Dock (structure)

Dock (structure), a type of harbor structure used for loading, unloading, or repairing ships. In accurate usage the term applies either to the water channel in which a ship is berthed beside a pier, or to a dry dock, in which a ship is placed for repairs. Commonly, dock refers to a pier or quay. A pier is a structure that extends out into the water, usually perpendicular to the shoreline; a quay is constructed parallel to the shoreline.

In harbors that have a large tidal range, ships are usually berthed in wet docks. These docks are actually basins that can be shut off from the rest of the harbor by movable gates that hold the water in the dock at the high-tide level. Wet docks are a necessity in most ports of the British Isles and in other localities where the height of the tide is more than about 3 m (10 ft). The London wet-dock system is the largest in the world; the combined length of the quays and piers in London amounts to about 72 km (45 mi).

In most United States seaports the rise and fall of the tide is small enough to permit the use of tidal docks. Such docks, used almost exclusively in the United States, consist of a series of rectangular water spaces between projecting piers. Because changes in water level are relatively small, there is no need to isolate the dock basins from the rest of the harbor.

Today, enormous container ships are primarily responsible for transporting cargo overseas (see Shipping Industry); as a result, major shipping ports of the world have container ship docks. Container ships transport the trailer components of tractor-trailer trucks, or large standard-sized rectangular boxes. The cargo is already packed in these large boxes, so at the docks these containers need only be placed on or removed from the ships. Container ship docks are often fitted with large cranes that can load and unload the containers. The docks must also be wide enough to accommodate vehicles that deliver and pick up the containers.

Dry docks are generally used to make repairs beneath a ship's waterline. The ship is maneuvered into a dry dock, then the structure is closed and pumped free of water, leaving the entire ship exposed for repairs. Dry docks are of two types: graving docks, fixed basins lined with concrete; and floating dry docks, usually made of steel. Floating dry docks have certain advantages over graving docks in that they can be built more quickly and economically than fixed docks, and can also be towed into place to meet a ship unable to make it to a port.

Caulking

I. Introduction

Caulking, process of sealing joints in wood or steel structures against leakage of liquids or gases. Caulking is commonly used in the shipbuilding, metalworking, and construction industries. The joints between planks on a wooden ship, for example, are caulked to prevent water from leaking into the ship; riveted seams in steam boiler drums and air tanks are caulked to prevent steam, hot water, and air from leaking out.

II. Caulking Wooden Ships

The planks of a wooden ship are grooved to allow space for the insertion of caulking material between adjacent pieces. There are several materials used for caulking planked wooden ships. Historically, a fibrous material called oakum was used; today a number of different plastics, known as elastomers, are also available.

Elastomers consist of long, tightly twisted molecules that stretch and recoil, much like a spring. Plastic caulking materials are thoroughly mixed with a liquid curing material just before application, and the combined paste is then injected into the clean seam. The outer surface of the seam is smoothed off until it is level with the adjacent planks. When properly applied, plastic materials are far superior to oakum because they adhere to the wooden planking like glue, and they retain their rubber-like elastic properties indefinitely.

Oakum may still be used for recaulking older ships; it is also used in places where plastics are not available. Oakum is made from old hemp rope that has been untwisted and picked apart. It is generally used in the form of loosely spun yarn and may be untreated (white) or saturated with a tarry substance (black). Oakum comes in balls or in rope form.

To caulk a ship using oakum, the seam must first be spread slightly, using wedges. The oakum yarn is then pounded into the seam with special chisel-like tools. White oakum is used for the first layer (nearest the inside of the hull) and black oakum for the rest. Care is taken to eliminate cavities in the oakum, as they may cause decay of the wooden planks. The seam is filled to a fraction of an inch below the outer surface of the planking, and the remainder of the seam is then filled with pitch or marine glue.

Small ships and boats built of plywood or plastic require little or no caulking. Plastic adhesives for plywood and other wood laminates are highly resistant to seawater and result in hulls that are extremely watertight.

III. Caulking In Building Construction

Caulking is also used in the construction of buildings. Joints between wood, metal, and plastics may be filled to prevent the leakage of water or air. Examples of such applications include sealing glass panes into a wood or metal window sash, sealing the edges around sinks and bathtubs, and sealing material around vent pipes, chimneys, and walls. Plastic materials are superior to older materials, and many plastic caulking substances are available in ready-to-use cartridges for use in caulking guns or other convenient applicators. These “mastics” are based on urethanes, acrylics, or polybutene or polysulphide elastomers. The formulations used are dependent upon the special properties necessary for specific applications.

IV. Caulking Riveted Seams

Riveted steel drums, tanks, and ships are caulked after riveting is completed. If a seam is to be caulked, it must be designed with that in mind. The spacing of the rivets along the joint must be sufficiently close so that the outer plate will not bulge between rivets, and the distance from the caulked edge to the first row of rivets must be small enough to prevent bulging in that direction.

Special chisel-shaped tools, operated with air hammers, are used for caulking riveted seams. A tool with two parallel edges is first used to score the edge of the outer plate and the face of the under one. Next, a blunt or square-edged chisel is passed along the scored grooves one or more times to seal the joint. Water or air pressure is then applied to the inside of the tank and the joint is examined for leaks. When water is used for testing, leaks are easily detectable through visual examination. When air is used for testing, leaks may be made visible by applying soap and water to the seam and looking for the expansion of the soap bubbles. If leaks appear, the joint is hammered with the caulking tools until all leaks have been stopped.

Boats Building

Boat building, one of the oldest branches of engineering, is concerned with constructing the hulls of boats and, for sailboats, the masts, spars and rigging.


Traditional boat building in South East Maluku, Indonesia

Parts

Bow - the front and generally sharp end of the hull. It is designed to reduce the resistance of the hull cutting through water and should be tall enough to prevent water from easily washing over the top of the hull.

Bulkhead - the internal walls of the hull.

Chines - are long, longitudinal strips on hydroplaning hulls that deflect downwards the spray that is produced by the hull when it travels at speed in the water. The term also refers to distinct changes in angle of the hull sections, where the bottom blends into the sides of a flat bottomed skiff, for instance. A hull may have 2 or more chines to allow an approximation of a round bottomed shape with flat panels. It also refers to the longitudinal members inside the hull which support the edges of these panels.

Deck - the top surface of the hull keeps water and weather out of the hull and allows the crew to stand safely and operate the boat more easily. It stiffens an enclosed hull.

Gunwale - The upper longitudinal structural member of the hull. Cannons were bolted to this in the earliest gun armed warships.

Keel - the main central member along the length of the bottom of the boat. It is an important part of the boat's structure which also has a strong influence on its turning performance and, in sailing boats, resists the sideways pressure of the wind

Keelson - an internal beam fixed to the top of the keel to strengthen the joint of the upper members of the boat to the keel.

Rudder - a steering device at the rear of the hull created by a turnable blade on a vertical axis.

Sheer - the generally curved shape of the top of the hull. The sheer is traditionally lowest amidships to maximize freeboard at the ends of the hull. Sheers can be reverse, higher in the middle, to maximize space inside or straight or a combination of shapes.

Stem - a continuation of the keel upwards at the front of the hull.

Stern - the back of the boat.

