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The limits of physics and economics that prevent mega-ships from continuing to grow in size – BBC News BBC Homepage

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  • Chris Baraniuk
  • Technology, BBC News

an hour ago

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There are approximately 5,500 container ships in the world.

When the Ever Ace, one of the world’s largest container ships, left the port of Yantian last August 14 and maneuvered cautiously through the South China Sea, it embarked on an unprecedented journey.

To date, no other ship has ever transported such a volume of containers: 21,710 6-meter units.

This 399.9 meter long and 61.5 meter wide vessel is a true giant, but dozens of similarly sized container ships sail today.

Many more are under construction. Two of them, stacked vertically, would be nearly as tall as the world’s tallest building, Dubai’s Burj Khalifa.

The largest cargo buses in the world are 400 meters long and around 60 meters wide. This is roughly the current upper limit for these ships and there are a surprising number of reasons why they aren’t getting bigger.

You are unlikely to see container ships much larger than this.

There are around 5,500 container ships in the world and together they are capable of carrying 25 million TEUs (twenty foot equivalent unit), equivalent to around 25 million 6 meter containers if they were all charged at the same time.

George Griffiths, editor of global container markets at S&P Global Platts, explains that the global order book for new cargo vessels will increase this total collective capacity by 25% in just a few years.

“We are seeing a lot more ultra-large container ships being built,” he says. “The proportion of new ships carrying more than 14,000 containers is staggering.”

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The global container fleet is growing.

In the last decade alone, the average capacity of a container ship has increased from less than 3,000 TEUs to around 4,500 TEUs. And there are now over 50 ships with a capacity of 21,000 TEUs or more. Almost all of them were built within the last five years.

However, these ships are crossing the limits of even the largest ports in the world, says Griffiths. To load and unload the containers, the cranes have to pass by the ships.

Container ships must also turn and pass through locks and canals, including the Suez and Panama Canals, which are subject to size restrictions.

It is also crucial that ships avoid running aground. In some ports, large ships are so submerged that they touch the bottom and slide on the sediment instead of floating, says Stavros Karamperidis, director of the shipping research group at the University of Plymouth, UK. . Such a maneuver should be treated with extreme caution.

What are the options?

To accommodate vessels much larger than the largest that exist today would require a major overhaul of port infrastructure. And that would be incredibly expensive.

“Why invest in bigger ships if it means you also have to invest huge sums in ports,” Griffiths points out.

Mr Karamperidis adds that large ships are also limited in terms of the routes they take, as they are very vulnerable to the weather. They tend not to cross the Pacific, for example, because of severe storms. Medium-sized container ships sometimes lose hundreds of containers in the Pacific.

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Containers are also strapped to hold them in place.

“That is why the ships [ultra-grands] approach the shore to avoid large waves. It’s a matter of stability,” Karamperidis says. He adds that most US ports aren’t big enough to accommodate the largest container ships. Only a handful of ships with a capacity close to 20,000 TEUs arrived at US ports.

Limits on ship size have less to do with the technical challenges of building very large ships than with the economics and logistics of operating such behemoths.

“Physically, there really is no limit,” says Rosalind Blazejczyk, managing partner and naval architect at Solis Marine Consultants.

Containers are also lashed down to hold them in place, and these systems have upper limits on the number of boxes they can safely hold, says John Simpson, Blazejczyk’s colleague at Solis.

Another issue is how these big, wide ships handle the waves. When sailing directly through a sequence of waves, ships can experience a phenomenon called parametric roll.

When waves pass the length of a very wide container ship, its bow and stern may stick out of the water as long as the peak of the wave is amidships. This leaves the top of the bow and stern unsupported by the water. The variation of this support, according to the waves, can cause the ship to oscillate oddly from side to side.

“You get very large roll angles with not very large wave heights,” says Blazejczyk.

Large ships are more at risk. Container ships also have very large hatches on their decks, which means that their overall structure is weaker than that of other ships and more susceptible to twisting.

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One of the drawbacks is the way very large and wide boats handle the waves.

“They’re like a shoebox without a lid,” Blazejczyk adds. Not a problem in calm seas but, again, limiting when or where a ship sails probably also limits its usefulness.

economy

In addition to all these reasons, we must take into account the economic climate. Mr Griffiths points out that the price of oil is extremely high at the moment and that large container ships need large amounts of fuel.

However, investing in even bigger ships might not be the smartest financial option in the future. At present, these costs are more than covered by the astronomical freight rates charged worldwide. This is the current demand for freight transport.

For container ships with a capacity well above 25,000 TEUs to be viable, the economics of operating them would need to change, says Mr Karamperidis.

The Suez Canal will probably always be a bottleneck for ships traveling from Asia to Europe, but it is not impossible to imagine a 30,000 TEU or similar ship traveling a route from China, for example, to a booming African port, says Karamperidis.

“Maybe we will see these kinds of ships going from Asia to Mombasa,” he adds, referring to Kenya’s biggest port.

The cap of 24,000 TEU set today for container ship capacity worldwide is, more or less, a reflection of economic limits as much as those of port infrastructure, the shape of the busiest waterways world and engineering.

But under the right conditions, there is always the possibility that someone with enough money will one day command a ship that dwarfs even the giant ships of today. It would certainly be a wonderful thing to see.

Source: www.bbc.com

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