With the anticipated growth of global trade, shipping would continue to play a dominant role in the transport of country's seaborne trade. Containerizations are still spreading all over the world. Based on present trends, it is expected that approximately 95% of all liner general cargo will be containerized. The trend in last few years, with the economic scale realized by large container vessels deployed on trunk routs worldwide, it is not cost effective to make direct calls in many ports. For this reason lines develop hub strategy, whereas larger mainline vessels connect only few larger transshipment terminals (hub ports). Smaller container vessels (feeder ships) distribute containers to and from regional ports. Feeder's services are one of the elements that contribute towards our ports being more competitive in the region. The beginning of container transport revitalization process in the Republic of Croatia started in 1999 with the feeder services Rijeka – Ploče – Gioa Tauro - Malta. The mentioned feeder services have enabled the best way of connecting the container terminals on the east cost of Adriatic with transshipment terminals in the Mediterranean. Congestion of North European ports and facts that the North Adriatic route is 2300 mile shorter than the North European route for expanded Asia market helped the port of Rijeka to outgrow its national context. Good traffic and infrastructure links are essential for Rijeka to become regional hub port in the next few years. In order to establish the efficiency maritime transport in the Adriatic sea it is necessary to organize short sea feeder services connecting Rijeka as regional hub port with Zadar, Split and Ploče. This dissertation aims at focusing particularly on modeling mainly one ship characteristic, the ship's capacity. The problem of optimal ship's capacity is by nature a sub - problem of optimal ship design. A mathematical model defines optimum capacity of small feeder ships employed on the mentioned line, in view of economy of ship's operation (ship's profitability, rates between profits and costs and ships productivity) for the prevailing parameters. Some of the principal model parameters, such as freight rate, loading / discharge rates, prices of bunkers and ship's capital cost have been changed and applied to the relative impact on optimal ships capacity.