Has anyone ever tried this less expensive experiment?

Few days ago I proposed an experiment that I thought could destroy the globe for good and people claimed it was too expensive and there were easier ways (though no one proposed an alternative). Since then I’ve been thinking about easier ways and I went back to Samuel Rowbotham’s Bedford level experiment, and the explanation of scientists was light being refracted. So a thought came to my mind: What if, we could do the same experiment with something that scientists won’t claim it can be refracted? Something that we know can create an undeniable straight line between two points of equal height over a long distance? There are bridges that do so already, but globe believers claim the bridges follow Earth’s curvature because they are built blocks by blocks and not in a straight concrete line moving from on end to the other. So, I thought of something more simple: What if the flags in the experiments of Samuel Rowbotham had ropes linking them to the shore at a specific height to confirm that refraction had nothing to do with the sight of that boat? I thought about the following: We tie one end of a rope to a beam at a height of 1m above water level and then we tie it to the boat’s mat at the same height above water too. This way, there will be a distance from the shore at which the rope will be fully extended and thus form a relatively straight line 1m above water level. Now, if water is being curved, it would be impossible to reach 5km with our rope being fully extended ABOVE water level even if it’s length allows it to be. Why? Because the end of the rope tied to the boat’s mat which was 1m above the surface at the beginning of the experiment is now supposed to be below water level. If, you manage to have a 5km rope perfectly floating above water level while the measured distance from water level remained relatively the same, that would be absolute proof of water’s flatness because NO ONE CAN POSSIBLY EXPLAIN HOW, WHY AND WHEN A STRAIGHT ROPE STRETCHING 5KM ABOVE WATER HAS BEEN ADJUSTED TO PERFECTLY ESPOUSE THE SHAPE OF THE GLOBE. It seems so obvious to me that I wonder if I’m the first to think about this, or if there is some flaw to it. Has anyone ever tried this other experiment?