KYS
When a ship approaches the horizon there's a mirror band caused by a mirage that forms at the water line, it obscures both the bottom of the ship and the top of the water. The magnitude or width of this mirror band is dependent on atmospheric conditions. As the ship travels further away convergence reduces its angular size and the mirror band covers more of it. Eventually the vanishing point is reached and the ship is no longer visible. There's no hump of curved water three miles out that ships sail up and over.
Here is how anybody can prove that flatlanders who use the horizon argument don't know what they are talking about.
The horizon is relative. Use 3 cameras.
Place 1 camera at 6 feet above the water level.
Place camera 2 at 20 feet above sea level, right next to camera 1.
Place camera 3 at 1 inch above sea level, right next to the other two cameras.
Make sure the cameras are all facing straight out to sea, next to each other, aimed at the same ship, and true to plumb with the gravity of the earth.
What do the cameras show when camera 1 shows some of the ship over the horizon?
Camera 2 shows the whole ship, just as it would be seen if it were sitting just a few feet away from the cameras.
Camera 3 can't even detect the top of the highest part of the ship.
This is because the horizon is different for each of the cameras. The so-called mirror band doesn't have anythign to do with ships beyond the horizon.
Now, of course, this test isn't described in completeness. Any old flatlander can say all kinds of stuff about how the test is not "microscopically" correct in testing detail.
But you all get the idea. Go out and do your tests. Better tests can be done with cars on a level road than with ships. Use the 3 cameras at different heights, and the same car at a particular distance.
Better yet, use a house. If the 3 cameras are all within 1 foot off the ground, the house can be so near that there is no chance for any kind of atmospheric aberration that can be considered a mirror effect. Because the house doesn't move, you can actually use one camera, and position it in 3 different positions for the shots.
Flatlander use of horizon to show flat Earth is totally negligible, and totally wrong.