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Gaps USBL systems: 20 years of innovation in subsea positioning
July 24, 2025
This year marks a major milestone for Exail: the 20th anniversary of Gaps, our industry-leading USBL (Ultra-Short Baseline) underwater acoustic positioning system. Developed and manufactured in Brest, Gaps has been at the forefront of subsea navigation technology since its first deployment in 2005, offering an unmatched combination of ease of use, precision, and versatility.
What is Gaps?
Introduced in 2004, Gaps was the first system to integrate a USBL acoustic positioning module with an inertial navigation unit in a single compact housing. This breakthrough eliminated the need for prior calibration, common in other systems, saving valuable time during maritime operations where every second counts. Designed for maximum flexibility, Gaps can be deployed from a wide range of platforms, including buoys, surface drones, vessels with winch systems, or lateral poles.
" We pioneered hybrid acoustic/inertial technology, where the acoustic antenna determines the relative position of an underwater vehicle, and the inertial unit compensates for orientation and movement, ensuring accurate geo-referencing,” says Paul Urvoas, USBL Product Manager. “While competitors have since integrated inertial sensors, Gaps continues to lead in performance and adaptability, especially in shallow-water environments."
A legacy of continuous innovation
Over two decades, Gaps has evolved through five generations of development, each expanding the system’s capabilities:
- 2005: Launch of Gaps Titanium, the original model, weighing nearly 50 kg.
- 2008: Introduction of Gaps Carbon, reducing system weight by two-thirds and enhancing portability.
- 2013: Launch of a new generation featuring a web interface, Ethernet connectivity, and compatibility with third-party acoustic beacons.
- 2018: Addition of telemetry features, enabling position and message transmission to Autonomous Underwater Vehicles (AUVs).
- 2020: Introduction of Gaps M5, optimized for shallow-water environments and intermediate performance needs.
- 2023: Release of the fifth-generation Gaps M7, featuring low-frequency positioning for greater depth and V2 telemetry for improved AUV control. This version is already deployed in the Belgian-Dutch (rMCM) and Latvian (IMANTA) mine countermeasure programs.
- 2024: Launch of Gaps M3, a version without an inertial unit, ideal for permanent installation alongside onboard gyro and MRU. Fifth-generation technology is now available across M3, M5, and M7 variants.
" Expanding the Gaps product range helps us address diverse operational needs and enter new markets with a comprehensive offering,” Paul Urvoas explains. “More than 25 experts contributed to the development of the fifth generation, and our outstanding production team has already delivered 50 Gaps Gen5 units. "
A trusted global solution
Widely regarded as the reference USBL system for shallow water operations, Gaps stands out for its compact form factor, plug-and-play usability, strong performance, and open compatibility with third-party beacons and navigation software.
To date, over 450 Gaps systems have been deployed worldwide across three distinct models, with more than 180 units delivered in just the past four years. Our client base spans a wide range of sectors:
- Defense: 30 Gaps M7 units are in service for the Belgian-Dutch rMCM program, equipping Exail Inspector 125 surface drones and mine warfare vessels.
- Offshore Oil & Gas: Since its inception, Gaps has played a critical role in ROV positioning and pipeline installation.
- Offshore wind: Thanks to its high performance in shallow water, Gaps supports geophysical surveys, inspections, and various phases of wind farm development.
- GNSS-denied environments: Gaps M7 provides offshore navigation and positioning using its integrated high-grade INS (Phins), aided by USBL and LBL ranges. It maintains a precise solution compatible with DP systems for navigation and station-keeping.
Looking ahead
As we celebrate two decades of success, our Brest-based underwater positioning and navigation teams are already shaping the future.
" One of our key R&D priorities is the development of a new range of beacons to cover all applications,” Paul Urvoas reveals. “We're also exploring next-generation USBL antenna designs to replace the current models. "
For 20 years, Gaps has pushed the boundaries of underwater positioning. As innovation continues to drive us forward, Exail remains committed to delivering high-performance solutions that empower the maritime industry worldwide.
