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.