ROV-installed stability monitoring system for submerged buoys


Ashtead Technology was contracted by Subsea 7 to design and supply instrumentation packages to monitor submerged buoys for heading, pitch, roll and depth. The buoys supported 27 steel catenary risers (SCRs).


The Asset Integrity team is made up of specialist Ashtead Technology engineers and equipment, dedicated to improving operational performance and safety during the design, construction, installation, maintenance, repair and decommissioning phases of offshore assets.

Subsea 7 approached the team with a requirement to monitor submerged buoys connected to subsea SCRs in Brazilian waters. To service this requirement, Ashtead Technology engineered a bespoke Autonomous Monitoring System (AMS+) to deliver heading, pitch, roll and depth data in a format suited to the client’s operating requirements.

Ashtead Technology installed, configured and tested an acoustic telemetry system, integrated with the client’s acoustic positioning system. Our team of specialist technicians also provided operations and calibration training to on-site staff, helping the client to unlock maximum benefit from the package.

The stability monitoring system consisted of an instrumentation package which could be removed and re-installed subsea by ROV and still maintain alignment accuracy. Subsea system data was transmitted to a topside vessel via an acoustic modem with a backup underwater LED display. Extended autonomy was achieved with power management and optimisation.

Benefits and value

The stability monitoring system provided essential data during critical stages of the installation process. Ashtead Technology’s AMS+ performed faultlessly throughout the project, delivering valuable data for the successful installation of the buoys and SCRs. In addition to its technical competence, this scope marked the first-ever use of an independent structural monitoring system integrated within a Sonardyne 6G USBL and LBL transponder/modem to send a non-standard data telemetry string.

The subsea control module embedded the subsea structural monitoring system AMS data within the standard acoustic positioning telemetry string, which was then decoded using custom Ashtead Technology software aboard the vessel. This system removed the potential for acoustic interference problems normally found when using two separate systems in close proximity. This scope was also the first long-term deployment of a structural monitoring system for the company, with 14 days’ autonomous operation availability.