This study is twofold. First, a comprehensive simulation framework of cable dynamics is introduced. This framework considers variable length cables and allows to incorporate elements such as buoys, ballast or Inertial Measurement Unit (IMU) sensors. The accuracy of this framework is assessed through experimental data.Second, a novel and improved solution for the instrumentation of a V-shaped buoy-ballast system using IMU sensors is investigated. This latter, designed for a neutrally buoyant tether between a Remotely Operated Vehicle (ROV) and an Unmanned Surface Vehicle (USV), is meant to improve operation safety. The discussed IMU-based solution provides wider information on the interaction between the ROV and the cable, including its 3D orientation and curvature amplitude, which could be used for both the control of the USV trajectory and its onboard winch.