RCMP and Transportation Safety Board investigators on Monday went aboard the coast guard icebreaker that was towing a fishing vessel when it overturned off Cape Breton over the weekend, killing three sealers and leaving a fourth presumed dead in icy waters.

The Canadian Coast Guard is also conducting an investigation, including a review of its towing policy. The review will be led by an independent investigator, the federal government announced Monday, adding that the name of the investigator will be made public in a few days.

"These various investigations will be thorough, will set out the facts, and determine what actually occurred," Fisheries and Oceans Minister Loyola Hearn said in a news release.

A federal official will also be sent to the area to offer help, he said.

A spokesman for the Fisheries Department, Luc Légère, noted that coast guard ships have a strong record, towing about 600 vessels a year.

"I think it's important to note that the coast guard is out there and they do good work, they're saving lives," Légère said.

"This was just a very unfortunate accident, but there is an investigation going on and that will tell us what really happened," he said.

The Sir William Alexander was tied up in Sydney Harbour on Monday morning, but it was expected to return to the ice floes in the Gulf of St. Lawrence later in the day.

A spokeswoman for the coast guard said stress counselling has been made available to the 27 crew members.

The icebreaker was towing the Acadien II early Saturday when the disabled fishing trawler overturned. Three sealers died and one is missing and presumed dead. Two survived.

"I am deeply saddened and wish to extend my most sincere and heartfelt condolences to the family and loved ones of the crewmembers of the L'Acadien II who tragically lost their lives this past weekend," Hearn said in his statement.

"Coming from a small fishing community myself, I know only too well the grief and pain being felt right now."

The crew of the coast guard vessel failed to notice they were pulling the trawler over a large chunk of ice, said Bruno-Pierre Bourque, one of the survivors.

Sealing boat had rudder problem

Bourque, who was at the helm of the 12-metre Acadien II, said he contacted the Alexander to alert the vessel to the problem.

He said he didn't see any crew on the coast guard vessel's deck watching out for trouble at the time. The sealing boat was veering to the left because of a rudder problem and could not directly follow the path cleared by the icebreaker, he said.

After the boat overturned, he and a second crew member, Claude Déraspe, ended up in the water and were rescued by a nearby fishing vessel.

RCMP and TSB investigators are talking with the crew of that ship, in addition to the two surviving crew members of the Acadien II.

"We want to know who was on deck, who was doing what and just basically probing to see what occurred," said Sgt. Mark Gallagher, an RCMP spokesman in Nova Scotia.

Autopsies were being conducted Monday in Halifax on the three Quebec sealers, who had been asleep at the time the boat overturned.

Maxime Arseneau, the representative for Îles-de-la-Madeleine in Quebec, is calling for a public inquiry into the incident.

The Acadien II reported a steering malfunction while navigating in thick ice late Friday, 70 kilometres north of Cape Breton. The Sir William Alexander was called to tow the boat to Sydney.