Operation and maintenance units in the offshore wind industry tend to be categorised as crew transfer or service operation vessels, but there is a ‘third way’ say owners of a small but growing number of mid-size units that fit into a niche between the two
Crew transfer vessels (CTV) have become a familiar feature of the offshore wind energy industry, transporting windfarm technicians to and from turbines in order to maintain them. They vary a little in size and capacity, and sometimes also undertake roles other than personnel transfer, which is usually accomplished by a pushing against a transition piece so that windfarm personnel can ‘step over’ onto a turbine.
But as windfarms have been built farther and farther from shore, so the need has arisen for larger vessels that can operate in more difficult conditions, remain at sea and provide accommodation for technicians and storage for their equipment.
These highly sophisticated, very specialised service operation vessels (SOVs) or ‘walk-to-work’ ships as they have become known are larger and more expensive but can remain at sea for long periods, provide accommodation for windfarm technicians, have significant storage space for equipment, and usually transfer workers to turbines via motion-compensated offshore gangways. Some now even have motion-compensated cranes and can service multiple windfarms.
But not all windfarms are alike and they can’t neatly be categorised as those that can be serviced by CTVs and those that are the domain of their larger cousins because they are farther offshore. It is increasingly being recognised that depending on factors such as distance from shore, the number of turbines to be serviced, conditions offshore, and the number of personnel and amount of equipment needed offshore that a mid-sized vessel with greater range, seakeeping and enhanced accommodation spaces can provide a third way while avoiding the expense associated with contracting an SOV.
Mid-size vessels of this type, sitting between a CTV and SOV in terms of capability and cost have been selected for a number of projects, among them by offshore wind developer Ørsted, which has contracted a 39-m unit from MH-O & Co in Denmark.
The new, mid-size unit, to be named MHO Esbjerg, is one of a number of vessels contracted by Ørsted for the Hornsea Project One offshore windfarm. To be based in Grimsby on the northeast coast of the UK, the three vessels include two Piriou-built 27.4-m vessels and the 39-m Fast Supply Cat (FSC) designed by MH-O director and board member Mik Henriksen working closely with naval architect Incat Crowther in co-operation with Ørsted. The smaller units are Rix Lynx and Rix Leopard, operated by UK-based Rix Sea Shuttle Ltd.
MH-O & Co is actually building two examples of the 39-m FSCs at BTS Shipyard in Surabaya, Indonesia with delivery of the first planned for late 2018/early 2019. This initial example of the type will go to work for Ørsted in 2019. The second is as yet uncontracted but is being actively marketed by the company.
Mr Henriksen said the 39-m units fit into a niche between CTVs and SOVs. “The vessels can still use boat landings,” he explained in an exclusive interview with OWJ, “but are large enough to carry a walk-to-work or bring-to-work system.” He explained the focus of the design was on enhanced seakeeping and the ability to remain offshore for up to 14 days without support.
With a length of 39.2 m and breadth of 10.5 m they will have a cargo-carrying capacity of 60 tonnes, a speed of 25 knots, 190 m2 of deck space and be able to transport containers on deck. The wheelhouse will have space for a charterers’ office, and Mr Henriksen said he anticipates they will be able to undertake personnel transfers in a significant wave height of 2.0m Hs.
“With support, the 39-m is built to remain offshore for up to 30 days, if required. There are eight single cabins on board, Ørsted requires six. It is also a fast vessel, however, so it can be used to do port runs at night or carry out operations from a base port on a daily basis,” Mr Henriksen said.
Mr Henriksen explained he has a background in fast ferries and was familiar with using catamaran hullforms in that market. The hullform adopted for the 39-m FSC is derived from this kind of vessel. He explained the company has also developed designs for even larger catamaran hullform vessels for the offshore wind industry, including a 48-m unit that could undertake transfers in 2.5m Hs.
Apart from opportunities in Europe, the company is also exploring the potential of the burgeoning offshore wind energy market in Taiwan, and is working with Windpal, a consortium of European companies capable of providing integrated solutions for offshore wind project developers in Asia utilising European best practice and experience in offshore wind. “We have been studying the conditions offshore Taiwan and believe the 39-m unit can do well there,” he said.
Another leading operator of crew transfer vessels for the offshore wind energy industry is to manage an innovative, purpose-built service accommodation and transfer vessel chartered specifically for use on a Taiwanese windfarm.
The 35-m service accommodation and transfer vessel (SATV) is being chartered by Siemens Gamesa Renewable Energy for use on the Formosa 1 offshore windfarm off the coast of Miaoli County in Taiwan. It will operate from the port of Taichung during the operations and maintenance phase of the offshore windfarm, starting in Q4 2019.
The vessel is capable of remaining offshore for at least seven days and will have 12 single cabins for wind turbine technicians. It will be registered under the Taiwanese flag and manned by Taiwanese crew trained by Njord Offshore.
Njord Offshore managing director Tom Mehew said the SATV was a significant milestone for the company’s footprint in the offshore wind market and provides “a new logistical model” which will enable technicians to be accommodated offshore and transfer directly to turbines without an offshore access gangway. “Ultimately this will save time and money,” he said.
“With the SATV, we’re offering a new offshore wind service solution which demonstrates our commitment to meeting our customers’ needs and reducing the cost of energy from offshore wind.
“The concept fits the bill perfectly for projects like Formosa 1 – a full 40-person service operation vessel would be oversized and standard crew transfer vessel, which would have to return to port every night, would be undersized.”
Siemens Gamesa head of maritime and aviation solutions Rene Wigmans said the SATV “will also allow us to safely and efficiently address the challenging tidal conditions in the Taiwan Strait.”
Earlier this year, the design phase and tank testing of another vessel that owner/designer Manor Renewable Energy described as “finding its inspiration somewhere between a CTV and walk-to-work vessel” were completed.
In July 2018, Manor Renewable Energy said it planned to begin building the first example of its 40-m ‘technician support vessel’ in 2019. The design has cabins for eight crew members and 20 windfarm technicians, and takes lessons learnt from the company’s 2017 newbuild, Manor Venture, while bringing what the company claimed is a new concept to the sector.
The vessel will have the ability to push against a transition piece due to an engineered piston arrangement that minimises the impact of doing so, despite its large size compared with CTVs. The company said tank tests have shown it has the capability to transfer personnel in conditions that would defeat a conventional crew transfer unit.
Manor Renewable Energy operations director Toby Mead said, “at present the market moves from a 26-m CTV directly to a walk-to-work vessel 3-4 times that length. There is little in the middle of that range and that’s the area we believe the sector is lacking. We believe a vessel in between the two could reduce the cost of operations and help reduce the levelised cost of energy.
“All-in-all,” he said, “the vessel will be fit-for-purpose, have extended endurance, be innovative in design and built for a team of technicians living in comfort.”
The vessel is being designed by Walker Marine Design and will be constructed at Manor’s own shipyard in Portland, Dorset.