Stellar Daisy Sank due to “Catastrophic Structural Failure” of Its Hull

Stellar DaisyImage Courtesy: Korea's Ministry of Oceans and Fisheries

A catastrophic structural failure of the ship’s hull was the likely cause for the loss of the very large ore carrier (VLOC) Stellar Daisy, that sank on March 31, 2017, according to a report by the Republic of the Marshall Islands.

The hull failure probably began in No 2 Port Water Ballast Tank (WBT) of the 266,141 dwt vessel, owned by Polaris Shipping and converted from a very large crude carrier in 2008 under the supervision of the Korean Register.

Findings of the report indicate that the structural failure was most likely a result of a combination of 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 conditions Stellar Daisy encountered between March 29 – 31, 2017.

KR noted that it agrees with most of the findings, including that the fatigue cracking was probably undetectable by visual inspection prior to the sinking, but added that there are areas areas of the report that are directed specifically at KR which require further explanation.

Material fatigue

The report states 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. 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 commented that the report correctly states that the FEA and fatigue strength assessment took into consideration allowable stress, corrosion, and stresses due to local notch effect. This is common practice for many IACS classification societies. An independent review conducted by BSR (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 findings show 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.

The register explained 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. 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 drydocking 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 states that the 2016 RO Agreement between the administrator and register requires that KR immediately inform the administrator of “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 to determine if there were any similar defects, concluding that there were no areas of concern. As a thorough inspection and comprehensive repairs were undertaken and KR determined that there was no “dangerous” structural issue that warranted reporting to the flag Administration.

However, mindful of the recommendations in the report, the Korean Register said it plans to review its reporting procedures to avoid any future misunderstandings.

The 1993-built vessel sank in the South Atlantic Ocean while transporting 260,000 tons of iron ore from Brazil to China. Twenty-two of the 24 crew, that include eight South Korean and 14 Filipino seafarers, went missing from the converted ore carrier.

Seabed survey and ocean exploration company Ocean Infinity deployed its search ship, Seabed Constructor, to look for the ill-fated Stellar Daisy on February 8 under a USD 4.3 million contract. Only days after starting the search efforts, Seabed Constructor located the wreck some 1,800 nautical miles west of Cape Town at a depth of 3,461 meter and managed to retrieve its voyage data recorder (VDR).

On February 20, the search teams deployed at the wreckage site found bones believed to be from at least one of the missing crew members some 1 km away from the wreck, Korea’s Ministry of Oceans and Fisheries reported.

The search vessel left the site on February 23 headed to Montevideo without recovering the remains, according to the International Stellar Daisy Network.

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