Based on these results, it was concluded that the downstream body 

 reduced the mean speed into the propeller by 14 percent for all con- 

 ditions. These reductions are somewhat larger than the 12 and 5 percent 

 reductions obtained by Boswell et al. (1976a, 1976b, 1978), respectively, 

 in which essentially the same dynamometer boat was used behind other 

 model hulls. However, in the earlier experiments the dynamometer boat 

 was not fully submerged. 



The downstream body will disturb the location of the shed and 

 trailing vortex sheets from the propeller. This may influence the 

 periodic and time-average propeller blade loads. No correction was made 

 for this effect. 



After the effects of centrifugal force were subtracted from the 

 measured loading components as discussed previously, the time- average 

 value per revolution of each hydrodynamic loading component was cor- 

 rected for the downstream body as follows: From the me^asured hydrodyna- 

 mic blade thrust (Fxj.) and hydrodynamic blade torque (>^) , effective 

 advance coefficients based on thrust identity (Jip) and torque identity 

 (Jq) were deduced from the open water data (Figure 7) . These values 

 were multiplied by (1/0.88) to obtain corrected values of J™_and Jq,_ 

 i.e., without the downstream body. The corrected values of Fxu and Mjj 

 were then obtained from the open water data at the corrected advance 

 coefficient Jj and Jq, respectively. It was assumed that the downstream 

 body dj^d not affect the radial centers of thrust F-^ and tangential 

 force Fy„. Therefore, 



M corrected = (F corrected/F measured) (M measured) 



'^n ^ ^ 



'H 



F corrected = (M corrected/M measured) (F measured) 

 ^H ^ ^ ^H 



No corrections are^ made to F^^ and K^ for the effect of the down- 

 stream body; however, F^^, M^ are small for all experimental conditions, 

 as discussed later. 



No correction for the effect of the downstream dynamometer boat 

 was made to the measured circumferential variations of the loading com- 

 ponents. Calculations made by the methods of Tsakonas et al. (1974) 

 and McCarthy (1961) indicated that the influence of the downstream body 

 alters the peak-to-peak circumferential variation of the loads by no 

 more than 2 percent. 



D. Operation in Calm Water Without Hull Pitching 



For operation in calm water without the hull pitching (Condition 1 

 in Table 1), Table 2 presents the time-average loads. Figure 8 presents 

 the variation of the F^^ component of hydrodynamic blade loading with 

 blade angular position, and Figure 9 presents the amplitude of the 

 first 25 harmonics of the F^^ component of hydrodynamic blade loading. 



Based on the dynamic calibration by Dobay (1971) , it was judged 

 that for all loading components the data are valid for the first 10 



11 



