I am not claiming that the earth is flat with this one. I have spent a lot of time at sea including crossing the Atlantic and Pacific. One of the claims to prove that the Earth is round, is that when a ship comes into view you see the masts first then the rest of it as you get closer. Even with binoculars I have never seen this I either see all of it of none of it. I have seen photos of it on the interweb.
Experience only. Other than in doldrums, I've only ever seen the effect with sailing ships, if the sails are up. They're huge compared to the mast which you'd have a hard time spotting. If you're close to the equator, you can sometimes see the top of tankers and container ships, but they usually look like colored smudges on the horizon. You can tell when you're close because you can see the hull, but that usually just appears suddenly, it's just that it appears after you see the smudges.
... it's easier to see in an airplane with no or light cloud cover, at between 1000 meters and say 5000 meters. Higher, the ground turns into a smudge. Then passing over city lights will do it.
I flew from Toronto Ontario in Canada, to Moscow a few times. By the time we got over Scotland, you could see the effect over Europe. But it looked literally like a slowly rolling marble. The flight was over 10,000 meters altitude.
