A Quick and Technically and Economically Feasible Response on Reducing the Underwater Radiated Noise (URN) by Existing Ships: Control of Propeller Cavitation and URN Simultaneously

In 2023, the International Maritime Organization (IMO) reviewed the guidelines for the reduction of underwater radiated noise from shipping to address adverse impact on marine life [1]. The propulsion of the ship is recognized as the primary source of URN, and the propeller cavitation, when occurring, stands as the dominant contribution to the ship's total URN. Shipowners are by now facing the fulfilment of greenhouse gas emissions (GHG) related requirements (Energy Efficiency Design Index (EEDI), Energy Efficiency Existing Ships Index (EEXI), Carbon Intensity Indicator (CII), European Policy ‘Fit for 55’), and the need for URN reduction cannot be detrimental to these. URN reduction related technologies are still at an early stage when it comes to the commercial maritime sector, although they are quite common on research vessels and the defense sector. An onboard real-time, digitally advanced, and easily adaptable monitoring solution, called Ni-CDS, is proposed to enable shipowners to manage their main URN sources and propulsion efficiency status of their ships. The solution, permanently installed, provides a reporting interface based on a previous proper characterization of the ship's URN with both onboard and offboard measurements, and when a mid-term analysis is considered, advice on the propeller's maintenance could also be estimated.