An accommodation ladder is a portable flight of steps down a ship's side. Accommodation ladders can be mounted parallel or perpendicular to the ship's board. If the ladder is parallel to the ship, it has to have an upper platform. Upper platforms are mostly turnable. The lower platform (or the ladder itself) hangs on a bail and can be lifted as required. To prevent damage to boats going under the ladder as the water level rises and falls, a boat fender is fitted to the end of the ladder. Use of a Jacob's ladder instead of the accommodation ladder to allow a maritime pilot to board is prohibited.