The angular size can be calculated by an arctan formula:

When a ship moves further away, its appearent size decreases related the distance. And D (height) stays same.

When there is a wave, it incases the ship when their apparent size becomes equal.

So,

If we take a wave has d heigh and l distance from observation point, so it turns to:

Apparent sizes have to be equal:

Now we can work on an example:

A ship has 10 metres high

A wave far us 100 metre and it has a high of 1 metre

So;

The distance of ship disappearing behind a wave:

Our formula was:

D/L = d/l

So;

10 metres / X = 1 / 100 metres.

X=1000

So ship disappears in a thousand metres.

If ship becomes 20 metres high, it disappears a 2.000 metres far.

If we use a highness, for example we are also have a high, it increases our sight range by itself. We'll examine this situation later.

PS: This working has been created after examine zorbakim's working as a base and support if it.