Define the machinery decision before measuring
A vibration survey may screen condition, diagnose an abnormal machine, verify a repair, support commissioning, investigate an RPM band or document acceptance. Those decisions need different points, operating states, analysis tools and evaluation criteria.
Write the decision, suspected equipment, relevant operating range and required evidence before selecting instrument settings. “Take vibration readings” is not a diagnostic plan.
Choose the measurement quantity for the frequency range and component
| Quantity | Useful role | Caution |
|---|---|---|
| Displacement | Lower-frequency motion and shaft relative vibration where the machine and probe arrangement support it. | Casing displacement and shaft-relative displacement are not interchangeable. |
| Velocity | General severity screening across a useful mid-frequency range on many machine housings. | An overall value can hide the frequency pattern and source. |
| Acceleration | Higher-frequency content, impacts and detailed spectrum/waveform work. | Bandwidth, mounting and integration strongly affect comparison. |
| Envelope/demodulated signal | Selected repetitive high-frequency impacts associated with rolling-element bearing or gear questions. | Requires suitable setup and corroboration; it is not a universal bearing test. |
Declare units, peak/RMS convention, frequency range, filters, sampling and integration. ISO 13373-1 provides general guidance on vibration measurement parameters, transducer selection, location, attachment, data collection and operating conditions.
Measure at points that represent the machine and transmission path
- Use identified bearing housings or casing points in consistent horizontal, vertical and axial directions.
- Record sensor type, mounting method, orientation and any access compromise.
- Include both sides of couplings, gearbox stages, driver/driven machines and structurally relevant mounts.
- Add foundation, connected pipework or nearby deck points only when they test a transmission hypothesis.
- Do not compare a hand-held probe point with a permanently mounted sensor as though the methods were identical.
Build an RPM, load and operating-condition matrix
Document shaft/engine RPM, electrical or process load, valve position, running auxiliaries, temperatures, vessel speed and relevant sea or berth condition. Stabilise each state and time-align changes with the vibration record.
For an issue at one RPM, measure below, through and above the band where safe and authorised. Run-up/coast-down evidence can separate a speed-sensitive structural response from a forcing component that simply follows rotational speed.
Use each analysis view for the question it can answer
Screen and locate
- Overall magnitude for screening.
- Spectrum for frequency/order relationships.
- Point and direction comparison for localisation.
Test the hypothesis
- Waveform for impacts and modulation.
- Phase for relative motion and response.
- Envelope for selected bearing/gear evidence.
- Run-up/coast-down for speed-sensitive response.
Common patterns are clues—not automatic fault labels
| Observed pattern | Possible investigation | Why more evidence is needed |
|---|---|---|
| Dominant 1× running speed | Mass distribution, eccentricity, bent shaft, alignment, forcing and structural response. | 1× is not proof of imbalance. |
| 2× or multiple harmonics | Alignment, looseness, distortion, rub, waveform shape and phase. | 2× is not proof of misalignment. |
| Harmonic series or impacts | Mechanical looseness, clearance, rub or intermittent contact. | Waveform and physical inspection should agree. |
| Gear mesh and sidebands | Load, tooth condition, eccentricity, modulation and gearbox stage. | Normal mesh energy depends on design and operating state. |
| High-frequency/envelope components | Bearing geometry, lubrication, speed, load and contamination. | Mounting and other impact sources can mislead. |
| Broadband hydraulic/aerodynamic energy | Cavitation, turbulence, recirculation, flow and valve condition. | Process evidence is needed to separate sources. |
| Narrow RPM-sensitive peak | Natural frequency, response shape, phase and source-path comparison. | Resonance needs speed-dependent evidence, not one steady reading. |
For expanded examples, read seven ship vibration patterns to investigate.
Separate source, transmission path and response
A machine can generate force without having an internal defect; a compliant foundation or deck can amplify a modest force; a cabin can respond strongly at a local mode. Compare technically related points under the same operating condition before deciding where the corrective action belongs.
If the main decision concerns occupied-space comfort or hull response, use the whole-body/habitability or structural/hull vibration canonical rather than forcing every query onto the machinery page.
Do not mix screening, troubleshooting, trending and acceptance
| Decision | Strongest route | Output |
|---|---|---|
| Why is this machine vibrating now? | Focused marine machinery vibration testing, measurement and diagnostics. | Fault hypotheses, corroborating evidence, confidence and targeted checks. |
| Is condition changing over time? | Vessel machinery condition monitoring. | Baseline, trend, alert logic, action and next interval. |
| Did overhaul or commissioning meet the agreed basis? | Controlled verification or acceptance measurement. | Operating matrix, results, criteria, exceptions and retest scope. |
| Where does noise/vibration travel through the vessel? | Source-path-receiver troubleshooting. | Controlled comparisons and ranked corrective options. |
What a defensible vibration-analysis report should contain
- Machine identification, arrangement, symptom and decision.
- Point/direction map, transducers, mounting, units, bandwidth and settings.
- RPM/load/process/vessel condition for every data set.
- Overall values plus relevant spectra, waveforms, phase or envelope evidence.
- Applicable manufacturer, project or standard basis and its limits.
- Measured fact separated from interpretation and probable cause.
- Confidence, competing hypotheses, limitations and required confirmation.
- Prioritised action, verification test and monitoring interval.
Class, flag and acceptance context
ISO 20816-1 gives general measurement and evaluation procedures; it excludes torsional vibration and does not replace the correct machinery-specific criterion. Class notation, supplier qualification, manufacturer limits, contract acceptance and ordinary troubleshooting are separate requirements. Confirm the applicable basis and review route for the actual vessel, class, flag and attending surveyor.
This guide supports planning for classed and flagged vessels but makes no approval, recognition or guaranteed-acceptance claim.
Five items to send for a fast diagnostic review
- Vessel and machine identification, arrangement and rating.
- Symptom, affected point/space and when it began.
- RPM/load range, duty cycle and operating state that reproduces it.
- Previous spectra, waveforms, trends, alarms, repairs or failures.
- Required decision, access window, location and report deadline.
Attendance can be assessed at berth, anchorage, shipyard, dry dock, harbour trial, sea trial and in service across Asia-Pacific and worldwide, subject to access and availability.
Turn the machinery question into a controlled onboard scope.
Send the vessel, machine, operating condition, symptom, available history and required decision. The scope will define the measurement route, analysis evidence and deliverables before mobilisation.
Review the canonical serviceRequest a technical scope