The main objectives of this study are to carry out technical feasibility study on the concept of the LNG fuel tank (prismatic IMO type B) and its supports equipped in 14,500 TEU container ship. The design of the fuel tank structures considering characteristics of the container ship was suggested in this study. Structural analysis, fatigue analysis and crack propagation calculation were performed to verify the adequacy of the structural arrangement and strength of the fuel tank structures. In addition, stress-concentrated area of the hull due to structural discontinuity between existing open deck and additional closed deck for the fuel tank and the fuel gas supply system (FGSS) room has been evaluated through whole ship structural analysis.
The environmental regulations have been reinforced globally and it is no exception in the maritime industry. Emission control areas (ECAs) will be expanded while the permissible level for emissions is tightened. Ultimately emission regulations on all of the high seas will also be strengthened. As a result, there is an increasing interest in the ship to use the LNG which has been attracting attention as a clean fuel. However, on the contrary to these situations, the rules and regulations concerning the LNG fuelled ships have not been established yet.
In order to use LNG as fuel for common commercial ships, there is a need for additional compartments of the FGSS room and the fuel tank. Many different types of tanks can be used as fuel tank for a container ship. The pros and cons of three typical types of tanks can be seen in Table 1.
In case of IMO type C tanks, they are already in operation on small ferries and offshore supply vessels. They are very reliable and have advantage that there is no need to boil-off gas handling due to high design pressure. In addition they are easy to fabricate and install. However the space efficiency is relatively low due to their cylindrical or spherical shape. This may severely reduce cargo capacity.
Membrane type tanks, which are widely used on the very large LNG ships by their high space efficiency, are vulnerable to sloshing impacts. To use membrane type tanks as a fuel tank, more careful assessment of the impact loads is required since loading conditions of the fuel tank are quite different from those of the cargo tank. The fuel tank experiences partial loading at any tank filling level during its lifetime.