The invention relates to a method for controlling a ship propulsion system (1) comprising a surface propeller (5) in which the desired capacity is interpreted as the target rotational value (nSL), the rotational speed control deviation is calculated from the desired rotational value (nSL) and the actual rotational value (nIST) of the internal combustion engine (2) and an injection quantity (qV) for the rotational control of the internal combustion engine (2) is determined using the rotational speed control deviation on a rotational speed controller (14). According to said method, the trim position (POS) of the surface propeller (5) is controlled by means of an arrangement controller (8) in accordance with the capacity reserve (PRES) of the internal combustion engine (2) and the actual trim position (POS(IST) ) and the effective rotational speed (nEFF), said trim position being determined from the rotational speed control deviation.