Consider a 3D model with an infinite perfectly flat plane. Any receding object on the surface gets smaller and smaller the more distant it gets, right? At the edge of the horizon, any imperfect increase in height, no matter how minuscule, will obscure the object from the bottom up as it shrinks into the distance.

At the horizon there are hundreds of waves, creating a distinct line to the horizon. This means that as the ship shrinks into the horizon it must also sink into mean height of the combined waves. The smaller the ship gets into the distance, the more the waves at the false edge of the horizon will obscure its hull from the bottom up.

Dr. Samuel Birley Rowbotham found that the vanishing point of the horizon is slightly below the edge of the horizon due the mean combined height of the waves.

It makes perfect sense. Would you like an illustration?