Design considerations for stretch conductors in oceanographic moorings

Abstract

A copper conductor formed into a helical configuration like a telephone cord can stretch by extending its geometry without elongating the conductor itself. This report establishes the proper configuration of copper conductors arranged in a helical pattern around a fiber core which can be used as center of a nylon rope with at least 20 percent working stretch. The calculation procedure allows the determination of the conductor's helix angle or pitch as function of the required assembly elongation, the cable assembly's geometry, and the fiber core's Poisson ratio. Limits of the geometry are established to assure defined flexibilty of the cable assembly to allow bending of a surrounding fiber rope without conductor layer blockage. A sample stretch conductor assembly was procured and initial testing is described, proving the calculation method's ability to determine the correct geometry of the conductor assembly. Such conductor assemblies can be used as conductive core of nylon ropes suitable for coastal and deepsea buoy moorings or as lift or trigger lines for instrumentation. They are also considered the most suitable configuration which can endure the high stretch requirements of embedded conductors in a stretch hose wall at its transition into a coupling section.