Category Science

SUBMARINES

A submarine is a vessel that can travel submerged under the water as well as on the surface. A submarine needs an extremely strong hull to resist the pressure deep under water. Ballast tanks in the hull are filled with water to make the submarine heavier so that it dives. The tanks are “blown” with air to empty them and make the submarine surface again.

While submerged, submarines are propelled by battery-powered electric motors that do not produce dangerous exhaust fumes. On the surface, diesel engines take over. They recharge the batteries at the same time.

Huge military submarines such as USS George Washington lurk under the water and attack enemy ships with torpedoes. Nuclear-powered submarines can stay submerged for months.

A submersible such as Alvin is a miniature submarine. Submersibles are mostly used for research in the ocean depths. Robot submersibles also carry out underwater repairs on oil rigs.

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MODERN SHIPS

Modern ships and boats can be categorized by the jobs they do. Merchant ships include cruise liners, ferries, cargo ships, and utility ships, such as dredgers and tugs. Military ships include warships and support ships, called auxiliaries. There are also numerous different types of fishing boat and leisure craft, from luxury yachts to sailing dinghies.

Small cargoes are carried in standard-sized metal boxes called containers on container ships, which are loaded and unloaded at dedicated container terminals. Cargoes such as ores, coal and grain are carried by bulk carriers. Oil and other liquids are carried by tankers.

The main part of a ship is its hull, the part that sits in the water. It keeps the ship watertight and forms a strong structure that supports the other parts of the ship and its cargo. Inside the hull are horizontal decks and vertical walls called bulkheads.

The parts of a ship above the main deck are called its superstructure. Most ships have a diesel engine housed low in the hull, which drives a propeller under the stern via a shaft. A rudder at the stern steers the ship. Large ships also have small electrically powered propellers called thrusters for manoeuvring accurately in port.

The SeaCat is a high-speed vehicle ferry. It is a catamaran, which means it has two hulls. Fast ferries like this are powered by gas turbine (jet) engines, giving them top speeds in excess of 40 knots (70 km/h).

Different types of ship have their own specialized parts. For example, vehicle ferries called roll-on roll-off (ro-ro) ferries, designed for a quick turnaround in port, have huge bow or stern doors, and uncluttered decks where the vehicles park. Container ships have their own on-deck cranes for moving containers about. Aircraft carriers have a flat main deck that forms a runway where aircraft take off and land, with hangars underneath.

A giant Nimitz-class aircraft carrier dwarfs a 15th-century carrack. The nuclear-powered Nimitz- class carriers are the world’s largest. They weigh nearly 100,000 tonnes and have a flight deck 333 m long. They provide an operations base for nearly 100 attack aircraft.

Ships are controlled from a room high up near the bow, called a bridge. From here, the crew navigates from place to place, using engine and steering controls, and keeping track of their position using charts, satellite navigation systems, lighthouses and buoys. Radar helps to avoid collisions at night or in fog, and sonar warns of shallow water under the ship.

Picture Credit : Google

STEAMSHIPS

During the nineteenth century, large sailing ships almost completely disappeared as steam power took over. The first successful steam-powered vessel was a river steamer built in the USA by Robert Fulton in 1808. On early steamships the steam engine turned paddle wheels that moved the ship along, but by the 1850s most ships were using propellers instead. Ocean-going steamships kept sails, too, because they could not carry enough coal or water for long-distance voyages, and their engines were not very reliable.

One of the most important sea routes in the nineteenth century was across the Atlantic from Europe to the USA. Millions of people immigrated to the USA in ships. The first regular transatlantic service, starting in 1837, was the wooden paddle-steamer Great Western, built by English engineer Isambard Kingdom Brunel. Larger and larger ships followed, including in 1858 Brunel’s Great Eastern, easily the biggest ship in the world at the time, which could carry 4000 passengers. Both passenger ships and merchant ships continued to increase in size, especially with the introduction of steel hulls in the late nineteenth century.

By the early twentieth century, huge luxury liners were crossing the Atlantic, and steam-powered merchant ships were carrying most of the world’s cargo. The fastest liners used the new steam turbine engine, in which the steam turned a fan-like turbine, which turned the propellers at high speed.

