Vassilopoulos and Mandel 



hull shape, using the "New Approach" with the additional three-dimensional 

 terms should be more realistic than the Korvin approach. Physically, the slen- 

 der body assumption assumes such a large length-beam or length-diameter ra- 

 tio that forward effects are neglected. The new approach corrected as indicated 

 above, would hold better for the fuller ships. As an extreme, the deeply sub- 

 merged sphere should have a coefficient E (or -M^) equal to zero; the corrected 

 new approach would give zero for this case, whereas the Korvin slender body 

 approach gives a relatively large quantity. (Of course a sphere significantly 

 violates the slender body assumption.) 



It should be pointed out that the corrected coefficients, listed under "New 

 Approach" in the attached figure, have the symmetry required by the Timman- 

 Newman analysis, i.e., d = D, e = E. 



DISCUSSION 



O. Grim 



University of Hamburg 



Hamburg, Germ,any 



Coefficients for added mass and damping force for some sections are shown 

 in the paper. They are computed using Porter's and my own method. The re- 

 sults found by both methods are compared and discrepancies have been ascer- 

 tained. However, these discrepancies appear not disturbing to me. The reason 

 is very simple. The computer program used for my method was not designed 

 for such a wide range of frequencies but only for the range important for the 

 motions in a seaway. In the meantime the program has been supplemented which 

 is valid for any arbitrary frequency and consequently the discrepancies have 

 vanished. 



DISCUSSION 



William R. Porter 



Massachusetts Institute of Technology 



Cambridge, Massachusetts 



These comments will be relative to the calculation of added-mass and 

 damping coefficients for two-dimensional cylinders. The numerical results for 

 all elliptic cylinders and for Models 2, 3, and 4, obtained by the procedures used 

 by the authors and attributed to Grim should agree with my results, because all 



364 



