How is a motion reference unit (MRU) used in offshore crane operations?
A Motion Reference Unit (MRU) is essential for safe and efficient offshore crane operations. Mounted on the vessel or platform, the MRU precisely measures the 6 Degrees of Freedom (6DoF) motion: Roll, Pitch, Yaw, Heave, Surge, and Sway.
The primary application in crane operations is Active Heave Compensation (AHC). The MRU provides high-accuracy, real-time heave (vertical motion) data to the crane's control system. This allows the winch system to actively compensate for the vessel's vertical movement caused by waves, keeping the crane hook and load stable relative to the seabed or a fixed structure.
Norwegian Subsea MRUs, deliver the high accuracy (up to ±0.01° Roll/Pitch) and reliability required for demanding AHC systems. Our sensors are rigorously tested in real sea conditions, ensuring robust performance. They integrate easily via standard protocols like Modbus TCP, Ethernet/IP, and UDP, and are often used as cost-effective drop-in replacements for older units in retrofit projects.
Related products
Usage area
50 m depth, IP 68
Connectors
Lemo or SubConn 8 or SubConn 16
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Usage area
Hazardous areas
Connectors
Pigtail cable
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Usage area
IP 65
Connectors
RJ45 or RJ50
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Further reading
Advanced motion compensation for sonars introduced at Ocean Business 2025
MRUs for vessel performance optimisation in focus at Europort 2025
Research Project to Test Value of MRU Data for Vessel Performance and Carbon Reduction
Related questions
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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.
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When navigating the complexities of motion sensing and navigation systems, it is essential to understand the distinctions between devices and systems like Inertial Measurement Units (IMUs), Inclinometers, Roll & Pitch sensors, Vertical Reference Units (VRU), Attitude and Heading Reference Systems (AHRS), Motion Reference Units (MRUs), Gyrocompasses, and GNSS-Aided Inertial Navigation Systems (GNSS/INS). Each serves specific purposes and offers different levels of functionality, accuracy, and application scope.
Gyrocompass
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The MRU Compact uses a standard RJ45 ethernet cable where power is supplied through Passive PoE (Power over Ethernet). In most cases you cannot connect the MRU directly to a an ethernet switch with PoE, since most of these are Active PoE.
We normally supply your first MRU Compact with a start kit containing a POE RJ45 spliter socket. You will only need standard RJ45 cat5 ethernet cables to connect the MRU to the spliter socket and the spliter socket to your PC or ethernet switch.
Related applications
Motion Compensated Gangways
Accurate measurements of all 6 degrees of freedom are essential for the automatic motion control of gangways.
Active Heave Compensation
Accurate measurement of vertical motion at the crane tip or winch is crucial for the operation of Active Heave Compensated (AHC) cranes and winches.
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