Uber, the fast-growing ride-sharing service, is taking to the water. Now, with the UberBOAT app, you can call your own boat to carry you around Croatia’s major tourist islands. The company says that several hundred people have used the service since it was started six weeks ago. If UberBOAT is successful in Croatia, it could move to Greece, Spain and the Caribbean. In the Croatia version, users can choose a one-way trip or an “adventure,” where you get to choose your own route. UberBOAT has about 60 boats there, and the company’s goal is to meet customers within 15 minutes…