compares the experimental and predicted results; presents conclusions 

 concerning the use of the two methods for predicting the configuration and 

 forces for a bare-cable towed system; and makes recommendations 

 for the use of a standard prediction method and associated loading force 

 coefficients for the case of bare towcables. 



GENERAL CONSIDERATIONS 



The steady-state equations of a cable-body system expressed in terms 

 of the hydrodynamic and hydrostatic forces acting on an element of cable 

 are given in Reference 1.* A diagram showing how these forces are resolved 

 is reproduced as Figure 1. Once the hydrodynamic characteristics of 

 the towed body and the towing cable are known, the cable configuration and 

 tension can be determined from the equations. Generally, the hydro- 

 dynamic characteristics of the towed body are known or can be readily 

 obtained. However, there are little data concerning the exact magnitude 

 of the hydrodynamic forces acting on the element of cable. Consequently, 

 the usual practice is to assume that these forces are some predetermined 

 function of the angle that the cable makes to the stream. Several attempts 

 have been made by investigators in the past to measure or resolve these 

 cable forces 3 ' 3 ' 4 ' 5 ' 6 . However, these attempts have been hampered by 

 inadequate instrumentation to measure the minute tangential forces involved, 

 as well as a variety of experimental difficulties such as mounting techniques 

 to avoid gap effects, end effects, etc., and thus obtain reliable two- 

 dimensional data. Furthermore, such factors as cable strands, roughness, 

 and cable vibration may affect the forces on a cable. The cable strands 

 and roughness may cause turbulent flow over the element of cable which 

 could either increase or decrease the hydrodynamic forces depending on 

 the Reynolds number. If the cable is vibrating, the effective frontal area 

 is increased and hence, the forces are increased. Severe vibration usually 

 occurs in bare-cable towing operations. 



Normal Force 



Tangential 

 Force 



Wds 



Figure 1 - Forces Acting on an Element of Cable 



* References are listed on page 39. 



