Ship captains in navigating great distances at sea never need to factor the supposed curvature of the Earth into their calculations. Both Plane Sailing and Great Circle Sailing, the most popular navigation methods, use plane, not spherical trigonometry, making all mathematical calculations on the assumption that the Earth is perfectly flat. If the Earth were in fact a sphere, such an errant assumption would lead to constant glaring inaccuracies. Plane Sailing has worked perfectly fine in both theory and practice for thousands of years, however, and plane trigonometry has time and again proven more accurate than spherical trigonometry in determining distances across the oceans.
They call us Flat Earthers “crazy” but crazy is believing that ships are stuck to the oceans upside down and on the side of a spinning ball because of an imaginary magical force called “gravity”. Common sense and real physics tells us that ships sail right side up on a Flat leveled surface. And no they don’t “sail over the horizon”, horizon means horizontal line parallel to the plane of the Flat horizon. Binoculars will bring ships back into view proving perspective not curvature.