Like electric cars, electric boats are not a new idea. In the early 1900s Clara Ford preferred driving her electric car around Detroit instead of one of the noisy gasoline-powered Model Ts her husband Henry had begun making. Around the same time, posh electric launches cruised silently along the River Thames in Britain, using dockside stop-offs to top up their batteries with electricity and their bars with champagne. These days, thanks to worries about climate change, electric cars are making a comeback (in eco-minded Norway, they account for more than half of new cars sold). Now electric boats are following. A number of manufacturers are vying to become the marine equivalent of Tesla, the Californian company which builds some of the most fashionable and fastest electric cars.