Development of Load-out Methodology for On-Ground-Build FSO
Authors: Yang Y.T. , Cho H.G. , Yoon K.Y. , Ha S.S. , Kang H.S. 
Published: October 2008

This paper presents the design concept and operation results of load-out for the FSO (340,000 DWT Class, ELF AMENAM KPONO Project) built on the ground without dry dock facilities. It was the first attempt to build FSO completely on the ground and launch it using barges.

The major characteristics of load-out structure, which depend on FSO configuration composed of general VLCC type hull and topside structure, were its heavy weight, i.e. 53,000 metric ton and long length compared to breadth and depth, i.e. 298 meters. So, special consideration was required for safe load-out operation comparing to previous load-out of other offshore structures where the weight was less than 30,000 metric tons. The strength and longitudinal deflection of FSO were carefully analyzed with appropriate weight distribution. All facilities for load-out including ground foundation, jack-up system, pulling system and link-to-barge system were designed based on this result and friction force along the skidway. The stability of quay wall located in HHI Offshore Yard was checked against loading condition during load-out operation. Two semi-submersible barges that were connected together by rigid frame structures were used for loadout of FSO. The ballasting operation of connected double barge unit (DBU) can be controlled like one barge using load master control software (LMC) developed by HHI. Relative deflection in way of DBU connection frames was monitored during load-out operation. And DBU motion during load-out, towing to float-off site and float-off phase were analyzed and compared to model test result.

The load-out concept and methodologies described here are verified through successful load-out operation of Amenam FSO project. These concept and experience can be adopted for load-out design of extra-heavy structure which weight is more than 100,000 metric tons. Guide lines for the development of an efficient construction method for offshore and ship type structures are also suggested for future application of this concept.

1. Introduction

Floating type offshore structures showed an overall increase in market share during the last several years in offshore construction field. Generally, the fabrication and assembly of floating offshore structures like FPSO (Floating Production Storage and Offloading system), FSO (Floating Storage and Offloading system), FPU (Floating production Unit), Rig, Jack-up etc., have been carried out in the dry dock of a shipyard by stacking unit blocks sequentially from lower to upper levels.

In case of ship type offshore structures, lower hull part fabrication and assembly are carried out in a dry dock as conventional ship construction method and topside modules are installed by heavy lifting crane near the quay side. This methodology has great dependency on dock schedule and tight fabrication process of yard. So, it was very important to match fabrication schedule between hull and topside part to meet total project schedule. In such cases, it is difficult to incorporate any design change or modification required by client