SeaBubbles, a French startup vowing to build flying river taxis, is seeking to close a third round of funding in less than a year and cement interest from the city of Paris, companies in the San Francisco Bay and other potential customers. To build the first battery-powered bubble-shaped ships that hover a few inches above the water and transport as many as six people at a time, founders Alain Thebault and Anders Bringdal last month raised 3.45 million euros from French insurer Maif and venture-capital fund Partech Ventures.