Shafting system analysis

Blending theory, measurement and experience

The risk of shafting system failure can be minimised through the classification design appraisal process. However, component failure or adverse operation can occur due to prolonged wear, faulty materials, overload, inadequate commissioning, or the knock-on effects of performance. 

We have been providing expertise in shafting system measurement and analysis since 1947. Our experience allows us to offer an integrated approach which isolates the cause of failure and identifies the optimum solution.

Impartial shafting system analysis Using our proprietary and commercial finite element software, we can undertake independent, impartial shafting system analysis for both investigative and design optimisation purposes. A combination of static and dynamic analysis techniques is employed to identify shafting system problems and propose rapid solutions. 

Static analysis 

We can predict the shaftline characteristics that will result from specified static forces, moments and/or displacements acting at any location on the shaftline, as well as the effects of gravity. 

Assessments include: 

• shaftline deflection, slope, shear force, bending moment and stress at any location on the shaft 

• shaftline stiffness and bearing influences 

• bearing reaction loads. 

Dynamic analysis 

Using a combination of modal, harmonic and transient analysis, we can predict the shaftline torsional, axial and lateral vibratory response characteristics that will result from specified vibratory forces, moments and/or displacements acting at any location on the shaftline. 

Assessments include:

• vibration natural frequencies and critical seeds 

• vibratory response amplitudes and barred speed range 

• fatigue analysis. 

We model the shafting system in detail using a combination of discrete rigid-body-mass elastic elements and continuous beams representing the propeller, shaftline, bearings, shaftline components and the engine. The interaction of the shafting system with the ship structure is represented using foundation stiffness values specified at the bearings.

Our experience

We have undertaken shafting system measurement and analysis for over 35 years, covering a wide range of systems, including both direct-drive and geared propulsion systems powered by single-and multi-cylinder, two- and four-stroke diesel engines. 

Moreover, as a result of our extensive technical investigation and shaft alignment survey experience, we have access to shaftline data from a wide range of ships, which can be invaluable in similar cases of shafting system analysis. 

We also use proprietary software for shafting system components for analytical purposes. Where necessary, in the absence of data from the manufacturer, this software can be used to estimate shafting analysis input parameters, including: 

• engine excitation forces and moments 

• propeller excitation forces and moments 

• propeller entrained water added mass and damping 

• sterntube bearing oil film stiffness and damping.

Benefits

• Rapid diagnosis and rectification of shafting and

shafting component failures, and reduced risk of

re-occurrence

• Permits fine tuning of design.

• Helps minimise downtime or off-hire time.

• Provides the potential for performance

improvements through proactive application of

lessons learned to other vessels in your fleet.

• Impartial service and support worldwide.

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