Free Surface Effects tn Hull Propeller Interaction 
Consequently, the increased value of 19/( -w) in Telfer's analysis 
would automatically lead to a lower value of mR: If we had started 
out with the conventional analysis yielding Ip<! , an opposite effect 
would have been achieved. Thus Telfer's analysis simply transfers to 
wake a part of the effect manifested in conventional analysis as rela- 
tive rotative efficiency, whether or not his argument is physically 
justified. 
Professor Telfer seems to interpret our results as provid- 
ing new evidence in favor of his hypothesis, This requires some clari- 
fication. First, it should be emphasized that our propulsion factors 
as depicted in Fig. 25 were derived by strictly conventional analysis 
and not by any special method as Professor Telfer seems to imply. 
Results for the three speeds chosen for detailed study are reproduc- 
ed below : 
Measured Measured in ieee ee oe 
behind hull at thrust ieee ee oe 
Speed 
parameter 
358 , ZO esate els). 95 
: . 636 Meee a 
. 124 Ae 1HO 615) 265 
If nominal wakes indicated by wake wheels (see III.6.2) had been used 
instead of the thrust identity wakes, the vache propulsion factors 
would have been obtained : 
From open-water at mean From open-water at0.7R 
nominal wake nominal wake 
