Don't ask me. I was in the Navy but was never a lookout. I'm just going by what I have read in The Navy Manual For Lookouts. Ask a real sailor !
Curious that you demand something of me which you haven't done even though you allegedly had ample opportunities.
Well, actually I have done it - but neither in an any official capacity nor as an official lookout in the crow's nest.
But I do know that the horizon is a very sharp and distinct line when you are at sea on a clear, calm, sunny day.
I do know that if you look out to sea....Even just on land from a beach or shore....That it was not just "A indistinct blur which fades away at an indefinite distance" which is the flat earth definition - the way it would have to be if the earth earth was flat.
And I do know I could see farther from the top deck than I could from a boat at sea level, from the main deck , or the bridge, going higher in my sightings.
I was just an ET assigned to radar maintenance and repair and would have done some checks on comparing visual sightings with the radar ranges and bearings.
I mentioned , merely suggested and certainly didn't it to be a "demand" that you talk to the "real sailors" such as QM's or BM''s or Officers.
Why ? Because they would have had more experience in their official duties as lookouts. And are trained to be proficient in their duties in these things. In other words , wouldn't you trust an expert in his field more than someone who was not ? That was the reason I suggested, not demanded, you talk to them instead of taking me at my word.
As the English would say, "Don't get your knickers in a twist ! " Let's face it. The earth IS a globe and there IS a horizon. LOL