Performance Prediction, Dynamic Simulation, and Foil Design
Competing in the IMOCA class presents unique challenges stemming from the stringent rules governing the design and performance of these offshore racing yachts. Key challenges include:
Absence of Rudder Elevators: Without rear lifting surfaces, stabilizing the boat in pitch becomes exceptionally challenging.
Eight Cubic Meter Rule: The product of the lateral center of effort position and the area of the projected surface of the foil is restricted to 8m³ for heels between 0 and 25 degrees. Adhering to this rule significantly limits foil power, necessitating a delicate balance between righting moment, stability, and ventilation.
No Servo-Tab or Flaps: As the sailor operates solo, adjustments to foil loading at high frequencies for stability enhancement are not feasible.
Global Circumnavigation Challenges: Considering the yacht’s global navigation, tackling varying sea states is a tough task. The goal is not merely achieving high peak speeds but maintaining elevated averages for extended durations. Foil stability gains prove pivotal in keeping the hull (the primary drag component) out of the water for more extended periods.
In this context, I had the privilege of being involved in the Charal 2 project nearly from its inception, allowing me to confront and address these challenges.
In the initial phase of the Charal 2 project in 2021, my primary focus was on dynamic simulation utilizing Gomboc. The challenge was to establish a robust workflow for the dynamic comparison of various appendages and configuration candidates.
Specialized tools were developed to automate different aspects of the Gomboc workflow, covering simulations, foil integration, and post-processing. This automation significantly boosted the efficiency of the process. Additionally, a dynamic optimization tool was developed to ensure that each configuration was evaluated under its optimal conditions, providing valuable insights for decision-making.
During the second phase, collaborating closely with Martin Fischer and Mathieu Durand, we aimed to refine the foils based on the insights from a year of sailing with the initial design. The emphasis was on addressing the challenges and limitations observed in the first version.
One enhancement in this phase was the development of a tool that could rapidly analyze foil derivatives (pitch, heel, and heave). This tool provided insights into the stability of various foil candidates, aiding in the iterative design process.
This phase involved an extensive testing process with nearly hundreds of foil variations, focusing on parameters like rondure shape, chord distribution, twist, and sections. The objective was to optimize performance and stability, particularly rectifying the V1’s tendency to pose difficulties for sailors in specific conditions.