Ship Maneuvering in Deep and Confined Waters 



In the next Section an approximate method will be given for 

 finding the control derivatives of a rudder of conventional design. 

 In the hypothetical case of an isolated rudder experiencing the nomi- 

 nal inflow at the stern of the ship it would be easy to calculate its 

 contribution to the total "hull + rudder amidship" derivatives from 

 a knowledge of its control effectiveness. In general the interference 

 effects in behind condition are much more complicated, and in fact 

 the contribution searched for mostly is quite small. Even more, 

 then, the effect of a modification to rudder and control derivatives 

 comes out as a very small change in the stability derivatives. The 

 diagram in Fig, 13 is compiled to correlate the effects of such modi- 

 fications as reported by Eda and Crane [ 38] and documented in test 

 results available at SSPA. Obviously new experiments are required. 



Reference shall here also be given to the methods of estimating 

 stability derivatives for surface ships as suggested and successfully 

 tested by Jacobs, [ 39] . 



The aerodynamic wing analogy should only be valid for small 

 Froude numbers as the limit solution of a general lifting surface 

 integral equation. The effects of finite Froude numbers on the 

 lateral stability derivatives of a thin ship of small draught-to-length 

 ratio was studied by Hu, [ 40] , According to Hu the force and 



0,20 



0,15 



0,10 - 



0,05 - 



P A(^Y-,,) 



^ -A(Yuv) 



-O- 2-A(Y^r) 



Dav. Lab.Exp. with 

 •■ Series 60 Block 60 Form 



HyA Exp. with 



SSPA Twin-Screw/ Twin-Rudder 



Tanker 



0,005 



0,010 



0,015 



m 



Fig. 13. Change of control force derivatives and total force 



derivatives in sway and yaw with change of relative size 

 of rudder. 



843 



