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A&M - Case Study Tachyssema OCG-Data Offshore Platform

Why Heave Matters

On the ocean, nothing stays still.

 

Vessels, cranes, platforms and surface robots are constantly moving up and down with the waves — a motion known as heave. Without accurate heave information, systems can’t maintain depth, stability and control.

 

The new Heave output from Xsens turns the Sirius and Avior into full industrial-grade MRUs, giving engineers the roll, pitch, and vertical motion reference needed to correct for wave-induced motion in real time.

 

Computed fully onboard using advanced sensor fusion, Heave provides marine engineers with precise motion data for stabilization, drilling, docking, and active heave-compensation systems.

 

Xsens offers Motion Reference Units (MRU) delivering heave output with a 5 cm. accuracy up to 29 seconds. 

A&M - Marine Offshore Drilling 3-Small

How It Works

Heave is derived directly from inertial data.


Xsens’ onboard algorithm performs double integration of acceleration, applying a proprietary phase-correction method to keep the calculated vertical displacement perfectly aligned with real-world motion.

 

The result: real-time, drift-free heave data, updated at 100 Hz and ready for immediate use in control systems.

 

After a short ~40 s convergence, the sensor tracks motion one-to-one with the vessel’s true vertical movement.

Learn More about how Xsens created its Heave algorithm

Heave measurement at offset points

 

When using Heave, it's crucial to specify the COR (Center of Rotation) and the POI (Point of Interest). Both of these points can be different from the location where the MRU is mounted. Defining the lever arms to these points ensures that heave measurements properly account for the vertical displacement arising due to vessel rotations.

A&M - Heave Convention 3D-Small
A&M - Heave Leverarms 3D-Small
A&M - Heave Charts 2

Xsens Heave Performance

The top chart shows how the Xsens Heave filter adapts when the wave period suddenly changes.

 

  • Top: Heave position (black = ground truth, blue = Xsens estimate)

  • Middle: Detected heave period

  • Bottom: Heave error

 

Within ~40 s, the filter re-converges and returns to centimetre-level accuracy.

 

The lower heat map shows the performance envelope of the algorithm across different wave amplitudes and periods.

 

The green region (<5 % error) demonstrates consistent centimetre-level accuracy, maintained up to 29 s wave periods. The grey region shows a <6 % error up to 40 s, confirming stability even under long, slow ocean motion.

What You Gain with Heave

Real-Time Vertical Displacement

Immediate heave data for active heave compensation systems — from offshore cranes to docking and drilling platforms.

Centimetre-Level Accuracy Across Long-Period Waves

Maintains precision even under large, slow marine motions typical of deep-sea operations.

Fully On-Device Processing

All computation happens within the sensor firmware. No extra hardware, no latency, no software post-processing.

Simple Integration

Enable Heave with a simple firmware update.
Outputs roll, pitch, yaw and heave via RS232,  RS422, CAN, or UART.

A&M - Marine Buoy 4-Small

Applications

Heave is fundamental for multiple surface applications where you need to account for wave motion and Active Heave Compensation is required.

 

  • Offshore drilling & crane operations

    Compensate vertical vessel motion to keep tools and payloads steady.

  • Docking & dynamic positioning
    Maintain safe, precise alignment during surface operations.

  • Marine robotics (ROVs, AUVs, ASVs)
    Improved control and navigation near the surface.

  • Buoys & surface monitoring
    Track and record wave-induced displacement.

  • Survey & mapping platforms
    Remove vertical motion noise for cleaner data.

Xsens IMUs are also a great fit for subsea applications and are deployed in hundreds of underwater vehicles.

Learn about all Marine applications

Xsens Motion Reference Units (MRUs)

A&M - Photo Xsens Sirius AHRS Workshop-Web

Xsens Sirius MRU

  • Designed to withstand the most harsh marine environments.
  • MIL-standard IP68 housing, resistant to temperature extremes, humidity, salt spray, shock & vibration, and electromagnetic interference.​
  • Built-in support for Heave.
Learn More
A&M - Photo Avior Workshop Background 2-Web-opt

Xsens Avior MRU

  • Premium OEM solution, low SwaP-C package.
  • High accuracy for demanding motion dynamics.
  • Wide interface support (UART, CAN, I2C, SPI, UART, RS232, RS424, optional EtherCAT).
  • Built-in support for Heave.
Learn More
Marine - 2

Trusted Across the Marine Industry

Xsens inertial sensors are already widely used in:

 

  • Offshore drilling and construction

  • Vessel stabilization and dynamic positioning

  • ROV/AUV navigation and control

  • Marine robotics, buoys, and surface platforms

Engineers worldwide rely on Xsens for dependable motion data that powers research, safety, and automation at sea.

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Inertial Sensors for Marine Applications - FAQs

What is an MRU?

An MRU (Motion Reference Unit) is an inertial sensor system designed to measure roll, pitch, and heave motion on marine platforms. MRUs are used on vessels, offshore rigs, and underwater systems to monitor and compensate for movement caused by waves and vessel dynamics.
Xsens Avior and Sirius are industrial-grade MRUs, combining high-accuracy orientation (AHRS) with integrated Heave output — delivering MRU-level performance in a compact and cost-efficient form factor.

What is Heave and why does it matter in marine systems?

Heave refers to the vertical up-and-down motion of a vessel or structure caused by waves.
Accurate Heave measurement is crucial for operations like drilling, crane stabilization, docking, and autonomous navigation — where vertical displacement must be known or compensated in real time.
Xsens sensors provide real-time Heave data processed onboard, helping marine engineers stabilize systems and improve safety and control.

How is an Xsens MRU different from traditional marine MRUs?

Traditional MRUs are large, certified, and costly systems designed for heavy-duty vessels and defense use.
Xsens MRUs — based on the Avior and Sirius platforms — deliver the same motion data precision (roll, pitch, and Heave) but in a more compact, industrial-grade form.
They are ideal for integrators building smaller, scalable, or cost-sensitive marine systems such as ROVs, AUVs, buoys, and autonomous surface vessels.

What kind of accuracy can I expect from Xsens Heave output?

Xsens Heave algorithms provide up to 5 cm accuracy for wave periods up to 29 seconds, and 6 cm for up to 40-second periods, matching or outperforming traditional MRUs in real-time performance.
Unlike many systems that require post-processing, Xsens Heave is computed directly onboard — ensuring real-time Heave data for control and monitoring applications.

What makes Xsens sensors reliable in marine environments?

Each Xsens module undergoes in-house calibration and rigorous testing for accuracy, temperature stability, and magnetic disturbance rejection.
Industrial-grade housings (up to IP68) protect against water and salt spray, while onboard algorithms ensure reliable performance in both calm and high-dynamic conditions.

What is the difference between Avior and Sirius MRUs?

Both are industrial-grade MRUs with Heave, sharing the same sensor fusion firmware.

  • Avior: Compact OEM module for integration into embedded systems and small vehicles.

  • Sirius: Housed, IP68-rated MRU ready for external mounting in marine environments.
    Both provide identical performance and data output — the difference lies in form factor and integration style.

Marine Case Studies