A method for a propulsion arrangement (101) for providing propulsive power to a marine vessel (1), the method comprising the steps of: —determining (S1) whether the vessel (1) is running by means of the propulsion arrangement at a constant vessel speed, —storing (S3) a value (V1) of the constant vessel speed, —detecting (S4) a value (n1) of a rotational speed of a rotatable part (102) of the propulsion arrangement while the vessel is running at the constant vessel speed, —storing (S5) the detected rotational speed value, —subsequently controlling (S6) the propulsion arrangement so as to change the vessel speed, —subsequently repeating (S7-S11) the steps of determining whether the vessel is running at a constant vessel speed, storing a value (V2-V4) of the constant vessel speed, and detecting and storing a value (n2-n4) of the rotational speed of the rotatable part, to obtain a plurality of stored pairs of vessel speed values and rotational speed values, and —creating (S12) based at least partly on the stored pairs of values a correlation record (126) correlating vessel speed values with rotational speed values.