1 30th Symposium on Naval Hydrodynamics Hobart, Tasmania, Australia, 2-7 November 2014 Mitigation of Slamming of Large Wave-Piercing Catamarans Jalal R. Shahraki 1 , Michael R. Davis 2 , Babak Shabani 1 , Javad AlaviMehr 2 , Giles A.Thomas 1 , Jason Lavroff 2 and Walid A.I. Amin 1 ( 1 Australian Maritime College, 2 University of Tasmania) ABSTRACT The Wave Piercing Catamaran (WPC) design of INCAT Tasmania reduces motion responses in moderate seas and provides a high level of protection against deck diving in large seas. However, in large seas slamming will occur as the arch between outboard and central bow hulls fills, imposing large transient loads which can exceed the vessel weight. Consideration is given here to reducing slam loadings by variation of key geometric parameters of the WPC bow design and by operation of ride control system (RCS). Due to the complexity of wave slam loads, model testing provides an essential basis for design development and validation of numerical solutions. A segmented hydro-elastic model of the 112m INCAT WPC has been developed with adjustable height of the wet deck and length of the centre bow. Dynamic wave slam forces and whipping responses are modeled on the basis of the whipping mode frequency and damping. It is found that increases of wet deck height reduce impulsive slam loadings but lead to increased motions. Shorter centre bows reduce slam loadings and also reduce the vessel pitch motions. When the ride control system (RCS) is operated as a pitch damper the relative motion between the centre bow and water surface can be reduced by as much as 58% at the frequency of maximum relative motion. This reduction will confer significant benefits in terms of slam amelioration. The maximum relative bow motion occurs at a dimensionless encounter frequency corresponding closely to that at which most severe slamming is observed in the model test program. INTRODUCTION For high speed light craft (HSLC) the catamaran configuration has been found to be structurally efficient. Military operation of HSLC often demands that speed is maintained in sea conditions that are much more severe than would be acceptable for the commercial passenger operations for which these vessels were originally conceived. This exposes vessels to slamming and deck diving due to large wave encounter giving rise to extreme loads on the bow area of the vessel superstructure. Therefore issues such as the impact of the bow into the water when operating in large waves, or wet deck slamming, can affect mission capability, incur voluntary slowdowns and cause structural damage (Lavroff et al., 2010). Different strategies have been used to reduce slamming. Figure 1: Natchan World, INCAT 112m wave-piercing catamaran. Conventional catamarans have very low reserve buoyancy in the bow area, exposing the front edge of the wet deck connecting the two hulls to wave impact damage (Lavroff et al., 2010). INCAT Tasmania have resolved this problem by introducing the Wave Piercing Catamaran (WPC) (http://www.incat.com.au/ , Figure 1). WPCs have wave-piercing demi-hull bows and a short elevated centre bow, offering small motions in short waves and low bow drag. The short central bow has its keel line approximately on the water line of the main hulls. The centre bow thus provides reserve buoyancy under the wet-deck level in the bow area to reduce heave and pitch motions. The central bow virtually eliminates deck diving (Thomas et al., 2003) and confers an inherently robust sea-keeping response. This makes possible a lower wet-deck height with savings in