The world’s largest offshore vessel, Allseas’ platform installation/ removal and pipelay vessel Pieter Schelte, has commenced sea trials near Daewoo Shipbuilding & Marine Engineering’s shipyard in Okpo, South Korea.
Pieter Schelte will be 382 m long and 124 m wide. Positioned at the bow of the vessel is a slot, 122 m long and 59 m wide, where topsides are lifted using eight sets of horizontal lifting beams. Two tilting lift beams, for the installation or removal of jackets, are located at the vessel’s stern. The tilting lift beams are also used for regular crane lifts, such as for the installation or removal of modules, bridges etc.
Pieter Schelte’s large ship size gives her a very good wave response behaviour, superior to semi-submersible crane vessels in operational wave conditions; topsides and jackets can be installed and/or removed in significant wave heights of up to 3.5 m.
The vessel is equipped with eight diesel generators, providing a total installed power of 95 MW, driving 12 azimuth thrusters for dynamic positioning (DP3) and for propulsion. The maximum speed will be 14 knots. The accommodation has room for up to 571 persons in two-berth cabins.
Pieter Schelte’s primary area of focus is the removal (in accordance with OSPAR ’98 regulations) of large steel jacket-based platforms in hostile areas such as the North Sea, but also more benign parts of the world. In particular, Pieter Schelte will target the topsides and jackets that are too heavy, or too large, to be lifted in a single section by crane barges. The primary aim will be for topsides heavier than 10,000 t and jackets higher than 70 m, although smaller platforms can be accommodated equally well.
Allseas has analysed in detail a large number of contemporary platforms to verify the vessel’s versatility and to develop viable solutions for lifting and lowering structures onto a cargo barge, transporting structures and skidding them ashore.
Gravity-based topsides, for which the leg spacing fits the slot on the vessel’s bow, can be lifted with pods fitted in the clamps of the topsides lift system. Platforms with a leg spacing of up to 58 m can be accommodated. Only a few of the widest gravity-based structures and jackets currently found in the North Sea do not fit Pieter Schelte’s bow slot; the topsides of these platforms can be removed modularly using the tilting lifting beams.
Reference: Maikel Stuijfzand / allseas.com