APPENDIX A 



A COMPARISON OF THE HYDRODYNAMIC LOADING FUNCTIONS 

 WITH SOME CRITICAL ANGLE TOWING DATA 



Figures Al and A2 show hydrodynamic data on ribbon towcables obtained in 

 critical angle towing tests by DTNSRDC. In these experiments long lengths of 

 cable were towed at the critical angle while cable tension at the towpoint, cable 

 angle and speed were measured. From these data a few points can be extracted for 

 comparison with the hydrodynamic loading functions and drag coefficients developed 

 earlier in the body of this report. 



Two ribbon towcable models were evaluated, the models differing primarily in 

 the thickness of the ribbon material. Models A and B each had a 0.84-in. (21.3-mm) 

 diameter, double-armored electrical cable weighing 1.02 lb/ft (1.51 kg/m) in 

 sea water. Ribbon configurations were as shown in Table A.l. 



TABLE A.l - RIBBON CONFIGURATIONS 



MODEL 



RIBBON 

 LENGTH 



RIBBON 

 WIDTH 



MATERIAL 

 THICKNESS 



% CABLE 

 COVERAGE 



A 

 B 



6D 

 6D 



2D 

 2D 



15 mil (0.38 mm) 

 30 mil (0.76 mm) 



50 

 50 



The ribbon material was polyurethane and the ribbon density (or percent cable 

 coverage) was 50% compared to 100% for the model described in the body of the 

 present report. Note, however, that the latter model and Model A have the same 

 material thickness, namely 15 mil (0.38 mm) which is one-half the material thick- 

 ness for Model B. 



In reviewing Figures Al and A2, which are the reduced hydrodynamic measure- 

 ments of towcable tension per unit length and towing angle, it can be seen that 

 the Model B cable tows at a more shallow angle and develops a much higher tension 

 than the Model A cable. (In the graphs showing 30-mil (0.76-mm) thick ribbon 

 cable data Model B refers to the curve marked R/S = 50/00. The other curves result 

 from parts of the test in which increasing percentages of the ribbon were clipped 

 off.) 



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