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Ships and Shipbuilding, the types and construction of any large buoyant type vessel in which people travel or transport goods over the surface of the water. The term boat usually denotes smaller vessels, but no criterion of differentiation is generally accepted. The term shipbuilding is applied to the construction of large vessels. See also Boats and Boatbuilding.
Structurally, a ship is a hollow beam
subjected to severe bending and twisting as it moves through waves and as its
own load changes. The principles of ship structure and the nomenclature of its
parts have long been established and are essentially the same whether the ship
is a wooden sailing ship or a large modern tanker. The backbone of all ships is
the keel, a longitudinal beam or girder located at the very bottom of the vessel
and extending from bow to stern. At the forward end of the keel is attached the
upright or nearly upright stem that forms the front of the vessel. A similar
sternpost is usually set at the after end of the keel. The ship is given its
shape by a series of symmetrically curved ribs or frames that run transversely
and that are fastened to the keel at their centers. At and near their centers on
the bottom of the ship the frames are made considerably larger than at the sides
and are known as floors. The ribs are held in position by longitudinal
stringers, or clamps, that run the full length of the ship and that are curved
to conform with the shape of the hull. Additional bracing is provided by beams
extending across the width of the ship and fastened at either end to the
opposite sides of the ribs. In very small vessels only one set of beams, set at
the ends of the ribs, is used, and these beams serve as supports for the deck.
In larger vessels, several series of beams are employed, the number
corresponding to the number of decks with which the ship is provided.
The skin of the vessel is mounted outside the frame. In steel
vessels the skin consists of a number of metal plates riveted or welded to the
frame, and in wooden vessels it consists of a number of horizontal planks called
strakes. The term strakes is also sometimes applied to individual rows of steel
plate in a metal hull. Transverse walls of wood or metal plate, depending upon
the type of vessel, run from one side of the ship to the other at several places
in the length of the hull. These walls, called bulkheads, stiffen the frame and
often are used to break the hull up into watertight compartments as a safety
measure, so that a leak in the hull will flood only part of the ship and
sufficient buoyancy will be maintained by the other compartments to keep the
ship afloat.
A number of modifications of the standard method of ship
framing have been devised, particularly for use in tankers. Many tankers use a
system of longitudinal framing in which a comparatively small number of large
transverse frames is employed and the chief framing members are longitudinal and
run the full length of the ship. The interior of the tankers built on this
system is divided into a number of compartments by a longitudinal bulkhead
running the length of the ship at the centerline and by a number of transverse
bulkheads. The longitudinal system of construction has been applied to other
forms of cargo vessels as well as tankers.
The actual construction of any type of
ship, whether made of wood or metal, is complicated by the various curves of the
hull, the compound angles formed by the joints between the various structural
members, and the necessity of producing a hull that is absolutely symmetrical
and "fair" (having regular curves and surfaces that are smooth). Because of
these requirements, it is almost impossible to build any form of ship directly
from small-scale plans, as is done in the case of other kinds of structures.
Instead the shipbuilder, before beginning work, must resort to the practice of
lofting, or laying down, the lines of the ship.
Lofting consists essentially of preparing in full size an
exact skeleton plan of the hull to be built. From this plan the builder
determines the dimensions and forms of the frames and plates, which, when
assembled, make up the ship structure. The entire plan of the ship structure is
laid down on the flat floor of a special room or building known as the mold
loft. Paper or wooden patterns, called templates, of the pieces of the hull are
then constructed from this plan and are used in the building shops to cut and
form the plates and frames to the required configuration. The more complex the
ship, the more detailed are the loft templates. Although the principles of
lofting have remained unchanged for centuries, specific techniques have been
improved in recent decades. The skeleton plan, instead of being laid down full
size, is prepared with great precision to small scale, typically one-tenth of
full size. Templates are taken from this plan and photographed, resulting in
transparencies less than one-hundredth of full size. The transparencies are
either projected onto an uncut piece of construction material and the piece
marked off, or the transparencies are used directly by automatic cutting
machines. For many parts of the hull, computers may be used to describe the
space of the part and the description may be used to control the cutting machine
directly.
Contributed by: Howard I. Chapelle
"Ships and Shipbuilding," Microsoft® Encarta® 97 Encyclopedia.
© 1993-1996 Microsoft Corporation. All rights reserved.
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Last Revised: July 19, 2006 07:32 PM.
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