A gap in structural safety rules for bulk carrier wing tanks may have contributed to the sinking of very large ore carrier Stellar Daisy, according to the long-awaited reported from flag administration Marshall Islands.
The 266,141-DWT vessel sank off the coast of Uruguay on 31 March 2017, taking with it all but two of the 24 crew. Two years and 19 days later, the accident report identified a rapid list as the direct cause of the accident. The list was caused by catastrophic structural failure and flooding thought to have begun in the No. 2 port water ballast tank.
The Marshall Islands Maritime Administration noted that big wing tanks had increased the potential for structural failure and loss of buoyancy if one of these tanks was flooded while the ship was laden. It also pointed to a gap in additional safety measures for bulk carriers in the Solas convention, which does not require an assessment of whether bulk carriers similar to Stellar Daisy can withstand such flooding.
According to the report, such an assessment is not required of bulk carriers which are: of 150 m or more in length; of double-side skin construction; designed to carry solid bulk cargoes with a density of 1,000 kg/m3 or more; constructed on or after 1 July 2006; and with any part of the longitudinal bulkhead located within one-fifth of the vessel’s beam or 11.5 m (whichever is less) inboard from the ship’s side at a right angle to the centreline at the assigned summer load line.
The report also cited ineffective assessments of structural damage identified when the Polaris Shipping-owned vessel was in drydock in 2011, 2012, and 2015 as likely causal factors. The inspections failed to determine the cause of the structural damage, identify any potential defects with the conversion design - Stellar Daisy was converted from a very large crude carrier to a very large ore carrier in 2008 - or require the development of appropriate repair plans.
In a statement released shortly after the Marshall Islands report was published, Korean Register agreed with most of the report and highlighted that fatigue cracking was probably undetectable by visual inspection. But it sought to dismiss any indication that its review of Stellar Daisy’s conversion design did not account for material fatigue. KR said that findings by Bruce Rosenblatt & Associates, a consultant hired by the flag administration to review the conversion, confirmed that the class society’s structural analysis was conducted properly.
The report also noted that KR did not conduct a failure analysis after several cracks were repaired in drydock in 2011. This was taken as an indication that KR’s assessment of the ship’s structural integrity was not as effective as it could have been. The class society cited standard practice that failure analyses are instigated at the discretion of the surveyor when damage is “out of the ordinary” and requires further scrutiny is required. Defects identified in 2011 were determined to be typical for ships of a similar age
KR also responded to claims that, as an organization recognized to act on behalf of the flag administration, it should have informed Marshall Islands of “any dangerous occurrences, accidents, breakdowns or failures”. The class society said that a failure analysis of a transverse bulkhead showed no areas of concern and proper repairs were made. Surrounding bulkheads – and those of 29 other converted ore carriers – were also examined and revealed no areas for concern.
In a statement KR noted: “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 plans to review its reporting procedures to avoid any future misunderstandings.”
The report concluded that the structural damage responsible for the sinking was likely due to factors including material fatigue over time, corrosion, multi-port loading and forces imposed as a result of severe weather.