32 



while the model results were taken from those of Taylor''^ and Kent," only ^ 

 and p were Identical. This coarse procedure may invalidate the comparison of 

 absolute values for moderate and low Proud e numbers but not the general trend 

 as a function of the principal dimensions. 



For P = 0.387 (Pigure 10) the agreement between theory and experi- 

 ment is good as to the character of the curves and reasonable with respect to 

 absolute values above an L/B of about 8. 



Pigure ^^ , valid for P = 0.24, shows a complete failure of the com- 

 parison. Allowing for the difference in forms mentioned above, it can be said 

 that: 



a. The values of the calculated wave resistance are much exaggerated 

 for smaller L/B ratios. 



b. Even the trend in the experimental residual-resistance curves and 

 calculated wave-resistance curves as functions of B/H does not agree. This 

 indicates that the "residual resistance" does not furnish any information 

 about the actual wave phenomena in the present case because of the presence 

 of viscous drag. An increase in this resistance with increasing B/H has been 

 found by experiments with double models. ■"■* 



c. The diagram (Figure 12) representing conditions for slow vessels 

 does not show such pronounced anomalies, but supports the impression that the 

 model results in question do not contribute to the analysis of wave resistance. 



To summarize, we may say that theory has contributed some rough es- 

 timates of the relations between principal dimensions and wave resistance; 

 their validity is limited mainly by the L/B ratio. Only a small number of ex- 

 periments exist which are reliable enough to check the theory and to deduce 

 simple empirical laws for the basic cases discussed. The presence of viscous- 

 form drag and other viscosity effects have so far seriously hampered the study 

 of wave resistance of slow full ships. 



5.3. THE WAVE RESISTANCE AS A FUNCTION OP THE HULL SHAPE 



3 • 3 • 1 • General Remarks 



The restrictions under which the concept of dimensionless form can 

 be used in resistance research have already been enumerated. The present task 

 is: a) To analyze theoretically the resistance properties of different forms, 

 b) to deduce some general rules from this analysis, and c) to report on 

 experimental checks. The influence of the longitudinal distribution of dis- 

 placement on resistance Is the most important problem, both from the viewpoint 

 of theory and practice. 



