Funtarctica.

There are far simpler explanations than flat earth that do not require mental gymnastics to attempt to explain vs. observable phenomena.

A water ball spinning at 2000 mph requires much more mental gymnastics than a flat Earth. Talk to some airline pilots and theyll set you straight. They're told on the first page of the pilots training manual that they will be flying over a flat plane.
Flat, calm water would be impossible on a spinning globe. The Earth's atmosphere would be sucked into the vacuum of space if Earth was a globe in space.

My father-in-law is a commercial airline pilot who definitely believes the earth is round.

Water can't fly off into space because Earth's gravity pulls it down in the same way the moon pulls it around to create tides. In addition, Earth has an atmosphere and a strong magnetic field, so the vacuum of space isn't sucking anything anywhere.

The oceans may appear flat, but you can easily notice the curve by watching ships sail into the distance. They disappear from the bottom up because they sail past the 'hump' from your line of sight. Same thing is visible watching cars drive away on the salt flats.

Put a single drop of water on a flat surface and take a look at the top of it. Water can definitely curve.

Think about a flat earth, the distance that pilots or sea captains would need to cover in order to navigate below the equator would be noticeably longer than above the equator—how would they not ALL have gotten suspicious?

If gravity was strong enough to keep the tremendous weight of the oceans glued to the Earth then how do birds fly? How do small children stand up against the strength of gravity? Or anybody, for that matter. We'd all be flat on our backs struggling against it. And how does a magnetic field keep the atmosphere from being sucked into the powerful vacuum of space? A vacuum can suck a boiled egg into a small bottle.
How does water stay calm on the surface of bodies of water on a ball spinning at 1000 mph? Try spinning a basketball and pour water on it. Even if the water didn't fly off, would it lay there placidly?
When you see a boat disappear over the horizon it's because it's reached the vanishing point of your vision. Videos taken by a Nikon camera with the highest zoom distance available. It shows the boat coming back into its viewfinder after it's no longer visible without zoom. So, no, the boat didn't go below the horizon. You can see Chicago across Lake Michigan 75 miles away. Ho