The paper aims at analyzing the structure of the ship’s cost at port as one segment of the total voyage cost in order to improve the efficiency of the shipping services. The optimum ship for a shipowner to be used on a particular route is defined as the ship that carries cargo at the lowest total cost per cargo unit. The problem of the optimum ship’s capacity, by the nature of things, represents one part of the general problem in defining the optimum ship’s characteristics, since the ship owner’s costs on the route concerned are an essential part in optimizing the ship’s optimum capacity. The main goal of this research is to contribute to defining the cost incurred during the ship’s stay in a port from the shipowner’s point of view as he is the one who, as a general rule, makes these costs seem as different port charges and costs. The synthesis of the mentioned costs at port is represented graphically as the daily cost at port per unit of the ship’s capacity.