The hydrodynamic performance of a novel float-over installation

Abstract

Floaters float-over (FFO) is a new method of topside/deck installations that has the concept of transporting the topside/deck using two groups of floaters connected at its opposite sides. By ballasting and deballasting the floaters, the system will be able to raise the deck from the transportation barge, and then lower it down to the jacket or spar. FFO can work in wider range of sea states than conventional float-over methods due to its small water plane area and large mass. FFO is, therefore, a competitive method compared to other heavy lift and float-over methods.In this paper, the concept and design philosophies are presented. The performance of the system during its consequential installation stages is discussed with regard to the stability, motions and strength aspects. The main stages of FFO installation, namely, transportation, lowering of the group of floaters, connecting them to the deck, separation of the deck from the transportation barge and mating of the deck with jacket legs, are presented. In each step, stability and motions are determined at the prevailing sea state. Based on the results of the motion analysis, the impact and internal forces at the deck are computed and evaluated according to the industry codes and standards. A case study for a deck that is to be installed by either heavy lifting or float-over is included, to indicate the suitable sea state for installation and the required stiffening for the deck.