Vibration analysis identified excessive alternator-side vibration, signs of unbalance and misalignment, and deteriorating resilient mountings that require corrective action.
The Problem
The diesel generator was operating with significantly elevated vibration. Green Sails recorded 33.89 mm/s horizontal vibration at the alternator side, compared with the report-stated IACS limit of 18.0 mm/s. The engine side also measured 21.24 mm/s, above the same reference limit.
What the Analysis Revealed
The vibration spectrum showed a dominant 1X component at 15 Hz, which the report identified as indicating unbalance and misalignment. Vertical measurements also showed a 2X component associated with misalignment, while additional plots indicated stator eccentricity.
Why It Mattered
Physical inspection also showed oil-soaked, cracked and deformed resilient mountings. The report warned that the excessive alternator vibration could contribute to terminal-box fastener loosening and cable vibration/rubbing, creating additional mechanical and electrical risk.
Recommended Action
Check and renew the engine–alternator coupling bolts and replace the deteriorating resilient mountings as a complete set for the generator engine and alternator.
Early diagnosis turns abnormal vibration into planned maintenance — before deterioration progresses further.
Recommended corrective action
Based on the vibration data and mounting condition, Green Sails recommended:
- checking and renewing the engine–alternator coupling bolts
- renewing the deteriorating resilient mountings as a complete set for the generator engine and alternator
- addressing the underlying vibration condition rather than treating only the visible symptoms
The report specifically identifies the resilient mountings as a concern and recommends renewal of the full set.
Technical Investigation
Diagnostic approach
Green Sails carried out vibration measurements on the diesel generator at both the alternator and engine sides, reviewing overall vibration levels together with FFT spectra, time waveforms and circular plots.
For Diesel Generator No.1, the alternator-side horizontal vibration measured 33.89 mm/s, with a dominant fundamental component at 1X / 15 Hz. The report references an IACS vibration limit of 18.0 mm/s. The engine side also measured 21.24 mm/s, above the same reference value.
Technical Investigation
Diagnostic approach
Green Sails carried out vibration measurements on the diesel generator at both the alternator and engine sides, reviewing overall vibration levels together with FFT spectra, time waveforms and circular plots.
For Diesel Generator No.1, the alternator-side horizontal vibration measured 33.89 mm/s, with a dominant fundamental component at 1X / 15 Hz. The report references an IACS vibration limit of 18.0 mm/s. The engine side also measured 21.24 mm/s, above the same reference value.
What the vibration spectrum indicated
The dominant 1X component was interpreted in the report as evidence of unbalance and misalignment. The vertical vibration data also showed a 2X component, which the report identified as an indication of misalignment.
Additional sidebands were observed in the spectrum. The report links these to stator eccentricity associated with the resilient mountings. Circular time-wave plots were also used to illustrate the eccentricity condition.
Physical condition supported the vibration findings
The vibration findings were not considered in isolation.
Inspection of the generator foundation showed visible deterioration of the resilient mounting, described in the report as oil-soaked, cracked and deformed.
Risks identified
The report highlighted that excessive horizontal alternator vibration could contribute to:
- loosening of terminal-box fasteners
- vibration of electrical cables
- rubbing of cables against penetrations
- resulting cable damage
- increased fire risk
The engine-alternator coupling bolts were also identified for inspection and renewal.
Recommended corrective action
Based on the vibration data and mounting condition, Green Sails recommended:
- checking and renewing the engine–alternator coupling bolts
- renewing the deteriorating resilient mountings as a complete set for the generator engine and alternator
- addressing the underlying vibration condition rather than treating only the visible symptoms
The report specifically identifies the resilient mountings as a concern and recommends renewal of the full set.
What the Client Receives
High vibration alone does not tell the whole story. By combining overall vibration values with frequency analysis, waveform behaviour, physical inspection and equipment condition, Green Sails was able to move from an abnormal reading to a specific set of maintenance concerns and corrective recommendations.
- Measured condition of actual vibration values from critical equipment locations.
- Spectrum analysis of FFT data showing dominant frequencies and abnormal vibration components
- Time-wave & circular plots Additional evidence used to understand machinery behaviour and fault patterns
- Photographic evidence Actual equipment condition documented during inspection.
- Risk assessment Explanation of what could happen if the developing condition is left unresolved.
- Corrective recommendations Specific maintenance actions to help technical teams plan repair rather than react after failure