Ship ladders can be used
for control rooms, unoccupied roofs or observation stations not more
than 250 square feet or for the use of more than three occupants. (Most
of this information is from the 2010 California Building Code Book).
The minimum tread depth is 5 inches.
The tread shall be projected such that the total of the tread depth, plus the nosing projection is no less than 8 1/2 inches.
The maximum that a ship ladder riser can be is 9 1/2 inches.
Both sides of the ship ladder will require handrails. I couldn't find a specific height on these handrails, but I would imagine that they are the same as other stairways.
I couldn't find any minimum widths, but I did find a website that sold ship ladders with standard widths of 27 inches.