of F , the amplitudes of which range from 2 to 13 percent of the time- 

 average value, also explain some of the complexity of the wave forms 

 shown in Figure 16. These harmonics have consistent variations in phase 

 angles of up to 45 degrees. 



G. Operation in Waves With Hull Pitching 



As discussed in the section on experimental conditions and pro- 

 cedures, for forced pitching in waves the phase of the wave at the pro- 

 peller $^ was varied relative to the phase of the hull pitching $^. 

 Three relative phases were evaluated: 



a. Wave crest at the propeller plane when the stern of the model 

 hull is pitched up at its maximum value, "S^ - $^ = (Condition 4 in 

 Table 1) , 



b. Wave crest at the propeller plane when the stern of the model 

 hull is pitched down at its maximum values, *r- - ^^ = 180 degrees (Con- 

 dition 5 in Table 1) , and 



c. Wave crest at the propeller plane when the hull pitch is pass- 

 ing through its mean value (^^^ - ^mtn^'^^ from stern down to stern up, 

 ^C ~ ^i) ~ ^^ degrees (Condition 6 in Table 1) . 



Experiments for each of these conditions were conducted at the 

 same model speed, propeller rotation speed, pitching period, wave 

 period of encounter as were the condition in calm water with hull pitch- 

 ing, and in waves without hull pitching, as described in the preceding 

 sections (see Table 1). However, in order to ensure a large influence 

 of the pitching or waves on blade loads while not flooding the model 

 hull, it was necessary to run each of the four pitching conditions with 

 a different pitch amplitude ij;^, and each of the four conditions in 

 waves with a different wave amplitude ^a (see Table 1) . 



The primary objectives of this portion of the experimental program 

 were: 



a. To determine the validity of linearly superimposing the in- 

 crease in blade loads due to pitching in calm water, and the increase 

 in blade loads due to waves without hull pitching, to obtain the net 

 increase in blade loads due to hull pitching in waves, 



b. To determine the influence of the phase of the hull pitch 

 relative to the phase of the wave ($^ - $^l) on the maximum absolute 

 values of the peak, unsteady and time-average blade loads, and 



c. To determine the values of ($^ - (J>^) which result in the 

 largest values of peak, unsteady and time-average blade loads for dif- 

 ferent relative values of pitching amplitude iip^ and nondimensional 

 wave amplitude, C^/Lpp. 



Therefore, the experimental results will be discussed and interpreted 

 from the viewpoint of these three objectives. 



In order to determine the validity of linearly superimposing the 

 increase in blade loads due to the pitching only and the increase in 

 blade loads due to waves only, the experimental results with hull pitch- 

 ing in calm water and the experimental results in waves without hull 

 pitching were linearly combined to simulate the blade loads for the 



