Sec. -fS.JZ 



WIND-WAVE AND SHIP-WAVE DATA 



175 



Elevotion of Undisturbed Water Level ,15. 4 ft in 



145 ft 



Composite Wave 



Profile ot Zero Time tn 



Steepness Ratio of Wave ot 

 Origin is about 1/18.7 or 0.0535 



Sections Token ot 70 deq True 



Actual Wove Slope l/5,66 - ton"'O.I768 



Oriqin in Space in the Center of Fiqs 46.& ond 48 H 



iOdeq.obt 



Vertical Scale is 6.308 times Honzontol Scale 



Profile ot to+3 seconds 



Fig. 48.1 Profiles at 70 Deg True for the Wave Patterns of Figs. 48.G and 48.H 



indicated in Fig. 48. H for a time 3 sec later. The 

 point of origin in space remains at the center of 

 the figure, as before. 



A vertical section through the origin at a 

 direction of 70 deg true is drawn in diagram 2 of 

 Fig. 48.1, again with the vertical scale multipUed 

 6.308 times. The "islet" which was in the center 

 has moved toward the ENE, but it is now only 

 7 ft high. The trough at the origin is slightly 

 deeper than before, 6.5 ft. To the east, the surface 

 is depressed but flatter than before, while to the 

 west a large wave is building up. 



The area depicted is not large enough to give 

 a reasonable indication of the variations to be 

 expected in resultant wave lengths and wave 

 periods, but within the confines of Figs. 48. G 

 and 48.H the lengths vary from 210 to 220 ft in 

 one group, 270 to 280 ft in another group, and 

 over 400 ft in a third. 



While the horizontal patterns of the waves in 

 these diagrams exhibit some systematic regular- 

 ities, a close examination of the contours reveals 

 that the surface is almost as irregular as one 

 expects the ocean to be. 



In fact, C. O'D. Iselin points out that wind 

 waves in nature are not symmetrical, and that 

 their dominant characteristic is the short length 

 of the crests of the individual waves, shown by the 

 plots of Figs. 48. G and 48. H ["Oceanography and 

 Naval Architecture," SNAME, New Engl. Sect., 

 Jun 1954]. The plots could be made more irregular, 

 if desired, by adding two more trains to build up a 

 five-component sea. Graphically, only three 

 components need be combined at once, since the 



three-component synthetic may be used as the 

 base and the two secondary trains added to it. 

 However, the three-component sea appears at 

 this time (1955) to be sufficiently irregular to 

 serve for ship-design purposes, as indicating the 

 kind of waves in which a ship is expected to travel. 



48.12 Tabulated Data for Actual Wind Waves. 

 A table embodying average relationships between 

 natural waves in deep water and the wind causing 

 them is given by Vaughan Cornish in his book 

 "Waves of the Sea and Other Water Waves" 

 [F. T. Unwin, London, 1910]. Additional data 

 are given in his Cantor lecture before the Royal 

 Society of Arts, London, 1914. Cornish's table is 

 quoted by E. L. Attwood, H. S. Pengelly, and 

 A. J. Sims on page 202 of their handbook "Theo- 

 retical Naval Architecture," 1953. It is repeated, 

 with some adaptations, in Table 48. k. 



It is noted from this table that as the length 

 of wave increases the steepness ratio hw/Lw 

 decreases. According to the figures given, the 

 standard structural-design ratio of li^l^w = 20 

 stUl used in many quarters can not fairly be 

 applied to ships longer than about 470 ft. 



More comprehensive and more modern data 

 on the relationships between the winds and 

 waves of nature are given in the tables of U. S. 

 Navy Hydrographic Office publication H.O. 602, 

 1947, especially Table 4 on page 18 and Table 15 

 on page 32. The latter embodies a third and 

 necessary variable in this relationship, namely the 

 duration of the wind which is generating the 

 waves. Both these tables appear to take it for 

 granted that the wind is blowing steadily m one 



