Vassilopoulos and Mandel 



systematic experimental data in seakeeping obtained to date and also because 

 they dealt with the effects of extensive variations of hull form shape and hull 

 weight distributions on model motions. The experimental data contained in the 

 NSMB reports covered variations in: 



1. block coefficient (c^), 



2. length to beam ratio (l/b), 



3. length to draft ratio (l/h), 



4. longitudinal radius of gyration (k^) 



for motion in regular waves of height (double amplitude) equal to 1/50 the model 

 length at four different speeds (Froude number of 0.10, 0.15, 0.20 and 0.25) and 

 several heading angles. 



To accomplish the extensive calculations involved in strip theory, a com- 

 puter program was written, debugged and used on the IBM 7094 digital computer 

 of the Computation Center at M.I.T. For a detailed description of the program 

 and its use, the interested reader is referred to Ref. [6]. The basic steps in- 

 volved in the digital computation are essentially similar to the ones proposed in 

 Ref. [5]. Thus, the whole computation is broken down into suitable packages 

 which can be easily modified or extended if this is deemed necessary. The ship 

 hull, however, and certain of the coefficients of the equations of motion are more 

 accurately defined in the M.I.T. computer program than in Ref. [5]. Also, a 

 subroutine based on Grim's theory for calculating damping and added mass co- 

 efficients was incorporated, in preference to the graphical data presented in 

 Ref. [5]. 



The results of the theoretical computations were compared with only a part 

 of the results reported in Refs. [18] and [19]. In particular, consideration was 

 given to non-dimensional pitching and heaving amplitudes together with their 

 associated phase angles which correspond approximately to directly ahead and 

 astern seas. The word "approximately" is used, since the experimental results 

 of Refs. [18] and [19] referred to actual headir^ angles of 10° and 170°, and 

 therefore some corrections had to be made for direct comparison at y = 0° and 

 y - 180°. These corrections were based on a suggestion of the authors of Ref. 

 [3] in which the model is considered to move at a modified speed in a fictitious 

 train of waves of the same amplitude but different wavelength. This suggestion 

 was recently justified by Lewis and Numata [20] for the case of small heading 

 angles. 



The correlation between theory and experiment was considered in two dis- 

 tinct phases. The first phase dealt solely with the effects of variation of hull 

 shape geometry and was accomplished for the range of hull parameters shown 

 schematically in Fig. 1. Table 1 indicates the main particulars of the family of 

 models chosen for the correlation. Further information required for the com- 

 putations, such as sectional area coefficients and load waterline shape were ob- 

 tained from Tables 4, 6, and 8 of the original paper on the Series 60 models 

 [21]. 



256 



