For Method 1, within the range shown in Table 3, the variation in 

 Cr has a significant influence on all three quantities. However, the 

 variation in f has little effect on depth and cable angle but has considerable 

 influence on the net tension. Thus, if a drag coefficient is selected to 

 give good agreement between predicted and measured values of depth and 

 cable angle, a value of f can be selected which will give good agreement 

 on net tension as well. 



For Methdd 2, within the range shown in Table 3, the variation in 

 Cr also has a significant influence on all three quantities. In this case, 

 the only value that can be changed in any given computation is the cable 

 drag coefficient. Consequently, if good agreement cannot be obtained 

 with one value of drag coefficient for all three quantities, then changes in 

 the drag coefficient to improve the agreement with one of the quantities 

 will result in poorer agreement with the other two quantities. 



COMPARISON OF MEASURED AND PREDICTED RESULTS 



Since the towpoint at the ship was above the water surface, the length 

 of the cable in the water changed with ship speed. Nevertheless, for 

 simplicity, the nominal scopes were used in making comparisons between 

 the measured and computed values. This simplification is considered 

 justified in view of the scatter in the experimental data. 



Based on the computer study described by the preceding section, 

 selections were made of the numerical values of the pertinent parameters 

 to be used in the predictions involving each of the two methods. The 

 selected values were those which gave the best overall fit to the measured 

 data on cable tension, cable angle, and body depth. On this basis, a C-^ = 

 1 . 5 in combination with an f = 0.02 was found to be best for Method 1 and 

 a Cr = 1.5 was found to best for Method 2. The predictions based on the 

 selected values for each method (Tables lOe and' 13b) are compared with 

 the measured data (Table 7) in Figures 14, 15, and 16 for the nominal 

 cable scope of 280 feet. In addition, the differences between the predicted 

 and measured data (faired curves) for the three nominal scopes are 

 summarized in Table 4 for a speed of 10 knots. 



TABLE 4 



Difference Between Predicted and 

 Measured Data at a Speed of 10 Knots 



Parameter 



100-foot scope 



200-foot scope 



280-foot scope 



Method 1 



Method 2 



Method 1 



Method 2 



Method 1 



Method 2 



Tension, lb 

 Depth, ft 

 Angle, deg 



-5 

 2 

 -1.5 



25 

 2 



- 1.5 



20 

 2 

 3.0 



80 

 2 

 3.0 



25 



3 

 3.5 



110 

 4 

 4.0 



NOTE: Positive values signify that the predicted value is larger than 

 the measured value. The predicted values are based on a Cr of 1 . 5 

 and an f of 0.02. 



16 



