Traditionally, inspections required draining and refilling, risking structural collapse due to pressure changes. Chile-based Skava Deep Solutions deploys a specialized remotely operated vehicle (ROV), equipped with a Nortek Nucleus 1000 navigation sensor, to inspect these tunnels without dewatering. This approach not only mitigates risk but also reduces downtime from several weeks to just two or three days.
Monitoring Tunnels
Over time, submerged tunnels are subject to degradation, including cracking, deformation, sediment build-up, and material deposition. Detecting and monitoring these changes is essential to ensure operational safety and avoid costly failures. In response, operators increasingly rely on ROVs equipped with advanced acoustic sensors, particularly multibeam echosounders (MBES), to generate detailed 3D models of tunnel interiors in the absence of light.
Yet, the accuracy of the resulting 3D reconstructions depends heavily on precise knowledge of the vehicle’s position, orientation, and motion throughout the survey. In confined, GPS-denied environments, even minor navigation or timing errors can lead to significant distortions in the data, underscoring the need for high-performance navigation and sensor integration solutions.
In confined, GPS-denied environments, even minor navigation or timing errors can lead to significant distortions in the data, underscoring the need for high-performance navigation and sensor integration solutions.
A Challenging Environment
As part of its operations, Skava Deep Solutions deploys its in-house designed and built SK500 ROV, equipped with a Nortek Nucleus 1000 navigation sensor. The system was recently used to inspect a 6- kmlong submerged tunnel at a hydroelectric power plant in Colombia. The scope of work included identifying scour holes, sediment accumulation, and debris such as rock deposits along the tunnel floor. Data acquisition for the inspection was carried out using BeamworX, which is compatible with the Nucleus 1000 system.
Operating in such environments requires a coordinated team and carefully managed workflows. A typical inspection involves an ROV pilot, a sensor specialist responsible for data logging and configuration, and at least two technicians handling vehicle support and cable management.
Surveys are conducted at approximately 1 km/h, meaning a full inspection of a 6 km tunnel, including inbound and outbound runs, can take up to 12 hours. This is typically g p yp y preceded by a full day of system installation and setup, along with up to three hours of pre-dive testing.
Acoustic sensors and MBES systems are deployed to help generate 3D models of dark tunnel interiors. (Credit: Skava Deep Solutions)
“The hardest part of our inspections is equipment setup and positioning,” explains Daniel Rossell, Head of Geophysics and Data Acquisition at Skava Deep Solutions. “We often work in high ambient temperatures, which means we need to move quickly to avoid exceeding equipment limits. At the same time, we’re navigating in long, inundated tunnels where no GNSS signals are available, so we must rely entirely on onboard navigation systems.” Historically, Skava relied on separate inertial navigation systems (INS) and Doppler Velocity Logs (DVL) from different manufacturers. While functional, this configuration introduced complexity and limitations. Misalignment between sensors, loss of bottom tracking, and difficulties in diagnosing system behavior frequently resulted in navigation drift and degraded datasets.
In some cases, drift reached tens of meters per hour, enough to significantly compromise data integrity. These issues often required extensive post-processing corrections or even the development of in-house algorithms to repair faulty datasets. In worst-case scenarios, this could lead to as much as 300 additional manhours spent on data recovery.
Combined Tech for Reliable Ops
Seeking a more robust solution, Skava transitioned to the Nortek Nucleus 1000, an integrated INS and DVL system designed specifically for subsea navigation in challenging environments. By combining both technologies into a single, tightly coupled unit, the system reduces integration complexity while improving overall performance.
“The impact was immediate and measurable. Navigation drift was reduced dramatically, from tens of meters per hour to near-centimeter-level stability over time, resulting in significantly improved trajectory control and data alignment. Tasks related to navigation adjustments during processing were accelerated by at least 50%, while overall processing workflows saw time savings of up to two weeks, equivalent to approximately 100 manhours. This is significant cost saving for us,” explains Rossell.
Equally important, the need for dataset repair was effectively eliminated, removing a major source of operational inefficiency and uncertainty.
“Implementing the Nortek Nucleus 1000 has significantly improved our setup times, data quality, and processing efficiency,” adds Rossell. “In addition, Nortek’s technical support has been a major advantage, consistently providing timely and effective assistance.”
Navigational Precision
The benefits extend beyond processing efficiency. Improved navigation accuracy directly enhances the quality of 3D models generated from sonar data. Features that were previously at risk of being lost, such as anchor bolts or structural reinforcements, can now be consistently resolved. In straight tunnel sections, even over distances of 50 meters or more, the system demonstrates negligible drift, ensuring reliable geometric representation.
The integrated design also simplifies ROV configuration. With fewer components to install, calibrate, and maintain, overall system complexity is reduced. This not only shortens setup times but also improves vehicle maneuverability by minimizing payload size and weight.
Despite these advances, some challenges remain inherent to the operating environment. Many hydroelectric tunnels are reinforced with steel elements, including anchor bolts and ribs, which can introduce localized magnetic disturbances. These can still affect navigation systems, highlighting the importance of robust sensor fusion and real-time diagnostics.
The SK500 ROV with a Nortek Nucleus 1000 to ensure precision navigation in challenging environments. (Credit: Skava Deep Solutions)
Operational Confidence
Skava’s experience also underscores the importance of reliability in mitigating operational risk. Prior to adopting the Nucleus 1000, failures in bottom tracking or attitude estimation occasionally resulted in unusable datasets, requiring costly rework and impacting project timelines. The ability to detect and address such issues in real time has significantly reduced these risks.
While client expectations in tunnel inspections are often driven by point density and data resolution; Skava aims to deliver positioning accuracy of under one meter across all projects. The improved stability and consistency provided by the Nucleus system have strengthened their ability to meet these expectations, while also improving confidence in the final deliverables.
Ultimately, the adoption of the Nucleus 1000 has not changed the fundamental nature of Skava’s services, but it has transformed how those services are delivered. By improving navigation accuracy, reducing operational complexity, and streamlining data processing, the system enables more The SK500 ROV with a Nortek Nucleus 1000 to ensure precision navigatio…efficient, reliable, and high quality inspections in some of the most challenging underwater environments. nortekgroup.com
