I have a friend who believes this and I can’t seem to debunk it for him. Ships get too small to see before the bottom disappears on the horizon. I can’t explai

I have a friend who believes this and I can’t seem to debunk it for him. Ships get too small to see before the bottom disappears on the horizon. I can’t explain to him why he can see things like bridges that should be below the horizon. I think the simplest proof would be that you see farther when you go higher. On a flat earth you could see tall things from any height.