This study shows the calculation of inland tanker's scantlings around its main frame, where the dimensioning is made by using set of Rules by Croatian register of shipping (CRS). The calculations were conducted through two phases. First phase was analytical phase were the dimensioning was made by using formulae from the Rules of CRS. Those calculated scantlings were then used to make the FEM model, which was the second phase of the project. The model itself required some modifications of its structure in order to satisfy the given conditions, which will be explained later in the thesis. General arrangement and 2D schemes of the tanker were used in order to define important parameters needed to create the model and also as an input to the Rules. Those parameters are: spans of the elements, location of the tanks (either cargo or ballast), location of the centers of gravity and spacing of the elements. Once all the elements were calculated by using the Rules, FEM model was created with all the scantlings of the elements as obtained by the CRS. The next step was to define restraints and apply loads on the model created, as the goal of the FEM is to observe deflections and stresses on the model when analysis is conducted. The 3D model was made by using plate and beam elements, which were connected by nodes as they interact with each other. It was important to take safety factors into consideration as well, especially buckling and bending safety factors, as all elements were designed according to those types of loads. Finally, in order to achieve the criteria for longitudinal strength and buckling, some elements of the structure were modified so they can satisfy all the conditions, or in other words, to prevent the structure from the collapse.