Norway’s Kongsberg Maritime has adapted a propeller concept used in naval applications to lower vessel sound signature and is offering it to commercial shipping customers to reduce the effect of underwater radiated noise on marine life.
By machining a channel into the leading edge of the propeller blades, Kongsberg’s Blade Air Emissions concept significantly reduces cavitation-induced noise and erosion risk.
The concept is applicable to both fixed pitch and controllable pitch propellers It uses the results of extensive research by the Kongsberg Hydrodynamic Research Center (KHRC) in Kristinehamn, Sweden, to offer a more silent propeller to the commercial marine market.
“Propellers optimized with the Blade Air Emission system have for some time been used on naval vessels to reduce and distort vessel signature,” says Robert Gustafsson, Senior Hydrodynamicist, KHRC “Following the success of the system we can now roll out the concept to the wider shipping industry as a way to reduce propeller noise and erosion risk.”
Propellers accept cavitation to optimize vessel performance and efficiency, but, says Kongsberg Maritime, by carefully balancing the amount of air circulated around the blades, Kongsberg Maritime can optimize the negative effects of cavitation without adversely affecting ship efficiency.
According to Gustafsson there is an equilibrium. “With too much air, the underwater radiated noise increases, and propeller efficiency reduces. There is a sweet spot. We can optimize the propeller using this concept to achieve the optimum noise reduction without affecting propulsion performance.”
Göran Grunditz, Manager, KHRC, said: “We see huge benefits in the commercial world for the Blade Air Emission technology. While there are financial advantages in reducing the cost of repairing or replacing propeller blades damaged by cavitation erosion, the concept minimizes substantially the underwater radiated noise from a ship’s propeller, which in some cases can be 180dB.
“This is a major environmental problem and is already being considered at a regulatory level. It affects the migratory, reproduction and feeding patterns of marine life, such as dolphins, whales and other species. It also causes high levels of stress for marine life.”
“We are offering the industry a more silent propeller for the benefit of the environment and the ship operator. It’s a real game-change in propeller design.”