Development of Frigate Designs with good Seakeeping Characteristics Thomas Eefsen 1) , Frans van Walree 2) , Daniele Peri 3) , Peter van Terwisga 4) , Hans Otto Kristensen 5) , Roberto Dattola 6) , Marcel Visser 7) 1)FORCE Technology, Lyngby, Denmark, 2)MARIN, Wageningen, the Netherlands, 3)INSEAN, Rome, Italy, 4)Royal Netherlands Navy, the Hague, the Netherlands, 5)Danish Naval Materiel Command, Copenhagen, Denmark, 6)Italian Navy, Rome, Italy, 7) Royal Netherlands Navy, the Hague, the Netherlands. Abstract Heading The paper summarises a design study of advanced mono-hull frigate concepts. Based on the parent design of a 120 m frigate, seven different alternatives of hull forms and concepts have been developed. The concepts have been evaluated according to their performance as regards a) ship motions in head, following and stern sea, b) linear operability for the North Atlantic and c) bare hull resistance and added power in head seas. The work was done as part of the THALES programme, which is a project with the Danish Naval Materiel Command (Denmark), FORCE Technology (Denmark), INSEAN (Italy), Italian Navy (Italy), MARIN (the Netherlands), Royal Netherlands Navy (the Netherlands) and Delft University of Technology (the Netherlands). The THALES programme has been completed in the period 2000-2004. Keywords Frigate; hull design; seakeeping; model tests; numerical optimization. Introduction The aim of the study was to develop new mono-hull concepts to be considered for the next generation of surface combatants and to explore the hydrodynamic performance and risks of these concepts. Compared to conventional mono-hull combatants, the concepts should provide improvements as regards resistance in the high-speed range and as regards operability in a seaway. The evaluation was based on model tests com- bined with numerical calculations. In order to evaluate the applicability of numerical design tools in the design process, comparisons between model tests and numeri- cal calculations have also been made. Furthermore a numerical optimization technique has been applied for development of the best compromise between good still water performance and good seakeeping characteristics. Description of Concepts Seven alternative designs have been made based on a parent design. The design of the parent hull form (PHF) has been developed under the framework program of ‘The Future Reduced Cost Combatant Study (MO2015)’, ref. Keizer, E.H.W. (1998). The hull lines are illustrated in Figure 1. The main dimensions of the hull and the alternative designs are listed in Table 1. Figure 1 : Bodyplan of Parent Hull Form (PHF). All design alternatives have been designed to have the same deadweight and internal volume. Furthermore all designs have been designed to meet the navy intact stability requirements. The GM T has been calculated to satisfy the ‘Stability and Buoyancy Criteria for U.S. Naval Surface Ships’, ref. Sarchin and Goldberg (1962). In order to have a fair comparison of the seakeeping characteristics, a GM T of 1.5m has been selected for all concepts, except the PHF-TH and PHF-TH-WP, which were tested with GM T =2.48m because of the said stabil- ity requirements compared to the other concepts. The COFEA concept (Center of Floatation Extreme Aft) is a mono-hull with the center of floatation shifted aft. The fore body is of SWATH type with reduced water plane area. The hull form has been developed in a previous study, ref. Kapsenberg G.K. and Brouwer R. 9th Symposium on Practical Design of Ships and Other Floating Structures Luebeck-Travemuende, Germany © 2004 Schiffbautechnische Gesellschaft e.V.