In the paper, some calculations are presented aimed to the definition of a procedure for the structural design of a type C tank and its supporting structures. More specifically, calculations have been performed on a bi-lobe type C tank for a LNG carrier. Different solutions are proposed for the numerical simulation of interaction between thanks and ship structures, giving suggestions to designers about the modelling of the contact of tank with its supports and on how to partially model the ship structures below tank and their boundary conditions. Moreover, a simulation procedure for heat transfer performed by FE analyses is presented, useful for an early stage evaluation of temperature distribution on ship hull structures.