VANCOUVER -- The mariner who was navigating the Queen of the North passenger ferry when it ran aground and sank off British Columbia's northern coast, killing two passengers, has been sentenced to four years in prison.

Karl Lilgert, 59, was convicted last month of criminal negligence causing the deaths of Gerald Foisy and Shirley Rosette, who vanished when the Queen of the North missed a routine turn and collided with a remote island in March 2006.

Judge Sunni Stromberg-Stein said Lilgert's relationship with quartermaster Karen Briker -- who was the only other crew member on the bridge when the ship struck land -- was a significant factor in the crash.

It was their first time working alone together since their relationship ended several weeks earlier, and the intimate details of the affair were laid bare during the trial.

"Clearly, he was distracted by personal issues related to his relationship with Ms. Briker," said Stromberg-Stein as she read her sentencing decision in B.C. Supreme Court on Monday.

"I do not need to speculate on what Mr. Lilgert was doing on the bridge that night. I know what he was not doing. He was not doing his job."

Lilgert sat at a table with his lawyer as the sentence was read. Once the judge finished, he was led away by a sheriff. One of his sons sat in the public gallery.

Last week, the Crown recommended a six-year prison term, while the defence asked for a conditional sentence with no time in custody. Lilgert's lawyer has already indicated that he plans to file an appeal of the conviction.

Lilgert was on the bridge of the Queen of the North shortly after midnight on the morning of March 22, 2006, several hours after leaving the northern community of Prince Rupert on an overnight voyage to Port Hardy on Vancouver Island. There were 101 passengers and crew on board.

The ship missed a scheduled turn as it entered a body of water known as Wright Sound, and evidence presented at trial indicated the vessel then continued on a straight line toward Gil Island, without making any significant course changes or even slowing down.

The Crown alleged Lilgert was distracted, possibly by the presence of Briker.

Both Lilgert and Briker insisted there were no hard feelings and that the affair had nothing to do with the sinking. The Crown accused Lilgert, who testified in his own defence, of either arguing with Briker or having sex with her as the ship sailed on its collision course -- both of which Lilgert denied.

Lilgert told the jury he was busy navigating the ship and ordering course changes as he was challenged with rough weather and unreliable equipment.

He said he had ordered at least two turns and was keeping an eye on the radar to ensure the ferry was a safe distance from Gil Island when, for reasons he couldn't explain, he spotted the island outside the ship's windows.

But Stromberg-Stein said the jury did not believe Lilgert's claims.

"It is clear the jury rejected Mr. Lilgert's evidence that he was carrying out his duties to the best of his abilities," said Stromberg-Stein.

"It is clear that the jury found that there was an extensive period of time where Mr. Lilgert did not follow any of the procedures, steps or policies of a professional navigator."

Data recovered from the ship's navigation system indicated the ferry made no turns and took no evasive action as it approached Gil Island, which one expert witness described as a "catastrophic dereliction of duty."

Lilgert delivered a tearful apology at his sentencing hearing on Friday, telling the judge of the "deep regret and sorrow" that he will carry with him for the rest of his life.

His lawyers described a "fragile man" who has suffered post-traumatic stress and has lost his marriage, his house and his livelihood since the sinking. He currently lives in Grand Forks in southeastern B.C.

The defence suggested seven years of investigations, legal battles and constant media scrutiny, including the persistent rumours about sex on the ferry's bridge, were punishment enough.

The sinking prompted both the Transportation Safety Board and BC Ferries to investigate and release reports on what happened, and both blamed human error. Neither report was shared with the jury.

The Transportation Safety Board report, released in 2008, concluded a "conversation of a personal nature" was among the factors that distracted Lilgert from his duties and that neither Lilgert nor Briker followed the "basic principles of safe navigation."

The safety board report also raised concerns about marijuana use on the ship.

The Crown wanted to call evidence about Lilgert's own marijuana use, telling a pre-trial hearing there was evidence to indicate Lilgert smoked pot after nearly every shift, but a judge ruled the evidence was inadmissble.

BC Ferries released its own report in 2007, also blaming human error. The report made 31 recommendations, including better training.

BC Ferries, the former Crown corporation that operates the province's ferry system, eventually settled lawsuits involving the missing couple's families and dozens of surviving passengers.