By David Hull • Lennaert van den Berg

In recent years, the untapped potential of USVs as a transformational capability for marine data acquisition has been well-studied and documented as an alternative to traditionally crewed survey platforms. At the forefront of this evolution is HydroSurv, a U.K.-based pioneer in the design and deployment of industrialized, turnkey USV solutions for inland, nearshore, and coastal environments. Since its founding in 2019, the company has delivered more than 90 successful projects, deploying 25 USVs globally across a wide spectrum of hydrographic, geophysical and oceanographic applications.

HydroSurv’s portfolio is anchored by the rapid environmental assessment vessel (REAV) series, based on an agile platform concept engineered to deploy quickly in environments with limited infrastructure, or in remote locations, often where data are otherwise inaccessible or unreliable. These values underpin HydroSurv’s broader vision to democratize ocean data by making non-invasive, efficient and cost-effective autonomous systems accessible across the supply chain.

A Third-Generation Milestone: REAV-47

HydroSurv’s mission to make autonomous systems accessible relies on technology that is industrialized, trusted, available and field-proven. The company’s latest REAV-47 platform represents the newest step in optimizing performance, endurance and efficiency.

Purpose-built for nearshore, multi-day coastal surveys, REAV-47 combines Mastervolt energy systems with a new electric propulsion system developed by the innovative Dutch company Rim Drive Technology. This milestone marks the first integration of a rim-driven thruster onto a HydroSurv platform.

The first-of-class vessel, named “USV Bris,” was delivered to Nordic USV AS of Bergen in early 2025. It is the first of three REAV-47s to be supplied to Nordic USV this year, supporting the company’s mission to deploy low-emission uncrewed survey capabilities in Northern Europe.

In parallel, HydroSurv is delivering a REAV-47 order from a key customer in Nigeria, scheduled for handover June 2025.

A Choice of Electric and Hybrid Powertrains

The REAV-47 is available in two variants: a fully electric, 24-kWh battery configuration and a 12-kWh battery-hybrid configuration designed for extended operation in remote locations. In its hybrid form, the vessel is powered by two 6-kWh Mastervolt lithium-ion (MLI Ultra) batteries and a highly efficient 4-kW, 24-V DC generator from Fischer Panda, which consumes less than a liter of fuel per hour under normal operating conditions. HydroSurv has relied on Mastervolt battery technology since the introduction of the REAV-60 in 2022, and the REAV-47 is the first to implement the system in a higher 48-V configuration, offering improved energy density and reduced cable losses.

The powertrain delivers an operational endurance of 72 hr. while reducing CO2 emissions by more than 97 percent compared with small diesel workboats used for similar missions. This underscores the environmental value of hybrid electric USV systems, even where they utilize conventional fuels.

However, where mission frequency is a more important consideration than endurance, the REAV-47 may be optimally installed with an automated mooring and charging system that will recover and recharge the vessel for a hand-off operation. An evaluation unit is installed on USV Bris, and a second unit will be extensively tested by HydroSurv this summer. Afterward, the technology will be available on all third-generation REAV platforms.

Virtual Watchkeeper for Remote Operations

At the heart of the REAV-47 lies HydroSurv’s proprietary Virtual Watchkeeper vessel control system, a patent-applied PLC-based control and monitoring suite that manages propulsion and power systems and controls the vessel’s onboard systems. Designed with fault tolerance and safety in mind, the system integrates redundant power supplies, backup uninterruptible power supply and multi-channel overcurrent protection, providing the resilience customers expect from industrialized USV platforms deployed to remote work sites.

The propulsion system of Rim Drive Technology is integrated with an updated firmware build of the Dynautics SPECTRE autopilot HydroSurv has been using since 2019, allowing for precise maneuvering and dynamic positioning.

Electric Propulsion

Rim Drive Technology develops, manufactures, and sells rim drive motors from 0.5 to 75 kW for private, commercial, industrial, and underwater applications. In order to guarantee and monitor the quality of their products, Rim Drive Technology’s production, R&D and office are located in the Netherlands. The motors are 100 percent electric and can be used as either main propulsion or secondary drives. In addition to motors, Rim Drive Technology provides a wide range of customizable complementary products, including batteries, monitors, throttle controls, motor controllers and cables.

Rim Drive Technology’s electric motors are designed to excel in the most demanding environments. Whether navigating through polluted waters or areas with heavy sediment and sand, these motors deliver outstanding reliability and efficiency. Thanks to the unique design, featuring no center shaft, there is minimal risk of entanglement from ropes, nets, or debris, making them an ideal solution for autonomous surface vessels and other critical applications.

