A vessel is made up of a hull, an engine, and a thruster that is frequently a propeller. A waterjet is a different thruster based on a water pump technology.
The efficiency, is the capacity of the thruster to convert the engine input power into a displacement force.
Average efficiency betwen the different kinds of thrusters
SHAFT PROPELLER : 50% to 65%
LOW PUMP EFFICIENCY WATEREJET : 70%
HIGH PUMP EFFICICENCY WATERJET : 90%
You can have a big engine with a poor thruster efficiency, the performance will be low. If you have a small engine coupled with a high efficiency thruster you have a good solution.
• Waterjets are appreciated for their efficiency savings, it’s the vision of naval industry for several decades
• It enables to reduce : drag, expensive and vulnerable parts under the hull, shaft, propeller, rudder… minimizing risks for the vessel and the environement like swimmers or divers.
• The manoevrabiliy is higher than other systems offering very short gyration radius, and spectacular stopping distances (less than the vessel length for 60 feet ships)