Prediction of Steering and Manoeuvring of Ships 



Fig. 11 - X and Y force gauges and a 

 two-degree-of-freedom gimbal at- 

 tached to the bulkhead in the model 



used in the static mode, i.e., if only constant forces resulting from drift and/or 

 rudder angles are to be measured, then the gauge signals are passed via control 

 units to pen recorders in exactly the same manner as the X forces, except that 

 the signals from forward and aft gauges are recorded individually and not 

 summed. When the mechanism is used in its "dynamic" mode, and periodic 

 forces are acting at the gauges, the signals are integrated before being recorded 

 on the pen recorders. 



INTEGRATION OF PERIODIC FORCES 



Basic Principles 



The periodic forces acting at the Y gauges in "pure sway" and "pure yaw" 

 tests are composed of velocity -dependent and acceleration-dependent compo- 

 nents. Assuming in the following, in order to simplify the discussion, that the 

 periodic forces are directly proportional to the motions and that there is no 



333 



