STRUCTURAL ANALYSIS OF A TRIMARAN FAST FERRY

摘要

In very recent years trimarans have gained the interest of designers and shipyards. Some small and medium size military units have already been realized. Larger versions of trimarans are under study for merchant purposes. A large amount of investigations has been carried out on this new typology, especially about hydrodynamic and sea-keeping performances; nevertheless some problems are still pending on the structural design. In last years, Classification Societies succeeded in developing codes for the scantling of fast units structures; High Speed Craft codes (HSC) are widely used for new monohull and catamaran passenger vessels. It seems quite difficult to extrapolate the HSC rules to trimaran hulls being this configuration substantially different from the point of view of loads and structural resistance definition. A new approach for this kind of vessels should then be considered particularly for the definition of design loads. Longitudinal, transversal and horizontal bending moments together with longitudinal and transversal torque should be taken into account. The definition of these loads can be performed with accuracy by using three-dimensional seakeeping analysis based on panel methods. In a preliminary stage simplified methods based on quasi static wave approach can be sufficient for the definition of complete, three-dimensional load sets and the scantling of the main structural elements of the main hull and the outriggers. On this basis, a first coarse finite element model of the resulting structure can be built and studied under the action of the previously calculated load sets. This allows to individuate the worst load condition and to refine the hull scantling through an iterative, optimising procedure. The aim of this paper is to describe the application of the above procedure to a large trimaran fast ferry. In the research framework the complete structural design of the vessel has been obtained. A comparison of different solutions is still under course and will lead to define the optimum solution.