Predicting the motions of high speed RIBs: a comparison of non-linear strip theory with experiments

Accurate prediction of the motions of high speed craft is an essential element in understanding the response of crew to a particular design configuration. The aim of this work is to evaluate the capability of a numerical method for use in the context of a procedure for designing high speed craft. A numerical model is used to predict the motions of a planing craft in both regular and irregular waves. The model is based on non-linear strip theory, through calculation of the forces occurring on wedge impact. This numerical model and its limitations are well understood for lower planing speeds (up to a length based Froude number of around 1.2). This paper investigates the limitations and accuracy for higher speed craft (Froude number around 3). At present there is an inadequate knowledge of the model performance at these speeds. Lower speed validation is carried out using results from published experiments although this data does not extend to the higher speeds. Validation of the model at higher speeds is achieved using experimental data attained from testing two scale models: A wave piercing rigid inflatable boat (RIB) and an Atlantic 21 RIB. The experiments are conducted in a range of regular wave frequencies for three wave height together with a realistic JONSWAP sea spectrum. Results are promising, with good correlation between the heave motion of the numerical model and the measured experimental data. Based on these results, a number of potential enhancements to the existing numerical model are discussed