Answer
Noise measurements are governed by the IMO Code on Noise Levels On Board Ships (Resolution MSC.337(91)), made mandatory under SOLAS Regulation II-1/3-12 for ships of ≥ 1,600 GT.
1. Required Instrumentation
- Sound Level Meter (SLM): Class 1 / Type 1 integrating-averaging meter complying with IEC 61672-1.
- Sound Calibrator: Class 1 calibrator complying with IEC 60942.
- Accessories: Microphone fitted with a foam windscreen.
- Measurement Weighting:
- 'A' Frequency Weighting (dB(A)): Simulates human ear frequency response for continuous equivalent sound levels (L eq).
- 'C' Frequency Weighting (dB(C)): Used for peak/impulse noise assessment.
2. Standardized Operating Conditions During Testing
Condition Parameter | Mandatory Requirement |
|---|---|
Vessel Loading & Speed | Underway at normal service speed (at least 85% MCR / CSR) in full load or normal ballast condition. |
Machinery Operating State | All main engines, generators, purifiers, air compressors, HVAC, and steering gear running under normal sea load. |
Environmental Limits | Deep water, calm weather (Sea state ≤ 3, wind ≤ Beaufort 3). |
Space Setup | Doors and windows closed; HVAC set to normal operating capacity. |
3. Step-by-Step Measurement Procedure
- Pre-Test Calibration: Place the Class 1 calibrator on the SLM microphone. Adjust reading to the calibrator's reference value (e.g., 94.0 dB or 114.0 dB at 1000 Hz).
- Microphone Positioning:
- Height: Hold or mount microphone at 1.2 m to 1.6 m above deck (eye/ear level).
- Distance: Minimum 1.0 m away from walls, bulkheads, or large reflecting surfaces.
- Sampling Duration: Record L eq for a minimum of 10 to 30 seconds at each measuring station (longer if noise fluctuates).
- Post-Test Calibration Check: Re-calibrate SLM after testing. If readings drift by > 0.5 dB, all measurements taken during that session are invalid and must be repeated.
4. IMO Maximum Allowed Noise Limits (MSC.337(91))
Space | Typical maximum |
|---|---|
Machinery spaces continuously manned | 90 dB(A) |
Machinery spaces not continuously manned | 110 dB(A) |
Machinery control room | 75 dB(A) |
Workshops other than those forming part of machinery space | 85 dB(A) |
Navigating bridge | 65 dB(A) |
Accommodation cabins | generally around 60 dB(A) depending on ship category |