Theory of Sailing Applied to Ocean Racing Yachts

A systems analysis approach is used to study the performances of ocean racing yachts, and to support a rating system which considers wind conditions and course angles. Basic aerodynamic and fluid-dynamic theory is applied to derive an engineering mathematical simulation of a boat's performance. The result is a set of five equations in five unknowns. Given the true wind velocity and course sailed, the equations are solved for boat speed, apparent wind speed, apparent wind angle, leeway angle, and heeling angle. The theory is compared with full-scale towing tests and sailing measurements for several yachts, ranging from a 23-ft cruiser to a 68-ft (12-meter) racer. The theoretical results fall within the measurement accuracies for all course angles and wind conditions. Yacht performance curves are then compared for the detailed effects of windward capabilities and rig variations for various true wind speeds. A "rating matrix" approach is discussed, which could be used to rate fairly a wider range of yacht sizes, types, wind conditions, and course angles than present rating systems can accommodate.