Strake - a strip of material running longitudinally along the vessel's side, bilge or bottom.

Transom - a wide, flat, sometimes vertical board at the rear of the hull, which, on small power boats, is often designed to carry an outboard motor. Transoms increase width and also buoyancy at the stern.

Construction materials and methods

Wood
The traditional boat building material that was and is still used for hull and spar construction. It is buoyant, cheap, widely available and easily worked. It is not particularly abrasion resistant and it can deteriorate if fresh water or marine organisms are allowed to penetrate the wood. Rot resistant woods such as cedar and oak are generally selected for wooden boat construction. Glue, screws and/or nails are used to join the wooden components. Some types of wood construction include:

1. Carvel, in which a smooth hull is formed by wooden planks attached to a frame. The planks may be curved in cross section like barrel staves. Carvel planks are generally caulked with oakum or cotton that is driven into the seams between the planks and covered with some waterproof substance. It takes its name from an archaic ship type and is believed to have originated in the Mediterranean.
2. Another method of building wooden boats is lapstrake, a technique originally identified with the Vikings in which wooden planks are fixed to each other with a slight overlap that is beveled for a tight fit. The planks may be mechanically connected to each other with copper rivets, bent over iron nails, screws or with adhesives. Often, steam bent wooden frames are fitted inside the hull. This technique is known as clinker in Britain and also as clench built.
3. Another method uses sheets of plywood panels fixed to a frame. Plywood may be laminated into a round hull or used in single sheets. These hulls generally have one or more chines. A type of the plywood panel boat building method is known as the stitch-and-glue method, where pre-shaped panels of plywood are edge glued and reinforced with fibreglass without the use of a frame. Metal or plastic wires pull curved flat panels into three dimensional curved shapes. These hulls generally have one or more chines.

Steel (and before that iron)
Either used in sheet for all-metal hulls or for isolated structural members. It is strong, but heavy. The material rusts unless protected from water. Modern steel components are welded or bolted together. Until the mid 1900s, steel sheets were riveted together.

Aluminium
Either used in sheet for all-metal hulls or for isolated structural members. Many sailing spars are made of aluminium. The material requires special manufacturing techniques, construction tools and construction skills. While it is easy to cut, aluminium is difficult to weld, and also requires heat treatments such as precipitation strengthening for most applications. Corrosion is a concern with aluminium, particularly below the waterline.

Fiberglass (Glass-reinforced plastic or GRP)
Typically used for production boats because of its ability to reuse a female mold as the foundation for the shape of the boat. The resulting structure is strong in tension but often needs to be either laid up with many heavy layers of resin-saturated fiberglass or reinforced with wood or foam in order to provide stiffness. GRP hulls are largely free of corrosion though not normally fireproof. These can be solid fiberglass or of the sandwich (cored) type, in which a core of balsa, foam or similar material is applied after the outer layer of fiberglass is laid to the mold, but before the inner skin is laid. This is similar to the next type, composite, but is not usually classified as composite, since the core material in this case does not provide much additional strength. It does, however, increase stiffness, which means that less resin and fiberglass cloth can be used in order to save weight. Most fiberglass boats are currently made in an open mold, with fiberglass and resin applied by hand. Some are now constructed by vacuum infusion where the fibers are laid out and resin is pulled into the mold by atmospheric pressure. This can produce stronger parts with more glass and less resin, but takes special materials and more technical knowledge.

Composite
While GRP, wood, and even concrete hulls are technically made of composite materials, the term "composite" is often used for plastics reinforced with fibers other than (or in addition to) glass. Cold-molded refers to a type of building one-off hulls using thin strips of wood applied to a series of forms at 45-degree angles to the centerline. This method is often called double-diagonal because a minimum of two layers is recommended, each occurring at opposing 45-degree angles. "Cold-molding" is now a relatively archaic term because the contrasting "hot-molded" method of building boats, which used ovens to heat and cure the resin, has not been widely used since WWII. Now almost all curing is done at room temperature. Other composite types include sheathed-strip, which uses (usually) a single layer of strips laid up parallel to the sheer line. The composite materials in question are then applied to the mold in the form of a thermosetting plastic (usually epoxy, polyester, or vinylester) and some kind of fiber cloth (fiberglass, kevlar, dynel, carbon fiber, etc), hence the finished hull is a "composite" of fiber and resin. These methods often give strength-to-weight ratios approaching that of aluminum, while requiring less specialized tools and skills.

Steel-reinforced cement (ferrocement)
Strong and long lasting. First developed in the mid 19th Century in France. Used for building warships during the war. Extensively refined in New Zealand shipyards in the 1950s and the material became popular among amateur builders of cruising sailboats in the 1970s and 1980s, because the material cost was cheap although the labour time element was high. The weight of a finished ferrocement boat is comparable to that of a traditionally built wooden boat. As such they are often built for slower, more comfortable sea passages. Hulls built properly of ferrocement are more labor-intensive than steel or fiberglass, so there are few examples of commercial shipyards using this material. The inability to mass produce boats in ferrocement has led there to there being few examples around. Many ferrocement boats built in back yards have a rough, lumpy look, which has helped to give the material a poor reputation. The ferrocement method is easy to do, but it is also easy to do wrong. This has led to some disastrous 'home-built' boats. Properly designed, built and plastered ferrocement boats have smooth hulls with fine lines, and therefore are often mistaken for wooden or fiberglass boats. See also concrete ship, concrete canoe.

Hull types

Round bilge hull - As its name implies, the hulls of these vessels are rounded and don't usually have any chines or corners.

Chined hull - These are hulls made up of flat panels. The flat panels are commonly made of plywood sheets, but some use more traditional methods of planking. Chined hulls range from flat bottomed boats such as banks dories, sharpies and skiffs, the side and bottom are 2 distinct pieces meeting at a sharp angle known as the chine. Flat bottomed boats are simple to build and shallow in draft. Most are intended for use in protected waters, though the banks dory evolved as a fishing boat in the open Atlantic. There are also many multichine boats that have more than the one chine each side of the flat bottomed boat. This can allow a round bilge hull shape to be approximated.

Displacement hulls - These are hulls which have a shape which does not promote planing. They travel through the water at a limited rate which is defined by the waterline length. They are often heavier than planing types, though not always.

Planing hulls - These are hulls with a shape that allows the boat to rise higher and higher out of the water as the speed increases. They are sometmes flat-bottomed, sometimes V-bottomed and sometimes round-bilged. The most common form is to have at least one chine to allow for stability when cornering and for a supportive surface on which to ride while planing. Planing hulls allow higher speeds to be achieved, and are not limited by the waterline length the way displacement hulls are. They do require more energy to achieve these speeds.

Boats and Boatbuilding

Boats and Boatbuilding, types and construction of any small, waterborne vessel that displaces and excludes the water surrounding it. Traditionally, boats were distinguished from ships by size—any vessel small enough to be carried aboard a ship was considered a boat. Today, the boundary between boats and ships is no longer defined with precision. Some larger vessels are called boats, although they are longer than some ships. This article focuses primarily on the design and construction of craft less than 20 m (65 ft) long. For a discussion of the history of all waterborne vessels.



