van Manen, Oosterveld and Witte 



or the starboard nozzles in such a manner that always a left- or right-hand 

 torque acted on the ship. The time lag of the valve action was very small com- 

 pared with the swinging period of the ship (Fig. 2). 



During the z manoeuvring experiments the relevant quantities were meas- 

 ured using the following methods: 



Water mass flow from two mercury filled U-tubes connected with the ven- 

 turi nozzles. 



Rudder angle h was adjusted on the servo motor moving the rudder. 



Yaw angle / and the drift angle /3 were measured with a gyroscope mounted 

 on the model. 



Yaw angle rate = di///dt was derived by electronic differentiation of the 

 gyroscope yaw angle signal with respect to the time t . 



The nozzle exhaust velocity u was calculated with the aid of the continuity 

 equation from the measured water mass flow rate and the known nozzle exhaust 

 diameter. During the experiments the following quantities were changed: the 

 draft H, the ship velocity v, the nozzle diameter D^, the nozzle exhaust veloc- 

 ity u for the jet steering model, and the rudder angle ' for the conventional 

 model. 



The following experimental program was started: 



Jet Steering 



H = 8.13, 14.3 m 



V = 5, 9, 13, 17 knots 



D^ = 1.10, 0.357 m 



U = 8.95, 12.1, 15, 17.9, 20.8 m/sec for D„ = 1.10 m 



U = 18.6, 38.4, 58.5, 77, 97 m/sec for D^ = 0.357 m 



Rudder Steering 



H = 8.13 m, 14.3 m 



V = 5, 9, 13, 17 knots 



S = 5, 10, 15, 20, 25 degrees 



For the adjustment of the nozzle exhaust velocity at model scale, Froude 

 scaling was used. Thus the velocity ratio V/U for model scale and true scale 

 remained the same. 



The experiments were done in such a way that the model propelled itself 

 with a certain desired model speed before rudder or jet action was initiated, 

 after which the response of the model to alternating rudder movement or jet 



258 



