Your "simple" observation relies on light travelling in straight lines, something that we both know to be extremely unlikely.

Given the DATA of the observation, and

*without any reference to the behaviour of light*, we can form the geometry;

Observation height 100m

Ship height 46m or so.

Distance to ship - between 14 and 22km, determined by it passing between two islands of known distance.

This yields a geometrical figure. The presumed flat plane of the sea, continued to a point under the observation point, forms a horizontal base of between 14 and 22km. A vertical at each end, one of 100m, one of 46m, and a fourth, angled side connecting the tops of the verticals.

Doesn't matter if light is bending or not, this is the physical geometry of the situation, IF we presume the lands and seas to be flat, and with the exception of the topography of the land that places the observer 100m above sea level.

This figure can be split into a rectangle and a triangle, and we can apply Pythagorean geometry to the triangle. See my diagram above. This gives us angle B. With angle B and the height of the observer, we can determine where the continuation of the hypotenuse of that triangle leads, and where it should meet the continuation of that flat base beyond the 46m side, IF the base is flat. This forms a triangle with side a being the observer height, side b the base formed by the (presumed) flat sea on which the ship sails, and a hypotenuse connecting observer to the base.

The continuation of that angle line SHOULD meet the flat base line somewhere between 25 and 39.29km away from the observer, according to simple geometry. It CANNOT miss the base.

If we could draw a rope or wire out from the observation point, not have it sag, bend, or wave in the wind, connect it to the top of the ship, and extend it in a straight continuation line onward past the ship, it would meet a presumed flat sea between 25 and 39.29km away. Regardless of how light behaves.

Agree?

I'll ask the same question I asked on YouTube, but which all the FEers over there avoided answering; "What do you SEE behind and beyond the top of the cranes on the ship? Sea? Sky? Something else?"

All the distances, heights and calculations are referenced in detail in my YouTube video on the observation. I know this has been removed once already for "spamming the forums", but since it's all written out there already, I am disinclined to retype it all here.

If mods want to remove it, then just say so, and I'll edit it out of this post, but it CONTAINS THE DATA pertinent to this discussion.