An Exploration Tool for Concept Design: the Seakeeping Performance Evaluation of Patrol and Frigate Ships

At an early stage of naval ship acquisition and design process, it is necessary to perform, in a reasonable time, trade-off studies assessing different ship solutions, often identified by very few parameters. A significant topic during this analysis is the dynamic behavior in waves, dependant on both ship features and sea state. Unfortunately evaluation tools, able to efficiently tackle with the typical lack of details during the ship design concept phase are not so many. In this paper an investigation tool, based on a semi-analytical approach, has been developed for the vertical motions evaluation of a mono-hull ship. For the necessary tuning activity, performed with both analytical and numerical procedures, available experimental data have been exploited. The tool is assumed to be suitable for frigate and offshore patrol vessel typology. It is based on a modular approach and built with a very user-friendly graphic interface; it assures an easy exchange of input data and results with other interfaces. Besides the vertical motions, the code is able to predict other basic seakeeping properties i.e. slamming, green water, propeller emergence, accelerations and comfort characteristics. An operability index is defined combining the above mentioned factors, in order to allow a comprehensive fast evaluation of ship behavior, through a single parameter. With reference to this index, the influence of main ship dimensions on global seakeeping performances is analyzed together with the influence of some operational parameters (e.g. speed or sea state).