RUDDER TRIALS, U. S. S. STERETT. 



307 



COBFFICISNT OF REDUCTION. 



Table of-rj- (from faired curves, Figs. 10 and 12) (Helm-angle d). 



For purposes of comparison, the theoretical twisting moment by Joessel's 

 formula was calculated at four helm-angles and a series of speeds. The 

 rudder area was considered in three parts in the conventional way, and for 

 each part, the center of pressure and twisting moment were computed. 

 (See Fig. i for dimensions of rudder.) 



6 = Rudder angle. 



d = Distance of center of pressure from leading edge. 



b = Width of part of rudder considered. 



A = Area of part of rudder considered. 



a = Distance of leading edge forward of axis. 



V = Velocity of approach in feet per second. 



il4'= Twisting moment in pounds-feet. 



d =(-i95 + -305 sme)b (i) 



M-- 



^/_^^7sin^X , 



(2) 



The three values of M were added to obtain the total twisting moment 

 at the rudder axis. The observed moment on steady turning was then 

 compared with the calculated moment for a given speed and helm, and their 

 ratio, the "coefficient of reduction" was plotted on velocity of approach 

 (Fig. 14, Plate 124). 



It appears that the coefficient of reduction is not a constant for this 

 ship, but falls off at high speeds and large helm-angles. On Fig. 15, Plate 



125, are plotted, on speed-length ratios (77^) as abscissae, the coefficients of 



