Abstract
Hydrofoils are a current hot topic in the marine industry both in high performance sailing and in new passenger transport systems in conjunction with electric propulsion. In the sailing community, the largest impact is seen from the America’s cup, where boats are sailed at more than 50 knots (over 100 km/h) with 100% “flying” time. Hydrofoils are also becoming popular in the Olympics, as in the 2024 Olympic games 5 gold medals will be decided on foiling boats/boards. The reason for the increasing popularity of hydrofoils and foiling boats is the recent advances in composite materials, especially in their strength to stiffness ratio. In general, hydrofoils have a very small wetted surface area compared to the wetted surface area of the hull. Therefore, after “take-off” speed, the wetted surface area of the hull, and consequently the resistance of the boat, is reduced considerably. The larger the weight of the boat and crew and the higher the speeds, the greater the loads on the hydrofoils will be. The current research investigates the interaction effects between the fluid and structure of the ZP00682 NACRA 17 Z-foil. The study is carried out both experimentally, in SSPA’s cavitation tunnel, and numerically using a fully coupled viscous solver with a structural analysis tool. The experimental methodology has been used to validate the numerical tools, which in turn are used to reverse engineer the material properties and the internal stiffness of the NACRA 17 foil. The experimental flow speed has been chosen to represent realistic foiling speeds found in the NACRA 17 class, namely 5, 7, and 9 m/s. The forces and the deflection of the Z-foil are investigated, showing a maximum deflection corresponding to 24% of the immersed span. Finally, the effects of leeway and rake angles on the bending properties of the Z-foil are investigated to assess the influence of different angles in sailing strategies, showing that a differential rake set-up might be preferred in search for minimum drag.
Highlights
The NACRA 17 is a high-performance catamaran that was designed to meet the criteria required by World Sailing, the world governing body for the sport of sailing
The experimental campaign has focused on finding the correlation between the measured structural deformation and the monitored forces and moments to understand the Fluid Structure Interaction (FSI) response of the NACRA 17 Z-foil
A series of experimental and numerical results that indicate the performance of a NACRA 17 Z-Foil in different operating conditions is presented in this research
Summary
The NACRA 17 is a high-performance catamaran that was designed to meet the criteria required by World Sailing, the world governing body for the sport of sailing. Changing the rake angle of the daggerboards with a range of −3◦ to 6◦. The wind turbine industry is leading the investigation on shape-adaptive blades, as turbine performance could be increased in a wide range of operational conditions by employing passive adaptation of the blade twist. Herath et al [6] investigated the concept of Differential Stiffness Bend-Twist to control the blade deformation by developing a numerical algorithm that determines the required composite layup to achieve optimal flexure stiffness value in the blade structure. Herath et al [7] later applied the bend-twist coupling in the design of hydrofoils and tested them in a water tunnel, which showed an increase in the Lift to Drag ratio of the foils. Light weight composite structures are desirable for high performance foiling marine vessels and are almost exclusively used in hydrofoil construction
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