Types of Boats
Boats are used in a number of ways. They can be purely recreational, or they can have more practical uses, such as serving as a home or as a method of transportation. Even boats with similar uses may differ in other respects. For example, methods of propulsion range from oars, to mechanical engines, to wind-catching sails.

Boats are classified primarily by method of propulsion—for example, sailboat, motorboat, and rowboat. They are also classified according to function, method of construction and type of materials used, rigging (in sailboats), and other factors.

Basics of Boat Design

Parts of a Sailboat
Although sailboat design varies widely, all sailboats share a few basic components. The boat’s main body is called the hull. The front of the hull is referred to as the bow, while the rear of the hull is called the stern. The rudder extends from the stern and is used to steer the boat. The centerboard, under the hull, helps sailors maintain a steady course by limiting the boat’s movement from side to side. The mast and the boom support the boat’s sails. The mainsail, the largest sail on a sailboat, is fastened to both the mast and the boom. The triangular sail in front of the mast is called the jib.

Only a few basic components are common to most boats of traditional style. The keel is a timber or other element running the length of the bottom of a boat along the center from the bow, or front, to the stern, or rear. The keel serves as the foundation for the frame, which is covered with a waterproof material to form the hull—the body of the boat. The terms keel, frame, and hull are also used in describing modern boats that are not built but are molded in one piece.

I. Buoyancy and Weight

For an object to float on the water’s surface, it must sink enough to displace a volume of water equal to its own weight. For example, if a boat is to carry three people, their fishing gear, an outboard motor, and a supply of fuel—a total weight of about 500 kg (1,100 lb)—then the boat must be made long and large enough to displace 500 kg (1,100 lb) of water without sinking below the water level. Boat designers also have to take into account the weight of the boat itself. The heavier the material used to build the boat, the larger the boat has to be.

II. Trim and Stability

In addition to considering the total weight of the boat and its contents, boat designers must also consider the distribution of weight. The weight of an outboard motor at the stern of a small boat tends to make the boat sink deeply in the water at that end (to “trim the stern”). If that tendency cannot be offset by placing a similar weight in the bow of the boat, then the offsetting must be obtained by broadening the hull at its aft, or back, end so that a greater part of the displacement occurs near the excess weight.

A balance of weights from side to side must also be arranged. Further, to lessen the danger of capsizing, the combined center of gravity of all weights must be sufficiently low in the boat. If other factors make it necessary that the center of gravity be high, then the chance of capsizing must be offset by increasing the width of the hull.

III. Structure

A boat must maintain its shape in the face of local internal weights, such as an engine or a heavy cargo, and it must be strong enough to resist the force of battering waves. Because a hull of sufficient strength can be built of thin material, the risk of local puncture can be great in a boat that is otherwise quite strong. For example, a traditional boat built of skins or of bark, or a modern inflatable boat, are sufficiently strong and buoyant, but all are vulnerable to puncture or perforation.

IV. Watertightness

Boats must also be watertight—that is, invulnerable to leakage through the joints of adjoining pieces. Boatbuilders made wood plank boats watertight by caulking between planks with fiber threads, pitch, or a combination of these materials. For boats of skin or bark, filling interstices with pitch was common practice. The contemporary practice of molding a hull eliminates the problem entirely. Without seams there is no possibility of leakage.

Skin and Bark Boats

The earliest known boats were constructed from a frame of animal bone or light wood covered by animal skins or bark. Historians believe people used such boats as early as 16,000 bc. Several thousand years later, round skin boats, called coracles, were developed in Asia, Africa, the British Isles, and the plains of North America. Coracles have been built in Ireland in fairly recent times. They typically have a framework of woven willow shoots or other soft wood suitable for basketmaking.


Kayak
A kayaker paddles on San Francisco Bay. First used by the Inuit thousands of years ago for fishing and hunting, kayaks are widely used today for recreation. Kayaks have an enclosed deck and an open cockpit, where the rower sits with a double-bladed paddle.

Another type of skin boat is the kayak, a type of canoe created by the Inuit. The kayak is completely enclosed with animal skins stretched over a rigid frame, except for an open cockpit in the center, where the paddler sits armed with a double-bladed paddle. The kayak is wide at the center and tapers to points at both bow and stern. Kayaks in use today have much the same shape that kayaks had centuries ago, although modern kayaks may be molded from plastic, fiberglass, or Kevlar (a synthetic fiber originally developed to replace the steel in radial tires).

Bark-covered boats came into use about the same time that skin-covered boats did. They typically had a light wood frame with a bark covering made of pieces sewn together with root fiber. The frame was separated from the bark covering by a plank sheathing. Gunwales, or side edges, ran from bow to stern and provided longitudinal strength to the frame. The sheathing was held in place by forcing the ribs of the frame under the gunwales. Birchbark canoes up to 14 m (46 ft) long are known to have been built in North America. Modern canoes still have the basic shape and design of their predecessors, but they are usually molded from aluminum, plastic, fiberglass, or other lightweight, durable material.

Ancient Egyptians fashioned reed skiffs by securely binding together bundles of papyrus stems. The extreme lightness of these reed boats made them ideal for fishing in the marshes along the Nile; moreover, they were easy to carry. Equipped with sails and oars, the reed boats also carried cargo and passengers.

Wooden Boats

The earliest wooden boat, a dugout, dates from about 6000 bc and was discovered in what is now The Netherlands. A dugout consists of a log hollowed out with tools or by controlled burning. Early boat builders also constructed craft of sewn planks. This form of construction was used extensively throughout history. Sewn-timber construction was common among the peoples of the Pacific Islands, whose dugouts often had topsides formed of irregular sewn pieces of timber.


Dugout Canoes
Dugout canoes are made from hollowed-out tree trunks and thus are naturally buoyant. They may be plain or elaborately decorated like the two pictured.

Craft constructed of wood planks appear to have been developed gradually from the modified dugout by about 5000 bc, or even earlier in some regions. Log construction methods were also used for ancient Egyptian boats, in which short planks of timber were bolted edge to edge to form a hull.

Framing and planking are the basic components of modern wooden boats. The frame is used to support and stiffen the hull, including the stem, keel, keelson, ribs, knees, and wales. The planking is the outer shell that is fastened to the framing.

I. Lapstrake Construction

In northern Europe, lapstrake, or overlapping, construction was developed to a high order by the 9th century ad, particularly by the Scandinavians. Lapstrake is also known as clinch-built or clinker-built construction. Planks apparently were split off a log by means of wedges, or they were hewn and assembled on the keel, one after another beginning with the garboard, the lowest. In the Viking ships and boats of the 10th century and somewhat later, lashings were still used to secure the planks to the frames. Such construction resulted in a very flexible hull, yet one of relatively great strength. The lashings eventually were replaced by through fastenings, that is, by pegs, and later were replaced by nails driven into the planking and frames.


Viking Ship
This Viking ship, on display at the Viking Museum in Oslo, Norway, is an example of lapstrake construction. In Viking ships of the 9th century and later, external planks were overlapped and lashed to the ship’s frame, producing a strong, flexible hull.

