West of Duddon Sands: Challenging the Irish waters

As West of Duddon Sands, one of the largest European wind farms, nears completion, global maritime services company Royal Boskalis Westminster, the appointed Transport & Installation (T&I) contractor, reflects on this vast project. The T&I contractor faced technical, operational and logistical challenges, particularly because the wind farm was developed at several locations at the same time. However, despite this the wind farm development is on time and on budget.

For Boskalis Offshore, based in Papendrecht in the Netherlands, this particular offshore wind farm is a milestone in the company’s history as it is the first time Boskalis has been a full T&I contractor in the wind industry. Boskalis has however been involved in the sector with its marine services and it has carried out scour protection for several wind farms in the past.

When the group acquired Smit Internationale in 2010, transport, heavy-lift, towage and salvage activities were added to its portfolio. This has opened up new possibilities for Boskalis to become a leading T&I contractor in offshore wind.

Developed by DONG Energy and Scottish Power Renewables, West of Duddon Sands is located in the Irish Sea, south of Wallney and west of Blackpool. Comprising 108 wind turbines, the wind farm will produce 389MW. It is located in a water depths between 18 and 24m and it has a large tidal difference of just over 8m. As well as the challenging conditions of the Irish Sea, developers also had to make adjustments to the project because of the presence of an underwater volcano.

Wim Vogelaar, Business Unit Manager for Boskalis Offshore and Rob van Gemert, Project Director, outline the scope of the T&I work. “Until West of Duddon Sands, Smit had been involved in the transportation of equipment as a subcontractor for wind farms and Boskalis had carried out scour protection. Now with Smit successfully integrated into Boskalis, the group was delighted to be able to take on a full T&I role. Our combined forces give us a much larger scope and we are fully geared up to do T&I jobs as the main contractor.”

This integrated company has given the organisation a lot of engineering capacity, Mr Vogelaar says. Boskalis carried out detailed engineering during the tender stage, with at least eight months spent on the engineering and design, he adds. Boskalis Offshore’s transportation and scour protection capabilities were other reasons it was awarded the contract. On top of this, he believes the group’s surveying ability and in-house resources helped make sure the project is a success. Many pieces of equipment and tools utilised were designed in-house.

Multiple locations

Given the multiple locations, Boskalis drew on its vast resources, which often saw at least 100 people working on the project at the same time.

Key locations comprised the Bladt Industries production facilities in Aalborg in Denmark where the foundations were produced and loaded, the port of Rotterdam in the Netherlands, where the installation vessels were mobilised, Belfast in Northern Ireland – the official Feeder Port – where foundations are temporarily stored, the installation area in the Irish Sea, and Barrow-in-Furness, the UK port close to the installation area where secondary works are conducted.

Boskalis also had installation crews on both of the jack-up vessels. Typically some 60 people were on board the jack-ups ranging from lifting supervisors for the hammer operations, to engineers, riggers and surveyors. Boskalis and its related companies were involved in one way in many aspects of the project beyond the T&I scope, including preparing the Feeder Port in Belfast. Boskalis Offshore and Volker Stevin Offshore created ‘Offshore WindForce’ (OWF), a joint venture for the project.

OWF was responsible for tailoring the Feeder Port site to the specific needs of the various installation and transport vessels and crane movements required during the complex logistical process.

A joint Boskalis and VolkerWessels project is also responsible for laying the export cable from the wind farm.

Even before the T&I job began, the Boskalis Rockpiper, the largest fallpipe vessel in the fleet, installed 108 round scour protection filter layers on the seabed. In total, 165,005 tonnes of filter rock and an additional 11 cable crossings were installed.

To reduce sailing times rock from a quarry in Visnes, Norway, was brought to the installation area in 10 trips, using the bulk carriers Sandnes and Stones. Ship-to-ship transfer was conducted in Holyhead in the Wales. A Combilift heavy lift vessel contracted by OWF took the monopiles and transition pieces from Aalborg in Denmark to Belfast, a journey of 1,500km.

Based in Rotterdam, the overall project team carried out the work preparation phase between May and December last year including the method statements, calculations and risk assessments. Then the team uprooted to Belfast.

Mr van Gemert comments: “The whole project has progressed very well and this is largely to do with the attitude of our client, who really supported us all the way through, the whole team of subcontractors and our crew. Our superintendents responsible for the offshore installation works are all captains from the Smit sheerleg fleet and incredibly knowledgeable about installation works. This experience was supported by the whole group having the same attitude to quality and safety awareness.”

