Transportation

Teacher Background Information

Historical Data:

People have long used the seas as a means of transportation, as it is often easier to move people and goods over water than land. Following is a list of ship development milestones:

	The earliest craft were log dugouts, rafts, and boats made of hides stretched over a wooden frame.
	About 6,000 years ago, the ancient Egyptians built reed boats powered by paddlers. About 5,200 years ago, they invented sails.
	Another breakthrough in sailing technology occurred in 3000 BC when the Egyptians learned to build vessels from wood planks.
	Around 500 BC the Greeks built ships with two masts.
	Shipbuilders in northern Europe devised the stern rudder in AD 1303.
	In the 1450's, shipbuilders in the Mediterranean developed the full-rigged sailing ship.
	The first workable submarine was constructed from a wooden rowboat covered with waterproof hides in 1620.
	The first commercial successful steamboat was built in 1807.
	In 1818, the first all-iron sailing ship was built.
	A propeller-driven steamship design was patented in 1836.

Buoyancy:

The ability to float is called buoyancy. When something falls into water, it presses down on it. The water pushes back with a force called upthrust. If the upthrust is greater than the object's weight, the object is pushed upward. At the water's surface, upthrust and weight balance, and the object floats. A wooden twig floats because the water's upthrust overcomes the twig's weight. A pebble sinks because its weight is greater than the upthrust.

Our ancestors probably began making boats after noticing that wood floats. They hollowed out tree trunks to make tree canoes or lashed them together into rafts. In marshy areas, where the tall grasses called reeds grew, people learned to shape bundles of reeds into boats.

Buoyancy is affected by shape as well as weight. A boat with a hull - a wide bottom and tall sides - can carry more weight than a raft. This is partly because it can settle lower in the water without sinking. And the lower the boat settles, the greater the upthrust pushing on it below. As it settles lower, the boat is also pushing aside water. This "pushing aside" is called displacement. The boat will float as long as the water's upthrust is equal to the weight of the water the boat displaces.

Steering and Rudders:

No matter how big or small they are, or whether they are propelled by wind or engine power, most boats are steered by the pressure (pushing force) of water acting against the rudder. When the rudder is turned, the pressure of the water becomes greater on one side of it than on the other. This pushes the stern sideways and brings the bow around. Big boats have a steering wheel, but in small boats a handle called a tiller is used to move the rudder.

In a big boat, the wheel is linked to the rudder by pulleys and cables. A pulley is a wheel with a grooved rim which holds the cable in. Turning the wheel to the left tightens the left-hand cable, pulling the rudder in the same direction.

The rudder pivots (turns) at the point where it is fitted to the stern of the boat. The further the steering wheel is turned, the further the rudder moves.

Moving the steering wheel to the left makes the boat turn to port (left). Moving it to the right makes it turn to starboard (right).

The tiller on a small boat can be turned by hand, but the water pressure on the rudder of a big boat is so great that muscle power alone isn't enough. The pulleys and cables in the steering gear help to magnify the effort used to turn the wheel. In the biggest ships, motors are used to turn the rudder.

When the rudder is in the midway position, water flows with equal force down either side. The boat sails ahead. Angling the rudder to the right makes it stick into the water flow. The water presses against it, forcing the boat round to the right. If the rudder is angled to the left, the boat turns to the left. The stern is thrust outward, bringing the bow of the boat round.

The bridge is where the officers steer and control the ship. It is high up so they get a clear view of other vessels nearby. All the information collected by the various instruments on board is brought together on the bridge, so that the officers can sail as safely as possible. A lot of ships now have electronic aids that show information on computer screens. Many of the systems automatically warn of faults in machinery, or of dangers such as shallow water.

Amazing Ships:

	Paddle Steamer: These flat-bottomed boats were used to bring supplies to the North to Whitehorse. The big paddle wheel pushed them along. Some of these boats, along the Mississippi, were show boats. When they tied up at the river bank, actors, singers and dancers put on exciting shows.
	Icebreaker: Icebreakers are used in northern waters to clear paths through ice so that other ships can move through. With their strong hulls, they can break through ice more than one meter thick.
	Jointed Ships: Over 100 years ago, people reported seeing a ship like this. They said it had hinges to help it move easily across rough seas. Each section could separate and sail by itself, but it probably never existed.
	Maori Canoe: Today the Maoris live in New Zealand. They sailed over 1,000 years ago in double canoes. The chief and his crew slept in a cabin on the crossbeam.
	Hovercraft: This ship does not have to push through the water. It hovers just above the surface. A cushion of air made by powerful fans is trapped under the craft by a sort of "skirt".
	Viking Longship: Long ago, Vikings from Scandinavia sailed across the Atlantic Ocean in ships like these. Each longship carried up to 64 rowers and had a single square sail. The dragon's head on the prow of the longship was carried only when it went on a voyage of war.
	Galley: Galleys were used over 2000 years ago by the Greeks and Romans. They had two rows of oars, as well as sails. The pointed bow was used to sink enemy ships, while the tower protected the soldiers.
	Bluenose: Canada's clipper ship - the fastest in the world!

Diving Vessels:

Modern submarines and submersible vessels can dive to astounding depths.

	Scuba divers can reach depths of 200 feet.
	Divers wearing a Jim Suit (cross between a diving suit and a small submersible) can reach depths of 1,500 feet.
	Submarines can travel at depths of about 3,000 feet.
	Bathysphere, the first ball-shaped diving craft dove to 3,028 feet.
	Pisces, a submersible reached 6,500 feet.
	Alvin, a deep-sea research craft, reached depths of 13,000 feet.
	Trieste reached 35,813 feet in the Marianas Trench in the Pacific Ocean.

Unlike other types of floating machines, submarines are specifically designed so that they can sink! Submarines have to be able to float too, of course, so that they can rise back up to the surface again. They control their depth with ballast, using it to make themselves heavier or lighter than the sea water around them. Submarines have to be strong enough to resist the crushing pressure of water, particularly because this gets worse the deeper they go.

Ballast is the extra weight that makes a submarine sink. It is usually sea water stored in tanks. The Triest used gasoline, sea water, and iron shot as ballast. When a vent at the top of the ballast is opened, air rushes out. Water surges in to take its place, through vents at the bottom of the tanks. The extra weight makes the submarine sink. When the water is forced out by pumping in compressed air, the submarine rises.

Submersibles do all sorts of underwater jobs. As well as laying, inspecting, and repairing underwater pipelines and telephone cables, submersibles are used to service oil rigs, to map the ocean floor, and to find and survey shipwrecks. In 1985, for example, Alvin discovered the wreck of the liner Titanic, which had sunk in 1912. Submersibles are also used by scientists to study curious plants and animals of the ocean depths.

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