In lapstrake construction the longitudinal seams of the planking are formed by overlapping the edges enough to allow continuous nailing. Thus, the skin, or exterior planking, adds strength to the boat. Frames are then added to give the required stiffness of form. Originally the frames were hewn of natural-crook timber, including root or limb knees and crooked trunks. Steam-bent frames became popular in the early 19th century.

II. Carvel Construction

The smooth-planked, or carvel-built, boat was developed in the Mediterranean region and was probably a natural evolution of the craft constructed of short planks bolted edge to edge used by the ancient Egyptians. Plank and frame construction was probably fully developed before ancient Greece rose to maritime prominence. As in lapstrake construction, the use of pegs probably preceded the use of metal fastenings between plank and framing.


Constructing a Wooden Whaler
Wooden ships like this 8-m (26-ft) whaler are built in stages. Because the timber must be steamed into the properly curved shapes, a fairly complex skeleton and bracing system is needed. Here, workers place horizontal planks called strakes to form the smooth curve of the hull on the starboard side of the ship.

A framing system made of almost equally spaced transverse frames fastened to a continuous keel and strengthened by a pair of gunwales running from bow to stern was a logical step in the development of smooth-planked boats. The problem of seam leakage was solved by using wood tar and caulking material, as in earlier lapstrake craft.

In so-called smooth-lap construction, developed in the 19th century, plank edges are rabbeted, or shaped, so that they lap and still remain smooth at the seams; the rabbeted laps are nailed in the usual lapstrake manner. See Woodworking: Carpentry.

In the early 20th century the use of lapstrake construction decreased, while carvel construction became more popular. The shift was caused largely by the need for extreme structural strength necessitated by the use of motors in small boats. Carvel construction also better met the demand for fast sailing craft used for racing.

III. Plywood Construction

Plywood boat construction began in the United States about 1918 and developed rapidly; the two basic types are paneled and molded. Panel construction involves securing flat sheets of plywood to transverse frames and to the keel and other units that supply longitudinal strength; it is used only with chine-model boats, that is, those with flat bottoms or V-bottoms. The amount of compound curve that may be used in a plywood panel is extremely limited.


Fishing in Newfoundland and Labrador
Plywood panel boats are flat-bottomed, a hull shape that lends itself well to fishing. Here, workers on a fishing boat haul a fish trap aboard off the coast of Cape Spear, the easternmost point in North America.

In molded-plywood construction the form of the boat is established by temporary transverse frames, or molds, and by longitudinal battens (thin, narrow strips of lumber often used to seal or reinforce joints), over which the planking is placed in two or three layers. The first skin is laid on diagonally and secured to the form by staples. Two or three skins are used, and after stapling, the mold is moved into a heating and pressure stage in which adhesion of the skins is accomplished. After adhesion, stiffeners and joinery are added; these usually include keelson, shoe, gunwale, guards, thwarts, decking, outside stem, transom (in a square-stern boat), and centerboard case and mast step (in a sailing hull).

Canvas-Covered Boats

In the construction of canvas-covered small boats, very thin planking is laid over light steam-bent frames; then canvas is stretched tightly over the hull by clamps and a tackle at bow and stern. After the canvas is secured, it is coated with a thin primer or is first wetted with water. The canvas shrinks as it dries, making a smooth surface. The canvas is then painted, outside guards are fitted at the gunwales, and an external keel and stempost and sternpost are fitted. The result is a light and tight boat suited for easy carrying and occasional use.

Aluminum Boats

The first aluminum boats built in the United States were for the polar expedition of American journalist and explorer Walter Wellman in 1894, although the first known use of aluminum was in Europe in 1891. After World War II (1939-1945), aluminum boats became common, usually in the form of canoes or simple craft used for sport fishing. These boats are built from sheets of aluminum, perhaps given curvature by stamping, and are fastened together with rivets. Sandwich-type constructions, intended to increase both lightness and strength, are under development.

Ferrocement Boats

Ferrocement, a closely spaced wire mesh made watertight by plastering of concrete, has some advantage for boats that must be built in small numbers by unskilled workers without sophisticated tools. Waterproof cloth can be formed into boat-shaped bags, which are then inflated to make small craft that are suitable and popular for some uses.

Fiberglass Boats

The greatest number of boats today are molded from composite plastic materials. The mold is a cavity having the exact shape of the boat.

Construction of the boat involves :
(1) Coating the interior of the cavity with a liquid plastic,
(2) Laying on reinforcing material in the form of a cloth or mat of fibers,
(3) Saturating the reinforcing material with liquid plastic,
(4) Possibly applying a layer of lightweight core material, and
(5) Applying more reinforcing and plastic.

The plastic hardens under the action of a catalyst that has been mixed with it; heat may be applied to hasten the hardening action. The result is a strong and relatively lightweight hull that has been built quickly and without the necessity for great skill on the part of builders.

In many cases, interior structure, such as bulkheads and foundations for an engine, is inserted while the hull is in the mold. The interior structure is then bonded to the hull by the plastic and its reinforcement.

The plastic used is generally a resin of the polyester type. Epoxy and vinyl ester resins are also used. The reinforcing material is often a glass fiber, giving rise to the generic term fiberglass boat. Structures of successively greater strength and stiffness for a given weight can be produced with Kevlar or carbon fiber reinforcement.

A core is required to give the composite structure the thickness needed for adequate stiffness and to make it resistant to puncture. If the part being molded is a flat sheet, such as an interior bulkhead, the core is likely to be a sheet of plywood. If a low-weight bulkhead is required, aluminum formed into a honeycomb is a likely core. Sheets of balsa wood or PVC (polyvinylchloride) plastic can also be used where lightness is important. For the sharp curvature common to boat hulls, the core sheets are provided with the material cut into small squares and attached to a cloth sheet. With balsa, they are arranged with the grain of the wood perpendicular to the sheet; the final structure then has a high resistance to impacts and crushing loads because of the natural strength of wood in the direction of its fibers.

Measuring and Modeling Boats

In primitive boatbuilding, the builder often used width of hand, length of forearm, and length between knuckles as units of measurement. Notched sticks also were used for measuring. More advanced building methods, using molds, required that the keel, the stem, and the sternpost be set up on stakes or blocks and that an arbitrary midship frame be erected in place. The curved members required for this frame were made from molds, used by shifting the butts to produce boats of varying size but similar form. After the midsection frame was put in place, two or more battens on each side were secured, one to form the sheer line, one along the turn of the bilge, and often one along the ends of the floor timbers, or short frame members, that crossed the keel. Sometimes other battens were fitted between the bilge and sheer battens and between the bilge and floorhead battens. Individual frame members were then shaped to fit inside the battens at selected intervals; when all the frames were made, the battens were removed and the hull was planked. All frames were hewn from crooked timber.

I. The Half-Model

The next development in boatbuilding was the use of drawings and the builders' half-model. Using drawings to delineate the shape of the hull apparently evolved slowly, but records are obscure. Similarly, little is known of the evolution of the half-model, but it appears to have developed along with the use of drawings. It is known that the use of such plans was common in 16th-century England, during the reign of Queen Elizabeth I, and Mediterranean builders probably employed crude drawings at least as early as the beginning of the 15th century. According to some authorities, the ancient Greeks and Romans also used drawings in shipbuilding and boatbuilding.

