Rudder Design for Ocean-Going Sailboats: Structure, Hydrodynamics, and Buildability

In the naval architecture of an ocean-going cruising sailboat, the design of the steering system —particularly the rudders— is a critical stage. It must not only ensure strength and reliability under demanding conditions, but also guarantee buildability and precise performance over thousands of nautical miles.

Design Process: From Concept to Execution

For this project, the sailboat was equipped with twin rudders — a decision based on its wide stern and the need to maximize control when heeled. The rudders were fully designed in marine-grade aluminum 5083, using 3D modeling from the outset to precisely integrate the blade, stock, skeg, and mounting points. Various foil shapes based on NACA profiles were analyzed to ensure efficient hydrodynamic behavior, minimizing drag while maximizing control.

Rudder Stock: Load Transmission and Strength

Each rudder stock was sized specifically to withstand the loads generated by hydrodynamic forces and the steering system, taking into account lever arm length, bearing support points, and torsional stresses. High-strength aluminum was used, and the geometry was optimized for both manufacturing and integration with bearings and seals.

Blade and Skeg: Protection, Stiffness, and Efficiency

The rudder blades were fabricated from welded 5083 aluminum and internally reinforced solely with ribs — no stringers were used — all precisely waterjet-cut to ensure consistency and accurate assembly. Each blade was paired with a structural skeg welded to the hull, which not only protects the rudder's leading edge from impact but also provides additional support and structural continuity between the hull and rudder.

Steering Compensation

The rudder blades were designed with 15% of their total surface area positioned forward of the pivot axis (semi-balanced rudder), significantly reducing the load on the steering system. This translates into increased responsiveness and less effort transmitted to the steering wheel. In this case, the sailboat is not equipped with a tiller, but with a single large-diameter wheel, offering precise and ergonomic control even under heavy conditions. The compensation was carefully calculated to maintain directional stability and prevent oscillations.

Buildability: Design with the Workshop in Mind

From the beginning, the rudder system was conceived to be efficiently built at the yard. Complex double-curvature surfaces were avoided, all flat parts were optimized for CNC waterjet cutting, and weld joints were designed for easy access and proper fusion. The assembly sequence, welding strategy, and dimensional control were all planned in detail to ensure structural accuracy and build quality.

This project is a clear example of how the integration of design, calculation, and hands-on construction experience leads to critical components that combine performance, safety, and manufacturing feasibility for serious offshore sailing.