Of course, these shaft generators can only be used when the ship is moving at sea with a fairly constant speed; if the propeller shaft isn't turning, then neither is the generator, and no electricity can be produced. Even though many ships are still built with conventional diesel plans, almost all new cruise ships such as Celebrity's Edge Class or Carnival Horizon feature some form of "diesel electric" propulsion.
On these ships, the main engines aren't connected to the propeller shafts; instead, the main engines are directly connected to large generators with one job: producing electricity. The electricity they produce is sent to electric motors, which then power and turn the propellers. Often, there are many comparatively smaller engines that make up the power demand for the ship; in port, only one engine may be online, but out at sea at full speed, they may all be online.
The primary advantage of diesel electric systems is efficiency; they allow the engines to operate near their most efficient settings regardless of whether the ship is moving at 5 knots or 20 knots. However, new technology and research is driving even greater efficiencies and more environmentally friendly ships. LNG-powered ships have engines that are modified to burn natural gas that has been turned into a liquid and kept at a temperature degrees below zero in specially insulated fuel tanks.
While the infrastructure in ports to supply LNG is not fully global, the advantages for cruise lines are many -- including reducing nitrogen oxides by up to 80 percent and carbon dioxide emissions by 20 percent. Hybrid propulsion plants are also gaining popularity. Much like a hybrid car, hybrid ships rely on two different types of power systems. Hurtigruten's Roald Amundsen is perhaps the best known example; the ship has extensive battery packs that will have enough stored power to operate and sail the ship, even with the main diesel engines shut down.
Currently, the batteries have enough power for only 30 minutes of silent, emission-free navigation before the diesel engines are needed again; as the battery technology improves, Hurtigruten expects that time to increase.
Even advances in the underwater hull are helping to make new cruise ships more efficient. Royal Caribbean's Quantum of the Seas, Norwegian Bliss and Celebrity Edge are using thousands of tiny air bubbles underneath the hull to gain more efficiency.
The bubbles, pumped out underwater from the bottom of the ship, reduce the surface area of the hull that is in contact with the sea. This thereby reduces friction that slows a ship down and improves its fuel efficiency by up to 10 percent. Losing electrical power on a ship can be devastating.
The main engines and even the generators themselves require electricity to keep going. Electrically driven pumps take in cold seawater from the ocean to help cool the engines; electrical pumps take fuel from the fuel tanks and supply it to the engine. Electrical power is critical to many operating functions, and without it, the ship comes to a halt. Of course, the production of electricity is vital to all aspects of a ship's operation. Large equipment such as the bow thrusters, or, in the case of diesel electric ships, the actual propulsion motor requires high-voltage electricity.
For smaller machinery, such as lights in your cabin or the equipment in the galley, the electricity goes through a transformer and is stepped down into a more useable, lower voltage -- such as V. To distribute the electrical power, large cables snake through the ship.
Hundreds of miles of cables carry power from the generators to switchboards and eventually through passageways, cabins and public rooms. Cabling can be a weak point in a ship's distribution system. Even ships with two engine rooms can suffer power failure if the electrical cables are not truly redundant. For instance, if two main engines in different engine rooms produce power that goes into a single cable that brings power to the propulsion motors, a problem to that electrical cable would cut off all propulsion power.
Consider it like a highway: If an accident closes the road, traffic i. When ships are docked and not moving, main engines and generators produce far more power than needed. In port, they are turned off, and smaller generators are used to supply the "hotel" load i. Moving the ship through the water takes up the vast majority of a ship's need for power -- somewhere in the vicinity of 85 percent of the power a diesel electric plant produces goes to the propeller.
The rest goes toward keeping the lights on and the passengers and crew comfortable. The world's biggest cargo ship has docked in Britain for the first time. The Globe was built in South Korea and has arrived on its first trip. It measures m long, 56m wide and 73m tall. So how can a ship so big work?
It can carry nearly 20, containers - the same as 14, buses - so how can it float? It's all down to the ship's massive size, and something called displacement. For a ship to float, it has to push its weight in water downwards - or displace it. Once it's pushed down by the ship, this water pushes back upwards - and floats the ship. For a review on buoyant force see Density, Temperature, and Salinity. Ship stability is determined by the balance between the forces of gravity and buoyancy.
For a vessel in a calm harbor, the two forces of gravity and buoyancy are in a line and are balanced, as shown in Fig. A stable ship rights itself when tilted. The center of buoyancy of the tilted ship is shifted to the right because the area submerged has been shifted. The opposing forces acting at the CB and CG will twist the ship back to an upright position. An unstable ship will not right itself; it will continue to fall over because the buoyant and gravitational forces act on the ship to keep it moving in the direction of the tilt Fig.
Cargo ships often travel with a load of cargo to their destination and then return to their home ports with empty or partially empty holds. The amount of fuel in the fuel tanks also changes in a ship as it progresses on its journey and burns fuel. The change in weight of both the cargo and the fuel can dramatically change the stability of a ship.
To compensate for this, ships have ballast systems Fig. Early sailing ships used large stones for ballast. Some of the roads in American colonial towns were paved with ballast stones from cargo ships arriving from Europe.
Modern ships rely on a ballast system in which water is pumped into and out of holding tanks. One of the unexpected impacts of the switch from ballast stones to ballast water has been the unintentional transport of marine and freshwater organisms around the world.
Planktonic larvae travel from one port to another in ballast water, where they can become established as an invasive species. Invasive species are organisms that are non-native to the area, and when established, can cause harm to the ecosystem.
For example, the zebra mussel Fig. Birds that are found in Europe, but not found in North America, prey upon the mussel. Without any predation from these birds in North America, the mussel outcompetes native species, leading to death of native species and an ecosystem made up of only a single species when there should be many.
Many marine species have become established as a result of ship transportation including sponges, algae, corallimorphs, and barnacles. Though many ecosystems have been overrun with invasive species, little has been done to address the problem of larval movement in ballast water, and it is an ongoing concern.
Ships convey enormous amounts of goods and people around the world. According to the U. Department of Transportation Maritime Administration, more than 2. Thousands of passengers embark on cruise ships and transport ferries every year. The size of the vessels needed to convey such a volume of goods and people is immense. Although we can readily visualize the dimensions of a vehicle, most of us cannot easily picture the size of a supertanker.
A sedan automobile, for example, is almost 5 m long and weighs about kg lbs. By comparison, some oil tankers are m long almost four football fields and weigh million kg , metric tons. Determine the criteria for evaluating cargo transportation across bodies of water and the optimal type of cargo conveyance for different distance and cargo load scenarios.
A ship architect must design a ship so that it has the strength to withstand a combination of forces: the upward force of buoyancy, the downward force of gravity, and the powerful force of ocean waves. The ship must also be streamlined for speed. For thousands of years, ships have been designed much like the bodies of vertebrate animals.
The ships' ribs have been covered with a skin or hide, bark, planks, or metal plates. The skin not only made the ships watertight and buoyant; it also provided the necessary strength for their hulls Fig.
Ship hulls were traditionally designed as small-scale models. The models were approved, and then sawed into sections. Blueprint measurements were made of each section. These were mathematically enlarged when the ship was built to full scale. From the full-scale measurements, parts were constructed and assembled to build the full-sized hull.
Sean and Robot are exploring how boats move in the water and look at some of the science that gets things moving. Ships are a great way of getting around — they help get across lakes and travel to France for our holidays. But how do these ships move through the water?
As a ship moves through the water it experiences an considerable opposing resistance force. In order to minimise this force, ship designers work hard to make the ship more streamlined. How a ship moves depends on its location.
If a ship is in a crowded harbour then small slow exact movements are required.
0コメント