Free Surface Effects tn Hull Propeller Interactton 
where the sum of the first three termsas defined by (B32) is relatively 
easy to calculate . Thus we see that the calculation of thrust deduc- 
tion requires no further effort beyond that already expended for the 
calculation of hull wake and the wavemaking resistance of hull alone , 
propeller alone and the total system hull with propeller . In particular, 
it is needless to calculate the flow induced by the propeller on the hull. 
Note that 6pRwy, is the total potential thrust deduction , i.e. 
the sum of the so-called ''potential'' component (zero Froude number 
effect) and the ''wave'' component (finite Froude number effect) . 
The thrust deduction fraction becomes 
to Hplyes dSpRwy/Ly 
= (8,2, /K_.,) (V2/gD)*(v/nb)? 
2 4 2 
(6 PRwy/ Kpy) (L/D )2(F,) 4( yy) ae 
At zero Froude number , of course , 
Rwt = Rwy = Rwp = 9 
and therefore 
= R 
'pRwy Su “wP (B67) 
Thus if we use the zero Froude number wake (B54) in (B64) to 
calculate 5yRwp , we can determine the '"potential'' component of 
thrust deduction t, from the simple principle of reprocity (B67) 
already exploited by Dickmann (1939) 
It must be emphasized that the force 6;;Rwp apparently exer- 
ted on the propeller by the hull does not necessarily have a physical 
meaning since the source disk is an inappropriate model for calculat- 
ing propeller forces . However , it is a perfectly valid mathematical 
artifice for a simple , although indirect , determination of the quantity 
dpRwr which is a real force exerted on the hull due to propeller 
action, viz. the force of thrust deduction. 
1903 
