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Breaking:Hull Fatigue Cause of Cheonan Sinking?

April 5, 2010

Now here is a twist on the South Korean corvette sinking mystery. From the Korea Times:

The Navy uses some vessels that have cracks or other flaws after maintenance, or whose lifespan was exceeded years ago, cable news network YTN reported Monday. The report said that although the military has denied it, a so-called fatigue fracture might be one of the probable causes of the sinking of the frigate Cheonan in the West Sea on March 26.

Citing documents submitted to Rep. Song Young-sun back in 2004, the report said nine Navy vessels that were used in military drills had stress-corrosion fractures or cracks…A 2006 report from the Navy also said about half of its ships were used beyond their lifespan ― 9 percent of them were nine years past their operational life.

The implications of this for the USN, might be a need to replace ships on a regular basis, thinking of the 30 year old Perry class and the Cyclone patrol craft to name a few, the latter entering its 3rd decade in service. It is one thing to keep a supercarrier in service for 40-50 years (how is that working out btw?), put a light-weight escort is meant to use and then replace quickly, especially if the price is right.

13 Comments leave one →
  1. susie h. permalink
    April 29, 2010 7:50 pm

    people are posting ignorant comments on this article.
    the main fact is that many people in korea lost their family members
    and loved ones.
    and it is known that a n. korean general was “awarded” for sinking the cheonan ship.

  2. John permalink
    April 14, 2010 12:07 am

    I am amazed at the ignorance that is so often evident in the comemnts submitted on issues such as this ‘Cheonan Incident’. Simply because a ship is ’20 years old’ (or whatever it may be) does not create a valid argument that it is ‘beyond its shelf life’ and likely to spontaneously destruct. The majority of self-respecting navies have maintenance programmes which can result in steel-hulled vessels running on until eternity. Plates, frames and stringers which are corroded can be cut out and replaced – as one may replace panels on a car. It is usually when, for a number of possible reasons, that it is no longer economically viable to upgrade the non-structural elements of a vessel (e.g. plant, sensors and systems) that a decision will be made to discard a vessel. I acknowledge that i have tried to make my comments as simple as possible, so there are other factors that may be considered. However, I have neither the time, nor inclination, to provide an in-depth education on Naval Construction to those contributors here who are blowing smoke through their sterns.

  3. B. Walthrop permalink
    April 8, 2010 11:39 pm

    “As to the possibility of the ship having been wrecked on a rock, Senior Chief Petty Officer Kim Byung-nam, the helmsman, said that it was unlikely.”

    SCPO as a helmsman? Really?

    There will not be a transparent accounting of this incident.


  4. D. E. Reddick permalink
    April 7, 2010 1:29 pm

    Here’s a second report regarding that news conference and what surviving crew members of the Cheonan had to say about its sinking.

    The Korea Times: ‘Cheonan on Routine Mission Before Sinking’

    One More Body Retrieved

    By Jung Sung-ki
    Staff Reporter

    Survivors from the sunken frigate said Wednesday that the ship was operating normally before an unidentified explosion tore the hull open.

    Some stated they had heard two loud explosions and immediately felt the ship tilt about 90 degrees to starboard. Other said they hadn’t seen a column of water at that time.

    The 1,200-ton Cheonan was sailing in waters off Baengnyeong Island near the western sea border on a routine mission before the blast occurred at 9:22 p.m. on March 26, investigators and survivors said at a press conference at the Armed Forces Capital Hospital in Seongnam, Gyeonggi Province.

    Dozens of sailors made their first public appearance since the naval disaster. Fifty-eight sailors, including the captain, Cmdr. Choi Won-il, were rescued. Two sailors have been found dead since last Saturday, while 44 others remain “missing in action.”

    “I’m curious myself about what caused the explosion. I knew the area like the back of my hand and was still unable to detect any unusual symptoms (before the blast),” said Cmdr. Choi. “I have not given up hope, I’m still waiting for the rest of my sailors to report their return.”

    Senior Chief Petty Officer Oh Seong-tak said he had been in a compartment two decks below sea level and felt his body lifted up in the air after a “booming” sound.

    “The electricity failed after an ear-splitting explosion,” Oh told reporters. “The ship immediately tilted about 90 degrees.”

    He said there had been no smell of gunpowder, raising doubts about an onboard explosion or blast from outside.

    Petty Officer 1st Class Hong Seung-hyeon, who was in charge of the ship’s sonar, said he hadn’t detected any unusual signals before the explosion.

    As to the possibility of the ship having been wrecked on a rock, Senior Chief Petty Officer Kim Byung-nam, the helmsman, said that it was unlikely.

    “If a ship is wrecked on a rock or stranded on a sandbank, the sound made is like a piercing shriek,” Kim said. “So I’m guessing the incident occurred because of an outside impact.”

