Rescuers had all but given up hope of finding five crewmen alive after their oil rig support vessel capsized off northern Scotland.
Three other sailors were confirmed dead in the accident. Seven crew members from the Norwegian vessel Bourbon Dolphin were rescued and were being treated at a hospital in the Shetland Islands .
A coast guard helicopter and navy divers with heat-seeking cameras scoured the frigid North Sea for signs of the missing crewmen, who included a 15-year-old boy and his father. They found no signs of survivors.
"The status has now changed from a search-and-rescue operation to a salvage-and-recovery operation," said Lt. Lee Madigan of the Clyde naval base in Scotland . A coast guard spokesman said the chances of finding the crew members alive were "extremely slim."
The Bourbon Dolphin capsized Thursday in calm seas west of the islands, off Scotland's northern tip, while performing a routine anchor-handling operation on a rig.
British officials said all the crew members were Norwegian, although media in Denmark reported that one was a Dane.
A 15-year-old boy, aboard the vessel on a work-experience placement with his father, was among the missing.
"One of our pupils is, unfortunately, missing," said Soelvi Lilleboe Remoey, principal of the Yttre Heroey school in Heroey, western Norway . She did not give the teenager's name.
"Even though it is just a missing report, it is painful just the same. The uncertainty is hard to handle," she told Norway 's NRK state radio.
British coast guards said the five missing crew members may have been trapped in the hull of the upturned vessel, which was operating at the Transocean Rather rig when it capsized.
Michael Coull, duty watch manager at Aberdeen Coastguard, said there might be an air pocket under the overturned vessel, "and if the remainder of the crew were in a watertight compartment, then there's a possibility that they could still be alive."
"However, the chances are extremely slim and it's highly unlikely that that's the case," he said.
The ship capsized at about 5 p.m. (1600GMT) Thursday and remained on the surface of the calm ocean in clear weather about 75 nautical miles west of the Shetland islands , coast guard spokesman Mark Clark said.
The ship is owned by Bourbon Offshore Norway AS. After the accident, 72 nonessential staff were evacuated from the oil rig, which is operated for Chevron Corp. by offshore drilling company Transocean.
Bourbon Offshore Norway said it had chartered a plane to take relatives of the crew, along with Norwegian police, company officials and religious ministers, to Shetland on Friday.
Norwegian authorities planned to set up a commission to investigate how the accident happened. The 72-meter (237-foot) Bourbon Dolphin was a new vessel, delivered in October, and was performing a routine operation in calm conditions.
Bourbon Offshore Norway said the boat had not sent a distress signal before it capsized.
Oystein Hovdkinn , Norway 's consul general in Scotland , said the accident was "a terrible tragedy which is difficult to understand."
"There should be no Russian who goes to sleep without wondering if they're going to get their throat slit in the middle of the night,” Milley said