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Fast ships are taking a relevant role with a clear interest for military purposes. Fast sea transportation encounters several problems to be solved. This article refers to the difficulties originated by brisk vertical motions. The waves encountered by fast ships induce such vertical motions, and this has negative effects: navigation risks, sea sickness, structural damages, and load displacement. It is also interesting for military uses to stabilize the ship when an aircraft is landing or when precision firing is required. By means of submerged actuators, it is possible to alleviate vertical motions. In this research, a pair of transom flaps and a T-foil near the bow are used to counteract the waves. These actuators must move with the maximum efficiency, taking into account the dynamical characteristics of the ship. As a consequence, there is a problem of automatic control design. To carry out this design, it is important to obtain mathematical models of all the aspects involved in the problem: the ship, the waves, the actuators, and the effect on crew and comfort. The aim of this paper is to present the development of these models and the use of them for problem analysis and control design.

The paper is an overview of a research initiated seven years ago by three groups of three universities, under the auspices of a Spanish shipbuilder. The research aims to improve the seakeeping performances of fast ferries, by using moving appendages such transom flaps and T-foil. There is a problem of control design to move the actuators in adequate way, to counteract the effect of encountered waves. The research focuses on alleviation of seasickness. Several aspects have been covered along the research, motivating a long series of papers. The overview gives an ordered account of the main results, with the corresponding references. Main results concerning seasickness and navigation, prediction of seasickness during ship design, experimental modelling, control design and experimental verification, are presented. . Copyright © 2005 IFAC

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