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...
https://maritime-professionals.com/why-its-important-to-reduce-propeller-noise/