Table 10 SS Gopher Mariner — Excerpts of Data for Several Severe Sea Conditions 



1 



s 



1 



Date, Time 



Location 

 Appiox. 



Direction Rel 

 loShip 

 Est'd 



Wind and Sea 

 Observed Cond. 



Computed Data for Waves 

 Fully Developed Under 

 Observed Conditions* 



1 



i 



1 



Number of Cyclic Stress Variations Falling Between Given Limits 

 Stresses Were Measured at Main Deck Near Amidships" 



J 



§ 



1 

 1 



s 



-g 



1 





^ e 



1 



jl 



J- e 



1 



i 



1 



^ 



4000 psi to 

 6000 psi 



6000 psi lo 

 8000 psi 



8000 psr lo 

 10,000 psi 



10,000 psi to 

 12,000 psi 



12,000 PSI to 

 20,000 PSI 



Over 

 20,000 psi 



Port 



Stbd 



Port 



Slbd 



Port 



Stbd 



Port 



Slbd 



Port 



Stbd 



Port 



stbd 



E 



2 



13-14 



0600 



47 

 N 



11.8 

 W 



Port 

 Beam 



Port 

 Beam 



6' 



0-37 



1400 



750 



37.5 



12.2 



14.0 



8 



30 



3M 



1822 



6 



415 







38 



























W 



2 



25-26 



0400 



48.4 

 N 



8 

 W 



Stbd 

 Bow 



Stbd 

 Bow 



62 



37 



1800 



800 



39.0 



12.6 



14.1 



18 



33 



1339 



1595 



109 



181 



22 



18 







3 



















w 



3 



4- 5 



1245 



35 



N 



67 

 W 



Port 

 Bow 



Port 

 Bow 



5' 



30 



450 



360 



26.1 



8.4 



7.0 



8 



5 



298 



918 







157 



8 



24 



3 



12 







3 











w 



4 



8- 9 



1130 



49 



19 



W 



Bow 



Bow 



10 



23 



2100 



570 



32.5 



10.5 



8.7 



12 



10 



1061 



1819 



83 



314 



21 



35 



3 



20 



















w 



4 



13-14 



1000 



41 

 N 



57 

 W 





4-5 



4-27 



350 



- 



- 



- 



- 



6 



15 



144 



446 



8 



6 



7 



14 







8 







1 







1 





Notes Taken from Ship's Log 

 '2100, 13 Feb lo 0100, U Feb, Greenwich Time; Vessel rolling very heavily and yawing wiilely in very hi|h W-tlW sea and very high NW swells. 

 ^000 lo 0800, 26 Feb, Greenwich Time; Very rough and high W-NW seas. Long, heavy NW swells. Vessel rolling and pitching very heavily, yawing moderately and shipping 



water over bow and slbd side. 

 ^0900 to 1300, 5 r^arch, Greenwich Time: Vessel pitching heavily and pounding occasionally. Shipping water over bow and port side of main deck. Very rough westerly seas and 



short high westerly swells. Reduce speed to ease vessel. 



tSea State Code as given by Hydrographic Otfice Publication No. 606-e publistied 1950 



•Computed from diagrams 1 and III of "The Forecasting of Sea and Swell Waves" tlaval Weather Service Memorandum f^o. 135/45, Admiralty, London, 1945. 

 ••These are the totat number of cyclic variations recorded during the given day. 



is approximately of the form given by Equation 

 [1 ] and that the cumulative distribution functions 

 of both the underlying and the extreme-value 

 distributions are compatible. 



It is concluded, on the basis of these several 

 tests of significance, that the basic hypothesis to 

 be tested is "probably" true; that is, the loga- 

 rithm of the sea-induced stresses is, at least approx- 

 imately, normally distributed. 



USS Fessenden 



The cumulative distribution function of stress 

 variation was obtained from data measured dur- 

 ing the periods December 1952 to April 1953 and 

 October 1954 to November 1954. The vessel was 

 instrumented with a 10-in. mechanical statistical 

 strain gage and counter (2). The measured 

 data are given in Table 9 and the corresponding 

 distribution pattern is shown in Fig. 18. The 

 deviation of the plotted experimental points 

 from the hypothetical distribution, which was 

 computed from the measured data on the as- 

 sumption that the stresses do follow the log-normal 

 distribution, was within the accuracy of meas- 

 urement. Thus it may be concluded, for the 

 USS Fessenden, that the distribution of hull- 

 girder stresses or bending moments can be ap- 

 proximated by a log-normal distribution. 



SS Ocean Vulcan 



This vessel has been subjected to extensive sea 

 tests. The general construction of the vessel 



as well as the statistical strain gage installed 

 thereon have been described elsewhere (21). 

 Stress variations which were measured over a 

 period of 23/^ years, have been reported in refer- 

 ence (7) from which the values given in Table 9 

 have been taken. Owing to the high degree of 

 truncation of the data, it was thought best to 

 estimate the degree of truncation from the meas- 

 ured average period of stress variation. The data 

 for this vessel appear to follow the log-normal dis- 

 tribution. Fig. 18. 



55 Gopher Mariner 



This vessel was instrumented with two TMB 

 mechanical strain-cycle gages and counters (2). 

 Measurements were made during six consecutive 

 transatlantic crossings, during which the vessel 

 encountered several days of very rough weather. 

 Excerpts of data are given in Table 10 in order to 

 give some idea as to the environmental conditions 

 encountered. The degree of truncation of the 

 data was estimated from the estimated average 

 period of stress variation. Fig. 18 indicates no 

 disagreement with the assumption that the log- 

 normal distribution applies. 



Destroyer 



The cumulative distribution of hull stress ex- 

 perienced amidships in the keel of a destroyer was 

 obtained from measurements made during the 

 winter season '55-'56 during operations in the 

 North Atlantic Ocean. The strains were meas- 



29 



