The standard Sunfish daggerboard is a good design for its vintage, especially considering the severe limitation of making it fit in a narrow trunk. Its vertical leading edge is prone to collecting weeds. The planform results in less than optimal lift (side force) distribution. The fiberglass construction is strong and smooth, but also brittle. It was a major improvement though over earlier boards!
Combining the most advanced flow prediction methods with 40 years of experience in wing design, AeroSouth has developed a new daggerboard that reduces drag and improves maneuvering. The board's hydrofoils and planform have been custom-designed for sailing craft at typical speeds. Nearly a hundred variants were studied before our final Sabre design was selected.
CL/CD (ratio of lift to drag) versus angle of attack for the new AeroSouth dagger board (red) and the standard Sunfish board (blue). Our new design has a 25% higher maximum CL/CD, meaning lower drag for the same side force. Drag is lowered by up to 40% at higher angles of attack. The smooth, curved leading results in softer 'stall' at higher angles of attack, reducing deceleration during maneuvers. It is less likely to collect weeds than the vertical leading edge of the standard daggerboard.
The first prototype is now in test (December 2019). Tests will be concluded by the end of 2019.
Production boards 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."