A method for determining the sloshing of a liquid loading of a vessel, implemented by a device for determining the sloshing of a liquid loading of a vessel, said method comprising: a step of determination of a monomodal excitation as a function of a multimode excitation to which said vessel is subjected, the multimodal excitation comprising a state of the swell and a wind sea state, wherein the state of the swell comprises a direction of the swell and the wind sea state comprises a wind sea direction, and wherein the monomodal excitation exhibits a total direction equivalent to one out of the direction of the swell and the wind sea direction closest to a direction at right angles to the longitudinal axis of the vessel, a step of determination of a datum relating to the sloshing of said loading as a function of the monomodal excitation, wherein the datum relating to the sloshing is determined as a function of the monomodal excitation through consultation of a previously established database, said database comprising data relating to the sloshing expressing the sloshing as a function of the monomodal excitation, wherein the data relating to the sloshing are determined by experimental measurements, and a step of determination of a probability of damage to a tank of the vessel comprising all or a part of the loading as a function of the datum relating to the sloshing and of a level of filing of said tank, wherein the probability of damage is relative to a density of probability of encountering a pressure on an internal surface of the tank greater than an internal resistance of the tank as a function of the datum relating to the sloshing and of the level of filling of the tank. a step of determination of a monomodal excitation as a function of a multimode excitation to which said vessel is subjected, the multimodal excitation comprising a state of the swell and a wind sea state, wherein the state of the swell comprises a direction of the swell and the wind sea state comprises a wind sea direction, and wherein the monomodal excitation exhibits a total direction equivalent to one out of the direction of the swell and the wind sea direction closest to a direction at right angles to the longitudinal axis of the vessel, a step of determination of a datum relating to the sloshing of said loading as a function of the monomodal excitation, wherein the datum relating to the sloshing is determined as a function of the monomodal excitation through consultation of a previously established database, said database comprising data relating to the sloshing expressing the sloshing as a function of the monomodal excitation, wherein the data relating to the sloshing are determined by experimental measurements, and a step of determination of a probability of damage to a tank of the vessel comprising all or a part of the loading as a function of the datum relating to the sloshing and of a level of filing of said tank, wherein the probability of damage is relative to a density of probability of encountering a pressure on an internal surface of the tank greater than an internal resistance of the tank as a function of the datum relating to the sloshing and of the level of filling of the tank.