Swaan and Wahab 



because the resistance and vertical motions were still considerable while com- 

 bined with the lateral force and yawing moment occurring in oblique seas. 



The effect of a variation in wave height is shown in Fig. 12. It indicates 

 that an increment of the wave height increased the motion amplitudes and re- 

 sistance about proportionally. At higher speeds, however, the amplitudes of the 

 lateral force, yawing moment and accelerations forward increased more than 

 proportionally. The accelerations aft were hardly affected by the wave height. 

 The effect of the wave height on the mean values of the lateral force and yawing 

 moment was small in comparison with that on the amplitudes. For small differ- 

 ences the rise height increased with increasing wave height. If the increments 

 exceeded a certain value the rise height remained constant. 



^ 100 



I ° 



HEAVE 



OCXJBL£ AMPLITUDE 



WAVE HEIGHT 6n 



'JZ 



RTCH ANGLES 



CXDUBLE AMPLITUDE 



rrzi-f= 



MOMENT OF YAW 

 DOUBLE AMPLITUDE 



rg — ■/■ — 



^2-3and eft 



HEAVE 



MINE RISE HEIGHT 



z= £ , 



WITH 15 KNOTS SIDE WIND 



RESISTANCE 



MEAN 



ACCELERATION FORWARD 



-niiltz 



ROLL ANGLES 



DOUBLE AMPLITUDE 



PERIODE 



2- 3 and en 



LATERAL FORCE 



DOUBLE AMPLITUDE ' 



2 -3 and 6ft 



ACCELERATION AFT 



— SPEED IN KNOTS 



SPEED IN KNOTS 



. SPEED IN KNOTS 



Fig. 12 - Effect of wave height and side wind, wave direction 90' 

 (beam sea), 2580 fan revolutions per minute 



708 



