Grand Ages: Medieval

To build a ship you need a shipyard/dock and to gain access to a dock, you need to spend a development point on it in the military tab. If you spend the development point on the shipyard/dock update then you can upgrade your barracks if your city is connected to water/sea. After the barracks update you can build a ship. This sounds harder that it is but it's 1 development point and a city connected to the water, plus you can do this after you become Emperor as you can continue playing.