Johnsson and Stfntvedt 



place, you could have corrected the wake by the method you used for 

 your lifting line calculations and, in the second place, it is not appa- 

 rent that including non-linearity would improve the comparisons, 

 since it would seem to me that non-linearities would cut off the peaks 

 of the amplitudes. I am not saying we should not include non-lineari- 

 ties in the theory, but in the light of your results, I do not see how 

 you can draw this conclusion. 



I am also disappointed that in a paper of this kind, since a 

 brief discussion was given of the effect of the propeller on the wake, 

 nothing was said about scale effect on wake, which may be much more 

 important than the effect of the propeller on the wake. The data in 

 Figure 11 from the tunnel where you ran two different speeds indicates 

 that this effect might be enormous. Do the authors have any comments 

 on the scale effect on wake on high block ships when the scale ratio is 

 so high ? 



REPLY TO DISCUSSION 



Carl-Anders Johnsson 



Statens Skeppsprovningsanstalt 

 Gotebovg, Sweden 



Regarding the model and full scale pressure fluctuations it is 

 concluded from the results in Figures 14-17 that they agree well in 

 fully loaded condition. This applies to the maximum peak to peak va- 

 lues, as well as the first harmonic, values of the latter, however, 

 being available in full scale only for the six-bladed propeller. In bal- 

 last condition the amplitudes were smaller in model scale. 



The lifting surface method used for the theoretical calcula- 

 tions, the results of which are shown in Figure 24, is that of Tsakonas, 

 The aim of this Figure is to show the importance of including the inter- 

 action between the propeller and the wake in the calculations. This is 

 done in a simple manner assuming continuity along a streamline, the 

 method being similar to that used when designing contra -rotating pro- 

 pellers. It must, however, be confessed that the effect of such a cor- 

 rection is unusually pronounced in the present case, the reason being 

 that there is a rather rapid change in the radial and peripherical wake 

 distributions just outside the propeller disk. 



656 



