Prehistory and antiquity Essay

Since the end of the age of sail a ship has been any large buoyant watercraft. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing, entertainment, public safety, and warfare. Historically, a â€Å"ship† was a vessel with sails rigged in a specific manner. Ships and boats have developed alongside humanity. In armed conflict and in daily life they have become an integral part of modern commercial and military systems. Fishing boats are used by millions of fishermen throughout the world. History The first known vessels date back to the Neolithic Period, about 10,000 years ago, but could not be described as ships. The first navigators began to use animal skins or woven fabrics as sails. Affixed to the top of a pole set upright in a boat, these sails gave early ships range. By around 3000 BC, Ancient Egyptians knew how to assemble wooden planks into a hull.[10] They used woven straps to lash the planks togetherand reeds or grass stuffed between the planks helped to seal the seams. A panel found at Mohenjodaro, depicted a sailing craft. Vessels were of many types Their construction is vividly described in the Yukti Kalpa Taru, an ancient Indian text on shipbuilding. This treatise gives a technical exposition on the techniques of shipbuilding. It sets forth minute details about the various types of ships, their sizes, and the materials from which they were built. The Swahili people had various extensive trading ports dotting the coast of medieval East Africa and Great Zimbabwe had extensive trading contacts with Central Africa, and likely also imported goods brought to Africa through the Southeast African shore trade of Kilwa in modern-day Tanzania.[21] Before the introduction of the compass, celestial navigation was the main method for navigation at sea. In China, early versions of the magnetic compass were being developed and used in navigation between 1040 and 1117. Renaissance Until the Renaissance, navigational technology remained comparatively primitive. This absence of technology did not prevent some civilizations from becoming sea powers. Examples include the maritime republics of Genoaand Venice, Hanseatic League, and the Byzantine navy. The carrack and then the caravel were developed in Iberia. After Columbus, European exploration rapidly accelerated, and many new trade routes were established.[38] In 1498, by reaching India, Vasco da Gama proved that the access to the Indian Ocean from the Atlantic was possible. These explorations in the Atlantic and Indian Oceans were soon followed by France, England and the Netherlands, who explored the Portuguese and Spanish trade routes into the Pacific Ocean, reaching Australia in 1606 and New Zealand in 1642.[39] A major sea power, the Dutch in 1650 owned 16,000 merchant ships. Specialization and modernization During the first half of the 18th century, the French Navy began to develop a new type of vessel known as a ship of the line, featuring seventy-four guns. This type of ship became the backbone of all European fighting fleets. These ships were 56 metres (184 ft) long and their construction required 2,800 oak trees and 40 kilometres (25 mi) of rope; they carried a crew of about 800 sailors and soldiers. Ship designs stayed fairly unchanged until the late 19th century. The industrial revolution, new mechanical methods of propulsion, and the ability to construct ships from metal triggered an explosion in ship design. Factors including the quest for more efficient ships, the end of long running and wasteful maritime conflicts, and the increased financial capacity of industrial powers created an avalanche of more specialized boats and ships. Ships built for entirely new functions, such as firefighting, rescue, and research, also began to appear. In light of this, classification of vessels by type or function can be difficult. Even using very broad functional classifications such as fishery, trade, military, and exploration fails to classify most of the old ships. This difficulty is increased by the fact that the terms such as sloop and frigate are used by old and new ships alike, and often the modern vessels sometimes have little in common with their predecessors. Today In 2007, the world’s fleet included 34,882 commercial vessels with gross tonnage of more than 1,000 tons,[42] totaling 1.04 billion tons.[1] These ships carried 7.4 billion tons of cargo in 2006, a sum that grew by 8% over the previous year.[1] In terms of tonnage, 39% of these ships are tankers, 26% arebulk carriers, 17% container ships and 15% were other types.[1] In 2002, there were 1,240 warships operating in the world, not counting small vessels such as patrol boats. The United States accounted for 3 million tons worth of these vessels, Russia 1.35 million tons, the United Kingdom 504,660 tons and China 402,830 tons. The 20th century saw many naval engagements during the two world wars, the Cold War, and the rise to power of naval forces of the two blocs. The size of the world’s fishing fleet is more difficult to estimate. The largest of these are counted as commercial vessels, but the smallest are legion.Fishing vessels can be found in most seaside villages in the world. As of 2004, the United Nations Food and Agriculture Organization estimated 4 million fishing vessels were operating worldwide.