Apologies for the misunderstanding! I came to this site to see if there was a credible alternative explanation for many of the things that a round earth would account for, such as the 'sinking ship effect'. So far there has been nothing convincing. I have also conducted a number of experiments and observations of my own, and given much thought to the possibility of a flat earth. I even started to formulate my own "flat earth theory"! All that I have achieved in all of this is to become more certain that what we are told is true: the earth is round, not perfectly round, but very close to it.
Go to the lighthouse video, pause it at 9 seconds, then again at 10 seconds. At 9 seconds, the lighthouse is not visible. At 10 seconds, it is visible, 1 pixel wide and about 3-4 pixels high (at the resolution of the posted video, and at the point I paused). If you keep playing until the lighthouse is well zoomed in, you'll see that the lighthouse is about 4 times higher than it is wide. What does this tell me? That the lighthouse has not been obscured in any way, it's just too small to see without magnification. Before the 10 second mark, the lighthouse is less than 1 pixel wide, so it doesn't show. This is equivalent to not being able to see a single human hair beyond a few metres: the angular resolution is less than the human-perceivable minimum at that distance. Does this make sense?
Keeping that in mind, pop back to the video of the tall ship going over the horizon. It only disappears from view after most of it has already been obscured by the horizon. What does this tell you? Please, also keep in mind that the prevailing swell would be physically incapable of hiding any more than a few boards of the hull, just above the waterline, given the vantage point of the observer.