renewables award
mounted round one of the legs, which also saves some space compared with the layout of the company’s other vessels. For
practical and safety brackets and hatches are reasons,
all flush with the
deck. The result is a completely uniform, flat surface, which makes it easier for the crew to move around without stumbling or falling, while minimising the risk of damaging components or the vessel during loading. The deck on Sea Installer has been reinforced so it can carry 15 tonnes per square metre, compared with the standard requirement of five tonnes per square metre. This makes it possible to load and transport larger wind turbine components, such as wind turbine towers and foundations. The size of the deck makes it possible to transport, for example, eight 3.6MW turbines. The first installation vessel in the A2SEA fleet could accommodate four 1.8MW turbines. The crane on Sea Installer is the vessel’s main tool, and is used to lift components from the quay onto the vessel, and to lift and position the components on site at the offshore windfarm. The electrically-powered crane was designed and built by Gusto MSC and has a capacity of 800 tonnes at 20m outreach or 600 tonnes at 30m outreach. The crane can also be adjusted to carry out 2 x 400-tonne dual lifts. As highlighted above, with its current equipment and design, Sea Installer is optimised to transport and install wind turbines of 3-6MW but can also transport larger components, if required. Very few turbine components weigh more than 300- 400 tonnes, but the capacity of the crane makes it possible to handle wind turbine foundations weighing 800-900 tonnes. The lifting height is 100m from the deck or 120- 130m measured from the surface of the sea if the height of the vessel is included. Due
Sea Installer loads components from the quayside using its own crane
to the many heavy lifts it will be required to carry out, the crane on Sea Installer has been designed with an increased fatigue lifetime. The lifting capacity of Sea Installer was for large-scale offshore
optimised wind
turbine projects; however, to further increase the capacity of the vessel, the crane will be updated in the next two to three years to increase the lifting capacity to 900 tonnes; this is the same capacity as sister vessel NB 002, which will be delivered in 2014. The raising or lowering of the vessel’s
jack-up legs is controlled from the bridge. During this operation, the entire vessel is jacked up to the desired height with the deck typically around 15-25m above the surface of the sea. An effective jacking system is essential to enable a vessel like Sea Installer to operate and function effectively. Sea Installer obviously cannot sail whilst jacking is taking
place, so to avoid wasting too much time waiting, it is important to be able to raise and lower the legs as quickly as possible. The jacking system can raise the fully loaded Sea Installer at a speed of approximately 1m per minute, which is twice as fast as standard jacking systems in the industry.
A day is normally set aside for each offshore wind turbine, so it is important that the jacking system functions effectively and reliably. Sea Installer is fully functional even with two jacking cylinders out of operation at each leg. To make sure the legs rest firmly on the seabed, each leg has a so-called spudcan – like the sole of a shoe. The spudcan on the legs have an area of 108m2, so Sea Installer has a solid 432m2 footprint once the legs have been lowered. A special jetting system at the bottom of the legs can flush the legs free of the seabed when they have to be raised. Depending on the soil conditions, the legs may have penetrated up to 21m into the seabed, and without a jetting system, lifting the legs would be much more difficult.
Flemming Hjorth, head of tenders and contracts at A2SEA, collects the award with Andries Hofman, project manager (right) and Mattijs Faber, sales manager, at GustoMSC
34 I Annual Offshore Support Journal Conference and Awards 2013
A huge amount of power is required onboard Sea Installer. The engineroom consists of three separate rooms, each equipped with two 3,020 kilowatt (kW) diesel engines. Together, the six engines have a combined capacity of more than 18,000kW, generating high voltage power to propel the vessel, and for the jack-up system, the cranes and the many cooling, heating and ventilation systems on board. Like the rest of the vessel, the engineroom is designed in such a way that operation of the vessel is optimised – even with two of the six engines out of operation, the vessel can remain fully operational. In a worst case scenario, the vessel can sail with only one engine. OSJ
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