Gaps on board Castoro Sei

iXblue has delivered two Gaps USBL positioning systems for the “SAIPEM’ semisubmersible pipelay vessel CASTORO SEI. The equipment will be used in the deployment of pipes for the “supergiant” Zohr gas field, located off the Egyptian coast in the Mediterranean sea.

The 2 Gaps are installed at the extremity of the pipelay stinger. An iXblue INS (Rovins) is installed in the ROV (Remote Operated Vehicle) and receives the USBL positions through the umbilical. Gaps and Rovins provide for accurate and robust positioning of the ROV that is monitoring the touch down point.
This installation of the Gaps on the stinger affords on the one hand a direct acoustic line of sight between the Gaps transceiver and ROV mounted beacon, and on the other hand excellent acoustic performance due to the transceiver being located far from the main noise sources.

This installation location is only made possible by the high performance INS embedded in the Gaps transceiver. The attitude and heading of the Gaps is precisely measured no matter what the movement of the stinger.

The CASTORO SEI deploys the pipe in shallow waters (up to 100 m of water depth). This involves slant ranges up to 400 m and high elevation tracking. The width of the corridor for the deployment is +/- 10 m. The specification for the positioning accuracy when crossing pipes is +/- 2.5 m.

“We have chosen Gaps because this is the only USBL system that doesn’t require calibration and can track with high elevation angles. Working on a barge without any possibility of making calibration patterns, this was the only alternative”, commented Tristan Fleury, in charge of the project for SAIPEM.