Ship launching
Ship launching is the process of transferring a vessel to the water. It is a naval tradition in many cultures, dating back thousands of years. It has been observed as a public celebration and a solemn blessing. In addition to the size and weight of the vessel, ship launching imposes stresses on the ship not met during normal operation, and represents a considerable engineering challenge, in addition to a public spectacle. Ship launching involves many superstitions intended to invite good luck, such as christening by breaking a sacrificial bottle of champagne over the bow as the ship is named aloud and launched.Methods of launch
There are three principal methods of
conveying a new ship from building site to water, only two of which are called
"launching." The oldest, most familiar, and most widely used is the
end-on launch, in which the vessel slides, usually stern first, down an inclined slipway. The side launch, whereby the ship enters the water
broadside, came into 19th-century use on inland waters, rivers, and lakes, and
was more widely adopted during World War II. The third method is float-out, used for ships that are built in basins or dry
docks and then floated by admitting water
into the dock. In all cases heavy chains are attached to the ship and the drag effect is used to
slow the vessel once afloat until tugboats can move the hull
to a jetty for fitting
out.
Stern-first launching
Normally, ways are arranged perpendicular to the shore line (or as nearly so as the water and maximum length of vessel allows) and the ship is 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 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.) 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; common mechanisms include weak links designed to be cut at a signal and mechanical triggers controlled by a switch from the ceremonial platform.
On launching, the vessel slides backwards down the slipway on the ways until it floats by itself.
Sideways launching
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 Great Eastern designed by 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.Air-bag launching
Sometimes ships are launched using a series of inflated tubes underneath the hull, which deflate to cause a downward slope into the water. This procedure has the advantages of requiring less permanent infrastructure, risk, and cost. The airbags provide support to the hull of the ship and aids its launching motion into the water, thus it is arguably safer than other options like sideways launching. These airbags are usually cylindrical in shape with hemispherical heads at both ends. The Xiao Qinghe shipyard launched a tank barge with marine airbags on January 20, 1981 and it is known as the first use of marine airbags.Tags: ship launching ceremonies, ship launching airbags, ship launching methods, ship launching sideways, cruise ship launching, launching a ship sideways, launching a ship from dry dock, ship launching rubber balloon, ship launching definition, define ship launching, ship launching into water,
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