I am an actual merchant mariner who actual sails on large commercial vessels. I've come here to admit that nearby every major port the US government has installed massive ship elevators that make ships appear to sink once they are outside of most peoples perception. This is assisted by the ships crew taking on ballast water at the same. On rare occasions when the elevators are not working the ship will actually scuttle itself if anybody is watching.
But in all seriousness if the earth is flat then why can you see further when you go up higher? What advantage would you get from having the bridge be on the top of a ship? Obviously we crafty sailors put the spot we look out from at the top of the ship so we can see roughly 10-15 miles out (depending on ship height). If you go down to the main deck of most ships you can hardly see anything. Also note that the bridge can see ships/land/buildings sooner than a watch set on the main deck (assuming it isn't a RORO vessel)
Also take note that ships are not as good at finding life rafts as helicopters are.
Maybe the first part of your post
explains
what happens to the container ship seeming "lower down" than the much smaller fishing boat at 3:29 in this video.
SHIPS OVER THE HORIZON - PART 1 : CONTAINER SHIP (FLAT EARTH) Matrix Decode
Matrix Decode is a well known Flat Earth photographer and producer of YouTube videos, but he does provide quite a bit of evidence for the Globe!
Even from 0:36 the ship seems a bit over the horizon, by 2:55 most of the hull has disappeared.
Then at 3:20 just the superstructure shows and a much smaller fishing about on the horizon comes in.
By 4:45 the ship has all but disappeared and another fishing boat comes past the line of sight.
What makes the video so convincing is that the trawlers and ship are in line,
yet the smaller trawlers are completely visible and the more distant larger ship gets hidden.
And finally at 7:45 after the ship has disappeared he puts up this closing screen:
I have noticed this before with
Matrix Decode, though he tries to prove the flat earth,
if his video seems to show some other conclusion, he does not hesitate to say so.
See
Flat Earth Q&A / Re: distance to the sun « Message by rabinoz on January 25, 2017, 01:29:22 PM » for some more out of his videos.