Physics and technology – Technology – Motor Ships
Using ships to transport goods by sea is more popular than ever. Technical innovations to improve security and profitability are constantly in demand.
Globalization has led to an increase in the quantity of goods exchanged between continents. For large quantities and heavy individual items, shipping by sea is still the most economical method of transport.
Popular in the first millennium B.C., sea transport has remained popular to this day and registered steady annual growth rates for many years.
Ship construction
As shipping companies demand faster, safer cargo and passenger ships, shipyards in Europe, North America, and Asia are eager to respond. Modern ship builders face the same basic problems as ship builders faced 2,000 years ago. The shape of the hull below the waterline governs the speed and stability of the ship. Container ships carry dry goods and manufactured products in truck- size containers.
They are wide and relatively flat, making them very large and stable, but slow. Powered by 12- or 14-cylinder diesel motors capable of 10,000 horsepower each, they can reach speeds of around 25 knots (29 mph or 46.3 km/h). Built on the same principles, bulk carriers transport unpackaged cargo, such as coal and wheat, while tankers transport bulk liquids, such as petroleum and chlorine.
Speedboats, designed to maximize speed rather than load capacity, are built differently than cargo ships. Speedboat hulls are designed to transverse water with minimum water displacement. At high speeds, speedboats actually lift out of the water. Motorboats can be powered by an inboard motor, an outboard motor, or a hybrid of the two.
Engines
At the core of every ship is the engine. Gas turbines, electrical motors, and diesel motors are all used to power ships. The power of the engine is transferred through the drive shaft directly to the propellers.
A gas turbine engine, used in aircraft carriers and nuclear submarines, has a high power-to-weight ratio, allowing for fast acceleration, jet propulsion and long distances between refueling.
SAFER SHIPPING
Supertankers and huge container ships often carry dangerous cargo, and their fuel (marine diesel) is an environmental hazard. For this reason, modern ships are built with double-hulled construction. Specially trained pilots board the ship for difficult maneuvers and harbor docking. A fully loaded container ship has an extremely long braking distance and a huge turning radius.
An ongoing problem is the tendency to cut costs by eliminating prudent safety measures, flying “flags of convenience,” and hiring inexperienced crew from low-wage countries. The threat of piracy also re- mains acute today, especially in Southeast Asia.
BASICS
HOVERCRAFT traverse both land and water They move by floating on a downward stream of air produced by fans. and thus appear to “hover.”
DRIVE GENERATORS powered by water currents produce little pollution and are important in inland shipping