[43] Types of ships[edit] Ships are difficult to classify, mainly because there are so many criteria to base classification on. One classification is based on propulsion; with ships categorised as a sailing ship, a steamship, or a motorship. Sailing ships are propelled solely by means of sails. Another way to categorize ships and boats is based on their use, as described by Paulet and Presles.[46] This system includes military ships, commercial vessels, fishing boats, pleasure craft and competitive boats. In this section, ships are classified using the first four of those categories, and adding a section for lake and river boats, and one for vessels which fall outside these categories. Commercial vessels Commercial vessels or merchant ships can be divided into three broad categories: cargo ships, passenger ships, and special-purpose ships.[47] Cargo ships transport dry and liquid cargo. Dry cargo can be transported in bulk by bulk carriers, packed directly onto a general cargo ship in break-bulk, packed in intermodal containers as aboard a container ship, or driven aboard as in roll-on roll-off ships. Liquid cargo is generally carried in bulk aboard tankers, such as oil tankers which may include both crude and finished products of oil, chemical tankers which may also carry vegetable oils other than chemicals and LPG/LNG tankers, Passenger ships range in size from small river ferries to very large cruise ships. This type of vessel includes ferries, which move passengers and vehicles on short trips; ocean liners, which carry passengers from one place to another; and cruise ships, which carry passengers on voyages undertaken for pleasure Special-purpose vessels are not used for transport but for other tasks. Examples include tugboats, pilot boats, rescue boats, cable ships, research vessels, survey vessels, and icebreakers. Most commercial vessels have full hull-forms to maximize cargo capacity.[citation needed] Commercial vessels generally have a crew headed by a captain, with deck officers and marine engineers on larger vessels. Special-purpose vessels often have specialized crew if necessary, for example scientists aboard research vessels. Commercial vessels are typically powered by a single propeller driven by a diesel or, less usually, gas turbine engine.[citation needed] The fastest vessels may use pump-jet engines.[citation needed] Naval vessels Naval vessels are those used by a navy for military purposes. There have been many types of naval vessel. Modern naval vessels can be broken down into three categories: surface warships, submarines, and support and auxiliary vessels. Modern warships are generally divided into seven main categories: aircraft carriers, cruisers, destroyers, frigates, corvettes, submarines and amphibious assault ships. The distinction between cruisers, destroyers, frigates, and corvettes is not rigorous; the same vessel may be described differently in different navies. Battleships were used during the Second World War and occasionally since then, but were made obsolete by the use of carrier-borne aircraft and guided missiles.[48] Most navies also include many types of support and auxiliary vessel, such as minesweepers, patrol boats, offshore patrol vessels, replenishment ships, and hospital ships which are designatedmedical treatment facilities.[49] Fast combat vessels such as cruisers and destroyers usually have fine hulls to maximize speed and maneuverability. They also usually have advanced electronics and communication systems, as well as weapons. Fishing vessels Fishing vessels are a subset of commercial vessels, but generally small in size and often subject to different regulations and classification. They can be categorized by several criteria: architecture, the type of fish they catch, the fishing method used, geographical origin, and technical features such as rigging. As of 2004, the world’s fishing fleet consisted of some 4 million vessels.[43] More than 60% of all existing large fishing vessels[51] were built in Japan, Peru, the Russian Federation, Spain or the United States of America.[52] Fishing boats are generally small, often little more than 30 meters (98 ft) but up to 100 metres (330 ft) for a large tuna or whaling ship. Aboard a fish processing vessel, the catch can be made ready for market and sold more quickly once the ship makes port. Weather vessels[edit] A weather ship was a ship stationed in the ocean as a platform for surface and upper air meteorological observations for use in marine weather forecasting. Surface weather observations were taken hourly, and four radiosonde releases occurred daily. [54] It was also meant to aid in search and rescue operations and to support transatlantic flights. Proposed as early as 1927 by the aviation community,[56] the establishment of weather ships proved to be so useful during World War II that the International Civil Aviation Organization (ICAO) established a global network of weather ships in 1948, with 13 to be supplied by the United States. Their crews were normally out to sea for three weeks at a time, returning to port for 10 day stretches.[54] Weather ship observations proved to be helpful in wind and wave studies, as they did not avoid weather systems like other ships tended to for safety reasons.[58] They were also helpful in monitoring storms at sea, such as tropical cyclones.