I don’t know about you guys, when I heard about the MOL Comfort going down, it brought up a lot of uneasy feelings about the vessels I ride on, especially during heavy weather. GCaptain himself has graced us with an article recently (http://gcaptain.com/mol-comfort-report-coming-soon-classnk/) indicating that ClassNK, a classification society in Japan, is about to release a report about the Bahamian flagged vessel. I’ve read this vessel used thinner, high tensile steel to achieve a lower lightweight than what otherwise would be possible. Just my tuppence worth, I think the steel was below spec, creating a situation where members were stressed within design tolerance though outside physical capability. Anyone want to take a bet?
high tensile steel in ships is a terrible idea and has been proven time and again to not work. Who remembers those US crude tankers that had high tensile steel hulls? A TOTAL FAILURE!
[QUOTE=c.captain;143585]high tensile steel in ships is a terrible idea and has been proven time and again to not work. Who remembers those US crude tankers that had high tensile steel hulls? A TOTAL FAILURE![/QUOTE]
The only two tankers I can remember that had similar catastrophic hull failures were the Erika and the Prestige, neither of which were flagged in the U.S.
And I get what you are saying in that since high tensile steel is much more prone to brittle fracture, it is not really a good idea to use that stuff on something that undergoes all kinds of flexing.
[QUOTE=c.captain;143585]high tensile steel in ships is a terrible idea and has been proven time and again to not work.[/QUOTE]
Oh shit. We have used high tensile steel in just about every project since the 70s or so. Better call an emergency meeting in the afternoon…
[QUOTE=TrainMan;143601]The only two tankers I can remember that had similar catastrophic hull failures were the Erika and the Prestige, neither of which were flagged in the U.S.
And I get what you are saying in that since high tensile steel is much more prone to brittle fracture, it is not really a good idea to use that stuff on something that undergoes all kinds of flexing.[/QUOTE]
no there was a series of crude carriers which I believe were ARCO ships which suffered repeated major hull cracking and eventually were pulled from service. Sorry I can’t recall the ships and the details but I remember them sitting in Portland. None suffered a catastrophic hull failure but the problem with the steel becoming too brittle was severe.
you are certainly correct that high tensile steel does not have the ability to flex over the years of a ships life without failing hence why mild steel is the better material to use even though it means a heavier hull.
Hate to tell ya, but almost all single hulled tankers have / had fractures in the structure. Say dozens and dozens, per ship, HTS or mild stl.
The trick is to find and repair them regularly, or modify the structure so it doesn’t happen again. Since the tanks on a ULCC are so big, it takes a LOT of effort to find them before they get problematic. You can go right to where the fractures are usually at, usually frame brackets closer to bulkhead, at the longitudinals and the big corner brackets.
Off hand, I’d say the main thing is not so much the material but the arrangement of the structure to distribute the loads and minimize fatigue. Any steel will fail with enough cycles approaching the yield point. I’ll read that MOL report…
And do not forget the affect of un-addressed corrosion or wastage. That’ll ruin your day, and had a lot to do with some structural failures of note in the 80’s & 90’s…
[QUOTE=+A465B;143612]Hate to tell ya, but almost all single hulled tankers have / had fractures in the structure. Say dozens and dozens, per ship, HTS or mild stl.[/QUOTE]
but ships built with high tensile steel hulls crack at a much greater rate than mild steel and are more costly to repair…
[QUOTE=c.captain;143611]no there was a series of crude carriers which I believe were ARCO ships which suffered repeated major hull cracking and eventually were pulled from service. Sorry I can’t recall the ships and the details but I remember them sitting in Portland… [/QUOTE]
Arco Spirit and Arco Independence, originally built by Gulf as the American Spirit and American Independence. http://www.aukevisser.nl/supertankers/part-1/id359.htm
I’m not sure they qwere liad up solely because of a propensity for hull failures. A 1989 study of vessels in the Alaska trade did not identify them as having an inordinately high incidence of hull fractures, and did not identufy them as needing special monitoring: http://www.shipstructure.org/pdf/91symp26.pdf (I’m aware of this study as one of the vessels I worked on, Mobil Arctic, was identified as needing heightened monitoring for hull failures). The report does discuss high tensile steel and notes that vessels constructed with it had higher than usual fauilure incidents. However they attributed these to design and construction issues and not solely because of the qualities of HTS.
As I recall, the Arco ships’ subsidy arrangements were such that they could only operate on of the two in the TAPS trade at any tuime, and there were problems finding non-TAPS work for the other ship, so they were rotated in and out of lay-up every six months.
[QUOTE=+A465B;143612]Hate to tell ya, but almost all single hulled tankers have / had fractures in the structure. Say dozens and dozens, per ship, HTS or mild stl.
The trick is to find and repair them regularly, or modify the structure so it doesn’t happen again. Since the tanks on a ULCC are so big, it takes a LOT of effort to find them before they get problematic. You can go right to where the fractures are usually at, usually frame brackets closer to bulkhead, at the longitudinals and the big corner brackets.
Off hand, I’d say the main thing is not so much the material but the arrangement of the structure to distribute the loads and minimize fatigue. Any steel will fail with enough cycles approaching the yield point. I’ll read that MOL report…
And do not forget the affect of un-addressed corrosion or wastage. That’ll ruin your day, and had a lot to do with some structural failures of note in the 80’s & 90’s…[/QUOTE]
On the MOL Comfort and sisters HTS was used to strenghen around the hatch openings. The inital crracks however were in the bottom plates. The areas were HTS was used was the last part to fail.
