Sec. 52.11 



FLOW PATTERNS AROUND SHIPS 



255 



Towing Tank, Stevens Institute of Technology, 

 and published in: 



(a) Sutherland, W. H., "Underwater Photographs of 



Flow Patterns," ETT, Stevens, Note 75, May 1948. 

 This includes some observations made from under- 

 neath a model during a turn. 



(b) Ashton, R., "An Underwater-Photographic Method 



for Determining Flow Lines of Ship Models," ETT 

 Tech. Memo 101, Feb 1949. 



Other published flow-test photographs showing 

 tufts attached to the model surface and ink or dye 

 injected into the water through small tubes are 

 found in: 



(c) Baier, L. A., "Trouble-Shooting the Martha E. Allen," 



Mar. Eng'g., Sep 1955, p. 54 



(d) Baier, L. A., and Ormondroyd, J., "Suppression of 



Ship Vibration by Flow Control," Proc. Third 

 Midwestern Conf. on Fluid Mech., Univ. of Minn., 

 Jun 1953, pp. 397-411 



(e) Harper, M. S., and Weaver, A. H., Jr., "Model Flow 



Studies Around Stern of U. S. Navy Fleet Tug 

 ATF-16S, TMB model 3531," TMB Rep. 810, 

 issued in Jan 1952. This report contains 10 photo- 

 graphs, showing both tuft positions and ink trails. 



If the flow contains eddies, vortexes, and 

 counter-currents, or otherwise varies with time, 

 motion-picture photographs are taken. However, 

 neither type of photographic record can compare 

 in vividness and reality with direct visual observa- 

 tion. Fortunately, this can include study and 

 interpretation also by continuing any given set 

 of test conditions in the circulating-water channel 

 for as long as may be desired, or until the observer 

 understands what is going on. 



References to the studies of various experi- 

 menters, relating to the off-the-surface flow on 

 models, are Usted in Sec. 52.12 and in Sec. 22.6 

 on page 311 of Volume I. 



52.10 Estimating the Ship Flow Pattern on the 

 Body Plan. It will some day be considered as 

 important, and as necessary, to estimate the flow 

 pattern around a newly shaped hull, in advance 

 of model tests, as it is to predict its resistance or 

 the effective (and shaft) power required to drive it. 



Based upon the physical aspects of flow around 

 a ship form, described in Chap. 4 of Volume I, 

 with emphasis on the flow around surface-ship 

 forms in Sees. 4.10 and 4.11, an attempt is made in 

 Sec. 66.28 to formulate a few preliminary instruc- 

 tions for guidance in predicting the flowline and 

 wave-profile positions. Following these instnic- 

 tions, a flow pattern is sketched for the transom- 

 stern ABC hull designed in Chaps. 66 and 67; 

 in fact, it was drawn out in ink before the flow 



tests on the ABC ship model were made. The 

 rather large variations between prediction and 

 observations revealed in Fig. 66. R, especially in 

 the forebody, show that the tentative instructions 

 of Sec. 66.28 require further attention and study. 



In this connection the comments made by 

 H. C. Sadler, W. Hovgaard, D. W. Taylor, and 

 others, in the discussion and closure of D. W. 

 Taylor's paper "An Experimental Investigation of 

 Stream Lines Around Ship Models" [SNAME, 

 1907, pp. 1-12], will be found most helpful. 



52.11 Prediction of the Ship Flow Pattern at 

 the Bilges. The portion of the hull flow pattern 

 of the most immediate and practical interest is 

 that in way of the propulsion devices, discussed 

 in Sec. 17.2, in Chap. 33, and in Sees. 52.16 and 

 59.12. The next in importance is that in way of 

 the bilge or roll-resisting keels, especially if these 

 keels extend beyond any parallel middlebody 

 that may be worked into the hull. 



In some quarters it is considered sufficiently 

 accurate to place the bilge-keel trace, as projected 

 on the body plan, along a line bisecting the angle 

 at the bilge between the side and the bottom at 

 the section of maximum area. This neglects the 

 effect of B/H ratio and similar factors. In other 

 quarters it is assumed that the flow must certainly 

 follow the bilge diagonal, at least close enough for 

 all practical purposes. Both rules of thumb ignore 

 the effect of the surface-wave pattern as far down 

 as the bilge. 



For slow ships, with low T, values, the surface- 

 wave effect probably is small but for fast ships, 

 with medium or high T^ values, the prediction 

 must be based on knowledge of the flow to be 

 expected in this region. There is ample evidence 

 that for ships operating at T^ values in excess of 

 0.85 or 0.90, F„ > 0.253 or 0.268, the crests and 

 troughs in the surface-wave system are reproduced 

 to a lesser degree at the bilge-keel level. The bilge- 

 keel traces of the Mariner class, shown by V. L. 

 Russo and E. K. Sullivan [SNAME, 1953, Fig. 18, 

 p. 127], determined by both the chemical method 

 and the vane or flag method, are excellent 

 examples of this situation. Unfortunately, the 

 wave profile (Fig. 12 of the reference) does not 

 appear on the same drawing as the bilge-keel 

 traces, so as to make the surface-wave effect 

 readily apparent. 



For ships with a considerable extent of parallel 

 side at the waterhne, the surface-wave profile is 

 not outhned well enough on a body plan to permit 

 predicting its effect on a bilge-keel trace. The 



