Propeller Excitation and Response of 230000 TDW Tankers 



DISCUSSION 



Harrison Lackenby 



British Ship Research Association 

 Wallsend 3 Northumberland, U.K. 



The paper is concerned primarily with the fluctuating pressure 

 forces acting on the hull surface. These are also, of course, the un- 

 steady forces and moments caused by the uneven wake distribution 

 which act on the stern bearing and also contribute to propeller excited 

 vibration. 



Figure 5 gives one of these, namely, the fluctuating thrust, 

 but there are also the fluctuating torque and the side forces and mo- 

 rn ent s . 



I should like to ask the authors whether they considered these 

 and wether measurements or calculations of them were made. 



Would they also care to express an opinion on the relative im- 

 portance of the hull-surface pressure fluctuations as against the bear- 

 ing forces and movements as affecting propeller excited vibration ? 



REPLY TO DISCUSSION 



Carl-Anders Johns son 



Statens Skeppsprovningsanstalt 

 Gbteborg 3 Sweden 



Calculations of different bearing forces were made at an early 

 stage of the project but reliable measurements were only made of the 

 thrust variations (and the mean thrust). 



The relative importance of the bearing and surface forces has 

 been discussed for many years and the investigations made indicate 

 that, in the non-cavitating case, they are of the same magnitude. 



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