A series of successful cable trenching and Seabed levelling campaigns in Taiwan’s offshore wind sector - with further contracts in the pipeline - has led Aberdeen-based Controlled Flow Excavation (CFE) & Suspended Jet Trenching pioneer, Rotech Subsea, to establish a new entity in the country. With three spreads of its cutting edge CFE equipment active in country presently, the company has secured works well into 2023.

Latest scope wrapped up

With an impressive track record in Taiwan, dating back to 2019, in June 2022 Rotech Subsea successfully completed its latest major scope of work in the country. Having been contracted by a leading international marine infrastructure player to assist with de-burial & cable trenching operations on a key offshore wind farm, Rotech mobilised its TRS1LD jet trencher in early May 2022.

The state-of-the-art TRS1LD tool was deployed by ship’s crane into water 30-55m deep to carry out de-burial of wet stored export cable sections, export cable remedial burial works, inter-array cable remedial burial works, and inter-array cable backfill works. With outriggers and clump weights set up forward and aft of the trenching tool and connected with running lines to control orientation, the TRS1LD remained suspended above the seabed / cable to complete all trenching operations. 

The vessel’s DP positioning system was used to move the trenching tool along the cable routes with USBL transponders fitted to the tool providing accurate data on the location of the tool at all times. Trench depth was monitored real time using a tool-mounted sonar imager with the client carrying out their own survey to confirm that the completed trenching ops met the required specifications.

Speaking about the successful campaign, Rotech Subsea Director of Subsea, Stephen Cochrane, said: 
"This was a technically challenging scope for a valued client and we were delighted to deliver it on schedule and on budget.

"To avoid possible free span, the de-burial and remedial trenching were completed using minimal power. The TRS1LD trenching tool has a maximum outlet pressure of 140kPa and a max jet flow of 2,600L/s. To establish the appropriate power level our crew completed trials on 10m sections at various levels (between 30-80%) and at various standoff distances from the cable/seabed (1.3m standoff from cable and 2-4m offset).

"Once the trials had been completed we were able to complete the actual trenching scope with the optimal settings to achieve the client’s desired trench specification so there were no ensuing issues with the schedule.”

Rotech’s TRS1LD experienced variable soil conditions at the site, from silty sand to clay and very dense gravel with cobbles. In currents of 2Kts and general sea states of 0.5-3m progress was made at 2-5m/min with BOT depths ranging from 0.35-1.20m.

Two further scopes ongoing

Having completed numerous OWF cable trenching and IRM scopes in Taiwan in recent years - including vital scopes at the state-owned wind farm offshore Taipei, trenching pioneer, Rotech Subsea, has two scopes for a global fixed OWF infrastructure leader ongoing in the country with more to come later in the year and into 2023.

In March 2022 Rotech Subsea deployed its TRS2 Sand wave levelling system, RSBG boulder grab tool and TRS1LD shallow water jet trencher at the Changfang and Xidao Wind Farm to conduct a significant sandwave clearance, debris de-burial and boulder removal scopes which is still currently ongoing.

In July, Rotech subsequently mobilised a further TRS2 to the region execute a sandwave clearance campaign at the Yunlin OWF, a scope which is again, ongoing.

Rotech Subsea’s in-house research, development and engineering team has created a suite of sector-leading non-contact CFE, Suspended Jet Trenching, cable/boulder grab & cutting tools. Making Rotech Subsea the partner of choice for offshore wind farm operations in pre-commissioning, commissioning & IRM globally. 

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