Design Project of a Trimaran Multipurpuose Frigate – Study of the Hydrodynamic Aspects

Object of this study is the design project of a trimaran multipurpose frigate with the aim of evaluating advantages/disadvantages of a multihull configuration for new combat ships in comparison with a corresponding traditional monohull vessel. As a first step, an analysis of existing technical literature was conducted in order to collect information about different aspects related to the project of a trimaran, then the main characteristics of the mono-hull chosen as reference were defined. On the basis of the same operational requirements adopted in the definition of the corresponding monohull and of the information deducted by literature, the main characteristics of a trimaran configuration, identified as target vessel, were defined (i.e. dimensions and hull geometry, main hull and outrigger positioning, internal compartments definition, lay-out of general and engine arrangements, hull appendages). Once defined the target vessel, 9 different configurations obtained changing outriggers position and hull forms were assumed in order to investigate the influence of these variations on main trimaran performances and in particular to analyse wave interference effects strictly depending on the distance between the hulls and their respective position. Therefore 10 different configurations were obtained and for these studies of propulsion, seakeeping, manoeuvrability and stability were developed in order to compare the performance of the trimaran with the corresponding monohull. From the results obtained it can be deduced that a trimaran offers a greater bridge area with a consequent improvement of the layout while the reduced breath of the main hull causes some problems in internal arrangement. With regard to propulsive performance a lower power is required at higher velocities but not at lower speed; the trimaran configuration moreover offers improved seakeeping even if special care is required to evaluate impacts on traversal connection between hulls. Considering manoeuvrability, the course stability of the trimaran is greater than that of an equivalent monohull with a consequent reduction of the turning ability; finally, the intact stability of the vessel is improved, while some problems can be related to damage stability. In conclusion of this analysis concerning advantages/disadvantages of a trimaran configuration, it can be concluded that it offers some aspects of great interest for future development.