That's not caused by Earth curve.From a boat
Same effect can be observed with mountains.
All this argument does is demonstrate when someone has a complete lack of knowledge and research on the topic.
Here's an experiment where the exact same effect is replicated at a much smaller scale, where there is no curvature.
And if that's not enough for you, you can even do this experiment yourself at home with a coin and a table:
Look down the surface of the table from one end, with your eyes at the same level as the table. Put a coin right up to your face then move it down the surface of the table away from you. The bottom of the coin will start to disappear.
Is the table curved?