Overview
ISO 20083-3:2019 specifies the elastic vibration method to determine the shaft power of ship propulsion systems by measuring shaft distortion. Part 3 of the ISO 20083 series describes the measurement principles, device components (shaft rings, torsion sensors, transmitting/receiving components and peripherals), the calculation method for shaft torque and shaft power, factors that affect measurement accuracy, and required on-board documentation for the shaft power meter.
Key topics and technical requirements
- Measurement principle: Shaft power is derived from shaft revolutions and torsional deformation measured by an elastic-vibration sensor assembly. The standard provides the mathematical relationship to compute torque from torsional deformation and then convert torque and rpm to shaft power.
- Device components: Two split shaft rings with mounted sensors (elastic vibrating material with excitation/pick‑up coils), a non-contact transmitting/receiving unit on the rings, and external peripherals (power supply, antenna, data-processing unit).
- Sensor behaviour and calibration: The device uses two sensors whose natural frequency changes with tension and displacement. Displacement is proportional to the square of the natural frequency; each sensor requires an individual sensitivity constant (C) determined by dedicated calibration equipment. Regular re-calibration is recommended.
- Accuracy factors: Key influences include sensor sensitivity, zero-point adjustment (zero determined with engine stopped), and the shaft G‑modulus. If no certificate is available, a G‑modulus of 82 400 N/mm² is prescribed.
- On-board documentation: The standard defines the documentation that must accompany the device to support correct installation, calibration, zero adjustment and operation.
Applications and who uses it
ISO 20083-3 is intended for practical use where accurate, on-board measurement of engine output and propulsion performance is required:
- Shipowners and operators verifying engine output and most efficient service speed
- Marine surveyors and classification societies performing performance trials and inspections
- Naval architects and shipbuilders assessing propulsion system delivery and commissioning
- Manufacturers and installers of shaft power meters and torsional sensors
- Maintenance teams monitoring propulsion degradation, hull fouling, or heavy propeller running
Practical benefits include confirmation of engine rating, optimization of operational settings, early detection of propulsion deterioration, and support for maintenance planning.
Related standards
- ISO 20083 series (other parts covering alternative measurement methods)
- ISO 15016:2015 (references the same G‑modulus value for shafts)
Keywords: ISO 20083-3:2019, shaft power, shaft distortion, elastic vibration method, shaft torque, shaft power meter, sensor sensitivity, G‑modulus, marine propulsion measurement.