Dynamic positioning of ROV in the wave zone during launch and recovery from a small surface vessel

Abstract

Dynamical positioning (DP) control of a remotely operated vehicle (ROV) using thrusters is investigated as a means to increase operability of its launch and recovery system (LARS) on relatively small surface vessels. The ROV uses its DP control system to dynamically track the wave-driven motion of the surface vessel that may also be under DP control. We consider the critical phase when the ROV position is very close to the LARS. In this phase, the ROV’s motion is strongly influenced by first-order surface waves and hydrodynamic couplings from the surface vessel motion. Hence, there is risk of collision between the ROV and the surface vessel and its LARS. We employ a time-domain dynamic system simulator that calculates the coupled motions of both the surface vessel and the ROV to analyse and optimize the operability of the system. It is based on coupled added mass, damping and wave force response amplitude operators (RAO) for both the surface vessel and the ROV, which can be calculated using WAMIT coupled hydrodynamic multi-body computations, accounting also for the moonpool water column dynamics. Simulation results show the positive effect of the ROV DP on the operability of the LARS using statistical environmental data from the North Sea.