Bourbon Offshore has taken delivery of the first of 76 new platform supply and anchorhandling/towing supply (AHTS) vessels under construction at the Sinopacific shipyards in China.
The Bourbon Liberty 100 and 200 series are diesel-electric ships designed for conventional and deepwater operations. Their advantages include improved fuel efficiency, cargo capacity, and maneuvering capabilities.
Vessels will continue to be delivered from China at regular intervals through September 2011. Bourbon placed its first orders with Sinopacific in April 2006, as part of an ongoing plan to transform its global fleet into the most modern available by 2012.
Artist’s impression of the Bourbon Liberty 200 AHTS.
Building 76 vessels in series within four years is unprecedented for the offshore sector, the company claims, and necessitated close cooperation from the project’s outset with the shipyard and the designer, Seattle-based naval architects Guido Perla & Associates. To meet the delivery schedules, the partners committed to a series design for a vessel which had to be simple to build and operate. Guido Perla had already developed a methodology geared to simplifying production while working for various US shipyards. The company also had solid experience in diesel-electric engines, Z Drive propulsion (Steerprop), and DP-2 dynamic positioning systems.
For the Liberty Series, it focused on optimizing the hull design through fluid flow analysis; lightening the structure through careful positioning of materials at the right locations; and applying various computer-assisted design techniques to create standardized components and modules.
Standardization allowed the partners to better organize the construction phases and to ensure flexibility in planning the assembly lines and production sections. As a result, Sinopacific Shipyards only requires nine days to assemble the hull forms for each vessel, followed by a straightforward installation of the diesel-electric engine on the main deck. In the same vein, piping is pre-arranged in the hulls prior to final assembly to speed up final completion.
To ensure a rigorous organization for the process of series construction, Bourbon and Sinopacific established a 40-strong team at the production sites in Dayang and Zheijang to monitor and control each phase of the vessel assembly. The Sinopacific design offices in Shanghai also interacted closely with the Guido Perla team, for instance in the use of Tribon 3D software for fabrication management.
Flexibility
Bourbon has ordered 22 of the Liberty 100 platform supply vessels. These have an overall length of 57.9 m (190 ft), a molded breadth of 14 m (45.9 ft), and a maximum draft of 4.9 m (16.07 ft). The 1,517-metric ton (1,672-ton) PSVs can travel at a speed of up to 12.5 knots, and at 10.5 knots in economy mode.
The diesel-electric propulsion system is designed for fuel efficiency and costs savings, as generator output can be varied according to operational load requirements. Power is supplied from one 487 kW and two 1.297 kW main generators: these have been placed on the main deck level, thereby freeing up 30% more below-deck cargo capacity, and greater liquid mud storage capacity (over 4,000 bbl) than other PSVs of a similar size.
Maneuvering is provided by two azimuth stern thrusters, one fixed stern thrusters and two bow thrusters. This configuration enhances reliability and improves vessel safety during offshore operations, Bourbon claims. The Class II DP system provides precise station-keeping, and allows the vessel to offload cargo alongside drilling rigs or platforms even in rough weather.
The Liberty 200 series AHTSs have similar maneuvering, propulsion, and fuel economy features. These vessels are 59.78 m (196 ft) long and 15 m (49.2 ft) broad, with a maximum design draft of 4.88 m (16 ft) and around 1,600 metric tons (1,764 tons) dwt. Each is equipped with a Mac-Gregor-Plimsoll electro-hydraulic, high-pressure double drum winch in a waterfall arrangement, with a rated pull of 150 metric tons (165 tons) on each drum.
Other handling/towing items include:
- A stern roller, reducing stresses on anchors and mooring systems during launch and recovery
- Shark jaws for safe stopping of chains and wires during anchor handling
- Retractable towing pins for centering, controlling and guiding the towing line and cables.
The first two AHTSs were due to be delivered early this year, followed by further commissioning at the rate of one vessel every three weeks until end-2011.
