326 



RUDDER TRIALS, U. S. S. STERETT. 



APPENDIX V. 



ANALYSIS OF FRICTION TESTS. 



On June 6, 191 1, the Sterett was placed in dry-dock, and water pumped 

 out of the dock. The dynamometer described in Appendix I, Fig. B, Plate 

 113, was inserted in the standing part of the port-tiller chain as indicated by 

 letter D, Fig. C. The steering wheel aft was locked, and power applied from 

 the steering engine forward to move the rudder. The helm was repeatedly 

 moved from 35° port to 35° starboard and back by means of the steering 

 engine. The dynamometer gave a continuous record of the tension in lead 

 A. Care was taken to move the helm at a constant rate (about 2° per 

 second), and the dynamometer table was rapped continuously to take out 



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any friction in the dynamometer. The conditions of the calibration tests 

 (Appendix 3) were further simulated by putting a greased plate between 

 the deck and the foot of the dynamometer. On June 8 the friction tests 

 were repeated with the ship afloat and moored alongside a pier. 



On the curves for friction (Fig. 17, Plate 127) the dynamometer readings 

 in pounds are plotted as ordinates on degrees helm-angle as abscissae. Since 

 the forces recorded in moving the helm from "hard over" to amidships did 

 not differ materially from those recorded on continuing the motion from 

 amidships to the other hard-over position, the friction curves represent only 

 one-half the total arc of helm motion. 



In the discussion of the friction tests, the following notation is used, 

 the various forces being in pounds : — 



D = Dynamometer reading, giving tension in lead A . 

 A = Force to overhaul lead A (port side). 



