Susan Blyth Neill-Fraser, 56, of West Hobart, has pleaded not guilty to murdering her de facto Mr Chappell, who went missing from the couple's yacht Four Winds in January 2009.

Senior Constable Kriss Lawler said as he and another marine policeman approached the sinking yacht just after 7am on January 27. He said it was heavily bowed down.

Senior Constable Lawler told the court he had assumed the water was coming through the front of the vessel.

He climbed on board and started searching for people.

He found no one.

Mechanical pumps were used to save the boat from sinking.

After battling the water for "some time", Constable Lawler said he heard a trickling sound.

"Next to the toilet there was a hose that had been cut and water was flowing freely into the vessel from the hose," he said.

After closing off the hose with a sea cock, or stop valve, another policeman alerted him to a second sea cock which had been opened to allow sea water to flow into the vessel, he said.

On cross examination, Constable Lawler said it would not be uncommon for vessels that had undergone renovation to have unused sea cocks covered up.

The trial continues.