When boats are offshore they need to generate their own power to run their weather instruments, navigation computers, the autopilot, water ballast and any other electronically driven systems. Traditionally this is done by using diesel fuel to generate power off the vessel’s engine. A hydrogenerator allows the Team to charge the batteries by using the movement of the boat through the water.
For a 25-day race the Team would need a gallon of fuel per day; so by using a hydrogenerator Hannah and Rob will be able to reduce fuel consumption by 25 gallons. 25 gallons of fuel is equal to about 200 pounds or 90kg. By not carrying that extra weight it will make the boat lighter and a little faster. It will also save time and physical exertion when Hannah & Rob need to move 'the stack' from side to side when tacking.
The hydrogenerator puts out about 25 amps of electricity at 10 knots of boat speed. Hannah and Rob's systems will draw about 8 amps with the autopilot on and all communication and navigational systems running. When needed the ballast pump will draw an additional 10 amps, but only for a 10 minute period to fill and drain the tanks.
In comparison to running the engine Hannah and Rob will need to run the hydrogenerator about twice as much as they would the engine, but that will equate to about 4 hours of run time per day.
Lastly, having a hydrogenerator in addition to the engine creates a redundant system for power generation in case something breaks.