Nowackt and Sharma 
DISCUSSION 
Georg P. Weinblum 
Institut fiir Sehiffbau der Untversttdt Hamburg 
Hamburg, Federal Republie Germany 
There exists a small number of investigations on the inter- 
action problem of the complete system hull-propeller-rudder. Herbert 
Voigt showed (JSTG 1932) that the thrust deduction t ofa single 
screw ship with an old fashioned square rudder post and a plate rud- 
der could be appreciably reduced by fitting a stream lined rudder. 
Results of a systematic investigation of the ''complete'' problem have 
been published by Ivchenko (publications of the Krylov Institute, 
Ship hydrodynamics II ; unfortunately, I was unable to obtain the re- 
port by the same author which show the pertinent proofs, Krylov Ins- 
titute, No 146). Ivchenko's findings are supported by extended expe- 
rimental work. 
Most advanced ideas on the subject are due to Yamazaki ; 
the first of a general and therefore rather programmatic character, 
the second one presenting the application of theory to a thin ship, 
showing an unexpected increase of t due to a streamlined rudder. 
Because of the complex character of our problem the authors 
justly restrict themselves to the classical hull-propeller system, 
emphasizing free surface effects while a recent paper by Dyne treats 
pertinent scale effects. It may be permitted to state, that the authors 
lived up to the high standard, set by Dickmann in his classical work 
on the subject. Especially they used all modern methods partially de- 
veloped by them and were not anxious to perform tedious calculations 
to obtain quantitative results. The choice of a simplified mathematic - 
al model is justified by the fundamental character of the investigation 
leading to the conclusion (Fig. 30), following which the wave thrust 
deduction t,. contrary to Dickmann's conjecture becomes heavily 
dependent pod the Froude number for F,=0.30. Indications of this 
dependence ty(Fn) have been communicated by Pien (SNAME Jubilee 
meeting, 1968). Because of the extremely bad wave making properties 
of the model this speed limit may be higher and the effect much less 
pronounced with usual practical forms, I disagree with the authors 
statement in concluding remarks that ''contrary to common belief 
the wave component can be dominant in the wake.... at F,#0.3". 
1948 
