calm water with no ship motions, in calm water with forced sinusoidal 

 pitching of the hull, in regular waves with no ship motions, and in 

 regular waves with forced sinusoidal pitching of the hull at the fre- 

 quency equal to the wave frequency of encounter. The experiments with 

 forced hull pitching in waves were run over a range of relative phases 

 between the hull pitching and the wave encounter. Six components of 

 blade loads were measured during the dynamic conditions simulated. 



The modulation of the blade load variation was correlated with pre- 

 dictions calculated from trochoidal wave theory and the periodic verti- 

 cal motion of the hull. The assumption of superposition of the effects 

 of pitching and waves was evaluated. Trends of modulations of the 

 periodic bearing loads were determined from the modulations of the 

 pertinent harmonics of the single-blade loads. 



The objective of these experiments was to obtain accurate system- 

 atic experimental data showing the effects of hull pitching and waves on 

 periodic and time-average blade loads under carefully controlled experi- 

 mental conditions so that the effects of ship motions and waves on peri- 

 odic and time-average blade loads could be isolated. It is anticipated 

 that these data will serve as a basis for developing procedures for cal- 

 culating periodic and time-average blade loads for operation in a com- 

 plex sea state. 



In these experiments the model speed and propeller rotational speed 

 were held constant at the values corresponding to operation in calm water 

 with no ship motions. In practice, when a ship operates in rough seas 

 the ship speed and propeller rotational speed at a given delivered power 

 decrease from the corresponding values in calm water due to increased 

 shaft torque resulting from increased resistance of the hull and change 

 in the propulsion coefficients (involuntary speed loss) (Lewis, 1967, 

 Oosterveld, 1978, Day et al. , 1977) . Furthermore, in rough seas the 

 delivered power is often deliberately reduced from the calm water value 

 (voluntary speed loss) as discussed by Day et al. (1977) and Lloyd and 

 Andrew (1977) . Therefore, the difference in blade loads between opera- 

 tion in calm seas and operation in rough seas can be represented as 

 being made up of two major parts: 



1. Differences in loads resulting from the difference in ship 

 speed and propeller rotational speed between calm seas and rough seas, 

 and 



2. Increases in loads due to the direct influence of waves and 

 ship motions at a given value of ship speed and propeller rotational 

 speed. 



The changes in propeller rotational speed, ship speed, and Taylor 

 wake fraction due to operation in rough seas can be estimated experi- 

 mentally or theoretically using methods or data summarized by Oosterveld 

 (1978), Day et al. (1977), and Lloyd and Andrew (1977). The resulting 

 changes in periodic blade loads can be estimated based on the systematic 

 experimental data or theoretical methods described previously by Boswell 

 et al. (1976a, 1976b, 1978). The experiments described in the present 

 paper provide information on the direct influence of the waves and ship 

 motions on periodic and time-average blade loads. 



