Ships can absolutely be beached without being up on shore though. So in the water.

Because they are super heavy and can thus run aground further out than a small boat might. They are beached, meaning they are stuck in sand of a beach, but they aren’t on the beach, and are wholly within the water. Because that definition had “especially” and not “only”, thus it can go out further than what we would traditionally label as a beach between high and low tide.