Watt&Sea Cruising 300 Hydrogenerator – 300W, Short 610mm Leg (for Boats up to ~35ft)

The Watt&Sea Cruising 300 (610mm) hydrogenerator gives sailors the opportunity for energy independence under sail. It converts the kinetic energy of your moving sailboat into electricity, allowing you to continuously charge your batteries while underway. With a maximum output of 300W, this model is optimized for yachts up to around 35 feet (10–11 meters) – a size range where onboard power consumption (lighting, navigation instruments, autopilot, refrigerator, etc.) typically averages about 5–10 amps. The Cruising 300 can significantly reduce or even eliminate the need to run your engine for charging during long passages, meaning quieter nights at anchor and lower fuel usage.

The short mast/leg version of 610mm is designed for optimal performance when mounted on lower transoms or swim platforms closer to the waterline. The shorter length means that even in moderate waves the propeller stays well submerged, maintaining the generator’s efficiency. This makes the model particularly well-suited for boats with a relatively low stern or open transom configuration (for example, boats with drop-down platforms or low cockpits). For vessels with a taller stern or higher mounting point, Watt&Sea also offers the Cruising 300 in a long mast 970mm version, which provides deeper prop immersion. Both versions use the same generator and have identical power output – the difference is the length of the support leg to accommodate different boat designs.

The hydrogenerator begins producing charge at very low speeds (~3 knots), and by around 5 knots it yields roughly 8 amps of charging current (approximately 100W at 12V) when equipped with the standard 240mm diameter three-blade propeller. As speed increases above 6 knots, the output rises substantially, approaching the 300W maximum around 8–10 knots (depending on propeller and conditions). Despite this strong generation, the device’s streamlined design and efficient propeller mean drag in the water is minimal – typically the speed reduction is less than 0.1 knot, which is almost imperceptible to the crew.

• Off-grid power while sailing: With the Watt&Sea Cruising 300, your boat can meet its electrical needs while under sail. This means your electronics, lights, refrigeration, and other onboard systems can keep running without requiring a diesel generator or engine alternator. For long voyages, ocean crossings, or extended cruising, this hydrogenerator provides peace of mind that your batteries are continuously being charged by renewable energy.
• Intelligent charging system: The included converter/regulator is the “brain” of the system – it automatically adjusts the charging profile to protect your batteries from overcharge and to provide optimal current. The unit is compatible with both 12V and 24V electrical systems, auto-detecting the voltage. A great convenience is the built-in Bluetooth connectivity – through a mobile app you can monitor real-time power production, battery voltage, and even tweak settings (for example, output voltage for lithium battery banks). The converter also features an input for a solar panel (7.5–50V, up to 14A), allowing you to integrate a solar panel for combined charging (wind + solar) and maximum energy harvest.
• Easy installation & use: Installing the hydrogenerator is straightforward – the kit comes with all necessary components: the hydrogenerator with a transom mounting bracket, a cam-cleat locking system with a securing pin, low-friction ring and line for lifting, cabling with connectors, and instructions. The transom bracket mounts securely on the stern (it’s recommended to offset it slightly from the rudder axis to avoid turbulence), and the hydrogenerator unit can be attached and removed quickly thanks to the cam-cleat mechanism. When not in use (for instance, in harbor or when motoring at high speed), the unit can be easily pivoted up out of the water and secured in a raised position.
• Lightweight, sturdy construction: The Cruising 300 is built with an anodized aluminum body and marine-grade composite materials. The system’s weight (generator + converter) is low – around 6–7 kg – which makes installation and handling easy. The device is engineered to withstand continuous loads in the marine environment – all moving parts are sealed or use low-friction bearings, and the propeller is designed with a shear feature or slip clutch to avoid damage if striking floating debris. Maintenance is minimal (a service is recommended every 2 years or ~10,000 NM to inspect and lubricate).
• Proven in real-world cruising: Watt&Sea is a pioneer in marine hydrogenerators, used by sailors worldwide including participants in transatlantic races and round-the-world voyages. The Cruising 300 model is favored by many cruising yacht owners because it offers an excellent balance of size, weight, and performance. It allows you to enjoy the silence of sailing while knowing your batteries are being topped up by the power of your movement through water – a true wind-and-water synergy that enhances the cruising experience.