300 



THEORY OF SEAKEEPING 



■■ Total number of counts was approximately 193,300. 



ally touching Iceland. The parts of the ocean and the 

 times of the year co\'ered by these \'oyages are known for 

 the great frequency of adverse weather. 



Lewis' (1957c) tabulations mcluded all days of the 

 voyages and all stress ranges just cited. The abstract 

 of these data, is given in Tables 12 and 13 and includes 

 only the data on stress ranges exceeding 8000 psi. 

 Figs. 46 and 47 show the number of counts per day of 

 stress ranges between 8000 and 12,000 plotted against 

 average wind force for head seas and for beam, quarter- 

 ing and following seas, respectively. 



A perusal of the described material shows that : 



1 The stress range of 12,000 psi is exceeded in a 

 relatively small number of cases. There is but a single 

 reading over lfi,000 psi. 



2 The number of stress counts in the range 8-12,000 

 psi in head and l)cam seas increases with wind force. 



3 At the wind strength 7, the stress range 8-12,000 



psi is encountered more often in beam seas than in head 

 seas. 



4 The stress range 8-12,000 psi is encountered in all 

 sea directions and in all winds from Beaufort 1 to 11. 



5 Sea dii'ections and wind strength appear to affect 

 onlv the freriuencj' of occurrence of stress in this range 

 and not the stress level. 



6 The conventional method of describing wind and 

 sea does not provide indication of stress magnitude, 

 although it provides indication of the frequency of the 

 stress occurrence. 



The difference in stress response of two apparently 

 identical ships is of interest. In the SS Mormacpenn 

 the stress range 8-12,000 psi was encountered 9 times 

 more often (in relation to the total number of counts) 

 than on the SS Mormacmail. The stress range 12-16,000 

 psi was encoiuitered 20 times more often. 



The author had the privilege of being aboard the SS 