[59] The removal of a weather ship became a negative factor in forecasts leading up to theGreat Storm of 1987.[60] Beginning in the 1970s, their role became largely superseded by weather buoys due to the ships’ significant cost.[61] The agreement of the use of weather ships by the international community ended in 1990. The last weather ship was Polarfront, known as weather station M (â€Å"Mike†), which was put out of operation on 1 January 2010. Weather observations from ships continue from a fleet of voluntary merchant vessels in routine commercial operation. Inland and coastal boats Many types of boats and ships are designed for inland and coastal waterways. These are the vessels that trade upon the lakes, rivers and canals. Barges are a prime example of inland vessels. Barges towed along canals by draft animals on an adjacent towpath contended with the railway in the early industrial revolution but were out competed in the carriage of high value items because of the higher speed, falling costs, and route flexibility ofrail transport. Riverboats and inland ferries are specially designed to carry passengers, cargo, or both in the challenging river environment. Rivers present special hazards to vessels. They usually have varying water flows that alternately lead to high speed water flows or protruding rock hazards. Changing siltation patterns may cause the sudden appearance of shoal waters, and often floating or sunken logs and trees (called snags) can endanger the hulls and propulsion of riverboats. Riverboats are generally of shallow draft, being broad of beam and rather square in plan, with a low freeboard and high topsides. Riverboats can survive with this type of configuration as they do not have to withstand the high winds or large waves that are seen on large lakes, seas, or oceans. Lake freighters, also called lakers, are cargo vessels that ply the Great Lakes. The most well-known is the SS Edmund Fitzgerald, the latest major vessel to be wrecked on the Lakes. These vessels are traditionally called boats, not ships. Visiting ocean-going vessels are called â€Å"salties.† Because of their additional beam, very large salties are never seen inland of the Saint Lawrence Seaway. Because the smallest of the Soo Locks is larger than any Seaway lock, salties that can pass through the Seaway may travel anywhere in the Great Lakes. Because of their deeper draft, salties may accept partial loads on the Great Lakes, â€Å"topping off† when they have exited the Seaway. Similarly, the largest lakers are confined to the Upper Lakes (Superior, Michigan, Huron,Erie) because they are too large to use the Seaway locks, beginning at the Welland Canal that bypasses the Niagara River. Since the freshwater lakes are less corrosive to ships than the salt water of the oceans, lakers tend to last much longer than ocean freighters. Lakers older than 50 years are not unusual, and as of 2005, all were over 20 years of age.[62] The St. Mary’s Challenger, built in 1906 as the William P Snyder, is the oldest laker still working on the Lakes. Similarly, the E.M. Ford, built in 1898 as the Presque Isle, was sailing the lakes 98 years later in 1996. As of 2007 the Ford was still afloat as a stationary transfer vessel at a riverside cement silo in Saginaw, Michigan. Architecture[edit] Some components exist in vessels of any size and purpose. Every vessel has a hull of sorts. Every vessel has some sort of propulsion, whether it’s a pole, an ox, or a nuclear reactor. Most vessels have some sort of steering system. Other characteristics are common, but not as universal, such as compartments, holds, a superstructure, and equipment such as anchors and winches. Hull For a ship to float, its weight must be less than that of the water displaced by the ship’s hull.[63] There are many types of hulls, from logs lashed together to form a raft to the advanced hulls of America’s Cup sailboats. A vessel may have a single hull , two in the case ofcatamarans, or three in the case of trimarans. Hulls have several elements. The bow is the foremost part of the hull. Many ships feature a bulbous bow. The keel is at the very bottom of the hull, extending the entire length of the ship. The rear part of the hull is known as the stern, and many hulls have a flat back known as a transom. Common hull appendages include propellers for propulsion, rudders for steering, and stabilizers to quell a ship’s rolling motion. Other hull features can be related to the vessel’s work, such as fishing gear and sonar domes. Hulls are subject to various hydrostatic and hydrodynamic constraints. The key hydrostatic constraint is that it must be able to support the entire weight of the boat, and maintain stability even with often unevenly distributed weight. Hydrodynamic constraints include the ability to withstand shock waves, weather collisions and groundings. Propulsion systems Propulsion systems for ships fall into three categories: human propulsion, sailing, and mechanical propulsion. Human propulsion includes rowing, which was used even on large galleys. Propulsion by sail generally consists of a sail hoisted on an erect mast, supported by stays and spars and controlled by ropes. Sail systems were the dominant form of propulsion until the 19th century. Mechanical propulsion systems generally consist of a motor or engine turning a propeller, or less frequently, an impeller