Many cities around the world see clean and efficient public transport as a crucial way to lower their carbon emissions. For cities with waterways, a high-tech ferry in Sweden could soon set a new standard. Speeding through Stockholm’s archipelago, electric boat maker Candela’s new P-12 vessel barely makes a sound as it flies 3 feet above the water. Its developers hope the boat, which was unveiled this week, will yield a new era of waterborne public transport.