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Underwater radiated noise (URN) impacts marine life and Naval vessels stealth

Marine anthropogenic noise has increased significantly over the past few decades, and a growing body of research is highlighting the negative impacts this is having on marine eco-systems.


Underwater radiated noise (URN) refers to the sound emitted by ships, boats, and other underwater vehicles and structures. URN is caused by the movement of water and the vibration of machinery and equipment, and can travel long distances through the water. It can have a significant impact on marine life, as many species rely on sound for communication, navigation, and hunting.


URN can have a significant impact on marine life, as many species rely on sound for communication, navigation, and finding food. It can also interfere with underwater communication systems and military sonar operations.


URN can also interfere with sonar and other underwater communication systems used for military, scientific, and commercial purposes. In the past, URN has primarily been a concern for naval vessels, particularly those engaged in anti-submarine warfare or mine counter-measure vessels, and also some research vessels. These sounds can travel long distances through water and can be detected by underwater microphones, also known as hydrophones.



To mitigate the effects of URN, regulations have been established to limit the amount of noise that can be emitted by ships, and mitigation measures such as underwater noise reduction technology are being developed. Industries are developing noise reduction technologies and regulations to limit the amount of noise generated by underwater vehicles and structures.


With increasing pressure to reduce the noise generated by commercial and Naval ships, there is a need to develop new technologies and look at how existing technology can be applied to reducing vessel noise.



Marine propulsion is the mechanism or system used to generate thrust to move a naval vessel across the water. At present, 90% of sea-going naval ship are diesel-powered. Navies are gradually adopting electric propulsion for their ships. There are numerous benefits to electric motor propulsion including that it’s quieter, more efficient at lower speeds, and less smelly. It’s also expected to lower overall costs of ownership by reducing or eliminating the need for oil and transmission fluid changes, filter and impeller replacements and starter problems. There’s less to winterize too. Additionally, unlike diesel or gas engines, electric motors provide full torque instantly so boats get up on plane faster.


Oscar Propulsion Develops Novel Technology To Reduce Underwater Radiated Noise From The Ship’s Propeller

A propeller technology capable of substantially reducing the underwater radiated noise (URN) generated by ships’ propellers has been developed by Oscar Propulsion Limited and the University of Strathclyde.

The patented PressurePores™ system reduces propeller tip vortex cavitation by applying a small number of strategically placed holes in the propeller blades. The addition of these pressure-relieving holes allows ships to operate with a more silent propeller.

Lars Eikeland, Marine Director, Oscar Propulsion, said: “Underwater radiated noise is one of the most adverse environmental by-products from commercial shipping, yet unlike other forms of marine pollution, there is currently no international legislation in place to prevent or reduce this source of environmental damage.

“Increasing noise levels, especially in the low-frequency range, is disorientating marine fauna and disrupting their communication signals, leading to behavioural changes or extinction. We now have a cost-effective, easy-to-apply solution that prevents this from happening.”

Following four years of comprehensive computational fluid dynamics (CFD), modelling and cavitation tunnel tests during the solution’s development phase at Strathclyde, it was demonstrated that PressurePores can reduce cavitation volume by almost 14% and URN by up to 10dB.

Results were further verified in tests on the sub-cavitating propellers on Princess Royal, a 19m research catamaran operated by Newcastle University. And last year, CFD Finite Element (FE) propeller stress tests were successfully completed in accordance with classification society DNV rules.

“We have found the optimum number of holes required to reduce the noise. So long as the right number of holes are placed in the most effective positions, a cavitation sweet spot can be achieved,” said Eikeland.

“It’s not a case of simply drilling holes into the blades, as this will affect the propeller’s thrust capability. We know exactly where to place the holes for maximum efficiency and for optimum noise reduction.”

It is interesting to note that propeller cavitation can generate as much as 188dB of underwater radiated noise and can be heard by marine fauna 100 miles away.

According to the US National Oceanic and Atmospheric Administration, anything above 160db can pose a significant risk to marine life.


Commenting on the impact noise has on marine life, Eikeland said: “Noise levels in the ocean due to maritime activity has been increasing for decades and expected to double by 2030. URN can cause irreversible damage to marine wildlife through stress, habitat displacement, reduced reproduction, lost feeding opportunities and even death, greatly changing the marine ecosystem and impacting biodiversity.”

Eikeland furthered: “PressurePores has a major mitigating effect on propeller cavitation and URN and can be incorporated into new propellers or retrofitted to existing propellers either in drydock or possibly in-water.”


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