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HM-422 designed for diesels to 1580 hp @ 2140 - 2300 rpm - This is the smallest HM series jet. So there are control options in the HM range that are far superior to those in the HJ series. This jet is frequently found on vessels exceeding 70 ft in length and frequently requires a gearbox to match the engine rpm to the impeller rpm, vessels over 100ft with quad installations and weights to 54,000 kg are not unusual.

General Description

The 422 waterjet is normally directly driven by a high speed marine diesel or gas turbine marine engines and can be used in planing and displacement craft or in a dual speed role as both loiter and high speed boost propulsion. With it's computer aided impeller designs the 422 waterjet provides high propulsive efficiencies, at least equivalent to the best propeller systems at planing speeds of  25+ knots. Any number of jets can be employed without loss of propulsive efficiency. The 422 is suitable for inputs up to 1180kW (1580hp) @ 2300 rpm. It should be noted that the increased power input capacity of the model 422 over the HJ-403 is suitable for higher boat speeds and not for heavier craft displacement. 

The waterjet mounts inboard at the stern, drawing water through an intake fixed to the hull bottom. The intake is protected by a highly developed screen which, at planing speeds, is largely self cleaning. An intake screen rake is optional. 

The pumping unit carries through the transom, where it is sealed with a rubber 'O'-ring seal, and discharges water directly aft through the outlet nozzle. The reaction of the water being thrust rearwards generates a powerful forward thrust which is fully transmitted through the intake base to the hull (no thrust is transmitted to the engine via the driveshaft).

Steering A steerable nozzle deflects the water to port and starboard, giving powerful steering. Steering is actuated via an inboard mounted tiller. Standard Control is by a manual hydraulic steering system, but power assisted steering is an available option.

Reverse A split duct thrust reversing deflector is mounted aft of the steering nozzle, providing an infinite range of ahead, zero-speed, or astern manoeuvring. Control is by a cable operated Hydraulic Servo Reverse Control (HSRC) system - a follow up system where the reverse deflector "follows" control lever movement. The HSRC system comes complete with jet unit mounted and driven  hydraulic powerpack (JHPU) and oil cooler integral with the jet intake, eliminating the need for an external cooling supply. 

Full steerage is always available regardless of reversing duct position i.e. regardless of of speed or direction. By working reverse and steering in unison a resultant thrust can be obtained in any direction giving 360 degrees manoeuvring. 

Designed and manufactured in corrosion resistant materials to international standards, 422 waterjets are further protected by fitting of sacrificial anodes. The units are supplied factory tested as a complete package including  integral steering and reverse control systems. Certification by Lloyds, ABS etc. is available at an extra cost. 

Installation is simplified as an aluminum intake base is supplied with each jet. This is fixed in the hull to form the correct jet inlet shape and provide a mounting for the builder to fit the jet. The intake block welds into an aluminum hull or is molded into GRP or wooden hulls. The GRP version eliminates the need for boat builders to mould a thick GRP block, saving both time and money. 

A gearbox is not necessary as the waterjet matches a large range of common marine engines directly driven off the engine's flywheel. The engine should be left hand rotation (anti-clockwise when looking on the engine flywheel).

Extensively tested in both HamiltonJet's Hydrodynamic Test Facility and operational vessels,  the 391 waterjet is an ideal propulsion unit for high speed work,  patrol boats, and pleasure craft where operators require proven performance and reliability.

422