The patent slip or Marine Railway was invented by Scot Thomas Morton in 1818 as a cheaper alternative to a dry dock for ship repair. It consisted of an inclined plane, which extended well into the water, and a wooden cradle onto which a ship was floated. The ship was then attached to the cradle and hauled out of the water up the slip.

In 1832, a House of Commons Select Committee, under the chairmanship of the, Rt. Hon. Sir George Cockburn, was convened to adjudicate on a petition by Thomas Morton to extend the duration of his patent. The committee eventually did not support the patent extension. It was claimed that not only was the cost of a slip one tenth of a dry dock but also by hauling completely onto a clear dry area that it was easier to carry out the maintenance.

Early designs would have used manpower and block and tackle to provide mechanical advantage, while later solutions used steam engines. One of the earliest surviving marine railways is the Creque Marine Railway on Hassel Island in the Caribbean.