The recently completed ‘Pieter Schelte’ is probably the most sophisticated workboat ever built. Designed primarily for the removal of offshore oil structures this complex vessel has been under development for the past 25 years by Swiss company Allseas.
The vessel went through several design stages before emerging from the Daewoo Shipyard in South Korea as the World’s largest ship, capable of installing and removing offshore oil topside structures and jackets as single units which will help oil exploration companies meet their obligation to remove offshore structures down to the seabed.
The vessel has hull length of 382 metres and a beam of 124 metres with the length increasing to 477 metres when the tilting lift beams and the pipe-laying stinger are included. The vessel can handle a topsides lift of 48,000 tonnes and a jacket lift of 25,000 tonnes.
The two hulls are separated by a slot at the bow that is 59 metres wide and 122 metres long. This size was selected after a detailed study of the existing platforms and the likely size of new platforms that might be required to be installed in the future. The vessel will be able to cope with the removal of around 95% of the existing topside structures in the North Sea utilising the eight sets of lifting beams that can span the bow slot.
At the stern the focus is on the installation and removal of conventional steel jackets and here the tilting beam system can also be used for regular crane lifts such as for the installation and removal of modules, bridges etc. Pieter Schelte is also equipped for pipe laying operations with a 170 metre long stinger (210 metres including the transition frame) that can be installed between the two hulls at the bow. Pipes up to 68 inches in diameter can be handled with storage space on deck for 27,000 tonnes of pipe and four 500 tonne tensioners.
The vessel is equipped with 8 MAN diesel generators providing a total installed power of 95,000 kW. The propulsive power is transferred through 12 Rolls-Royce azimuth thrusters which give a maximum speed of 14 knots and which are also used for the fully redundant Kongsberg DP3 dynamic positioning system. Accommodation is provided for 571 people in the offset central superstructure.
The development of Pieter Schelte represents a huge investment with the vessel’s cost estimated in the region of €2.4 billion, making it not only the World’s largest vessel but also the most expensive. Allseas is already looking to the future with plans well advanced to build a second vessel of this type which will be even larger and which will be able to handle the installation and removal of virtually all of the existing platforms worldwide.
The two hulls are separated by a slot at the bow that is 59 metres wide and 122 metres long.