Rotech Subsea has completed cable de-burial and re-burial work at the Saint-Nazaire offshore wind farm off France’s Atlantic coast.
The Aberdeen-based subsea trenching and excavation company used its RS2 CFE equipment spread to perform the four-month campaign on the omega joints and cable ends at the wind farm off the Guérande peninsula.
Operating in heavy/dense sands at a depth of 20-30m, Rotech Subsea’s RS2 tool de-buried 650 metres of cable, including two joint areas and four cut points in a single pass. With backfill occurring quickly at the site, repeat passes on the four client-specified cut points enabled divers to sling the cable to carry out cutting operations.
Once remedial works had been carried out, the cable was buried to 1.5-2 metres DOL in one pass, save for two small remedial sections. With a maximum outlet pressure of 60kPa and a max jet flow of 4000L/s, the heavy/dense soil conditions experience posed no problem for the RS2 the tool progressed at 1-2 metres per minute.
Launched using the support vessel crane, forward and aft tugger winches controlled the orientation of the RS2 tool which remained suspended above the seabed/cable as the vessel travelled along the cable route. Trench depth for the de-burial and burial operations was monitored real time using a tool-mounted sonar imager.
Rotech Subsea Director of Subsea Stephen Cochrane commented: “The RS2 performed as expected in the soil conditions and the rapid backfilling on the trench posed no problems for the 60kPa tool. Its efficient performant led to a saving on total project costs.”
He added: “We look forward to working with the client again later in the year on a new award with them in the United States for cable trenching ops off the Eastern Seaboard.”