CHAPTER 58 



Running-Attitude and Ship-Motion Diagrams 



58.1 

 58.2 



58.3 



General 325 



Data for Predicting Sinkage and Change of 58.5 



Trim in Open, Deep Water 325 



General Conclusions as to Changes of Level 58.6 



and Trim with Speed 325 



Data on Sinkage and Change of Trim in 58.7 



Shallow and Restricted Waters 328 



Changes of Attitude and Trim of Ships with 



Fat Hulls 329 



Variation of Attitude and Position of Planing 



Craft with Speed and Other Factors . . . 329 



References to Published Data 331 



58.1 General. The diagrams in this section, 

 representing the in-motion trim attitude of models 

 and ships of various proportions and shapes, 

 supplement the general discussion in Chap. 29. 

 These data are likewise related to the wave- 

 profile data of Chap. 52, since the trim attitude 

 for displacement-type hulls at sub-planing speeds 

 is related directly to the wave profile. 



58.2 Data for Predicting Sinkage and Change 

 of Trim in Open, Deep Water. It is beheved 

 that most of the large model-testing establish- 

 ments have a great amount of data on file relating 

 to the change of level and trim of ship models 

 undergoing test. Unfortunately, most of the 

 published data apply to single ships or models, 

 here and there, or to hull forms of unrelated and 

 unsystematic proportions and shape. Examples 

 of this are the data presented by D. W. Taylor 

 [S and P, 1943], where in Figs. 21-25 on page 24 

 of the reference there are only trim indications 

 and no numerical data, and where in Figs. 84-93 

 on page 73 there are given data on ten more-or-less 

 unrelated models. W. P. A. van Lammeren, 

 L. Troost, and J. G. Koning give change-of-trim 

 data on only one model [RPSS, 1948, Fig. 38, 

 p. 88]. J. L. Kent and R. S. Cutland present some 

 change-of-trim data for models of high-speed 

 ships [INA, 1935, Vol. 77, p. 81ff and Pis. XI, 

 XII]. H. Lackenby shows the change of trim, for 

 several different conditions, of the 190.5-ft Lucy 

 Ashton and its 16-ft model, for a range of ship 

 speeds from 6 to 15 kt [INA, Apr 1955, Vol. 97, 

 Fig. 15 on p. 124]. 



The published data of D. W. Taylor on the ten 

 models referenced have been incorporated in one 

 set of graphs, embodied in Fig. 58. A. These 

 endeavor to present the information in somewhat 

 systematic fashion, although this is difficult when 

 based on data from only ten models. 



For the fifth approximation to the hydro- 

 dynamic features of the ABC ship of Part 4, 

 covered in Sec. 66.11 and listed in Table 66.e, 

 the Cp is 0.62 and the fatness ratio F/(0.10L)' is 

 4.327. To estimate the probable sinkage and trim 

 from Fig. 58.A, at a T, of 0.908, the 0-diml change 

 of level of the bow is found by inspection and 

 interpolation to be —0.46 per cent or — 0.0046L. 

 For the stern it is —0.145 per cent or — 0.00145L. 

 With a waterline L of 510 ft, these work out as 

 — 2.35 ft and —0.74 ft, respectively. The change 

 of trim at 20.5 kt, by the bow, is 2.35 - 0.74 or 

 1.61 ft, corresponding to an angle of (1.61/510)/ 

 0.01745 = 0.181 deg. 



It is significant that, at the trial speed, the 

 designed load draft at the FP, reckoned to the 

 undisturbed water surface at a distance, increases 

 from its nominal at-rest value of 26.00 ft to 

 28.35 ft, an augment of 9 per cent. What is more 

 to the point, the freeboard at the FP decreases 

 by 2.35 ft at the same speed, without any com- 

 pensating advantages. 



Published change-of-trim data on self-propelled 

 models are almost nonexistent, possibly because 

 experimenters thought that there would be little 

 or no difference in level or attitude between the 

 model when towed bare hull and when self- 

 propelled with appendages. Figs. 58. B and 58. C, 

 embodying the data for TMB models 4505 and 

 4505-1, representing the transom-stern and arch- 

 stern variations of the ABC ship hull of Part 4, 

 show that for this design at least the changes in 

 level and attitude with speed are significantly 

 different. 



58.3 General Conclusions as to Changes of 

 Level and Trim with Speed. Despite the handi- 

 caps enumerated in Sec. 58.2, it is possible to 

 draw certain rather comprehensive conclusions 

 from the available model-test data on change of 



325 