By the middle of the 17th century the art of designing boats by drawing plans was known throughout Europe. The sections were formed by compound curves made with the compass; the longitudinal curves were arbitrarily made according to the same principles that had governed the use of battens. The designers employed shifting molds based on the midsection form, so that one set of frame molds could be used by shifting butts to form all the frames; this system became known as whole molding. The boat design was drawn to reduced scale, and then, in a process known as lofting, a full-size drawing of the ship or boat was made. By 1800 drawing up the plans for ships and boats was fully developed, as was the lofting process.

The use of the half-model in lieu of the reduced-scale drawing appears to have originated in Europe at an early date; by the early 18th century carving a model from a solid block of wood was a popular method of design in commercial boatyards and shipyards. The shape of the model was determined by the judgment and art of its maker. The sections needed to form the mold frames controlling the hull shape of the boat were obtained by sawing the model at the desired transverse mold stations and scaling off these sections by drawing ordinates.

II. Lift Models and Lofting

By the middle of the 18th century, builders had developed another type of model, consisting of a blackboard cut to the shape of the hull profile, with the sections formed of thin plank secured at the desired mold stations. The sections were made fair, or capable of being planked smoothly, by battens at suitable locations. Finally, about 1795, the so-called lift model was developed, made of boards of equal thickness pegged together and shaped to the desired hull form. The shape of the mold frames was obtained by taking the model apart and tracing the shape of the lifts, or planks, in their proper relation to one another. By drawing lines across these shapes at frame stations, the transverse widths at the ordinates formed by the lift thicknesses could be determined. The lift model is still in use in many boatyards and remains practical for small craft.

Lofting consists of drawing the full-size shape of the hull on a suitable platform or floor. The required drawing shows the mold sections, or transverse forms, usually five to seven in number. These sections usually are tested by drawing in some longitudinal curves, such as the sheer, and a few waterlines or level lines duplicating the so-called lift lines of a half-model. In addition, buttock and bow lines, longitudinal vertical sections parallel to the centerline of the hull, may be used. Diagonals, representing the batten curves over the molds, may be drawn in. In making the longitudinal drawing, the profile of the hull usually is drawn full size. Lofting is an important operation in boatbuilding, for it is the only way a design may be reproduced accurately or repeatedly. In the more advanced boatshops the structural details also are drawn full size, the lofting being done in minute detail.

Boat Propulsion

Inboard-Outboard Motorboat
Motorboats are popular recreational vehicles, present on many lakes and oceans throughout the world. Inboard-outboard (I/O) motorboats such as this Donzi Z-25 are capable of reaching speeds of 80 kilometers per hour (50 miles per hour).

Until the 20th century, boats were propelled by oar and sail (see Sailing), just as they had been since ancient times. Paddles and poles (for pushing against the bottom of the waterway) were variations on the oar suitable for small craft. The rapid rise of the steam engine to dominance among ships did not affect boats until the late 19th century, when steam engines and boilers had become compact enough to fit into a small hull. The age of steam-propelled boats was brief, however, for the advent of commercial internal-combustion engines came within a few years of boat-size steam machinery. By the late 20th century, the internal-combustion engine, either in diesel or spark-ignition (gasoline) form, had become almost universal in boat propulsion, save for sail, oar, and paddle that survive with many types of recreational boats (see Motorboat).

I. Inboard Motors

The internal-combustion engine was applied to boats as early as the 1880s, and many two- and four-cycle engines of one cylinder or more were developed. The engine, permanently mounted inside the hull, drives a screw propeller by means of a horizontal shaft. Today many of these engines are automotive or truck engines that have been altered superficially to make them suitable for marine service.


Cabin Cruiser
Powerboats are popular as a leisurely form of yachting. A modern yacht may include a kitchen, sleeping cabins, and other conveniences below decks.

A variation on the inboard engine arrangement is to place the engine horizontally at the extreme stern of the boat, connected through a watertight aperture in the stern to a lower unit that is similar to the housing for the right-angle gears of an outboard motor. Craft with such engines are called I/O (inboard/outboard) boats.

II. Outboard Motors


Outboard Motors
Outboard motors, like the ones mounted on these skiffs, are the most common means of propulsion for boats. Because it is mounted external to the hull, the motor is adaptable to almost any boat.

The outboard motor is probably the most common means of propulsion for boats. This machine is nearly always a two-stroke spark-ignition (gasoline) engine, mounted vertically at the stern of a boat in order to drive a shaft that in turn drives a conventional screw propeller through right-angle gears. It has the great virtue of being mounted external to the hull, thus being easily adaptable to almost any boat. Outboard motors operate on a mixture of gasoline and marine oil.

The development of the outboard motor was rather slow in the early years of the 20th century. After World War I (1914-1918), the popularity of the outboard motor grew steadily, and as a result its power gradually was increased, and it was made more reliable. The popularity of the outboard motor increased tremendously after World War II (1939-1945), and small cruisers, runabouts, utility boats, and various classes of racers became available. By the late 1970s, powerful outboard motors, ranging up to 200 horsepower rating, were available, as was special equipment for handling such engines at the water's edge. The use of two outboard motors on cruisers and runabouts was common.

Because of the great power available and because the low transom required by this type of motor creates the danger of the boat being swamped, the safety of the outboard motorboat has become a matter of public and governmental concern. The popularity of this type of boat also has produced crowded waters at lake and seaside resorts. In many areas measures have been adopted to prevent accidents caused by excessive speed, careless or reckless operation, and poor boat design.

III. Water-Jet Drive

Several innovations in propulsion became important during the late 20th century. One is propulsion by a high-speed jet of water ejected from the stern by a pump within the boat hull. The pump is driven by an engine that is identical to the one that might drive the conventional propeller. Water-jet propulsion is most suitable for high-speed boats, since for good propulsion efficiency the forward speed of the boat must be close in magnitude to the afterward speed of the jet. Regardless of boat speed, water-jet propulsion is often used for craft that must operate in shallow or rocky waters, where a conventional propeller might be damaged.

IV. Surface-Piercing Propeller

An innovation of great interest to designers and users of high-speed boats that was introduced in the 1970s is the surface-piercing propeller, in which the propeller is mounted with its center at the water surface. It is most commonly seen in the form called the Arneson surface drive. The drive shaft projects through the stern of the boat, supported by two hydraulic cylinders that adjust the vertical position of the propeller, a feature of great importance because the angle and level of the boat change as the boat speed changes. The engine is fixed in its position, but two universal joints accommodate changing shaft angles.

Merchant Ships

Merchant ships are classified as passenger carriers, cargo ships, and tankers. During the height of passenger travel by ship, the largest as well as the most glamorous ships afloat were the famed liners of the North Atlantic, which, beginning in the mid-19th century, sailed regular schedules between the Americas and Europe. Competing in speed as well as in size and appointments, such ships as the Mauretania, the Queen Mary, the Queen Elizabeth, the United States, and the France gradually reduced the time for the North Atlantic crossing to less than four days. Their size, from about 45,000 to 75,000 metric tons and up to 300 m (1,000 ft) in length, was gigantic by the standards of the first half of the 20th century, but they have been dwarfed by the oil tankers of the 1970s and '80s. Today's passenger liners operate principally in the cruise trade.

