In the design of a ship, the LCB position is also dependent to some extent on consid- 

 erations other than low power and good sea behavior. Chief of these is the problem of 

 achieving correct trim under a variety of loading conditions, particularly in tankers and 

 other bulk carriers. The tendency to place machinery aft in dry-cargo ships and passenger 

 ships also gives rise to trim problems and in such cases the size of machinery may restrict 

 the hull shape aft and, by requiring additional volume there, also influence the LCB position. 



In the discussion on one of the Series 60 papers (Reference 63), Professor Manning 

 set out very clearly the importance of LCB position in designing the single-screw merchant 

 ship, and one cannot do better than quote his remarks. "Taylor states very clearly that his 

 use of th.3 prismatic coefficient as a major parameter was based on the fact that it is an 

 excellent measure of the longitudinal distribution of the volume of displacement ... In the 

 case of the Taylor Standard Series, the prismatic coefficient was sufficient in itself as a 

 measure of the longitudinal distribution of displacement by reason of the process used in 

 determining the offsets of all the models of this family and the fact that none of the models 

 had parallel middle body. Whenever a ship has parallel middle body, a substantial change in 

 the longitudinal distribution of the displacement may be made without any change in the 

 prismatic coefficient. For example, if the lengths of entrance, parallel middle body and run 

 are held constant, and the prismatic coefficient of entrance is given to the run, and that for 

 the run to the entrance, the prismatic coefficient of the entire hull has not been altered, but 

 the longitudinal distribution of the displacement certainly has. The wave-making resistance 

 and viscous form-drag have therefore also been changed in substantial magnitude. The 

 difference between the longitudinal distribution of the displacement of vessels which have 

 the same value of prismatic coefficient may be related to differences in the longitudinal 

 position of the centre of buoyancy. This paper (Reference 63) is essentially a study of the 

 effect of changes in the longitudinal jsosition of the centre of buoyancy on the resistance 

 and power required for parallel middle body ships at speeds which reflect current practice. . . 

 From this paper, the ship designer can not only estimate with good precision the position of 

 the centre of buoyancy which gives the least resistance or shaft horsepower, but how much 

 he must pay in terms of these if other conditions favor a different location for this point. 

 The latter is just as important as the former." 



For all the above reasons, it was agreed by the Panel that before proceeding to the 

 last phase of this project-the effect upon resistance and propulsion of variations in — 

 and ratios-the effect of change in LCB position should be investigated for each of 



the Series 60 parents in order, if possible, to determine the optimum location. 



The positions of the LCB chosen for the five parent fiodels are shown in Figure 1, 

 together with the variation in these positions for the other 17 models making up the complete 

 set. The positions of LCB are shown in Tabte 10, and the principal particulars of the models 

 are given in Tables 11 through 15. 



VI-2 



