Pioneering Spirit (formerly Pieter Schelte) is a catamaran crane vessel owned by the Switzerland-based Allseas Group designed for the single-lift installation and removal of large oil and gas platforms and the installation of record-weight pipelines. The , vessel is the world's largest vessel by gross tonnage, and since September 2021 also the largest floating sheerleg in the world. It was built in South Korea by Daewoo Shipbuilding & Marine Engineering in 2013 at a cost of €2.6 billion. It commenced offshore operations in August 2016. Development The initial concept, by Allseas technical director W.P. Kaldenbach, was of a vessel capable of lifting entire platforms, and in 1987 Allseas declared its intention to build it. The initial idea featured two rigidly connected, self-propelled supertankers, with a large slot at the bows enabling it to install platform topsides in one piece. Early designs featured a flotation and ballasting system and active motion compensation system to facilitate a controlled transfer of a topsides' weight from the vessel to a platform substructure. Allseas developed the original idea to include steel jacket installation, jackets and topsides removal and rigid pipelay capabilities. The emphasis switched from the conversion of two existing tankers to a new-build hull in 2004, though retaining the catamaran concept. The decision was prompted by a lack of suitable vessels to convert, the lower costs associated with a new-build, and the need to house sophisticated equipment – such as a dynamic positioning system – in the hull. In 2007, twenty years after the idea was first conceived, Allseas announced plans to build the Pieter Schelte, a twin-hulled platform installation / decommissioning and pipelay vessel. Named after the offshore pioneer , the father of Allseas' owner Edward Heerema, the design featured a lifting system at its bows for lifting platform topsides up to and a lifting system at its stern for lifting steel jackets up to . The design also included pipelay equipment to handle pipe diameters ranging from at water depths exceeding . Construction Allseas placed orders for machinery, including generators and thrusters, in 2007, and for the high-tensile steel for the lifting systems in 2008. After the global financial crisis weakened funding, the company was forced to postpone the building schedule and as a result delayed the awarding of the hull construction contract. Finnish engineering company Deltamarin performed detail engineering in 2009. Allseas eventually was able to sign the main construction contract