Ecosse Subsea Systems (ESS) has completed a £4.7 million boulder clearing and pre-lay trenching project which it claims has been one of the most successful ever conducted for the wind energy sector.
As subcontractor to Siem Offshore Contractors (SOC), the Banchory-based subsea specialist completed 86 boulder clearing passes followed by 172 first and multi-passes over a 90km route during a 13-week boulder clearing and trenching campaign on the EnBW Baltic 2 offshore wind farm project.
The project was on schedule and on budget and now ESS is looking to secure a frame agreement with SOC for similar works on renewables schemes across Europe.
Several thousand boulders ranging up to 4m in size were cleared from the individual cable routes and ESS performed 260 individual route passes in varying and sometimes challenging soil conditions.
ESS managing director, Mike Wilson, said: “We created a lot of firsts on EnBW Baltic 2. It was our largest contract to date, our first non-U.K. trenching workscope and our first project for a German offshore wind farm project.
“It couldn’t have gone better and our client is now convinced that our zero-risk pre-trenching option – where the hard work is done before the cable is present – is the future for cable installation.”
Mobilization on the 86 cable route workscope started in Gdansk, Poland, with ESS transporting its SCAR ploughing technology by road from Aberdeen.
Installation onboard of the SOC operated DP-2 anchor handling tug and supply vessel AHTS Siem Topaz, including a combined ROV and survey spread, took 48 hours with demobilisation taking place in Sassnitz, Germany, and being completed in only 12 hours.
ESS deployed a seven-man trenching crew plus a 10-man ROV and survey personnel, a huge reduction on the 40-strong teams typically used by other cable trenching companies.
Mr. Wilson added, “Our technology and equipment was easily adaptable for use on the SOC operated vessel and having our own ROV and survey spreads meant we were able to provide a completely integrated solution.
“Performing trenching before the cable is present removes any risk of cable damage and means we can work faster and use more powerful machinery. Meeting the schedule is hugely important to the client in terms of cost and also brings environmental savings.
“We are hopeful that following the success of EnBW Baltic 2 that we will secure a frame agreement for boulder clearing and pre-lay trenching services for Siem Offshore Contractors, who are tendering on a range of renewables schemes.”
EnBW Baltic 2 is an 80 turbine development located 32km north of Rügen island in the German exclusive economic zone of the Baltic Sea and owned by the German utility company EnBW. The 27km² site spans water depths ranging from 20m to 45m LAT and has a wide array of soil conditions from fine sands to glacial tilt with areas of gravels and cobbles with numerous boulders.