19 



Thus, it may be recommended to drop entirely the concept of wave- 

 makiiig length and to estimate the regions of high and lovf wave making, as 

 functions of Proude number, from suitable experimental or theoretical curves. 

 Particulary, it should be emphasized that the so-called @ "theory, " based on 

 similar reasoning and used to prophesy the positions of humps and hollows on 

 the resistance curve, is at best an interpolation formula valid for a limited 

 range of ship forms and Proude numbers, and that the use of 



© = l^fe^ ni] 



<*Lg 



as abscissa when plotting resistance curves should be abandoned. 



A great deal of confusion has been caused by substituting for the 

 ship simple -pressure systems. Commonly, a positive and a negative pressure 

 system are assumed to illustrate the action of the bow and the stem. This 

 choice is based on the doubtful assumption that bow- and stern-wave patterns 

 are similar in character except that crests and troughs are interchanged. The 

 argument is not consistent, however, since the wave profiles due to the finite 

 angle of stern and bow have the same sign, i.e., they both start with crests. 



While two positive pressure systems are sometimes substituted for 

 the ship, this also leads to an erroneous concept as the contributions of the 

 curved sides of the hull to the wave pattern generated at the bow and stern 

 have opposite signs. This is clearly brought out by Havelock^^ and Wigley/" 

 whose work should be consulted by anybody interested in the subject. 



4.1 . CALCULATED AND MEASURED WAVE RESISTANCE 



Various papers have been written with a similar purpose as the pres- 

 ent one: a. To give a synopsis of the more important results obtained by the 

 evaluation of existing theories, b. to describe the results of comparisons be- 

 tween theory and experiments, and c, to decide how far theory is able to help 

 In the solution of practical problems. We begin with a synopsis of a recent 

 publication by Glers and Sretenskjr"-^ which represents the most general attempt 

 to answer the three points mentioned although we do not agree with the basic 

 results reached . 



Plgures 4 and 5 have been recalculated from this paper. ^^ They rep- 

 resent values of the coefficient r = -^ as a function of P, where R is the 

 wave resistance calculated by Mlchell's integral for a family of elementary 

 ships : 



V= X(0 Z (f) [12] 



*The accuracy of the curves, Figures U and 5, may be sufficient for qualitative estimates only. 



