In this thesis oscillation of a floating semicylinder is presented with focus on rotation about its longitudinal axis. In the first part, I derive the equation for calculating the ship's oscillation period and highlight the problem of the influence of the surrounding fluid in calculating the moment of inertia. Furthermore, without considering the surrounding fluid, I theoretically analyze the ways for which I think are the candidates for the approximation of oscillating semicylinder on the water surface. For each way, I write the term for the oscillation energy and for the period of oscillation and plot graphs of position-time dependence for the center of gravity and axis of rotation. With a reflection on the operation of forces on a floating semicylinder, I develop a simple analytical model in which I describe one of the effects of the surrounding fluid on a floating semicylinder during oscillation.
In the practical part, I describe the experiments in which I examine the theoretical assumptions about kinematics and the oscillatory time for a particular mode of oscillation. The measured values match the theoretical ones. Data, obtained from the experiment in which the semicylinder floats on the water, are used to check the correctness of the analytical model by calculating the added mass of the water which affects the oscillation. Computer tracking method is used for analysis of the position of the centre of gravity of a floating semicylinder during oscillation. Using the data obtained, the analytical model is upgraded and the equation for the assumption of oscillation energy is derived. On the basis of a comparison between the modeling modes of motion and the measured motion of a floating semicylinder, I conclude that the best model is the one in which the center of gravity of the semicylinder fluctuates only in the horizontal direction.