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www.sname.org/sname/mt January 2013 stricter stability demands, we also increased the colli- sion damage zone beyond the demands of the NMA. is was to account for the growth in size of oshore supply vessels in recent years. e rig positioning system is an automatic thruster- assisted, all chain pre-laid 12-point 84 mm mooring system. e rig has chain lockers to carry 8 complete chains and 4 for runners. A 12-point pre-laid moor- ing system provides exibility compared to most NCS rigs operating with 8 lines, exibility on water depth, and to handle obstacles and infrastructure on the sea oor. In extreme cases, ber inserts may also be used to increase the capacity of the mooring system. e size of the rig and the large forces from wind, current, and wave drift call for a more robust solution than what has been chosen in the past. e vessel has relatively large thrusters and can operate in DP class 3 in up to Beaufort 7 and automatic thruster assisted (ATA) moor- ing. A limitation in the thruster force output in ATA is enforced, as there is a concern that with large thrusters in combination with mooring the thruster force may pull out the anchors, if not limited. Motion characteristics of the rig design were closely followed up as the rig design progressed. e harsh metocean environment on the NCS calls for units that can work under rough conditions, both from a safety perspective and for high eciency in operation. Some of the rigs in operation have had to be tted with sponsons and blisters at the construction yard or in retrot to cope with topsides weight growth. In general, such additions to the hull will lead to poorer motion characteristics, particularly in heave. Avoiding having to put on sponsons or blisters on the hull has had a high focus in design. Performance was quality assured in wave basin and wind tunnel tests during the FEED process. Whats next? The MODU group at Statoil is currently working on future concepts to further strengthen the drillrig portfo- lio. e business model and design philosophies applied on the category D and J projects have so far been suc- cessful, and future projects may use the same hands on approach for MODU project development. MTErlend Hovland is principal engineer?marine concepts and ship technology with Statoil in Houston, Texas. Anders K. K. Attramadal is MODU new built support manager with Statoil. Ongoing studies include the I ca tegory for arctic drilling.