The standard Sunfish rudder is a simple design with high sweep and a relatively flat cross-section. It creates more drag than the standard daggerboard despite having 40% less area. With the daggerboard retracted, it produces most of the underwater parasite drag. Its high sweep reduces maximum side force while increasing drag at higher angles.
Combining the most advanced flow prediction methods with 40 years of experience in wing design, AeroSouth has developed a new rudder that significantly reduces drag and fits existing rudder cheek hardware for quick retrofits. The board's hydrofoils and planform have been custom-designed for sailing craft at typical speeds.
CL/CD (ratio of lift to drag) versus angle of attack for the new AeroSouth Sabre rudder (red) and the standard Sunfish rudder design (blue). The Sabre rudder has has a 60% higher maximum CL/CD, meaning significantly lower drag for the same side force. Lower sweep and a modern hydrofoil shape result in better performance when maneuvering.
The first prototype is now in test (December 2019). Tests will be concluded by the end of 2019.
Production rudders are made from a laminate of Sapele wood, a widely-available species of mahogany. Surfaces are accurately shaped using modern CNC milling equipment and then sealed with epoxy coatings for near-impervious protection from water and UV radiation.
Watch here for progress reports!
Figure 168 in the classic reference for sailboat design, 'Sailing Theory and Practice' by C.A.Marchaj, shows what a difference of only one degree lower drift angle makes - 106 feet when sailing close-hauled over a course of only one mile length. Drift angle is directly related to the ratio of lift to drag for the daggerboard and rudder. Marchaj further states: "Over a typical triangular regatta course 10 miles long, some half of it the windward leg, the gap between the two yachts will be over 500 feet."