The Cap Blanc sank Tuesday after it capsized about four nautical miles off the Newfoundland port of Marystown. (Courtesy Roger Etcheberry)

Search and rescue officials waited about 10 hours before starting a full-scale air search for a capsized French cargo ship after the coast guard repeatedly tried to make radio contact with the vessel.

The 37-metre Cap Blanc, a vessel from the French islands of St-Pierre-Miquelon, sank about 16 kilometres south of Marystown on Tuesday afternoon. None of the four crew had been located by Wednesday evening.

The disappearance of the vessel remained an unsolved mystery for search and rescue officials, who say they never received any distress signal before the ship capsized in the mouth of Placentia Bay.

The roll-on, roll-off ship left Argentia with a load of road salt bags at around noon on Monday for the journey home.

Chris Fitzgerald, a director of the rescue co-ordination sub-centre in St. John's, said the coast guard communications centre for Placentia Bay attempted to reach the vessel at 8:30 p.m. on Monday to confirm where it was after the vessel failed to give a scheduled report on its location.

"They tried communications to raise her ... the area where she was in is sort of a flat area for VHS [radio] coverage, and there was no big immediate concern. They just figured she wasn't in communications range," he said.

Maj. Denis McGuire, a spokesman for the joint rescue co-ordination centre in Halifax, said the centre continued to attempt to reach the ship by radio and then telephoned the owners, Alliance SA, in St-Pierre-Miquelon.

"They [the agent] felt this was a fairly common occurrence for loss of communications due to the nature of their travels, and there was no concern at that time," said McGuire.

About an hour later, the coast guard ship George R. Pearkes also attempted to reach the cargo vessel by radio, without success.

McGuire said the coast guard ship was assigned to follow the expected route of the missing vessel.

"The ship proceeded from roughly the area of Marystown, heading out to St-Pierre-Miquelon … and then returned," he said.

The coast guard centre also requested harbour searches to check if the vessel had pulled into port to avoid winds of 50 to 70 km/h, but that proved fruitless.

Air search would have been 'less effective' in night conditions

McGuire and Fitzgerald said a request for aircraft was made at about 8 a.m. on Tuesday, about 10 hours after the first attempt to make radio contact.

McGuire said there was a time lapse because search and rescue officials believed a surface search was sufficient.

"Given that it was night time, an air search would have been less effective," he said.

The capsized bow of the vessel was located by the Hercules aircraft by 11 a.m. on Tuesday, and the vessel sank early in the afternoon.

An empty life raft was located by an RCMP boat, along with a few other pieces of debris.

Fitzgerald said it also appears that the vessel's emergency beacons didn't emerge from the vessel when it overturned, possibly because they got caught up in the ship's rigging.

"It she rolled very quickly, it's quite possible they didn't float free," he said.

An RCMP patrol vessel, the Murray, reported hearing some sounds from the bow of the vessel prior to its sinking, but it was unclear on Wednesday what the noises were.

McGuire said that search-and-rescue divers were preparing to attempt a dive to investigate the sounds, but the ship sank as they were evaluating the safety of the effort.

There were five survival suits on board, but none were found.