I. Cargo Ships

Unloading a Cargo Ship
A large cargo ship is unloaded at the Brooklyn pier in New York. Both containers and wooden crates protect the shipped goods from destruction and vandalism.

Cargo ships carry packaged goods, unitized cargo (cargo in which a number of items are consolidated into one large shipping unit for easier handling), and limited amounts of grain, ore, and liquids such as latex and edible oils. A few passengers are accepted on some cargo liners. Specialized ships are designed and built to carry certain types of cargo, for example, automobiles or grain.

II. Container Ships



In the late 1950s container ships set the pattern for technological change in cargo handling and linked the trucking industry to deep-Sea shipping. These highly specialized ships carry large truck bodies and can discharge and load in one day, in contrast to the ten days required by conventional ships of the same size. The rapid development of the container ship began in 1956, when Sea-Land Service commenced operations between New York City and Houston, Texas. Barge-aboard, or lighter-aboard, ships, also called seabees (sea barges) or LASH (lighter-aboard ships), resulted from an evolutionary development of the container ship. They are capable of carrying about 38 barges, or up to 1,600 containers, or a combination of containers and barges. Their design enables them to deliver cargo to developed or undeveloped ports, without the need for berthing.

III. Tankers

Oil Tanker
As their name suggests, tankers are mammoth floating tanks that transport liquid cargo such as petroleum and natural gas. A tanker has several individual compartments inside the main body, allowing it to carry thousands of tons of petroleum. Under the Oil Pollution Act of 1990, passed by the United States Congress, tankers with single hulls are to be gradually phased out and replaced by double-hulled tankers. Single-hulled tankers have been responsible for devastating oil spills that have polluted beaches and killed marine life. Under the legislation, only tankers with double hulls will be able to enter U.S. waters by the year 2015.

Tankers, designed specifically to carry liquid cargoes, usually petroleum, have grown to many-compartmented giants of a million metric tons and more. Despite their great size, their construction is simple, as is, for the most part, their operation. A major problem with the giant tankers is the severe environmental damage of oil spills, resulting from collision, storm damage, or leakage from other causes.
Specialized tankers transport liquefied natural gas (LNG), liquid chemicals, wine, molasses, and refrigerated products.

IV. Treaties and Conventions

Many treaties and conventions have been adopted over the years with the objective of increasing the safety of life at sea. One of the most important agreements provided for the establishment of the International Iceberg Patrol in 1913, after the Titanic disaster. Under the International Load-Line Convention of 1930, ship loading was regulated on the basis of size, cargo, and route of the vessel. The International Convention for the Safety of Life at Sea, which governs ship construction, was ratified by most maritime nations in 1936, and updated in 1948, and again in 1960 and 1974.

Nature of the Shipping Industry

Shipping is a private, highly competitive service industry. The activity of the industry is divided into several categories, namely, liner service, tramp shipping, industrial service, and tanker operation, all of which operate on certain well-established routes.

I. Trade Routes

Most of the world's shipping travels a relatively small number of major ocean routes: the North Atlantic, between Europe and eastern North America; the Mediterranean-Asian route via the Suez Canal; the Panama Canal route connecting Europe and the eastern American coasts with the western American coasts and Asia; the South African route linking Europe and America with Africa; the South American route from Europe and North America to South America; the North Pacific route linking western America with Japan and China; and the South Pacific route from western America to Australia, New Zealand, Indonesia, and southern Asia. The old Cape of Good Hope route pioneered by Vasco da Gama and shortened by the Suez Canal has returned to use for giant oil tankers plying between the Persian Gulf and Europe and America. Many shorter routes, including coastal routes, are heavily traveled.

Major Shipping Trade Routes
This map shows shipping routes from the perspective of the north pole, which falls roughly at the map’s center. Called a polar-azimuthal map, it was created by flattening the globe from the top, which provides a better understanding of the way the routes curve around the planet. Although there are hundreds of potential shipping paths across the world’s oceans, almost all ships travel on a few well-established routes. Determined by geography, economics, and historical tradition, the routes serve to connect major industrial regions to one another and to areas that produce raw materials.

II. Coastwise Shipping

Technically, coastal shipping is conducted within 32 km (within 20 mi) of the shoreline, but in practice ship lanes often extend beyond that distance, for reasons of economy and safety of operation. In the U.S., coastal shipping is conducted along the Pacific, Atlantic, and Gulf coasts. Under the restriction known as cabotage, the U.S. and many other nations permit only vessels registered under the national flag to engage in coastal trade. Among many small European countries cabotage does not apply, and short international voyages are common. A special feature of coastal shipping in the U.S. is the trade between the Pacific coast and the Atlantic and Gulf coasts. Vessels engaged in this trade traverse the open sea and utilize the Panama Canal; however, they are covered by cabotage laws. In coastal and short-distance shipping, special-purpose ships are often employed, such as car ferries and train ferries.

III. Inland Waterways

A major part of all the world's shipping moves on inland waterways—rivers, canals, and lakes. Usually such shipping employs smaller, lighter vessels, although in some cases oceangoing ships navigate inland waterways, for example, the St. Lawrence Seaway route to the Great Lakes of North America. Containerization, lighter-aboard-ship, and barge-aboard-ship operations have facilitated the shipping of cargoes between oceangoing vessels and those of the inland waterways.

IV. Liner Services

Liner service consists of regularly scheduled shipping operations on fixed routes. Cargoes are accepted under a bill-of-lading contract issued by the ship operator to the shipper.

Competition in liner service is regulated generally by agreements, known as conferences, among the shipowners. These conferences stabilize conditions of competition and set passenger fares or freight rates for all members of the conferences. In the U.S., steamship conferences are supervised by the Federal Maritime Commission in accordance with the Shipping Act of 1916. Rate changes, modifications of agreements, and other joint activities must be approved by the commission before they are effective. Measures designed to eliminate or prevent competition are prohibited by law.

V. Tramp Shipping

Tramps, known also as general-service ships, maintain neither regular routes nor regular service. Usually tramps carry shipload lots of the same commodity for a single shipper. Such cargoes generally consist of bulk raw or low-value material, such as grain, ore, or coal, for which inexpensive transportation is required. About 30 percent of U.S. foreign commerce is carried in tramps.

Tramps are classified on the basis of employment rather than of ship design. The typical tramp operates under a charter party, that is, a contract for the use of the vessel.

The center of the chartering business is the Baltic Exchange in London, where brokers representing shippers meet with shipowners or their representatives to arrange the agreements. Freight rates fluctuate according to supply and demand: When cargoes are fewer than ships, rates are low. Charter rates are also affected by various other circumstances, such as crop failures and political crises.

Charter parties are of three kinds, namely, the voyage charter, the time charter, and the bareboat charter. The voyage charter, the most common of the three, provides transport for a single voyage, and designated cargo between two ports in consideration of an agreed fee. The charterer provides all loading and discharging berths and port agents to handle the ship, and the shipowner is responsible for providing the crew, operating the ship, and assuming all costs in connection with the voyage, unless an agreement is made to the contrary. The time charter provides for lease of the ship and crew for an agreed period of time. The time charter does not specify the cargo to be carried but places the ship at the disposal of the charterer, who must assume the cost of fuel and port fees. The bareboat charter provides for the lease of the ship to a charterer who has the operating organization for complete management of the ship. The bareboat charter transfers the ship, in all but legal title, to the charterer, who provides the crew and becomes responsible for all aspects of its operation.

