Study on the design requirements of external turret mooring for FLNG

In recent years, the use of natural gas as an oil alternative energy has been increasingly expected. To ensure the stable supply of natural gas, the construction of floating LNG (FLNG) is now under investigation around the world to develop small or middle scale gas fields, so-called stranded gas field. In most cases, the FLNG under investigation is equipped with a turret mooring system to keep its own position at each installed gas field. However, detailed methods to design the mooring system are not indicated in guidelines published by the typical classification society, or designers have to decide by themselves which of the guidelines they should adopt at the time of beginning design because of different design requirements for every guideline. In this paper, the author investigated combinations of severe direction of environmental forces, such as wind, current, wave and swell, selected from items indicated in the different design requirements. This paper also presents the results of investigation on the method of statistics analysis to evaluate the extreme value of line tension.