Shipboard noise technical guide · Updated 2026-08-23
IMO MSC.337(91) Onboard Noise Surveys: What Shipowners and Yards Should Prepare
A shipboard space-noise survey, a crew member’s daily exposure measurement and an acoustic source investigation answer different questions. A defensible plan identifies the governing requirement first, reproduces representative vessel operations and records enough time, task and equipment evidence to explain the result.
1. Choose the evidence from the decision
| Decision | Primary method | Evidence | Boundary |
|---|---|---|---|
| Verify cabins, workspaces, control stations or machinery spaces. | Space-based onboard noise survey. | Defined positions, operating matrix, averaging period, machinery state and calibration checks. | A space value does not reconstruct one worker’s daily exposure. |
| Assess a mobile engineer, deck rating, watchkeeper or maintenance role. | Personal sound-exposure measurement or justified task/job strategy. | Representative people, microphone placement, task log, durations, abnormal events and agreed calculation. | A personal result does not identify the dominant source by itself. |
| Investigate why a cabin or work area is too noisy. | Source-path-receiver diagnostics. | Synchronous acoustic, vibration and operating references with controlled comparisons. | Compliance measurements may be insufficient for repair selection. |
| Support newbuilding, sea-trial, class, flag or owner acceptance. | Project-specific plan. | Named rule edition, spaces, conditions, witness route, deviations and traceability. | Report acceptance is not blanket supplier approval. |
2. Start with the controlling requirement
IMO resolution MSC.337(91) adopts the Code on Noise Levels on Board Ships. The Code addresses shipboard noise limits, exposure and hearing conservation, but applicability depends on ship type, build or contract date, flag implementation, exemptions, class notation and owner specification. Record the exact basis before selecting spaces, conditions or acceptance statements.
A contract or voluntary notation can require additional rooms, operating points or stricter limits. Personal monitoring may follow a flag-state or workplace regime. Do not combine limits or convert dose percentages between regimes without confirming criterion level, exchange rate, threshold, integration period and reference duration.
3. Plan representative ship operating conditions
Define propulsion RPM or power, pitch, generator combination and load, HVAC state, pumps, fans, cargo equipment, thrusters, exhaust systems, doors, draught, vessel speed, heading, weather, sea state and water depth where relevant.
| Context | Useful scope | Limitation |
|---|---|---|
| Berth or anchorage | Auxiliaries, HVAC, cargo-support systems and accommodation complaints. | Propulsion sources may not be represented. |
| Harbour trial or commissioning | Equipment combinations and defined quay-side states. | Mooring, restricted load and shallow water can alter results. |
| Sea trial or pre-delivery | Agreed propulsion points and acceptance evidence. | Weather, manoeuvres and incomplete systems must be disclosed. |
| In-service investigation | Real watchkeeping, maintenance, cargo and hotel loads. | Controlled isolation may be limited. |
4. Execute the space-noise survey with traceability
- Agree measurement positions, height, room state, boundaries and averaging period.
- Record meter, microphone and calibrator identity, capability and calibration status.
- Complete field checks before and after the survey and retain the drift decision.
- Log speech, doors, alarms, impacts and nearby work instead of silently deleting data.
- Preserve time histories and frequency evidence for tonal, low-frequency or source questions.
- Identify the criterion beside each result and separate fact, deviation and interpretation.
A room survey supports IMO, flag, class, owner or yard review only when actual applicability and conditions are established; it is not a universal certificate.
5. Personal noise exposure: follow the worker’s real pattern
ISO 9612:2025 specifies methods for measuring occupational noise exposure and calculating exposure level. It includes full-day, task-based and job-based strategies and requires observation and analysis of exposure conditions. The strategy depends on work variability and the decision—not an arbitrary percentage of crew.
Build representative exposure groups
Group people only when duties, watch pattern, machinery and locations create reasonably similar exposure. Separate roles or sample multiple periods when maintenance, mooring, cargo work, drills, weather or overtime changes the pattern.
Control the measurement chain
- Program the personal sound-exposure meter for the agreed method and verify settings.
- Place the microphone in the prescribed hearing-zone position, brief the wearer and record interference.
- Complete required field calibration checks and document instrument status.
- Keep a time-synchronised task, location, machinery, PPE, break and event log.
- Review time history against the log before normalising an incomplete period.
6. Turn high exposure into a control decision
An integrated exposure level indicates risk across time; it does not show what to repair. Rank influential tasks from the time history and log, then add focused area, task, octave-band, source-vibration or transfer-path measurements. For control verification, match before-and-after role, duration, load, route and vessel condition.
7. Produce reviewable reporting
Identify the vessel, purpose and governing basis; spaces or exposure groups; strategy and rationale; instruments, settings and calibration chain; operating matrix; task logs; raw and processed results; calculation basis; uncertainty and excluded periods; findings; control priorities; limitations; and exact retest conditions. Keep space-noise, personal-exposure and diagnostic conclusions separate.
8. Class, flag and supplier-status boundaries
ABS, BV, CCS, CRS, DNV, IRS, KR, LR, ClassNK, PRS, RINA and Türk Loydu can apply society-specific rules, notations, witnessing or supplier requirements. Flag administrations including Singapore, Panama, Liberia, Marshall Islands, Bahamas, Malta, Cyprus, Hong Kong and Isle of Man may implement or review requirements differently. Confirm the flag notice, class rule, contract and surveyor expectation before attendance.
IACS does not approve service companies. Vessel Doctor does not claim class or flag approval, recognition, appointment or guaranteed report acceptance. Project acceptance and formal supplier qualification are separate questions.
9. What to send before attendance
Send vessel and IMO number, ship type, build or contract date, flag and class, governing basis, general and machinery arrangements, crew roles and watch pattern, affected spaces or tasks, operating states, prior surveys, recent changes, safety limits, port or yard, trial window, witness need and deadline.
Attendance can be assessed for berth, anchorage, commissioning, harbour trial, sea trial, dry dock and in-service work in Singapore, Malaysia, India, Sri Lanka, Indonesia, Thailand, the Philippines, the Middle East, Asia-Pacific and worldwide, subject to access and availability.