Wärtsilä 2-speed Gear

The Wärtsilä 2-speed gear is designed to serve vessels having multiple operational modes or reduced transit speeds. These vessels can gain notable economic & environmental benefits:
‑ fishing vessels
‑ rescue tugs
‑ offshore support vessels
‑ seismic support vessels

  • All single screw vessels with redundant propulsion system (“take me home system”) will benefit from this gear type.
  • Reducing the speed & increasing the pitch of the propeller procures greater propeller efficiency at reduced load.
  • Less fuel consumed means that nitrogen oxide (NOx) and sulphur oxide (SOx) emissions are lowered. 

The Wärtsilä 2-speed gear is available with a high degree of modularization in the 2 MW to 13 MW power range.

Fuel savings of up to 15% can be achieved compared to a single speed mechanical propulsion system, thanks to the key feature of the 2-speed gearbox: the option to reduce the propeller speed while the vessel speed remains constant.

Key benefits

    High propulsion efficiency
    • 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.
    Hybrid propulsion
    • 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.
    Redundant propulsion
    • 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.
    Reduced noise and vibration
    • 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.




    The Libas, delivered 2004, is a combined purse seiner and trawler designed by Wärtsilä Ship Design for the future needs of the global pelagic fleet.

    Read more about Libas

    Product hologram

    Main features

    Power take-off (PTO)

    All Wärtsilä gears can be supplied with one or more PTOs for driving the shaft alternator, compressor or pump. For single vertical and horizontal gears, the standard PTO is primary driven. For double gears, the PTO is optionally primary or secondary driven.

    A primary driven PTO rotates whenever the engine is rotating.

    A secondary driven PTO rotates whenever the propeller shaft is rotating.

    Special gears

    Based on the standard Wärtsilä gear types, customized solutions can be delivered upon request.


    • Combined vertical and horizontal offset
    • Multiple power take-off (PTO)
    • High power PTO
    • High power power take-in / dedicated hybrid propulsion gears

    Power take-in (PTI)

    Most Wärtsilä gears can be supplied with a combined PTO/PTI. In PTI mode the shaft alternator can also be used as an electric motor. PTI is normally used for the following operational modes:

    PTI “Booster” mode is used when the main power of the engine is insufficient in order to increase the total propulsion power. For this mode, no clutches are required on the gear.

    PTI “Take me home” mode is used in case of emergency should the prime mover be inoperable. For this mode a minimum of 2 clutches are required on the gear.

    Hydraulic power unit

    Most Wärtsilä gears are purpose-designed with an integrated hydraulic system for both the gear and the CP propeller. As a separate hydraulic power unit for the CP propeller is superfluous, both installation costs for the yard and operational costs for the owner are reduced. For safety reasons the gear mechanically drives the main pump for the propeller. All gears can also be interfaced with a separate hydraulic power unit.

    The introduction of a gear, able to select from two propeller speeds while the engine speed remains constant, results in excellent propulsion efficiency at varying loads.

    Technical Info

      Power Range
      2-speed gears Power range
      Fuel savings of up to 15% with the Wärtsilä 2-speed gear”
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