Manufacturing deviations in Hydrofoils and their impact on performance

Abstract

The Nacra 17 is a foiling catamaran selected to compete in the 2024 Olympic Games. The Nacra 17 is a one-design class, which requires all equipment to be identical. The Dutch Olympic team found through testing the bending stiffness that there is a slight difference in how each of their hydrofoils performed. The question was asked: What are the manufacturing deviations in the Nacra 17 hydrofoils and how do they impact the performance? This research aims to answer the previously stated question. The 3D scanned hydrofoils validated that there is indeed a measurable difference in shape between the different hydrofoils of the Olympic team. A successful method was proposed that automatically extracts 2D profile section properties from the point-cloud data of a 3D scanned hydrofoil. This method used a rough orientation using the profile plotted in polar coordinates. The mean camber line could be extracted using the Voronoi vertex points and the offset of the profile surface. The resulting data set was fitted using non-periodic cubic B-spline curves. This produced a curve for the mean camber line and the thickness profile. Comparison of profile properties resulted in the conclusion that profile thickness (yt) could show that the two female mould halves were probably spaced differently for the different hydrofoils by a standard deviation of 0.0669 mm at a thickness of 22.6 mm. Differences are found in the maximum thickness location (xt), Leading edge radius (rle), maximum camber (yc) and its location (xc). However, the differences in lift over drag for the different hydrofoils are minimal. The size of the drag bucket did not differ more than 0.1 of the lift coefficient (cl) for the same drag coefficient. With the exception of in general one section that presented an early separation. The specific profile showing early separation changes along the span, not allowing for the generalisation for the complete hydrofoil. It shows that the curvature at the leading edge of the profile is critical for the performance of the Nacra hydrofoil. Knowing which part of the profile shape is critical. Companies can take this area into account when designing the production process for the next hydrofoil, and the Olympic team can focus on maintaining these areas of the hydrofoil. Allowing the best preparation to be competitive at the next Olympic games.