Acta Marine's Acta Auriga construction support/walk-to-work vessel has been built with stability and comfort firmly in mind
With its distinctive hullform incorporating builder Ulstein’s X-BOW and X-STERN, Acta Marine’s Acta Auriga construction support/walk-to-work vessel certainly has visual impact – but a closer look shows the vessel’s capabilities are just as impressive.
Measuring in at 93.4 m in length by 18 m in breadth with a maximum draught of 6 m and a dwt of 3,200, the vessel has a maximum speed of 13.5 knots, a deck area of 500 m2 and can accommodate 120 persons. The inverted shapes of the X-BOW and X-STERN increase Acta Auriga’s stability, both in motion and while stationary.
To provide safe and flexible walk-to-work operations, the vessel is fitted with an SMST motion-compensated Telescopic Access Bridge L-Series gangway. Mounted on a height-adjustable tower with an integrated lift, the unit can operate on both sides of the vessel and allows for stepless cargo access and flow of people from different deck levels to the gangway platform without exposure to weather. Motion compensation means the gangway can lift cargo weighing up to a tonne using electronic cargo trolleys loaded with 300 kg Euro pallets.
Acta Auriga’s access system and cargo tower allow for safe transfer of personnel and cargo up to a significant wave height of 3 m and the landing height adjustment system allows access to platform heights up to 23 m.
SMST also supplied the vessel’s 3D motion-compensated knuckle-boom crane. The crane has a lifting height of 36 m above water level at maximum draught and a radius of between 5 and 29.5 m. In offshore mode it can lift loads of up to 20 tonnes without compensation, or up to 6 tonnes with compensation in sea conditions up to Hs 2.5 m.
With 500 m2 of indoor cargo space and a further 500 m2 of cargo space on Acta Auriga’s weather deck, the vessel does not want for storage. The vessel can undertake longer offshore campaigns for clients as 25 TEUs can be stored on the two decks. It is capable of operating autonomously for approximately 30 days.
Consideration has also been given to crew comfort, whether at work or rest. The vessel has capacity for 120 people to be accommodated, with vibration and noise levels in compliance with DNV GL’s Comfort Class Level 2 notation. It contains 40 double cabins and 40 single cabins, all of which have connected sanitary facilities and WiFi internet access. Cabins are also equipped with integrated entertainment systems with “bring-your-own-device” functionality and TV and video on-demand services.
On the work side, there are five offices fitted with internet, external telephone lines and TV screens, two changing rooms (one male, one female), a dry room on the main deck and two charterer workshops. Crew have access to a 64-person capacity mess room with a hot and cold buffet counter, a cinema area with a large TV screen, multiple lounge suites with facilities including games, TV screens and a library, a sauna and gym, as well as TV and music facilities. A centrally-located hospital is easily accessible from both external and internal areas of the vessel.
Acta Auriga’s power plant comprises two Caterpillar 1,700 ekW diesel generators, two Caterpillar 940 ekW diesel generators and a 200 ekW emergency generators. Norwegian Caterpillar marine dealer Pon Power chose Auto-Maskin to provide engine and generator controls, which comprise engine control and safety systems for the vessel’s diesel generators, along with a complete system for generator load sharing and synchronising, based on the Auto-Maskin LSU 408 Loadshare and Synchroniser Unit.
Propulsion takes the form of two 1,500 kW stern thrusters, a 1,040 kW bow-mounted tunnel thruster and two 880 kW bow-mounted swing-up thrusters. The dynamic positioning (DP) system comprises three wind sensors, three motion reference units and three position reference units, comprising two DGPS units and a Guidance Marine CyScan unit, giving the vessel a DP2 class. Along with a Dynpos (AUTR) notation for the DP system, class society DNV GL has also awarded the vessel a Clean (Design) notation
The contract for the vessel’s construction was announced in January 2017, with Acta Marine managing director Rob Boer saying at the time: “This vessel will be the next level in the market and very well suited to operate in the offshore, and specifically the renewable, market.”
He continued: “Ulstein Verft is renowned for its quality and on-time deliveries, and a vital part of the ship construction is carried out in a roofed and controlled environment.”
Ulstein worked alongside Acta Marine to develop the vessel’s design to meet the client’s needs, prioritising in-field flexibility, winter workability, safe transfer of people and cargo, optimised on-board logistics, high productivity and high crew comfort.
Sea trials were successfully completed in March 2018, following which the vessel returned to Ulstein for completion before delivery was made on 28 March 2018, three days ahead of schedule.
Ulstein managing director Kristian Sætre said “We know how important it is to get a vessel completed on time. In just 19 weeks we have completed the outfitting of this vessel and feel certain that the Acta Auriga will be a good work platform for the owner and their clients.”