or wave propulsion fins. Steam engines were first used for this purpose, but have mostly been replaced by two-stroke or four-stroke diesel engines, outboard motors, and gas turbine engines on faster ships. Nuclear reactors producing steam are used to propel warships and icebreakers, and there have been attempts to utilize them to power commercial vessels For ships with independent propulsion systems for each side, such as manual oars or some paddles,[64] steering systems may not be necessary. In most designs, such as boats propelled by engines or sails, a steering system becomes necessary. The most common is a rudder, a submerged plane located at the rear of the hull. Rudders are rotated to generate a lateral force which turns the boat. Rudders can be rotated by a tiller, manual wheels, or electro-hydraulic systems. Autopilot systems combine mechanical rudders with navigation systems. Ducted propellers are sometimes used for steering. Some propulsion systems are inherently steering systems. Examples include the outboard motor, the bow thruster, and the Z-drive. Some sails, such as jibs and the mizzen sail on a ketch rig, are used more for steering than propulsion. Holds, compartments, and the superstructure[edit] Larger boats and ships generally have multiple decks and compartments. Separate berthings and heads are found on sailboats over about 25 feet (7.6 m). Fishing boats and cargo ships typically have one or more cargo holds. Most larger vessels have an engine room, a galley, and various compartments for work. Tanks are used to store fuel, engine oil, and fresh water. Ballast tanks are equipped to change a ship’s trim and modify its stability. Superstructures are found above the main deck. On sailboats, these are usually very low. On modern cargo ships, they are almost always located near the ship’s stern. On passenger ships and warships, the superstructure generally extends far forward. Equipment[edit] Shipboard equipment varies from ship to ship depending on such factors as the ship’s era, design, area of operation, and purpose. Some types of equipment that are widely found include: Masts can be the home of antennas, navigation lights, radar transponders, fog signals, and similar devices often required by law. Ground tackle includes equipment such as mooring winches, windlasses, and anchors. Anchors are used to moor ships in shallow water. They are connected to the ship by a rope or chain. On larger vessels, the chain runs through a hawsepipe. Cargo equipment such as cranes and cargo booms are used to load and unload cargo and ship’s stores. Safety equipment such as lifeboats, liferafts, and survival suits are carried aboard many vessels for emergency use. Design considerations Hydrostatics[edit] Boats and ships are kept on (or slightly above) the water in three ways: For most vessels, known as displacement vessels, the vessel’s weight is offset by that of the water displaced by the hull. For planing ships and boats, such as the hydrofoil, the lift developed by the movement of the foil through the water increases with the vessel’s speed, until the vessel is foilborne. For non-displacement craft such as hovercraft and air-cushion vehicles, the vessel is suspended over the water by a cushion of high-pressure air it projects downwards against the surface of the water. A vessel is in equilibrium when the upwards and downwards forces are of equal magnitude. As a vessel is lowered into the water its weight remains constant but the corresponding weight of water displaced by its hull increases. When the two forces are equal, the boat floats. Hydrodynamics[edit] The advance of a vessel through water is resisted by the water. This resistance can be broken down into several components, the main ones being the friction of the water on the hull and wave making resistance. To reduce resistance and therefore increase the speed for a given power, it is necessary to reduce the wetted surface and use submerged hull shapes that produce low amplitude waves. To do so, high-speed vessels are often more slender, with fewer or smaller appendages. The friction of the water is also reduced by regular maintenance of the hull to remove the sea creatures and algae that accumulate there. Antifouling paint is commonly used to assist in this. Advanced designs such as the bulbous bow assist in decreasing wave resistance. A simple way of considering wave-making resistance is to look at the hull in relation to its wake. At speeds lower than the wave propagation speed, the wave rapidly dissipates to the sides. As the hull approaches the wave propagation speed, however, the wake at the bow begins to build up faster than it can dissipate, and so it grows in amplitude. Since the water is not able to â€Å"get out of the way of the hull fast enough†, the hull, in essence, has to climb over or push through the bow wave. This results in an exponential increase in resistance with increasing speed. This hull speed is found by the formula: or, in metric units: Where L is the length of the waterline in feet or meters. When the vessel exceeds a speed/length ratio of 0.94, it starts to outrun most of its bow wave, and the hull actually settles slightly in the water as it is now only supported by two wave peaks. As the vessel exceeds a speed/length ratio of 1.34, the hull speed, the wavelength is now longer than the