A new series of subsea support vessels have been engineered with versatility firmly in mind, offering operators economical access to a wide range of configurations
In 2014, Maersk Supply Service ordered four advanced subsea support vessels in a market very different to that of today. The driving concept behind the development of the Stingray-class subsea support vessels (SSVs) was to create a series of vessels that would be flexible, supporting a broad range of operational requirements while offering reliability, efficiency and economy.
“When we started this project, it was very clear that these vessels would be operating for the next 20 years,” explains Maersk Supply Service (MSS) head of technical organisation Peter Kragh Jacobsen. “Since we weren’t building these vessels for a specific contract, we wanted to make them attractive for a wide range of work scopes.”
Peter Kragh Jacobsen (Maersk Supply Service): "The vibration and noise levels on our vessels are just below cruise-line standard"
Starting with Marin Teknikk’s MT 6027 as a base design, the Stingray-class SSVs evolved into a “Swiss Army knife” frame, according to Mr Jacobsen; one that can be transformed with minimal intervention to a specific client task or requirement.
Built by COSCO Dalian Shipyard in China, the four Stingray-class SSVs are the Maersk Installer, Maersk Involver, Maersk Inventor and Maersk Implementer.
The SSVs combine an energy-efficient propulsion train and dynamic positioning class 3 (DP3), with a 400-tonne Huisman active heave compensated crane. Six large thrusters provide the vessels with a high level of manoeuvrability.
Complementing this capability are two work-class remotely operated vehicles capable of operating in up to 3,000 m of water, with the option of being deployed over the side or through an internal moonpool. The vessels also have a free deck area of 1,850 m2 with a large number of sea-fastening features for project cargo.
A new hybrid design, Huisman’s highly flexible rope luffing knuckleboom crane has a number of advantages compared with a conventional unit. Chief among these is that it maintains the knuckleboom functionality – providing a low suspension point, which is essential for offshore construction activity – without the disadvantages of conventional knuckleboom cranes, such as a heavy boom that affects a crane’s load curves and adversely affects stability.
A new hybrid design, Huisman’s highly flexible rope luffing knuckleboom crane has many advantages over a conventional unit
Since it is mainly electrically driven, the hybrid crane also does not experience the same kind of idling losses as a conventionally powered crane and it eliminates the possibility of potential environmental damage from hydraulics on deck.
The vessels have accommodation for 120, all in single cabins, which was “high on our list,” according to Mr Jacobsen. “We wanted our crews and clients to have a good experience onboard. The vibration and noise level on our vessels are just below cruise-line standard.”
With a year and a half operational experience since the first vessels were delivered, Mr Jacobsen says: “The market has received the vessels very well. The Stingray vessels have performed subsea construction work, decommissioning, walk-to-work, as well as light well intervention operations in APAC, Europe, West Africa and Mexico. They can also be used in IMR, ROV, firefighting, rescue, salvage and are prepared for flexlay operations. We intentionally made these platforms flexible and attractive to a wide range of clients, which so far include oil majors and tier 1 and 2 contractors. The references of the jobs we have done have proven the design concept,” he said.
Currently, three of the four I-class vessels are engaged in light well intervention operations in deep, as well as shallow, water. “Although class requirements for well intervention are very demanding, the base design has made it very simple for us to be able to do the necessary modifications to obtain the required notations,” noted MSS senior chartering manager Thomas Danielsen.