Johnsson and Stfntvedt 



From the diagrams in Figures 22 and 23 it is evident that the 

 maximum extent of cavitation in different blade positions is rather 

 similar for the different hull -propeller configurations. 



The main difference between the cavitation patterns for the 

 five- and six-bladed propellers seems to be that, for the five-bladed 

 propeller, the extension of the cavitation was more fluctuating with 

 time than for the six-bladed. This may be one explanation of the fact 

 that the high pressure pulses from the five-bladed propeller were of 

 such a short duration that they were not manifested on the registra- 

 tions of the filtered signals. It should also be mentioned that rather 

 small band widths were used when filtering the signals. 



The extension of the cavitation was rather similar, whether 

 the model was fitted with fins or not. In spite of this a beneficial in- 

 fluence of the fins could be noted on the amplitudes of the pressure 

 fluctuations. 



A type of cavitation, which is regarded as important in connec- 

 tion with fluctuating pressures on the hull, is the so called propeller - 

 hull - vortex cavitation Ql J . This type of cavitation was observed fre- 

 quently during the tests, but to about the same extent for the two pro- 

 pellers. This kind of cavitation was probably present during the full 

 scale trials with the first ship, see Ll2j , but could not be observed on 

 the second ship, when making visual observations in connection with 

 the photographing of cavitation. 



VI. CAVITATION PATTERNS AND PRESSURE FLUCTUATIONS, 

 THEORETICAL CALCULATIONS AND COMPARISON WITH 

 EXPERIMENTS 



VI. 1 . Calculation of Circulation Distributions 



Proper results for hydrodynamic loading particulars require 

 the solution of a complicated lifting surface problem. With boundary 

 layer aspects included, the downwash surface integral equation for a 

 twisted wing of finite span should ideally be completely solved. 



The importance of obtaining a reliable method for prediction 

 of external loading was strongly emphasized by various authorities 

 some years ago. Research was then initiated in Scandinavia to meet 

 this demand along the following lines of approach : A method of cal- 

 culation was desired, which should be able to reproduce open water 

 diagrams within experimental accuracy for all relevant values of J . 

 By combining unsteady effects, effects of curved flow and interaction 

 with the inlet wake field one should then be able to simulate experi- 



598 



