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The Sinking of MS Estonia: Case Re-opened Part II

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Vixen said:
Once again another false premise as the lug was not of an 'o' shape but an ellipse due to earlier modifications (which the JAIC mistakenly believed was due to the accident).
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As quibbles go that one is pathetic.
 
Captain_Swoop said:
Maybe they should have replaced it as it seems to be the welds that finally gave out.
I would hope they had their own welding suitable tested after it was complete.
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My recollection (which I should perhaps not trust quite so confidently) is that the welds were cracked and damaged but did not yield - the pin was instead torn out of the lugs on the lock side so it could then slip out of the visor lug, which was bent somewhat to one side and elongated (though that elongation may have been historical).

Now I wasn't completely clear about the description in the report but that's what it appeared to say to me.
 
Captain_Swoop said:
If anything the lug being forced out of round in to an oval shape is an indication that something was seriously wrong and the part was being over stressed.
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JayUtah said:
^^ This.
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Agreed.

Could also be long term fretting and impact wear. If the latching, or even hinging, mechanism is not secure the pins could oscillate inside the lugs sliding back and forth as well as chattering against one side of the lugs. The long term wear would elongate the opening of the lugs in the direction opposing the major restraining force (what holds the thing closed). Perhaps exacerbating weld deficiencies or even causing fatigue failure of the support structure.

If the reports of the warning system being compromised are true it could be a indication of the bow not securely staying closed. Resulting in annoying intermittent warnings.
 
GlennB said:
As quibbles go that one is pathetic.
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The Man said:
Agreed.

Could also be long term fretting and impact wear. If the latching, or even hinging, mechanism is not secure the pins could oscillate inside the lugs sliding back and forth as well as chattering against one side of the lugs. The long term wear would elongate the opening of the lugs in the direction opposing the major restraining force (what holds the thing closed). Perhaps exacerbating weld deficiencies or even causing fatigue failure of the support structure.

If the reports of the warning system being compromised are true it could be a indication of the bow not securely staying closed. Resulting in annoying intermittent warnings.
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As apparently the pins had to be forced home with big hammers I don't think there was a problem with them oscillating. More likely the forcing home would wear and stretch the part
 
The official report (Section 8.6.1) explicitly deals with what failed and what did not fail wrt the bottom lock:

The three lugs that were attached to the hull all failed.

The single lug that was attached to the bow visor, plus the bolt itself, did not fail.

So the failure mode was clearly as follows:

The bottom lock - in which a bolt passed through the three hull-side lugs and the single visor-side lug, thereby locking the hull and the visor together - was placed under stress in the storm and swell.

This, plus (almost certainly) a combination of cumulative fatigue and poor maintenance, caused the three hull-side lugs to fail.

And this in turn resulted in the lock separating, with the visor-side lug (plus the bolt itself, still passing through that visor-side lug) remaining attached to the visor as it swung up by its top hinges.

Simples.
 
Incidentally, the description of the lug-and-bolt mechanism of this lock makes it highly likely that the single visor-side lug was a double lug - so that the connecting bolt went through, in order:

Hull-side lug #1
First aperture of visor-side lug
Hull-side lug #2
Second aperture of visor-side lug
Hull-side lug #3
 
I seem to recall the diagram of the lock shown <waves hand> somewhere back there shows a tube joining the first and second hull side lugs, which the pin would retract into. So there was only one visor lug, between the 2nd and 3rd hull lugs.
 
LondonJohn said:
Incidentally, the description of the lug-and-bolt mechanism of this lock makes it highly likely that the single visor-side lug was a double lug - so that the connecting bolt went through, in order:

Hull-side lug #1
First aperture of visor-side lug
Hull-side lug #2
Second aperture of visor-side lug
Hull-side lug #3
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spread the load
 
Captain_Swoop said:
As apparently the pins had to be forced home with big hammers I don't think there was a problem with them oscillating. More likely the forcing home would wear and stretch the part
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OK, hadn't seen that. The report did note that one of the visor hinge pins had a tendency to move out of position but that was repaired.


One of the visor hinge pins had, according to verbal information, a tendency to move out of position, breaking away the locking plate. This was repaired once at the Finnboda yard by pushing the hinge pin back in place and drilling for new locking bolts.
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Perhaps this is where someone got the impression that the main locking lugs had been drilled. The reference to drilling for new locking bolts here would only be for the locking bolts for that wandering hinge pin.

ETA:

Also ,as I recall, in the report the warning system showed the ramp as unlocked because one pin had a tendency not to full seat. The visor showed as locked and the mode of failure kept the sensor apparatus intact even when the visor attachment failed.
 
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Jack by the hedge said:
I seem to recall the diagram of the lock shown <waves hand> somewhere back there shows a tube joining the first and second hull side lugs, which the pin would retract into. So there was only one visor lug, between the 2nd and 3rd hull lugs.
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Ah yes, that's a good possibility too. I don't recall ever having seen a diagram of that bottom lock before - does anyone has a link to it?

In any event, it's of very limited relevance to any analysis of the failure of the bottom lock, since it's already clear that the lock failed because its hull-side lugs failed (even though the visor-side lug and the bolt itself remained intact and viable)
 
The Man said:
Also ,as I recall, in the report the warning system showed the ramp as unlocked because one pin had a tendency not to full seat. The visor showed as locked and the mode of failure kept the sensor apparatus intact even when the visor attachment failed.
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Which is another reason to severely question the competence of the design of this lock (along with the total lack of redundancy in this (demonstrably) critical component, the failure of which would (demonstrably) risk the total loss of the ship).

No wonder the German shipyard is searching for - and providing funding for - an alternative cause of the disaster........
 
LondonJohn said:
Which is another reason to severely question the competence of the design of this lock (along with the total lack of redundancy in this (demonstrably) critical component, the failure of which would (demonstrably) risk the total loss of the ship).

No wonder the German shipyard is searching for - and providing funding for - an alternative cause of the disaster........
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No crap, that part just blew me away when I just read it. Oh, the locks and sensors are still attached while the visor's on it's way down to be the new door for Davy Jones' locker!
 
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