Wärtsilä Modular Waterjets

  • The modular design allows flexibility in the scope of supply.
  • A compactly designed axial pump with excellent efficiency, cavitation and noise characteristics.
  • High performance components in stainless steel to prevent wear and corrosion.
  • The water lubricated bearing in the stator bowl provides an environmentally friendly solution.
  • Water lubricated Face type sterntube seal with an optional inflatable emergency seal.
  • Inboard mounted thrust bearing block, for increased life and easy maintenance.
  • Tailor-made inlet design based on the shape and operational profile of the vessel.


    The characteristics of a waterjet make it a good propulsor for numerous applications.

    • High speed vessels; waterjets have better propulsion efficiency at ship speeds over 25-30 knots.
    • Shallow draft vessels; the integrated steering function provides benefits for rescue vessels, inshore passenger ferries, landing crafts & special work boats.
    • High power density; the pressure built-up in the waterjet inlet allows small dimensions.
    • Maneuverability; waterjets have integrated steering and reversing with quick response times.

    Examples of such applications include:

    • Fast ferries
    • Littoral combat ships
    • Fast patrol boats
    • Rescue vessels
    • Fast yachts
    • Fast supply vessels and workboats
    • Landing craft

    Key benefits

    • Wärtsilä axial waterjets provide an average reduction of 25% in transom occupation. 

    For naval architects this creates the possibility to apply a larger power density onto narrower hulls so as to achieve top vessel performance.

    Jet sizes are indicated by the front side diameter of the impeller seat ring. Unlike a non-axial design

    (Figure left), the Wärtsilä axial design waterjet (Figure right) does not expand in a radial direction downstream.

    Modular waterjets Key benefits
    • The use of a water-lubricated stator bearing in the stator bowl is beneficial for the environment and enhances the reliability and maintainability of the waterjet.
    • The inboard location of the thrust bearing block (TBB) enables excellent maintainability, and allows the use of large size bearings for increased operating life. The bearing block is designed with a sump to ensure lubrication to the bearings under all circumstances.
    • The cavitation margins of the axial pump are shifted backwards by 35% (see figure below).
    • As a result of this increase in the cavitation margin and the lower impeller tip speed, more power can be utilised during manoeuvring, thus giving a 15% higher manoeuvring thrust. Thanks to the additional cavitation margin, operation with a reduced number of shaft lines is possible at a higher load of the remaining engines, resulting in better operating flexibility.
    Modular waterjets Key benefits 2

    Technical info

    Modular waterjets Technical info
    Marine Solutions 160-1
    Marine Solutions 160-2

    Waterjet size selection

    The selection graphs indicate the jet size required based on the relation between the engine power and the design speed of the vessel. For instance a ship with four 1250 kW engines and a corresponding vessel speed of 33 knots will need four 510 size waterjets. A ship with a design speed of 40 knots at 1250 kW power can use 450 size waterjets. The correct jet size is thus indicated by the line above the intersection of the power and the corresponding vessel speed (see examples in the graphs below).

    We are available from the earliest design stages of the vessel to work with you on an optimised propulsion system. Please contact us  for  an  optimised  jet  selection  based  on  specific  vessel  design parameters, operating profile or for details of waterjets above 50 knots or 30 000 kW. DXF/DWG format general arrangement drawings of the most often used sizes are available.

    Additional design information can be found in the “Waterjets Product guide”, which can be downloaded here.


    Modular waterjets principle 1

    During operation, water enters the waterjet through the inlet duct, which is part of the ship’s construction. After passing the pump impeller, the rotation in the flow is removed and the water is accelerated in the stator bowl. This creates the thrust necessary to propel the ship. For steerable waterjets, the jet stream is deflected by a jetavator which is mounted behind the stator bowl. The jetavator is actuated by an inboard mounted hydraulic cylinder and can be turned 30° to port and 30° to starboard.

    Modular waterjets principle 2

    The jetavator contains a hydraulically activated reversing plate through which part or all of the jet stream can be deflected forward. The reversing plate can be gradually moved, which makes it possible to vary the thrust from full ahead via the zero thrust position to full astern and vice versa.

    The zero thrust position prevents the ship from moving when the impeller shaft is clutched in. The reverse cylinder is equipped with a counter balance valve (load holding valve). This safety device keeps the reversing plate movement controllable and prevents that, in the event of a hose failure, the reverse plate from moving to full astern without control.

    Modular waterjets principle 3

    Scope of supply

    In addition to the main waterjet hardware, Wärtsilä can supply other equipment that can be integrated as part of the Wärtsilä solution.

    • Intermediate shafting
      Shaft line to the gearbox including the flexible elements, support bearings and bulkhead seals.

    • Shaft line calculations
      Whirling and aligning calculations for the complete shaft line.

    • Propulsion Control System

      The Wärtsilä control system can control all propulsors onboard, including the waterjets.
    Propulsion control system
    • Customized hydraulics
      If needed, the hydraulics can be customized to include, for instance, additional functionality.


    • USS Independence
      The USS Independence (LCS 2) entered service in 2010 as the first of a series of initially ten. The vessel design is based on that of a high-speed trimaran and is capable of speeds in excess of 40 knots.

      This innovative combat ship is equipped with Wärtsilä Waterjets.

      USS Independence

    • USNS Spearhead
      The USNS Spearhead is the first of the ten Joint High Speed Vessel (JHSV) supporting the US Navy, Marine Corps, and Army with the intra-theatre manoeuvres of personnel, supplies and equipment.

      It is equipped with Wärtsilä waterjets and designed to reach 43 knots without payload.

      USNS Spearhead

    • SAS Amatola
      The SAS Amatola, commissioned in 2006, is the first of four South African Valour class frigates. These vessels have a ‘Waterjet and a Refined Propeller’ or WARP propulsion solution with three shaft lines. (photo courtesy of Blohm+Voss GmbH)

      SAS Amatola

    • Saad Subahi Class
      The Subahi Class cutters are operated by the Kuwaiti Coast Guard since 2004. Each vessel is equipped with two Wärtsilä waterjets LJ65E. (photo courtesy of OCEA)

      Saad Subahi Class


    Wärtsilä keeps Incat in the fast lane

    For 30 years, Wärtsilä's waterjets have played a vital role in helping Incat build some of the world's...
    28 February 2018
    • Twentyfour7. article

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