Rondal’s Hydro Generators enables regenerative sailing for all large sailing yachts, independent from the propulsion system. These systems are designed for efficiency, to minimize drag while maximize electrical output. With the Rondal Hydro Generator system, the diesel generators can be turned off, while the sailing speed is sustained, to enjoy the experience of sustainable sailing under sail.

   REGENERATIVE
SAILING

Regenerative sailing has been feasible for several hybrid and diesel-electric superyachts that use the propulsion propeller for both propulsion and regeneration. Rondal has developed the Hydro Generator series to provide a standalone solution for refits that do not have such a dual-purpose propeller. The Hydro Generator is an electric pod with a specially designed fixed-pitch propeller. Rondal developed the Hydro Generator in collaboration with Norwegian pod specialist SeaDrive and the research institute MARIN. The propeller was designed using optimization software, and the Hydro Generator was validated in the MARIN towing tanks.

Since the efficiency of the dedicated regeneration system is much higher compared to dual-purpose systems, it offers a simpler solution without requiring modifications to the propulsion system. The Hydro Generator features a fixed-pitch propeller with a low-drag ‘freewheeling’ mode when not in use. For a typical yacht, the additional drag from a Hydro Generator in freewheeling mode is not noticeable.

   THREE 
HYDRO GENERATORS

The Hydro Generator family has three variants: the Hydro Generator 1500 for very large yachts, the Hydro Generator 9000 Performance for large yachts with moderate cruising speeds, and the Hydro Generator 9000 High Speed for large yachts with high cruising speeds.

Hydro generator 15000

Being the largest Hydro Generator 1500 from the Rondal Hydro Generator family, it can continuously produce 15 kW of electricity. It is designed for large yachts with a cruising speed under sail between 12 and 16 knots. The propeller is designed for an extremely high efficiency at a wide speed range. The e-motor has a high capacity and therefore the pod has a slightly larger diameter. The shaft and bracket are standardized and the same for the entire Hydro Generator family. The propeller is made from bronze and has a diameter of 670 mm. The output voltage is 100 volt DC. 

Hydro generator 9000 performance

The Hydro Generator 9000 Performance is designed for sailing yachts in a range between 20 and 50 meters, with a typical sailing speed between 9 and 14 knots. The e-motor has a small diameter to reduce drag. The propeller design is optimized in the range between 11 and 13 knots and provides an unparalleled 76% efficiency, resulting in maximum output for minimal drag. The propeller is made from bronze and has a diameter of 670 mm. 

Hydro Generator 9000 high speed

The Hydro Generator 9000 High Speed is designed for sailing yachts in a range between 20 and 50 meters, with a typical sailing speed between 9 and 16 knots. The pod is the same as the Hydro Generator 9000 Performance, but the propeller is different. The propeller is designed for a higher speed compared to the Hydro Generator 9000 Performance, which makes it suitable for yachts with a (very) high sailing speed, including multihulls. The propeller is made from glass reinforced Nylon, which makes the Hydro Generator 9000 HS more economical. 

  DESIGNED
FOR EFFICIENCY

Operational data from yachts that are using regeneration shows that the feature is used the most when the drag is low. Therefore, the Rondal Hydrogenerator is designed for the highest efficiency. This includes the use of the right e-motor and gearbox, but the highest gain is made with the propeller design at MARIN. The dedicated propeller design by MARIN has led to an unparalleled efficiency of 0.73 to 0.76 (depending on the model). The regeneration efficiency is depending on the propeller power, the speed and the drag of the total unit.

   LOW DRAG
DURING REGENERATION

The data models of MARIN are validated by measurements in one of the towing tanks of MARIN. These measurements showed that the propeller performed according to the calculations. The tank tests even showed a lower drag than calculated.

  LOW DRAG
DURING FREEWHEELING

When not in use, the propeller is freewheeling to reduce the drag. Since there is no propulsion requirement, the shape and pitch of the propeller is very different compared to a normal propeller. This leads to a much lower drag during freewheeling and therefore it is not necessary to create additional complexity by folding of feathering the propeller. The freewheeling drag at 10 knots is between 0.22 and 0.25 kN, for which the speed loss is not noticeable on a typical yacht.