Solid-state MRU and MGC solutions

Why a solid state MRU and MGC from one technology manufacturer has seen industry-wide take up

The maritime industry utilises a spectrum of applications that require precise attitude, heading and position data, as well as reliable performance over time. The use of technology manufacturer Kongsberg Discovery’s solid-state Motion Reference Unit and its Motion Gyro Company (MGC) has therefore become the de-facto industry standard.

Here we explain how the company has spent the past three decades harnessing the understanding of inertia to develop the highly versatile sensing technology that underpins these technologies.

“In 1986, we embarked on a mission to simplify and commercialise inertial navigation technology for the maritime market at an affordable cost. Our engineers spent six years honing the technology, and in 1992 we launched our first MRUs. They deserve huge credit as pioneers,” says Vidar Bjørkedal, vice president SEATEX sales at Kongsberg Discovery.

Key legacy

With over 20,000 MRUs installed and the product name now known as an industry-wide generic term, the Kongsberg MRU has had considerable influence on the industry. Following the success of the MRU line, the MGC was first released in 2014 and more recently, the company launched the miniMRU.

The company’s MRUs feature a cluster of highly tuned accelerometers and Kongsberg-developed MEMS gyros that deliver precise measurements of rotations and accelerations with incredible accuracy. Based on this, the MRUs can calculate speed, attitude and many other parameters. The MGCs, with their north-seeking gyros, also bring true heading output. Particular benefits include a high output data rate, high reliability, compact size, light weight and low power consumption. Neither the MRUs nor the MGCs require any maintenance as there are zero wear-out parts. For most applications, recalibration is also a thing of the past.

Unrivalled motion compensation tool

MRUs can be used as embedded sensors in just about any piece of equipment or working platform that requires accurate motion stabilisation, from offshore jack-up operations, dynamic positioning (DP) systems, riser monitoring and motion damping for fast ferries, to helideck monitoring and even motion compensation for beds on cruise ships. Typical Active Heave Compensation (AHC) applications include offshore cranes, gangways, winch systems, Launch & Recovery Systems (LARS) and hoisting equipment in drilling draw-works.

The MRU feeds data to the controller that regulates the motion compensation system. “Customers can select from more than 350 variables for a particular application, making these units extremely flexible,” says Bjørkedal.

Highly versatile single sensor

Kongsberg’s type-approved and wheelmarked MGCs go on to provide not only simultaneous motion compensation for multiple onboard applications but also replace conventional gyrocompasses for navigation of all ship types. “We’re one of very few vendors globally that can supply a single type-approved sensor that can cater to all applications onboard a vessel – for navigation, cranes, DP, you name it. That is revolutionary,” says Bjørkedal.

Similar to the MRU family, the MGCs are scoped to cater for different use cases and accuracy requirements. The MGGs are built using a different gyro technology, with ring-lasers (RLG) replacing the MRUs’ MEMS-based gyros. These gyros are so sensitive they are able to detect the Earth’s rotation, enabling the MGC to calculate true north.

Simplifying navigation

For vessel navigation, the stability of the MGC can be translated to less rudder usage and thus reduced fuel consumption and emissions. “This is because fewer course adjustments are necessary, which reduces the impact of the rudder and extends the lifespan of the steering system. That also goes for high-speed vessels,” Bjørkedal says.

The exceptional north-seeking capabilities of the MGC outperform conventional gyrocompasses, and this is especially visible in high latitudes. “This capability is beneficial not only for dedicated Polar ships but will also be very relevant if northern sea routes are used amid retreating Arctic sea-ice,” Bjørkedal adds.

The latest generation of MRUs and MCGs is built on the legacy of more than 30 years of experience. “Customers report that the units just keep on working, which is a clear testament to their reliability and durability,” Bjørkedal says.

He adds that both product families are “bottom-line sustainable” due to their maintenance-free design. By eliminating the need for regular servicing and the associated downtime, they ensure continuous operation. This not only removes the necessity for service engineers to visit the vessel but also results in substantial cost savings. Consequently, the uninterrupted performance and reduced operational expenses directly enhance the financial health and efficiency of the operations.

Accuracy is king

The MRU and MGC form the core of Kongsberg Discovery’s Seapath platforms targeting complex hydrographic surveys and seabed mapping. The latest Kongsberg EM2042 MBES brings the miniMRU fully embedded to simplify installation and create a unified INS and multibeam system. The inertial sensor works together with state-of-the-art multi-frequency GNSS receivers and processing algorithms to provide the best possible position, velocity, attitude, time and heading data. All available GPS, GLONASS, Galileo, Beidou and QZSS satellites are used in the position solution.

Customised to requirements

In summary, inertial technology is critical for robust and accurate maritime operations and all Kongsberg Discovery’s MRU/MGC solutions are uniquely flexible. “The segments we serve tend to be bespoke, so in addition to providing standalone units for integration into third-party systems, we also collaborate directly with customers to adapt the technology to their unique challenges.” Bjørkedal says.