392 



HYDKAULICS AND ITS APPLICATIONS 



the vessel in a direction parallel to A B. This explains why a constant 

 rudder angle will not enable a vessel to describe a circle. 



The point in the rudder body, at which it is pivoted, does not affect this 

 force or the couple produced, and advantage has been taken of this to 

 mount the rudder on pivots near its centre. Being then approximately 

 in balance, the moment necessary to rotate it is considerably reduced, and 

 a much greater proportion of the steering force is directly transmitted 

 through the pivots (Fig. 177 b), instead of through the rudder chains. 



Experiments by Stanton 1 show that the divergence of the stream 



FIG. 177. 



impinging on the rudder, produced by the hull of the boat, considerably 

 reduces the normal pressure on the rudder. Where the lines of the stern 

 of the boat converged at an angle of 10, the ratios of the pressures obtained, 

 to those obtained with the hull removed were as follows : 



1 "Trans. Inst. Naval Architects," 1909. 