The leading tramp-owning and tramp-operating nations of the world are Norway, Britain, the Netherlands, and Greece. The carrying capacity of a typical, modern, well-designed tramp ship is about 12,000 dwt, and its speed is about 15 knots. The recent trend is toward tramps of 30,000 dwt, without much increase in speed.

VI. Industrial Carriers

Industrial carriers are vessels operated by large corporations to provide transportation essential to the processes of manufacture and distribution. These vessels are run to ports and on schedules determined by the specific needs of the owners. The ships may belong to the corporations or may be chartered. For example, the Bethlehem Steel Corp. maintains a fleet of Great Lakes ore carriers, a number of specialized ships that haul ore from South America to Baltimore, Maryland, and a fleet of dry-cargo ships that transports steel products from Baltimore to the Pacific coast. Many oil companies maintain large fleets of deep-sea tankers, towboats, and river barges to carry petroleum to and from refineries.

VII. Tanker Operation

All tankers are private or contract carriers. In the 1970s some 34 percent of the world tanker fleet, which aggregates about 200 million dwt, was owned by oil companies; the remaining tonnage belonged to independent shipowners who chartered their vessels to the oil companies. So-called supertankers, which exceed 100,000 dwt, are employed to transport crude petroleum from the oil fields to refineries. The refined products, such as gasoline, kerosene, and lubricating oils, are distributed by smaller tankers, generally less than 30,000 dwt, and by barges.

History of Shipping Industry

Commercial shipping began perhaps with the activities of the Phoenician merchants who operated their own vessels, transporting goods in the Mediterranean. The practices they developed were adopted by the merchants of ancient Greece and Rome and were continued by the maritime powers through the Middle Ages to modern times. The Venetians, from 1300 to 1500, owned a huge merchant fleet that served the interests of the merchant traders and the city-state exclusively. From 1600 to 1650 the Dutch ranked first in shipping activity, operating a globe-circling tramp service for merchants of western Europe.

Advances in the 19th Century

Until the 19th century, ships were owned by the merchant or by the trading company; common-carrier service did not exist.

On January 5, 1818, the full-rigged American ship James Monroe, of the Black Ball Line, sailed from New York City for Liverpool, inaugurating common-carrier line service on a dependable schedule. A policy of sailing regularly and accepting cargo in less-than-shipload lots enabled the Black Ball Line to revolutionize shipping.

Two technological developments furthered progress toward present-day shipping practices: the use of steam propulsion and the use of iron in shipbuilding. In 1819 the American sailing ship Savannah crossed the Atlantic under steam propulsion for part of the voyage, pioneering the way for the British ship Sirius, which crossed the Atlantic entirely under steam in 1838. Iron was first used in the sailing vessel Ironsides, which was launched in Liverpool in 1838.

The opening of the Suez Canal in 1869 was of great economic importance to shipping. Coinciding with the perfection of the triple-expansion reciprocating engine, which was both dependable and economical in comparison with the machinery of the pioneer vessels, the completion of the canal made possible rapid service between western Europe and Asia. The first steam-propelled ship designed as an oceangoing tanker was the Glückauf, built in Britain in 1886. It had 3,020 deadweight tons (dwt; the weight of a ship's cargo, stores, fuel, passengers, and crew when the ship is fully loaded) and a speed of 11 knots.

The 20th Century

Among the technological advances at the turn of the century was the development by the British inventor Charles A. Parsons of the compound steam turbine, adapted to maritime use in 1897. In 1903 the Wandal, a steamer on the Volga River, was powered by the first diesel engine used for ship propulsion. The Danish vessel Selandia was commissioned as the first seagoing motor ship in 1912.

After World War I significant progress was made especially in the perfection of the turboelectric drive. During World War II, welding in ship construction supplanted the use of rivets.

The keel of the first nuclear-powered passenger-cargo ship, the Savannah, was laid in Camden, New Jersey, on May 22, 1958, and the ship was launched in 1960. In 1962 it was chartered to a private company for experimental commercial use, but it did not prove financially successful.

Shipping Industry

Car Ferry
Passenger operations comprise a large portion of the shipping industry. Here, the British Sealink ferry carries both walk-on passengers and cars. Ferries are usually used for coastal or short-distance transportation.

Shipping Industry, the industry devoted to moving goods or passengers by water. Passenger operations have been a major component of shipping, but air travel has seriously limited this aspect of the industry. The enormous increase, however, in certain kinds of cargo, for example, petroleum, has more than made up for the loss of passenger traffic. Although raw materials such as mineral ores, coal, lumber, grain, and other foodstuffs supply a vast and still growing volume of cargo, the transportation of manufactured goods has increased rapidly since World War II.

New Trends in Ship Design

Experimental Ship, Sea Shadow
The experimental ship Sea Shadow was developed in total secrecy by the United States Navy and its contractors, Lockheed Martin Corporation and the Advanced Research Projects Agency, during the 1980s. The Navy finally unveiled the stealth ship to the American press and public in 1993, nearly a decade later. Sea Shadow moves through the water almost silently, and stealth technology renders it virtually undetectable to radar, sonar, and the infrared sensors used by heat-seeking missiles. The ship measures 50 m (164 ft) long, 21 m (68 ft) wide, and has a 4-m (14-ft) draught.

Although the ship remains the most economical way to transport bulk cargoes over the world’s oceans, naval architects recognize that room for improvement remains. Most of today’s cargo vessels travel at a speed of about 20 to 23 knots, limited by their hull design. Naval architects are exploring the use of multiple hulls—instead of having one large hull, ships might have two or three hulls connected to each other. These designs are prominent in small- to medium-sized boats but have not been applied to bulk carriers. The catamaran (two hull) or trimaran (three hull) offers great stability with much less water resistance.

Concerns about applying such designs to bulk cargo carriers persist, however. Some question the potential strength of large, multiple-hulled ships in rough seas. Others argue that multiple-hulled cargo carriers would not have adequate carrying capacities to make them economical.

Naval architects are also exploring the use of narrower hulls in single-hulled cargo vessels. Military vessels throughout history have used slender hulls, which enable ships to travel faster because they experience less drag in the water. Many question the potential stability of the slender-hulled cargo ship, which will undoubtedly make transoceanic crossings with containers stacked high on its decks. Moreover, a narrow-hulled ship cannot carry as much cargo as a modern freighter of equivalent length.

The solution may lie in the semiplaning monohull. This hull design has a sharp V-shaped bow for cutting the waves and a wide, shallow rear with a slightly concave profile underwater. This design creates waves that help lift the vessel and reduce drag in the water. These hulls, similar to those used in many modern pleasure boats, would become more efficient as the ship goes faster.

New designs in ship propulsion will also increase the efficiency of ship transport. When compared to marine diesel engines of the same weight and volume, gas turbine engines produce far greater amounts of power without using more fuel. They also burn cleaner, emitting only 4 percent of the sulfur oxides and 5 percent of the nitrogen oxides emitted by diesels of the same power. Gas turbine engines currently power small passenger and car ferries, but they have been prohibitively expensive for use in bulk cargo transport.

