Quality Marine Products Distributor


C.W.F.Hamilton & Co.


HJ-241 designed for big block gas engines and medium speed diesel engines 3200 - 4000 rpm @ 350 hp - boat weight 3635 kg for singles and 7270 kg for twins with hydraulic bucket controls

HJet single 241

General Description

The 241 waterjet is normally directly driven by a high r.p.m. diesel or 'big block' gasoline 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 241 waterjet can give high propulsive efficiencies, at least equivalent to the best propeller systems at planing speeds. Any number of jets can be employed without loss of propulsive efficiency. 

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. Preferred control is by a manual hydraulic  system however, less effcient rotary cable steering is optional. 

Reverse A split duct thrust reversing deflector cuts the jetstream aft of the steering deflector, providing an infinite range of ahead, zero or astern manoeuvring speeds. Control is by a cable operated Hydraulic Servo Reverse Control (HSRX) system - a follow up system where the reverse deflector "follows" control lever movement. The HSRX system comes complete with hydraulic powerpack (JHPU) and oil cooler integral with the jet. 

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, 241 waterjets are further protected by fitting of sacraficial anodes. The units are supplied factory tested as a complete package including  integral steering and revese systems with controls and powerpack. 

Installation is simplified as an aluminium intake base is supplied which is fixed into the hull and forms the correct jet inlet shape and mounting for the builder. This block welds into aluminium hull or is molded into G.R.P. or wooden hulls. The GRP version eliminates the need for builders to mould a thick GRP block. This system saves boat builders 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 water tunnel and test craft, the 241 waterjet is an ideal propulsion unit for high speed work and patrol boats, and pleasure carft 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



 3 - 4 tonnes

6.5 - 9 tonnes

10 - 14 tonnes

Power to Weight

48 kW/tonne
(65 hp/ton)

42 kW/tonnne
(55 hp/ton)

38 kW/tonne
(50 hp/ton)

Maximum Power 
Input per jet

260 kW (350 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: 115 kW (150 hp)




Single Jet

Twin Jet

Triple Jet



7.5 tonnes

16.5 tonnes

26 tonnes

Maximum Power
input per jet

80 kW (105 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 241 waterjets are a simple solution ot 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 241 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, however they are 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.

Jastram Logo and page style © Jastram Technologies Ltd.
Hamilton Jet Logo & graphics © C.W.F.Hamilton & Co. Ltd.
last updated 30th May 2005