Free Surface Effects tn Hull Propeller Interactton 
The dependency of the wake uponthe Froude number was an important 
finding by F.Horn, several times published by him and his school, 
also in English, and recommended as design principle. The authors 
being thoroughly familiar with the German school, I would prefer a 
statement that their findings nicely support these well known results. 
It is a matter of opinion and of considerable importance with 
regard to scale effects that the difference between measured and cal- 
culated t-values is due to an appreciable viscous component, 
Ivchenko corrected the disagreement by a factor caused by non unifor- 
mity and unsteadiness. As pointed out by the authors here much re- 
mains to be done. 
DISCUSSION 
Kiaus W. Eggers 
Institut fiir Schtffbau der Untversttdt Hamburg 
Hamburg, Federal Republte Germany 
I have a short comment regarding the analytical method for 
determining the wave-thrust deduction, which was performed here 
following Eq. (B65) in order to avoid explicit calculation of the flow 
generated by the propeller singularity at the hull surface. I want to 
suggest a more elegant and direct method. As the wave flow generat- 
ed by the hull within the propeller area is available through closed 
form integration over the hull, the wave induced drag on the hull due 
to the propeller field can easily be calculated as a Lagally-force on 
the propeller singularities induced by the inverse flow due to the hull. 
i.e. the flow for the case that the ship travels astern with the same 
speed. I wonder if such a calculation would confirm the numerical re- 
sults obtained so far only indirectly through (B65). 
1949 
