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In the dark undersea world, sound is essential. Marine life relies on sound for communication, foraging, reproduction, and navigation. However, as human activity in the oceans increases, so does underwater radiated noise. Various industries contribute to ocean noise—offshore energy, construction, military operations, and of course vessel traffic. With growing activity from commercial shipping, offshore developments, fishing and recreational vessels, underwater noise from vessels is increasing.
This increase has serious consequences for marine life , particularly species that rely on sound to survive, such as marine mammals. Underwater radiated noise can mask natural sounds, which may make it difficult for individuals to communicate, find a mate or prey, or even avoid predators. Some may change their behaviours, such as communicating less or avoiding or abandoning important habitats. Underwater radiated noise may also increase stress and cause other health problems.
In response to these concerns, Transport Canada’s Quiet Vessel Initiative is stepping up to support research to reduce underwater vessel noise. The Quiet Vessel Initiative provides federal funding for research and development projects to advance and test promising technologies, vessel designs, retrofits and operational practices to make vessels quieter and more efficient, contributing to the protection and recovery of the marine environment and endangered marine mammals. This series of articles explores the results and shares the challenges identified by some of the Quiet Vessel Initiative-funded projects.
How do ships make underwater noise?
All vessels, from small recreational boats to large cargo ships, generate noise that impacts marine life. This noise comes from various sources. Propellers are the primary source of noise, especially during a state of cavitation – when water undergoes a rapid (and loud) change from liquid to vapour due to a change in pressure as a result of propeller motion. The change from liquid to vapour creates bubbles, or cavities, in the water – hence “cavitation”. Engines and other propulsion-related machinery rank as the second-largest noise source, followed by other onboard machinery. Even the design of the hull and the way the vessel moves through the water affects the amount of noise made.
Innovative, quieter designs and technologies that can be built into new vessels or retrofitted into existing ones can play a significant role in reducing vessel noise. Several of the Quiet Vessel Initiative projects focused on developing ways to make propellers, propulsion systems, and machinery quieter.
Learn more about how sound moves underwater.
When to consider underwater noise in vessel design or retrofit decisions?
Noise reduction has not been a common consideration in the design and construction of commercial ships. Instead, ship owners look to maximize efficiency and cargo carrying capacity. However, with growing awareness of the impact of underwater vessel noise on marine life and with international efforts to reduce vessel noise expected to continue, the ships of tomorrow could be designed and built to be much quieter.
Designing a vessel from scratch allows naval architects and marine engineers – the people who design ships – to incorporate quieter technologies and noise-reducing features from the start. Everything, from the shape of the hull to the type of propulsion system, can be optimized to be quieter. However, vessels can operate for many years, sometimes 40 years or longer. Waiting for older, noisier ships to be replaced by quieter new ships would take decades, with the marine environment continuing to get noisier as human activity on the ocean increases. Retrofitting existing vessels – replacing older components or systems with newer ones – can offer a faster way to reduce underwater vessel noise.
Retrofitting vessels with new, quieter components has limitations and deciding whether to retrofit or build a new vessel depends on many factors. First, the physical design of older ships may not be compatible with newer technologies. Equally, retrofitting may not achieve the same level of noise reduction as building a quieter vessel from scratch, as older ships were not designed with noise reduction in mind and each ship operates as a unique system with interdependent parts. The shape of the hull influences the type of propeller, and both elements influence the vessel’s speed and efficiency. Cost-effectiveness also needs to be weighed. Retrofitting can involve significant downtime for the vessel.
For commercial vessels in particular, this downtime translates into lost revenue, on top of the capital cost of new equipment or components to replace older, noisier ones. Furthermore, return on investment for retrofits must be considered in relation to the vessel’s remaining lifespan. Retrofitting an ageing ship may not be cost-effective if the vessel is nearing the end of its operational life.
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.
Cavitation: Propeller cavitation is created by rapid changes in water pressure around the propeller. When a propeller turns, it creates a low-pressure area on one side of the blade and a high-pressure area on the other. When the propeller turns quickly, or the vessel and propeller are under a heavy load, the rapid pressure drop causes the water to evaporate and form vapour bubbles that move over the blades. As the bubbles reach the high-pressure area, they collapse, making noise.
Commercial shipping: Vessels engaged in the transport of goods or people for the purpose of economic trade, including (but not limited to) container ships, bulk cargo carriers, vehicle carriers, tankers, cruise ships and ferries.
Marine life: Mammals, fish, and invertebrates living in the ocean environment.
Mask, masking: A phenomenon where one or more sounds influence how another sound is perceived. This interference makes it difficult for the listener to accurately grasp and identify the sound of interest, causing it to become harder to understand. Masking can occur underwater when background noise, such as waves, wind, rain, or human activities, interferes with the detection or communication of sounds of interest and importance to marine life.
Retrofit: replacing or modifying a ship’s original structure, engine, or other equipment with newer models or technology to improve the ship’s performance, such as increased energy efficiency, reduced greenhouse gas emissions, or reduced noise emissions. One example of a common retrofit for ships is the installation an exhaust gas cleaning system (scrubber) to be compliant with the IMO 2020 sulphur emissions reduction regulation.
Underwater noise: sound generated below water by human activity in the ocean environment. Various industries contribute to underwater noise—offshore energy, construction, military operations, and of course vessel traffic. The noise generated by vessels is referred to as underwater radiated noise.
