On the Collision Safety of a Gas Fuelled 6500 TEU Container Vessel

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Scheduled international environmental regulations are resulting in an increasing interest to use Liquid Natural Gas (LNG) as fuel for ships. However, the well known potential of LNG to reduce emissions must not increase the potential risks compared to conventional fuels. The Maritime Safety Committee has published an Interim Guidelines MSC.285(86) which includes a collision safety rule for gas fuelled vessels which requests a minimal distance of the LNG storage tanks from the ship outer shell (B/5-Rule). However, research work is needed regarding the actual crashworthiness of alternative ship designs with an LNG tank position closer to the ship shell than the B/5-Rule. A minimum safety concept actually discussed requires that LNG fuelled vessels shall have a collision resistance at least similar to the one of LNG carriers. In the present paper a case study is presented where the collision resistance of a gas fuelled 6500 TEU Container Vessel is investigated based on the GL-Rules I-1-33. The Container Vessel has an alternative design to the B/5-Rule exploiting more cargo hold space for LNG bunckering by placing the LNG tanks at 8% of B from the side shell. The crashworthiness of the Container Vessel is compared to the one of an LNG tanker of approximately the same size. Numerical computations indicate that the critical collision speed up to penetration of the inner hull is larger for the LNG carrier. For the more relevant case of LNG spill the Container Vessel with alternative design has an increased crashworthiness compared to the LNG tanker. It is shown that the critical collision speed for the Container Vessel is almost twice the one of the LNG tanker in case of an LNG spill.