Electromechanical Cables for Deep Ocean Operations
Authors: Tan Felix C. , Liu Cheng L. 
Published: October 2008

A single electromechanical cable provides a simple and practical link between an instrumented submerged ocean payload and the surface platform. Such a cable, consisting of core elements for the transmission of electrical signals and/or power, can also support the payload and perform other mechanical functions. Typical applications include many deep water acoustic sensing arrays and towed fishes. The increasing use of electromechanical cable systems for deeper and heavier payload deployments justifies a comprehensive consideration of the problems associated with such cable systems. Further, to aid the engineers in selecting a suitable cable, it is necessary to devise a method that takes into account environmental factors, such as dynamic induced loads.

This paper presents a systematic examination of the pertinent parameters involved in a long electromechanical cable system for a typical tethered deep ocean emplacement and recovery operation. The system requirements on the cable are determined first. A simple graphical methodapplicable to varied ocean systems is then developed to define the cable required for a given system. This method utilizes the total cable eight (air) per unit length as a variable which is shown to be the controlling parameter. The cable weight per unit length in turn defines the cable geometries for a given class of cable configurations. The significance of eight contributed by the electrical elements of the cable is also discussed. The limiting case where the cable is simply a rope is presented for comparison. Conventional steel armored cables in conjunction with an assumed payload package are included as an illustrative example. A substantial amount of the steel armor is shown to be required to support a relatively light core.

Introduction

For many tasks to be performed in the open sea, an electromechanical cable is an essential system component for which there is no substitute. The electromechanical cable is basically an extension of ordinary wire ropes in which electrical elements are integrated to allot, the transmission of signal and/or power. These elastic, flexible, tensile force-transmitting members are, therefore, power transmission lines and signal conduits at the same time. The ability of these cables to transmit forces over great distances alones the ocean engineer to extend his influence through deep water to ocean bottom. If properly utilized, an electromechanical cable offers a simple means for the exploration of the deep ocean. As the trend toward heavier and more sophisticated loads for deeper deployment continues, the demands on the electromechanical cable become more severe. A closer examination of this often neglected -system component is, therefore, imperative to insure system success.

The general problem posed here is that of deploying an instrumented payload to ocean depths by means of a tether. The mission for such a tethered payload could be the acquisition of scientific data, object recovery, or the exploration for oil and mineral deposits. The payload is assumed to be deployed from a surface support platform. The cable width which shall concern ourselves is the only link between the payload and the surface platform.