Just want to say I'm surprised that you put stock in the "hull restoration" story - anyone with half a brain knows that couldn't possibly be true. Regardless of how powerfull, a telescope can not "change perspective" - it simply enlarges it. So any trick of perspective that would give the illusion of a ship sinking below the horizon would simply be magnified when looked at through a telescope. If the ship appears "intact" through said telescope, it must appear "intact" to the naked eye, even if very very small. Basic optics.
Human perspective ends at the vanishing point.
On the sinking ship, Rowbotham describes a mechanism by which the hull is hidden by the angular limits of the human eye - the ship will appear to intersect with the vanishing point and become lost to human perception as the hull's increasingly shallow path creates a tangent beyond the resolving power of the human eye. The ship's hull gets so close to the surface of the water as it recedes that they appear to merge together. Where bodies get so close together that they appear to merge to human eyesight is called the Vanishing Point. The Vanishing Point is created when the perspective lines are angled less than one minute of a degree. Hence, this effectively places the vanishing point a finite distance away from the observer.
Usually it is taught in art schools that the vanishing point is an infinite distance away from the observer, as so:

However, since man cannot perceive infinity due to human limitations, the perspective lines are modified and placed a finite distance away from the observer as so:

This finite distance to the vanishing point is what allows ships to shrink into horizon and disappear as their hulls intersect with the vanishing point from the bottom up. As the boat recedes into the distance its hull is gradually and perceptively appearing closer and closer to the surface of the sea. At a far off point the hull of the ship is so close to the sea's surface that it is impossible for the observer to tell ocean from hull. From the limits of the human eye, the two appear merged.
While the sails of the ship may still be visible while the hull is perceptively merged, it's only a matter of time before it too shrink into the vanishing point which rests on the surface of the sea and becomes indiscernible from the surface.
We know that this explanation is true because there are reports of half sunken ships restored by looking at it through a telescope.