The Grand Princess (launched 1998) is one of the largest of the new generation of cruise liners designed especially for holiday cruising. It is larger than even the biggest of the transatlantic liners. On the ship’s 18 decks there are cabins for 2600 passengers, including luxury suites with balconies, several swimming pools, bars, cafes and a theatre. At the stem is a night club suspended over the ocean.

The Queen Elizabeth was one of the largest and most luxurious liners ever built. It was 314 m long and weighed more than 80,000 tonnes. It entered transatlantic service in 1946 after carrying troops during World War II, and retired in 1968.

In the middle of the twentieth century, steam power began to give way to diesel power. Diesel engines are smaller, cleaner, far more efficient, and need fewer crew to operate them. Steam had almost completely disappeared by the 1980s.

As air travel became convenient and cheap in the 1960s, passengers stopped travelling by sea and the age of the liner came to an end. But as cruise holidays became popular in the 1980s, construction of new, giant cruise liners began.

The French liner Normandie, launched in 1935, was nearly 300 m long, accommodated 1975 passengers and needed 1345 crew. It was the first of what were called the “1000-foot” liners.

HMS Dreadnought, launched in 1906, was the first battleship driven by steam turbines.

Picture Credit : Google

SAILING SHIPS

People made their first journeys across water tens of thousands of years ago. Their first craft must have been logs, used as buoyancy aids. Later, they tied logs together to make rafts, or hollowed them out to make canoes. Where there were no big trees, they made boats from locally available materials, such as reeds or animal skins. Their boats allowed them to travel on rivers and lakes, searching for better fishing, or visiting hunting grounds.

These early craft were propelled by simple paddles, or poles pushed into the river bed. The first sailing boats we know about were built in ancient Egypt in about 3500 BC. Some were built from reeds bundled together, others from wood. They had a single mast with a square sail, which was used in addition to oars when the wind was blowing in a favourable direction. The crew steered with long oars hanging over the stern (rear).

The ancient Greeks and Romans used sturdy, seaworthy cargo boats and sleek fighting boats called galleys, both with a square sail. In battle, the galleys were propelled with oars and attacked enemy ships with a ram on their bows.

About 1000 years ago, the Vikings, who lived in northern Europe, started to explore new lands. Their ships were called knorrs. Each had a hull (body of vessel) made of overlapping or “clinkered” planks.

Chinese boats called junks had sails stiffened by thick bamboo poles, and a sternpost rudder for steering. Until the 15th century they were the world’s biggest and best boats.

The arrangement of sails on a boat is called its rig. A square rig consists of sails hung on a boom across the boat (as in ancient Egyptian and Viking boats). This sort of rig cannot make the best use of wind blowing from side-on. The fore-and-aft rig, with a triangular sail hanging from a boom parallel with the boat’s sides, is more effective. The Chinese had developed a similar rig on their early junks in about 500 BC. It was developed in the Mediterranean in the third century AD. In Europe in the fifteenth century, ships began to appear with a mixture of rigs – square-rigged sails on some masts and fore-and-aft rigs on others. Through the centuries, sailing ships grew larger, with more, taller masts and more sails on each one.

The fastest sailing ships were the “clippers”, which had a huge sail area to take advantage of light winds, and streamlined hulls. They were used to carry important cargoes around the world, such as the new crop of tea from China to Europe.

By the 16th century, small, sturdy ships such as carracks and galleons were capable of long ocean crossings. With the aid of compasses to stop them accidentally sailing in circles, sailors set out from European ports to explore the world and to try to find new sea routes to the Spice Islands of Asia.

Among these explorers was the Portuguese navigator Ferdinand Magellan, who left Spain in 1519 with five ships to sail to Asia around the southern tip of newly-discovered America. Magellan himself was killed in the Philippines, two years into the voyage. Only one of the ships, the Vittoria, under the captaincy of Sebastian del Cano, finally got back to Spain, 1082 days after it left. It was the first ship to circumnavigate the world.

Barques were high-capacity, multi-masted sailing ships that carried bulk cargoes such as grain between Europe, South America and Australia. A small crew could operate the barque’s simple rig. This particular barque, France II, built in 1911, was the biggest sailing ship ever built. Its steel hull was 127 metres long.