It seems to be a typical rust bucket sinking. A 24 years old converted VLCC to VLOC just sinking in calm weather is no surprise. Haven’t I seen it before? Maybe she was a 1st generation double hull VLCC with its leaks in the inner hull making her difficult to operate, so she was converted to VLOC with centre tanks double bottoms reinforced for ore. Like an old 00. And then the ballast tank coatings died after 10/15 years, fatigue cracks started to develop everywhere and CRACK one crack developed in the shell, went up to the deck and suddenly the ship was in two unstable parts.
No factual information, but if it’s a VLCC-VLOC conversion, it means almost certainly that the ore holds are located in the center hull tanks while the side tanks are either dry (void) or ballast tanks - one does not simply remove longitudinal bulkheads in a vessel like that. This would mean that there’s less room for cargo shifting as I wrote above.
I wonder if it was built as a double-hull tanker. Without a double hull, a structural failure on the shell would quickly result in quite significant flooding.
edit: Stellar Daisy has six sister ships, all converted from VLCCs.
Berge Istra and Berge Vanga were Yugoslav built single hull ore/oil carriers of doubtful quality but with IG systems, etc… There were always leaks between cargo tanks/holds and ballast tanks. The centre cargo ore holds/oil tanks were fitted with a funny double bottom arrangement. To discharge oil from the centre cargo holds/tanks, square ducts were fitted in the double bottom, from which the cargo pumps aft were sucking from to deliver to the deck cargo pipes. These ducts could be accessed via vertical trunks at the bulkheads.
The double bottom was thus part of the cargo tanks of the ship.
But there were no means to clean and gas free these double bottom cargo ducts!
So the ships could never be made gas free!
Unless you filled the double bottom cargo ducts/access trunks with water.
Anyway, seagoing hot work (welding) repairs were done aboard in fully (ore) loaded conditions and someone forgot that there was hydrocarbon gas in the double bottom ducts. BANG!
The double bottoms exploded and the ships sank within minutes.
Yes, if you load say 270 000 tons of ore in 9 holds in 24 hrs - 30 000 tons in each hold at a rate of >10 000 tons/hour - you really have do it correctly. To avoid ship getting to stiff with all cargo in the bottoms of all holds, you may load alternative holds, and then it gets interesting. It is quite easy to put 10 000 tons extra in one hold and then anything may happen. Things get worse at sea, when waves start to bend the ship, which you can see and feel from the bridge aft. .
Were do you get your info from? According to Arne Sagen the arrangement for pumping out the hold/ctr.tanks was via a tunnel along the centreline in the double bottom: [quote] He claims that the ship was designed so that lasterørsledningene[Cargo piping] was passed through a tunnel in the double bottom, under the cargo holds, and that a bulkhead between the pump room and cargo section was not passed through this double bottom (tunnel).[/quote]
Thus the double bottom was NOT used to carry oil. The only part of the double bottom which could get oil/gas filled would have been this tunnel.
The problem that was highlighted by Capt.Johnny Eilers was that the inertgas system that was intended to keep the wing tanks, which was used to carry oil but not always cleaned during voyages carrying iron ore, inerted:
These combination vessels were phased out after the three accident;, Berge Istra/Vanga and Derbyshire.They became used as pure Ore Carriers, or Tankers.
You are right, usually only every second hold are used when loading heavy ore cargo, which was probably the case on the Stellar Daisy as well.
According to a report the Stellar Daisy was carrying “fine iron ore”, which is much more exposed to liquefaction than the normal “course” iron ore. Several accidents caused by liquefaction of other ore cargos has occurred lately due to too high humidity content in the cargo when loaded.
There were no cargo oil pipings in the double bottom of Berge Istra and Berge Vanga. There were three square ducts in the double bottom of the centre holds, through which the oil was pumped. Valves were fitted at the entries from the holds. The cargo pumps aft took suction from these three ducts and pumped the cargo ashore. There was no double bottom in the wing, cargo tanks.
I agree it was a stupid arrangement, but those were the days. How do I know? I inspected a sister ship many years ago.
VLOC Stellar Daisy had started its days as a VLCC 24 years ago and you should wonder about the coatings of the ballast tanks. If it was not effective any longer, you must close up inspect these tanks every year to look for cracks and defects, which I have also done … and found plenty - 1000’s - of cracks.
It would be interesting to know how the conversion was done so you could carry ore in alternate center holds. As you also fitted big hatch openings in the center, you must have doubled up the upper deck plates of the wing tanks. Then there is the question how to transmit the big loads on the double bottom to the side shell. Plenty of locations where cracks can start!