Impact of Methanol-Based Fuel Cell Propulsion on the Acoustic Signature of a Marine Vessel

In this work, the underwater acoustic signatures of marine vessels are investigated, with a focus on the impacts of methanol-based high-temperature proton exchange membrane fuel cell (HT-PEM FC) propulsion systems and their coupling with structural dynamics. The acoustic field is modeled through a monopole–dipole representation directly linked to the vibration and dynamic response of the vessel structure and propulsion units. The model is validated against experimental sound pressure level (SPL) data as a function of depth, showing excellent agreement: the SPL decreases from about 140 dB at 5 m to approximately 120 dB at 50 m, where the model prediction (119 dB) closely matches the experimental value (121 dB). Representative numerical results indicate the suppression of the monopole component for the HT-PEM FC and a reduction in the dipole pressure amplitude by approximately a factor of 19 relative to the diesel engine (DE) configuration. In the 20–100 Hz band, at r = 10 m, the acoustic pressure amplitudes range from O(101−102) Pa for the diesel engine (DE) to O(100−101) Pa for the HT-PEM FC, while, at r = 105 m, they decrease to O(100−101) Pa and O(10−1−10−2) Pa, respectively. The absolute levels depend on the assumed structural excitation and vibro-acoustic coupling and are mainly used here to quantify the relative reduction achieved by the HT-PEM FC with respect to the DE. A distance-normalized formulation is introduced to account for geometric spreading, enabling a consistent comparison despite differences in source characteristics. Overall, the proposed framework establishes a direct link between structural vibrations and underwater radiated noise and provides a physically consistent and quantitatively validated approach for the design of low-signature marine propulsion systems.