The patent slip – one holding a
landing craft and the other a
split dump barge (on right) In 1817, the total cost of dragging up
Kent was £ 1,436. The cost of bringing a first rate into a dry dock was only £ 35. However, building a dry dock cost about twenty times as much as constructing a regular (building) slip. No wonder that people sought for cheaper ways to put a ship dry for large repairs. In 1819,
Thomas Morton of
Leith, Scotland introduced the first modern slipway. As it was an invention, he applied for a
patent in the United Kingdom and its dependencies and obtained it. The patent led to the name
patent slip. In a very extensive 1832 parliamentary discussion about a possible renewal (prolongation) of the patent, it was never called a 'slipway'. It was named 'patent slip', or simply 'slip'. About fifty years later, the patent slip was seen as the first slipway. In many respects, the way that a patent slip got a vessel out of the water resembled the traditional method used on a building slip. Therefore, some people dared to say it was only an adaption of other inventions. After its inquiry, the House of Commons — which decided on these matters — clearly established that it was an invention. A patent slip could be built upon an existing slip. It required relatively heavy
piling directly below the keel of a vessel and somewhat lighter piling where its sides would be supported. If there was little or no tide, the slip had to be extended below the water level. Upon the slip itself, three lines of 'ways' were fixed. These ways carried three
cast iron rails that formed a
railway. A
ship cradle moved over the slip's railway. At high tide it was placed below a vessel. As it settled upon the cradle, the blocks were drawn under the ship when it was still two-thirds water-born. Cradle and ship were then towed up. Using a cradle on wheels was a decided change from simply placing rollers under a vessel. The patent slip's
ship cradle consisted of a long beam which supported the keel of a docking vessel, just like it was done in shipbuilding. On this beam were placed
keel blocks to match the form of the keel. As soon as the keel rested on the keel blocks, other blocks were drawn in to fix the vessel in an upright position. The latter did not bear a substantial part of the weight. At the tip of Morton's cradle was a purchase tackle by which the cradle was pulled up by a chain. A big advantage was that there was no pull on the ship. There was a security mechanism that kept the cradle from slipping down in case the chain broke. At first, pulling was done by hand, later steam power was used. A patent slip required substantially more investment than a building slip. In 1832, Mr. George Graham, a shipbuilder of Harwich declared that he had spent £ 3,040 to change his simple (building) slip to a patent slip. £ 200 of this was for the Morton's patent, i.e. the license. Graham also stated that it would cost about £ 2,000 to establish a slip similar to the one he had before he changed it. It was therefore not economical to use a slipway as a building slip. In spite of this, it was probably done at times.
The slipway after 1832 , the red banner reads: 'railway', 1857 Thomas Morton acquired his patent for Scotland on 18 August 1818. It would last for a period of 14 years. Somewhat later, he acquired the same patent for England, Ireland, and the colonies. In 1832, it was still quite clear that the term 'patent slip' referred to Thomas Morton's slipway. By August 1832, the meaning of the term 'patent slip' would have become confusing. The patent had expired, but it would still be practical to make a distinction between slips configured for shipbuilding and those configured for repairs. It is probable that writers tried to solve this by re-using existing terminology. Two new terms were used: slipway and slipdock. The word 'slipway' as in 'patent slip-way' was used to refer to two patent slips in 1834. This is obviously related to the shipbuilding practice of laying down the keel on a series of blocks. The way on which these blocks were laid could be called ground way or slip way. The upper part of the standing or ground ways from which a ship was launched was also referred to as the slipways (plural!). The term 'slip dock' or 'patent slip dock' can also be traced back to at least 1834. This was repeated in 1837 and the term would remain about as popular as slipway. The logic of this term is in how a slipway was used. A
dock was basically a facility where a ship could moor or attach without any preparations. A typical characteristic of the patent slip was that a vessel could be hauled up with its full load and rigging. In the United States of America, the term 'Marine Railway' can be traced back to at least 1840. The term was generally accepted. In e.g. Maine alone, three companies with the words 'Marine Railway Company' in their name were incorporated in the 1840s. In British English, the term Marine Railway had earlier been applied to plans to transport ships across the Panama Isthmus by loading them onto railway cars. In Canada, this idea led to the
Big Chute Marine Railway.
Improvements An improvement to the cradle of some slipways was to make it telescopic. This meant that it was short while it was at the lower, shallow, end of the slipway and became longer as a vessel was hauled up. Some other slipways were provided with gates which shut at ebb. This meant that the slipway could be made shorter. == Related concepts ==