Watt & Sea Hydrogenerator

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The principle is simple: using the speed of the boat to turn an immersed propeller and produce electricity.

An innovation: Watt&Sea has engineered a hydrogenerator with excellent output, performance, and reliability.


We are excited to be dealers of Watt&Sea Hydrogenerators for Canada and the USA – and our customers elsewhere in the world.  A green product that is very much in line with our high standard of quality and engineering, the Watt&Sea is, like the Hydrovane, of huge value to the offshore cruiser. The fit was not hard to see.

Please also visit www.wattandsea.com/en to find out how a Hydrogenerator will make your life at sea more comfortable….


We look forward to answering all your questions and will provide complete quotes for potential customers in Canada and the USA.

Please email Will for more information or for a quote. Include your boat type, a photo of the transom, average cruising speed, and location.


  1. Designed and manufactured by top racers and engineers in France
  2. High electric output and negligible drag
  3. Safety at sea… No reliance on the engine or other systems for power
  4. A source of green power
  5. No need to run the engine to charge: savings in fuel consumption
  6. Silent, for everyone’s comfort!
  7. Light
  8. Easy to install and use
  9. Maintenance free
  10. Has a sleek design and look… just like the Hydrovane!
  11. New: Watt&Sea bracket for Hydrovane owners…. Install your Watt&Sea in the perfect position – attached to the Hydrovane shaft! No extra holes in the transom, and very easy to use and remove.

HV Bracket

The Watt&Sea Hydrovane bracket… one strength testing method!

Prototype... now in development

The early prototype…. now in production! More photos coming soon!

ABOUT WATT&SEA Cruising Series

The CRUISING series hydrogenerator is a simplified variation of the RACING version. It is even lighter, more manageable, more hydrodynamic, and more corrosion resistant.

  • It is available in 2 outputs: 300 or 600 Watts, and 2 lengths: 610 or 970 mm
  • It uses “brushless” technology
  • The 12-24 Vlt regulator has an advanced electronic architecture
  • It is 2kg lighter than the RACING series, which makes lifting and removal even easier
  • It has been redesigned with optimized hydrodynamics
  • The generator housing has enhanced corrosion resistance


Power: 120W at 5 knots, depending on the model and size of the propeller (10A – 12V; 5A -24V)

Start-up speed: 2 knots

Aluminium leg: 610 or 970 mm

Cruising 300: nominal output 300 Watts (24 A in 12 Vlt) DATA SHEET

Cruising 600: nominal output 600 Watts (48 A in 12 Vlt) DATA SHEET

Includes the latest generation of 12-24 Vlt regulator, one 240 mm propeller (the 200mm and 280mm propellers are options), the bracket with its cam-cleat and one mounting kit.

Frequently Asked Questions 

Which model, leg, and propeller size is best for me?

Please email Will with your boat type, a photo of the transom, average cruising speed, and shipping location. He can provide further information, answer any questions, and send a complete quote.

Can I use the device while I run my boat main engine?

The system in not designed to replace the alternator of your engine. It can nevertheless be used while running your main engine although the output may be lower because of engine propeller turbulence.

What should I do when I’m in port?

You may either leave the device on the transom in the lifted position, or remove and store it away if you have the space. If not lifted, it is necessary to have lines that prevent the cradle and blade from backing against the transom. 

Is there a risk of damage to the batteries?

No. The regulator monitors battery voltage levels.

What happens when my batteries are fully charged?

The electronic regulator monitors battery levels and when fully charged the propeller switches to “freewheel” which diminishes the drag.

What type of batteries can it charge?

The system is compatible with any type of battery: lead (acid or gel), lithium… If you have special batteries Watt&Sea can set the output for you before shipping.

What if I hit something?

The lifting system has a release in case of impact. However, the risk of direct impact on the device is quite minimal given its position on the transom, behind the keel or centerboard, and rudder.

What speed loss is to be expected?

Watt&Sea doesn’t have any specific data on the effective drag of the device, or about the speed loss it generates. All immersion and lifting trials at constant speed have not shown any substantial difference on the speedometer. Testimonials back this up.

What power output can I expect?

The power generated increases exponentially as boat speed increases. At 5 knots, the output power is about 120W (or about 10A on a 12V battery) with the 280mm propeller. At 8 knots, the system produces 4 times more power, i.e. 480W (about 40A on a 12V battery raw). These output may differ depending on sea conditions.

To reload a 200 Ah 12V battery bank to 50% of its capacity, on average, 10 hours at 5 knots or 3 hours at 8 knots would be necessary.

Cruising 300 Output graph

Cruising 300 Output graph

Cruising 600 Output graph

Cruising 600 Output graph

Can I replace the propeller?

Yes, replacing the propeller is simple and only requires an allen wrench and an extractor screw.

How should I maintain the device?

Wash down the outside with fresh water from time to time.  The device does not require any specific maintenance.

What is the anti-corrosion treatment?

The aluminum parts are anodized, and coated with paint. They are also electrically insulated from the other metallic parts to prevent electrolytic corrosion.

How reliable is the system?

The Watt&Sea has been designed with the latest technology. All metal parts are made either in specially treated aluminum or in 316 stainless steel.

The generator housing is sealed with hi-tech ceramic-carbon gaskets. These gaskets have a lifetime of several thousands of hours and will painlessly support a circumnavigation.

The housing is filled with a lubricating oil and slightly pressured to prevent any water seepage.

In addition, the alternator is immersed in a resin that encapsulates electrical conductors. Should any dampness occur, the electric parts would not be damaged.

Overall, the system is impeccably designed and built – and is therefore highly reliable.