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 the water instead of air. The propelling force is generated by accelerating a certain flow of water in an astern direction. Water flow from beneath the vessel is fed through an inlet duct mounted at the transom flush to the hull bottom. Inside the duct lies the “impeller” which driven by an engine accelerates the water, increases it‚s pressure and therefore provides a propulsive jet stream to the water. This jetstream provides the thrust that drives the boat forward.

Just before the water discharges out of the jetbody, the jet stream flow passes through stator. The stator has a number of blades which are designed to straighten the water flow, which is going in a rotational direction created by the turning impeller. The stator by removing the swirl discharges a straight high speed water jet which is faster than the boat speed. This accelerated water creates the thrust necessary to propel the boat.

Steering and reversing thrusts are generated by deflecting the jet flow by means of a nozzle for steering, and a deflector (bucket) for reversing.

When reversing , thrust is achieved by deflecting the jetstream in a forward direction and not by changing the rotation of the impeller. A similar principle to jet planes reversing the thrust of the turbine after landing.

If the reversing deflector is placed in an intermediate neutral position, the water flow tforward and backwards is equalized. Neutral thrust is achieved resulting in zero forward and astern thrust which maintains the boat at standstill with full steering available for precise manoeuvring.

Forward, astern and side movements can be achieved merely by raising and lowering the reversing deflector from the neutral position and by moving the steering deflector. As a consequence, some typical and exclusive benefits available to water jet propulsion are possible as follows:

Safety:

» Fast and strong stopping ability as there is no need to change the rotation of the impeller.

» Absence of open rotating blades and of any appendage under the hull.

» Minimal damage susceptibility to floating debris and in case of grounding.

» Possibility to operate in shallow areas.

» Minimal impact to marine life in sensitive areas.

Manoeuvrability:

» Great manoeuvrability at all speeds.

» Easier handling for docking
(zero speed with high thrust availability all around 360°).

» In multiple installations, vessel can move sideways.

Others:

» No interference in multiple installation.

» Jet’s power absorption is insensitive to boat’s speed. This means constant jet thrust at boat drag variation.

» 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.

These exclusive features grant to Castoldi Waterjet Drives unique benefits..