The Magazine for Underwater Professionals

Nov/Dec 2016


GOSL's flexible friend

Multitasking Nexus USBL boosts efficiency at Nigerian operator Geodetic Offshore Services

1000 Series beacon on GOSL's Argus Mariner XXL52

Geodetic Offshore Services Ltd (GOSL), a major operator in the Nigerian energy industry, has purchased two Nexus USBL positioning systems from UK-based Applied Acoustics to deploy on its various offshore projects including underwater installation, diver monitoring, seabed surveys and ROV operations.

Emanuel Ekpeyong, managing director at GOSL, says that he is more than satisfied with both the versatility and flexibility of the rack-mount USBL system. “The Nexus system has been mobilised as a stand-alone underwater positioning reference, back-up reference to vessel DP system and, in a complex setup, utilised with other equipment. Its compatibility with the additional systems we own is a real plus,” he explains.


The company deploys its Nexus USBL systems with 1000 Series Mini positioning beacons and the smaller 200 Series Micro beacons from Applied Acoustics. The larger beacons are most often mounted on the GOSL work-class ROVs, such as its Argus Mariner or its Super Mohawk, but are also used to track divers during inspection work, for example during a subsea hose change-out project that took place in waters offshore Equatorial Guinea.

One of the most recent projects using one of GOSL’s Nexus systems was a mattress and spool piece installation in Escravos, offshore Nigeria. Here the Nexus system was deployed for both underwater accurate positioning of the mattresses within tight tolerances and diver monitoring (air and saturation dives at various depths). The mattress and spool piece operation was a subset of a field development project which includes pre-lay surveys, pipelay and as-laid surveys in water depth up to 60 metres. The Nexus system was particularly effective during pre-pipelay mattress installation works, where it was able to accurately detect the exact pipeline crossings on which the mattresses were eventually laid. The mattresses were installed to accuracy ranging from 0.21 metres to 0.99 metres which was well within the tolerance requested in the scope of work. The tolerance for the spool piece operations was also achieved.

  • 1000 Series beacon fixed on diver's jacket by GOSL survey crew

“Our positioning services are constantly in demand in shallow and deep water for a variety of customers such as Exxon Mobil, Chevron and Shell, which require underwater intervention, inspection and installation services, so GOSL have undertaken numerous projects utilising Applied Acoustics’ equipment which has always proved easy to use and reliable,” says Ekpeyong. “We are convinced that our overall operational efficiency has improved with these purchases.”

The Nexus system is just one of the USBL systems manufactured by Great Yarmouth-based Applied Acoustics that are deployed to determine the position of static and dynamic subsea targets through the transmission and reception of acoustic signals between the submerged transceiver and the target beacon. This particular design, the top-of-range Nexus USBL, incorporates bi-directional Spread Spectrum technology that reduces susceptibility to interference and rejects unwanted reflected signals that have made operating in challenging locations such as ports or harbours difficult in the past.





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