If boats or any object go over the curvature of earth how comes we can't see this curvature they are going over or hidden behind?
Just what do you expect to see? A giant mountain with a sharp peak?
The ground rising up well above you?
The curvature you will see is distant objects having their bottom obscured, or being entirely obscured.
Go to this website with earths curve calculator https://www.omnicalculator.com/physics/earth-curvature scroll down and find the diagram with the curvature and an object hidden from curvature
They have that diagram just for simplicity in the presentation.
The first thing to note is which way is down.
On Earth, down points ~towards the centre of Earth.
A better diagram for that would be this:
The important point here is that Earth curves "down" away from you.
So there wont be a big hump rising up. It will all be below you.
This is actually a difference between a FE and a RE. A FE should have the "horizon" "rise to eye level" unless you can see the edge of this FE.
But for a RE, it will be below you, with the amount below depending on your altitude.
But even at a height of 100 m, it is still quite a small angle of dip, only 0.3 degrees.
The other big issue is scale.
Because of just how small the curvature is, it is quite difficult to show on diagrams. Because of this they will normally use diagrams which show objects that are massive or a tiny Earth.
For example, using your link, the red object on the Earth, if that was too scale, would be ~1200 km high. That is well into space.
I know you are going to say earth is too big to see the curvature but then objects ain't going over the curvature you can't have it both ways.
No, I would say Earth is massive and you are tiny.
For a person viewing an object from 2 m above the surface, you need thousands of m before the object even starts being hidden. Then as it moves on to a few more thousand, you end up with a few m being hidden.
Notice the massive difference in scale?
Thousands of m of distance, to hide a few m.
If you want to see Earth as a small ball you need to be 10s of thousands of km away.
Here is a to scale diagram of the curve of Earth over those 10 km:
The change in y position of Earth across the image is less than a pixel. That is because each pixel corresponds to 10 m.
You can't see the observer, because they are less than a pixel.
You can see the 20 m tall boat, but it looks like a dot because it is so small.
If someone can show me on a small scale an object going over a curvature without seeing the tilt or the curvature then that would disprove my point.
The problem is that on a small scale, the tilt would be quite significant and the curvature is readily apparent.
The circumference of Earth is ~ 40 000 km. That means that if you want 1 degree of tilt, the object needs to be ~111 km away.
And this tilt is in the direction that is hardest to see.
This 1 degree tilt would be like looking at a building that is 100 m away, but instead of looking level, you are looking at a point ~ 1.7 m above your eye line.
If you wanted to simulate it on a small scale, if you had a ball with a radius of 6.4 m, the 2 m high observation point would correspond to roughly 2 um above the surface of the ball. Try finding a camera small enough to put there.
A 20 m tall boat, would correspond to ~20 um.
And the 5 km distance needed for the bottom to start being obscured would be ~5 mm.
One big problem is finding a ball smooth enough.
So your best option is to use simulation software you can trust.