Obviously, this painting is a paradox. This is not possible and self-contradictory. The fact is that the sea has been merged with the sky which can't exists in real world. But for the painters, anything is possible. The land is getting merged with the water and the water is getting merged with sky. The ships thus appear to be sailing in the sky. However if you look at the far end, it is sailing rightfully in the water. The overall effect of this illusion is quite interesting.