The Supreme Court in Hobart also heard Phillip Triffett, a former friend of the accused, did not think to report the conversations to the police at the time.

Susan Blyth Neill-Fraser, 56, of West Hobart, has pleaded not guilty to murdering her partner of 18 years Bob Chappell, who has been missing since Australia Day 2009.

Mr Chappell was last seen on board the couple's yacht Four Winds, which was moored on the Derwent River and found to be sinking on January 27.

Mr Triffett said he came to know the couple in 1991 or 1992.

He said that in the mid-1990s he was on board a yacht with Ms Neill- Fraser, which she then owned.

He said Ms Neill-Fraser told him of a dispute regarding her mother's property and that she wanted to take her brother, Patrick, out to sea and throw him overboard, weighed down by a toolbox.

"I was to take it (the yacht) closer to shore and sink it," he said.

Mr Triffett said he was unsure if Ms Neill-Fraser was serious but that she did not say anything to indicate that she was joking.

He said that soon after that conversation, Ms Neill-Fraser told him Mr Chappell was mean with his money and that he was dangerous around her children because he had been drinking.

"She more or less said he had to go ... (and) what we talked about with Patrick had to happen to Bob," Mr Triffett said.

He said Ms Neill-Fraser had suggested wrapping Mr Chappell's body in chicken wire.

When cross-examined, Mr Triffett said he did not report either of the conversations to the police at the time.

Defence counsel David Gunson, SC, also revealed Mr Triffett had prior criminal convictions.

Mr Gunson also suggested the two conversations Mr Triffett told the court were completely fabricated, a claim Mr Triffett denied.

The court also heard from Queensland marine mechanic James McKinnon, who was employed by Ms Neill-Fraser and Mr Chappell to complete mechanical work on Four Winds in Queensland where it was moored when the couple bought it.

Mr McKinnon said he received a phone call from Ms Neill-Fraser on February 4 or 5, 2009, during which she told him Four Winds had sunk.

"She just explained to me that her belief was that somebody had murdered him (Mr Chappell) on board and used the fire extinguisher to weigh the body down," he said.

Mr McKinnon said Ms Neill- Fraser also told him that a rope was used to winch the body up from the boat's saloon area.

"She claimed that's what the police told her," he said.

Mr McKinnon said while he was working on Four Winds at Scarborough Marina in Queensland, he was concerned someone was unlawfully gaining access to the boat.

He said he noticed an electrical panel had been removed, but that he later found out an electrician commissioned by Ms Neill-Fraser and Mr Chappell had removed the panel.

The jury heard earlier in the trial that Ms Neill-Fraser had concerns the boat was being used by drug smugglers.

Constable Brian Purcell yesterday told the jury he boarded Four Winds on January 27 with a police dog and that no detections were made by the dog.

But Constable Purcell said that due to water on the floor of the boat at the time the search was not effective.

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