defined by the directions of F, G, and H may be obtained by first rotating the 

 spatial system by an angle /3 about the X-axis and then rotating the resulting 

 intermediate (X', Y', Z') coordinate system by an angle 4 about the Y-axis. In 

 towed systems nomenclature, the angles /3 and ^ generally are referred to as the 

 kite angle and the cable angle, respectively. Since the orientation of the cable 

 changes in space, the angles /3 and ^ are functions of cable length s. 



EQUIPMENT 



3 

 The depressor used during the evaluation was a DTMB Mark 1 knotmeter which 



was modified by replacing the standard knotmeter wing with a larger wing and 



adapting a towpoint that allowed limited pitch, roll, and yaw freedom relative to 



the towline. Top and side views of the knotmeter with the larger wing installed 



are shown in Figure 6. The new knotmeter towpoint, illustrated in Figure 7, 



allows the knotmeter approximately 18 degrees of port and starboard roll freedom, 



20 degrees of pitch freedom, and 30 degrees of port and starboard yaw freedom. 



At the towing carriage, the towline was attached to a gimbaled towpoint 



through a swivel and tension dynamometer arrangement as shown in Figure 8, The 



gimbaled towpoint permitted port and starboard kite angles from to 60 degrees 



and cable angles from 90 to 40 degrees. Both kite and cable angle measurements 



were provided by rotary potentiometers attached to the gimbaled towpoint and to 



the kite and cable angle pivots through anti-backlash gear sets. Both gear sets 



were arranged so that the potentiometer shaft rotation was three times that of the 



corresponding kite or cable angle pivot. The swivel located immediately above the 



towline socket provided the towline 360 degrees of yaw freedom. Tow speed was 



limited to 9.28 m/s (18 knots), which is the maximum speed of the deep-water basin 



towing carriage with this towing load. 



INSTRUMENTATION 



Instrumentation located at the depressor consisted of a +20-degree pendulous 

 potentiometer which provided depressor roll angle measurement with an overall 

 accuracy of +0.5 degree. 



Instrumentation and analog recording equipment located at the towing carriage 

 provided measurements of towing tension, kite angle, cable angle, carriage speed 

 and records of all measured data. The tension dynomometer used during the 

 evaluation had a 2.7-kN (600-lb) load capacity and provided towing tension 



12 



