3o8 



RUDDER TRIALS, U. S. S. STERETT. 



reduction published for the Condor and Cassini of the French Navy, together 

 with the coeflficients of reduction for the Sterett at 31° helm-angle. These 

 ships are of somewhat similar type with principal dimensions as follows: — 



Sterett. 



2 Screws, O. T. 



Condor.* 



2 Screws, O. T. 



Cassini. t 



2 Screws, O. T. 



Displacement, tons 



V maximum, knots 



Length, load water-line 



Beam 



Draught 



Rudder area (A ), square feet 



A 



LXD 



Fraction of compensation 



Rate of moving helm, degrees per second 



835 



29 



289 



26' oj" 



8' 4" 



52.1 



.0218 



• 173 



3 



1,272 



30 

 323 



960 



30 



262 



53.8 

 .021 

 .215 



3 



The coefficient of reduction for the Sterett was computed with reference 

 to the twisting moment on steady turning, with no correction for friction 

 (see Appendix V). 



The coefficients of reduction for the Condor and Cassini are the maxi- 

 mum recorded moments corrected for friction, and divided by the moments 

 obtained by Joessel's formula. The curves of coefficients of reduction for 

 the three ships, plotted on Fig. 15, Plate 125, have the same general charac- 

 teristics, and seem to show that for similar ships, at the same helm-angle 

 and with the same speed-length ratio, the coefficient of reduction is practi- 

 cally constant. But, for the same ship, the coefficient of reduction is not 

 constant for different speeds or helm-angles. 



PROPOSED FORMULA FOR TWISTING MOMENT. 



From the curves of twisting moment on steady turning plotted on 

 speed of approach (Fig. 10, Plate 120) and on degrees of helm-angle (Fig. 12, 

 Plate 122), it appears that the twisting moment varies neither as the square 

 of the speed, nor as the sine of the helm-angle, as proposed by Joessel, but 

 rather with some other function of these two quantities. 



•Pollard et Dudebout, Theorie du Navire, Tome IV, p. 36. 

 tM. Laubeuf, Bulletin de I'Association Maritime, 1897, p. 215. 



