Oscar Propulsion and the University of Strathclyde have developed technology that substantially reduces the underwater radiated noise generated by ships’ propellers. 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.
‘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,’ says Lars Eikeland, Marine Director, Oscar Propulsion. ‘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.’
Holes in propeller blades
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 fourteen per cent and underwater radiated noise (URN) by up to 10 dB.
Results were further verified in tests on the sub-cavitating propellers on Princess Royal, a 19-metre 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.
Eikeland explains: ‘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. 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 188 dB 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 160 db can pose a significant risk to marine life. Eikeland points out that noise levels due to maritime activity have been increasing for decades and are expected to double by 2030.
For new and existing propellers
Eikeland: ‘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.’
While Oscar Propulsions technology is suitable for all types of vessels, they are particularly suitable for naval vessels, yachts, fishing fleets, offshore vessels and cruise and research ships operating in sensitive environments. The technology can be applied to all types of propellers, including pods and thrusters.
The following video shows Oscar Propulsion’s patented PressurePores.