3 Attachment(s)
Tanker ENERGY CONCENTRATION Story
And here's the other case John(Arton) mentioned .I find them fascinating.
The s.t.ENERGY CONCENTRATION was a 212,269 dwt VLCC which arrived at Rotterdam after partial discharge at Le Havre. Her cargo was part crude, part fuel oil. Following another partial discharge at Europoort, she was to go to Immingham and complete discharge. She broke in half alongside after severely hogging. At the time of the failure (22/7/1980) a a total of 115,000 tons was still left in her tanks; however, the centre tanks and two ballast tanks alongside were both empty at the time .
43 crew members safely left the ship.
Cargo was eventually discharged, and the two sections towed away and broken up.The forepart was towed to Split and broken up 16/2/81 and the afterpart broken up Barcelona 16/4/81.
The Captain and Chief Officer were sentenced to four months for negligence by a Rotterdam court. The Master won on appeal; the C/O ended up being fined 10,000 guilders.
From the subsequent enquiry that followed the incident, it transpired that the sequence of discharging the cargo at Rotterdam was such as to increase the hogging moment above the already high value as a result of cargo transfer at the previous port of Antifer. The eventual distribution of weight and buoyancy induced a hogging bending moment which exceeded the ultimate longitudinal strength of the tanker.
Journal of Ship Research, Vol 40, No 1 March 1996, pp 60-69.
This casualty attracted all kinds of academic attention because it was a full scale experiment, a VLCC hull failure in which the loading conditions were well known. In this 1996 paper, Gordo, Guedes Soares, and Faulkner review the attempts to analyse this problem and present their own. In the as-built condition, the estimates of the hogging moment required to cause progressive hull failure range from 18979 to 20630 million N-m, with these author's estimate at 19164. The moment which actually failed the ship was 17940 MM N-m. If these numbers are right and the nearly 10 year old ship had not had any corrosion, the Chief Officer probably would have gotten away with his mistake. However, Gordo et al say :
The last survey report found all cargo and ballast tanks in good condition with the exception ballast tanks 3 where a greater degree of corrosion was found. The location of these tanks is coincident with the location of the failure.
The last survey was in late 1979, early 1980 at Singapore. or possibly in 1977 when the ship switched from DNV to BV, We of course dont have the Class survey data, nor do we know whether 3P and 3S were coated. In 1977, the ship switched from DNV to BV; we don't know why.
Anyway given the loading pattern, we only need a reduction in strength from the as-built condition of about 10 pct to generate a failure. Class rules allow 25 pct reduction in wastage before renewal is required, and in practice wastage worse than this is often not caught. It is not surprising that the hull failed.
Khan, Das, Parmentier, Ultimate Strength and Reliability of a VLCC
This VLCC broke her back in July, 1980 during a discharge of oil at Rotterdam. During the period Decmber 1979 to March 1980, the ten year old ship, Energy Concentration was surveyed by Bureau Veritas at Singapore. [One of the authors of this paper, Parmetier, is a BV employee.] It was found that all cargo and ballast tanks were in good condition, with the exception of ballast tanks No 3, where a greated degree of corrosion was found. The location of these tanks is coincident with location of the failure.
The last voyage of Energy Concentration was from the Persian Gulf to Rotterdam. The sequence of loading and discharging of the ship during this voyage was complicated by some changes of plans by the charterers, and by the need to carry five different grades of cargo, loaded at three ports for discharge at three other ports. Details of these transactions, including the ship's departure conditions from the Persian gulf and cargo discharges at Immingham and Antifer have been described in reference [1]. It may be noted here that the sequence of loading, dischaging and cargo transfer (exacerbated by the many grades of oil being carried) evidently led to the ship leaving Antifer on 20 July 1980, not only heavily trimmed by stern, but also with very severe hogging still water moment. The ship's drafts recorded in the deck logbook indicate a hog of about 43 cm. Subsequent calculations show that the ship commenced the final leg of the voyage from Antifer to Rotterdam with a still water bending moment more than twice the value permitted under the rules by which the ship was classed. The tanks were arranged in a 5x3 pattern plus two wing slop tanks aft. The three across were half sized and 3P and 3S were the segregated ballast tanks. The pictures show she failed just forward of the manifold, which would be in way of these tanks. The failure was in compression of the bottom structure. The deck folded at about Frame 76, but did not fracture.
CTX Database Comment
An extremely interesting structural failure which we must get to the bottom of. Was it a crew screw-up, or fatigue, or corrosion, or just an underbuilt structure? One reference is Rutherford and Caldwell, Ultimate Longitudinal Strength of Ships, SNAME 98:441-471,1990.
A glaringly obvious question is: why did the ship not put ballast in 3 wings before leaving Antifer?
Based on what we know now, sounds like the proximate cause was crew fatigue. A three port discharge with five parcels means two things:
Very little flexibility in how you handle the parcels and the order in which you discharge the tanks. The Chief Mate would not have been able to do things the way he normally would. Often these sort of cargos are accepted by the chartering people with no idea of the operational implications, or even if the cargo is indeed structurally doable. In this case, however, the inexplicable failure to start ballasting the midships permanent ballast tanks (3P and 3S) indicates that the Mate had not done all he could to minimize hogging stress.
No sleep. All three discharge ports are less than a days sailing from each other. In a normal discharge, there are calm times in the middle of the discharge where not much is happening, but with part discharges Chief Mates have no rest time. In situations like this the owner should put another Chief Officer onboard, but they rarely do.
Thank God, this ship had her cargo tanks inerted. (Newton, p 162). Otherwise could easily have been a Betelgeuse. (-Bantry Bay tanker explosion disaster 8.1.78)
No Oil spill is mentioned in ETC or other spill databases, so any spill must have been small, which seems strange, but indicates that the cargo tank in way of the midships ballast tanks was empty or nearly so. End.
