About
Supertankers are large ships, commonly used to carry oil, liquefied natural gas, or liquefied petroleum gas.
Among tanker ships, the very largest are called supertankers. The largest of these are the Very Large Crude Carrier (VLCC), which can carry 200,000 tons or more of oil, and the Ultra Large Crude Carrier (ULCC), which can manage over 300,000 tons.
These ships can weigh 200,000 to 400,000 tons all by themselves. The top speed of a supertanker when carrying a full load can be as much as 18 mph (or nearly 30 km/h).
VLCCs are so big that their load of crude oil, held in several cavernous tanks each the size of a cathedral, could meet the energy needs of a small city for a year. Three supertankers can carry all of the oil used by Japan in a day.
VLCCs are more than 300 meters in length, (almost a quarter of a mile). They are as long as the world’s tallest buildings are high. They’re also half a football field wide.
Crew members use bicycles to get around on them. Unfortunately, you may never get to see such a ship, even if you live on a seacoast, because supertankers are too big to enter most ports.
These gigantic ships have been built for a reason. Their small crews and giant payloads maximize shipping company profits. The volume of a ship increases as a function of the cube of its length. In other words, if you double the length of a ship, keeping all dimensions proportional, you increase its size and cargo capacity by eight times.
Although the ship will probably also cost eight times as much to build, with high oil prices, a supertanker carrying crude oil from Saudi Arabia to the east coast of North America can pay for itself after about four successful voyages.
The huge size of these ships, however, does not make them immune from accidents. Large storms and human error have caused many sinkings and spills since the first supertankers were built (in response to the temporary closing of the Suez Canal in 1956).
Supertankers are highly automated. Computers and GPS satellite navigation take care of most of the work. Only a small crew is needed, and the ships can be driven by a single person.
Japanese shipbuilders are now planning huge, unmanned, computer-guided supertankers that might cross the oceans in fully automated mode. (The risks may be too great, however. Small private vessels are difficult to spot on radar, and are occasionally hit by manned tankers when crews aren’t watching the sea too carefully).
The immense size of these ships, as well as the heavy loads they carry, mean that each supertanker has enormous inertia.
A crash stop maneuver (from ‘full ahead’ to ‘full reverse’) can stop a fully loaded supertanker within approximately three kilometres, which takes about 14 minutes. The turning diameter is almost two kilometres. (These values vary according to ship size and weight, of course).
Only the most experienced ship captains are permitted to train for supertankers.
When the ship has reached port and is near the wharf, giant ocean-going tug boats come and pull and push it until it is tied up.
Strong as they are, however, these tugboats cannot move a fully loaded supertanker in rough weather, as they can other ships.
The inner hull of an oil tanker is divided into tanks that are loaded and unloaded by pumps; there are many pipes running across the deck of these ships, which are used to load and unload the crude oil onto and off of the ship.
A typical VLCC is the Vela, seen at the right.Main Characteristics: Length 333 m Width 56 m Depth 32 m Weight 301,860 tonnes Speed fully loaded: 14 mph (22 km/h)Supertankers are the longest man-made vehicles, and the only ones which are long enough to perhaps necessitate taking the spin of the earth into account when navigating.The ‘Coriolis Effect’ is noticeable on the surface of the earth when an object moves north or south; it results in an apparent ‘force’ which causes the motion of the object to have an east/west component. Actually, this isn’t a force at all …Here’s an explanation.Imagine a very powerful cannon firing a shell northward from the equator. While at that position on the surface of the earth, the cannon shell shares the earth’s eastward rotational speed, 1600 km/h, which is highest at the equator. As the cannon shell moves northward, say as far as Greenland, it still has this high eastward speed, but the earth’s surface rotates more slowly at this latitude … perhaps as little as 900 km/h. In the time it took the cannon shell to move north, Greenland won’t have moved as far east, because the rotational speed is slower.The end result is that an object moving northward will also have moved towards the east, according to the land below. But only because the land below hasn’t kept up.Theoretically, supertankers are long enough such that this effect could be accounted for during navigation. In other words, if a supertanker is moving northward, the back end is rotating with the earth faster than the front end, and will affect the direction of travel measureably, unless corrected for. However, Roy Philpott, a recent visitor to this page, who has worked at sea for 20 years “on some of the biggest ships afloat”, tells us that the coriolis force is not taken into account when navigating. He suggests that sea currents, wind and general steering inaccuracies are much greater, and for this reason the coriolis effect is unnoticeable. We thank him for his contribution to the accuracy of our page.Supertankers are constructed in various stages. Components of the ship are made in advance, and assembled in stages. Then the components are put together using huge cranes. Finally, the completed hull is floated, and work begins on the inside fittings. |