Game changer at top end of the heavy load market

Unique in design and capacity, Dockwise Vanguard has been commissioned to serve the premium end of the heavy-load market. As the world’s largest semi-submersible heavy-lift carrier, she offers an unprecedented capability for transporting fully-integrated offshore structures and units, including floating production, storage and offloading (FPSO) vessels, and for undertaking the offshore drydocking of such assets.
Dockwise Shipping’s new addition has a Type O categorisation by virtue of a load capacity in excess of 110,000 tonnes, accommodated on an open-ended, free deck space of 275m x 70m. Hitherto, the largest heavy-lift semi-submersible has been of the Type-I designation, which reflects a load capacity within the 41,000-73,000t range. The absence of a raised bow and conventional forward superstructure means that there are no restrictions on load overhang either forward or aft.
The Dutch owner’s bold, $240m investment in this heavy cargo transport ship of record size is founded on considerable experience in the field, and its identification of evolving and future demand for transfers of new and larger generations of semi-submersibles, tension leg platforms(TLPs), and deep-draught, floating caisson-type platforms known as spars, as well as floating production units. The shift of offshore exploration and production activity to deeper water and more remote areas is expected to lead to increased requirements for such equipment to be transported in its entirety, rather than in separate elements.
Incorporated in Bermuda, Dockwise is headquartered at Breda, in the Netherlands, and operates a fleet of some 19 semi-submersible heavy load vessels of different concepts. The latest project is testament to the construction skills of Hyundai Heavy Industries, employing a design developed by the owner in conjunction with Deltamarin of Finland and the shipbuilder’s offshore division. Model tank tests were conducted by MARIN at Wageningen.
Optimised deck strength, extreme wide-load capabilities and exceptional load length capacity, surpassing previous heavy marine transport limitations, are at the heart of the design philosophy. The unique appearance derives from the absence of a raised bow on a pontoon-like hull having narrow casings at each corner. In place of a more conventional forward superstructure, the accommodation block and surmounting navigation bridge form the narrow casing on the starboard side at the extreme forward end of the hull. A smaller casing comprising two elements in staggered configuration is arranged on the opposite. The two aft casings are movable, allowing positioning at various points along the hull sides so as to facilitate loading and unloading and to accommodate different shapes of cargo.
One of the main challenges for the designers was the prevailing regulations, and specifically the requirements as regards bow and freeboard. Deltamarin and Dockwise worked in collaboration with MARIN, Det Norske Veritas and the Dutch Inspectorate for Transport, Public Works and Water Management in order to secure the requisite exemptions. The distribution of safety zones necessitated particular attention during the design process. While both port and starboard side rescue stations are normally required, the rules were adapted for Dockwise Vanguard’s longitudinal, lateral accommodation block, so as to designate forward and aft zones in the accommodation superstructure, denoted by the inset lifeboat stations.
The vessel will operate at a maximum draught of 11m. When submerged, the draught can be as much as 31.5m, allowing a water depth of 16m above the cargo deck for float-on, float-off cargo handling. The considerable ballast capacity is encapsulated within the hull.
Dockwise Vanguard brings a ‘dry tow’ capability to delivery and positioning logistics for offshore units or structures that have previously had to be transferred by conventional towage means or broken down into sections for transport. The ‘dry tow’ option can offer significant benefits from an overall cost and project requirement standpoint, enabling complete assemblies to be delivered in a generally shorter transit time, and less subject to weather-induced delays. The new vessel affords the client industries greater scope in having the entire construction of an offshore unit, be it the topsides and hull of a floating production facility, for instance, undertaken at one shipyard rather than at different locations.
In addition, the vessel confers scope for providing an offshore drydocking service. This is especially salient to the inspection, maintenance and repair of the increasing number of offshore units such as FPSOs located in remote areas lacking support infrastructure, as a way of cutting downtime and associated costs. Moreover, the technical design and engineering of the Dockwise Vanguard is such that a docked FPSO could remain connected to its turret mooring system, keeping the riser systems intact, with the possibility of limited production being maintained. In this scenario, the FPSO aboard the dock ship would still be able to weathervane around the turret mooring, with control of heading exercised through the latter’s propulsion and manoeuvring systems.
