Interceptor design for optimum trim control and minimum resistance of planing boats

Interceptors are vertical blades installed symmetrically aft of the craft. This article aims to investigate the main geometrical (height and span length) parameters in interceptors. Different Models with and without interceptors at different heights and spans have been analyzed based on the finite volume method and SIMPLE algorithm using dynamic mesh. In order to validate CFD results, the grid convergence index (GCI method) has been used to estimate the uncertainties caused by grid-spacing and time-step. Although it has been proved that the interceptors are very useful in trim control and resistance reduction, choosing wrong size interceptors could not only destroy their effectiveness, but also endanger the planing boat due to the creation of a strong moment leading to negative trim. The results of this study show that among all effective variables, the boundary layer thickness (h) at the stern (where the interceptor is installed), is far more important than, some other particular parameter, on interceptor performance and should be taken into account in estimating the interceptor height (d) and span (s). Generally, the interceptor height should not be higher than 60 percent of boundary layer thickness at transom. For optimum efficiency, when the interceptor height equals 60 percent of the boundary layer, the interceptor span length should be seven times as much as the interceptor height. At the end, based on Reynolds number the paper presents three figures, setting the basis for optimal interceptor sizes for its use in planing boats.