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.

This paper compares performance predictions from a Reynolds Averaged Navier Stokes (RANS) based Velocity Prediction Program (VPP) to on the water testing of a J70. The J70 has been outfitted with a system to determine sail flying shapes, apparent wind conditions and performance data. The on the water testing is conducted in both racing and controlled sailing conditions. Data taken during racing conditions is analyzed to determine optimal performance envelopes while data taken in controlled conditions is used to match exact sailing and VPP states. The data acquisition system combines a number of standard marine sensors including a sonic anemometer, a GPS, a digital compass, an accelerometer and a gyroscope with custom sensors that measure rudder and boom angles as well as a custom sail shape acquisition system. The RANS based VPP developed by Doyle CFD has three main components; an aerodynamic force model, a hydrodynamic force model and an algorithm to balance the forces. The force balance routine uses four degrees of freedom; boat speed, yaw, heel and rudder angle to balance the aerodynamic and hydrodynamic forces for a given true wind speed and angle. The force models are derived from RANS CFD data calculated using OpenFOAM. The aerodynamic forces are calculated using steady state RANS as a function of apparent wind angle, apparent wind speed and sail flying shape. The VPP force model is derived by fitting response surfaces to this data. The aerodynamic CFD is run with sail flying shapes recorded from on the water testing. Using accurate flying shapes is critical for picking out slight aerodynamic differences in sail and rig setup. The hydrodynamic CFD data points are calculated using RANS Volume of Fluid CFD (VOF) as a function of boat speed, rudder angle, yaw angle, heel angle and displacement. Response surfaces are generated from a 128 data point array of RANS VOF simulations.

The time-varying influence of a sailor’s position is typically neglected in dinghy velocity prediction programs (VPPs). When applied to the assessment of dinghy race performance, the position and motions of the crew become significant but are practically hard to measure as they interact with the motions of the sailboat. As an initial stage in developing a time accurate dinghy VPP this work develops an on-water system capably of measuring the applied hiking moment due to the sailor’s pose and compares this with the resultant dinghy motion. The sailor’s kinematics are captured using a network of inertial motion sensors (IMS) synchronised to a video camera and dinghy motion sensor. The hiking moment is analysed using a ‘stick man’ body representation with the mass and inertial terms associated with the main body segments appropriately scaled for the representative sailor. The accuracy of the pose captured is validated using laboratory based pose measurements. The completed work will provide a platform to model how sailor generated forces interact with the sailboat to affect boat speed. This will be used alongside realistic modelling of the wind and wave loadings to extend an existing time-domain dynamic velocity prediction program (DVPP). The results are demonstrated using a single handed Laser and demonstrate an acceptable level of accuracy.