Numerical investigation of the effect of transverse step location on hydrodynamic behavior and longitudinal stability of planing catamaran in calm water

In this study, the effect of transverse steps location on hydrodynamic components and the longitudinal stability of the vessel has been investigated. The vessel studied in this research is a planning catamaran, each demi-hull with two transverse steps. At first, vessel resistance with a weight of 5.3 kg within a range of length Froude number of 0.49 to 2.9 in calm water has been calculated. Then, craft behavior was evaluated at displacements of 5.3, 4.6, and 4 Kg using the numerical method. The numerical simulation results have been validated with similar experimental results. The craft in 4 and 5.3 kg weights, in Froude numbers greater than 2.43 and 2.9, respectively, has a Porpoising instability. In order to improve the longitudinal stability of the vessel, the Taguchi test design has been used to determine the optimal location of the transverse steps. The results showed that by placing the transverse steps in the optimum location, the Porpoising instability in the vessel has been resolved. In planing mode, vessel resistance decreased by 12%, 9.5%, and 6.6% in the optimum state of transverse steps compared to the base state for the mentioned weights. In similar conditions, the lift force on the vessel increased by 15, 10, and 7 percent for the mentioned weights, respectively.