A highly specialized analysis of functionality of a retractable keel lifting mechanism is presented in the paper. Because of its special design a retractable keel is vulnerable to rough sea conditions. To alleviate possible malfunctions or even damage to the keel, an analysis of lifting the keel during rough sea (WMO sea state 6) is performed. Reliable estimation of load acting on a keel is crucial for the subsequent functional or structural analysis of the keel. Aiming to obtain these loads, a

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... sea wave analysis is performed first, where a wave train is determined by respecting statistical data regarding the required sea condition. Two wave cases are considered: head seas (waves coming from the front) and beam seas (lateral waves). A deterministic dynamic analysis on the wave-hull-keel system is then performed. The response of this system is obtained in the form of a time dependent acceleration of the centre of gravity of the vessel and in a time dependent lifting force, i.e., the force which is required for lifting the moveable part of the keel during rough sea. Finally, the required pulling force of the lifting mechanism is determined.