Topside Installation by Float over – Engineering Challenges

Abstract In recent years there has been a significant rise in heavy integrated Topsides for the new offshore fields in the Arabian Gulf. The Topside designs are increasingly becoming more complex and heavy. Installation of these decks through float over philosophy is the most sought after method. With its proven efficiency and cost effectiveness in installing those heavy topsides, this method has become well known in the Arabian Gulf. The significant savings in time and cost of offshore hook up and commissioning and the relatively reduced risks offshore makes it the preferred option in comparison to modularized lifting of the topside. Float over is an operation of mating of a topside structure, carried on a cargo barge, to a fixed (jacket) substructure. Normally the layout of the jacket and topside are designed such that it will be suited for a specific barge size in mind. The selection of barge size (dimension) corresponds to the target weight of topside and center of gravity location. Although the method appears simple, it requires meticulous planning from very early stages of the FEED design. Float over installations are comparatively weather sensitive and responses (motion behavior) of the float-over barge, carrying the topside, in waves are crucial and must be determined. The impact loads due to barge motions during mating are extremely important for jacket and topside design. The involvement of experienced Naval Architects from the FEED stage of design to carry out all installation studies leading up to float over is an absolute necessity to ensure good platform design. Awareness of potential challenges during float over design and installation shall help in the design of the platform and thereby avoid surprises later. This paper presents the float over philosophy, method of performance, systems used, technical aspects and various parameters to be considered during engineering for float over installation in the Arabian Gulf from a Naval Architect's perspective. This includes discussion on the importance of weight control of topsides, selection of barge for float over installation, finalization of support heights for topsides on barge, typical float over installation aids etc. The paper also discusses the typical technical analyses required to be performed for the design. The discussion in this paper is limited to float over installations using conventional load transfer method (by ballasting) and using normal spread mooring arrangement.