Fourteen years ago in 2002 the Sif Group made 80 monopiles for the Horns Rev wind farm off the Danish coast near Esbjerg. These piles were four metres in diameter, the thickness of the steel was five centimetres, and they weighed between 180-230 tonnes depending on their length.
In 2016, Offshore WIND was invited to visit the new Sif Group production, storage and load-out terminal built on Maasvlakte 2, the new area of reclaimed land extending the Port of Rotterdam even further out into the Southern part of the North Sea.
The foundations they were working on during the visit were 80 metres long, 7.7-metre diameter monopile foundations for the Galloper Wind Farm off the Suffolk coast, South East England. When this new Sif Group site becomes fully operational by the end of this year they will have the serial production ability to make and ship out monopiles with a diameter of 11 metres weighing 2,000 tonnes. No order has yet been confirmed for such large foundations, but they will have the facility to make them when required.
In April 2016 the largest monopile foundations ever made were placed at the Veja Mate offshore wind farm, situated 95 km NW from Borkum island in the German sector of the North Sea.
These foundations weigh 1,302.5 tonnes, they are 82.2 metres long and have a diameter of 7.8 metres. The monopiles were manufactured by EEW Special Pipe Constructions GmbH in Rostock.
Reaching the Limit
It is foundations such as these that will provide work in the years to come for only a handful of WTIVs that are operational today. The 11 metres diameter, 2,000 tonnes foundations will require other, different, vessels. Currently there are no jack-up installation vessels that can place monopile foundations heavier than the Veja Mate monopiles.
The largest jack-up installation vessel today is the Seajacks Scylla which began operations in April this year. The Huisman main crane wrapped around the aft starboard leg has a safe working load rated at 1,540 tonnes, and it was this vessel that placed the largest Veja Mate monopiles starting in April this year. The Seajacks Scylla was working very close to limit of its current lifting capacity.
It is not the weight of the turbine nacelle that will be the problem. The current largest turbine, the MHI Vestas Offshore V164-8.0 MW nacelle weighs 390 tonnes, the blades only 35 tonnes each. Typically a 100-metre high tower with a 6.5-metre base diameter weighs 400 tonnes, and the weight of the transition piece about 220 tonnes. The height of the hub and the other parameters are all well within the reach of the upgraded and the new installation vessels. The monopile foundation is the only factor that is growing out of the reach of the installation vessels.
Making the SWL of existing installation vessels higher is one solution that is possible. At about the same time as the Seajacks Scylla was placing the 1,300 tonne foundations the Dutch offshore wind contractor Van Oord was getting ready to announce an upgrade to their installation vessel Aeolus. Not just an upgrade but a complete removal of the 900 tonne crane and replacing it with a 1,600 tonne Huisman crane, which will give it the heaviest lifting capacity of all the jackup installation vessels. The new crane is planned for being placed on board early next year.
Earlier this year the Fred. Olsen Windcarrier installation vessels Brave Tern and Bold Tern both completed an upgrade with 14 metre leg extensions and a boom adaption to allow for the insertion of a 20 metre boom extension in the future. An extension was also placed in the A frame of the main crane. These vessels can now work in water depths of up to 55 metres in the winter and to 60 metres in the summer and have an increased lifting height of 120m from the main deck.
After the current round of upgrades there will be 9 installation vessels with lifting capacity of 1,000 tonnes or more of which only 3 will have SWL lift capacity of 1,500 tonnes or more.
- Aeolus (1,600 tonnes in 2017)
- Seajacks Scylla (1,500 tonnes)
- Innovation operated by GeoSea n.v. (1,500 tonnes)
The remaining 7 vessels in the range of 1,000 to 1,500 tonnes are:
- Vole au Vent operated by Jan de Nul n.v. (1,400 tonnes)
- Pacific ORCA operated by Swire Blue Ocean (1,200 tonnes)
- Pacific OSPREY operated by Swire Blue Ocean (1,200 tonnes)
- Seafox 5 (1,200 tonnes)
- MPI Adventure (1,000 tonnes)
- MPI Discovery (1,000 tonnes)
- MPI Enterprise (1,000 tonnes)
It remains to be seen whether any of these vessels will be upgraded to match or even surpass the Aeolus.
At the time of writing GeoSea n.v. have the Apollo in build in Croatia. Due for delivery in 2017 the vessel is a GustoMSC NG-5500X design and has an 800 tonne wrap around the leg crane. GeoSea refer to the vessel as an installation vessel or an offshore maintenance and service vessel. a large deck space is available for either extra accommodation units, work area or seafastenings for deck loads. With leg extensions to 106.8 metres the Apollo will have a maximum working water depth of 70 metres.
The overall work situation has improved since last year with the majority of vessels in the fleet at work in the summer, although not all working in the offshore wind sector.
There are crane vessels such as the Seaway Heavy Lifting vessels that have a proven track record with foundations, however that capability does come with a high price. Finally there is an option for 2,000-tonne foundations that would be possible open under certain conditions… they are Conquest MB1, Gulliver, Rambiz and Svanen.
All these vessels and others are listed with their details in the installation and construction vessels section of the Offshore WIND Vessel Directory, which is available in print or online, www.offshoreWIND.biz, under the VESSELS tab. SOURCE: OW