Study: Electric motors no quieter than conventional combustion engines

What's the fuss about?

A new peer-reviewed study conducted by University College London (UCL) examined underwater noise emissions at various speeds in detail. The researchers compared electric and conventional motors on various yachts and vessels. The study, titled "A Comparative Analysis of Underwater Noise Emissions from Electric and Conventional Vessels," was published in the Journal of the Acoustical Society of America (JASA). 

Source: advancedmaritimetechnologyinternational.com

The study was conducted by UCL's Department of Mechanical Engineering in collaboration with RAD, a British company specializing in electric marine propulsion systems. The authors set out to assess the noise levels produced by electric vessels and to scientifically test the widely held belief that they are quieter than their internal combustion engine (ICE) counterparts.

Although electric boat motors are typically quieter to the human ear, the study yielded unexpected results. Spoiler alert: electric motors can generate significant high-frequency underwater noise. This makes them more "noticeable" to species with acute high-frequency hearing, including harbour porpoises and other small cetaceans.

Field testing of engines

The project began with preliminary testing on the River Hamble in Hampshire, UK. A UCL team led by Dr. Tom Smith compared the RAD 40 electric outboard motor with a gasoline-powered equivalent. To ensure the integrity of the experiment, RAD provided two boats that were as similar as possible.

Source: radpropulsion.com

Initial measurements showed that the electric system indeed produces less noise in several frequency ranges. To confirm these findings, a second round of testing was conducted, this time in a controlled environment on a lake near Shrewsbury, England. Two identical boats were tested over several days: one with a RAD 40 electric motor, the other with a combustion engine of the same power.

Data collection methodology

To obtain the most complete picture, an integrated approach was used:

• Acoustic measurements: data were recorded using two hydrophones (underwater microphones).
• Visual inspection: High-speed underwater video was used to analyze cavitation and water flows.
• Airborne noise: Sound levels were measured above the water surface.

The tests were conducted over a wide range of speeds, from 4 to 20 knots, which allowed us to evaluate the noise both during calm maneuvering and during planing.

Experts' conclusions based on the measurement results

"Small vessels are largely out of the discussion when it comes to underwater noise, but they can still be quite loud. They operate in many fragile ecosystems, such as shallow lakes and marshes, so reducing their noise levels is critical," notes Dr. Smith.

Source: maritime-executive.com

The RAD electric motor also showed interesting results. For example, at low speeds, its high-frequency noise was, on average, lower than that of boats with other electric motors. Some might see this conclusion as native advertising—it's no coincidence that the company is one of the sponsors of the study—but the scientists reach a different, elegant conclusion. According to the authors of the study, the RAD's low noise level proves that the problem of high-frequency noise is solvable.

Key figures and conclusions

Here are the results scientists have drawn in comparing internal combustion engines and electric motors:

• 43 dB noise reduction: that's the difference at a speed of 4 knots between an electric motor and an internal combustion engine.
• Broadband Noise: The electrical system exhibited lower noise levels across the entire speed range tested.
• The reason for the difference: The absence of combustion processes and the release of exhaust gases underwater - the main sources of noise in traditional engines, including the specific noise from the release of exhaust gases through the propeller hub

Nuances of the high-frequency spectrum

The researchers detected a high-frequency tonal noise from the motor controller on the electric boat, but its level was lower than in other previously published studies.

Source: advancedmaritimetechnologyinternational.com

Thus, electric motors offer a distinct advantage in waters inhabited by species sensitive to low-frequency noise. However, for animals with highly developed high-frequency hearing (such as toothed whales and pinnipeds), controlling cavitation noise at high speeds remains a critical challenge for both types of motors.

The study confirmed that above 6 knots, cavitation becomes the primary source of noise for both types of engines. However, on an electric boat, this effect can also manifest itself at higher speeds, depending on the propeller design.

From Theory to Practice: Namibia Safaris and Industry Implications

The study's authors also reached another important conclusion: high-frequency noise on electric vessels can be significantly reduced through more careful design of the engine and power electronics.

To test their findings in real-world conditions, the scientists conducted additional observations in Namibia, on the Chobe River. There, Pangolin Photo Safaris already operates boats equipped with RAD propulsion systems. The UCL team compared these vessels with those of other operators to assess underwater noise levels in the real environment.

Source: advancedmaritimetechnologyinternational.com

The conclusions, overall, remain the same: electric motors are indeed quieter than their internal combustion engine counterparts up to a certain point. At low speeds, however, electric motors are still significantly quieter.

Expert opinion

Peter Byford, RAD's Technical Director, notes: "We've always believed that an engineering approach to electric propulsion is crucial not only for performance but also for its real environmental benefits. This study confirms that belief with rigorous scientific data. We're proud to support UCL in this work, which is crucial for the future of sustainable shipping worldwide."

Why is this important for yachting?

The study's findings provide valuable data for marina equipment designers and operators, particularly in regions where underwater noise is strictly regulated. The RAD statement emphasized: "This study provides important guidance for policymakers, conservationists, and the entire maritime industry, confirming the importance of quiet technologies for preserving aquatic ecosystems." 

However, to achieve maximum efficiency, the transition to electric propulsion must be accompanied by a reduction in operating speeds and an improvement in the hydrodynamics of the incoming water flow to the propeller. This means much work remains to be done.

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03.04.2026