Hey, Truthexplorer, I checked out your link.
I have no idea what this guy saw when he said he still saw the entire boat at 6 miles. I have no way to verify his experience, but I think that 6 miles is a pretty short distance on an ocean horizon. You can easily see much longer than that. This goes against my own and others' reported experiences of seeing the mast first when appearing and last when disappearing on the horizon.
As regards the argument that roads that are thousands of miles long and are entirely level proving a flat earth, what comes to mind is that 'level' is relevant to a specific point on the earth and subject to the gravity that exists on the surface of that particular point of a sphere. Thus, it would measure as level even though you travel around the sphere, curving as you go. I have no idea how scientific this explanation is, but it only took about 30 seconds to come up with a possible idea to refute the flat earth evidence.
Good on you for sharpening your critical thinking skills. The standard for evidence we are conditioned with in the Truth is low. It takes practice to learn to be logical about acceptable evidence.