228 



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FIGURE 2. Controllable-pitch propeller geometry. 



tion studies in the circulating water channel at 

 DTNSRDC indicated that yaw angles of less than 

 four degrees would provide satisfactory inflows 

 to the propeller disk, and still exclude the wake 

 of the roll fins. Subsequent self-propulsion 

 model experiments using only one shaft, indicated 

 that with the rudder set at one degree to port, 

 the ship would have less than one degree of yaw 

 and insignificant sway. Therefore, the decision 

 was made to propel the ship on one shaft rather 

 than to tow the ship. 



The instrumentation which was installed on the 

 ATHENA consisted of three types. Five- and 

 thirteen-hole pitot tubes were used to determine 

 the velocity field in the propeller plane on the 

 starboard side, and ahead of the struts on both 

 the port and starboard sides.* A set of eight 

 boundary layer probes were used to measure the 

 boundary layer profile at four symmetric locations 

 on the port and starboard sides of the ship. 

 Finally a piezoelectric pitot tiobe, a five-hole 

 pitot tube with piezoelectric pressure transducers 

 mounted on its face , was used to measure the time- 

 varying flow ahead of the operating propeller. 



The locations of the pitot tube rakes and bound- 

 ary layer probes are shown in Figures 3 and 4. The 

 location of the struts and the shape of the after 

 stations are shown in Figure 5. As can be seen in 

 these figures and in Figures 6 and 7 , which show 

 photographs of the actual pitot tube rakes mounted 

 on the ship, two rakes of four pitot tubes each 

 were mounted on opposite sides of the propeller 

 hub. These rakes were attached to the crank disks 

 for two of the propeller blades. The details of 

 one rake with pitot tubes mounted are shown in 

 Figure 8. 



*For the details of the instrumentation design and operation 

 see Troesch et al. (1978). 



Figure 9 shows a close-up photograph of one of 

 the full-scale boundary layers probes. These 

 probes, which extended 0.46 meters from the hull, 

 contained 13 pitot tubes. Ten of the pitot tubes 

 were total head tubes, and three were Prandtl 

 tubes. 



4. CORRELATION MODELS AND INSTRUMENTATION 



The model correlation experiments were performed 

 using two fiberglass models designated DTNSRDC 

 Models 5365 and 5366. These models, which were 

 built to the lines of the ATHENA, had a scale 

 ratio of 1 to 8.25; the principal dimensions of 

 these models are listed with the ship dimensions 

 on Figure 1. A full set of appendages including 

 shafts, V-struts, rudders, roll stabilizer fins, 

 and a centerline skeg were fitted to each model. 

 Model 5365 was a ship model which was used for the 

 correlation wake surveys performed in the towing 

 tank to investigate the scale effects between the 

 model and ship wake surveys. Model 5356 was a 

 mirror image double model obtained by reflecting 

 the lines of the ATHENA about the mean water line 

 corresponding to a full-scale speed of fifteen 

 knots. This model was used for the boundary layer 

 correlation experiments which were made in a wind 

 tunnel. 



The model-scale wake survey was made on the ship 

 model. Model 5365, using five-hole pitot tubes. 

 The pitot tubes were mounted on a rake, the shaft 

 of which was placed through the strut bossings and 

 stern tube on the model. Figures 10, 11, and 12 

 show the model which was used for the wake 

 surveys, and the details of the pitot tube rake 

 mounted on the stern of the model . Two papers , one 

 by Hadler and Cheng (1965) and the other by Hale 

 and Norrie (1967) , give a thorough description of 



