Underwater radiated noise characteristics of small vessels - An analysis of the HearMyShip database

Underwater Radiated Noise (URN) from vessels has become a significant area of focus in the marine pollution research agenda due to its potentially adverse effects on marine life. URN monitoring and mitigation efforts have been directed primarily toward large commercial vessels (e.g., container ships), which has led to the accumulation of extensive data through standardized measurements. However, this is not the case for small vessels. Small vessels, such as motorboats and yachts are much more abundant in coastal waters and previous studies have implied that URN levels from such vessels may be comparable to those emitted by large commercial vessels. Nevertheless, the complexity of measuring URN emissions from small vessels in the shallow coastal area infers that such vessels have not been subjected to extensive standardized measurements. To address this gap, we created a designated web-front dataset named "HearMyShip" comprised of in-situ acoustic and optical data from >1000 small vessels (<55 m in length) in the coastal area of Croatia. In this paper, we provide a detailed analysis of this dataset, including the relation between the vessel's speed, size, and type on URN levels and frequency characteristics compared against current commercial notations (Lloyd's Transit and Lloyd's Silent). Our analysis provides novel insights regarding the frequency and level characteristics of URN emitted by different types of small vessels under various operating conditions, the conclusions of which can be utilized to promote URN mitigation efforts in coastal waters.