Ships do not disappear over the curve. they can be brought back into focus using a powerful lens. there are videos available showing this. Rising in height will naturally allow you to see further, but distant vision is limited by atmospheric occlusion and the resolution our eyes can see at. Part of what i find so strange about this whole argument is people typically refer to moving lights in the sky to determine the shape and movement of the ground below our feet. Shouldnt there be a better way? Perhaps measuring the physical curvature or motion instead of relying on so called distant lights?