Quality Marine Products Distributor


C.W.F.Hamilton & Co.


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.

Alaska Dream 4x422

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.





Not all hull forms are suitable for jet propulsion. The hull shape should be optimized for the craft displacement and design speed. The following Scope of Use is only a guide to achieving best performance and it is important to seek a fully detailed application analysis from HamiltonJet before proceeding, especially if the proposed application is outside any of the limits shown.



Single Jet

Twin Jet

Triple Jet



 12 - 15 tonnes

26 - 33 tonnes

43 - 54 tonnes

Power to Weight

35 kW/tonne
(45 hp/ton)

30 kW/tonne

25 kW/tonne
(35 hp/ton)

Maximum Power 
Input per jet

1180 kW (1580 hp)


  • Above guidelines assume hull size and shape are suitable for the planned displacement.
  • Plan for a minimum cruising speed of 25 knots laden but keep in mind that the higher the boat speed, the better the propulsion efficiency achieved.
  • For speeds above 30 knots, monohedron or constant deadrise of the aft sections of the hull are recommended. This maintains directional stability and deadrise angles between 5° and 25° are typical.
  • For speeds between 25 and 30 knots, some warp in the hull lines may be acceptable, though some keeling could be required to maintain directional stability.


  • Hull resistance in this speed range can be extremely high for some craft - consult HamiltonJet in all cases 
  • Long narrow hulls are best suited, including catamarans of semi-planing or semi-displacement  design. 
  • Maximum Recommended Power Input per jet:   450 kW(600 hp)



Single Jet

Twin Jet

Triple Jet



30 tonnes

60 tonnes

90 tonnes

Maximum Power
input per jet

350 kW (470 hp)


  • a conventional vee stem bow and 5° minimum deadrise aft is recommended to avoid air entry into the the jet. 
  • Minimum jet immersion is with the waterline at the jet mainshaft.
  • For displacement hulls, speed depends more on efficient hull shape than displacement or power input.
  • Best efficiency will be obtained using low power input at, or below, the hull's natural displacement speed. 
  • The displacement guidelines shown above can be at least doubled for long, easily driven hulls.


Because engine overload does not occur and appendage drag is eliminated, model 422 waterjets are a simple solution to multiple speed capability such as loiter and/or boost functions, whether mixed with other size waterjets or other types of propulsion systems.

Please note that dimensions above are indicative only - refer to 422 designer's manual for complete technical data. Due to HamiltonJet's policy of continuous development, all specifications are subject to change without notice or obligation. 

While Hamilton Jet provides typical data for each of its jets, they are however, subject to change without notice and are provided for comparison purposes only. Hamilton Jet is very interested in the success of your installation as is Jastram Technologies. For this reason anyone considering a jet purchase is encouraged to contact Jastram in the earliest planning stages to provide boat hull and engine information so Hamilton Jet can advise the best matches for impellor to engine, and jet to boat in your application and provide preliminary performance estimates.

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last updated 30th May 2005