Advances in the Alba Series of Hybrid Underwater Gliders for Long-Term Ocean Operations

Autonomous underwater gliders have become a key technology in long-term ocean monitoring due to their low power consumption and high endurance. These vehicles, typically propelled by buoyancy variations, can cover thousands of miles over weeks or months at sea. However, their main limitation lies in their low cruising speed—usually around 0.2-0.3 m/s—which restricts their ability to respond quickly to dynamic environmental conditions. Navigation in strong currents, rapid vertical profiling, and precise maneuvering in complex underwater terrain are often beyond the capabilities of conventional buoyancy-driven gliders. To address these challenges, this work presents the advances from the first operative version of the Alba series [1], a hybrid underwater glider with three independent propulsion systems. These systems are based in an oil-based buoyancy engine complemented with a compressed gas module for rapid depth changes, and a pair of electric propellers for active thrust. This configuration allows the vehicle to switch between passive gliding and active propulsion depending on mission needs and environmental conditions. The oil-buoyancy pump system enables long-range energy-efficient navigation. The compressed gas-based system adds vertical mobility during fast transitions by increasing the total buoyancy force in case of the presence of water column high energetic condition. Meanwhile, the electric propellers offer enhanced yaw control, and extra thrust in the previous conditions and the fine maneuverability, and the ability to navigate confined or turbulent areas. By combining these three systems, the Alba22 glider improves overall responsiveness, flexibility, and adaptability, offering a promising platform for a new generation of smart, autonomous oceanographic vehicles. This hybrid architecture imposes significant design changes over conventional gliders, which are also addressed in this work to inform future development of multi-modal underwater propulsion systems.