Sec. r,6.2S 



STEPS TN PRELIMINARY DESIGN 



14 6 4 i£ 4 8 \h \h 



4% 



G 1 

 Fig. 66. R Predicted and Observed Wave Profiles and Flowlines for Bow and Single-Skeg Transom Stern 



or whaleboat type; there are no known data to 

 indicate what the stern-wave height would be 

 for a transom-stern hull. Since the water closes 

 in at a much slower rate along the small waterline 

 slopes ahead of the transom, one might estimate 

 a wave height above the surface of the undis- 

 turbed water at a distance of something less than 

 2/3 the predicted amount for a normal stern, 

 say 3.55 ft. 



The stern-wave crest may be expected to 

 climb up the side of the ship at the outboard 

 corner of the transom by this amount plus the 

 stern sinkage of 0.74 ft, or about 4.29 ft. 



The data listed in Sec. 52.6 indicate that a ship 

 corresponding to the ABC design, running in a 

 range of T, values from 0.828 to 0.908 (from 18.7 

 to 20.5 kt), F„ of 0.247 to 0.270, is accompanied 

 by transverse waves of the Velox system about 

 half as long as the ship. At 20.5 kt there is a first 

 crest about 0.027L abaft the FP, a second crest 

 at about amidships, and a third crest at or near 

 the stern. As a matter of interest, the length of a 

 trochoidal wave at the 20.5-kt speed of the ABC 

 ship is, from Table 48. d and the accompanying 

 formulas, 234.3 ft; This is roughly 0.46L. The 

 general pattern for these and other speed ranges, 

 on cargo-ship models, is shown in Figs. 52.1 

 and 52. J. 



Furthermore, it is known that when the T, 

 value coincides with the position of one of the 

 hollows along the lower edges of Fig. 66. A there 

 is a prominent wave crest at the stern. When it 



coincides with a hump, there may be a wave 

 hollow at the stern, or a crest of greatly diminished 

 height. 



The exact shape of the accompanying wave 

 profile is manifestly a function of the shape of the 

 hull and of certain distinctive features, some 

 known and some unknown. If a ship waterline 

 has pronounced shoulders, not necessarily as 

 sharp as those of the parallel-sided, wedge-ended 

 form of Fig. 10. F, secondary wave systems are 

 generated. Their transverse Velox waves combine 

 with those of other systems to form a rather 

 complex pattern. A predicted wave profile for the 

 ABC hull with a single-skeg transom stern is 

 sketched in light lines in Fig. 66. R, before any 

 test runs are made on a model. 



To predict the flowline positions it is estimated 

 that the dividing point on the stem, between 

 the water passing around the side and that under 

 the bottom, is relatively high, because of the 

 large B/H ratio and the expected drop of the 

 bow of about 2.4 ft. A figure of O.SH or 7.8 ft 

 below the DWL appears about right; this is at 

 the 18.2-ft WL. The flowlines sketched in the 

 forebody resemble those of diagram 3 in Fig. 

 4.0, and of the many illustrated in Chap. 52. 



It is to be expected that the wave profile, 

 representing a constant-pressure upper boundary, 

 will influence the shape of the flowlines passing 

 around the side, perhaps down to the 10-ft 

 waterline or below. 



The flowlines under the nearly flat bottom, not 



