Editing Slipway (section)

== Slipways in ship construction ==
{{main|Ceremonial ship launching}}
[[File:Ecorse Mi 1909 - panoramio.jpg|thumb|left|[[Lake freighter]] ''Shenango'' in a parallel slipway in 1909]] 
For large ships, slipways are only used in construction of the vessel. They may be arranged parallel or perpendicular to the shore line (or as nearly so as the water and maximum length of vessel allows). On launching, the vessel slides down the slipway on the ways until it floats by itself.<ref>[https://books.google.com/books?id=pigDAAAAMBAJ&dq=Popular+Science+1931+plane&pg=PA36 How Biggest Ship Was Safely Launched, February 1933, Popular Science] slipway and launching of French passenger liner Normandie in 1933 – excellent drawing and illustrations showing basics of process</ref> The process of transferring the vessel to the water is known as ''launching'' and is normally a ceremonial and celebratory occasion. It is the point where the vessel is formally named. At this point the hull is complete and the [[propeller]]s and associated shafting are in place, but dependent on the depth of water, stability and weight the [[engine]]s might have not been fitted or the [[superstructure]] may not be completed.

In a perpendicular slipway, the ship is normally built with its [[stern]] facing the water. Modern slipways take the form of a reinforced concrete mat of sufficient strength to support the vessel, with two "barricades" that extend to well below the water level taking into account [[tide|tidal]] variations. The barricades support the two launch ways. The vessel is built upon temporary cribbing that is arranged to give access to the hull's outer bottom, and to allow the launchways to be erected under the complete hull.  When it is time to prepare for launching a pair of standing ways are erected under the hull and out onto the barricades. The surface of these ways are greased ([[Tallow]] and [[whale oil]] were used as grease in sailing ship days).<ref name="statestreet">{{Cite book
  | author = State Street Corporation – State Street Trust Company
  |author2=Walton Advertising and Printing Company, Boston.
  | title = Some ships of the clipper ship era, Their builders, owners, and captains
  | publisher = Printed for the State Street Trust Company
  | year = 1913
  | location = Boston, MA
  | page = 16
  }}
</ref> A pair of sliding ways is placed on top, under the hull, and a launch cradle with bow and stern poppets is erected on these sliding ways. The weight of the hull is then transferred from the build cribbing onto the launch cradle. Provision is made to hold the vessel in place and then release it at the appropriate moment in the launching ceremony, these are either a weak link designed to be cut at a signal or a mechanical trigger controlled by a switch from the ceremonial platform.

[[Image:slipway at portland.JPG|thumb|right|Two slipways at [[Portland Harbour]] – one holding a [[landing craft]] and the other a [[hopper barge|split dump barge]] (on right)]]

Some slipways are built so that the vessel is side on to the water and is launched sideways. This is done where the limitations of the water channel would not allow lengthwise launching, but occupies a much greater length of shore. The ''[[SS Great Eastern|Great Eastern]]'' built by [[Isambard Kingdom Brunel|Brunel]] was built this way as were many [[landing craft]] during [[World War II]]. This method requires many more sets of ways to support the weight of the ship.

In both cases heavy [[Link chain|chain]]s are attached to the ship and the drag effect is used to slow the vessel once afloat until [[tugboat]]s can move the [[hull (watercraft)|hull]] to a [[jetty]] for [[fitting out]].

The practice of building on a slipway is dying out with the increasing size of vessels from about the 1970s. Part of the reason is the space requirement for slowing and maneuvering the vessel immediately after it has left the slipway, but the sheer size of the vessel causes design problems, since the hull is basically supported only at its end points during the launch process and this imposes stresses not met during normal operation.
[[File:Harbour 1, South Shields, South Tyneside, Tyne and Wear, England.JPG|thumb|right|Slipways in the harbour of South Shields, Tyne and Wear, England]]
[[Image:Porthgwarra Slipway.jpg|thumb|right| A slipway and [[winch]] at [[Porthgwarra]], [[Cornwall]], UK]]