Aero- and Hydrodynamic Performance Analysis of a Speed Kiteboarder

Abstract

Motivation: Speed sailing can be seen as the ultimate challenge for a sailing craft. Kiteboarders have recently shown to be capable of extremely high sailing speeds using a relatively cheap and simple combination of a kite and a board. They proved to be the world’s fastest sailing crafts during a record attempt in October 2008, in September 2009 the record was broken again by a large hydrofoil trimaran. Only little is known about the performance characteristics of a kiteboarder. Research is required to investigate the possibilities to further increase the sailing speed and reach the maximum speed potential of a kiteboarder. Problem statement: This thesis aims to obtain a general understanding of what properties are of importance to obtain a high kiteboarding velocity and to understand how each component contributes to the finally obtained velocity. Approach: A kiteboarder can be seen as a sailing system. It is first explained how to calculate the sailing velocity when wind velocity and both the aerodynamic and hydrodynamic efficiency is known. The kiteboarder is divided into four components; the board, the rider, the lines and the kite. Each component is separately analyzed. The aerodynamic forces on the rider and the lines are estimated using available theory. A special effort is made to investigate the kite’s lift and drag coefficients. A new kite testing method is proposed. The test is based on steering the kite in a horizontal path from one side to the other while constantly monitoring kite velocity, line tension and wind velocity. The hydrodynamic properties of the board are analyzed using available empirical results and by analyzing measured data from a kiteboarding session. Two steady state models are built to combine all the obtained knowledge. In the first model the sailing velocity is one of the input parameters. This model serves to provide an overview of all forces involved in a realistic sailing situation. Variations of wind velocity over height are taken into account. Two cases are described and worked out to obtain an overview of the drag distribution over the kiteboarder. The second model serves to predict the improvement in velocity after improving one of the components and is used to optimize line length and sailing direction. Results: It is found that during record sailing conditions 20 to 21 percent of the total drag is created by the kite, 13 to 18 percent by the rider, 3 to 6 percent by the lines and 56 to 63 percent by the interaction of the board with the water. Research focused on the board could thus lead to a large velocity increment. It is also found that optimizing line length and sailing direction could result in substantial velocity increments.