given. This line is also shown in Fig. 7.6 and it may be noted that this plot
reasonably confirms the near optimum nature of the line as its intersections with
the F, lines occur fairly near to the points at which the C, values start to increase
rapidly with increasing C,.