Acoustic positioning technology employed for pipe laying project

Sonardyne GyroUSBLs mounted on Lorelay’s stinger will track an ROV during touchdown monitoring operations Photo: Allseas Sonardyne GyroUSBLs mounted on Lorelay’s stinger will track an ROV during touchdown monitoring operations Photo: Allseas

A global offshore pipeline installation and subsea construction company will use Sonardyne International’s GyroUSBL acoustic positioning technology for its latest pipe laying contract.

Allseas will use the GyroUSBL onboard its 236-metre long lay vessel, Lorelay, in conjunction with a Ranger 2 USBL (Ultra-Short BaseLine) topside, to acoustically track an ROV deployed to ensure a pipe is accurately touching down in the permitted corridor.

“Locating a transceiver on the stinger is a great solution for ensuring that vessel noise disruption is rejected. The time-saving features of GyroUSBL results in reduced operational costs with the ability for users to move it from vessel to vessel with minimal downtime whilst maintaining the highest levels of positioning performance,” said Alan MacDonald, sales manager at Sonardyne in Aberdeen

Target tracking

USBL transceivers are routinely deployed through the hull or over-the-side of a vessel, enabling targets to be tracked below, to the side and far behind.

However, on a large DP pipelay vessel such as the Lorelay, a transceiver cannot reliably ‘see’ through the thruster wash created at the rear so touchdown monitoring operations are often conducted by an ROV operating from a survey vessel (equipped with its own USBL system) following on behind.

But the stinger-mounted GyroUSBL offers a proven alternative. The unit combines a 6G HPT transceiver (either 5,000 or 7,000 model) and Lodestar Attitude and Heading Reference System in the same assembly and is supplied pre-calibrated to eliminate the mechanical alignment errors seen in conventional USBL setups.

These features allow an acoustic transceiver to be sited well away from noise interference, even on a dynamic structure such as a stinger, and deliver outstanding positioning performance. It also means that a pipelay vessel is able to employ its own ROV to carry out touchdown monitoring, allowing the accompanying survey vessel to get on with another task, or eliminating the need for it altogether.

The Lorelay will be third vessel in the Allseas fleet to be equipped in this way, with systems already in operation on the Pioneering Spirit and Solitaire.

By Anne-Marie Causer

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