The two new jack-up vessels deployed for the installation, Pacific Orca and the Sea Installer, are not Boskalis vessels. Pacific Orca is owned by Swire Blue Ocean, and with a crane capacity of 1,200 tonnes and measuring 160 x 50m, the vessel is one of the largest jack up vessels in the market. Pacific Orca can transport five monopiles and transition pieces, while the SEA INSTALLER has a crane capacity of 800 tonnes and is able to carry three sets at a time. SEA INSTALLER is owned by A2SEA, a joint venture between DONG Energy and Siemens.

Shared responsibility

Although the jack-ups were operated and crewed by their owners, OWF was responsible for the installation deck to the aft of the vessel. And indeed even before the job began, OWF was responsible for the extensive mobilisation operation to prepare the two vessels for their specialist work at the Keppel Verolme shipyard in Rotterdam.

One difficult factor was the hard subsurface in one section of the wind farm, so shorter and wider monopiles were used than had been planned originally.

The new dimensions of the piles mean that they only attain stability just before they are totally vertical when being upended, this situation affected the design and positioning of equipment such as the piling frame. Boskalis Offshore developed an entirely new approach together with Volker engineers.

To safeguard the efficient and ongoing installation by the jack-up vessels and to prevent delays, the foundation elements were stockpiled in Belfast. The chartered vessel ‘EIT Palmina’ undertook 22 voyages to deliver the 108 monopiles and transition pieces.

108 monopiles and transition pieces

In early April, the jack-up vessels arrived in Belfast and the installation of the first batch began. The monopiles weigh more than 500 tonnes each and they are almost 60m long depending on their individual location, while the transition pieces are 35m high and weigh 340 tonnes. One cycle, from the loading in Belfast, sailing and installing the monopiles and transition pieces takes up to seven days. One foundation is being installed every day.

Mr van Gemert emphasises: “We hit all the major milestones and the overall installation was much faster than the initial cycle times expected, going down from nine to seven days, representing a 15% to 20% time saving. We managed this by exhaustive planning and overlapping work by planning ahead. Working smartly, essentially.” On deck, the monopile is upended using an upending tool and hinge and the monopile is lowered into a special gripper frame, which was also specially designed. It is then driven into the seabed using the world’s largest hydrohammer.

New upending tool

The speed of delivery has been achieved by deploying some innovative equipment and techniques, he adds, such as IHC’s 2000 hydrohammer. “The upending method we designed is very simple. The gripper is 14m below deck level and is 100 tonnes lighter than normal. We upend above the deck and lower into the pile gripper 14m below deck level.”

Meanwhile, the operation is carefully monitored by survey equipment. Once installed, the transition pieces are levelled and the annulus between the transition piece and monopile is grouted. When the grout is cured a specialist team removes the levelling bolts and cover tents are installed.

After the installation of the cables, a Boskalis fallpipe vessel will place the final scour protection layer under water around the piles. Another 95,000 tonnes of rock will be needed for this operation. The whole project, including final scour protection, is expected to be completed in mid2014.

On time delivery

Undoubtedly, the project has been a learning curve in terms of it being the first T&I contract for Boskalis Offshore in the wind industry.

“The tender team was maintained into execution and engineers who were involved in the design got the chance to see how everything works in reality, which builds up knowledge for future projects. Preparation and front-end engineering is certainly key in making the project as safe and efficient as possible,” stresses Mr Vogelaar.

The success of the project has also been down to the client and contractor sharing the risks involved, he adds. “For Boskalis it was a real help that the client provided the installation vessels and that the responsibility was divided, with Boskalis responsible for the installation works and the client, the marine works.”

Integrated approach

Mr van Gemert adds that the clients are very hands-on in terms of scheduling, monitoring and control but also in advising the company, which has been a great help.

Having this integrated project approach makes the process more efficient and ultimately reduces the cost of wind energy, they point out. Installing 100 plus foundation sets in one season is quite an achievement, they add.

One of the reasons Boskalis took over Smit was to be able to take on a broader scope and to be able to offer total T&I solutions. They emphasise that West of Duddon Sands has proven this ability and is an important milestone for the company.

Boskalis has the resources and the ambition to seek out further opportunities in the offshore wind market. “We would hope that there can be more clarity from governments for prospects in the longer term. But we are in continual talks with the developers and the utilities about where they are heading, and, if we are given enough time, we will find satisfactory solutions for them,” stresses Mr Vogelaar.

Helen Hill