TOWCABLE TENSIONS AND ANGLES 



The cable tensions measured at the detector vehicle as a function of 

 speed are shown in Figure B-2 for the vehicle in the suspended condition 

 on 12.5 feet of cable and in the survey condition of 12.5, 25, and 50 

 feet of cable. As shown by the figure, the tensions for the survey con- 

 dition are less than the tensions for the suspended condition for all 

 speeds less than 3.h knots for the 12.5-foot cable, k.O knots for the 

 25-foot cable and k.3 knots for the 50-foot cable. When the tension in 

 the survey condition equaled the tensions in suspended condition, the 

 vehicle lost contact with the bottom. This was substantiated by observa- 

 tions made during the tests. However, there occurred in the suspended 

 condition a tension difference for each speed as a function of towcable 

 length. This difference is attributed to an increase in vehicle drag 

 due to proximity of the vehicle to the bottom of the basin. 



The cable angle at the detector vehicle and at the towing carriage 

 are shown in Figure B-3 for the suspended condition. The cable angles 

 obtained when the vehicle was towed in the survey condition are not shown 

 since they are of no practical value. 



PREDICTION TECHNIQUE AND CONFIGURATIONS 



Cable configurations were predicted using the computer program 

 described by Cuthill (196*0 . The program is based on the theory of 

 Pode (1951) and the following conditions and assumptions: 



1. All calculations are for standard sea conditions (*+5° North 

 Latitude, 3.5 percent salinity, and 59° Fahrenheit. 



2. A mean cable diameter of 1.0 inch is used for the cable. 

 The towcable consists of two bundles of electrical con- 

 ductors and a .25-inch-diameter wire rope. 



3. The weight of the cable per unit length in water is 0.*+ 

 pounds per foot . 



h. The drag coefficient for the cable when perpendicular to 

 the stream is 3.0. The assumed coefficient is based on 

 iterative calculations to fit computed angle predictions 

 to the measured cable angle data. The coefficient is higher 

 than that used for single cables, but this can be expected 

 because of the mult i- cylindrical shapes in close proximity 

 to each other and because of the vibrations associated with 

 unfaired towcables . 



5. The ratio of drag per unit length of cable when parallel 

 to the stream to the drag per unit length of cable when 

 perpendicular to the stream is 0.02. 



B-5 



