18 



The resistance curve can be split up into a monotonically increas- 

 ing part and fluctuating components. Neglecting the parallel middle body, we 

 obtain the resistance of the parabolic cylinder as the algebraic sum of 5 

 terms, due to: 



a. Bow and stem patterns (as if each existed alone). 



b. Curved sides (entrance and run). 



c. Interference of bow and stem. 



d. Interference of bow or stern with entrance or run. 



e. Interference of entrance and run. 



Patterns a and b are not oscillatory, being proportional respective- 

 ly to the 6th and 8th power of Proude's number P. For low values of P the 

 finite angle at bow and stem is more important, but with increasing P the 

 second term gains in value. Terms c, d, and e give fluctuating resistance 

 curves. 



The influence of the various terms depends on the speed and the form 

 of the ship. Results obtained by Wigley for a prismatic pile with a trape- 

 zoidal half waterline differ widely from those corresponding to the parabolic 

 waterline. The very pronounced shoulders (comers) in the former cause a 

 strong interference effect between the bow and the shoulder system, while the 

 influence of the shoulders is of secondary importance for the parabolic lines 

 with parallel middle body.*^**'^^ 



Many discussions have been devoted to the length of separation on 

 wave-making distance. Even the definition of this concept is not unique. 

 Following D.W. Taylor,'*^ the most pronounced interference effects are due to 

 the first crest just abaft the bow and the first crest of the stemwave sys- 

 tem somewhat abaft the stern; hence, the distance between these crests may be 

 considered as length of separation. On the other hand, in the opinion of the 

 Proud es, this length should be defined as the distance between the bow crest 

 and the trough caused by the after- shoulder. In the light of the preceding 

 remarks and more detailed investigations by Wigley and Havelock, we quote the 

 latter: 



"Although simple empirical formulae for so-called wave-making dis- 

 tance may be of some use it is doubtful whether they are worth the time in 

 inventing them, or in proving or disproving them " 



*When there are no corners in the waterline — as nearly alvays in actual practice — the concept of 

 shoulder wave system becomes somewhat arbitrary. 



