Rotech Subsea completes St Nazaire cable work

4C Offshore | Tom Russell
By: 21/09/2022 Rotech Subsea
Subsea trenching and excavation specialist Rotech Subsea (Rotech) has wrapped up a four month cable de-burial and re-burial campaign at an offshore wind farm off France’s Atlantic coast.

Under contract with a submarine cable system company, which had retained Aberdeen-based Rotech on a similar scope of work in November 2021, Rotech Subsea’s RS2 CFE equipment spread carried out cable de-burial and re-burial on omega joints and cable ends at the
Saint-Nazaire offshore wind farm off the Guérande peninsula.

Operating in dense sands at a depth of 20-30m, Rotech Subsea’s RS2 tool de-buried 650m 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 1.5m-2m 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 RS2 the tool progressed at 1 to 2m/min.

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 traveled 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: “It was great to work again with this leading submarine cable player in Saint Nazaire. 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 and we look forward to working with the client again in the future.

“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.”

The 480 MW Saint-Nazaire wind farm, currently owned by EDF (50%), Enbridge (25.5%) and CPP (24.5%), is expected to be fully commissioned by the end of 2022. It is located between 12 and 20 kilometres off the Loire-Atlantique coast. It will consist of 80 GE
Haliade 150-6MW wind turbines. Work is scheduled to run throughout the summer and autumn.

According to GE, each Haliade turbine powers 5,000 homes; the project is expected to generate the equivalent of 20% of Loire-Atlantique’s electricity consumption.

For more information on offshore wind farms worldwide,
click here. Alternatively, you can view projects across the globe using 4C Offshore's Interactive Map.