Ochi 



4 6 8 



Pressure in PSI 



Fig. 20 - Histogram of pressure ex- 

 perienced on deck due to green water 

 (high speed research ship, Sea State 6, 

 ship speed 20 knots, design draft) 



forward perpendicular is 23.7 ft. Tests were made in a head Sea State 6, at 20- 

 knot ship speed [11]. (All values have been converted to those for a 400-ft ship.] 

 In these tests, 36 deck wetnesses were observed in 236 wave encounters, hence 

 the probability of deck wetness per cycle of wave encounter was 0.153. For 

 computing the pressures by Eqs. (30) through (32), the variance of the relative 

 motion was estimated from Eq. (26) by using the above probability. 



On the basis of the reasonable agreement between theory and experiment 

 shown in Figs. 19 and 20, it may be concluded that the pressure associated with 

 green water on the deck follows a modified Rayleigh probability law. 



CONCLUSIONS 



A theoretical study was made to predict the probability of occurrence and 

 severity of ship slamming, and the time interval between successive slams in 

 rough seas. The theory was also applied to the deck wetness problem. The 

 theoretical results were compared with experimental results obtained from 

 tests conducted on a 13-ft MARINER model. On the basis of the results of this 

 study, the following conclusions are drawn: 



1 . The linear theory of superposition of ship motion in waves may be used 

 to obtain realistic engineering estimates of frequency and intensity of slamming 



578 



