When a ship appears over the distant horizon, the mast is seen before the hull. This phenomenon can be explained by considering the shape of the Earth and how light travels.
The Earth is a large sphere, and because of its curvature, objects that are farther away become obscured by the Earth's surface as they move over the horizon. The upper parts of an object, such as the mast of a ship, are further away from the Earth's surface compared to the lower parts, like the hull. As a result, the top parts become visible first as an object like a ship comes over the horizon.
Therefore, due to the curvature of the Earth, the mast, being higher and more elevated, comes into view before the hull as the ship approaches from a distance.