A 15-year-old boy is among five crew missing after a boat capsized in the Atlantic, killing three people.
The Bourbon Dolphin, anchored to an oil rig drilling platform north of Scotland, overturned about 80 miles west of the Shetland Islands.
The missing teenager is thought to have been doing work experience with the oil rig crew. His dad is also missing.
Seven crewmen were rescued but Royal Navy divers and rescue experts are trying to find a further five people.
The ship's owners, from Norway, said divers are using heat seeking cameras in the search but will not go into the boat until safety checks have been made.
Jim Sinclair, from the Shetland coastguard, said four helicopters and up to seven boats are involved in the operation.
He said: "It's a very complex and delicate operation as the vessel is actually upside down and stability is uncertain so they want to make sure of their own safety before they enter the hull."
Scottish police said they would begin an investigation into the incident once the search and rescue operation was completed.
The ship, which is less than one year old, had been working in the area of the Rosebank oilfield with a crew of 15.