Boskalis (United Kingdom)

Abstract The Aasta Hansteen Field development in 1300m water depth is the deepest field on the Norwegian Continental Shelf (NCS) and is developed using a Truss Spar FPSO. The platform was made ready with platform mooring chains after which Topsides were installed by float-over method in a fjord before the complete platform was being towed to the field vertically in summer of 2018. The Topsides of 25,300 t and the hull of 46,000 t were both constructed by Hyundai Heavy Industries in Korea and transported to Norway on Boskalis heavy transport vessels. Due to its size and weight, the Truss Spar FPSO had to be transported by the largest heavy transport vessel in the world, BOKA Vanguard. Topsides mating onto the Spar hull was carried out by Boskalis in a Norwegian fjord by a dual barge float-over operation. The Topsides was first transferred from HTV White Marlin to two S-class vessels, then from the two S-Class vessels to the Spar hull. Load transfer was obtained by simultaneous ballasting of the dual barge hulls and de-ballasting of the Spar hull. The paper will focus on the engineering and design process of the dual barge float-over operation and the subsequent translation to a real time simulation model followed by the actual dual barge float-over and mating operation. The information and discussion provided in the paper can be used for planning and design of other large floater applications. There were several firsts in the execution of this scope ranging from transporting the world's largest Spar platform on the world's largest heavy transport vessel to executing a dual barge float-over and mating operation using two heavy transport vessels. The use of real time simulation as validation and training tool has been a highlight of this scope.