but you can zoom-in that disappearing boat with camera just like you can zoom-in stars with telescope , curvature has nothing to do with it it's just law of perspective .
Nope. That boat gets 12 miles away. and if you're standing in a rowboat t sea level, you're going to see its hull disappear below the horizon. If you're standing at the masthead of a windjammer or in the gun director of an old battleship, you'll see it several miles further away, but it's still going to drop below the horizon. whether you're using the world's biggest telescope or 10X50 binocs.
I'm a sometime ham operator, and we work with, and against, the curvature of the earth all the time. For instance, if I'm working the 2 meter band, my signal is, generally speaking, strictly line of sight. It's not going to skip off the ionosphere, and it there's nothing else to bounce the signal off of, or to carry it for me, it's going to zoom off into space never to be heard in this world again. If I want to talk around Middle Tennessee, a QTH on a good hill and a 30 foot stick will let me keep up with all my pals. If I want to talk to someone in Jackson, I'll need a much taller antenna, and if I want to reach Memphis, I have to switch to an HF band, because there's too big a chunk of planet between here and there for me to transmit through. It's not a matter of signal strength, I could, and have, bounced CW signals off the moon and talked to other hams that way. (Too much like work to do it a lot, some geezers love it, though.)
But here's one your flat earth concept can't explain. HF signals (10 meters and longer) will skip off the ionosphere and, under the right conditions, allow you to talk around the world. Say I'm trying to work VK4BWI in Queensland, but getting a lot of interference from stations between here and there, or just general atmospheric crud, what can I do? I have my beam (yagi) antenna pointed straight at him, but no luck. So I turn the beam around 180 degrees, and go around the world the other way. Boom, there he is, coming in 5 9, just like he was next door. (And again, I've done that, more than once.) How do you 'splain that without a spherical earth?
Why isn't the sun visible everywhere, all the time? We know it's always visible somewhere at any given time, and we know precisely where it is and isn't visible all the time That's important for hams as well, because other than charging up the ionosphere for us, the sun isn't our friend, and "greyline" areas, where it's dawn of dusk, provide some of the best signal propagation. None of that makes sense with a flat earth.
Why the varying length of days and nights in different hemispheres? Why white nights in Iceland with sunless days at Cape Horn, and vice versa? What makes the tropics tropical and the poles cold?
Any one of these these things seem to me to put paid to the idea of a flat earth.Add to that the fact that simple observation of astronomical bodies, and of the earth from space, show in all it's marvelous elegance the perfect interactions of God's design, all obeying the laws of physics that He has established to make everything work. The flat earth cosmos looks cartoonish in comparison.