SHIP MOTIONS 



193 



Legend 

 W.RI "Wave Profile Indicators 

 P.G. = Pressure Gage 

 ^ = Junc+ion Box 



30 W, His 



2P.GS 30WP.1S 3o^.p.,3 3p^p,^ 

 3P.GS 3pg3 3p(t,3 



-,n,., n, 30W.P.15 



30W,Pls 30W.P.1S ^PW.RIS jpQj 

 3PGs 3P.Gs 3P.Gs 



Fig. 31 Disposition of wave-profile indicators and pressure gages (from Admiralty Ship Welding Committee, 1953) 



lengths also were estimated from the i^eriods of encounter 

 using relationships \-alid for trochoidal \va\-es. "Fore- 

 east" estimates of swells made by the Admiralty Mete- 

 orological Department also were taken into account. 

 Wave profiles recorded on the ship's sides were used for 

 the detailed analysis of bending moments. 



When planning the sea trials, the Admiralty Ship 

 Welding Committee decidetl that the trials should ex- 

 tend o\'er a minimum period of 12 months. iMght round- 

 trip \'oyages were made cku'ing the pei'iod from Decem- 

 ber 29," li)45 to June 2, 1947. This period totalled 521 

 days, during which 290 days were spent at sea, 20o days 

 of which (i.e., o9 per cent of the total) were in the open 

 ocean. A study of eight cargo ships, chosen at random, 

 was made. On an a\'erage they were found to Ije in the 

 open ocean o5 per cent of the time. The voyages were 

 made between l^^nglish ports and the east coast of North 

 America (Montreal, New \'ork, and Boston), except 

 one voyage to Galveston, Tex. The conditions were 

 mostly mild, Init the sixth \-oyage was much rougher 

 than any of the others. Howe\-er, even on this voyage 

 a wind force of 8 to 9 f)n the Beaufort scale occurred only 

 on one day. 



Ship motions and ship stresses are affected mostly 

 by the ratio of the wave height to its length, generally 

 I'eferred to as "steepness." Fig. 37 shows the wa\-e 

 height plotted versus the wa\-e length taken from data 

 obtained by several observers. Fig. 38 shows the data 

 collected on voyages of the SS Ocean Vulcan. The 

 solid line on the latter figure corresponds to the dotted 

 one in F'ig. 37. 



A summary of the ship-molion data was gi\-en in 



C,B<t 



Fig. 32 Locations of wave-profile indicators ( — ) and of pres- 

 sure gages ( ) along contours of ship sections (from Admiralty 

 Ship Welding Committee, 1953) 



.Vdmiralty Shi]) Welding Conuuittee Report Xo. 8 

 as charts of am]>litudc and jjeriod disti'ibution. The 

 motions were generally mild. The greatest amplitude 

 of pitching obser\^ed diu'ing the trials was ±7.() deg. 

 The greatest angle of roll recorded throughout the trial 

 was 20 deg. The observations were made by photo- 

 gra])hically recfirding the instrument panel at inter\als 

 of about 0.4 sec so that continuous eui ves of pitching 



