a. For given amplitudes of waves and pitching the maximum values 

 of the time-average loads per revolution, peak loads, and the periodic 

 variation of loads with angular position vary substantially depending 

 upon the difference in phase between the hull pitch and the wave at the 

 propeller. The time-average loads, peak loads, and periodic loads are 

 near their respective greatest values for any difference in phase where- 

 by the crest of the wave reaches the propeller between 0.3 and -0.1 of 

 the period of encounter before the maximum stem-up position. 



b. Linear superposition of the increases in blade loads due to 

 pitching in calm water and due to waves without hull pitching, taking 

 into account the phase between the waves and the pitching, gives a sat- 

 isfactory, or slightly conservative, estimate of the net increase in 

 blade loads due to operation in waves with hull pitching. For engineer- 

 ing calculations, it is recommended that the absolute values of the 

 maximum increases in time-average, peak, and periodic loads due to the 

 separate influences of waves and hull pitching be added without regard 

 to the relative phase between the wave and the hull pitching. 



IV. DISCUSSION 



The results presented in this paper showing the effects of hull 

 pitching and waves on the dominant once per propeller revolution varia- 

 tion of loads provide extensive insight to the flow patterns in the 

 propeller plane under these conditions. These data and insights should 

 form a basis for developing and validating a computational procedure for 

 predicting blade loads under these conditions. 



The experimental results presented here are applicable to only high 

 speed transom stern configurations. The Influences of the hull bound- 

 ary of more complex stern geometries, such as for full stem cargo 

 ships, are more complex. Experiments of the type described in this 

 paper would serve as a valuable guide for validating any computational 

 procedure applied to cargo ships. 



The prediction of the modulation of bearing loads due to waves and 

 pitching cannot be performed using the simple procedures described in 

 this paper. More elaborate models of the interaction between the pro- 

 peller wake and the waves and pitching influences may capture the 

 fundamental nature of the modulation of the bearing loads. 



All results presented in this paper are in the absence of cavita- 

 tion. It is anticipated that if cavitation were sufficiently extensive 

 to influence blade loads it would reduce the maximum time-average and 

 periodic loads. Therefore, it is judged that neglecting cavitation 

 results in a conservative estimate of maximum loads. 



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