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www.sname.org/sname/mt April 2013 design purposes, but unless the force coe cients have been derived from extensive model testing on the exact yacht geom- etry, many simplifying assumptions must be made about how the aerodynamic forces are applied to the rig and how the rig reacts to those forces. is leads to designers needing to build in high safety factors to account for the uncertainties in the details of the loads. Today yacht and sail design o ces are starting to use high- resolution computational uid dynamics and nite element models to accurately model the aerodynamic forces created by the sails and the resulting structural loads in the sails and rigs. Computer technology and simulation codes have now progressed to a point where it is practical for yacht and sail designers to create detailed coupled RANS CFD-FEA models for new and existing sailing yacht projects in order to predict loads. e detailed nature of coupled RANS CFD-FEA simulations makes it possible to incorporate all of the relevant geometry and physics involved in sailing yacht load analysis, reducing much of the uncertainty in the load analysis. To save weight and money, nal structural designs often are optimized using coupled CFD-FEA simulations in order to opti- mize both the weight and the cost of structural components. As an example, a recent project we worked used a detailed para- metric model of a sail furling mandrel to decide whether or not to add another $100,000 of carbon ber into the mandrel or not. Using a standard force coe cient analysis led to the mandrel being 1.5 times heavier than the detail computational analysis showed that it needed to be. is procedure can be applied to all the major structural components of the rig such as the mast, deck hardware, and rigging. e optimized structural designs can be safe and millions of dollars cheaper than what would be possible to design with lower-resolution force estimates. Coupled simulations Coupled RANS CFD-FEA models are set up using a base geome- try that de nes the geometry for both the CFD and FEA models. Surfaces pressures and shear forces are solved for in the CFD model and transferred to the FEA model across the models sur- faces. In this way, the details of the uid ow geometry and the mechanics of the structural components interaction can be accurately modeled. Turbulent ow is present everywhere in sailing simulations, so it is important to use RANS CFD in order to capture important turbulent ow phenomena like ow separation and viscous wake e ects. Structural non-linearity is also present in most sailing simulations and thus nonlinear FEA must be used. e analysis codes have been capable of analyzing large yachts using these techniques for some time; however, these simulations are computationally expensive and only recently have powerful parallel processing workstations and clusters come along at prices affordable to design offices. To prop- erly resolve the mesh for a RANS simulation of a 60 m sloop Leading the way for multi-mast yachts is the 141 m schooner Dream Symphony , due to launch in 2016. The progression of sailing yacht sizes. From left to right: a 38 m 1930s-era J-Class yacht; the 75 m Mirabella V ; the 88 m Maltese Falcon ; a 101 m super sloop; and the 141 m Dream Symphony .