[lukan]

The standard nonsens reply to this is something with perspective. Like a train track in the distance get closer together, the ship gets closer to the ground and then infinitely small. Doesn't make sense, but abstract enough to make some believe there is another explanation possible.

[blueflow]

Standard answer: Ships do not get infinitely small - they visibly "sink" behind the horizont. Starting with the bulbous bow, which you stop being able to see at a distance of, i estimate, 10 kilometers?

[lukan]

Yes and standard reply then is quickly distracting (also themself?) with lots of other "facts" they quickly throw in, or some more vague mystic mumblings about perspective.

Edit: Oh and also there is some "proof" with a certain camera model they present. Where they zoom in closely to ships on the horizont, while not knowing the difference between optical and digital zoom. I am still not sure what they were trying to proof with that, but I did saw a visual glitch of the image processing on high digital zoom. Some vague impression that indeed you can enlarge the ship again fully, despite it being over the horizon. To me it was rather pixel soup, but for them confirmation. So to be on topic a bit again, if you want to influence irrational people of anything, logic only gets you so far and appealing on emotion quite further.