Here is a Demonstration that simulates this phenomenon. When the ship nears the horizon, you begin to view it through a telescope. You can then observe it dipping under the horizon until it disappears from view. For example, if your eyes are at an elevation of 1.7 meters (approximately 5' 7"), the visible horizon is about 5 km away. The ship will disappear from view at about 20 km. Because of refraction of light rays, you can actually see about 15% farther than the actual distance when the air temperature is 20°C.