Velocity prediction programs (VPPs) are valuable design tools that allow designers to parametrically study yacht performance. The three main components of a VPP are an aerodynamic force model, a hydrodynamic force model and an algorithm to balance the forces. VPP force models can be derived from many sources such as model testing, empirical or analytic formulations, computational fluid dynamics (CFD) or often a combination of these. This paper describes an approach to VPP force modeling based on Reynolds Averaged Navier Stokes (RANS) CFD. RANS CFD captures turbulent flow effects important for sailing such as separation, viscous drag and wakes. The aerodynamic forces are calculated using steady state RANS and the hydrodynamic forces are calculated using free surface RANS Volume of Fluid (VOF) with OpenFOAM. VOF simulations are computationally expensive and many data points are needed for the VPP force models. A cost effective approach to running VOF simulations using OpenFOAM and cloud computing is described. This approach allows the method to be used on a wide range of projects and not only those with large R&D budgets such as the America’s Cup and Volvo campaigns. The force models are derived by direct interpolation of CFD data using both structured and unstructured data point sampling. As a test case the method is applied to analyze three keel options for a 125’mega-yacht as well as make comparisons to flat water sailing performance. Modelling turbulent flow effects is especially important for mega-yachts because they have many drag producing design features.

There are many uncertainties in the interpretation of full-scale sailing vessel data taken under dynamic conditions, and even more uncertainties when forensic analysis is attempted based only on survivor’s recollections. Frequently, the analysis is based on static equilibrium assumptions, sometimes modified to steady-state motions of the wind and heeling response of the vessel. Dynamic conditions are generally non-deterministic and statistical methods must be used. Even more complicated is the non-stationary random process nature of most accidents. In the wind-heel research carried out on Pride II, it has been shown that wave action frequently adds uncertainty to the correct attribution of contributions to establishing the cause of the resulting heeling action. The best data are found in steady 10 to 20 knot wind strengths in minimum waves found in the lee of a shoreline. This criteria can be interpreted as minimizing the uncertainties in characterizing the wind-heel performance of a given sail combination at normal angles of heel...

For the useful prediction of the performance of a sailing yacht using a generic Velocity Prediction Program (VPP) an accurate assessment of the hydrodynamic and aerodynamic forces and moments involved is essential...