A ship or floating support for carrying or storing liquid inside a reservoir and including a large tank, said liquid consisting of a liquefied gas, preferably chosen from methane, ethylene, propane, and butane, cooled in said large tank, said large tank having its length disposed in the longitudinal direction of the ship and being preferably cylindrical and of cross-section that is at least in part polygonal and of axis in the longitudinal direction of the ship, said large tank being thermally insulated and of large size with at least its smallest dimension in the horizontal direction, in particular its width, being greater than 20 m and preferably in the range 25 m to 50 m, and presenting a volume greater than 10,000 m3, wherein said reservoir is equipped with at least one attenuation device for attenuating movements of said liquid and comprising movement means for moving said liquefied gas liquid inside said reservoir so as to form a horizontal stream immediately below the free surface of said liquefied gas at least locally over a depth of at least 0.5 m, and preferably at least 2 m.