Fully electric ship propulsion reduces airborne noise but not underwater noise

Electrification of ships offers zero-emission travel and is spreading rapidly, but the relation between electric ship propulsion and noise pollution is not generally understood. Here, three different types of diesel-electric hybrid ferries have been measured in two operating modes: running in hybrid mode with the diesel engine powering an electric generator; and running in fully electric battery powered mode. Measurements were performed to simultaneously quantify airborne and underwater radiated noise. Findings are that on-board diesel engines for electricity generation do not contribute a large extent of the underwater radiated noise, whilst a major source of airborne low-frequency radiation. •Diesel-electric vessels radiate less airborne noise in battery-powered propulsion mode. Potentially disturbing low frequency tones are present in both modes.•Small or no changes in underwater noise levels were observed between electric and hybrid propulsion; diesel engines are a minor contributor to underwater noise at cruise speed.•Airborne and underwater ship noise radiation can be simultaneously measured in route, even in busy shipping lanes. This requires close cooperation with ship operators.