ISO 20283-2:2008

Overview

ISO 20283-2:2008 - "Mechanical vibration - Measurement of vibration on ships - Part 2: Measurement of structural vibration" provides guidelines, required procedures and reporting formats for measuring and diagnostically evaluating structural vibration of ships excited by the propulsion plant. The standard focuses primarily on global structural vibration (hull girder, superstructure, aft body) and excludes transient phenomena (e.g., slamming) and most torsional shaft/crankshaft issues (see ISO 20283-4). It gives practical rules for sea-trial measurements to validate theoretical predictions and to characterise a ship’s vibration behaviour.

Key topics and technical requirements

• Measurement scope
  • Global structural vibration; local vibration is primarily outside this part (see ISO 6954 and Annex D for background).
  • Excludes transient slamming-induced vibration and detailed torsional shaft vibration.
• Test conditions
  • Free-route condition: steady speed and course (helm ±2°), speeds covering ~30%–100% of maximum continuous rated power.
  • Sea state preferably below 3; water depth > 5 × ship draught (adjust if operating in shallow waters).
• Measurement programme
  • Fixed-pitch propellers: discrete speed steps (~2% increments) or slow continuous run-up (≥45 min) with quasi-stationary conditions.
  • Controllable-pitch: use standard combinatory curves to produce ~20 measurement sets across operational range.
  • Typical recording: ≥60 s per step; if not quasi-continuous, key steady conditions recorded for 3 min.
• Instrumentation & signal processing
  • Multi-channel systems recommended (minimum two channels with reference).
  • Frequency range: 1 Hz to 80 Hz; system magnitude accuracy ±5%; frequency resolution ≥0.125 Hz.
  • Preferred spectral windows: flat top or Hanning; use stable mean averaging (not peak-hold). Order-tracking methods are acceptable.
  • Store measurement data on reproducible electronic media for further analysis.
• Reporting & units
  • Include ship/proplusion data, drafts, stern wave/immersion above propeller, damping/balancer arrangements, etc.
  • Preferred units: acceleration (mm/s²), velocity (mm/s), displacement (mm), pressure (kPa).
  • Document peak vibration velocity and optionally overall frequency-weighted RMS (for habitability assessment per ISO 6954).

Applications and users

• Practical uses:
  • Sea trials and acceptance testing to diagnose global hull vibration and validate numerical models.
  • Comparative benchmarking across ship series and verification of propulsion-induced excitation.
  • Identification of resonances, operational deflection shapes and dominant excitation orders (propeller/engine).
  • Support for vibration engineering, mitigation design and habitability assessment.
• Typical users:
  • Shipbuilders, ship owners/operators, naval architects, vibration and structural engineers, test laboratories and classification societies.

Related standards

• ISO 20283 series (other parts): Part 3 (pre-installation vibration measurement of shipboard equipment), Part 4 (propulsion machinery vibration - under reference).
• ISO 6954 - local deck/habitability vibration guidance and reporting format.
• ISO 2041 - vibration terminology and definitions.

Keywords: ISO 20283-2:2008, ship vibration measurement, structural vibration measurement, mechanical vibration, propulsion-induced vibration, global structural vibration, sea trials, vibration transducers, modal analysis.