In alt.home.repair, on Sat, 8 Dec 2018 18:00:17 -0600, Dean Hoffman
wrote:

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?

Never saw one. Looks like a great idea when horizontal space is scarce.
You'd have to practice to get good at using it, but I've found that when
I was fat and one knee hurt, I'd make a point to start with one leg, the
same leg, each time. If I can learn to do that without much trouble,
someone can learn to use these stairs properly. Newbies should be
warned.