Propeller Excitation and Response of 230000 TDW Tankers 



the distances of interest from the cavity volumes an asymptotic repre- 

 sentation of these by pulsating point sources should be quite exact. 

 Thus I find the principal contribution to be due to the second-time de- 

 rivative of the cavity volume and "the secondary" term arising from 

 convection to be proportional to the first time derivative of the cavity 

 volumes. The basic problem of first magnitude is to calculate these 

 derivatives. Essentially I think they should be measured from three- 

 view high speed photographs. 



Finally, I hope that the authors will detail their method for 

 accounting for the induction effects on the ship wake since their com- 

 parison with the measurements exhibited in Figure 24 is certainly 

 fantastic ! 



REPLY TO DISCUSSION 



Carl -Anders Johns son 



Statens Skeppsprovningsanstalt 

 Goteborg 3 Sweden 



We think that most of the points raised by Professor Breslin 

 are covered by our answer to Dr Morgan. 



However, we certainly do not want to attack the unsteady lift- 

 ing surface program developed at Davidson Laboratory. We are fully 

 aware of its capabilities in dealing with wake components of order 

 enabling force transfer to the shaft for most grid wakes available. We 

 like to repeat that no method can work correctly with wrong boundary 

 conditions e. g. the inlet wake containing no radial variations of the 

 wake outside the propeller disc and the slip stream assumed to have 

 constant radius and moving in axial direction. 



By application of momentum theory the change in propeller 

 load may be illustrated to be large. The authors cannot agree with 

 Professor Breslin' s word "fantastic" and hope that we have succeed- 

 ed in illustrating a simple physical concept used in the theory. 



665 



