Ship Performances and Sea State Condition: an Assessment Methodology Integrated in an Early Design Stage Tool

In the naval ship acquisition process and design, especially at an early stage, it is increasingly crucial the application of commputational tools able to individuate feasible design solutions in a reasonable time and to assess at the same time the ship configurations in terms of operational capabilities. A Ship Synthesis Model (SSM) can be an useful computational tool in this exploration phase. In relation with a specific operational profile, environmental conditions might have a fundamental importance. Therefore a methodology to assess the mutual effect between an actual sea-state and a ship configuration, in terms of vertical motions and accelerations, has been developed. A semi-analytic method is implemented in order to have the approach compatible with the general parametric structure of the SSM tool. In this paper the outline of the methodology is described and an application case is presented for an offshore patrol vessel. As an outcome, the influence of ship characteristics can be quantitatively analysed in direct relation with a possible set of acceleration threshold at fixed position to complied with, for example in a helicopter operational perspective. Furthermore, in the paper a possible methodology to estimate the environmental condition effect on the ship resistance is going to be presented as well. The “added resistance” component in relation with the sea state can be in fact evaluated and compared with the ship capability to sustain a defined speed in that sea condition. A parametric study is going to be carried out in order to formulate a possible parametric expression suitable to be integrated within the SSM structure.