International Defense Security & Technology Your trusted Source for News, Research and Analysis
Related Articles
The electrification of ships is revolutionizing the maritime industry, offering the promise of zero-emission travel and the potential to mitigate noise pollution. Yet, the relationship between electric propulsion and noise radiation—both airborne and underwater—remains largely unexplored. A recent study investigating three diesel-electric hybrid ferries operating in hybrid and fully electric modes has provided crucial insights. These findings not only have implications for marine ecosystems and port communities but also touch on the military’s use of sonar and underwater communication systems.
The Maritime Push for Electrification
Maritime transport accounts for 90% of international trade, making it a cornerstone of global logistics. However, growing ship traffic poses environmental and operational challenges. The International Maritime Organization (IMO) mandates net-zero greenhouse gas (GHG) emissions from shipping by 2050, spurring the development of energy-efficient and low-emission technologies like electrification.
While electrification offers a clear path to zero-emission travel, its impact on noise pollution—particularly underwater—remains critical for both civilian and military operations.
Highlights of the Study
The study “Fully Electric Ship Propulsion Reduces Airborne Noise but Not Underwater Noise” examines how transitioning to fully electric propulsion systems can effectively reduce airborne noise emissions from ships, but does not significantly mitigate underwater noise, highlighting the need for additional solutions to address underwater radiated noise (URN).
Electrification in ship propulsion systems brings notable advancements in reducing environmental impacts, with specific implications for noise pollution. Reduced Airborne Noise in Electric Mode is one such benefit, as diesel-electric vessels operating in battery-powered propulsion mode radiate less airborne noise. However, low-frequency tones, which are disruptive to port communities, persist in both hybrid and electric operations, highlighting the need for further refinement in noise control strategies.
In contrast, the study observed Minimal Impact on Underwater Noise between electric and hybrid propulsion modes. Diesel engines, often presumed to be significant contributors to underwater noise, were found to have a minor role during cruise speeds. This underscores the dominant influence of propeller cavitation and hull design on underwater noise radiation, rather than the propulsion mode alone.
The study also explored the Implications for Military Sonar and Communication, revealing that electrified ships could positively influence underwater acoustics by reducing noise interference. This reduction enhances the clarity and range of sonar systems and improves the reliability of underwater communication networks, which are critical for both civilian and military operations. Furthermore, quieter propulsion systems can provide strategic advantages in naval stealth operations by minimizing the acoustic signature of military vessels.
Finally, the study showcased an innovative approach to Simultaneous Noise Measurements, capturing airborne and underwater noise data during regular ferry operations. Achieving this in busy shipping lanes required close cooperation with ship operators, illustrating the potential for real-time noise monitoring to better understand and mitigate the environmental impacts of ship propulsion technologies.
These findings collectively highlight the transformative potential of ship electrification in reducing noise pollution while addressing operational and environmental challenges across various sectors.
Noise Pollution and Its Dual Impacts
Airborne Noise
Airborne noise from ships is a significant issue for communities near ports and shipping lanes. Low-frequency noise, primarily from diesel engines, can disrupt sleep and cause long-term health issues. Electrification mitigates this by reducing overall airborne noise levels in electric propulsion mode, though low-frequency tones remain a concern.
Underwater Noise
Underwater noise affects marine life, commercial sonar systems, and military operations. Propellers and machinery—especially cavitation during cruising speeds—are the primary noise sources. While the study found minimal differences in underwater noise levels between hybrid and electric modes, the implications for underwater acoustics, especially for the military, are significant.
Military Impacts: Sonar and Underwater Communication
Underwater noise pollution significantly affects sonar systems and underwater communication networks, both of which are essential for naval operations. The adoption of electrified propulsion systems offers transformative potential for enhancing operational capabilities and reducing acoustic disturbances in military contexts.
Sonar Interference:
Military sonar systems rely on detecting and interpreting acoustic signals to navigate, detect threats, and conduct surveillance in marine environments. Excessive underwater noise, often attributed to traditional shipping methods, can interfere with these signals, reducing sonar effectiveness. Electrified propulsion systems, known for their reduced machinery noise, could help minimize background noise, thereby improving the clarity, range, and precision of sonar systems. This enhancement is particularly crucial in environments where high noise levels impede accurate threat detection.
