If the boat is supposed to be hidden behind 50m of curvature, saying it appears to descend hull-first is somewhat risible. FE explains that apparent effect as what we always see at the vanishing point - the 'melting' of the object into the horizon 'below' it. That's even visible to the naked eye, particularly on a hot day. Nothing magical about it.
The only problem with that is that it isn't true. It's a contrived "explanation", eaily shot down by using magnification to change the "vanish point" of the observed craft. Best I tried was a 5" refractor. You could see the ferry clearly - except for the bits below the horizon. Your "explanation" works on an invented magical property of the horizon (come to think of it, why is there a horizon at all in a flat earth?) that makes things disappear from the bottom up. As my London friends might say, 'that's a load of cobblers".
Correct, but plans for long straight roads, for example, do not take into account any compensations for curvature.
Because it's irrelevant. They don't take into account the procession of the equinoxes, either, because they have nothing to do with anything. Roads follow the terrain, end of.
This is the same with railroads
For the same reason. It's irrelevant.
A canal is a ditch filled with water. What's on the bottom is of no importance as long as it holds sufficient water to float boats. The water, however, does conform to the curvature of the earth by its very nature. So does the tea in your cup, for that matter.
Bridges go from point A to point B, from one support to the next. The supports may be anything; the side of a hill, a riverbank, a big rock, a tower, a pier, whatever. Ever see an arched bridge? It doesn't conform to anything but its own design and the supports it rests on. It if's tower supported, the towers will generally be vertical so they're carrying mostly compression load, and thus if there are two or more of them they won't be parallel, since they're not in the same plane.
Sorry, bruv, but there is no such thing.
First I've heard of this phenomenon, so I'll have to look into it.
I don't think you'll fiomd it much discussed amongst flatties. I don't think they even necessarily admit the possibility of HF communication.
Are you saying they bounce around the ball-to-ionosphere until they land safe and sound on the far side?
I couildn't have said it better.
The ionosphere lol - so you're reflecting/ refracting off something in the air?
Reflecting, or in the general parlance, "skipping". The distance of the skips is easily calculable. The ionoshere is an ionized layer of the atmosphere (hence the name), and HF frequency radiation usually (but not always) bounces off it. That's how long distance radio comunications worked until the advent of satellites that allowed reliable communications at higher frequencies. Working long ranges on HF was often difficult, which was part of the fun of hamming. If it was easy, why bother?
Which stops the signal flying off into space?
Sometimes nothing. During sunspot minimums that happens more often than not. But when the ionospheere is nice charged up yoiu can work the world with a very little power. I talked to a guy in the Marshall Islands one night who was using a 5 watt handy talky (I was in Tennessee). Signal was 5-9 halfway around the world. During those times I could talk to my pal in Queensland on 20 or 40 meters almost any night, especially if one of us was in the grey line.
Higher frequencies, VHF and above, don't bounce, they just go zinging out into space. That's why they're strictly good for line-of-sight work, and require giant towers or satellites to get a decent footprint.
And has different layers?
Yep, several.
Utterly absurd.
What I do know is that line of sight point to point radio waves consistently travel much further than they should on a globe model.
Depends on the footprint of the antenna and the amount of power they're using, plus various propagation quirks you can run into. I talked from Erie PA to Philadelphia one morning on a 2 meter handy talkie, a
lot farther than that signal had any right to go. Apparently there was a tropospheric "duct", formed that was acting as a wave-guide that allowed us to talk over hundreds of miles as though we were across the street from each other. That's what makes hamming fun! 73 DE JIPSAH