What is "patent slip"

The patent slip or marine railway is an inclined plane extending from shoreline into water, featuring a "cradle" onto which a ship is first floated, and a mechanism to haul the ship, attached to the cradle, out of the water onto a slip. The marine railway was invented by Scot Thomas Morton in the early 19th century, as a cheaper alternative to dry docks for marine vessel repairs, in particular below waterline. Larger modern marine railways can handle vessels of thousands of tons.