Why are MRUs important for DNV's ASP class notation?
What is the purpose of the MRU in classed vessels?
The MRU (Motion Reference Unit) monitors vessel motions to evaluate risks related to sloshing and structural fatigue in cargo containment systems. It supports a condition-based inspection regime under DNV’s Alternative Survey Programme (ASP).
When is the MRU required?
The MRU is required for vessels with the ASP class notation that include the MRU qualifier. It is not mandatory for all vessels but becomes necessary when motion data is used as part of the alternative inspection strategy.
What documentation must be provided for annual surveys?
For vessels with the MRU qualifier, the following must be submitted:
- Motion sensor records (MRU data).
- Evaluation report if motions have exceeded design assumptions.
- Valid calibration certificates for the MRU.
Why is the MRU important in the Alternative Survey Programme (ASP)?
The MRU enables reduced physical tank inspections by supplying motion data that confirms operational conditions remain within design limits. This supports a risk-based approach to cargo tank survey requirements.
This information relates to DNV-RU-SHIP Part 7 Fleet in service – retention of class - Chapter 5 Periodical surveys - in-operation class notations
Further reading
MRUs for vessel performance optimisation in focus at Europort 2025
Research Project to Test Value of MRU Data for Vessel Performance and Carbon Reduction
Advanced motion compensation for sonars introduced at Ocean Business 2025
Related questions
- Read the full answer
Motion Reference Units (MRUs) are critically important for Helideck Monitoring Systems (HMS) because they provide precise, real-time measurements of the vessel's or platform's motion. Safe helicopter landings and takeoffs depend heavily on understanding the dynamic movement of the helideck, particularly its roll, pitch, and heave.
An MRU accurately measures these key parameters, delivering essential data to the HMS. This information allows the system, pilots, and deck crew to assess whether the helideck's motion is within the established safe operational limits. Without accurate motion data, attempting landings or takeoffs, especially in challenging sea conditions, poses significant safety risks.
- Read the full answer
What is the difference between the MRU Marine and MRU Marine SW?
- The MRU Marine has an IP-68 rating, uses a Lemo 16-pin connector and has indicator lights.
- Read the full answer
Although an Inclinometer, Roll & Pitch Sensor, and VRU all measure attitude (roll and pitch), they vary significantly in accuracy, capabilities, and ideal applications:
- Inclinometer: Best suited for basic static tilt measurements. It is ideal for stationary or slow-moving applications where simplicity and low cost are primary concerns
Check out
Pariatur ullamco aute exercitation nostrud ullamco tempor officia pariatur occaecat eu ex pariatur. Adipisicing amet sunt minim do tempor duis ea cillum ea nulla ipsum ex. Nisi tempor nisi cillum ex dolor proident eu. Nisi velit elit eu pariatur magna aliqua Lorem amet duis. Eiusmod pariatur consequat elit aliqua cupidatat deserunt nostrud exercitation ullamco voluptate enim reprehenderit velit exercitation occaecat. Exercitation incididunt ut consectetur nostrud dolor aute. Deserunt amet occaecat enim exercitation ut dolore ad ullamco proident non nulla. Qui aute tempor culpa amet.