free surface and modification of the flow pattern into the propeller 

 disk. This flow pattern is influenced by (1) direct orbital velocities 

 from the ocean waves, (2) relative velocities of the propeller due to 

 ship motions, and (3) modification of the hull wake pattern due to the 

 ship motions in the rough sea. 



In general, the rough sea modulates the amplitudes of the periodic 

 loadings on the propeller blades and bearings from the corresponding 

 values in calm water. The periodic loads on individual blades, includ- 

 ing modulation by a rough sea, must be considered in the design of the 

 propeller blades from consideration of fatigue. This is especially 

 important for controllable pitch (CP) propellers. Periodic bearing 

 forces, including modulation by a rough sea, are important for consid- 

 eration of ship vibration, especially in the main propulsion system, 

 noise, and fatigue strength of components of the main propulsion system. 

 Extreme modulation of the periodic thrust in the main propulsion shaft- 

 ing can result in reversals of the thrust on the main thrust bearing 

 which can cause extensive damage. 



Procedures for calculating periodic propeller blade and bearing 

 loads in calm water are reasonably well refined. These procedures have 

 been summarized by Boswell et al. (1968, 1981), Breslin (1972), and 

 Schwanecke (1975) . 



Procedures for calculating the blade and bearing loads in a seaway 

 are much less refined than for steady operation in calm water. Lipis 

 (1975) and Tasaki (1975) review the mechanisms and procedures for pre- 

 dicting the effect of the seaway on periodic bearing forces which, in 

 principle, also apply to unsteady loading on an individual blade. Keil 

 et al. (1972), Watanabe et al. (1973), and Lipis (1975) present data 

 from strain measurements on the blades of full-scale propellers in both 

 calm and rough seas. Gray (1981) presents the modulation of blade rate 

 hull vibration due to ship motion in a seaway. 



These existing data and procedures provide valuable information 

 regarding increases in periodic blade and bearing loads due to operation 

 in a seaway. However, they address the overall complex problem in a 

 statistical manner including the net influence of a complex sea state, 

 complex ship responses, and numerous interactions. However, to the 

 authors' knowledge, before the present study there were no experimental 

 measurements of periodic loads on individual propeller blades that 

 demonstrated the influence of waves and ship motions in a controlled 

 environment . 



An extensive systematic model experimental program was undertaken 

 to obtain fundamental information on the influences of rough water and 

 ship motions on periodic propeller blade loads on high speed open-shaft 

 transom stern configurations. The experiments were conducted under 

 carefully controlled idealized conditions in which sinusoidal hull pitch- 

 ing motions and regular head waves were independently varied. Experi- 

 ments with hull pitching were conducted on three hull forms, two of 

 which were reported previously by Boswell et al. (1976a, 1976b, 1978) 

 and Jessup et al. (1977), and the third of which is presented in this 

 paper. Restrained model experiments in waves, including forced sinus- 

 oidal pitching of a model in waves, were conducted on only one model, 

 and are presented in the present paper. Experiments were conducted in 



