Assessment of Early Detection Methods of Derelict Fishing Gear Entanglement in Mooring Systems

Abstract This paper documents an assessment of methods to detect the presence of derelict fishing gear on mooring lines of floating offshore wind turbines. Per the sponsors of this work, early detection of gear may enable its prompt removal, thereby reducing threats to marine life. The work focuses on detection, not on the hazard to marine life. The paper briefly discusses the following points: A literature survey of ghost fishing gearEstimates of hydrodynamic properties of various ghost gear attachments.Three presumed mooring system configurations (100 m catenary with polyester inserts, 100 m catenary with nylon inserts, and 750 m taut system with polyester inserts).A modal analysis of each mooring system under various scenarios.Simulations of the complete system of ocean waves, currents, mooring lines, the FOWT hull, and a 15 MW offshore turbine. These results quantify the effects of various attachment scenarios and the magnitude of changes in line acceleration that an accelerometer-based system would need to detect.Specification that such accelerometers would require. This work has shown that in some scenarios, it is conceivable that fishing gear entangled on FOWT mooring lines can be detected through measurement of mooring line acceleration response; however, for many scenarios no significant difference in spectral response is observed between simulations with and without the presence of entangled fishing gear. Lastly, this paper discusses the potential of detecting entangled fishing gear through vibration monitoring. Consequently, this study has shown that detection of entangled fishing gear may be possible in certain conditions and may require complex post processing algorithms to be developed. However, for benign environments, vibration monitoring alone will likely be insufficient.