What is a VRU and how does it differ from an MRU?
A Vertical Reference Unit (VRU) is an advanced device that measures the attitude of an object, specifically its Roll and Pitch. Like MRUs, VRUs use accelerometers and gyroscopes, combined with advanced sensor fusion algorithms, to deliver accurate readings even in dynamic and irregular motion conditions.
VRUs are used in applications that require real-time, high-accuracy Roll and Pitch data to ensure effective control system response. Examples include GNSS antenna motion compensation for dynamic positioning (DP) systems, stabilizing fins on vessels, or instrument compensation where only angular measurements are needed. In such cases, where Heave, Surge, and Sway data are not required, a VRU offers a cost-effective and reliable solution.
MRU vs. VRU: Key Differences
Norwegian Subsea’s VRUs and MRUs share the same high-quality internal hardware and sensor precision. The main difference is in the output. A VRU is essentially an MRU configured to output only Roll and Pitch data. It retains all the benefits of the MRU, including rugged construction, high accuracy, and stable performance in complex motion conditions, but it excludes Heave, Surge, and Sway outputs.
All MRU models from Norwegian Subsea (Compact, Marine, Subsea, Ex) are available in VRU versions. These provide the same exceptional Roll and Pitch accuracy (±0.05°, ±0.02°, or ±0.01°, depending on the model) and are a practical, affordable option for applications that do not require full 6DoF motion data.
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
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%
Usage area
6000 m depth
Connectors
SubConn 8
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%
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
MRUs provide accurate roll, pitch, and heave data essential for Helideck Monitoring Systems. This real-time motion data ensures helicopter operations meet safety standards like CAP 437 in dynamic offshore conditions.
- Read the full answer
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).
- Read the full answer
The MRU Marine is IP-68 rated with Lemo connectors and LEDs. The Marine SW supports 50m depth, uses SubConn connectors, and comes in two versions differing by available output combinations.
Related applications
Dynamic Positioning
Dynamic positioning (DP) of vessels necessitates roll and pitch compensation of the GNSS antenna to ensure accurate positioning of the ship's control point.
Stabilising Fins
Stabilising fin and roll damping systems rely on motion sensors to accurately measure the roll motions of a ship.
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.