Dockwise obtained an ‘approval in principle’ from ABS for offshore drydocking following the commissioning of a hazard identification(HAZID) safety assessment. The HAZID methodology assessed the safety and efficiency of performing offshore dry inspection, maintenance and repair of internal turret moored and also external spread moored FPSOs under stopped production and reduced production modes.
The Norwegian company Autronica has provided the vessel’s entire fire detection system, by way of the proprietary AutroSafe interactive solution. Communication between all system units is undertaken via a local network called Autolon.
In competition with two other manufacturers of engines and propulsion systems, Wärtsilä made a detailed study of the vessel’s intended operating profile in order to develop an optimal propulsion and powering proposal for the owner. This involved the determination of power needs at full speed, slow speed and in survival mode, and defining the overall propulsion requirement, encompassing engines, propellers, retractable and tunnel thrusters. Economic and operational considerations included fuel and lube oil consumption, maintenance requirements, lifecycle costs, reliability and safety. Having presented Dockwise with five possible solutions, Wärtsilä won the bidding process.
Dockwise Vanguard incorporates a fully-redundant diesel-electric power and propulsion system that confers two main propulsion trains, each comprising two diesel engines, electric propulsion motor, reduction gear and controllable pitch propeller. The four main genset drives are Wärtsilä 38-series medium-speed engines, arranged in a ’father-and-son’ configuration. The two smaller prime movers are six-cylinder in-line diesels, rated at 4,350kW apiece, and the two larger units are 12-cylinder vee-type engines, each producing 8,700kW, such that the plant’s total nominal maximum power is just over 26,000kW. A further genset for auxiliary shipboard power needs is based on a Wärtsilä 6L20 engine, while several smaller aggregates use Cummins and Hyundai HiMSEN engines.
Diesel-electric installations more commonly use frequency-drive electric motors, running at variable speeds. The main propulsion system in the Dockwise ship is thereby unusual in its adoption of controllable pitch propellers driven by fixed-speed e-motors. The propellers are incorporated within nozzles. Even with motor operation at a fixed speed, thrust can be controlled from minimum to maximum, ahead or astern, by altering the cpp blade angle.
Furthermore, two 3MW retractable azimuth thrusters are installed forward to help maintain heading in adverse weather, drawing their electrical energy from the main switchboards. Manoeuvrability is further enhanced by a 2,650kW bow tunnel thruster.
The plant configuration allows flexibility, providing the requisite power for full speed to be maintained with heavy loads and to better ensure cargo delivery reliability, while requiring only the two smaller engines to be run when making a passage at low speeds. Given the fundamental importance of cargo delivery dependability, for the competitiveness of the ’dry tow’ mode as well as for the timely executing of offshore projects, sustained speed performance and plant reliability had a major bearing on system and machinery choice for Dockwise Vanguard.
The arrangements allow for a laden speed in the 11-13 knots range, and for 14 knots-plus to be made when running light. Besides the 38-series engines, originating from Wärtsilä’s Italian production plant at Trieste, and the 6L20 auxiliary, the Wärtsilä ‘package’ also encompassed the 5m-diameter 4D1540 main controllable pitch propellers in HR nozzles, the two TCH270-type gearboxes, the two CS2510/MNR retractable thrusters and single CT300M-D bow thruster.
The vessel has been equipped with Amarcon’s Octopus-Onboard system, for motion monitoring, response prediction and heavy-weather decision support during heavy cargo transportation. She has been fitted with a three-sensor motion measurement set-up, so that multiple critical locations can be considered, gauged and displayed on the bridge. The Octopus product line forms part of Amarcon parent ABB’s vessel information and control (VICO) systems suite.
Dockwise Vanguard departed Hyundai’s Ulsan yard in February, sailing west along the coast of the Korean peninsula to Samsung Heavy Industry’s Geoje complex to pick up the giant hull of the semi-submersible production unit built for Chevron’s Jack/St Malo deepwater project in the Gulf of Mexico. The oil and gas facility has a topsides weight of 33,000t and will be installed in waters 7,000ft (2,150m) deep, to act as a hub for 43 subsea wells.
The new Dockwise carrier has also been booked in 2013 to deliver the world’s largest circular FPSO, the Goliat, from Hyundai’s shipbuilding premises to her namesake field in Norwegian waters on behalf of EniNorge. Two years’ hence, she is due to revisit Ulsan so as to load Statoil’s Aasta Hansteen spar platform for the North Sea.
Source: MotorShip