A new, peer-reviewed study conducted by University College London’s Department of Mechanical Engineering in collaboration with RAD, a UK-based electric marine propulsion company, examined underwater radiated noise across a range of operating speeds, comparing electric and conventional boats. Their aim? To discover if electric boats really are quieter.
The study, titled ‘A comparative study of underwater radiated noise from electric and conventional boats’, is published in the Journal of the Acoustical Society of America (JASA). It was conducted by UCL’s Department of Mechanical Engineering in collaboration with RAD, a UK-based electric marine propulsion company.
The authors set out to quantify the noise made by electric vessels and scientifically test the commonly held assumption that they are quieter than their combustion counterparts. While their engines are generally quieter to human ears, for example, electric vessels can produce significant underwater noise at higher frequencies, making them increasingly audible to species with good high-frequency hearing capabilities, including porpoises.
Following initial measurements indicating lower electrical system noise across several frequency ranges, a second trial was conducted in a controlled lake environment near Shrewsbury. Two identical boats were tested over several days, one fitted with a RAD 40 and the other with a combustion engine of the same output. Data collection included acoustic measurements from two hydrophones, high-speed underwater video and airborne noise readings. Tests were conducted on the boats at speeds ranging from four to 20 knots. The study reports a reduction of 43 dB at 4 knots when comparing the electric vessel with the combustion engine vessel. Lower broadband noise levels were also recorded for the electric system across the full speed range tested.
The findings attribute differences in noise output to the absence of combustion processes and associated exhaust discharge in electric propulsion systems. The research notes that electric propulsion, therefore, offers advantages for species sensitive to low-frequency noise. For species with stronger high-frequency hearing capabilities, such as odontocete cetaceans and pinnipeds, managing cavitation noise at higher speeds remains an important consideration for both propulsion types.
In a statement, RAD says: “The study provides valuable insights for policymakers, conservationists, and the marine industry, reinforcing the importance of quieter technologies in preserving aquatic ecosystems.”
Download the study: The Comparative Study