Compared to a single mechanical propulsion system, a fuel consumption reduction of 8% was verified with W?rtsil?`s two speed gearbox during sea trials. It is anticipated that further reductions of up to 15% can be achieved, with a similar lowering of nitrogen oxide (NOx) and sulphur oxide (SOx) exhaust emissions.
These cost savings and environmental benefits are achieved by operating the ship`s propeller at low speed when maximum vessel speed or propeller thrust is not required. At the same time, the engine speed is kept constant, thereby allowing the electric power generation from the Power Take-Off on the gearbox to remain uninterrupted. Furthermore, the W?rtsil? two speed gearbox will reduce noise emissions by as much as 20dB both inside the ship and externally. This allows greater comfort for passengers and crew, while the reduced underwater radiated noise is important for fishing and seismic vessels, and is beneficial to marine life in general.
The first ship to utilise the new W?rtsil? two speed marine gearbox is a rescue vessel owned by the Rescue & Salvage Bureau of the People`s Republic of China`s Ministry of Transport. Sea trials have been successfully carried out at the Huangpu shipyard in China. The vessel operates mostly in low speed mode and reaches full speed only for limited periods of time. The W?rtsil? two speed gearbox allows the operator to make the necessary adjustments as needed, thereby saving costs even when operating at low speed.
"The W?rtsil? two speed gearbox is the best solution for our rescue vessel in terms of both economy and overall efficiency, says Mr Sun Lu Ming, deputy chief engineer of MOT Rescue and Salvage Bureau. “This gearbox enables a proper balance between full speed operation and the ship`s daily operating mode, which is important because its operating profile varies."
The W?rtsil? two speed gearbox will be available with a high degree of modularization in the power range from 2MW to 10MW. W?rtsil? will continue to introduce its range of two speed marine gearboxes throughout 2014 and 2015.