2. Event and Consequences:
This 1984-built Cape Size Dry Bulk Carrier was on passage loaded with iron ore from Brazil to China.
On 7th June 2006, following a period of adverse weather between 2nd and 5th June (gale force 8/9
with a heavy easterly swell of up to 7 metres) no.1 cargo hold bilge showed an increase in water level.
Further increase was noted on 8th June and there was water in the duct keel.
On 9th June the weather had improved, permitting an internal inspection of no. 1 hold.
Severe damage to both port and starboard shell frames was discovered.
The vessel diverted to Cape Town arriving at the anchorage on 9th June
where company and South African Maritime Safety Authority (SAMSA) personnel
inspected no. 1 hold, no 1 port d.b. and no.1 port top side tanks.
The vessel was then sent to False Bay with a tug escort for
further assessment and temporary repairs.
Port side shell frames 310,311,312,313 and 314 were found sheared from hopper tank end brackets
and detached from shell plating and tripped.
A section of the web of fr. 316 was also found detached from the side shell.
There was a 350 – 400mm-long vertical crack in the shell plating in way of the weld seam of fr. 311;
panting of the shell plating even in the calm sea at the time of the preliminary inspection was noticeable.
The port side shell plating was set in approx 300 mm generally over the area of detached and tripped frames.
There was a crack in the flange section of fr. 322 stbd. in way of a tripping bracket,
extending through the frame flange and along the fillet weld seam to the topside tank bracket.
This was allowing a (small) ingress of water. The frame was also found partially detached.
(Entry of water into the duct keel was found to be via an open bolt hole of a manhole cover).
Following temporary repairs the vessel continued its loaded voyage to China
where permanent repairs and completion of special survey were carried out.
1. Although the weather was heavy it was considered by the investigators
not to have been of a severity to cause failure of the side shell frames unless there was a pre-existing weakness.
1a. Very significant wastage was found to the damaged side shell frames.
The areas of greatest diminution were in way of the frame connection with the side shell plating (grooving).
The major cause of the failure of the side shell was therefore considered to be corrosion wastage to the frames.
2. At the vessel’s Intermediate survey in June 2004,
to comply with IACS UR S31 the lower part (1500mm approx) of port side frames 315 to 327 together with the lower brackets were renewed.
To comply with the UR the web plate thickness of the renewed frames was increased to 16 mm from an original 12mm
and there was an increase in the scantlings of the face flats.
Although thickness measurements of frs. 310 to 314 port were taken at the intermediate survey,
the readings recorded of the web plates of these frames were in the region of 11.8mm
and it was found unnecessary to strengthen and/or part renew these frames or coat them.
The investigation report suggests that the recorded readings may not have been representative
of the web plate thicknesses at the connection to the shell plate, where grooving might have been present.
2a.The port side shell and frame failure occurred in an area
where new steel had been connected to old existing steel
and it appeared that the older steel corroded at a faster rate than the newly installed steel.
Moreover the adjacent new steel was 16mm thick – the original being 12mm when new;
the resulting difference in rigidity may have contributed to the failure.
3. The vessel had carried two consecutive coal cargoes in the two-year period following the last intermediate survey.
This may have contributed to the significant amount of corrosion found.
4. Subject to a satisfactory Occasional survey, the vessel’s 4th Special survey, due 12th May 2006,
was postponed with the agreement of Class (BV) and flag (Bahamas) until 7th August 2006 due to a lack of drydock facilities.
Although an Occasional survey with the scope of an Annual survey was carried out on 7th and 8th April 2006,
both for a change of flag and to allow the postponement of Special Survey,
the wastage of the frames which subsequently failed was not detected and rectified.
4. Issues Raised/Lessons Learned:
1. Current Class and Statutory survey regimes failed to detect
the potentially catastrophic weakness due to excessive corrosion.
The regime should be re-examined to determine what improvements can be made to prevent a recurrence.
2. Postponement of major surveys, especially special surveys, should be avoided,
especially on bulk carriers and for any vessels approaching the end of their design life.
3. Unacceptable local stresses may be generated when additional strength has been added
and adjacent structure remains significantly weaker;
additionally the connection of new to old steel could be the
cause of accelerated corrosion rates in the old steel.
4. The requirements and standards for cargo hold protective coatings should be re-examined.
5. Permanent arrangements for access to all remote and high-risk areas
within the cargo holds should be considered for existing vessels,
currently only a requirement for bulk carriers constructed on or after 1 January 2006.
6. Had a port of refuge not been made available to this vessel
the consequences may well have been catastrophic.
The need for “Port of Refuge” – with regard to IMO Resolution A.949(23) should be re-emphasised.
7. Additional visual inspection may be required to be carried out by crew and/or surveyors
with regard to the ships structure following carriage of corrosive cargoes, such as coal.
8. During periods of prolonged adverse weather Masters should consider all possible options
to reduce the stress on any seaworthy vessel by altering course and/or a reduction in speed.
[Note there is no suggestion in the report that the vessel’s course and speed caused this casualty].
9. Owners should consider the use of independent weather routing.
[Note there is no suggestion in the report
that the vessel’s route and prevailing weather directly caused this casualty].
10. It was determined during the investigation
that the mandatory water alarms fitted in the cargo holds
had been turned off prior to the incident due to them being permanently in alarm.
This was attributed to the high moisture content of the cargo –
declared at approximately 9% at the time of loading in Brazil.
The bilges were however being sounded manually and water ingress in No 1 hold was thus detected.
Nevertheless the acceptance [dismissal] of water ingress alarms
(e.g. making an assumption that false alarms are due to the high water content in the cargo)
without further immediate investigation on bulk carriers should be avoided.
5. Observations on the Human Element:
No significant Human Element issues contributing to the casualty were raised.
However the matter of turning off water ingress alarms is noted.