178 



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-10 



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 c 

 9 X> 



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 i 10 



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 >-20 



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Sectic- 

 FiG. -l.S.K 



Distances Across Wove Profile, Expressed in feel 



TiiKKK rnoKii.Es TiiHoraii an Ocean Wave as Determinkd by G. P. Weinhli m and \V. Bixjck on 

 THE M. S. San Francisco 



for a considerable transverse distance from the 

 ship, say 1,500 ft. 



Short-duration simultaneous exposures are made 

 at the midpoint of a roll; for this instant the planes 

 of the two negatives are vertical. The pairs of 

 stereoscopic photographs thus obtained are placed 

 in a photogrammctric machine and the wave 

 section quickly traced for any plane lying at a 

 selected distance parallel to the ship centerplane. 

 Fig. 48.L is one such photograph taken by C. G. 

 Moody of the TMB staff on the aircraft carrier 

 Oriskany (CVA 34), during a storm west of Cape 

 Horn in June 1952. 



Fig. 48.M shows nine straight or plane sections 

 through the waves recorded by this pair of photo- 

 graphs, at offset or transverse distances in ft, 

 from the plane of the camera lenses, indicated by 

 the numerals at the left of the diagram. Because 

 of the greater distance from the camera for a 

 wave in the background than for one in the fore- 

 ground, a unit linear width across the diagram 

 indicates a greater distance along the wave section, 

 parallel to the ship axis, a-s the transverse distance 

 increases. Scales are given at the right of two of 

 the wave profiles in Fig. 48. M. 



Knowing the focal length of the canicra.s and 

 the distance of the cameras above the mean 

 water level or above the at-rest waterlinc, it is 

 possible to plot sections along a vertical trans- 

 verse plane extending outward from the mid- 

 pfjHitioii between the camera lenses. The trace of 

 such a plane is shown by the vertical line 0-0 

 on the diagram of Fig. 48. M. Similarly, it is 

 poHKible to plot a section along a diagonal plane 

 extending outward from the point midway 



between the len.scs. The trace of such a plane is 

 the vertical line A-B on Fig. 48. M, drawn on the 

 original at a distance 4 inches to the left of 0-0. 

 At 500 ft distance this offset plane intersects the 

 nearest crest at a point 4(23) = 92 ft to the left 

 of the plane through 0-0. At 1,500 ft distance 

 the diagonal plane intersects the farthest crest 

 at a point 4(70) = 280 ft to the left of 0-0. 



Obviousl}', profiles of wave faces behind crests 

 or otherwise hidden from the cameras are not 

 determined. 



Pitching of the ship tilts both cameras, as 

 indicated bj' the small counter-clock\nse rotation 

 of the principal axes of Fig. 48. I>, with reference 

 to the apparent horizon. This tilt may be cor- 

 rected if desired in the photogrammctric analysis 

 procedure. It docs not, however, change the wave 

 profile in the particular vertical plane considered. 



A further discussion of photographic and plot- 

 ting methods for sea surfaces is not warranted 

 here. However, as the references on this subject 

 contain many sets of wave contours and profiles of 

 interest to the marine architect the principal 

 papers and books are listed: 



(1) I.!i!i.s, \V., "Pliotogriii)liischo Me,ssung dt-r Mecreswcl- 

 IcM (I'liotogrnphic Observations and Mo-n.iuremcnt 

 of Sea Waves)," Zeit. d. Xcr. Dout,srli. Iiik-i 25 Nov 

 1905, pp. 1S89-1S95; 2 Dec 1905, pp. 1937-1942; 

 9 Dec 1905, pp. 1976-1981. The last of tlieso pages 

 earries a HhI of 13 refereiiee.s. 



The ohservatioiiH df.scriheil in thiH .series of 

 papers wero mude from the five-niiiMtoii ■•jailiiiR sliip 

 Prcussen on a voy«K<^ from HanilnirK arii\ind the 

 Horn to l(|uic|Ue, iM-uador, niul return, during tlie 

 period Sop 1904 to 3 Kel) 1905. The photographs 

 wero apparently made witli the optical axi.s of the 



