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Vessels are usually designed on a case-by-case basis, each suited to the different operating requirements of the owner/operator. Differences in design, materials, machinery, and other factors can all influence a vessel’s noise profile. As such, there is no single one-size-fits-all solution for vessel design that will reduce noise. For vessel operators looking to retrofit their vessels, even picking a single component to change is not necessarily a straightforward decision. Changing a propeller, for example, could also involve changing a drivetrain and other engine components. To make a difference to a vessel’s noise profile, you need to understand its operational requirements and what noise sources you are trying to reduce or eliminate.
Noise isn’t the only factor vessel operators will likely have to consider in the future, with increasing pressure (and legislation) to reduce greenhouse gas emissions coming to the fore. Fortunately, as VARD Marine Inc.’s project, Ship Energy Efficiency and Underwater Radiated Noise Matrix, demonstrates, there are plenty of opportunities to simultaneously reduce greenhouse gas and noise emissions and increase the vessel’s energy efficiency. Presented to the International Maritime Organization in 2023 at a Workshop on the Relationship between Energy Efficiency and Underwater Radiated Noise from Ships, the report highlights win/win technologies. Increasing the vessel’s energy efficiency while reducing underwater radiated noise increases the likelihood that a ship operator will invest in the technology with the expectation of seeing a return on that investment in reduced fuel costs.
The Ship Energy Efficiency and Underwater Radiated Noise Matrix looks at multiple measures to reduce noise and greenhouse gas emissions. Crucially, it summarizes each measure’s effectiveness, potential performance, advantages and disadvantages, technology readiness, cost factors, and whether they were suited to new builds or retrofits – or both. The assessment revealed that energy efficiency and underwater radiated noise are often closely correlated, with increased energy efficiency resulting in decreased underwater vessel noise. With this information, ship operators can make more informed choices. The matrix presents about one hundred technologies to reduce underwater vessel noise under the following themes:
- Hydrodynamics: measures to reduce the ship’s resistance through water
- Propulsion: better propellers
- Powering: different energy sources, like batteries
- Other technologies: like wind power
- Operational planning: reducing vessel speed, routing for weather conditions, or avoiding critical marine habitat areas – all effective measures.
With some proven technologies and evidence of co-benefits, it is possible to prioritize ship designs that increase energy efficiency, lower greenhouse gas emissions, and reduce underwater radiated noise. This design prioritization needs to be both intentional and integrated to accelerate progress toward both decarbonization and ship quieting.
Overall, underwater vessel noise is an area in need of more research to understand how to balance reducing noise with other, sometimes competing priorities like energy efficiency and greenhouse gas emissions, both of which are more widely understood. Increased data collection and knowledge sharing, for both energy efficiency/greenhouse gas emissions and underwater radiated noise is required. With more shared knowledge, risk and uncertainty can be reduced for ship owners looking to improve fleet performance on multiple measures.
Future directions: filling the knowledge gap on noise impacts
Research on underwater noise and its impact on marine life is a relatively new science. Alongside understanding exactly how and why vessels make different types of noise, one common challenge that quiet vessel designers (and indeed regulators) face is knowing what frequency, level, and type of noise will cause harm to marine life.
In Europe, mandatory limits on underwater noise came into effect in March 2024. These limits, which consider both short-term and continuous underwater noise sources, were created by a technical working group in 2022 based on the best available knowledge. However, there are still many unknowns about the impact of noise on marine life.
For example, how different marine mammal species change their behaviour in the face of different noise sources, frequencies, durations, and the cumulative impact of noise, combined with other stressors like water contaminants and food availability, are not fully understood.
Equally, the effect noise has on other species, like invertebrates, has received less attention than marine mammals, but studies suggest that low-frequency noise can, for example, impair burrowing activity or embryonic development.
Other knowledge gaps relate to the influence of different oceanographic conditions on underwater noise. In particular, scientists have yet to fully understand how climate change and a warming ocean will affect the level and behaviour of noise in the ocean. Understanding these changes can help create “future-proof” solutions. These knowledge gaps have also been identified in the Government of Canada’s Ocean Noise Strategy for Canada. Future research will shape and guide the evolution of regulations and other measures to minimize noise from vessels in Canadian waters and beyond.
This article is part of a five-article series on ship design to limit underwater vessel noise.
Continue learning about the new discoveries and challenges in making vessels quieter with the other topics in this series here:
The Quiet Vessel Initiative is a federally funded program through Transport Canada. Industry partners and researchers interested in potential research and development collaborations to advance innovative solutions in marine technology are invited to contact the Quiet Vessel Initiative team at Marine-RDD-maritime@tc.gc.ca.
