Depending on the type of support, vessels are classified as displacement, semi-displacement and planing. But all types of vessels are in the displacement mode when they operate at low speed. In planing, due to the supportive hydrodynamic pressure, the hull wetted surface area reduces leading to low frictional resistance and consequent increase in speed for the same power input. Planing vessels are used for different purposes such as for fast patrol, sport activities, service, ambulance, rescue and recreation. The use of stern flaps, both fixed or controllable, interceptors and integrated interceptor-flap in high speed boats has become an acceptable option to control the running trim of the vessel to enhance its speed and powering performance. The interceptor-flap changes the pressure distribution underneath the hull which in turn causes reduced resistance acting on ships aftbody. The integrated stern interceptor-flap effect on planing craft performance depends on its parameters and also on those of the craft. So, an in depth study on the hydrodynamic behaviour of integrated interceptor-flap is essential, before it is adapted to a vessel, to get the best performance during the craft operation. In recent years, the computational fluid dynamics (CFD) technique has proved to be accurate and robust for hydrodynamic calculation of high-speed planing hulls. The aim of this paper is to study numerically on the performance of planing hull fitted with integrated stern interceptor-flap configuration. These studies help in understanding the flow field and other parameters on resistance of planing hulls with different flap angles. The study shows that the interceptor-flap performs well compared to bare hull. The guidelines that could be derived from these studies help in improving the interceptor-flap design for a high speed planing craft. © 2018 ASME.