The report says the sister ships have buckling in the bottom plates. Ships were only 5 years old. Wastage likely not an issue.
[QUOTE=Kennebec Captain;143620]On the MOL Comfort and sisters HTS was used to strenghen around the hatch openings. The inital crracks however were in the bottom plates. The areas were HTS was used was the last part to fail.
The report says the sister ships have buckling in the bottom plates. Ships were only 5 years old. Wastage likely not an issue.[/QUOTE]
Thanks Kennebec. Figured wastage wasn’t an issue for MOL, but it was in some tanker and bulker structural failures. I’ve put 150 tons of new steel in a forepeak tank that everyone thought was just peachy fine until we mucked it out, then we started on the cargo block …
It’s interesting that the designers were unable to replicate using computer models the bottom shell buckling found on the ships. Maybe the models don’t capture something or perhaps some combination of over-wight containers, quality control in the shipyard and pushing the ships too hard in rough seas is not being taken into account.
EDIT: Interesting reading her here
One of the ships had to have emergency repairs after being sailed 14 kts into 12 meters (40 foot) seas. I would think that would do it.
[QUOTE=c.captain;143614]but ships built with high tensile steel hulls crack at a much greater rate than mild steel and are more costly to repair…[/QUOTE]
I’d be curious to see some data backing up those two statements.
I’ve done a lot of repairs and seen a whole lotta ships of all sorts. HTS is used mainly around openings or maybe a sheer strake, and of course on floaters. So if in the old days they tried a bit more (those tankers you mentioned ??) and it flunked, okay. I think you are absolutely right for those tankers that went light on the scantlings in the 70-'s & 80’s
The Common Structural Rules across IACS class societies now used are intended to encourage better design from the start.
I do not sense that repair material and handling cost by the kilo is very different for mild v. HT stl, at least in the B-D grades. EH can be a pain, especially if pre-heating is needed to weld it, but who uses a lot of it ? It is just used here and there. I’ve seen some seriously mean high pressure vessels made with all HTS and the weld preheat was close to 400 deg F - a bummer for the welder inside, and yes, they had to get inside.
Nowadays in my new life I still deal with a lot of boats with HTS in 'em, and I think overall they have no higher failure rate nor repair costs that I can detect, but we maintain and inspect pretty heavily so stuff doesn’t run amuck.
The repair cost depends on how conservative the original design, the maintenance along the way, what are the operating profiles and how good are the coatings. From our view we would rather design - build - operate with grade A mild stl, but sometimes the solution needs to be a bit more elegant to meet the performance spec …
But hey, I am wrong all the time, so send along that data. You’re very good about finding and posting some real some cool stuff and it is quite enjoyable to read, be it educational, humourous or even just plain pissy !.
[QUOTE=Kennebec Captain;143620]On the MOL Comfort and sisters HTS was used to strenghen around the hatch openings. The inital crracks however were in the bottom plates. The areas were HTS was used was the last part to fail.
The report says the sister ships have buckling in the bottom plates. Ships were only 5 years old. Wastage likely not an issue.[/QUOTE]
Well I know the crews are just going to nip right on down to those DB SWB tanks, pop the manholes, ventilate and do a regular walk through in all that spare time. 1000 footers, why hell, they are probably up to 18 crew nowadays.
Deformed (did it say buckled?) bottom plate / structure can be a bummer in the mid body, specially if it was concentrated right there at the bulkhead. But hey, 20mm deformation over 20 meters is basically meaningless. 20mm deformation in 2 meters is deep shit coming.
But the real story is we are internet bullshitters that aren’t going to know, and no one is gonna fess up to more than that plain Jane report.
We had never ending deck cracking on the Keystone Canyon and the Kenai on the TAPS run. There is no shortage of info on HTS issues on that run.
However, I think it is bogus to claim the MOL issue is the result of using HTS, if you look at the only place it was used you will see that was the last piece of structure holding the hull together before it finally parted.
There is a drawing somewhere online that shows where HTS was used on those ships and it shows clearly where the hull did not fail.
[QUOTE=+A465B;143628]Well I know the crews are just going to nip right on down to those DB SWB tanks, pop the manholes, ventilate and do a regular walk through in all that spare time. 1000 footers, why hell, they are probably up to 18 crew nowadays.
Deformed (did it say buckled?) bottom plate / structure can be a bummer in the mid body, specially if it was concentrated right there at the bulkhead. But hey, 20mm deformation over 20 meters is basically meaningless. 20mm deformation in 2 meters is deep shit coming.
[/QUOTE]
Yeah it says buckled, 20 to 40 mm, enough to knock the paint off.
Since we’re on he subject, this sounds like a QC and heavy weather incident:
If part of the committee’s findings or hypothesis is that the buckling existed for 3-1/2 years, how was it missed on dry dock survey? I mean they DO have superintendents, captains and chiefs that are actually supposed to look. Just sayin THAT doesn’t make sense.
With all due respect I have not seen many captains crawl double bottoms. None that I sailed with anyway.
[QUOTE=Chief Seadog;143646]With all due respect I have not seen many captains crawl double bottoms. None that I sailed with anyway.[/QUOTE]
I’ve seen 'em do it after they done run the container ship aground.
But more importantly, they darned well better be under the ship in dry dock for a good “look see” before and after water washing. And the chief too.