The fastest and most efficient means of communication at the time was by sea and river. Inland cities like Milan and Florence depended on reliable and fast boats that cud freely pass along the rivers.
Leonardo sketched a type of crank-operated paddle boat with shovel-shaped paddles, based in part on the shape of the fins of fish. The operator worked two pedals with their feet. Using the principle of reciprocating motion, the pedals would set the paddle wheels moving in a counter-clockwise direction to propel the craft forwards. Leonardo's drawings do not show the whole boat but suggest how parts of it might look.