Firstly, I'm a serving Electrical Engineer (Artficer) in the British Royal Navy and I've spent some time at sea using/fully understanding equipment that simply would not add up if the world were not round.
Starting with navigational Radar, it is designed to only travel around 10-15 miles around the ship and at sea you CANNOT see that far. For example if we pick up a ship at say, 8-9 miles you cannot see it through high powered binochulars on the bridge wings (which can pick up targets past 10 miles if they are higher up). At sea the furthest you can see before the curvature of the horizon turns to a point where you can't see it is proven by the basic formula, d=√(13h)*1000 where h is your current height and d being the distance you can see until the horizon. So on a ship I'm stood say, 10 meters up so that means I can see a maximum of 11km, around 7miles. So why is it then that my navigational radar can pick up a target that I cannot see? Bending light? Light bouncing off the surface off the sea is very irregular, therefore I would
at least see slight images of another ship right? because I don't.
Also, radar can't travel underwater more than a few inches due to massive attenuation of the radio wave, hence why sound (sonar) is used underwater.
I won't mention the electromagnetism yet, because that is quite in-depth and will take alot of time to explain (and I'll probably have to get the books out myself
). I'd just like an explanation for this first.