A method to assess the seakeeping behaviour of a merchant ship in its early stage of design

In the early stage of ship design a first choice of the main dimensions can be performed utilizing several methodologies available in literature. A further optimization process is then necessary and, in doing so, useful tools are furnished by standard series and data bases for the prediction of performances in calm sea. Such a philosophy may also be applied to seakeeping responses in order to predict the behaviour and the relative merit of a series of different design solutions all verifying the same contractual requirements and constraints. In this paper a procedure is presented to compare different ship designs in their early stage from the seakeeping point of view. The first phase of the proposed procedure consists in the computation of the seakeeping quantities of interest, utilizing a matrix of seakeeping data calculated for a standard series of merchant ships. In the second phase the responses are weighted on the base of the environment in which the ship will operate and a merit index, similar to that proposed by Bales, is determined. As an illustrative example, the procedure has been applied to four different classes of Ro-Ro ships.}