I just showed you footage that debunks that.
The horizon is apparent, and distance to the apparent horizon changes depending on temperature, humidity, etc. All you ever see out on the water is a flat surface because that's what it is. Everything else is perspective and atmospheric refraction effects. It doesn't matter how small the body of water is, it will always lie flat. This doesn't change just because you can't see the other side of the container the water is in.
Even in your model, the claim is you wouldn't see a curvature until you're hundreds of miles up.
There's a skipper with >100,000 nautical miles who has sailed in "global" races that goes in depth regarding speeds over water as well as timezones.
https://www.youtube.com/watch?v=lMhheDWThxE
https://www.youtube.com/watch?v=ECDKI0skBVU
This are all rudimentary arguments though. The real meat to the position comes from a deeper examination of physics, Kepler's lies, kinematic and dynamic equivalences in validity between the models, measurements of the cosmic microwave background which repeatedly prove that Earth does have a special position, the fact that GPS uses a geocentric WGS 84 coordinate system as well as coordinate transforms which are kept secret (all relating to how you establish your position over water, since there is no reference point). That leads to how flight distances can be fucked with, because of ground-speed vs airspeed and the reliance on GPS.
Deny all you want, but the measurements are repeatable and conclusive, and they do not corroborate the claimed curvature:
https://youtu.be/b8ML87EHat4
https://youtu.be/ZsnmX0XRNTk