Ships never fail to capture my interest. Every time there is a new record in shipbuilding or a major maritime accident, I would rush to collect information about it to bring myself up to date.
The sinking of the Oriental Star on June 1, which claimed more than 400 lives, was heartbreaking.
What exactly caused the tragedy is still unknown, and the truth is blurred by China’s censorship.
Snippets of information point to the bad weather and fairway conditions in the section of Yangtze River where the sinking occurred. Negligence on the part of the captain and his crew is also possible.
This column aims to focus on a more objective aspect rarely touched by the media so far – the Oriental Star’s seaworthiness.
It is not a purely technical issue; whether the cruise ship was suitable for voyage that night may entail a lot of questions about responsibility and supervision.
Sailing along inland waterways is both difficult and risky because of the constantly flowing river. A ship is hard to control once it loses power.
If the riverbed is already covered with loose sediment and mudflats, dropping anchor to moor the ship won’t help much either, especially against the torrent of water.
It’s also very difficult to rescue passengers entrapped in a capsized ship because of low visibility underwater and challenges in positioning.
There are other factors such as winding river channels, large rocks and turbulent flows at turnings.
Also, if both banks are steep cliffs – just like the Yangtze River – the channel can become a gusty and dangerous wind tunnel.
Given all these, the design and construction of river vessels must be done with utmost care.
The Yangtze River is over 6,300 kilometers in length with complex variations in water flow, riverbed, etc.
If a ship is built to cruise the entire river from downstream Nanjing all the way up to Chongqing, where a major tributary joins the river, its design must give absolute priority to safety with precautions and adequate room to respond to contingencies.
Unfortunately, the Oriental Star was doomed in its design. Two rounds of retrofitting over the years to enhance its capacity and recreational facilities had compounded its fatal deficiencies.
The first aspect concerns its length, width and height and the corresponding ratio.
Sediment constantly thickens the riverbed and a vessel’s hull must be shallow enough for it to sail through. For this reason, most river ships, including the Oriental Star, are flat-bottomed without any ballast attached to the bilge.
This is indeed a compromise on safety: the vessel is prone to gale-force gusts and thrusts that may overturn it.
Once capsized, such a vessel can hardly rollback on its own.
The rule is that for a flat-bottomed vessel, it cannot be too long nor too high. That’s because the specific wind exposure area is roughly the product of the vessel’s height above the water multiplied by its total length. The thrust is determined by wind exposure area and wind speed.
Built in 1994, Oriental Star’s original size was 65.5 meters in length and 11 meters in width. It had four storeys above its draught line.
I found a riverboat of similar size in the United States for comparison: the American Eagle, which cruises the Hudson River in eastern New York state.
The American Eagle is 43.5 meters in length and 12 meters in width and it only has three storeys. In other words, its length/width ratio is more optimized, making the ship much safer.
My calculation shows that the American Eagle’s exposure to thrust is 45 percent less than that of the Oriental Star.
The Chinese vessel became 11 meters longer after retrofitting, which meant the thrust exposure would be 2.6 times that of the American Eagle. It is also said that it didn’t undergo stability tests before being recommissioned.
Usually, there will be a powerful bow thruster installed outside the bottom to generate propelling force horizontally to help stabilize a vessel, especially a longer one, and make corrections to its tack as well. The American Eagle has such a bow thruster; the Oriental Star had none.
From the Chinese ship’s positions, as shown by its automatic identification system 12 minutes before it sank, we know that it was blown further offshore to the middle of the channel and it lost power amid the captain’s failed efforts to turn the ship to align it with the gust direction. It was pushed to the eastern shore and ultimately capsized.
Had it not been for the flawed design, subsequent modifications and the lack of bow thruster, the tragedy could have been avoided.
One more fact is that the Oriental Star’s maximum speed is 6 knots, which is obviously inadequate against the Yangtze River’s prevailing centerline water velocity of 3-4 meters per second (5.8-7.7 knots) near its Chongqing section.
This means the ship can only sail close to the bank where the river flow is slower in order to go upstream. The American Eagle can navigate at 13 knots.
Regardless of China’s economic success, it is still a developing country. Compared to the developed world, both the government and the public are not putting enough emphasis on safety yet.
While directing investigators to find out who should be responsible for the accident, authorities are also obliged to review the safety standards for vessel design and construction.
The article first appeared in the Hong Kong Economic Journal on June 9.
Translation by Frank Chen
[Chinese version 中文版]
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