Finland: Bugsier and Wärtsilä Develop New Wind Farm Installation Vessel Concept

Reducing costs for offshore wind generated electricity is one of the major challenges in the European energy market. The novelty about the jointly developed concept for reducing costs during installation, from the Bugsier-, Reederei- und Bergungs- GmbH & Co. KG and Wärtsilä is, that the tasks for transport and installation are separated, by which loading components onto the installation vessel, is carried out offshore at the building site.

The newly developed installation vessel jacks-up on site and only then it receives its cargo. The vessel is then ready to install foundations, topsides and turbines with its own onboard crane.

Erecting offshore wind turbines (OWT) is presently done by installation vessels, which load components at a base harbour, transport them to the wind farm location and install them there. The majority of installation vessels are built as jack-up vessels. Their jack-up system enables them to operate independent from any wave movements; they work as a stable working platform.

The installation concept developed by Bugsier and Wärtsilä consists of three components: Installation jack-up, feeder barges and suitable tugboats.

As opposed to traditional installation gear, the installation vessel has no cargo deck but a cargo dock. Arrived at the location, the installation vessel – under full ballast – puts down its legs until a firm stand on the seabed is achieved, the cargo dock is flooded, the dock gate can be opened, a feeder barge loaded with wind turbine components can be docked, and the dock gates are then closed.

Next, the dockship jacks-up to its working position above the sea, releasing its ballast water and bailing the cargo dock. Inside the dock the barge rests on the keel blocks on the enforced dock bottom. Now wind turbine components can be installed by the vessels crane independently from the wave motion. Finally the dockship jacks down, ballasts again and releases the emptied feeder-barge, ready for the next barge with new cargo.

Dockships with their short turnaround time have been well proven worldwide, for quite a long time. New challenges in engineering and design in respect to the installation-dockship is the strength and stability with the loaded barge during jacking and the installation process using the heavy lift crane.

The advantage of the feeder barge is that it can enter a vast majority of harbours. This is because its draught and main dimensions are significantly smaller than any installation vessel. Loading is possible de-centralized at the component manufacturers site, thus gaining not only the load transfer times between the production harbour of the components and the base harbour but also avoiding the storage area, as well as expensive infrastructure in the base harbour can be reduced.

The feeder concept also includes AT/Bs (Articulated Tug Barge), which are used integrated (ITB) with the tug in harbour, estuaries and when docking and undocking the installation vessel.  Using this proven concept, which is in particular popular in North America, the AT/B can then even continue on its mission – as tugged barge – when manoeuvring and at transit, when the integrated configuration (ITB) is not possible due to weather.

Through decades of collecting know-how by working offshore, Bugsier has the knowledge for the development of the AT/B. The transport of heavy components is one of the core businesses of the Hamburg based shipping company, with a fleet of 28 tugs and 4 offshore-barges.

Furthermore the Bugsier and Wärtsilä – developed AT/B Concept uses integrated steerable thrusters for the barge. These propulsors are controllable from the Tugs bridge, making it is possible to use the ITP in Dynamic Positioning (DP) mode. This mode is also used to provide the suitable manoeuvrability for the docking and undocking operation at sea under adverse weather conditions. Allowing the concept meet the challenge to dock safely with reduced risk to the installation-dockship and the AT/B.

The particular technical challenge in this project is the development and operation of a sophisticated DP – system with a multitude of different algorithms, which enables the optimized time cooperation between different feeder barges with different tugboats at different loading conditions.

Bugsier and Wärtsilä are aiming at the efficient use of the installation vessel, which should be enabled to stay out at sea and work full time in the wind farm. Even going into port for refuelling is not necessary, if the feeder barge is equipped with fuel bunkers. The concept also includes the possibility to switch to LNG as an alternative fuel and the usage of low emission Gas – Engines for all onboard energy.

Another advantage of the concept is that many cost drivers can be eliminated. In spite the of being more expensive due to the high tech equipment and the sheer size compared to a similar installation vessels with the same payload capacity, the total cost of the installation-dockship  system is reduced significantly. One installation dockship, three barges and two tugs can do the work of three traditional installation vessels. Potentially this can save – carefully estimated – one third of the investment cost. Additional cost advantages compared to other installation vessels are generated by the reduced operational costs, reduced crewing for transport of components and increased productivity.

Investment costs are significantly reduced through avoiding the use of a base harbour. Being able to reach the production sites of component manufacturers, where wind farm site specific or general restrictions regarding draught, breadth, height (air draught), and distance to the wind farm restricted jacking locations, tidal restrictions apply, are further increasing the savings. Conflicts with other commercial traffic when using locks or on entry or departure at harbour sites are minimized.

Furthermore the wind farm installation time is reduced, because valuable weather windows are not wasted on transit and loading operations. The purpose of the installation-dockship – a 5^th generation installation vessel – is only the installation of the OWT. Harbour logistics and time consuming transit, in particular with more distant construction sites, is done by inexpensive, flexible feeder units. Once the installation-dockship is at the construction site, it can stay there. A separate jacking operation for the docking of the feeder barges in unnecessary. The vessel only has to jack down to its loading draught.

The entire project has already entered the concept design phase. The next months will be used to mature the basic design, so that the first vessel could be available in 2016. First customers have expressed severe interest in the solution.

[mappress]

Press release, August 5, 2013; Image: Wärtsilä