Not to criticize you, but have you tried this experiment using land in front of you instaed of water?
because any RE could say that somewhere in between you and the hill there might be a wave covering the view (the wave wouldn't need to be too high in order to cover the view, because it is closer to you than the hill is)
Why would the coast appear fully sometimes, and not other? Are you saying that the light rays are not constant?
PS im only referring to the pictures where the coast is visible