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Offshore Support Journal

Offshore Support Journal

Starfish AHTS series proves its worth around the world

Mon 17 Sep 2018 by Ed Martin

Starfish AHTS series proves its worth around the world
The remaining two Starfish AHTS vessels are due for delivery in October 2018 and January 2019, respectively (credit: Salt Ship Design)

With the last two vessels due for delivery soon, Maersk's Starfish AHTS fleet is living up to its promise as fuel-efficient and capable

Maersk Supply Service’s Starfish AHTS series of vessels are no strangers to the pages of Offshore Support Journal, with Maersk Master winning the Vessel of the Year award at the 2018 OSJ Conference & Awards gala in London.

Since then, a further two vessels in the series have been delivered, Maersk Mover in January 2018 and Maersk Minder in May 2018, joining Maersk Master, delivered in April 2017 and Maersk Mariner, delivered in July 2017; the final two vessels are scheduled for delivery from shipbuilder Kleven at the end of October this year and the end of January 2019, respectively.

Work on the Starfish series began in 2014 when “the world looked a bit different,” as Maersk Supply Service chief technical officer Peter Kragh Jacobsen told OSJ. “The main driver was that we wanted to develop an asset that was second to none,” said Mr Jacobsen, adding “We wanted an asset that was reliable, energy efficient, comfortable and safe.”

“It was clear that when we started this project we would not go for a generic model,” said Mr Jacobsen, so Leirvik-based Salt was chosen to assist in developing the model for the Starfish class. The next step was selecting a builder - “to make this project a success, we needed a yard that could contribute to the development,” said Mr Jacobsen. After looking at several yards, Ulsteinvik-based Kleven Verft was selected. “It was obvious that for us, Kleven was in a very good position to support this project and also capable of building to the required quality,” he added.

As the new design was effectively a prototype, there were challenges, big and small, to be overcome in the detailed engineering phase. Maersk Supply Service believes “it takes transparent dialogue and excellent collaboration with the designer and the yard to overcome challenges that naturally occur,” said Mr Jacobsen, with the parties involved choosing to "not be arrogant about who is right but focus on finding the right solution”.

Built for deepwater operations, the Starfish vessels are 95 m long, with a beam of 25 m and are equipped with a raft of innovative features, including an anchor-recovery frame that simplifies operations over the stern roller and a remotely operated deck-handling gantry crane.

“It would be arrogant to say we have built the perfect vessel, but we are really close to it; it is a unique asset for sure” 

Unlike existing anchor-recovery frames, which have a 90° operating angle, the equipment on board Maersk Master and other Starfish-class vessels can be operated at a 126° angle to the deck, by way of two hydraulic cylinders and a 1.68 m-diameter, free-rotating roller.

Capable of operation in temperatures ranging from -20°C to 45°C, the 8.84 m wide, 7.99 m high recovery frame has a nominal towline tension capacity of 200 tonnes, with a lateral force of 50 tonnes.

The vessel has an open deck area of more than 800 m² with an additional 102 m² of covered deck area and comes equipped with a 450-tonne anchor handling winch, housed in an enclosed garage to protect crew and equipment in harsh environments.

Lifting capacity comes from a Macgregor Triplex Multi Deck Handler-42, with a maximum lifting safe working load of 42 tonnes and a maximum pulling safe working load of 30 tonnes.

Dynamic positioning capability from Kongsberg gives the vessel a DP 2 rating, with an Environmental Regularity Number of 99.99.99.99.

Wärtsilä provided all thrusters and propulsion systems for the vessels, along with the engines, integrated alarm system and the electrical system, which includes low-loss concept switchboards and drives. Powered by five medium-speed engines – two W8L32 units, two W6L32 units and one W9L20 unit - with a total output of more than 23,000 bhp, the Starfish-class vessels have a fuel-efficient and flexible hybrid propulsion system, controllable-pitch propellers and fixed-pitch thrusters, a combination of features that is expected to provide high reliability, good fuel economy, low emissions and excellent stationkeeping capabilities. When low-load operations are required, the vessel’s hybrid propulsion system allows it to switch to a diesel-electric operating mode. The thruster layout includes 1,580 bhp bow-mounted tunnel thrusters and two 1,580 bhp stern-mounted tunnel thrusters.