In the future, water jet drive may replace the screw propeller. Both of these propulsion systems spin and push water to move the vessel. But while the screw propeller becomes less efficient at high speeds, the water jet drive gains efficiency as speed increases.

Such changes will undoubtedly make the ships of tomorrow faster and more efficient. Naval architects and engineers predict that a ship with a semiplaning monohull, gas turbine engine, and water jet drive will easily reach a speed of 45 knots. These and other innovative ship designs will cut the cargo crossing time between Europe and North America from 14 to 35 days to a week or less.

Naval Vessels

U.S. Navy Third Fleet
One of the larger, more powerful fleets in the U.S. Navy is the Third Fleet based in San Diego, California. The purpose of the fleet, composed of a group of warships under a single command, is to protect U.S. interests in the Pacific Ocean.

Like their sailing predecessors, power-driven naval vessels are designed for various operations involved in modern naval warfare. Contemporary naval fleets include aircraft carriers, cruisers, destroyers, frigates, mine craft, and a variety of transport and support vessels. Naval vessels generally have a slender hull shape that gives them greater speed than their merchant counterparts, which cannot economically sacrifice cargo-carrying capacity for speed.

1. Aircraft Carriers


Nuclear-Powered Aircraft Carrier
Nuclear power propels the huge bulk of the Abraham Lincoln through the water. Part of the fleet of the U.S. Navy, the Abraham Lincoln provides a flight deck for high-performance planes. By naval standards the ship is very long, but its runway is still shorter than most air strips on land. To compensate for this, incoming planes use hooks on their undersides to catch arresting cables on the ship’s deck.

The most important naval ships of modern times, aircraft carriers are massive vessels equipped with flight decks to support the takeoff and landing of military aircraft. The largest and most advanced carriers in the world belong to the Nimitz class. Nimitz carriers stretch 333 m (1,092 ft) in length and carry 85 aircraft. Their crews number more than 3,000, and they also house aircrew and support teams numbering almost 2,500. They are powered by a two-reactor power plant.

2. Battleships

The modern battleship traces its ancestry to the first-rate ships-of-the-line of the sailing era. Until recently, modern battleships served on the front lines of sea battles throughout the world. They have largely been replaced by aircraft carriers.

The last battleships built in the United States were of the Iowa class. The four Iowa-class vessels entered service in the 1940s. The U.S. Navy modernized them in the 1980s, then removed them from service in the 1990s. These steel-hulled ships measured 270 m (885 ft) and traveled at an unprecedented speed of 33 knots.

3. Cruisers

Modern cruisers measure from 162 to 243 m (533 to 796 ft) in length, travel about 30 knots, and have an average crew of 550. The mission of modern cruisers is to destroy enemy surface ships, submarines, aircraft, and missiles. They are equipped with 5-inch guns, Harpoon and Tomahawk guided missiles, antisubmarine warfare helicopters, and torpedoes. Many cruisers now have the Aegis surface-to-air missile system, a highly sophisticated and capable weapons system.

4. Destroyers

The modern destroyer is a light, fast, ship that serves a great variety of functions because of its speed, armament, and maneuverability. It replaced the navy war sloop of the sailing era. Destroyers provide antiair, antisurface, and antisubmarine warfare capabilities. They carry 5-inch guns, a variety of antiship missiles, antisubmarine helicopters, and torpedoes. They range from 133 to 172 m (437 to 563 ft) in length, travel at speeds ranging from 30 to 33 knots, and have crews of about 400.

5. Frigates


Halifax-Class Frigate HMCS Toronto
Canadian Forces navy personnel tie off the massive bowline of the HMCS Toronto. One of seven Halifax-class frigates in the navy fleet, Toronto stretches 134-m (440-ft) long and 16-m (52-ft) wide. The ship carries a 17-m (55-ft) helicopter on its deck and houses up to 225 officers and crew members.

Like its sailing predecessor, the modern naval frigate serves as an ocean escort. It ranges from 126 to 136 m (414 to 445 ft) in length and cruises at below 30 knots. Modern frigates require crews of between 200 and 300 sailors. Most are lighter armed than destroyers, although some frigates carry missiles, antisubmarine rockets, and helicopters, torpedoes, or other weapon systems.

6. Mine Craft


Navy Minesweeper
The USS Swift, a Navy minesweeper, cruises off the coast of Norway in 2004. Minesweepers are used to detect and sweep away underwater mines so that ships can pass safely.

Mine craft include minesweepers and mine countermeasure ships. Minesweepers detect and clear, or sweep, explosive underwater mines so that ships can pass safely. They measure 57 m (188 ft) long and carry a crew of 45. Mine countermeasure ships detect and sweep underwater mines and serve as command and control facilities for mine countermeasure operations. Mine countermeasure ships measure 68 m (223 ft) in length and have a crew of 74.

The First Nuclear-Powered Vessels

The most revolutionary development in ship propulsion was nuclear power, first used in the submarine USS Nautilus in 1954. Nautilus cruised at more than 20 knots and could remain submerged for almost unlimited periods. In 1958 the Nautilus made the first undersea crossing at the North Pole. The Nautilus could fire guided missiles or ballistic missiles at enemy land targets from a submerged position. Nautilus’s successes were legendary, and soon all the major naval powers had nuclear submarines in their fleets.

In 1962 the first commercial nuclear-powered ship, the NS Savannah, was launched in Camden, New Jersey. Named for the Savannah, the famous 19th–century steamship that pioneered transatlantic steam travel, NS Savannah measures 182 m (596 ft) and is powered by nuclear-driven turbines. Although it was an engineering success, NS Savannah proved a commercial failure. It could not carry enough cargo to be competitive and required a larger crew than comparable oil-powered ships.

NS Savannah remains the only commercial nuclear-powered vessel ever built. Nuclear power proved prohibitively expensive for commercial purposes. The military recognized the potential for nuclear power. Unrestricted by cost, navies of the United States, Russia, Britain, and France developed a variety of naval vessels operated by nuclear power.

Hovercraft

Hovercraft
This British hovercraft is held above the water by blown air. Once the craft is hovering over the surface, it moves much more efficiently than a boat plowing through water. The propellers on the rear help to power as well as to steer the hovercraft.

Hovercraft, also called air-cushion vehicles, travel over the surface of, rather than through, the water. They use large lift fans to push down air, which is trapped inside a heavy rubber skirt. The skirt gives the craft the hover height necessary to clear waves and other obstacles. Without water resistance, these ships can travel at up to 65 knots over the water. If their skirts or lift fans fail, the hovercraft settles onto the surface of the water and floats for the rest of the trip to port.

The first commercial hovercraft entered service in 1968 as a passenger transport across the English Channel. Most hovercraft in use today operate as high-speed passenger and automobile ferries. The largest of these craft measure 39 m (128 ft) or more and carry up to 610 passengers. The United States military commissioned hovercraft for use in amphibious warfare. Military hovercraft can transport troops across the water and the beach safely and more efficiently than other amphibious vehicles.