The captain of a Turkish tanker had not slept for more than two days before the vessel's costly crash into a US Gulf offshore oil platform.

The US National Transportation Safety Board (NTSB) said the 159,500-dwt suezmax Atina (built 2015), managed by Besiktas Ship Management, caused $72.9m of damage to the SP-57B rig in the accident on 17 October off Louisiana.

The operating company's decision to change masters without a handover period led to the smash, the probe found.

The Atina, owned by Ciner of Turkey and with a crew of 21, was attempting to anchor in the Southwest Pass Fairway Anchorage when it struck the platform.

Four workers on the platform, and one technician, were evacuated to a nearby rig by helicopter after activating the emergency shutdown device to shut in wells.

Estimated damage to the platform was $72.3m and $598,400 to the suezmax, the report said.

NTSB found the operator did not comply with its own safety management system (SMS).

The replacement master boarded the vessel underway to the anchorage, only seeing the departing master on the tanker's deck.

"The company placed the accident master into critical vessel evolutions, such as navigating downriver and anchoring at night, without any overlap with the departing master," the NTSB said.

The SMS required a minimum one-day turnover between senior personnel.

The report said the new master told investigators he wanted to anchor the ship as soon as possible because he was tired.

He had travelled from Turkey to join the vessel and told investigators he had no sleep for over 50 hours.

The anchorage location he chose did not follow the passage plan location, which was supposed to be 3.2 miles north-east of SP-57B.

The actual anchoring spot was about 0.7 away from the platform.

Investigators determined the probable cause of the contact was the operating company not ensuring sufficient time for the master's turnover, which resulted in the master's acute fatigue and poor situation awareness during an attempted night-time anchoring evolution.

​"Vessel operating companies should ensure that joining crew members/personnel are given the opportunity to obtain a sufficient handover period and adequate rest before taking over critical shipboard duties, such as navigation, that could impact the safety of crew, property, and the environment," the report said.

A Texas offshore oil producer secured the arrest of the tanker in October, claiming it caused hundreds of millions of dollars-worth of damage to the platform.

Dallas-based Cox Operating filed a lawsuit against the vessel, owning company Hanzhou 1 and captain Onur Hurmuzlu.

The lawsuit in the US federal court in New Orleans alleges their negligence caused $225m-worth of damage.

No injuries, no pollution

Ciner Ship Management told TradeWinds in October that no joint survey of the platform had at that point been conducted, and there were no injuries and there had been no pollution.

The company said visible, above-water damage to the platform was minimal and there was no need to repair the ship after classification society ABS and the US Coast Guard inspected it.

Ciner said $40m in security had been posted for the Atina.

The Turkish owner said the vessel was seaworthy immediately after the incident and suffered only minor scratches.

The ship is insured by the Standard Club.