Timeline to disaster

Eight days after leaving Riga, Latvia, bound for Singapore with a cargo of nearly 77,000 tonnes of heavy fuel oil, Prestige hit trouble off Cape Finisterre in heavy seas. Six days later the ship was on the sea bed, having been refused a port of refuge and defying all the efforts of salvors to stabilise her. As this issue of The Motor Ship went to press, oil was still leaking from the two broken sections of hull and heading for Spanish coasts which had already been blighted by tonnes of oil. Hopes that remaining cargo would solidify and remain in the ship appear slim, as inspections by the French submersible Nautile revealed cracks in both the bow and stern sections and continuing oil leakage.

The final throes

Details released by ABS, which classed Prestige, show that it first encountered difficulties at around 1400 on November 13. The vessel developed a reported 25 deg. starboard list while on passage in heavy seas and high winds (storm force 10-11) in the region of Cape Finisterre, between 25-30 nautical miles off the coast of Galicia in northwest Spain. The list followed what the crew describe as an explosive sound and shudder. This appears to be the result of failure in the empty Number 2 Aft starboard and No 3 starboard wing tanks. About 15 minutes later the vessel was beam on to the sea. The Spanish government refused to offer the vessel or the salvors a sheltered location for the vessel and ordered it to be held more than 60 miles offshore.

The Bahamas Maritime Authority states that the Master ordered the righting of the vessel by intentionally flooding the No 2 port aft wing tank and the No 3 port wing tank, both of which were empty and intact. ABS says that this action reportedly brought the vessel back to a 3-5 deg. list.

The class society carried out an analysis of the hull girder strength in this condition based on data provided by the operator and concluded that the maximum still water bending moment had increased to 163 percent, or 63 percent in excess of the allowable level in calm seas, assuming the vessel?s structure had remained intact. However, any damage to the structure would have implied a further increase in the bending stress.

In this condition the vessel?s hull structure was subject to severe overloading. Unless the vessel could be quickly brought into calm waters, the additional dynamic wave loads to which the hull structure would be subject in open waters would lead to a progressive deterioration in the hull structure until ultimate failure as subsequently occurred.

Stewart Wade, ABS? vice president for marketing, told The Motor Ship that “according to the calculations performed by the ABS Rapid Response Damage Assessment team, based on loading and tank sounding data provided by the managers of the Prestige, once the vessel had been counter ballasted to right the initial 25 deg. list, the hull girder was significantly overstressed.” He explains, “at that stage, it is our opinion that, if the vessel had been afforded immediate access to a sheltered area, the cargo could have been transhipped and the vessel saved with little, if any, additional pollution. However, the stresses placed on the ship were such that the subsequent deterioration and break up of the vessel could be predicted if it was left in the dynamic environment of the open sea.”

Smit Salvage, the Dutch experts called in to attend the stricken ship, believed that bringing the ship into a sheltered bay or port would have given them a chance to pump the oil off or otherwise prevent it spilling into the sea (see incident timeline below).

Ship?s history

Prestige was built to ABS class requirements by Hitachi Zosen in 1976 and, at the time of the incident, was in full compliance with all ABS classification requirements, including the IACS Enhanced Survey Program for older tankers. The last Classification Annual Survey was carried out at Dubai in May 2002 and the last Classification Special Survey and drydocking was carried out in Guangzhou in China in May 2001. There are no outstanding class or statutory issues attached to the vessel.

The vessel?s Port State Control history shows that it was inspected five times since 1998 with a record of zero detentions and only four minor deficiencies.

The Prestige was a Category 1 vessel under the new Marpol 13G requirements. The tanker was not configured for protectively located, segregated ballast tanks (PLSBT). But it was approved for Hydrostatic Ballast Loading and ABS had initiated a comprehensive review of the sloshing and other analyses undertaken as part of that approval. The vessel?s phase out date under Marpol would have been 2005.

Repairs carried out

The vessel had its Fifth Special Survey completed on May 19 2001 after some 362 tonnes of steel was renewed. Inspection, thickness measurements and hydrostatic testing of the tank boundaries were carried out afloat at Guangzhou and, on completion, the vessel was moved to Guangzhou Cosco Shipyard for repairs on April 10 2001. Before commencement of the repair, the material for repair was verified against mill certificate and tested. The welding procedures and the welders? qualification records, the NDT (Non Destructive Testing) equipment records and the operators? qualifications were verified. The welding sequence, gouging process were also discussed with the shipyards quality control department and the ship owner representative.

The major repairs were undertaken in the side ballast/cargo tanks No.3 (P&S) and concentrated mostly on the transverse bulkheads and the frames at the upper levels within the tank. ABS says the tanks were fully staged at Frames 61 & 71 and between Francs.65 – 70 and staging was also extended to various areas for the repair of shell and longitudinal bulkhead longitudinals.

ABS says that there was no area of concern noted on the ballast/cargo tank Nos. 2 (aft) & 3, shell plates. And that thickness measurement results showed that the average wastage on the shell plate was less than 10 percent. No repair was considered necessary on the shell plate at the time. The starboard shell longitudinals were found below 10 percent wastage in side ballast/cargo tank No.2(S) aft and the starboard shell longitudinals were found mostly between 10-15 percent wastage in side ballast/cargo tank No.3(S).

The repair works were carried out under supervision of ABS surveyors and found satisfactory after which non-destructive testing by radiographic & ultrasonic method was selectively carried out, confirmatory hydro-test and air-tests were also carried out and all found satisfactory.

The vessel?s last Annual Class Survey and Statutory Surveys were carried out by the Dubai office of ABS while the vessel was in the UAE, in May 2002.

Cause of the incident

While the cause of the disaster cannot yet be concluded there are several possible initiators. These include the striking of cargo lost overboard from other vessels in the area at the time. Containers, pipes and logs were all lost overboard by vessels in the same storm. The vessel could have also filed due to a breaking wave impact. ABS discounts the possibility of explosion because there is no explosive deformation in the surrounding structure. However, it is looking into the possibility of structural failure in the way of Frame 71. This is of particular interest as the vessel had been used in bunkering service for two years previous to the start of the voyage and had a large fender positioned at Frame 71.

The extensive structural repairs carried out by Guangzhou Cosco Shipyard in China in way of Frame 71 require further investigation. n

Further technical details of the casualty and subsequent investigations can be found at ABS?s website, www.eagle.org, and from Smit Salvage at www.smit.com

Disaster unfolds: five-day salvage struggle in vain

November 14

11.00 hours CET: SMIT Salvage contracted to provide emergency assistance; a salvage team and two tugs head for the scene.

16.00 hours: Smit?s team gets a tow line fixed to vessel, stopping its drift towards the Spanish coast; . Another SMIT team is airlifted to the Prestige.

November 15

By order of Spanish authorities, two tugs holding the vessel some 60 miles off the Spanish coast begin moving it in a SW direction to a position at least 120 miles offshore. SMIT has 10 people on board, damage to side plating is being examined and the ship?s list has been corrected.

November 17

Towing continues, having survived force 9 winds during the night. Smit?s intention is to seek better weather and a ship-to-ship cargo transfer. Spanish authorities order the towing convoy, now five tugs with a sixth on the way, to hold station and await instructions.

November 18

Smit observes that the ship is vulnerable to the weather and should be taken to calmer waters.

November 19

09.00: Smit reports Prestige breaking up.

12.30: Aft section sinks.

16.15: Fore section sinks.