Ship ladders are a hybrid. Part stair and part ladder, they make vertical circulation more comfortable in mechanical or service spaces. Ship ladders are generally preferred to normal ladders since they are more like stairs.
The dimensions of ship ladders vary based on available space so they are always custom fabricated. The angle of the ladder is usually 60°-75° and the design should use the shallowest angle possible within this range. Vertical rise between treads is generally between 9"-12". The width of ship ladders is usually 24" and the tread depth is 6". Handrails are always provided.
Ship ladders cannot be used as a means of egress. They appear in mechanical spaces or on rooftops. They are also sometimes used to access roof hatches.