Steep ladder-stair geometry for tight spaces: run, rake, and step count at a chosen angle.
A ship ladder (or alternating-tread stair) is steeper than a normal stair, typically 50 to 75 degrees, for very tight spaces like lofts and mezzanines. It is not a code egress stair and usually requires a continuous handrail.
Typically 50 to 75 degrees from horizontal, far steeper than a normal stair (30 to 38 degrees).
Generally no. Ship ladders are permitted only for limited access (lofts, mezzanines, equipment platforms), not as a required egress stair.
A very steep stair with treads shaped for left and right feet alternately, allowing a steeper pitch in minimal floor space.