The final report on the structural failure of the MT Castor has been completed and released by ABS as the classification society of record. This report addresses the damage sustained in heavy weather by the MT Castor while fully loaded on a voyage in the Western Mediterranean on 30 December 2000. The Castor experienced deck cracking between frames 72 and 73 with the overall crack extending approx. 22 meters from the portside deck stringer strake to the starboard deck strake.

ABS has conducted a series of investigations to determine if remedial measures can be recommended that can prevent and minimize the risk of similar incidents in the future. The MV Castor is a 30,577 DWT single-hull tanker. It was built in 1977 at Korea Shipping & Engineering Corp. as an oil carrier to ABS class and has remained in ABS class throughout its service life. The Castor had scantlings in excess of the minimum requirement satisfying the hull girder section modulus criteria used at the time of construction. Calculations of Castor’s hull girder section modulus at the time of the incident determined that the vessel satisfied the present ABS Rules and IACS minimum standards for a vessel in service. This conclusion explains why the vessel was able to survive for 39 days in heavy weather even after sustaining the deck cracking.

While the overall condition of the structure was sound, i.e., it met minimum hull girder section modulus requirements, the survey after damage found that substantial corrosion did exist on the underside of the main deck plating and supporting longitudinals in way of No. 4 cargo/ballast tanks. While the area of corrosion was limited, the extent of the corrosion was excessive. In the most severe areas, steel originally 16 mm had wasted to 5.5 to 6.6 mm, or 60 to 65% wastage. Steel in No. 4 tank which had been renewed with uncoated 14.5 mm plate in 1997 had wasted to 12 mm at the time of the incident. This represents corrosion rates of up to 0.71 mm/year or seven times the nominal 0.10 mm/year corrosion rate assumed in ABS Rules.