Page 270 - Practical Ship Design
P. 270

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,.
   265   266   267   268   269   270   271   272   273   274   275