NUMERICAL AND EXPERIMENTAL HYDRODYNAMIC PERFORMANCE OF SLICE HULL FORMS Stefano Brizzolara and Diego Villa Marine CFD Group University of Genova – Dept. of Naval Architecture and Marine Engineering, DINAV ABSTRACT The paper presents the main results achieved during the investigation of an independent research about the hydrodynamic performance of unconventional SWATHs, with particular regards to SLICE hull forms types. The hydrodynamic characteristics of a SLICE hull form will be presented and assessed by means of systematic series of towing tank tests and CFD calculations, carried out using a potential flow method and a RANSE solver. The accuracy of the solvers to predict the total resistance of SLICE hull forms is validated by comparison with available sets of resistance tests in the towing tank of the department. The analysis is aimed to investigate the effects of the main geometrical parameters, essentially the longitudinal and transversal mutual positioning of the hulls. The hydrodynamic efficiency of the optimum SLICE hull form is critically compared with equivalent SWATH vessels having conventional and unconventional underwater hull forms (optimized for high speed). Interesting conclusions about the opportunities to adopt a SLICE hull form for the design of a SWATH are finally discussed with regards to the different speed ranges. 1. INTRODUCTION The SLICE hull typology is a relatively new unconventional alternative to “traditional” SWATH vessels featuring four underwater hulls grouped in two couples each one symmetric with respect to the centre-plane: one in the fore part of the vessel and the second at stern; they can be differently spaced in the transversal direction, as presented for instance in the vessel of Figure 1. This hull typology is deemed to offer several interesting advantages for realizing a fast speed SWATH vessel. From the hydrodynamic point of view, the characteristic concept behind the SLICE with respect to a SWATH is the subdivision of each long underwater bodies in two shorter and thicker bodies (of nearly equivalent displacement) which can be opportunely shifted not only longitudinally but also transversally, in order to obtain, among other design goals and constraints, the lowest wave resistance. An example of vessel designed on this technology by Lockheed Martin is presented in figure 1. Each of the two shorter underwater hulls, when advancing at the same speed of a conventional SWATH, operates at a higher Froude number relative to its length, where opportunely the wave resistance has surpassed the hump region attaining to drastically lower values than those of conventional SWATHs. Indeed, the validity of this principle could be already envisaged by the analysis of several SWATH fast speed design examples or studies, like for instance the “Sea Shadow” (figure 2) whose hull forms are very similar to the ones firstly introduced by Salvessen et al. (1985). More recently, the results of an automatic method for SWATH hull form optimization published by Brizzolara (2004) demonstrated how a conventional SWATH underwater hull Figure 1 - The Sea-Slice developed by Lockheed Martin Figure 2 The unconventional SWATH Sea Shadow