The waterjet drive, basic principles and consequent benefits


Essentially a waterjet drive is like an aircraft turbojet with the difference that the operating fluid is water instead of air.

The propelling force is generated by adding momentum to the water through accelerating a specific flow of water sternward.

Water flow from under the vessel is fed through an inlet duct mounted at the transom, flush to the hull bottom, into an inboard pump (the impeller) adding head to the water. A movable grid is fitted at the duct water inlet to protect the intake.

From the pump, the water flow passes through an integrated stator which removes the water swirl generated by the impeller and converts all this pressurized energy into speed, discharging a straight high-speed jet much higher than the boat speed.
This water acceleration generates the thrust which propels the boat.

Steering thrust is achieved by deflecting the water flow by means of steering nozzle while reversing thrust is achieved by deflecting the water flow in forward direction by means of a reversing bucket.

When the reversing deflector is placed in an intermediate neutral position, the water flow is equalized.
In this way, vertical neutral thrust can be achieved independently from the pump speed resulting in zero forward and backward thrust which keeps the boat at a standstill, while full steering is available for precise manoeuvring.
Fine trimmable forward, backward and side movements can be achieved simply by raising and lowering the reversing bucket from the neutral position and by moving the steering nozzle.

As consequence there are some benefits typical and exclusive of the waterjet propulsion system such as:



  • Emergency crash-stop capability
  • Absence of open rotating blades and of any appendage under the hull
  • Minimal damage susceptibility to floating debris and in case of grounding





  • Great manoeuvrability at all speed
  • Easier handling for docking (zero speed with high thrust
    availability all around 360°)
  • In multiple installations, vessel can move sideways





  • No interference in multiple installation
  • Waterjet power absorption is insensitive to boat’s speed. This means constant jet thrust even at boat drag variations
  • Operation in shallow water and beach landing capability
  • Absence of vibrations and reduced internal noise
  • Eco friendly
  • Low underwater acoustic signature
  • Low drag due to the absence of underwater appendages reducing hull resistance