- The vanishing point is at eye level with the observer, at the edge of the horizon.

- All receding objects overhead must appear to decline in altitude until they reach the vanishing point.

- The sea level of the earth must appear to incline in altitude until it reaches the vanishing point.

- Everything converges at the vanishing point.

Take a perspectives class sometime.

True enough, but these points are completely irrelevant to what he's bringing up. Allow me to show you. In these diagrams we are assuming that we have a perfectly flat surface and a person with perfect eyesight.

1. The tree is close up and entirely visible.

2. The tree is very far away and entirely visible. Obviously it will remain so no matter how far away it is.

3. The tree is close up and there is a low wall. The wall obscures only a small amount of the tree because it is close up and we can see over it.

4. The tree is very far away with a low wall. The wall obscures more of the tree because we can no longer see over it as easily. The amount that it obscures will continue to decrease as the distance increases but will clearly never increase past its own height.

5. The tree is close up and there is a high wall. The wall obscures much of the tree because it is so close to the observer.

6. The tree is very far away with a high wall. The wall obscures less of the tree than in case 5 because it is further away and we can see over it. The amount it obscures will continue to decrease as the distance increases but will clearly never decrease below its own height.

From this we conclude that as any object gets further and further away from an observer, the height of the area not visible due to an obstruction will approach the height of the obstruction.

This means that, on a flat Earth, in order for a tanker (20 feet of freeboard) to be obscured by waves so that its hull appears, say, half below the horizon, you would need waves 10 feet high! That's pretty choppy seas. An even more significant result from this is that if what Tom says is true the "distance to the horizon" would be significantly different based upon the average wave height. In calm seas, the horizon would stretch on nearly forever!