Method for calculating the surface vector of at least one ship and calculating each drift vector at any point on the path of said ship travelling at the engine cruising speed, comprising the following steps aa) to cc): - aa) implementing the method for calculating the surface speed of said ship according to the following steps a) to e) performed in a given position of said ship: - a) obtaining parameters of said ship, including the position, the heading, the background speed and the background route; - b) obtaining measurements selected from wind and current, using means external to said ship, said measurements being made in the vicinity of said ship, said vicinity being spatial and temporal, the spatial vicinity being an area centred on the position of said ship and the temporal vicinity being an interval of time; - c) defining the drift vector from one or more measurements obtained at step b) selected from wind and current; - d) defining the background vector from parameters selected from the position, the background speed and the background route obtained at step a); - e) calculating the norm and the direction of the surface vector of the ship from the drift vector at step c) and the background vector of said d); - bb) obtaining the navigation parameters of the ship, including the position, the heading, the background speed and the background route, collected in real time or in deferred time at any instant and at any point on the path of the ship in a given space for calculating the background speed; - cc) calculating, at any point on the path of the ship, the drift vector by adding the surface vector, the norm of which was calculated at step aa) and the direction of which is given by the heading of the ship, and the background vector calculated from the parameters obtained at step bb). - aa) implementing the method for calculating the surface speed of said ship according to the following steps a) to e) performed in a given position of said ship: - a) obtaining parameters of said ship, including the position, the heading, the background speed and the background route; - b) obtaining measurements selected from wind and current, using means external to said ship, said measurements being made in the vicinity of said ship, said vicinity being spatial and temporal, the spatial vicinity being an area centred on the position of said ship and the temporal vicinity being an interval of time; - c) defining the drift vector from one or more measurements obtained at step b) selected from wind and current; - d) defining the background vector from parameters selected from the position, the background speed and the background route obtained at step a); - e) calculating the norm and the direction of the surface vector of the ship from the drift vector at step c) and the background vector of said d); - bb) obtaining the navigation parameters of the ship, including the position, the heading, the background speed and the background route, collected in real time or in deferred time at any instant and at any point on the path of the ship in a given space for calculating the background speed; - cc) calculating, at any point on the path of the ship, the drift vector by adding the surface vector, the norm of which was calculated at step aa) and the direction of which is given by the heading of the ship, and the background vector calculated from the parameters obtained at step bb).