Nowaekt and Sharma 
and that his formula is likely to yield a better approximation to the 
source density of a moderately loaded propeller. As we have provid- 
ed two complete sets of calculations, one based on Dickmann's uni- 
form sink disk and the other on the Hough and Ordway generalized 
sink disk, and since Dr. Dyne's approximation would lie between 
these two extremes, we do not consider it necessary to provide a 
third set of calculations at this time. However, it is interesting to 
observe that the reduced source strengths following Dr. Dyne would 
lead to calculated values of the thrust deduction fraction (t_ + to) 
which are substantially lower than the measured value of t, asis 
also the case in Dr. Dyne's (1972) paper. It is unlikely that such large 
differences can be attributed soleley to the viscous component t,. 
This suggests that it would probably be necessary to invoke a mathe- 
matical propeller model involving finite chord length and finite blade 
number even for calculating such ''simple"' time-averaged effects as 
the thrust deduction. Professor Weinblum's reference to Ivchenko's 
hypothesis that the discrepancy between calculated and measured 
thrust deduction might be due to unsteady effects is a valuable hint in 
this direction. 
Dr. Dyne further suggests that the oscillations of the measur- 
ed thrust deduction with respect to Froude number observed in our 
Figure 30 might simply reflect random measuring errors. We beg to 
disagree, As explained in the paper (see Figure 23) the propulsion 
factors at the ship self-propulsion point were not determined from 
single runs but by least squares polynomial interpolation between 
five or more measurements at different loadings. It is unlikely that 
such faired results would randomly produce oscillations with respect 
to Froude number in obvious correlation with the calculated wave re- 
sistance and wake, 
We agree with Dr. Dyne that our theoretical wavemaking 
calculations probably represent upper bounds for the true magnitude 
of these effects ina real fluid. Finally, we regret that we are not 
contemplating a follow-up investigation of our wake by means of Pitot 
tubes as suggested by Dr. Dyne, but we would consider it a valuable 
extension if others working on this problem would care to do so. 
REFERENCES 
BEVERIDGE, J.L., ''Performance of wake-adapted propellers in 
open-water and propulsion conditions as determined by theory and 
experiment'', DTMB Report N° 1777 (1963a). 
1960 
