Thus the problem of predicting the steady-state towing configuration becomes 

 one of expressing the hydrodynamic force on the towcable. As noted previously, 

 DTNSRDC has developed a method for directly measuring the hydrodynamic loading 

 functions in (two-dimensional) towing basin experiments. These measured loading 

 functions must ultimately be verified by at-sea measurements since there are some 

 artificialities introduced with the two-dimensional model. In time, as this 

 verification process proceeds on different designs, confidence in the two-dimen- 

 sional measurements as a basis for loading functions will grow and the need for 

 at-sea verification diminish. 



The second method is based on an at-sea experiment in which measurements are 

 made of cable tension, body depth, and cable angle, all as functions of cable 

 scope and speed. The computer model is then exercised assuming different values 

 of hydrodynamic loading until an acceptable match of predicted-to-measured con- 

 figurations obtains. This regression analysis method is used here to develop 

 ribbon cable loading functions. 



A towcable configuration can be defined mathematically by specifying an end 



condition (tension and angle) and by knowledge of the loading along its span in 



2 

 terms of the normal, Q, and tangential, P, force components expressed as follows: 



Q = F - w sin<j) 



P = G - w cos<j> 



where F is the normal component of hydrodynamic force per unit length, 



G is the tangential component of hydrodynamic force per unit length, 



w is the cable weight in water per unit length, and 



<J> is the cable angle relative to horizontal. 



The effort of this report is to evaluate these expressions of P and Q for the 

 ribbon towcable. Since the weight of cable is readily measured the task becomes 

 one of determining by regression analysis the normal and tangential hydrodynamic 

 force components which produce a fit of computed-to-measured data and which can 

 be expressed as: 



F = f (<j>)-R 



n (2) 



G = f (<fr)-R 



