A simplified method for the evaluation of the total resistance of a foiling yacht in upright condition

TL;DR

The paper tackles the challenge of quickly evaluating total resistance for foiling yachts in upright condition using limited input data. It combines a hull force model from potential-flow CFD with finite-span foil corrections derived from 2D foil data and AR-based fits, producing a new resistance curve to identify speed regimes where foils offer advantages. A test-case with NACA 4412 foils demonstrates potential resistance reductions at moderate speeds and highlights how foil dimensions influence performance. The work is intended as a screening tool, with validation against high-fidelity CFD recommended for practical design.

Abstract

An extremely schematic model of the forces acting an a sailing yacht equipped with a system of foils is here presented and discussed. The role of the foils is to raise the hull from the water in order to reduce the total resistance and then increase the speed. Some CFD simulations are providing the total resistance of the bare hull at some values of speed and displacement, as well as the characteristics (drag and lift coefficients) of the 2D foil sections used for the appendages. A parametric study has been performed for the characterization of a foil of finite dimensions. The equilibrium of the vertical forces and longitudinal moments, as well as a reduced displacement, is obtained by controlling the pitch angle of the foils. The value of the total resistance of the yacht with foils is then compared with the case without foils, evidencing the speed regime where an advantage is obtained, if any.

Figures (8)

• Figure 1: Schematic representation of the forces acting on the hull due to the foils. W is the hull weight, the forces generated by the foils are also indicated with F.
• Figure 2: Longitudinal force, vertical force and pitching moment acting on the bare hull in fixed horizontal position in a range of displacements and speeds. Values are hidden due to confidentiality.
• Figure 3: Non-dimensional values of lift and drag as a function of the aspect ratio of the wing (dots). Data are fitted with and exponential-type curve (green line)
• Figure 4: Response surface of the total resistance as a function of speed and displacement. Second order polynomial model.
• Figure 5: Lift coefficient, drag coefficient and efficiency as a function of the angle of attack for the 2D foil. Data are scaled in order to be of the same order of magnitude on the plot.