An official from the Lower Saxony Ministry for the Environment, Energy, Building and Climate Protection, Ingelore Hering, acted as godmother at the vessel’s formal naming ceremony at Südkai, in its home port of Emden on 20 June.
Even before this however, Acta Auriga won its first contract, with Ocean Breeze Energy (OBE) snapping it up for a two-year contract performing maintenance work on the Bard Offshore 1 windfarm in the German North Sea.
Service contract for Bard Offshore 1
Bard Offshore 1 is Germany’s first commercial windfarm and is located in the German Bight, about 100 km northwest of Lower Saxony. OBE’s service partner Reetec, based in Bremen and Emden, will be putting the vessel to work servicing the 80 turbines, with a nominal capacity of 400 mW, that comprise the windfarm. Acta Auriga will be providing year-round support, meaning the vessel has to be able to cope with the worst weather conditions and sea states that the North Sea can throw at it.
“The vessel is expected to increase the productivity of offshore personnel by around 25%, because it will enable our teams to operate in a much more flexible manner with even shorter waiting times than before,” said OBE managing director Jean Huby.
OBE’s commercial managing director Jens Hagen said: “The increasing offshore capacity in the North Sea is creating a need for innovation in the shipbuilding industry for the offshore sector. The shipping industry is thus helping to reduce the operating costs for offshore windfarms and ultimately the electricity generation costs for offshore wind energy.”
Deutche Offshore Consult marine operations manager Sebastian Zehmke-Marahrens, who advises OBE, noted that Acta Auriga was chosen “due to a favourable combination of capability, design and fuel consumption,” adding that the fact that Ulstein was delivering the vessel was also important.
He noted that part of OBE’s requirement was a centrally-placed crane and gangway system, explaining “we would be losing significant operational time if we were only to use the crane and gangway on one side of the vessel.” Mr Zehmke-Marahrens went on to say “We believe there will be a tremendous performance advantage with this vessel. It will reduce the time needed to bring the teams to the turbine significantly, and we can therefore access more turbines per day.”
Benefits of the X-BOW and X-STERN
First used in 2006 aboard Bourbon Orca, the X-BOW works by providing a vessel with greater displacement volume, starting at the waterline. This means that rather than rising with waves then dropping down with great force, the vessel’s bow has a wave-piercing capability and can absorb impacts more consistently across its surface, resulting in greater stability and comfort, and using less fuel.
The X-STERN, meanwhile, was an evolution of the X-BOW introduced in 2016. By turning the X-STERN toward the weather, a captain will experience a number of benefits, including reduced pitch motion and increased operational window, a significant reduction in wave response and slamming and a reduction in trim and draft sensitivity. The system was designed to boost operability and station-keeping while in dynamic positioning mode.
In contrast to the traditional vertical transom plate that a lot of vessels have as their aft shape, the pointed, sloping, higher stern boosts crew and passenger comfort as well as having positive effects on station keeping, wave response and safety, reducing power and fuel consumption requirements, according to Ulstein.
A further benefit is that an X-STERN vessel can achieve almost the same speeds travelling astern as it can moving forward. In the case of Acta Auriga, during sea trials it achieved a speed of more than 12.5 knots in astern mode, compared with a bow-first speed of more than 13.5 knots. This means that the vessel can more easily move between offshore structures located close together, such as wind turbines, as the vessel is not always required to face its bow toward its destination.
Acta Auriga is only the third vessel built to date to feature both X-BOW and X-STERN hullforms, after SOV Windea La Cour and sister vessel Windea Leibniz. Acta has already ordered a second vessel due for delivery in 2019, Acta Centaurus, the contract for which was announced at sister publication Offshore Wind Journal’s 2018 conference, with steel being cut just over a week later.
Meanwhile, Bernhard Schulte Offshore, owner of Windea La Cour and Windea Leibniz, has also ordered a third yet-to-be-named SOV from Ulstein; both hullforms are due for delivery in 2020, with steel cut on 10 September 2018. Acta Centaurus’s hull is set to be towed from Crist, Poland to Ulsteinvik in Norway at the end of November 2018 for outfitting and installation of the SMST motion-compensated gangway and 3D crane. It will build on Acta Auriga’s successful design, with the addition of a helideck and hybrid battery package.
When the contract signing for Acta Centaurus was announced, Acta Marine’s managing director Rob Boer said: “We are convinced that the Acta SX195 vessels will enhance the efficiency of offshore logistics operations and reduce the overall cost of constructing offshore windfarms. At the same time, the vessel will help to enhance turbine uptime.”