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Keyword : rudder
Results 1 - 5 of 27
A Case Study on the Effect of Sweep and Variations in Free-Surface Cross Section Geometry on the Lift and Drag of Transom-Hung Sailboat Rudders
Conventional transom-hung rudders are often used on small sailboats because of their simplicity compared to rudders mounted under the hull; however, they present substantial performance penalties, including (1) the rudder is more likely to ventilate by drawing air down from the free surface, (2) the effective aspect ratio, and therefore the lift-to-drag ratio, is not increased by the mirror-plane of the hull bottom and (3) there is additional spray and wavemaking resistance that arises as a result of the rudder passing through the free surface. This case study focuses on a means to mitigate the last of these penalties, the increased spray and wavemaking resistance. While many transom-hung rudders are essentially parallel, or tapered with the maximum chord at the top where it meets the tiller handle, the reader will recognize that having the largest cross section of rudder at the free surface will generate significant spray and wavemaking resistance, especially when the rudder is turned. This study investigated the use of minimizing the rudder chord length where it passes through the free surface, demonstrating the findings by full-scale towing tests of a series of rudders designed for a Fireball-class dinghy. Running the tests at full-scale, therefore matching Reynolds number and Froude number, eliminated questions on scaling. Experimentation on the effects of sweep angle, section shape and chord length at varying angles of attack and velocities showed a noticeable increase in lift-to-drag ratio of foils with reduced chord length at the free surface and by sweeping the rudder forward. To complete the case study, a velocity prediction program was used to estimate the change in speed around a notional race course.
Performance Evaluation and Ranking of 7 Rudders for the Finn Dinghy
As a follow up to the Olympic Games, 7 commercially available Finn dinghy rudders were tested to determine their hydrodynamic performance. The 7 tested rudders make up 78% of the rudders that were measured for competition at the 2016 Olympic Games, thus representing a large portion of the rudders used by sailors. The remaining two not tested are of semi-custom or custom design or manufacture. All rudders were tested in 7 different conditions, selected to cover a wide range of sailing conditions. The testing revealed considerable differences, both in performance and handling.
A Measurement System for Performance Monitoring on Small Sailing Dinghies
This paper describes a new performance
monitoring system for dinghies and small sailing boats,
developed in a collaborative project of the Yacht Research
Unit Kiel (YRUK) and the Mads Clausen Institute (MCI)
of the University of Southern Denmark. The system under
development features a complete set of nautical
instruments (wind, boat speed and heading, position) as
well as dynamic sensors measuring the motion of the
dinghy with additional audio and video streams for crew
observations. Most sensors are integrated in a small
lightweight housing also containing a main processing unit
to be mounted on a dinghy. Some external miniaturized
sensors (wind and water anemometers) are connected
wirelessly. Data and media streams are recorded. Further a
telemetry system allows online data transmission to a
remote client operated on a coach boat. Analysis software
allows the coach to visualize and analyze the performance
of the dinghy. Both, the hardware system and the analysis
software are presented here including first results from a
field trial.
Estimating a yacht’s Hull-sailplan balance and sailing performance using experimental results and VPP methods
This paper describes an approach to calculate the longitudinal position of the hydrodynamic and aerodynamic force centres on a sailing yacht, and the resulting rudder angle required to hold a steady course across a complete range of sailing conditions. The paper discusses the effect on performance, in terms of boat speed, by means of experimental tank testing to derive the hydrodynamic data; wind tunnel testing to derive the aerodynamic data; and the use of a 4 plus degree of freedom (DOF) velocity prediction program (VPP). It highlights the data required to carry out such analysis and is summarised in a worked example. The main objective of this paper is to outline a process which is achievable within a design office environment and skill set, whereby a designer can use generic data derived from experimental or CFD and amalgamate it with theoretical and regression models for individual components to ensure that the “balance” question is satisfactorily addressed at a stage in the design and development process where meaningful changes can be made to geometry.
RVPP: Sailing Yacht Performance Prediction Fully Integrated into a RANSE Based Flow Code
One of the most important tools in today's sailing yacht design is the Velocity Prediction Program (VPP). VPPs calculate boat speed from the equilibrium of aero- and hydrodynamic flow forces...