Bavin, Vashkevich, and Miniovich 



DISCUSSION 



G. G. Cox 



Naval Ship Research and Development Center 

 Washington, D.C. 



The excellent agreement between experimental measurements and lifting- 

 surface calculations with uniform inflow shown in Fig. 4 is very encouraging, 

 and the authors are thanked for their fine work. This result will surely stimu- 

 late continuing efforts to develop lifting -surface theory and numerical proce- 

 dures for the varying wake situation. 



Do the authors intend to study this problem where the wake contains tan- 

 gentially varying components in addition to axially varying components? This 

 would, of course, imply experimental measurements behind a ship model rather 

 than a wake screen. 



It has been our experience at the Naval Ship Research and Development 

 Center that the theory for the freestream pressure field gave good results for- 

 ward of the propeller but not aft. This is outside the slipstream and was traced 

 to the loading effects. The thickness effects correlated very well. 



DISCUSSION 



J. p. Breslin 



Davidson Laboratory , Stevens Institute of Technology 



Hoboken, New York 



This paper by Mr. Bavin and his colleagues is a welcome addition to the 

 growing literature related to the excitation developed by propellers operating in 

 nonuniform inflow. We at Stevens Institute have been devoting considerable ef- 

 fort on this problem. About 1960 I first became aware of the interesting cou- 

 pling between the blade loading and the dipole propagation function in the propel- 

 ler pressure field integral. The significance of this is that in principle all of 

 the wake harmonics play a role in the makeup of the total blade frequency pres- 

 sure. For example in the case of a single-screw ship with a three-bladed pro- 

 peller the strong first, second, and fourth shaft harmonics of the wake will con- 

 tribute in addition to the mean loading arising from the zero shaft harmonics. 

 Thus these strong harmonics of the wake will contribute to the surface forces. 

 In contrast the shaft forces and torques arise only from the second, third, and 

 fourth harmonics of shaft frequency. 



To give some idea of the importance of the various harmonics I have re- 

 cently calculated the lateral form induced on a cylindrical hull by a propeller 

 in a wake. Here the loading is taken from the solution by unsteady lifting sur- 

 face theory carried out by S. Tsakonas and W. Jacobs. 



14 



