The offshore services ship Bourbon Dolphin capsized last year off Shetland due to a series of mishaps, an investigation commission has concluded.

Eight of the 15 crew were killed when the six-month-old ship, owned by Bourbon Offshore Norway AS, capsized on April 12, 2007.

Shortly afterward, the Norwegian government appointed the six-member commission to investigate.

"It is not possible to demonstrate that a single error, technical or human, caused the accident. The accident is explicable in terms of a number of unfortunate circumstances interacting," said the commission's 208-page report.

The document was based on testimony from 38 witnesses given over five hearings.

The Bourbon Dolphin had been working together with another ship, the British vessel Highland Valour, to move the oil rig Transocean Rather's anchor and chain weighing an estimated 330 tons.

The Bourbon Dolphin was hauling the massive chain onto its rear platform, when the chain came out of position and went over the side of the ship in strong winds, causing the vessel to capsize.

The report blamed the accident on a series of factors, including weaknesses in the ship's design, bad weather and ocean currents, the load from the chain, faults in planning and executing the operation, misunderstandings and the crew's failure to properly use a quick release mechanism that would have dropped the chain and saved the ship.