The increasing size and distance from shore of offshore wind farms poses a stern test for the shipping industry but also opens a window of opportunity. In the early days of the offshore sector, neither developers nor shipping anticipated the extent to which offshore development and maintenance would require new types of installation and service vessels. Today, this has become evident and the shipping industry supply chain, from designers through to operators, has swung into action to provide the required vessels.
Offshore energy is not new, and major fleets of sophisticated specialist vessels have been developed to serve the oil and gas industry. While many of these can be deployed in the offshore wind market, they are often not exactly the right tool for the job. There is also a squeeze on availability, as demand for oil and gas developments offshore is high. Wind developers and operators are realising that only purpose-built vessels will deliver cost-effective installation, connection, and operation and maintainence.
Move to specialist vessels
The first ships customised for wind power installation were converted cargo vessels, and later jack-up rigs, with the deck space needed for component assembly. Designers, yards and ship owners were not convinced of the market potential for tailored new builds. That has changed quickly in the past five years and now specialist wind vessels are becoming the norm.
This move has been partly driven by the experience of offshore wind developers, who were slow to appreciate just how tough the marine environment is. Power companies used to onshore work took some time to understand that they needed support from experienced contractors with purpose-built vessels. But the lessons have been learned and a new generation of wind farm ships is in operation, with more in the pipeline. Developers now integrate marine logistics into their planning, rather than making them an add-on, and their plans call for specific vessels delivering specific performance. These vessels are being built and operated by companies with deep marine and offshore energy experience, such as Belgium-based Geosea.
Right at the beginning of the chain, manufacturers see the need to transport large components such as blades or pre-assembled nacelles cost-effectively. That has led to the design of a new generation of project cargo ships with very long open holds. These can carry turbine components from factory to site or assembly base, and then can back-haul general project cargo in the open market.
Installation vessels share many of the characteristics of offshore vessels for conventional energy, but they do not need to be built to operate in dangerous oil and gas environments. The essentials are:
A practical loading/offloading procedure with a large crane
A practical storage deck optimised for a large number of pre-assembled turbines
A large dynamic positioning (DP) and jacking systems capacity
Enhanced operability in terms of number of days offshore.
Some of the existing offshore service vessel fleet, such as crew vessels and platform support vessels, can perform the tasks necessary for developing and maintaining offshore wind farms. But there is an increasing need for specialist craft to get the tasks done at lower cost. These include specialised vessels for servicing offshore wind farms. The particular characteristics and levels of efficiency needed call for new designs.
Service ships need:
A comfortable personnel transportation area
A capacity for light to medium-sized cargo, possibly with a mounted crane
A DP system or semi-automated approach device
A safe system for the transfer of personnel
Enhanced operability in terms of number of days offshore.
Industry standards
New vessel types pose issues for yards and designers, who need to ensure they are building vessels that are safe, economic and meet all international rules. That is where classification societies play a key role. They have to follow the industry’s development, understand the role of the new ships and devise rules and standards to be user friendly and ensure safe construction and operation of the new vessels.
Bureau Veritas (BV) has developed two sets of rules — NR579 for wind turbine installation vessels and NI589 for wind farm service ships — to address the specific needs of the range of vessels needed for offshore wind.
BV’s new notations for ships dedicated for wind farm service are aimed at maximising their efficiency. These vessels have to move people and turbines safely and quickly in harsher conditions further from shore.
The approach we took to developing the rules was to adapt the best experience available in our current offshore rules to specific wind farm needs. So the rules for installation vessels are based on BV Offshore Rules NR445 for the site installation phase, but allow the use of Ships Rules NR467 when in transit. That means the vessels can be optimised for carrying turbines to the site as well as for the onsite installation phase.
BV’s guidance for wind farm service ships will help designers and yards use its rules for steel ships and for high speed craft, combined with the rules for vessels under 500 gross tonnage, to develop new designs that will be light, fast, safe, and have good sea-keeping abilities. They will be able to work close to turbines yet will also be cost-effective.
BV NI589 is a service notation that covers ships designed to transfer wind personnel from shore, mother ships or accommodation units to offshore wind farms and perform the lifting operations required for turbine servicing. These requirements are very different from those for vessels built for turbine installation and assembly, or heavy maintenance and repair for which transportation of wind turbine main parts is needed. These are covered by the installation vessel rules.
Wind farm service ships have to transfer people quickly in rough offshore conditions; that is why we have developed a specific notation.
Typically, service vessels will have seating for up to 60 people, a deck area for cargo, some form of device for connection and access to the turbine tower, lifting devices, a motion-damping system, a DP system and a high service speed.
Hybrid vessels
We are also seeing a new hybrid type of vessel emerge, with tug designs that are small and highly manoeuvrable, yet are fitted with a good-size crane and have an extended range compared with similarly sized anchor-handling tugs (AHTs). An example is the Offshore Ship Designers’ compact but powerful AHT offshore support vessel for Netherlands-based Neptune Marine Service. The 44-metre, 70-ton vessel will be used for anchor handling, ocean towage and wind farm construction support duties. The vessel is designed for worldwide operation, high reliability and low maintenance costs, and has accommodation for 22 people. Two powerful propellers with nozzles and three transverse thrusters will give the vessel DP-1 station-keeping ability.
The next generation of designs will be for maintenance vessels able to stay for longer periods in offshore fields and deploy smaller service craft safely for regular maintenance. They will be able to accommodate components like blades and have a big crane, yet be economical enough for extended stays on station.
We are already looking at such designs. The rules are there, the industry knows it needs specialist vessels and there are designers and owners ready to meet those challenges and take up the opportunities. The rest is down to the market.
Maxime Pachot is product manager, Marine Renewable Energies & Offshore Support Vessels, Bureau Veritas
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