Compact and lightweight, the motors easily fit into even the smallest installations, while also reducing drag to enhance efficiency and speed. At the same time, full system access through the motor controller gives users immediate insight into all essential motor and battery data, simplifying integration. Wireless, CAN-based control adds another layer of flexibility, eliminating the need for physical connections while ensuring smooth performance.

Maintenance is often a major cost driver in marine operations, but not with Rim Drive motors. With only one rotating part, the simplified mechanism drastically reduces wear and tear. The result is lower maintenance needs and reduced operational costs.

Rim Drive Technology also offers direct, high-quality service. By partnering with the company, HydroSurv gains from short communication lines, expert support, and quick access to updates and spare parts, ensuring reliable performance.

 

 

Propulsion Range

Rim Drive Technology offers a wide range of propulsion options, providing efficient and reliable solutions for various vessel types and applications. For main propulsion, we provide fixed PODs, steerable PODs and outboard options.

The Rim Drive pod features a minimalist design with only one rotating part, requiring straightforward maintenance and delivering over 90 percent efficiency at medium speeds, ideal for cruise operations. The fixed pod is available from 0.5 to 75 kW and is fully waterproof (IP68). The steerable pod configurations include an entry-level option as a cost-effective solution that integrates easily with existing systems, available from 2.5 to 15 kW. Another option is the steerable pod available from 2.5 to 75 kW, with 320° rotation for superior maneuverability. It can be controlled by joystick, steering wheel or CAN interface.

For outboards, the steerable outboard offers 320° rotation and 360° propulsion, with remote adjustment capabilities. It’s mountable on the transom or a tilt-and-trim bracket and is available in 11 and 15 kW. The entry-level outboard, available from 2.5 to 15 kW, provides affordable propulsion with a manual tilt-and-trim bracket. This outboard is compatible with all standard steering cylinders, perfect for easy refitting.

For secondary propulsion, the company also offers a range of bow and stern thrusters, available from 0.5 to 75 kW. The bow thruster box makes it easy to access the motor because installation of the lid of the box is above the waterline, eliminating the need to take the boat out of the water. The thruster tunnel set is designed for difficult conditions, where the bow thruster remains protected.

Driving Innovation, Together

The REAV-47 is equipped with two entry-level Outboard 5.0 propulsion systems. The motor controller is separate from the outboard and can be installed inside the hull, allowing for an IP68-rated system without the need for additional sealings or oils.

The entry-level Outboard 5.0 is a compact and efficient solution designed for straightforward integration. Operating at a nominal voltage of 48 V with a current draw of 104 A, it delivers a static thrust of 60 kg. The unit weighs just 23 kg and features a propeller diameter of 133 mm and a total length of 967 mm. With the two Outboard 5.0 units, REAV-47 achieves a cruising speed of 4.1 kt. and a maximum speed of 6.5 kt., operating at a combined power output of 10 kW.

Rim Drive Technology’s electric motors are a natural fit for HydroSurv, not just technically but strategically. Both companies are ambitious and committed to continuous innovation in the field of autonomous marine technology. As HydroSurv expands its fleet with versatile platforms such as the REAV-47, Rim Drive Technology’s range of compact, scalable motors supports that growth with propulsion solutions tailored to vessels of all sizes.

The company’s fully waterproof, shaftless rim drive systems reduce drag, require minimal maintenance, and provide real-time access to motor and battery data; a necessity for remote nearshore survey. Combined with Rim Drive Technology’s global service partner network, this ensures that HydroSurv can support its USV customers efficiently and reliably around the world. It’s a strategic alignment rooted in shared vision, technical compatibility, and a commitment to shaping the future of marine autonomy.

 

A Scalable USV Platform

Looking ahead, HydroSurv is extending the benefits of the Rim Drive propulsion system into its upcoming REAV-25. Based on the popular REAV-28 platform, the REAV-25 has been reiterated to comply with U.K. Maritime Guidance Note 702, offering a 24-V version of the Rim Drive Technology configuration for day-works-capable USVs, with a focus on evolving regulatory and safety standards for small maritime autonomous surface ships.

As demand grows for clean, compact, and versatile survey platforms that can be delivered quickly and generate a rapid return on investment for their users, HydroSurv sees strong market traction for its third-generation USVs from a diverse pool of customers seeking to lower operational carbon emissions while increasing data availability.

HydroSurv’s latest collaboration with Rim Drive Technology demonstrates the power of engineering partnerships in realizing the promise of industrialized, forward-looking robotic solutions for the marine sector’s toughest challenges.

 

David Hull is the founder and CEO of HydroSurv.

 

 

 

Lennaert van den Berg leads international sales at Rim Drive Technology.