problem which seems to be most peculiar to the hydrodynamics of ships. 

 The lecture will deal with four topics, namely: 



1. Wave resistance of ships in uniform forward motion, 



2. Hydrodynamic forces on oscillating slender ships, 



3. Wave pressure on slender ships, and 



4. Added resistance of ships in ambient ocean waves. 



WAVE RESISTANCE OF SHIPS IN UNIFORM 

 FORWARD MOTION 



Short Comments on Thin Ship Theory 



The theory of wave resistance is a rather classical problem. It was 



1* 

 as early as the end of the last century that Michell established the 



theory for thin ships. His theory was already so complete that nothing 

 needed to be added for a first approximation of thin ships. More than 

 eighty years have passed since then; nevertheless the progress in the 

 theory of wave resistance has been comparatively slow. 



Michell 's thin ship theory is based on the assumption that the beam- 

 to-length ratio is so small that its square can be neglected. There are 

 several examples of comparison of computed wave resistance with measured 



resistance. Among them are instructive results with a series of models 



2 

 whose breadth is varied systematically. It is indicated that the wave 



resistance calculated by Michell' s formula agrees well with measured 

 results, provided that the beam-to-length ratio is not greather than one 

 fifteenth, as shown in Figure 1. This criterion of beam-to-length ratio is 

 too small for practical hull forms. The beam-to-length ratio of practical 

 hulls is at least one seventh. Consequently, considerable discrepancy 

 appears between theory and experiment in conventional hull forms. This 

 fact does not mean, however, that the thin ship theory is useless for 

 practical purposes. It is known that the Michell thin ship theory has be- 

 come a very powerful tool for the purpose of designing low resistance hull 



forms. A direct application of the theory for this purpose is known as 



3 

 the theory of minimum wave resistance. The method is an application of 



calculus of variations. One can determine the optimum curve of a sectional 



*A complete listing of references is given on page 119. 



2 



