ABSTRACT 



Hydrodynamic loading functions and drag coefficients have been 

 developed for a ribbon towcable. These functions represent a mathe- 

 matical fit to data measured on a towcable at sea. The functions 

 should be used with caution in predicting the towing configurations 

 of other types of ribbon cable design or other cable diameters because 

 of the difficulty in scaling ribbon characteristics such as material 

 stiffness. 



ADMINISTRATIVE INFORMATION 

 The work described in this report was performed in support of a number of 

 projects sponsored by the Naval Sea Systems Command, the Naval Ship Engineering 

 Center and the Naval Air Systems Command. The effort was carried out jointly by 

 David Taylor Naval Ship Research and Development Center under Program Element 

 Number 62543N, Task Area Number SF 43-400-001, Work Unit Number 1507-101 and MAR 

 Associates, Inc. under DTNSRDC Contract Number N00600-79-D-2507. J. Nelligan is 

 with MAR Associates, Inc. of Rockville, Maryland. 



INTRODUCTION 



Various devices can be attached to round towcables to improve hydrodynamic 

 performance. A streamlined fairing reduces the normal component of drag allowing 

 the towline to span a greater depth per unit of scope, at the same time reducing 

 cable strumming. Fairing, however, is expensive and can be difficult to store 

 and stream reliably, especially in certain applications, e.g., submarine towed 

 systems. 



Ribbon towcable does not have the hydrodynamic efficiency of streamlined 

 fairing, but it is much more easily stored and handled, in addition to being less 

 costly. Ribbon is used primarily to reduce cable strumming which can be a source 

 of noise or cause early fatigue. In so doing it appears also to reduce the 

 normal component of drag below that of the fully strumming bare round cable. The 

 mechanism by which strumming is suppressed is not fully understood but is thought 

 to involve the disruption of spanwise coherence in vortex shedding and drag 

 damping. A negative in the use of ribbon as with all cable-attached devices is 

 the increase in the tangential component of drag (tension) relative to bare cable. 



