New waterjets from Wärtsilä

Wärtsilä Corporation has introduced a new compact, high-performance waterjet that is optimized for fast vessels. The new Wärtsilä LJX waterjet offers, in comparison with other waterjets available today, a 25% reduction in mounting flange diameter, a 10% overall weight reduction and a 35% increase in cavitation margin. The LJX waterjet allows further innovation in fast vessel design and is being developed to allow an optimum number of waterjets to be chosen for a given propulsion power requirement without requiring an excessive transom width in high-speed vessels.

Generally, when selecting waterjets, the required power is distributed between multiple waterjet units to create an installation with lower weight, higher efficiency and, above all, lower costs than when using fewer, larger units. But multiple waterjets have a penalty in increased transom width, which is usually unacceptable in high-speed vessels as transom width is an important vessel design parameter.

In addition, waterjets currently available on the market are designed to cover all propulsive requirements for extremely high vessel speeds, up to more than 70 knots, and for very high powers on relative small diameters. However, the Wärtsilä LJX waterjets cut out the extremes in hydrodynamic design parameters and are based on a completely new design approach to create more compact jets with heavily increased cavitation margins.

The mechanical design of the Wärtsilä LJX waterjet is similar to the current Lips Jets series with all main parts of the stator and the steering assembly fabricated from stainless steel plates. This approach allows Wärtsilä to achieve minimum weight with maximum design flexibility. It is thus possible to have not only common steering/reversing and booster jets, but also jets for fast crash stop and reversing, jets with nozzle closing devices, and jets with inboard hydraulic systems. The oil-lubricated thrust bearing remains inboard in the jet room with a water-lubricated marine bearing supporting the shaft in the stator bowl; a design choice that is made for reasons of easy maintenance, access and reliability.