how hi are the waves in the open sea?

Answer 1

If there is no storm then they are not that big at all, out in the open ocean, because the water is deep, most waves can go virtually unnoticeable. It's only when they get closer to a land mass, and shallower water, that what we see as a normal wave appears.

Answer 2

Pen is right

Waves are caused by the wind and the bottom
the bottom slows down the water and the wind speeds it up
this causes the wave to take the form that we see it in