  5. D. E. Reddick permalink
    April 7, 2010 1:09 pm

    There has now been a news conference with the surviving crew of the Cheonan. Crew members speak directly about an explosion causing the corvette to break into two.

    Al Jazeera English: S Korea sailors recount ship blast

    The surviving crew said the cause of the blast appeared to come from outside the ship

    Survivors of last month’s deadly explosion aboard a South Korean patrol boat have been recalling their ordeal for the first time, describing a huge blast that tore through the ship as it sailed near the disputed border with North Korea.

    On Wednesday the 58 survivors from the sunken ship appeared at a televised news conference at a military medical facility near Seoul recounting the deafening explosion followed by a desperate struggle to escape the ship as it was plunged into darkness.

    “I was preparing to report for duty when there was a sound of an explosion which hurt my ears and I was thrown in the air,” said Oh Seung-tak, a senior petty officer.

    “Power was immediately cut. I was hit in the face by a flying computer and lost consciousness momentarily. When I regained my senses, everything was dark.”

    Oh, who was in charge of munitions storage, said that he detected no smell of explosives from inside the ship and nothing unusual before the blast.

  6. D. E. Reddick permalink
    April 6, 2010 5:48 pm

    The South Koreans are moving quickly to salvage the stern section of Cheonan. There is now a 2,200 ton floating crane situated at the site to raise the stern section of the sunk corvette. Go to the following site. The discussions there are lively. Two photos show the crane in place near Baengnyeong Island. We may soon learn much more regarding the sinking of the Cheonan.

    Another, -very- lively and informative discussion regarding the sinking of Cheonan can be found at the following site and thread. Some commenters do appear to be knowledgeable regarding torpedoes and so their commentary seems to be directly pertinent to how the sinking of Cheonan should be evaluated. The discussion gets really good and informative around pages 16 through 18.

    A third source for information and discussion regarding the sinking of Cheonan can be found here.

  7. B. Walthrop permalink
    April 6, 2010 2:36 pm

    While I am by no stretch of the imagination an ardent supporter of corvette sized vessels as our host, it is probably a bit of a stretch to use the sketchy information available about this incident to argue against them.

    It seems very unlikely to me that we will ever get a completely satisfying public accounting of the cause of this sinking.

    There is just too much at stake politically regardless of the technical details to expect a completely transparent account.

    Something to keep in mind if the US, UK, or AUS experience a similar occurrence.


  8. Moose permalink
    April 6, 2010 12:25 pm

    As in the US, Korean cable networks’ first responsibility is to get more viewers. Cheonan didn’t suddenly split in half, all aboard and nearby confirm an explosion which rocked the ship to one side. Stress fractures d0n’t do that, no matter how catostrophic.

  9. Chuck Hill permalink
    April 5, 2010 6:30 pm

    TV program exploring the probable cause of the MAINE sinking showed that in-rushing water may cause plating to bend inward, even if explosion was internal.

  10. Scott B. permalink
    April 5, 2010 6:19 pm

    ROKS Cheonan was commissioned in 1989, so that it may have suffered such a catastrophic structural failure after 20 years of service might give an indication of how solid all those mythical 1,000-ton corvettes actually are.

    For some reason, this *incident* (if confirmed) also reminds me of what happened to HMS Branlebas (895 tons fully loaded) back in December 1940.

    And I am supposed to believe that the mythical 1,000-ton corvette is the way to go for a Navy that’s meant to deploy globally ?


  11. D. E. Reddick permalink
    April 5, 2010 6:11 pm

    And here’s a totally different view on what happened to Cheonan.

    The Chosun Ilbo: Rescue Divers Believe the Cheonan Was Hit from Below

    Observation from Navy divers appears to support theories that the corvette Cheonan may have been dealt a heavy blow to its underside by a torpedo before it sank.

    Divers said structures at the rear of the Cheonan were bent as if they had received a strong blow from beneath. The comments also give weight to theories that a “bubble jet effect” had caused the Cheonan to sink, referring to an intense shock wave and high-pressure bubbles that may have caused the vessel to split in half.

    But visibility on the sea floor was extremely poor, allowing divers to see barely 30 cm. They ventured forward while closely observing the severed section so it is difficult to say exactly where, but the aluminum structure above the chief petty officer’s mess was bent upwards as if due to shock from beneath.

    The body of Senior Chief Petty Officer Nam Ki-hoon was found lodged inside the aluminum structure on the ceiling of the mess hall. Only the upper structure was bent upward, divers said, adding that it was difficult to determine how far the metal had been bent. A military spokesman said, “Those signs point to the vessel suffering from a strong blow from below.” / Apr. 05, 2010 11:48 KST

  12. Chuck Hill permalink
    April 5, 2010 5:44 pm

    How do you think the Coast Guard is doing in this regard?


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