Wärtsilä 2-speed Gear

• The Wärtsilä 2-speed gear enables vessels that operate regularly with varying propeller loads to be designed with a propulsion system that is highly efficient. The losses from the prime mover to the controllable pitch propeller are small, and the introduction of a gear with a choice of two propeller speeds at a constant engine speed results in excellent propulsion efficiency at varying loads. Thus, by reducing the speed and increasing the pitch of the propeller, at reduced loads greater propeller efficiency is achieved.
• By operating the ship’s propeller at low speed when maximum vessel speed or propeller thrust is not required, fuel consumption can be reduced by as much as 15% compared to a single mechanical propulsion system. At the same time, nitrogen oxide (NOX) and sulphur oxide (SOX) emissions are similarly lowered.
• Despite the low propeller speed, the engine speed is kept constant, thereby allowing the electric power generation from the Power Take-Off (PTO) on the gear to remain uninterrupted.

• The Wärtsilä 2-speed gear is designed for heavy duty application, with outstanding reliability as a priority feature.
• The gearwheels have precision ground single helical teeth, with profile correction to ensure good load distribution and low noise operation.
• Plain bearings are used on the pinion and output shaft, and low friction bearings on the PTO shaft. The plain thrust bearings are of the tilting pad type.
• The high capacity, multiple-disc clutches are hydraulically operated and cooled. The system utilises only soft clutches to ensure shock-free engagement of the main engines and changes in propeller speed.
• Coolers and electric pumps are built onto the gear.

• With hybrid propulsion, the propeller is driven by either or both a diesel engine and/or an electric motor. For vessels that seldom need full propeller power, the hybrid option is ideal.
• Rather than installing a main engine that is unnecessarily large and which will be mostly running at unfavourable loads, full propeller power can be achieved by using the main engine and an electric motor in parallel.
• The electric motor is powered from the auxiliary engines. In other cases, hybrid propulsion is used to improve the propulsion efficiency at reduced vessel speeds.
• For a twin screw vessel steaming at reduced speed, a single main engine can power both the propeller and shaft generator. The power from this shaft generator can be transferred to an electric motor on the other propulsion train. In this way a single main engine can power both propellers. The main engine will operate at high load and high efficiency, and the propellers will operate at low speed and high efficiency.

Certain single screw vessels, such as product tankers and fishing vessels, might have an extra class notation for redundant propulsion in case of a main engine failure. With such a class notation, the Wärtsilä 2-speed gear has a special functionality, since the shaft generator can be used as an electric motor, while the propeller runs at its lowest speed. Thanks to the choice of having two propeller speeds, the actual propulsion power needed to comply with the redundant class notation can be reduced significantly.

The Wärtsilä 2-speed gear reduces noise emissions by up to 20 dB, both inside the ship and externally. This allows greater comfort for crew and passengers, while the reduced underwater radiated noise is important for fishing and seismic vessels, and is beneficial to marine life in general.