Sec. 48.10 



WIND-WAVE AND SHIP-WAVE DATA 



171 



plex waves with sinusoidal components, such as 

 those forming the basis of Figs. 48. G and 48.H of 

 Sec. 48.11, diagrams 2 through 5 of Fig. 48.F give 



0.0245 ■ 0.2061 0.5000 0.7939 0.9755 



0.0 0.0955 0.3455 0.6545 0.9045 



Ordinotes at Equollvj Spaced Stations 



1.0 0.667 0.500 0.333 0.0 



Fraotions of Half-Lenath of Wove from Crest 



Fractions of HolfLenath of Wove from Crest 



1.0 0.770 0.667 0580 0.420 0333 0230 



Fractions of Half- Length of Wove from Crest 



0.705 Q564 0.436 0.295 

 Fractions of Half-Length of Wove from Cre5t 



Fig. 48.F Abscissa and Ordinate Data for 

 SiNiTsoiDAL Waves 



the spacing in the direction of wave motion of 

 ordinates which differ by successive even fractions 

 of the wave height hw , such as 1/4, 1/6, 1/8, and 

 1/10. 



48.10 Standard Simple and Complex Waves 

 for Design Purposes. There are clear indications 

 that the use of the "static" L/20 wave or of the 

 Niedermair wave for the structural design of a 

 ship hull will shortly be paralleled by the use of 

 dynamic waves for what might be termed the 

 wavegoing design of the hull. Although the classi- 

 fication societies rather than the owners and 

 operators usually specify the hmiting stresses in 

 a ship girder, it may be expected that those who 

 run the ship will have a far greater interest in 

 its wavegoing performance at sea in heavy 

 weather. They may be expected to stipulate that 

 under certain wave conditions its augment of 

 resistance at reduced speeds, its wave-induced 

 motions, and its wavegomg behavior shall be 

 limited to specified values. 



Two problems arise here, possibly more. The 

 first is the manner in which the wavegoing per- 

 formance is to be predicted in the paper stage of 

 the design. This is discussed in Part 6 of Volume 

 III. The second is the establishment of standard 

 dynamic waves in which the ship is to give the 

 wavegoing performance stipulated. These must 

 be of such nature that the principal features of 

 ship behavior in them can be calculated, just as 

 the girder stresses are now calculated for the 

 "static" wave. 



The question as to whether these waves are 

 to be statistical, embodying averages and func- 

 tions for a great mass of data, or whether they 

 are to be geometrical (or mathematical) is not yet 

 decided (1955) and is not discussed here. It is 

 assumed for the time being that the effects of 

 the waves of nature can be produced by profiles 

 that are of sinusoidal, trochoidal, or some other 

 shape lending itself to graphic construction or to 

 calculation. 



It seems clear that the standard dynamic waves 

 embodied in the wavegoing specifications of the 

 future will be both (1) single regular trains and 

 (2) complex seas made up of specified combina- 

 tions of single trains. It is shown in Sec. 48.11 

 that a combination of three such traiiis produces 

 an irregular wave system which possesses many 

 of the characteristics of the natural waves of the 

 sea. A single train suitable for the testing of 

 models at angles of encounter a(alpha) of 180 

 deg (head sea) and deg (following sea) is com- 



