Method for determining an optimum propulsion parameter and a maximum power saving of a wind propulsion system of a ship by means of a data-processing device (119, 123) comprising a real-time-capable interface to at least one associated measuring apparatus (103, 105, 107, 111, 113, 115) of the ship, wherein a wind parameter or a plurality of wind parameters and a ship parameter or a plurality of ship parameters are captured by means of the measuring apparatus or measuring apparatuses, comprising the following steps: - transmitting data captured on board from the associated measuring apparatus or the associated measuring apparatuses via the real-time-capable interface to the data-processing device, - determining the optimum propulsion parameter and the maximum power saving of the wind propulsion system by means of the data-processing device from the transmitted data by o determining a current true wind angle and a current true wind speed, wherein the current true wind angle is a currently present true wind angle and the true wind angle is an angle between a meteorological wind and a keel line of the ship, and wherein the current true wind speed is a currently present true wind speed and the true wind speed is a wind speed of the meteorological wind, o determining the optimum propulsion parameter, wherein the propulsion parameter is an operating parameter and/or a power parameter of the wind propulsion system, for a maximum power saving using an apparent wind angle, an apparent wind speed and the ship parameter or a plurality of ship parameters, o defining true wind angles in an angular range of from 0 to 360 degrees, o determining the apparent wind angle and/or the apparent wind speed for each defined true wind angle in the angular range of from 0 to 360 degrees using the determined current true wind speed, and o determining the optimum propulsion parameter and the maximum power saving for each defined true wind angle as previously described in the angular range of from 0 to 360 degrees, such that the optimum propulsion parameter and the maximum power saving for each defined true wind angle are provided, on the basis of which an optimum course of the ship can be set in real time, wherein the method has a cycle time of less than or equal to 5 seconds, such that determining the optimum propulsion parameter and the maximum power saving is carried out dynamically in real time on the basis of changing wind and/or ship parameters. - transmitting data captured on board from the associated measuring apparatus or the associated measuring apparatuses via the real-time-capable interface to the data-processing device, - determining the optimum propulsion parameter and the maximum power saving of the wind propulsion system by means of the data-processing device from the transmitted data by o determining a current true wind angle and a current true wind speed, wherein the current true wind angle is a currently present true wind angle and the true wind angle is an angle between a meteorological wind and a keel line of the ship, and wherein the current true wind speed is a currently present true wind speed and the true wind speed is a wind speed of the meteorological wind, o determining the optimum propulsion parameter, wherein the propulsion parameter is an operating parameter and/or a power parameter of the wind propulsion system, for a maximum power saving using an apparent wind angle, an apparent wind speed and the ship parameter or a plurality of ship parameters, o defining true wind angles in an angular range of from 0 to 360 degrees, o determining the apparent wind angle and/or the apparent wind speed for each defined true wind angle in the angular range of from 0 to 360 degrees using the determined current true wind speed, and o determining the optimum propulsion parameter and the maximum power saving for each defined true wind angle as previously described in the angular range of from 0 to 360 degrees, o determining a current true wind angle and a current true wind speed, wherein the current true wind angle is a currently present true wind angle and the true wind angle is an angle between a meteorological wind and a keel line of the ship, and wherein the current true wind speed is a currently present true wind speed and the true wind speed is a wind speed of the meteorological wind, o determining the optimum propulsion parameter, wherein the propulsion parameter is an operating parameter and/or a power parameter of the wind propulsion system, for a maximum power saving using an apparent wind angle, an apparent wind speed and the ship parameter or a plurality of ship parameters, o defining true wind angles in an angular range of from 0 to 360 degrees, o determining the apparent wind angle and/or the apparent wind speed for each defined true wind angle in the angular range of from 0 to 360 degrees using the determined current true wind speed, and o determining the optimum propulsion parameter and the maximum power saving for each defined true wind angle as previously described in the angular range of from 0 to 360 degrees,