Rotech Subsea, the leading provider of innovative subsea trenching and excavation tools to the energy industry, has completed a cable de-burial, grab, cut, recovery and post-lay trenching on an inter array cable at a leading southern North Sea offshore wind farm.

Engaged by a global dredging contractor and marine services provider, Rotech Subsea mobilised its cutting edge RS2-3 Hybrid Jet Trencher and RSG-C Integrated Cutter & Grab tool from Waalhaven in the Netherlands. Deployed via ships crane, the hybrid RS2-3 hybrid Jet Trencher tool completed de-burial operations of the 200m section of cable which was buried at up to 3.5m below MSBL in just 1 pass at 3-4m/min with the tool suspended 1.5m above the seabed. Upon completion the RS2-3 performed a single pass over the entire cable to assist with recovery.

Cable recovery

The grab, cut and recovery of the 150mm cable was executed by Rotech’s patented RSG-C tool. The tool was positioned by USBL transponder, NBI Sonar and monitored by survey nav screen in the control cabin. A tool-mounted sonar confirmed the cable had been grabbed with the cutting process taking less than 15 minutes at each cable end. The RSG-C tool then recovered the cable to deck.

Seabed conditions experienced on the job varied from loose silty sands to very dense gravelly sand, with stiff to hard clays also located along the cable route. Water depth was 29-50m with currents recorded at 1-3 knts and sea state 1m Hs.

Speaking about the IRM works, Rotech Subsea Director of Subsea, Stephen Cochrane, commented: 
"This was another extremely successful deployment for our revolutionary hybrid Jet Trencher system for a repeat client. Short work was made of the conditions by the RS2-3 with the high-pressure RS3 jet trenching system on the hybrid tool operating at a maximum jet outlet pressure of 300 kPa, capable of cutting very stiff soils. The other tool head - the RS2 - with its much lower outlet pressure provided the very high flow required to fluidise the soils and excavate up to the 3.5 m depth the cable was buried too.”

Rotech Subsea’s research, development and engineering team has created a suite of 18 sector-leading non-contact CFE, Suspended Jet Trenching tools in-house at its Aberdeen HQ. With enhanced capabilities, Rotech Subsea’s CFE & Hybrid Jet Trenching suite of tools is firmly established as the method of choice for offshore wind farm cable trenching and excavation in Europe and beyond.

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