hull, and the stern is no longer supported by the wake, causing the stern to squat, and the bow rise. The hull is now starting to climb its own bow wave, and resistance begins to increase at a very high rate. While it is possible to drive a displacement hull faster than a speed/length ratio of 1.34, it is prohibitively expensive to do so. Most large vessels operate at speed/length ratios well below that level, at speed/length ratios of under 1.0. For large projects with adequate funding, hydrodynamic resistance can be tested experimentally in a hull testing pool or using tools of computational fluid dynamics. Vessels are also subject to ocean surface waves and sea swell as well as effects of wind and weather. These movements can be stressful for passengers and equipment, and must be controlled if possible. The rolling movement can be controlled, to an extent, by ballasting or by devices such as fin stabilizers. Pitching movement is more difficult to limit and can be dangerous if the bow submerges in the waves, a phenomenon called pounding. Sometimes, ships must change course or speed to stop violent rolling or pitching. How it has been convincingly shown in scientific studies of the 21st century[65][66], controllability of some vessels decreases dramatically in some cases that are conditioned by effects of the bifurcation memory. This class of vessels includes ships with high manoeuvring capabilities, aircraft and controlled underwater vehicles designed to be unstable in steady-state motion that are interesting in terms of applications. These features must be considered in designing ships and in their control in critical situations. Lifecycle A ship will pass through several stages during its career. The first is usually an initial contract to build the ship, the details of which can vary widely based on relationships between theshipowners, operators, designers and the shipyard. Then, the design phase carried out by a naval architect. Then the ship is constructed in a shipyard. After construction, the vessel is launched and goes into service. Ships end their careers in a number of ways, ranging from shipwrecks to service as a museum ship to the scrapyard. Design A vessel’s design starts with a specification, which a naval architect uses to create a project outline, assess required dimensions, and create a basic layout of spaces and a rough displacement. After this initial rough draft, the architect can create an initial hull design, a general profile and an initial overview of the ship’s propulsion. At this stage, the designer can iterate on the ship’s design, adding detail and refining the design at each stage. As environmental laws are strictening, ship designers need to create their design in such a way that the ship -when it nears its end-of-term- can be disassmbledor disposed easily and that waste is reduced to a minimum. Construction[edit] Ship construction takes place in a shipyard, and can last from a few months for a unit produced in series, to several years to reconstruct a wooden boat, to more than 10 years for an aircraft carrier Generally, construction starts with the hull, and on vessels over about 30 meters (98 ft), by the laying of the keel. This is done in a drydock or on land. Once the hull is assembled and painted, it is launched. The last stages, such as raising the superstructure and adding equipment and accommodation, can be done after the vessel is afloat. Once completed, the vessel is delivered to the customer. Ship launching is often a ceremony of some significance, and is usually when the vessel is formally named. Repair and conversion Ships undergo nearly constant maintenance during their career, whether they be underway, pierside, or in some cases, in periods of reduced operating status between charters or shipping seasons. Vessels that sustain major damage at sea may be repaired at a facility equipped for major repairs, such as a shipyard. Ships may also be converted for a new purpose: oil tankers are often converted into floating production storage and offloading units. End of service Most ocean-going cargo ships have a life expectancy of between 20 and 30 years. A sailboat made of plywood or fiberglass can last between 30 and 40 years. Solid wooden ships can last much longer but require regular maintenance. Carefully maintained steel-hulled yachts can have a lifespan of over 100 years. As ships age, forces such as corrosion, osmosis, and rotting compromise hull strength, and a vessel becomes too dangerous to sail. At this point, it can bescuttled at sea or scrapped by shipbreakers. Ships can also be used as museum ships, or expended to construct breakwaters or artificial reefs. Many ships do not make it to the scrapyard, and are lost in fires, collisions, grounding, or sinking at sea. There are more than 3 million shipwrecks on the ocean floor, the United Nations estimates. Buoyancy A floating boat displaces its weight in water. The material of the boat hull may be denser than water, but if this is the case then it forms only the outer layer. If the boat floats, the mass of the boat (plus contents) as a whole divided by the volume below the waterline is equal to the density of water (1 kg/l). If weight is added to the boat, the volume below the waterline will increase to keep the weight balance equal, and so the boat sinks a little to compensate.