Johnsson and Srfntvedt 



These results show the beneficial influence of the fins and it is 

 further evident that the amplitudes in ballast condition are larger than 

 in fully loaded condition. 



In Figure 6 the two ship configurations having five-bladed 

 (first ship) and six-bladed (second ship) propellers are compared, 

 both being fitted with fins. The results were obtained for the trans- 

 ducers 4 and 2 respectively, which were placed at the bottom of the 

 fin, on the starboard side, close to the centerline of the ship. The 

 positions were slightly different for the two ships, as is shown in 

 Table II and Figure 2. The difference is, however, small enough to 

 allow direct comparison of the results. 



The positions correspond approximately to measuring point D 

 in model scale. The diagram shows that the pressure fluctuations 

 measured on the two ships are very similar, in spite of the fact that 

 the first ship was equipped with a five-bladed and the second with a 

 six-bladed propeller. In fully loaded condition the six-bladed propel- 

 ler caused somewhat larger amplitudes than the five-bladed. (The 

 fact that only the second ship was fitted with bilge keels is not consi- 

 dered when making this comparison). 



A sample record, obtained at the full scale measurements, is 

 shown in Figure 8. 



Propeller cavitation 



Some of the photographs taken during the trials with "Norse 

 King" were reproduced and discussed in [_4J . In the present report 

 some sketches based on these photographs are given in Figures 14 

 and 17 together with the results of the measurements of the pressure 

 fluctuations and the corresponding cavitation patterns, obtained at the 

 model tests. 



Noise Level in the Afterbod y 



The noise level in the afterbody of "Thor shammer" is of a 

 transient type, varying directly as the vibratory response in the struc- 

 ture of the ship and the recorded pressure fluctuations. This observa- 

 tion is valid for the ship with and without fins installed. 



The noise level onboard "Norse King" is stable (mainly pulses 

 of short duration, occurence frequency equal to blade frequency) in 

 the higher speed range (70-85 RPM). 



590 



