Design, Optimization and Control of a Hydrofoil System for High-Performance Marine Vessels

Problem & Motivation

Conventional displacement hulls face a fundamental speed limitation: as velocity increases, wave-making resistance grows dramatically. Hydrofoils solve this by lifting the hull clear of the water at speed, but this introduces a new challenge - maintaining stable flight above the surface requires active control of the foil angle of attack in real time.

This project addressed both the design optimization (choosing the right foil geometry for maximum lift-to-drag ratio) and the control problem (keeping the vessel stable in foilborne mode).

Foil Design & Optimization

The foil geometry was optimized for the target operating speed and vessel displacement using MATLAB and low-order flow simulation. Key design parameters included foil span, chord, section profile, and strut configuration.

Fig 2. Foil free body diagram - lift (L), drag (D), angle of attack (α), and coordinate frames

Fig 3. NACA 2415 polynomial fit error - RMSE for Cl and Cd coefficients

Hullborne Performance — Savitsky Method

Before designing the foil system, the baseline hullborne performance was characterized using the Savitsky method. This established the trim angle and resistance curves that the hydrofoil system needed to improve upon.

Fig 4. Hullborne trim angle vs speed - Savitsky method

Fig 5. Hullborne resistance vs speed - baseline for foilborne comparison

Active Ride Control with LQR

An LQR (Linear Quadratic Regulator) controller was designed for active ride control, maintaining near-zero pitch angle and a target ride height of 0.5 meters. The controller modulates the foil angle of attack in real time based on heave and pitch state feedback.

The LQR was tuned to balance ride comfort (minimizing pitch oscillations) against actuator effort (preventing excessive foil deflections that could cause ventilation or stall).

Fig 6. Surge velocity response - settles to steady-state 10 m/s (~19.4 knots)

Fig 7. Ride height response - converges to target 0.5 m with minimal overshoot

From CAD to Water

In foilborne operation at 19.4 knots, resistance dropped from 7.47 kN (hullborne) to just 812 N - an 89% reduction. The vessel maintained approximately 0° pitch angle and stable 0.5 m ride height under the LQR controller, demonstrating the viability of the combined design-and-control approach.

Fig 8. CAD model - hull with propulsion system and frame

Fig 9. First towing tank test at IIT Madras

Publication

This work was presented and published at the ASME International Conference on Ocean, Offshore and Arctic Engineering (OMAE) 2025 in Vancouver, Canada. The paper details the integrated framework for hydrofoil vessel design spanning geometry optimization, dynamics modeling, and LQR-based active ride control.

Connection to SAVTOA Internship

This academic work built upon foundations laid during my R&D internship at SAVTOA Software Technologies, where I consulted on the design of an autonomous hydrofoil catamaran. At SAVTOA, I developed predictive AoA control and optimized foil geometry that increased vessel speed by 87% and reduced drag by 35%. The preliminary design was adopted for the ongoing construction of one of India's first autonomous hydrofoil vessels.