Underwater Communication:
Submarine and underwater drone operations depend on acoustic communication, which is highly sensitive to environmental noise pollution. Electrified ships, with their quieter propulsion systems, could significantly reduce acoustic disturbances, enabling more secure and reliable underwater communication. This improvement ensures seamless communication among naval assets, enhancing coordination and mission success in complex underwater environments.
Stealth Operations:
One of the most compelling advantages of electric propulsion in military applications lies in its potential to enhance stealth operations. Reduced underwater noise from electric propulsion systems makes military vessels less detectable to enemy sonar systems, offering a strategic advantage in covert operations. This capability is especially beneficial for submarines and surface vessels engaged in surveillance, reconnaissance, or combat missions.
As naval fleets increasingly adopt autonomous underwater vehicles (AUVs) and advanced sonar technologies, the potential to minimize noise interference through electrified propulsion aligns with broader efforts to modernize military operations. The quieter acoustic profile of electrified ships supports the effectiveness of these emerging technologies, solidifying their role in the future of naval warfare and underwater operations.
Insights from Comparative Studies
Previous research has shown that electric vessels are generally quieter than their diesel-powered counterparts. However, differences in vessel size and engine power often complicate interpretations. The recent study on hybrid ferries offers a more controlled comparison, providing valuable insights for both commercial and military stakeholders.
Measuring Noise Pollution: Collaboration and Innovation
The study demonstrated the feasibility of simultaneously measuring airborne and underwater noise during routine ferry operations. This breakthrough required close collaboration with ship operators, showcasing the importance of joint efforts in addressing complex environmental and operational challenges.
The Way Forward: Designing for Quieter Seas
To maximize the benefits of ship electrification and reduce both airborne and underwater noise pollution, noise-reduction strategies must become an integral part of vessel design and operational planning. These measures will not only enhance environmental sustainability but also support military and commercial operations reliant on acoustic clarity.
Propeller and Hull Optimization:
Advanced propeller and hull designs play a pivotal role in minimizing underwater noise. By reducing cavitation and turbulence, these innovations can significantly lower noise emissions, which benefits marine ecosystems and enhances the acoustic environment for military sonar and underwater communication. Propeller and hull optimization also improves propulsion efficiency, aligning with the industry’s goals of energy efficiency and reduced greenhouse gas emissions.
Low-Frequency Noise Mitigation:
The persistence of low-frequency airborne noise in both hybrid and electric propulsion modes poses challenges for port communities and naval operations. Effective mitigation strategies—such as soundproofing machinery spaces and optimizing generator configurations—are critical to reducing this type of noise. For military applications, addressing low-frequency noise is particularly important, as it can interfere with sonar systems and underwater communication networks, potentially reducing their effectiveness.
Holistic Environmental Policies:
Electrification must be part of a comprehensive strategy to minimize both emissions and noise pollution. Policymakers and industry stakeholders should collaborate on setting stringent environmental standards for ship designs, integrating noise reduction as a key parameter alongside energy efficiency and emission control. Such holistic policies will ensure a sustainable maritime future while supporting operational requirements for naval fleets and safeguarding marine biodiversity.
As the maritime sector continues its transition toward electrification, the integration of noise-reduction measures into ship design and broader environmental strategies will be essential for achieving quieter seas. These efforts will not only address ecological and community concerns but also enhance the capabilities and security of military and commercial maritime operations.
Conclusion
Electrification of ships offers a transformative opportunity to reduce greenhouse gas emissions and noise pollution, benefiting civilian, commercial, and military stakeholders alike. While airborne noise sees a clear reduction in fully electric modes, underwater noise remains influenced by factors beyond propulsion, such as hull and propeller design.
For the military, quieter seas mean improved sonar capabilities, more reliable underwater communication, and enhanced stealth operations. As the maritime industry embraces electrification, a dual focus on emissions and noise reduction will be essential for creating sustainable and secure oceans for future generations.
References and Resources also include:
https://www.sciencedirect.com/science/article/abs/pii/S0029801824009533
