More than two years after VLOC Stellar Daisy
sank, the Marshall Islands flag has published its report into the tragedy,
which killed 22 of the 24 crew on board. The ship's class society Korean
Registry quickly issued a response to the report, agreeing with much,
disagreeing with some points, and saying that it would act on others.
The Stellar Daisy, owned by South Korea-based
Polaris Shipping, sank in the South Atlantic on March 31st 2017 while on
a laden voyage from Ilha Guaíba, Brazil, to Qingdao, China. At the time of the
sinking she was more than 1,700nm from the coast of Uruguay and 1,800nm from
the west coast of South Africa. She sank to a depth of about 3.5km.
The marine safety investigation conducted by the
Republic of the Marshall Islands Maritime Administrator determined that the
likely direct cause of Stellar Daisy foundering was a rapid list to port
following a catastrophic structural failure of the ship’s hull. This caused a
loss of buoyancy and uncontrolled flooding.
The structural failure and flooding were
thought to have begun in the No. 2 port water ballast tank (WBT) and then
progressed rapidly to include structural failure and flooding in multiple WBTs,
voids, and cargo holds.
The report ascribed the structural damage to a
combination of probable factors, including the strength of the ship’s structure
being compromised over time due to material fatigue, corrosion, unidentified
structural defects, multi-port loading, and the forces imposed on the hull as a
result of the weather conditions encountered by the vessel between March 29th
and 31st.
The Administrator’s marine safety investigation
also concluded that the likely causal factors include:
- the large port and starboard wing tanks
increased the potential for a major structural failure and loss of
buoyancy in the event that one or more of these tanks flooded while the
ship was in a laden condition;
- a gap in the additional safety measures
for bulk carriers contained in the International Convention for the Safety
of Life at Sea (SOLAS), 1974, Chapter XII, regulation 5. This does not
require an assessment to ensure certain types of bulk carrier could
withstand the flooding of any one wing tank in all loading and ballast
conditions;
- ineffective assessments of structural
damage identified when the ship was in dry dock in 2011, 2012, and 2015
which failed to determine the cause of the structural damage, identify any
potential defects with the conversion design, or require the development
of appropriate repair plans.
The Stellar Daisy was formerly a very large crude carrier
(VLCC), which completed its conversion to a VLOC in January 2009.
The investigation included interviews with the two surviving
crew members, a detailed review of documents related to the ship’s conversion
design, maintenance and inspection history, and cargo records, and a third party
and Classification Society technical analysis. It also included a review of a
video taken during a deep-sea search that was conducted by the Republic of
Korea.
The Administrator thanked the marine safety investigation
authorities from Korea, the Philippines and from Brazil for the assistance they
provided as Substantially Interested States. The Administrator also thanked
Polaris Shipping, the Korean Register (KR), and Vale SA for their cooperation.
KR said that in general it agreed with the majority of the
content contained within the report and concurred that the most likely
explanation for the loss of the vessel was due to a catastrophic structural
failure of the ship’s hull which probably began in No 2 Port Water Ballast Tank
(WBT).
KR also agreed with the report that the fatigue cracking was
probably undetectable by visual inspection prior to the sinking.
KR said that, in its opinion, areas of the report that were
"directed specifically at KR which require further explanation".
KR’s areas of concern were focused on page 71 of the report:
Material fatigue
The report stated that KR’s review and approval of the
conversion design was based on the assumption that all of the scantlings,
including those from when the ship was constructed as a VLCC in 1993, were as
original and did not take into account material fatigue. KR responded that
"the basis for this assumption was that the Finite Element Analysis (FEA),
which was conducted in accordance with the requirements of the KR Rules for
Steel Ships, took into consideration allowable stress, corrosion, and stresses
due to local notch effect."
KR said that the report correctly stated that the FEA and fatigue strength assessment took into consideration allowable stress, corrosion, and stresses due to local notch effect. It said that this was "common practice for many IACS classification societies. An independent review conducted by Bruce S. Rosenblatt & Associates – the third-party hired by RMI to technically review the conversion process – confirmed that KR’s structural analysis was conducted properly".=
KR said that the report correctly stated that the FEA and fatigue strength assessment took into consideration allowable stress, corrosion, and stresses due to local notch effect. It said that this was "common practice for many IACS classification societies. An independent review conducted by Bruce S. Rosenblatt & Associates – the third-party hired by RMI to technically review the conversion process – confirmed that KR’s structural analysis was conducted properly".=
Failure analysis
The report stated that, although KR did conduct a failure
analysis of the damage to the transverse bulkhead at frame No 65, it did not
conduct a failure analysis after an extensive number of cracks were identified
and repaired when the ship was in drydock in 2011, within two years after the
conversion was completed. As a result, potential weaknesses with design details
were not identified. This is an indication that KR’s monitoring and assessment
of the ship’s structural integrity was not as effective as it might have been.
KR said that "a failure analysis is carried out at the discretion of the
attending surveyor when, in their assessment, a defect or damage is 'out of the
ordinary' and further scrutiny is required. This is in accordance with KR
procedures and in common with other IACS classification societies. The RMI
report correctly states that a failure analysis of the damage to the transverse
bulkhead at frame No. 65 was conducted as it was determined by the attending
surveyor to be 'out of the ordinary' and similar damage was not found in other
parts of the ship. However, the cracks/defects identified and repaired at the
time of dry-docking in 2011 were determined to be those typically found on
board ships of a similar age. Based on this observation, the attending surveyor
determined that the cracks/defects were not 'out of the ordinary' and as long
as proper repairs were performed, a failure analysis was not needed".
Reporting to Flag Administration
The report stated that KR was authorized to serve as an RO on
behalf of the Administrator. The 2016 RO Agreement between the Administrator
and KR required that KR immediately inform the Administrator of, among other
things, “any dangerous occurrences, accidents, machinery or structural
breakdowns, or failures that they are aware of on a Vessel.” KR did not inform
the Administrator of the damage to frame No. 65 in 2016. KR responded that, as
stated in the casualty investigation report, a failure analysis was carried out
to assess the structural integrity of damage to the transverse bulkhead at
frame No. 65, the result of which showed that there was no area of concern and
proper repairs were undertaken to renew the damaged part to its original
condition. KR also examined the surrounding bulkheads of Stellar Daisy as well
as bulkheads on 29 other converted VLOCs (approximately 230 bulkheads in total)
to determine if there were any similar defects. The result of this extensive
investigation was that there were no areas of concern. As a thorough inspection
and comprehensive repairs were undertaken, KR determined that there was no
“dangerous” structural issue that warranted reporting to the Flag
Administration".
However, mindful of the recommendations in the report, KR said that it intended to review its reporting procedures to avoid any future misunderstandings.
However, mindful of the recommendations in the report, KR said that it intended to review its reporting procedures to avoid any future misunderstandings.
Full reports may be read at,
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