Final answer:
On a flat Earth, an approaching ship would appear uniformly larger with no parts obscured, unlike on a spherical Earth where the hull appears first and disappears last, indicating the Earth's curve.
Step-by-step explanation:
How an Approaching Ship Would Appear on a Flat Earth
If the Earth were flat, the way we observe an approaching ship would differ significantly from our observations on a spherical Earth. On a flat Earth, as a ship approaches from a distance, it would uniformly increase in size. Its entire form would become visible at the same time, with no part dipping below a horizon, simply growing smaller as it recedes into the distance. However, on a round Earth, we notice that ships seem to emerge or sink over the horizon, with the hull becoming visible first when approaching and disappearing last when departing, suggestive of a curved surface.
Climbing higher, such as by going up a hill or to the top of a tower, allows one to see a ship that has disappeared on the horizon, confirming the curvature of the Earth. Similarly, sailors used to climb the masts of their ships to extend the distance to the horizon, giving them a greater vantage point. Posting lookouts on the mast would confer no such advantage on a flat Earth, where one could see the ship approaching from much farther away without height playing a factor.