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"The curvature adds an ~8 inch drop per mile" = WRONG
How can you speak up when you don't even know the fucking curvature formula. All the while spouting off like your know about this shit.
7.98" per mile squared unless you don't trust Pythagoras either.
Let's say your eyes are at 5 feet and you're standing at the edge of the water. Your horizon is at ~3 miles, so you'll see pretty much the whole boat at that distance.