As for today, modern container fleet keeps growing in size and capacity. For example, the container ship MSC Oscar with a length of 395 meters, a width of 59 meters and a draft of 16 meters, with a capacity of 19,224 TEU was launched in 2015. Despite the fact that the total number of navigational accidents (collisions, piles, groundings) has decreased in the last decade, emergency cases involving largetonnage vessels are quite frequent. At the same time, according to the results of AGCS (Allianz Global Corporate & Specialty), the loss of a container ship with a cargo capacity of 19,000 TEU could cost as much as 1 billion US dollars. Obviously, with the increase in the size of ships, the problem of ensuring their navigation safety in narrow waters becomes even more critical. Mathematical modelling and simulation is a necessary process involved into design and operation of ships and port facilities. At the same time, physical modelling using scaled models is time consuming and expensive, which, if necessary, is performed at the final design stage. Proper mathematical modelling helps to find out limitations and possible problems or look for optimal solutions at early design stage as well as in the subsequent design process.A manoeuvring model of an ultra large container vessel equipped with single screw fixed pitch propeller and semi-balanced spade rudder is represented in the paper. In order to check model's validity simulated data had to be compared with trial report data, which was obtained in ballast condition with significant trim. In such circumstances model coefficients cannot be calculated by known methods and have to be corrected as per trial data. The correction algorithm with a specifically developed objective function obtained as a result of this study are given in the paper.