This maximum ratio, which does not consider the effect of the hull on 

 the vertical component of the trochoidal wave velocities, is predicted 

 to occur when the wave elevation at the propeller plane is increasing 

 through the calm water level, i.e., t, = 0, t>0. The measured increase 

 in the variation of loads with blade angular position for operation in 

 waves was somewhat smaller than this calculated increase in tangential 

 velocity; for example: 



F /(F -F) = 1.17 



(F >1MAV r/(F ), = 1.12 



X IMAX,^ X 1 



This simple analysis is believed to provide an upper bound to the in- 

 crease in variation of loads with blade angular position due to opera- 

 tion in waves, since the hull boundary above the propeller would tend 

 to reduce the vertical component of the trochoidal wave velocity. The 

 corresponding measured increase for other components of blade loading 

 are presented in Table 5. 



The maximum absolute values of the peak loads per revolution in- 

 creased by as much as 22 percent of the time-average loads in calm water 

 without hull pitching above the corresponding peak loads in calm water 

 without hull pitching (see Table 5) . This increase in peak loads is 

 made up of the increase in the time-average loads per revolution (up to 

 14 percent) and the increase in the circumferential variation in loads, 

 or peak minus time-average loads per revolution (up to 12 percent) . 

 The increases in the time- average loads per revolution and the increases 

 in circumferential variations of loads are thought to arise from dif- 

 ferent physical characteristics of the flow as discussed previously; 

 however, the maximum increase in the time-average loads and circumfer- 

 ential variations of loads occur in the same portion of the wave period. 

 Therefore, these two separate increases tend to add almost in phase 

 relative to the wave period so that the maximum increase in peak loads 

 is almost the algebraic sum of the maximum increases in the time-average 

 loads per revolution and the maximiun increase in the circumferential 

 variation of loads. 



Figure 16 shows the variation of the F^ component of blade load 

 with angular position for different times during one wave cycle. The 

 variation of the circumferential distribution to waves appears to be 

 more complicated than the corresponding variation due to pitching. This 

 is attributed to the combined effect of the longitudinal and vertical 

 velocities induced by the wave. As in the case of pitching, the great- 

 est magnitude of loading occurs at blade angles around 90 degrees, 

 corresponding to the outboard position of the blades relative to the 

 propeller shaft. Also, the phase angle of the maximum load varies with 

 position relative to the wave, but with the combined effects of mean and 

 unsteady load variations no clear trends are observed. The variation 



22 



