Ochi 



conditions. This is due to the following reason: that is, if different speeds are 

 used for comparison, two factors (speed and loading condition) both of which 

 significantly affect the frequency of occurrence of slamming are involved in the 

 results, and hence we cannot identify which factor had the greatest effect on the 

 frequency. For example, the result of full scale trials introduced by Professor 

 Aertssen shows that the slam number for full loading condition is higher than 

 that for light loading condition. However, we cannot conclude from this result 

 that full loading is more severe than the light loading, since the speed was 

 higher for the full load than for the light load condition. It is also noted that the 

 slam number as defined by Professor Aertssen is expressed in terms of whip- 

 ping stress. This automatically includes the ship mass effect. In other words, 

 even if the ship motions are the same for two different drafts, whipping stresses 

 are quite different since the dynamic characteristics are entirely different. 

 Thus, we cannot identify which factor increased the slam number for full load- 

 ing. Thus, in order to obtain the effect of loading condition the same speed was 

 used for evaluating the frequency of occurrence of slamming for light and full 

 draft so that the difference in slamming rate could be attributed to the differ- 

 ence of ship motion characteristics. 



Mr. Vassilopoulos questioned whether or not the relative motion between 

 wave and ship bow is a narrow-band Gaussian process. It cannot be said, of 

 course, that the relative motion is a sharp narrow- band Gaussian process as is 

 frequently observed in strongly resonant vibratory systems. However, the fol- 

 lowing table may provide some information on this subject. 



The above table pertains to a ship speed of 10 knots and light draft condi- 

 tion. Since the expected frequencies lie in the domains of significant energy in 

 the observed spectra, it may be said that the relative motion can be treated as 

 a narrow-band Gaussian process. 



Mr. Vassilopoulos pointed out that the condition r > h be used instead of 

 r = H in Eq. (5) of the paper. Although the final result is the same for both 

 conditions, r > H is the correct expression. 



The author agrees with Mr. Vassilopoulos' opinion that the deck wetness 

 condition should be considered in the freeboard requirement. The author would 

 like to continue further studies of the effect of section shape on the magnitude of 

 threshold velocity as was suggested by Professor Lewis, although the values 

 obtained on five different ships have shown fairly consistent values. 



596 



