5 year old container ship breaks in half

I wonder if the local navy will use the containers as target practice, to prevent other vessels from up close and personal relationships with them. I think my new inflatable girlfriend, was in one of those containers too . . . Damn . . .

 

If she had auto lnflation she may have survived when they blew the door off the container. Could be floating around with her feet behind her ears as we speak.

 

I would have thought that Japanese inspectors (she was built under Class NK - Japanese classification society) are more meticulous in doing their job than any other, but evidently I was wrong...

 

From the company MOL

Walmart is very happy. It will have been a nightmare if all the containers with hundred of millions dollars of plastic craps from China was lost

 

After the June 24 news release, the aft part with those containers sank.
The fore part with those containers is being towed making "about 2 knots"
http://gcaptain.com/comfort-towed-stern-images/

 

The results of an investigation into the hull failure on the mol-comfort has been released and is reported on gcaptain.

http://gcaptain.com/mol-comfort-investigation-classnk-unable-replicate/

 

interesting that they would depend so much on their simulations that clearly are incorrect.

the reports states " buckling deformations of approximate 20mm had been found on the sister vessels of the MOL Comfort, however the committee was unable to reproduce the deformations under their structural simulations, “even when applying loads near the ultimate hull girder strength,” according to the report."

the simulations are only as good as the assumptions that go into the programing. clearly there are forces here that they are missing, meaning that their simulations is worthless as a diagnostic tool, or even as a design tool.

 

Leave the salvage to the respective insurance companies after all this disaster was covered.

 

The bow portion later caught fire while under tow. The fire apparently originated in one or more containers. After the fire burned out the containers, the tow line parted and the bow was later reported sunk.

http://gcaptain.com/molcomfort-fire/

Both ends of the MOL Comfort are now safely on the bottom of the Indian Ocean several hundred miles apart. She is survived by several sister ships, however.

 

What an end for PAR's new girlfriend . . . ​

 

It's classic overloading of the ends. A steel ship doesn't hog as much as a wooden ship does when the ends are overloaded, so it doesn't get noticed until it breaks.

Here is a quote from a Wikipedia article

"If the ship's structure, equipment, and cargo are distributed unevenly there may be large point loads into the structure, and if they are distributed differently from the distribution of buoyancy from displaced water then there are bending forces on the hull."

There is a good article in the Wooden Boat Magazine #113 (pp 70 - 81) on the causes of hogging in wooden ships which looks at the whole picture. It points out that the buoyancy of a hull is concentrated at midships but the loads tend to be distributed more evenly.

Apparently the prevention of hogging in classic ships under preservation is poorly understood. You'd think after a couple of thousand years . . .

 

The material matters not. On large vessel one performs a simple loading curve v buoyancy. Like the image on the left. And from this data we can get the shear forces, image on the right. The sequence of loading in the operating manual that the Capt must adhere to is based upon this type of analysis. The maximum loading condition dictates the structural arrangement.



The hull girder must have a modulus that can withstand such a load. This is the structural "EI". The I = the second moment of inertia and the E, the material property.

The response of the hull girder from an applied load must be within safe limits.

The flexing is a result of what the designer has used as their safety limit coupled with the material of choice. However, if the hull flexes too much WTB doors etc will pop out, WTBs become prone to cracking and leaking, main structural girders/longts can crack and of course the fatigue aspect. Thus flexing is a structural consideration whether within safe stress limits or not.

So a carte blanche statement of wooden ships flexing different may or may not be true, but also may or may not be depending upon the type of boat and the loadings and then one must compare like for like with a steel one. Since the criterion of max deflection would be the same for both vessels, regardless of the stress values.

If there is a problem with large wooden vessels, then the analysis has either not been done properly or simply not done at all.

 

Class NK issued some preliminary findings about the MOL Comfort casualty in November 2013:

http://gcaptain.com/classnk-issues-preliminary-findings/

For a while, the sister ships were withdrawn from service temporarily.

Then, at the end of the year, Class NK issued a press release saying that their analysis was unable to reproduce the cause of this casualty:

http://gcaptain.com/mol-comfort-investigation-classnk-unable-replicate/

However, the title to this story is 'Container ship sinks, Underwriters hardest hit', because the value of the cargo may be approx. 10 times the value of the ship:

http://gcaptain.com/mitsui-osk-lines-sues-shipbuilder-mol-comfort/

 

AH, your quite correct in what you say and the material does not effect the analysis but the assembly method matters a great deal to the subsequent behavior of the hull. Caulking fails and fasteners creep in a wooden hull. That wasn't really the point I wished to make; the articles I referenced noted that when load is distributed differently to buoyancy an imbalance of forces occurs. For a steel ship loaded to its limit out to both ends sugjected to certain conditions of wave length and height the some total of forces can be disasterous especially if fatigue has set in. When the cargo value greatly exceeds that of the ship greed over-rules caution and common sense.

Ship owners and inspectors can't always know what is going on in the depths of their vessels: I recall Canadian Coastguards being especially concerned a couple of decades ago by a spate of bulk ore carrier losses; the ore was literally wearing the bottom of the ship to half its original thickness or less and they had no reliable way to test for it, at least back then. Loaded bulk ore carriers go down fast when they break so the evidence is lost.

Do loading procedures and rules take account of wear and tear on the hull, the potential for cargo to shift in a storm and the effect of sea conditions on a hull? It would be nice to think so, but reading that some analysis doesn't explain the demonstrated damage doesn't restore confidence. Aircraft manufacturers and authorities are less cavalier.

BTW, there is indeed a problem specific to large wooden vessels, built before the modern age with its excellent adhesives. It shows up when a classic ship is unloaded for restoration and preservation. Typically the holds are emptied and the ship lightened but often the heavy gear at the ends is left for tourists to admire, resulting in worse hogging forces than the ship experienced in service. Later wood ships were built with diagonal iron or steel struts to help prevent the condition. I suppose creep doesn't occur in a welded steel hull but fatigue does. I have read that wood is one of the most fatigue-resistant materials.

 

A hull has buoyancy and a buoyancy curve. Unless the hull form is different this is common whatever the material choice.

Loading a vessel to its limits, must be taken into consideration by the NA. As such the response will be dictated by the materials choice for the stress and deflection given that the hulls shape is the same for both materials.

Thus whatever the hull material, what ever the sea conditions, the same methodical procedure for designing the hull structure is taken.

If a hull is over loaded or loaded in a manner that is not in keeping with the operating manual, one cannot blame the hull material or wave length or whatever one wishes to drag up.

Fatigue is just a flexural issue which all vessel experience. The stress range ratio, amplitude as well as the environment and localised issues along with quality of manufacture come into play. Again, common to both materials. But so long as the NA has taken these issues into account...no difference between the 2 hull materials.

Thus, i'm still not sure what your point is?