Estimation of Source Levels of Small Vessels Based on Controlled Measurements in Shallow Waters

Underwater radiated noise from small recreational vessels can have significant ecological impacts on near-shore habitats, yet it is often overlooked in soundscape assessments. The objective of this study is to present measured source levels for small recreational vessels and to evaluate an existing source level model (JOMOPANS-ECHO model). The existing model was developed based on data from larger vessels, and the current study focuses on how to modify it for smaller vessels with different hull types. Errors associated with shallow water measurements are also discussed; more specifically, existing methods for accounting for propagation loss are evaluated. Controlled measurements were conducted at five coastal sites for 25 vessels spanning different hull forms, propulsion systems, and operational speeds. Frequency-dependent source level spectra were derived and categorised by hull class (planing, semi-displacement, displacement). The results show clear speed-dependent increases in source level for planing and semi-displacement vessels at higher frequencies (>250 Hz), whereas data for displacement vessels were insufficient to establish statistical trends. The JOMOPANS-ECHO model consistently overestimates the speed dependence. The parameterisations developed here provide class- and speed-specific models suitable for integration into soundscape mapping and cumulative impact assessments.