I was watching a show called Maine Cabin Masters. They were redoing
a camphouse
and built a Shipman's ladder for second floor access. Another name is
alternating tread stair. It looks something like this:
http://www.stairsuk.co.uk/assets/images/alternating-tread-staircase-gallerie/images/birch_24_spacesaver_jpg.jpg
Has anyone actually seen one?