192 



THEORY OF SEAKEEPING 



Table 6 Summary of Instruments Used on MS Ocean Vulcan 

 (from Admiralty Ship Welding Committee, 1953) 



T3 

 u 

 O 



EFFECT TO BE MEASURED 



INSTRUMENTS FITTED 



Normal water pressure 



Wave profiles at ship's 

 side 



Accelerations 



Angles of roll and pitch 



Angles of yaw . . 



Wind force ano direction 



Ship's speed 



Engine revolutions 



Shaft horse power 



Stresses un transverhe 

 section near amidships 



63 pressure gauges 



700 wave profile indicators 

 arranged on 12 transverse sec- 

 tions 



4 accelerometers, each capable of 

 measuring accelerations in three 

 directions 



Gyroscopic roll and pitch re- 

 corders 



Repeater from ship's gyro-com- 

 pass 



3 anemometers 



Chernikecll log (also ship's Walker 

 lot;) 



Tachometer on main shaft 



Ford torsionmeter, also strain 

 gauges on shaft 



'20 complete groups of strain 

 gauges giving a heart of plate 

 stress 



Survey of wave heights 



Stresses and accelera- 

 tions at particular 

 places 



Statistical data on mag- 

 nitude and frequency 

 occurrence of large 

 waves 



Slamming phenomena . , 



One pair of cameras for stereo- 

 photography 



Two portable strain gauges and 

 one portable accelerometer 



An automatic statistical gauge 

 (fitted after sixth voyage) 



Visual observations of pressure 

 gauges, stress gauges, accelero- 

 meters, etc. 



IM Hogging and Sagging Tests on A11-\V('](1(>(1 



Tanker JNIV Neverita. 

 R.2 Hogging and Sagging Tests on Iiivetcd Tanker 



MV Newcombia. 

 R.6 Ocean Vulcan Static Expei'inients. 

 R.7 Clan Alpine Static Experiments. 

 R.8 SS Ocean ]'ulcan sea Trials. 

 R.9 1 

 R.IO- Detailed Analysis of Ocean \'utcun Sea Trials 



R.in 



R.l'-' Structnral Trials on SS Ocean Vnlran and SS 

 Clan Alpine. Discnssion and resnlts. 



Report No. 8, prepared by F. B. Bnll (lOS;!), is par- 

 ticularly relevant to the subject of the present mono- 

 graph. Since the report is of recent origin and is readily 

 available, only a brief description will be given here. 

 Observations pertaining to the structural loading and 



stresses will he for tlu> most part deferred until Chapter 

 5. In this chapter attention is concentralcd on sliip 

 motions. 



The SS Ocean Vulcan is a largely welded ship built 

 in 1924 in the United States for the British go\-ernment. 

 The design is based on a small standard British 10, 000- 

 ton tramp design, of which the riveted SS Clan Alpine 

 is typical. These shijis are close to American Lilierty 

 ships. The ])rinci))al dimensions are: 



Length BP, ft -in 41G-0 



Breadth molded, ft -in .5()-10V4 



Draft molded (Summer), ft-in 20-1078 



Displacement (Summer), tons 18752 



I'jUgine; triple-ex))ansioii reciprocating, ihp. . . . 2500 



The ship was instrumented extensively. A list of 

 instruments is given in Table 6 and the arrangement of 

 the instruments is shown in Figs. 30 and ol. The dis- 

 position of the wave-profile indicators and the pressure 

 gages along the contours of the ship's sections is shown 

 in Figs. 82, 88 and 84. 



Most of the relationships between stresses and im- 

 jjosed loads were to be obtained by static tests in smooth 

 water. The sea trials of the SS Ocean Vulcan were 

 conducted for the primary pvirpose of evaluating loads 

 impo>ed on the ship structure by waves. The loads 

 were evaluated from records of pressure gages, wave- 

 profile indicators, and accelerometers. However, a 

 ship section at frame 77 1 2 was instrumented with strain 

 gages tlisposed as shown in Fig. 85. Fig. 8fi shows the 

 (■onii)arison of bending moments deduced from strain 

 gages with those deduced from jjressure gages, accel- 

 erometers, and so on. 



The instrumentation was designed for recoriling water 

 pressures and relati\-ely long-period acceleration cycles, 

 disregarding such rapidly occurring phenomena as 

 slamming. Under these conditions correct accelerometer 

 readings were obtained l)y using pick-ups designed to 

 ha\'ea short resonant period (SOcps). 



Cameras for stereophotographic measurements were 

 installed. The shutters of the camera were synchronized 

 electrically, while the hlm-winding mechanism was 

 power-driven and set to make exposures automatically 

 at about 2-sec intervals. The cameras were in exposed 

 ])ositions on the flying bridge and were difficult to main- 

 tain in working order despite the protection pro\'ided. 

 It was not considered worth while to take records undei' 

 mild or moderate sea conditions since the analysis of 

 such cases would be ilifficult owing to the ab.sence of 

 identifiable features in the .sea. During .-ievere weather 

 the stereophotogiaphy was hindered by rain and spray 

 collecting on the lenses. On the whole the results were 

 unsatisfactory although some successful records were 

 obtained. The.se did not represent maximum sea con- 

 ditions. The I'cmarks made in reference to Weinbhrnt 

 and Block's (1U8()) stereophotographic data (Section 

 5.12) also apply to those for the SS Ocean ]'iili'(in. 



Most sea conditions were ol)tained by visual observa- 

 tions of the wa\-e length, height, and direction. Wave 



