Free Surface Effects tn Hull Propeller Interactton 
14) From the now known source representations of the hull 
and propeller free-wave spectrum and wavemaking resistance are cal- 
culated and compared with the corresponding results of the Fourier 
analysis of the wave profiles measured in step E5. This provides a 
check on the principle of linear superposition of hull and propeller 
waves, 
15) The mutual flow patterns of hull and propeller can now 
be calculated and thence by Lagally's theorem the potential and wave 
thrust deduction. 
16) Finally the viscous component of thrust deduction can be 
estimated indirectly by subtracting the potential and wave components 
from the total thrust deduction of step I1. 
III. DISCUSSION OF RESULTS 
III. 1. Choice of Hull and Propeller 
Since our work was to consist essentially of a single concrete 
example of the actual application of the sequence of operations out- 
lined in the previous section it was rather important to choose as in- 
structive and useful an example as possible. After considering various 
alternatives we finally selected the somewhat idealized hull propeller 
configuration of Figure 1 that has a sufficiently simple geometry for 
the ease of theoretical calculations and yet quite realistic proportions 
for the results to be of practical value. The arguments leading to this 
choice can be summarized as follows. 
In order to keep the wavemaking calculations manageable it 
was decided to use a symmetric hull form with parabolic waterlines 
and frames. The wetted surface is then defined by the equation 
y apf - (2x/4)™} 41 - (-2/7)" (3) 
The hull above water is a simple continuation of the underwater form 
with vertical sidewalls. The integer powers m,n and the form ratios 
L/B, B/T were chosen to satisfy the following requirements : 
1) sufficiently thin hull for linearized theory to be valid, 2) sufficient- 
ly large angle of run to get measurable interaction with the propeller, 
and 3) realistic value of block coefficient. 
This led to the following set of parameters : 
1851 
