Prediction of Steering and Manoeuvring of Ships 



—1 1 1 — [ — I — I 



to 11 12 13 U. 15 



iu'=!i^i 



Ship Speed , kn. 



Fig. 32 - Variation of dimensionless 

 rudder-angle coefficients with speed 



FREQUENCY AND TANK-INTERFERENCE EFFECTS 



Resonant Standing Waves 



The following consists of a brief description of some aspects of the influ- 

 ence of frequency-dependent surface waves on force measurements made with 

 the HyA planar-motion mechanism used in the dynamic mode. Not much infor- 

 mation is available, as the policy adopted has been that of avoiding these effects, 

 but in order to be able to do this, two series of exploratory tests were made 

 soon after the mechanism was completed, and it is felt that the results of these 

 tests are of sufficient interest to warrant description. 



It is not unnatural that oscillation of a body in a free surface should give 

 rise to waves which are dependent on frequency and amplitude of oscillation as 

 well as on the speed of the body through the water. When the frequency of such 

 waves corresponds to the natural frequency of the water in the towing tank, then 

 tank resonance may be expected. Such resonance can result in the buildup of 



375 



