The thing with inventions like this is that there are every few places in the world where things are constant. A strong flowing river that flows year round or a strong wind that always blows. In the places where they exist, people take advantage of them. In windy areas you see windmills and turbines. <br><br>In the rest of the world we have seasons. Rivers freeze for half the year or wind blows in any direction at different speeds or not at all. Humans are good at adapting to the environment they are in, but put them in a different one and it takes a while to figure out how to adapt.,(reply>), You don’t need a river with a constant water level or speed for such ferries to work. Even in temperatures well below 0°C rivers rarely freeze.,(reply>), Welcome to the largest issue of renewable resources.