The Harding Move: Opening Up New Horizons

Abstract

Abstract During July-September 1995 Dockwise successfully completed the unique load-out, transport and discharge operation of the 22,870 ton BP-Harding PDQ-unit from Korea to the North Sea via the Suez Canal on board [he self-propelled heavy-lift vessel "Transsbelf'. This unique loading operation involved skidding the 22,870 [on platform via the side of the vessel over four skidbeams. Special solutions had to be found for stability, load spreading, mooring, ballasting and manoeuvring. Due to the 2.6 meter grillage height, special procedures were required for maintaining stability during discharge by float-off. The experience gained in this project may lead to a further extension of load-out and transport possibilities on a worldwide scale, utilizing the presently available fleet of heavy-lift vessels. Introduction For the development of the Harding Field, located in the Central North Sea, BP Exploration Ltd ordered a Technic Geoproduction designed TPG 500 from Hyundai Heavy Industries (HHI) in Ulsan, Korea. The TPG 500 is a fully integrated Production Drilling and Quarters (PDQ), three leg, jack-up platform. The legs were specifically designed for installation above a preinstalled concrete Gravity Base Tank. The design was such that the legs could not be fully retracted leaving a protrusion of 2.2 meters from the hull, which was to have a major impact on the transport concept, The platform had a transport weight of 22,870 tons and measured 88.72 meters in length, 111.75 meters in width and had a total leg length of 121.5 meters (Fig. 1). Due to the fact that the unit was built on a normal construction quay rather than inside a dry dock, loading took place by a skid-on method via the side of the 'Transshelf'. To facilitate this the vessel was fitted with four transverse skidbeams on deck, connected to the skidbeams on the quay. The actual loading was carried out using a skid-shoe and pulling system, the resulting elevation above the vessel's deck amounted to 2.6 m. Furthermore, in order to optimize the initial stability, sponsoons were fitted on each side. The load transfer onto the vessel was carefully monitored and compensated with the vessel's own high capacity ballasting system. Unique events come with unique problems, which needed to be solved by a multi-discipline team, Skidding 22,870 tons via the side of a vessel would be a unique operation in vessel or barge load-outs. In April 1993 a successful cooperation started with all parties involved (BPX, TPG, HHI and Doekwise, which resulted in the 4-track skidding concept to facilitate the transverse load-out. Skidshoe Arrangement A hydraulic-jack-skidshoe system had to be designed to linearize the loads on the skidbeams to avoid overstressing of the vessel and the PDQ. A special low profile skidbeam was designed to stay within the limits of the grillage height which had grown to 2.6 meters.