In this article, a mathematical model based on the 2D T theory has been developed to predict the performance of
two-stepped planing hulls in calm water. It has been attempted to develop a mathematical model without using regression
formulas. It leads to development of a computational model with no common limitations related to empirical models
which have an individual range of applicability. For this purpose, theoretical solution of water entry of a twodimensional
wedge section has been implemented to compute the pressure distribution over wedge section entering
water, and then normal forces acting on the two-dimensional sections are computed. Bottom of the boat has been
divided into three different planing surfaces including fore, middle and aft bodies. Computations are performed for each
of these surfaces. By integrating the two-dimensional sectional normal forces over the entire wetted length of the vessel,
the trim angle, wetted surface and resistance have been obtained. To evaluate the accuracy of the presented method,
the obtained results are compared against experimental data and a previous empirical-based method developed by
authors. The comparison suggests that the proposed method predicted dynamic trim angle, wetted surface and resistance
of double stepped boats with reasonable accuracy. The mean errors in prediction of trim angle, wetted surface
and resistance are, respectively, 13%, 16% and 8%. It should also be noted that although computation of running attitudes
and resistance of double-stepped planing boats are targeted in this article, the mathematical model has been developed
in such a way that it has the potential to model transverse and vertical motions of two-stepped planing hulls in future
studies.
