CJR design strategy can be called holistic approach to the propulsion system. We don’t only make propellers, we analyse entire propulsion system of each boat starting from hull resistance prediction and hull propulsive factors. We select most efficient gear ratio, recommend changes if needed and analyse flow in every point under the hull using the most advanced CFD tools developed specifically to our requirements. This approach gives us the widest picture of possibilities we can use to run your boat more efficiently, quietly and fast or to any other specific, most demanding requirements.

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Propeller and sterngear Design procedure

Resistance prediction

Every propeller enquiry initiates estimation of effective power of the boat the needs to be propelled through the water at certain speed and resistance prediction plays a big part of it. As a first step CJR uses quick and reliable prediction software based on regression line developed by Southampton University on the basis of hundreds tested hulls. Much more sophisticated tool is Computational Fluid Dynamic software that can predict with a great detail and show flow around the hull, pressure field as well as running trim angle. The latter feature of the program can be used to find the most optimum trim angle for the boat.

Optimum reduction ratio selection

Having speed prediction of the hull natural step forward is to select optimum gear ratio that gives the most efficient propeller operation. Gear ratio and engine power govern almost all shaftline parts sizes including propellers, shafts, P-brackets and all associated parts. Gear ratio is a factor that has a huge influence on overall propeller performance.

Propeller sizing

Strictly connected to the reduction ratio, power of the engine and speed of the boat. CJR uses purpose built software based on number of different propeller series for quick selection of diameter, pitch and number of blades. Lifting line software is utilised for more detailed selection that allows checking blade area requirement due to cavitation.  If you would like to read more about lifting surface software please click on the link

Strength and Rule check

Safety at sea is the most crucial and paramount objective for CJR. Every component designed and built under classification society rules is sized to meet their requirements. CJR in-house software allows for checking of all parts of the sterngear to RINA, BV, LR and many other Societies rules. Additionally propellers blade thickness and stress level can be checked using software based on beam theory taking into consideration nonuniform loading over the blade. This method is approved by most IACS societies and can be used as an alternative to the rules to make propeller blade thinner and more efficient.

Besides Classification Society requirements, newly designed and fit for purpose components are analysed using Finite Element Method software ANSYS, which gives ultimate picture of component strength under most extreme loads. Please read more about FEA here.

Hull wake and propeller inflow

It is the most important information that shows the difference between good and bad propeller design. It can make even decent propeller noisy, vibrating and inefficient. Without knowledge about water inflow to the propeller, every propeller is a guess work. Using CFD software tailor made to suit planing and displacement crafts CJR introduced propeller wake calculation as a standard procedure. That allows CJR also to optimise propeller inflow by changing shaft brackets design and position or propeller tunnel shape and recommend these changes to boat designer.

Final propeller design

The most advanced vortex-lattice code in propeller market is used to tune propeller final design. Propeller is run by the software in behind hull condition and every blade parameter like chord length, pitch, camber, profile shape can be separately adjusted to the flow to get highest possible efficiency at the propeller design point. Different type of cavitation can be detected on the blade and pressure pulses induced on the hull, the biggest source of noise, are calculated. Propeller model is generated together with pattern model and machine program.

Propeller slipstream and rudder design

Rudder area is calculated on the basis of boat size and type, and rudder sections are carefully selected, dependent on flow regime. Purpose built software that couples CFD and propeller code together allows CJR to replicate propeller slipstream under the hull. That is a great advantage in rudder design as detailed inflow velocities is known. Rudder sections will be aligned with the flow to generate minimum drag going on straight line and maximum lift force while turning.

Shaft Brackets and shaftline design

Knowledge about flow around the hull and sterngear allows designing shaft brackets with the least impact on water inflow to propeller as well generating lowest possible drag. Location of the bracket and other supporting bearings along the shaftline as well as  entire shaftline can also be analysed using Shaft Lateral Vibration Calculation to find out if shaft stresses are within limits under all operation conditions and there is no thread of excessive vibration. 

  • Bearings

    Suitable bearings are required in stern tube and rudder tube assemblies.

  • CJR Propellers

    Every boat is different and the first sign of this difference can be seen in propeller operation.

  • Couplings

    Couplings are the elements that transfer torque from gearbox to the shaft and because of their role they are under strict supervision of class societies.

  • Ducted Propellers / Nozzles

    CJR can offer ducted propellers systems including any type nozzles and impellers under full IACS approval.

  • Rudder Tubes Assemblies

    CJR manufactures rudder tube assemblies designed for hull trough installation to suit stock diameter from 30mm up to 180mm.

  • Rudders

    Rudder profile and sections are carefully selected to specific regime of the flow around sterngear.

  • Shaft Brackets

    Our shaft brackets are designed bespoke to achieve optimum performance in line with every vessel individual requirements.

  • Shaft Seals

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  • Shafts

    Shaft design starts from designing entire shaftline incorporating all the components from the propeller to the gearbox and including the bearings to make the system safe, vibration free and efficient in operation.

  • Stern Tubes / Shaft Logs Assemblies

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  • Tie Bars

    Tie bars connect both rudder tillers on twin rudder boats to simply synchronise them together.

  • Tillers

    Tiller is important part of steering gear which design is covered by strict rules of classification societies when the boat is built under class.

  • Shaft Alignment

    Using laser technology and precision engineering a bespoke shaft alignment tool has been developed to aid the boat builder’s task of accurately fitting and aligning the stern gear.

  • PropSmith

    For the fast, simple and precise installation and removal of propellers, PropSmith is the professionals’ choice.

  • TrialDAS

    TrialDAS is a new data acquisition system specifically tailored for monitoring sea trials. The system is based on rate gyros, GPS, accelerometers and magnetic field sensors to record every movement of the boat.

  • Keyless Hub Hydraulic Kit

    Quick and convenient method of pushing and releasing large propellers or couplings to and from the keyless shaft cone.

  • Hydraulic Propeller / Coupling Pusher / Puller

    Quick and convenient method of pushing and pulling propellers or couplings to and from keyed shaft end.

  • TrialsAPP

  • Quality Policy

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  • Design

    We don’t only make propellers, we analyse entire propulsion system of each boat starting from hull resistance prediction and hull propulsive factors.

  • Pattern Making

    Precise pattern assures high accuracy of final product and it is one of the most important stages in manufacturing process

  • Casting

    CJR's foundry team has the combined benefits of over 150 years experience in the industry.

  • Machining

    CAD/CAM controlled machining of the cast propellers, P brackets and rudders are undertaken to the fine tolerances of their original design

  • Finishing

    Our processes ensure that the geometry of our finished castings is always true and accurate to the original design.


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CJR Propulsion Ltd
70-72 Quayside Road
Bitterne Manor
SO18 1AD
United Kingdom

Tel: +44 (0)23 8022 2032
Fax: +44 (0)23 8021 1832