Above speeds of approximately 30 knots the traditional fixed pitch propeller, an open stream machine, cannot operate due to the poor priming of its blades.
The introduction of a case which produces a radial discontinuance with the outside, allows an increase of the priming of the turbo-machinery blades and the achievement of higher speeds (40 – 60 knots depending on marine waterjet design).
The marine waterjet drive gives a boat the widest possible operating range: from open sea to shallow waters, due to the elimination of all under keel protrusions. This also contributes greatly to the reduction of night time operational risks.
The absence of open rotating parts provides complete safety for people in the water. Rescue operations by divers for survivors can be safely performed with the engine running to withstand wind or currents.
The reversing bucket may be quickly activated to stop the boat at any speed, within 1.5 times its length. It is possible to shift from full forward to full backward with no strain on the engine as the direction of the water flow is the only thing that is altered in stopping or reversing.
The absence of high speed cavitation pressure peaks, caused by proximity of the propeller blades to the hull and torque effects, drastically reduces hull vibrations and under water noise.
The marine waterjet propulsion system, not having open rotating parts or under hull appendages, cannot cause damage to aquatic fauna.
The intense water flow and the option of directing it downward, allows the waterjet to oxygenate stagnant waters. Furthermore, as water is suctioned to the surface, suspended mucilage is dissipated.
It is impossible to damage the impeller, shafts or steering and reversing actuators in the event of grounding as nothing protrudes from the keel.
Therefore, unscheduled down-times are eliminated. The increased blade tip clearance of the axial flow impeller, caused by wear after extended use in sandy waters, does not affect speed as dramatically as mixed flow impellers do.
There is no danger of vital components (control levers, hydraulic rams) being affected by sea incrustations, by corrosion or by impact as these are all inboard mounted where they are serviceable without docking the vessel.
The impossibility of over-loading the engine leads to reduced engine wear as the characteristic of the waterjet is to maintain constant power absorption and engine speed (according to cubic law); regardless of boat speed.
The boat speed and direction can be adjusted continuously, independently from the pump speed, by setting the bucket, without the impeller losing its grip on the water, because it is never disengaged.
This is a great advantage because the maximum thrust is available at low speed for performing precise maneuvers while in severe conditions, in contrast to traditional propulsion systems in which thrust increases boat speed.
In a twin installation, using one drive in reverse, the other in neutral (and balancing their thrusts to keep the boat at a standstill), it is possible to move the boat sideways while adjusting the steering nozzles, without the use of bow thrusters or electronic control systems.