Propeller Excitation and Response of 230000 TDW Tankers 



For these kinds of tests it is further required to define the 

 loading cases for the propeller. In the present investigation two com- 

 binations of advance ratio J and cavitation number a were tested, 

 one corresponding to the values of J and effective wake w-p , obtained 

 from the propulsion tests in the towing tank, the other corresponding 

 to the predicted full scale values of J and w-pc . The prediction 

 method used for obtaining the latter values was discussed injjlj. 



The desired combination of J and a was realised in the tun- 

 nel by using thrust identity with the open water tests. 



Most of the tests in the tunnel were carried out at a water 

 speed of V = 4 m/s and an air content ratio of a. / a. s ~ 0.4, but 

 in some cases these parameters were varied. 



Non-Cavitatin g Flow : 



V. 3. Test Results , Pressure Fluctuations in Non-Cavitatin g Flow, 

 Comparison with Theoretical Calculations 



In Figure 12 the first harmonics of the pressure fluctuations 

 obtained for the model with fins, fitted with the six-bladed propeller, 

 are shown in fully loaded, as well as ballast condition. Amplitudes, 

 obtained in the following manner, are included in the diagram : 



A) Measurements in the towing tank, model speed 1.2 - 1.5 m/sec. 

 Amplitudes registered on oscillographic recorder, original signals. 

 These curves give the mean values over the speed range 11-18 knots. 



B) Measurements in the cavitation tunnel, water speed 4 m/sec. 

 J-value = J^owins tank ' Amplitudes registered on oscillographic re- 

 corder, filtered signals. Measuring accuracy about the same as in 

 towing tank. 



C) Theoretical calculations, carried out by SSPA. Wake influence 

 considered. Method of calculation described in \l~\ . 



D) Theoretical calculations, carried out by DnV. Wake influence 

 considered. Method of calculation described in [ji-9~] . 



From the diagram in Figure 12 it can be concluded that the 

 agreement between the measurements in cavitation tunnel and towing 

 tank is reasonably good. Also the agreement between calculation and 

 experiment is satisfactory. 



The influence of number of blades and fins on the pressure 



593 



