Harnessing the power of computational fluid dynamics to address a significant threat to our oceans

Underwater Radiated Noise (URN), commonly referred to as noise pollution, represents one of the most pervasive human-induced impacts on marine environments. Recent studies indicate that approximately 91% of Europe’s oceans are exposed to continuous noise from commercial shipping, highlighting the scale of this often-overlooked issue.

With pressure for the maritime sector to adopt more sustainable practices growing across both within and outside the industry, reducing underwater noise pollution is gaining increasing attention throughout the maritime sector.

Although measures to regulate the advent of URN from maritime operations are under development, current International Maritime Organization (IMO) guidelines are voluntary.

However, many industry organisations are already taking proactive steps to develop and implement mitigation measures in anticipation of future regulatory requirements, recognising the growing importance of URN management as part of broader environmental goals.

URN refers to the sound waves generated by maritime operations beneath the water’s surface. Primary sources of this underwater noise include ship propellers and engines, as well as sonar, seismic surveys, and construction activities such as dredging and piling. These sound emissions have a profound effect on marine life, particularly species that rely on sound for communication, navigation, and hunting. 

URN is measured primarily through Sound Pressure Levels (SPL), which track the spatial and temporal distribution of noise, and Sound Energy Density (SED), which captures the total acoustic energy within a region. 

As global maritime traffic increases, the combined impact of vessel noise is expected to intensify, further exacerbating these challenges for marine ecosystems.

Despite the shipping industry’s significant contribution to URN, mandatory regulations remain underdeveloped, with operators currently relying on non-binding guidance to manage underwater noise emissions.  

In 2023, the IMO released revised guidelines for the reduction of URN from commercial shipping. While non-mandatory, these guidelines provide comprehensive recommendations aimed at minimising noise throughout a vessel’s lifecycle, from design and construction to daily operations.  

Key measures include optimising hull and propeller design, maintaining ship machinery, and adopting quieter technologies for engines, propellers, and onboard systems, offering practical approaches for shipbuilders and operators to reduce their environmental impact. 

The IMO’s Sub-Committee on Ship Design and Construction (SDC) has also introduced an action plan to support the reduction of URN.

The plan includes a three-year experience-building phase (EBP), allowing member states and international organisations to share lessons learned and best practices.

It also focuses on enhancing public awareness, education, and seafarer training, developing targets, policies, and tools to monitor and reduce noise, and promoting further research into the impacts of URN, providing a comprehensive framework for advancing noise mitigation across the shipping industry. 

Regionally, the EU Marine Strategy Framework Directive (MSFD) mandates that no more than 20% of a marine area should experience continuous underwater noise, distinguishing between impulsive sources such as piling and continuous sources such as vessel operations.  

In June 2025, the High Ambition Coalition for a Quiet Ocean was launched after the 3rd UN Ocean Conference, marking the first global political coalition dedicated to URN reduction. However, mandatory, legally binding regulations remain limited, slowing progress toward comprehensive mitigation.

While regulatory measures for URN continue to evolve, the private industry is providing a practical pathway for future-proofing vessels against incoming regulation, and innovation is fundamental to this effort.  

Computational fluid dynamics (CFD) provides the opportunity to simulate fluid flow and noise propagation, enabling designers to predict noise sources from propellers, appendages, and hull surfaces, as well as to simulate how noise radiates into the marine environment. These simulations allow for the optimisation of designs and operational parameters to minimise noise impact.  

In addition, noise emissions modelling can help identify and reduce noise from onboard machinery, pumps, and piping systems. Notably, many of these technologies and design methods can also be applied in retrofit projects, offering a practical pathway for existing vessels to enhance both energy efficiency and noise performance without requiring major structural changes.

By integrating these technologies, ship owners can operate quieter vessels, significantly reducing their environmental footprint. 

Through a joint research partnership, Elomatic and Aalto University have developed targeted methods to predict URN levels during the design phase by optimising hull shapes, propellers, and machinery layouts to reduce cavitation and vibration.

Aside from these solutions, techniques such as slow steaming have been found to have a positive impact on reducing URN levels, where speed reductions of 20% have been found to lower URN by approximately 6 dB in fixed-propeller vessels. Wind-assisted propulsion offers the potential for noise reductions of up to 10 dB, while air lubrication technology has been shown to cut URN by more than 10 dB, demonstrating the significant impact that operational and vessel design innovations can have on minimising underwater noise.  

Research by the University of Southampton, supported by BIMCO, indicates that energy efficiency measures could account for 32% of the industry’s decarbonisation by 2050, with noise reductions of 5 dB-10 dB. Currently, around 28% of the global fleet is fitted with energy-saving devices, but early-stage design interventions could further future-proof vessels against URN.

URN represents a silent but significant threat to the marine environment. While regulatory frameworks are slowly progressing, technological innovation offers the most immediate opportunity to mitigate URN. Through optimised vessel design, energy efficiency measures, and advanced noise modelling, the global fleet can operate more sustainably, safeguarding marine life for decades to come.