Sawitsky 3 Roper _, and Benen 



for measuring thrust, torque and RPM. These were "reaction" type 

 dynamometers having capacities of 10 lb. thrust, 5 in-lb. torque, 

 RPM up to 10, 000 and 0. 50 HP. The averaging of the force and 

 motion signals, as well as additional data processing, was accomplish- 

 ed using a PDP-8E computer on line. The computer has a built-in 

 analog -to-digital converter and is programmed to carry out operations 

 such as signal averaging, correcting for zero levels, and multiplying 

 by calibration factors to obtain results in engineering units. 



Davidson Laboratory uses the overload and underload testing 

 procedure where a group of test runs are carried out at fixed speed 

 with various rates of propeller rotation. This type of test provides 

 information which may be applied for any desired assumptions concern- 

 ing appendage drag, roughness allowance, scale ratio, air drag or 

 rough water-drag increment. 



Some typical propeller-hull interaction factors, derived from 

 the test data for the model self-propulsion point (towing force = 0), 

 are given for a speed corresponding to 45 knots and a displacement 

 of 150, 000 lbs. 



1 - W = 0. 99 



Wake fractions = , ,„ _ n , 



1 - W = 0. 9o 



Relative rotative efficiency = = Q /Q = 0. 92 



RR o B 



Thrust deduction 1 - t = 0. 94 



These values of wake fraction, relative rotative efficiency 

 and thrust deduction are used to select the particular propeller design 

 which absorbs the installed power at the proper RPM and speed and 

 has good efficiency even while operating under cavitating conditions. 



It is interesting to note that the thrust wake fraction is 0. 99 

 indicating an essentially undisturbed flow to the propeller. The thrust 

 deduction is small, 1-t = 0. 94 , indicating a small effectof propeller- 

 induced flow on the hull resistance. 



Rough Water Tests 



The rough water performance was measured for several 

 loads and LCG positions in a variety of sea states. Measured quan- 

 tities included heave and pitch motions, vertical accelerations at the 

 bow and CG, and mean resistance in waves. During each test run, the 



43 8 



