Ship launch

Ceremonial 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.

Ship launching imposes stresses on the ship not met during normal operation, in addition to the size and weight of the vessel, and it represents a considerable engineering challenge as well as a public spectacle. The process also involves many traditions 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.

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 down an inclined slipway, usually stern first. With the side launch, the ship enters the water broadside. This method came into use in the 19th-century 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.

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 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 is erected under the hull and out onto the barricades. The surface of the ways is 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.

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Wikipedia