Maersk Master has a deadweight of 4,900 tonnes, accommodation for 52 people in single cabins and is equipped with a work-class remotely-operated vehicle in a hangar. The vessel has FiFi 1, Ice 1A classification and has oil recovery capabilities.

Discussing the strengths of the design, Mr Jacobsen noted that the winch capacity allows for coiling up of flexibles and umbilicals during decommissioning, duties that an AHTS would not usually be able to undertake. The large deck size is beneficial when transporting anchors offshore, allowing multiple units to be transported at once. The chain locker arrangement allows for two different types of anchor chain to be used simultaneously and distributed among the four lockers without the need for disconnection and rearrangement. Mr Jacobsen also noted that all passengers have their own cabin and that the vessel generally has high comfort levels and a good working environment.

Maersk Master recently towed a semi-submersible rig from Las Palmas to North-Western Australia via the Cape of Good Hope, a distance of 10,230 nautical miles

Accommodation complies with DNV GL’s Comfort Class V(2), C(3) which is very close to cruise-vessel specifications regarding noise, vibration and indoor climate. The engine room is fitted with an automatic high-pressure water mist system, which can be triggered by a single fire-detector. Exhaust pipes and turbo chargers are protected from oil spray and all machinery is guaranteed to maintain a surface temperature of below 60 degrees at maximum engine capacity.

“It would be arrogant to say we have built the perfect vessel, but we are really close to it; it is a unique asset for sure,” said Mr Jacobsen.

Prize-winner Maersk Master was previously involved in the Janice decommissioning project in the North Sea, which commenced in 2016. A fleet of Maersk Supply Service vessels, comprising an F-class PSV, L-class AHTS vessels, an I-class subsea support vessel of the Stingray new-build series and SSV Maersk Achiever carried out work across the project including supply duties, infield rig moves, tow-away of the Janice floating production unit and subsea recovery work. Maersk Master’s involvement is in the subsea recovery aspect of the project, working alongside Maersk Achiever to remove 772 tonnes of product from the seabed, including 31 km of umbilicals, flowlines and flexible jumpers and 1,400 tonnes of structures, manifolds and more than 100 concrete mats.

Another project in which Maersk Master flexed its muscles was the towing and installation of the Ailsa floating storage and offloading facility, also in the North Sea. Contracted by Total E&P UK for the work in the Culzean field, eight Maersk vessels were involved, with Maersk Master again being joined by Maersk Achiever alongside several L-class AHTS vessels. This time around Maersk Master carried out installation and tensioning of the platform’s drag anchors; 12, 50-tonne anchors were constructed and installed in two mobilisations, complete with 140 mm bottom chain assemblies. Holding tension of 723 tonnes was achieved using a stev tensioner, making it the highest-tensioned mooring system in the North Sea.

It was announced in January this year that Maersk Master and Maersk Mariner had been chartered by Quadrant Energy for a contract commencing in March. The vessels would be working as part of the Phoenix South and Van Gogh drilling campaign, which was initially set to cover three wells for 150-200 days, supporting Transocean’s semi-submersible rig DD1 with supply and anchor-handling duties. Maersk Master also towed a semi-submersible rig from Las Palmas to North-Western Australia via the Cape of Good Hope earlier this year. The journey was a total of 10,230 nautical miles and took 87 days of towing.

Maersk Mover is on a long-term engagement carrying out rig towing and anchor-handling work in the Asia-Pacific region, while Maersk Minder is active on the UK North Sea spot market at the time of writing.

The vessels have been well-received by clients, said Mr Jacobsen, noting that they all found jobs more or less straight from the yard and have performed their duties without any off time. “We have received absolutely positive feedback from our clients so far,” he added.

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