Ulstein Presents Benefits of Its SX121 Design
Advancement in technology is permitting the offshore oil and gas industry to move into progressively deeper and colder waters in remote locations. ULSTEIN supports this development by providing products and solutions that contribute to safer, smarter and greener operations.
A case in point is the versatile and flexible OCV/subsea vessel design SX121, which ULSTEIN is currently building customised versions of for GC Rieber Shipping and Island Offshore. The design can be tailored for a multitude of offshore construction and subsea operations in deep and ultra-deep waters both below and above the Arctic Circle.
Deepwater and ultra-deepwater projects occur outside of the continental shelf at water depths between 400 and 1,500 metres and depths greater than 1,500 metres respectively. Deep waters mean remote locations, harsh weather conditions and sensitive ecosystems. This type of environment requires vessels that are reliable and safe, cost-efficient and environmentally sound.
“We aim to develop ships that can operate reliably, safely and efficiently in harsh conditions with as small an environmental footprint as possible. The robust configuration, system integration and X-BOW® hull line of the SX121 ensure safety and comfort for the crew, an increased operational window and significantly reduced environmental impact,” says sales manager in Ulstein Design & Solutions, Lars Ståle Skoge.
Currently, there are four sailing SX121 vessels designed and built by ULSTEIN. The vessels, which operate in different segments such as offshore construction, riserless well intervention and inspection/maintenance/repair, have received very good feedback.
Gordon L. Wilkinson in Veolia ES said the following about ‘Viking Poseidon’’s work in the Gulf of Mexico: “She is the Queen of the Gulf.”
At the end of 2012 shipowner Island Offshore, together with their American partner Edison Chouest Offshore, ordered another SX121 vessel from ULSTEIN currently under construction at Ulstein Verft. “We’ve received very good feedback on our two operating vessels of this design, ‘Island Constructor’ and ‘Island Intervention’,” says Technical Manager in Island Offshore, Trond Hauge. “I’m confident that this type of vessel is a safe and comfortable platform for the performance of advanced work in the years to come.”
Optimised for heavier installations
“The SX121 is a compact vessel that can perform deepwater and ultra-deepwater operations for which currently larger vessels are frequently used, thus providing the customer with a more cost-efficient solution,” says Håvard Stave, Sales Manager in Ulstein Verft.
“The typical SX121 vessel operates at depths down to 3,000 metres, which comprises most current oil & gas activities. The need to deploy heavier equipment in deep waters such as offshore Brazil and Africa and in the Gulf of Mexico, has spurred market interest in OCV vessels with a 400-tonne crane, which we’ve now incorporated in the SX121 design.”
ULSTEIN has drawn on experiences from its latest SX121 projects, and optimised the utilisation of the hull with regards to work from deck as well as crane construction work, resulting in an even more versatile OCV/subsea vessel.
The robust platform is optimised for efficient operations in deep waters with a crane capacity of up to 400 tonnes and a substantial remaining deck loading capacity, and it can be configured for a variety of mission equipment. There is a large deck area of 1,750 m2, and the area around the main moon pool is reinforced in order to sustain a VLS or module handling system. The ROV installation is designed and chosen for operations in significant wave heights of 4.5 metres or more. Two heavy-duty work ROVs are situated in the enclosed hangar, one to be deployed from the starboard side, the other through a dedicated moon pool.
A reliable vessel is key for cost-efficiency, as down-time and aborting on-going operations are costly affairs, particularly when operating far from shore.
The SX121 vessel meets the highest standard for position keeping, DYNPOS-AUTRO, with redundancy on all major components. Featuring the ‘Operation+’ concept, an increase in redundancy in AUTR operations if a single major failure occurs, the vessel will still maintain system redundancy throughout the most critical areas. The typical configuration is diesel electric propulsion powered by six identical medium speed main generator sets. The switchboard system, propellers and diesel motors can be configured in groups of two, three or four. If a major failure occurs, the vessel will only lose one third of its power and propulsion. The combination of system architecture and power stations, three side thrusters and three main thrusters, ensures that the operation can be safely completed using two thirds of its capacity.
Smart and safe
In order to optimise capacities and performance of the vessel, the freeboard has been increased by one metre compared with the previously built vessels of this design. This increase also improves safety and ensures a dry work deck. In addition, the helideck has been moved further back in order to increase the weather window for helicopter landings.
The vessel’s X-BOW provides good motion characteristics for safe operations. It also reduces the vessel’s environmental footprint through lower fuel consumption and reduced emissions. With optimised resolution of the power generation plant, the vessel will have high fuel efficiency in all operational modes.
The vessel accommodates a crew of 130 and complies with all international requirements for comfort and safety.