227 



naval vessels. The ship had to be available for an 

 extended period of time and a means of propelling 

 the ship had to be available. 



Of the ships which were in the U.S. Navy fleet, 

 four classes seemed to meet the geometric criteria, 

 and a means of propelling them could be identified. 

 These were the Gearing Class (DD 710) , Forrest 

 Sherman Class (DD 931) , Spruance Class (DD 963) , 

 and the Asheville Class (PG 84) . However, of these 

 classes, only the Asheville Class, which was being 

 decommissioned, met the criterion of long term 

 availability. As it tourned out, the David W. 

 Taylor Naval Ship Research and Development Center 

 (DTNSRDC) already had one of these ships under its 

 control, the Research Vessel (R/V) ATHENA. 



The ATHENA had the added advantage that an ex- 

 tensive series of model- and full-scale correlation 

 experiments were already planned. Unsteady blade 

 loads, stresses, and pressure distributions were 

 going to be obtained full scale. The blade loading 

 measurements were also going to be repeated at model 

 scale. This blade loading data complement the full- 

 scale wake data, and would result in some of the 

 most complete correlation data of this type for any 

 ship and model . 



The R/V ATHENA is a twin-screw aluminum hull 

 CODOG (combined Diesel Or Gas Turbine) propelled 

 high-speed displacement ship. Formerly designated 

 PG 94, the 46.9 meter LWL ship was decommissioned 

 in 1975 and placed in service as a high-speed 

 towing platform for DTNSRDC. The hull form and 

 propulsion arrangements are similar to today's 

 destroyers and frigates which are propelled by 



controllable-, reversible- pitch propellers using 

 gas turbines as prime movers. The principal di- 

 mensions and form coefficients for R/V ATHENA are 

 presented in Figure 1. Figure 1 also shows the 

 body plan, and bow and stern profiles of the ship. 

 Figure 2 shows a drawing of the propeller. 



The ATHENA is equipped with two Cummins 750 

 V-12 diesels for low speed propulsion and a single 

 General Electric LM 1500 gas turbine for high- 

 speed propulsion. In the diesel mode, the ATHENA 

 is capable of speeds of around 14 knots. Under gas 

 turbine power, she can attain a speed of 40 knots. 

 The ATHENA is appended with twin shafts, struts, 

 and rudders typical of most high-speed transom 

 stern ships. In addition, she also has two anti- 

 roll fins located just aft of amidships. 



Once the ATHENA was selected for the study of 

 wake scaling, the question of how to propel the 

 ship had to be resolved. The ATHENA is small 

 enough that she could be towed by either one or 

 two ships at speeds high enough to provide useful 

 data, or she could be propelled on one shaft and 

 measurements could be made on the other shaft. The 

 two-ship tow would have been the most ideal means of 

 propelling the ship during the experiments, because 

 it would have allowed the ATHENA to be towed with no 

 yaw angle, and outside the wake of another ship. 

 However, the logistics of this option made it much 

 less practical than propelling on one shaft. 



A series of model experiments was instituted, 

 aimed at determining whether or not single shaft 

 propulsion could provide good course keeping 

 ability with minimal yaw angles. ' Flow visualiza- 



Coefficients 



Scale Ratio 

 Block Coefficient 

 Prismatic Coefficient 

 Length/Beam Ratio 

 Beam/Draft Ratio 

 Displacement/Length Ratio /^ 



c^ 



p 



L/B 

 B/T 



8.25 

 0.48 

 0.63 

 7.04 

 3.89 

 7.15 



FIGURE I. 



